Bio

Academic Appointments


Administrative Appointments


  • Chair, Administrative Panel on Radiological Safety, Stanford University (2012 - Present)
  • Director, Stanford Radiation Oncology Physics Residency (2006 - 2013)
  • Chief of Clinical Physics, Stanford Hospital and Clinics (2000 - 2009)
  • Vice Chairman, Department of Radiation Oncology, University of Southern California (1989 - 1998)
  • Director of Radiation Physics, Dept. of Radiation Oncology, University of Southern California (1983 - 1998)

Professional Education


  • B.Sc., McGill University, Physics (1964)
  • Ph.D., California Institute of Technology, Physics (1970)

Patents


  • Wu Liu, Gary Luxton, Lei Xing. "United States Patent 8,229,070 Intra-fraction Motion Management using a Rough to Accurate Monitoring Strategy", Leland Stanford Junior University, Jul 24, 2012

Research & Scholarship

Current Research and Scholarly Interests


1. Development of clinical implementation of hypofractionated extracranial radiosurgery with intensity-modulated radiotherapy (IMRT).
2. Analytic modeling of normal tissue effects in fractionated radiotherapy and radiosurgery.
3. Characterization of accuracy and methodology for system quality assurance in the use of automated high-performance radiation delivery systems.

Teaching

2013-14 Courses


Publications

Journal Articles


  • Impact of chemotherapy on normal tissue complication probability models of acute hematologic toxicity in patients receiving pelvic intensity modulated radiation therapy. International journal of radiation oncology, biology, physics Bazan, J. G., Luxton, G., Kozak, M. M., Anderson, E. M., Hancock, S. L., Kapp, D. S., Kidd, E. A., Koong, A. C., Chang, D. T. 2013; 87 (5): 983-991

    Abstract

    To determine how chemotherapy agents affect radiation dose parameters that correlate with acute hematologic toxicity (HT) in patients treated with pelvic intensity modulated radiation therapy (P-IMRT) and concurrent chemotherapy.We assessed HT in 141 patients who received P-IMRT for anal, gynecologic, rectal, or prostate cancers, 95 of whom received concurrent chemotherapy. Patients were separated into 4 groups: mitomycin (MMC) + 5-fluorouracil (5FU, 37 of 141), platinum ± 5FU (Cis, 32 of 141), 5FU (26 of 141), and P-IMRT alone (46 of 141). The pelvic bone was contoured as a surrogate for pelvic bone marrow (PBM) and divided into subsites: ilium, lower pelvis, and lumbosacral spine (LSS). The volumes of each region receiving 5-40 Gy were calculated. The endpoint for HT was grade ≥3 (HT3+) leukopenia, neutropenia or thrombocytopenia. Normal tissue complication probability was calculated using the Lyman-Kutcher-Burman model. Logistic regression was used to analyze association between HT3+ and dosimetric parameters.Twenty-six patients experienced HT3+: 10 of 37 (27%) MMC, 14 of 32 (44%) Cis, 2 of 26 (8%) 5FU, and 0 of 46 P-IMRT. PBM dosimetric parameters were correlated with HT3+ in the MMC group but not in the Cis group. LSS dosimetric parameters were well correlated with HT3+ in both the MMC and Cis groups. Constrained optimization (0

    View details for DOI 10.1016/j.ijrobp.2013.09.017

    View details for PubMedID 24161422

  • Verification of dosimetric accuracy on the TrueBeam STx: Rounded leaf effect of the high definition MLC MEDICAL PHYSICS Kielar, K. N., Mok, E., Hsu, A., Wang, L., Luxton, G. 2012; 39 (10): 6360-6371

    Abstract

    The dosimetric leaf gap (DLG) in the Varian Eclipse treatment planning system is determined during commissioning and is used to model the effect of the rounded leaf-end of the multileaf collimator (MLC). This parameter attempts to model the physical difference between the radiation and light field and account for inherent leakage between leaf tips. With the increased use of single fraction high dose treatments requiring larger monitor units comes an enhanced concern in the accuracy of leakage calculations, as it accounts for much of the patient dose. This study serves to verify the dosimetric accuracy of the algorithm used to model the rounded leaf effect for the TrueBeam STx, and describes a methodology for determining best-practice parameter values, given the novel capabilities of the linear accelerator such as flattening filter free (FFF) treatments and a high definition MLC (HDMLC).During commissioning, the nominal MLC position was verified and the DLG parameter was determined using MLC-defined field sizes and moving gap tests, as is common in clinical testing. Treatment plans were created, and the DLG was optimized to achieve less than 1% difference between measured and calculated dose. The DLG value found was tested on treatment plans for all energies (6 MV, 10 MV, 15 MV, 6 MV FFF, 10 MV FFF) and modalities (3D conventional, IMRT, conformal arc, VMAT) available on the TrueBeam STx.The DLG parameter found during the initial MLC testing did not match the leaf gap modeling parameter that provided the most accurate dose delivery in clinical treatment plans. Using the physical leaf gap size as the DLG for the HDMLC can lead to 5% differences in measured and calculated doses.Separate optimization of the DLG parameter using end-to-end tests must be performed to ensure dosimetric accuracy in the modeling of the rounded leaf ends for the Eclipse treatment planning system. The difference in leaf gap modeling versus physical leaf gap dimensions is more pronounced in the more recent versions of Eclipse for both the HDMLC and the Millennium MLC. Once properly commissioned and tested using a methodology based on treatment plan verification, Eclipse is able to accurately model radiation dose delivered for SBRT treatments using the TrueBeam STx.

    View details for DOI 10.1118/1.4752444

    View details for Web of Science ID 000310101900055

    View details for PubMedID 23039672

  • Fidelity of dose delivery at high dose rate of volumetric modulated arc therapy in a truebeam linac with flattening filter free beams. Journal of medical physics / Association of Medical Physicists of India Kalantzis, G., Qian, J., Han, B., Luxton, G. 2012; 37 (4): 193-199

    Abstract

    The purpose of this study is to assess fidelity of radiation delivery between high and low dose rates of the flattening filter free (FFF) modes of a new all-digital design medical linear accelerator (Varian TrueBeam™), particularly for plans optimized for volumetric modulated arc therapy (VMAT). Measurements were made for the two energies of flattening filter free photon beams with a Varian TrueBeam™ linac: 6 MV (6 XFFF) at 400 and 1400 MU/min, and 10 MV (10 XFFF) at 400 and 2400 MU/min. Data acquisition and analysis was performed with both ionization chambers and diode detector system Delta(4), for square radiation fields and for 8 VMAT treatment plans optimized for SBRT treatment of lung tumors. For the square fields, a percent dose difference between high and low dose rate of the order of 0.3-0.4% for both photon energies was seen with the ionization chambers, while the contribution to the difference from ion recombination was found to be negligible. For both the VMAT and square-field deliveries, the Delta(4) showed the same average percent dose difference between the two dose rates of ~0.8% and ~0.6% for 10 MV and 6 MV, respectively, with the lower dose rate values giving the greater measured dose compared to the high dose rate. Thus, the VMAT deliveries introduced negligible dose differences between high and low dose rate. Finally, reproducibility of dose measurements was good for both energies.

    View details for DOI 10.4103/0971-6203.103604

    View details for PubMedID 23293450

  • NORMAL TISSUE COMPLICATION PROBABILITY ESTIMATION BY THE LYMAN-KUTCHER-BURMAN METHOD DOES NOT ACCURATELY PREDICT SPINAL CORD TOLERANCE TO STEREOTACTIC RADIOSURGERY INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Daly, M. E., Luxton, G., Choi, C. Y., Gibbs, I. C., Chang, S. D., Adler, J. R., Soltys, S. G. 2012; 82 (5): 2025-2032

    Abstract

    To determine whether normal tissue complication probability (NTCP) analyses of the human spinal cord by use of the Lyman-Kutcher-Burman (LKB) model, supplemented by linear-quadratic modeling to account for the effect of fractionation, predict the risk of myelopathy from stereotactic radiosurgery (SRS).From November 2001 to July 2008, 24 spinal hemangioblastomas in 17 patients were treated with SRS. Of the tumors, 17 received 1 fraction with a median dose of 20 Gy (range, 18-30 Gy) and 7 received 20 to 25 Gy in 2 or 3 sessions, with cord maximum doses of 22.7 Gy (range, 17.8-30.9 Gy) and 22.0 Gy (range, 20.2-26.6 Gy), respectively. By use of conventional values for ?/?, volume parameter n, 50% complication probability dose TD(50), and inverse slope parameter m, a computationally simplified implementation of the LKB model was used to calculate the biologically equivalent uniform dose and NTCP for each treatment. Exploratory calculations were performed with alternate values of ?/? and n.In this study 1 case (4%) of myelopathy occurred. The LKB model using radiobiological parameters from Emami and the logistic model with parameters from Schultheiss overestimated complication rates, predicting 13 complications (54%) and 18 complications (75%), respectively. An increase in the volume parameter (n), to assume greater parallel organization, improved the predictive value of the models. Maximum-likelihood LKB fitting of ?/? and n yielded better predictions (0.7 complications), with n = 0.023 and ?/? = 17.8 Gy.The spinal cord tolerance to the dosimetry of SRS is higher than predicted by the LKB model using any set of accepted parameters. Only a high ?/? value in the LKB model and only a large volume effect in the logistic model with Schultheiss data could explain the low number of complications observed. This finding emphasizes that radiobiological models traditionally used to estimate spinal cord NTCP may not apply to the dosimetry of SRS. Further research with additional NTCP models is needed.

    View details for DOI 10.1016/j.ijrobp.2011.03.004

    View details for Web of Science ID 000301891300082

    View details for PubMedID 21531516

  • Stereotactic Radiosurgery Yields Long-term Control for Benign Intradural, Extramedullary Spinal Tumors NEUROSURGERY Sachdev, S., Dodd, R. L., Chang, S. D., Soltys, S. G., Adler, J. R., Luxton, G., Choi, C. Y., Tupper, L., Gibbs, I. C. 2011; 69 (3): 533-539

    Abstract

    The role of stereotactic radiosurgery in the treatment of benign intracranial lesions is well established. Although a growing body of evidence supports its role in the treatment of malignant spinal lesions, a much less extensive dataset exists for treatment of benign spinal tumors.To examine the safety and efficacy of stereotactic radiosurgery for treatment of benign, intradural extramedullary spinal tumors.From 1999 to 2008, 87 patients with 103 benign intradural extramedullary spinal tumors (32 meningiomas, 24 neurofibromas, and 47 schwannomas) were treated with stereotactic radiosurgery at Stanford University Medical Center. Forty-three males and 44 females had a median age of 53 years (range, 12-86). Twenty-five patients had neurofibromatosis. Treatment was delivered in 1 to 5 sessions (median, 2) with a mean prescription dose of 19.4 Gy (range, 14-30 Gy) to an average tumor volume of 5.24 cm (range, 0.049-54.52 cm).After a mean radiographic follow-up period of 33 months (range, 6-87), including 21 lesions followed for ? 48 months, 59% were stable, 40% decreased in size, and a single tumor (1%) increased in size. Clinically, 91%, 67%, and 86% of meningiomas, neurofibromas, and schwannomas, respectively, were symptomatically stable to improved at last follow-up. One patient with a meningioma developed a new, transient myelopathy at 9 months, although the tumor was smaller at last follow-up.As a viable alternative to microsurgical resection, stereotactic radiosurgery provides safe and efficacious long-term control of benign intradural, extramedullary spinal tumors with a low rate of complication.

    View details for DOI 10.1227/NEU.0b013e318218db23

    View details for Web of Science ID 000293586200003

    View details for PubMedID 21832967

  • Point/counterpoint: pulsed reduced dose rate radiation therapy is likely to become the treatment modality of choice for recurrent cancers. Medical physics Ma, C. C., Luxton, G., Orton, C. G. 2011; 38 (9): 4909-4911

    View details for DOI 10.1118/1.3583794

    View details for PubMedID 21978035

  • Dose verification for respiratory-gated volumetric modulated arc therapy PHYSICS IN MEDICINE AND BIOLOGY Qian, J., Xing, L., Liu, W., Luxton, G. 2011; 56 (15): 4827-4838

    Abstract

    A novel commercial medical linac system (TrueBeam™, Varian Medical Systems, Palo Alto, CA) allows respiratory-gated volumetric modulated arc therapy (VMAT), a new modality for treating moving tumors with high precision and improved accuracy by allowing for regular motion associated with a patient's breathing during VMAT delivery. The purpose of this work is to adapt a previously-developed dose reconstruction technique to evaluate the fidelity of VMAT treatment during gated delivery under clinic-relevant periodic motion related to patient breathing. A Varian TrueBeam system was used in this study. VMAT plans were created for three patients with lung or pancreas tumors. Conventional 6 and 15 MV beams with flattening filter and high-dose-rate 10 MV beams with no flattening filter were used in these plans. Each patient plan was delivered to a phantom first without gating and then with gating for three simulated respiratory periods (3, 4.5 and 6 s). Using the adapted log-file-based dose reconstruction procedure supplemented with ion chamber array (Seven29™, PTW, Freiburg, Germany) measurements, the delivered dose was used to evaluate the fidelity of gated VMAT delivery. Comparison of Seven29 measurements with and without gating showed good agreement with gamma-index passing rates above 99% for 1%/1 mm dose accuracy/distance-to-agreement criteria. With original plans as reference, gamma-index passing rates were 100% for the reconstituted plans (1%/1 mm criteria) and 93.5-100% for gated Seven29 measurements (3%/3 mm criteria). In the presence of leaf error deliberately introduced into the gated delivery of a pancreas patient plan, both dose reconstruction and Seven29 measurement consistently indicated substantial dosimetric differences from the original plan. In summary, a dose reconstruction procedure was demonstrated for evaluating the accuracy of respiratory-gated VMAT delivery. This technique showed that under clinical operation, the TrueBeam system faithfully realized treatment plans with gated delivery. This methodology affords a useful tool for machine- and patient-specific quality assurance of the newly available respiratory-gated VMAT.

    View details for DOI 10.1088/0031-9155/56/15/013

    View details for Web of Science ID 000292885000014

    View details for PubMedID 21753232

  • Clinical development of a failure detection-based online repositioning strategy for prostate IMRT-Experiments, simulation, and dosimetry study MEDICAL PHYSICS Liu, W., Qian, J., Hancock, S. L., Xing, L., Luxton, G. 2010; 37 (10): 5287-5297

    Abstract

    To implement and evaluate clinic-ready adaptive imaging protocols for online patient repositioning (motion tracking) during prostate IMRT using treatment beam imaging supplemented by minimal, as-needed use of on-board kV.The authors examine the two-step decision-making strategy: (1) Use cine-MV imaging and online-updated characterization of prostate motion to detect target motion that is potentially beyond a predefined threshold and (2) use paired MV-kV 3D localization to determine overthreshold displacement and, if needed, reposition the patient. Two levels of clinical implementation were evaluated: (1) Field-by-field based motion correction for present-day linacs and (2) instantaneous repositioning for new-generation linacs with capabilities of simultaneous MV-kV imaging and remote automatic couch control during treatment delivery. Experiments were performed on a Varian Trilogy linac in clinical mode using a 4D motion phantom programed with prostate motion trajectories taken from patient data. Dosimetric impact was examined using a 2D ion chamber array. Simulations were done for 536 trajectories from 17 patients.Despite the loss of marker detection efficiency caused by the MLC leaves sometimes obscuring the field at the marker's projected position on the MV imager, the field-by-field correction halved (from 23% to 10%) the mean percentage of time that target displacement exceeded a 3 mm threshold, as compared to no intervention. This was achieved at minimal cost in additional imaging (average of one MV-kV pair per two to three treatment fractions) and with a very small number of repositionings (once every four to five fractions). Also with low kV usage (approximation 2/fraction), the instantaneous repositioning approach reduced overthreshold time by more than 75% (23% to 5%) even with severe MLC blockage as often encountered in current IMRT and could reduce the overthreshold time tenfold (to < 2%) if the MLC blockage problem were relieved. The information acquired for repositioning using combined MV-kV images was found to have submillimeter accuracy.This work demonstrated with a current clinical setup that substantial reduction of adverse targeting effects of intrafraction prostate motion can be realized. The proposed adaptive imaging strategy incurs minimal imaging dose to the patient as compared to other stereoscopic imaging techniques.

    View details for DOI 10.1118/1.3488887

    View details for Web of Science ID 000283483700016

    View details for PubMedID 21089763

  • Dose reconstruction for volumetric modulated arc therapy (VMAT) using cone-beam CT and dynamic log files PHYSICS IN MEDICINE AND BIOLOGY Qian, J., Lee, L., Liu, W., Chu, K., Mok, E., Luxton, G., Le, Q., Xing, L. 2010; 55 (13): 3597-3610

    Abstract

    Volumetric modulated arc therapy (VMAT) has recently emerged as a new clinical modality for conformal radiation therapy. The aim of this work is to establish a methodology and procedure for retrospectively reconstructing the actual dose delivered in VMAT based on the pre-treatment cone-beam computed tomography (CBCT) and dynamic log files. CBCT was performed before the dose delivery and the system's log files were retrieved after the delivery. Actual delivery at a control point including MLC leaf positions, gantry angles and cumulative monitor units (MUs) was recorded in the log files and the information was extracted using in-house developed software. The extracted information was then embedded into the original treatment DICOM-radiation therapy (RT) file to replace the original control point parameters. This reconstituted DICOM-RT file was imported into the Eclipse treatment planning system (TPS) and dose was computed on the corresponding CBCT. A series of phantom experiments was performed to show the feasibility of dose reconstruction, validate the procedure and demonstrate the efficacy of this methodology. The resultant dose distributions and dose-volume histograms (DVHs) were compared with those of the original treatment plan. The studies indicated that CBCT-based VMAT dose reconstruction is readily achievable and provides a valuable tool for monitoring the dose actually delivered to the tumor target as well as the sensitive structures. In the absence of setup errors, the reconstructed dose shows no significant difference from the original pCT-based plan. It is also elucidated that the proposed method is capable of revealing the dosimetric changes in the presence of setup errors. The method reported here affords an objective means for dosimetric evaluation of VMAT delivery and is useful for adaptive VMAT in future.

    View details for DOI 10.1088/0031-9155/55/13/002

    View details for Web of Science ID 000279004300002

    View details for PubMedID 20526034

  • IMAGE-GUIDED RADIOTHERAPY IN NEAR REAL TIME WITH INTENSITY-MODULATED RADIOTHERAPY MEGAVOLTAGE TREATMENT BEAM IMAGING INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Mao, W., Hsu, A., Riaz, N., Lee, L., Wiersma, R., Luxton, G., King, C., Xing, L., Solberg, T. 2009; 75 (2): 603-610

    Abstract

    To utilize image-guided radiotherapy (IGRT) in near real time by obtaining and evaluating the online positions of implanted fiducials from continuous electronic portal imaging device (EPID) imaging of prostate intensity-modulated radiotherapy (IMRT) delivery.Upon initial setup using two orthogonal images, the three-dimensional (3D) positions of all implanted fiducial markers are obtained, and their expected two-dimensional (2D) locations in the beam's-eye-view (BEV) projection are calculated for each treatment field. During IMRT beam delivery, EPID images of the megavoltage treatment beam are acquired in cine mode and subsequently analyzed to locate 2D locations of fiducials in the BEV. Simultaneously, 3D positions are estimated according to the current EPID image, information from the setup portal images, and images acquired at other gantry angles (the completed treatment fields). The measured 2D and 3D positions of each fiducial are compared with their expected 2D and 3D setup positions, respectively. Any displacements larger than a predefined tolerance may cause the treatment system to suspend the beam delivery and direct the therapists to reposition the patient.Phantom studies indicate that the accuracy of 2D BEV and 3D tracking are better than 1 mm and 1.4 mm, respectively. A total of 7330 images from prostate treatments were acquired and analyzed, showing a maximum 2D displacement of 6.7 mm and a maximum 3D displacement of 6.9 mm over 34 fractions.This EPID-based, real-time IGRT method can be implemented on any external beam machine with portal imaging capabilities without purchasing any additional equipment, and there is no extra dose delivered to the patient.

    View details for DOI 10.1016/j.ijrobp.2009.04.068

    View details for Web of Science ID 000269941600040

    View details for PubMedID 19735886

  • MRI GUIDANCE FOR ACCELERATED PARTIAL BREAST IRRADIATION IN PRONE POSITION: IMAGING PROTOCOL DESIGN AND EVALUATION INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Ahn, K., Hargreaves, B. A., Alley, M. T., Horst, K. C., Luxton, G., Daniel, B. L., Hristov, D. 2009; 75 (1): 285-293

    Abstract

    To design and evaluate a magnetic resonance imaging (MRI) protocol to be incorporated in the simulation process for external beam accelerated partial breast irradiation.An imaging protocol was developed based on an existing breast MRI technique with the patient in the prone position on a dedicated coil. Pulse sequences were customized to exploit T1 and T2 contrast mechanisms characteristic of lumpectomy cavities. A three-dimensional image warping algorithm was included to correct for geometric distortions related to nonlinearity of spatially encoding gradients. Respiratory motion, image distortions, and susceptibility artifacts of 3.5-mm titanium surgical clips were examined. Magnetic resonance images of volunteers were acquired repeatedly to analyze residual setup deviations resulting from breast tissue deformation.The customized sequences generated high-resolution magnetic resonance images emphasizing lumpectomy cavity morphology. Respiratory motion was negligible with the subject in the prone position. The gradient-induced nonlinearity was reduced to less than 1 mm in a region 15 cm away from the isocenter of the magnet. Signal-void regions of surgical clips were 4 mm and 8 mm for spin echo and gradient echo images, respectively. Typical residual repositioning errors resulting from breast deformation were estimated to be 3 mm or less.MRI guidance for accelerated partial breast irradiation with the patient in the prone position with adequate contrast, spatial fidelity, and resolution is possible.

    View details for DOI 10.1016/j.ijrobp.2009.03.063

    View details for Web of Science ID 000269328700045

    View details for PubMedID 19632067

  • Real-time 3D internal marker tracking during arc radiotherapy by the use of combined MV-kV imaging PHYSICS IN MEDICINE AND BIOLOGY Liu, W., Wiersma, R. D., Mao, W., Luxton, G., Xing, L. 2008; 53 (24): 7197-7213

    Abstract

    To minimize the adverse dosimetric effect caused by tumor motion, it is desirable to have real-time knowledge of the tumor position throughout the beam delivery process. A promising technique to realize the real-time image guided scheme in external beam radiation therapy is through the combined use of MV and onboard kV beam imaging. The success of this MV-kV triangulation approach for fixed-gantry radiation therapy has been demonstrated. With the increasing acceptance of modern arc radiotherapy in the clinics, a timely and clinically important question is whether the image guidance strategy can be extended to arc therapy to provide the urgently needed real-time tumor motion information. While conceptually feasible, there are a number of theoretical and practical issues specific to the arc delivery that need to be resolved before clinical implementation. The purpose of this work is to establish a robust procedure of system calibration for combined MV and kV imaging for internal marker tracking during arc delivery and to demonstrate the feasibility and accuracy of the technique. A commercially available LINAC equipped with an onboard kV imager and electronic portal imaging device (EPID) was used for the study. A custom built phantom with multiple ball bearings was used to calibrate the stereoscopic MV-kV imaging system to provide the transformation parameters from imaging pixels to 3D world coordinates. The accuracy of the fiducial tracking system was examined using a 4D motion phantom capable of moving in accordance with a pre-programmed trajectory. Overall, spatial accuracy of MV-kV fiducial tracking during the arc delivery process for normal adult breathing amplitude and period was found to be better than 1 mm. For fast motion, the results depended on the imaging frame rates. The RMS error ranged from approximately 0.5 mm for the normal adult breathing pattern to approximately 1.5 mm for more extreme cases with a low imaging frame rate of 3.4 Hz. In general, highly accurate real-time tracking of implanted markers using hybrid MV-kV imaging is achievable and the technique should be useful to improve the beam targeting accuracy of arc therapy.

    View details for DOI 10.1088/0031-9155/53/24/013

    View details for Web of Science ID 000261310200013

    View details for PubMedID 19043177

  • LINAC-based on-board imaging feasibility and the dosimetric consequences of head roll in head-and-neck IMRT plans MEDICAL DOSIMETRY Kim, G., Pawlicki, T., Le, Q., Luxton, G. 2008; 33 (1): 93-99

    Abstract

    Kilovoltage imaging systems on linear accelerators are used for patient localization in many clinics. The purpose of this work is to assess on-board imaging (OBI) detection of systematic setup errors and in particular, the dosimetric consequences of undetected head roll in head-and-neck intensity modulated radiation therapy (IMRT) plans when using these systems. The system used in this study was the Trilogy linear accelerator and associated software (Varian Medical Systems, Palo Alto, CA). Accuracy of OBI localization was evaluated using an anthropomorphic head phantom. The head phantom is rigidly attached to a specially designed positioning device with 5 degrees of freedom, 3 translational and 2 rotational in the axial and coronal planes. Simulated setup errors were 3 degrees and 5 degrees rotations in the axial plane and displacements of 5 mm in the left-right, anterior-posterior, and superior-inferior directions. The coordinates set by the positioning device were compared with the coordinates obtained as measured by using the image matching tools of paired 2-dimensional (2D) orthogonal image matching, and 3D cone-beam computed tomography (CT) volume matching. In addition, 6 physician-approved IMRT plans of nasopharynx and tonsil carcinoma were recalculated to evaluate the impact of undetected 3 degrees and 5 degrees head roll. Application of cone-beam CT (CBCT) for patient localization was superior to 2D matching techniques for detecting rotational setup errors. The use of CBCT allowed the determination of translational errors to within 0.5 mm, whereas kV planar was within 1 to 2 mm. Head roll in the axial plane was not easily detected with orthogonal image sets. Compared to the IMRT plans with no head roll, dose-volume histogram analysis demonstrated an average increase in the maximal spinal cord dose of 3.1% and 6.4% for 3 degrees and 5 degrees angles of rotation, respectively. Dose to the contralateral parotid was unchanged with 3 degrees roll and increased by 2.7% with 5 degrees roll. The results of this study show that volumetric setup verification using CBCT can improve bony anatomy setup detection to millimeter accuracy, and is a reliable method to detect head roll. However, the magnitude of possible dose errors due to undetected head roll suggests that CBCT does not need to be performed on a daily basis but rather weekly or bi-weekly to ensure fidelity of the head position with the immobilization system.

    View details for DOI 10.1016/j.meddos.2007.05.004

    View details for Web of Science ID 000253610200015

    View details for PubMedID 18262130

  • A new formula for normal tissue complication probability (NTCP) as a function of equivalent uniform dose (EUD) PHYSICS IN MEDICINE AND BIOLOGY Luxton, G., Keall, P. J., King, C. R. 2008; 53 (1): 23-36

    Abstract

    To facilitate the use of biological outcome modeling for treatment planning, an exponential function is introduced as a simpler equivalent to the Lyman formula for calculating normal tissue complication probability (NTCP). The single parameter of the exponential function is chosen to reproduce the Lyman calculation to within approximately 0.3%, and thus enable easy conversion of data contained in empirical fits of Lyman parameters for organs at risk (OARs). Organ parameters for the new formula are given in terms of Lyman model m and TD(50), and conversely m and TD(50) are expressed in terms of the parameters of the new equation. The role of the Lyman volume-effect parameter n is unchanged from its role in the Lyman model. For a non-homogeneously irradiated OAR, an equation relates d(ref), n, v(eff) and the Niemierko equivalent uniform dose (EUD), where d(ref) and v(eff) are the reference dose and effective fractional volume of the Kutcher-Burman reduction algorithm (i.e. the LKB model). It follows in the LKB model that uniform EUD irradiation of an OAR results in the same NTCP as the original non-homogeneous distribution. The NTCP equation is therefore represented as a function of EUD. The inverse equation expresses EUD as a function of NTCP and is used to generate a table of EUD versus normal tissue complication probability for the Emami-Burman parameter fits as well as for OAR parameter sets from more recent data.

    View details for DOI 10.1088/0031-9155/53/1/002

    View details for Web of Science ID 000252792400002

    View details for PubMedID 18182685

  • Quantification of motion of different thoracic locations using four-dimensional computed tomography: Implications for radiotherapy planning INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Maxim, P. G., Loo, B. W., Shirazi, H., Thorndyke, B., Luxton, G., Le, Q. 2007; 69 (5): 1395-1401

    Abstract

    To assess the respiratory motion of different thoracic nodal locations and its dependence on the presence of enlarged nodes; to assess the respiratory motion of different parenchymal tumor locations; and to determine the appropriate margins to cover the respiratory motion of targets at these locations.We reviewed the four-dimensional computed tomography scans of 20 patients with thoracic tumors treated at our institution. The motion of four central thoracic locations (aortic arch, carina, and bilateral hila), parenchymal tumor locations (upper vs. lower, and anterior vs. middle vs. posterior thorax), and bilateral diaphragmatic domes was measured.For the central thoracic locations, the largest motion was in the superoinferior (SI) dimension (>5 mm for bilateral hila and carina, but <4 mm for aortic arch). No significant difference was found in the motion of these locations in the absence or presence of enlarged nodes. For parenchymal tumors, upper tumors exhibited smaller SI motion than did lower tumors (3.7 vs. 10.4 mm, p = 0.029). Similarly, anterior tumors exhibited smaller motion than did posterior tumors in both the SI (4.0 vs. 8.0 mm, p = 0.013) and lateral (2.8 vs. 4.6 mm, p = 0.045) directions. The margins that would be needed to encompass the respiratory motion of each of the evaluated locations in 95% of patients were tabulated and range from 3.4 to 37.2 mm, depending on the location and direction.The results of our study have provided data for appropriate site-specific internal target volume expansion that could be useful in the absence of four-dimensional computed tomography-based treatment planning. However, generalizing the results from a small patient population requires discretion.

    View details for Web of Science ID 000251561100008

    View details for PubMedID 17869025

  • A study of image-guided intensity-modulated radiotherapy with fiducials for localized prostate cancer including pelvic lymph nodes INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Hsu, A., Pawlicki, T., Luxton, G., Hara, W., King, C. R. 2007; 68 (3): 898-902

    Abstract

    To study the impact on nodal coverage and dose to fixed organs at risk when using daily fiducial localization of the prostate to deliver intensity-modulated radiotherapy (IMRT).Five patients with prostate cancer in whom prostate and pelvic nodes were irradiated with IMRT were studied. Dose was prescribed such that 95% of the prostate planning target volume (PTV) and 90% of the nodal PTV were covered. Random and systematic prostate displacements in the anterior-posterior, superior-inferior, and left-right directions were simulated to shift the original isocenter of the IMRT plan. The composite dose during the course of treatment was calculated.Compared with a static setup, simulating random shifts reduced dose by less than 1.5% for nodal hotspot (i.e., dose to 1 cm(3)), by less than 1% for the 90% nodal PTV coverage, and by less than 0.5% for the nodal mean dose. Bowel and femoral head hotspots were reduced by less than 1.5% and 2%, respectively. A 10-mm systematic offset reduced nodal coverage by up to 10%.The use of prostate fiducials for daily localization during IMRT treatment results in negligible changes in dose coverage of pelvic nodes or normal tissue sparing in the absence of a significant systematic offset. This offers a simple and practical solution to the problem of image-guided radiotherapy for prostate cancer when including pelvic nodes.

    View details for DOI 10.1016/j.ijrobp.2007.02.030

    View details for Web of Science ID 000247284600035

    View details for PubMedID 17459610

  • Investigation of linac-based image-guided hypofractionated prostate radiotherapy MEDICAL DOSIMETRY Pawlicki, T., Kim, G., Hsu, A., Cotrutz, C., Boyer, A. L., Xing, L., King, C. R., Luxton, G. 2007; 32 (2): 71-79

    Abstract

    A hypofractionation treatment protocol for prostate cancer was initiated in our department in December 2003. The treatment regimen consists of a total dose of 36.25 Gy delivered at 7.25 Gy per fraction over 10 days. We discuss the rationale for such a prostate hypofractionation protocol and the need for frequent prostate imaging during treatment. The CyberKnife (Accuray Inc., Sunnyvale, CA), a linear accelerator mounted on a robotic arm, is currently being used as the radiation delivery device for this protocol, due to its incorporation of near real-time kV imaging of the prostate via 3 gold fiducial seeds. Recently introduced conventional linac kV imaging with intensity modulated planning and delivery may add a new option for these hypofractionated treatments. The purpose of this work is to investigate the use of intensity modulated radiotherapy (IMRT) and the Varian Trilogy Accelerator with on-board kV imaging (Varian Medical Systems Inc., Palo Alto, CA) for treatment of our hypofractionated prostate patients. The dose-volume histograms and dose statistics of 2 patients previously treated on the CyberKnife were compared to 7-field IMRT plans. A process of acquiring images to observe intrafraction prostate motion was achieved in an average time of about 1 minute and 40 seconds, and IMRT beam delivery takes about 40 seconds per field. A complete 7-field IMRT plan can therefore be imaged and delivered in 10 to 17 minutes. The Varian Trilogy Accelerator with on-board imaging and IMRT is well suited for image-guided hypofractionated prostate treatments. During this study, we have also uncovered opportunities for improvement of the on-board imaging hardware/software implementation that would further enhance performance in this regard.

    View details for DOI 10.1016/j.meddos.2007.01.004

    View details for Web of Science ID 000246485600002

    View details for PubMedID 17472885

  • A quality assurance program for the on-board imager (R) MEDICAL PHYSICS Yoo, S., Kim, G., Hammoud, R., Elder, E., Pawlicki, T., Guan, H., Fox, T., Luxton, G., Yin, F., Munro, P. 2006; 33 (11): 4431-4447

    Abstract

    To develop a quality assurance (QA) program for the On-Board Imager (OBI) system and to summarize the results of these QA tests over extended periods from multiple institutions. Both the radiographic and cone-beam computed tomography (CBCT) mode of operation have been evaluated. The QA programs from four institutions have been combined to generate a series of tests for evaluating the performance of the On-Board Imager. The combined QA program consists of three parts: (1) safety and functionality, (2) geometry, and (3) image quality. Safety and functionality tests evaluate the functionality of safety features and the clinical operation of the entire system during the tube warm-up. Geometry QA verifies the geometric accuracy and stability of the OBI/CBCT hardware/software. Image quality QA monitors spatial resolution and contrast sensitivity of the radiographic images. Image quality QA for CBCT includes tests for Hounsfield Unit (HU) linearity, HU uniformity, spatial linearity, and scan slice geometry, in addition. All safety and functionality tests passed on a daily basis. The average accuracy of the OBI isocenter was better than 1.5 mm with a range of variation of less than 1 mm over 8 months. The average accuracy of arm positions in the mechanical geometry QA was better than 1 mm, with a range of variation of less than 1 mm over 8 months. Measurements of other geometry QA tests showed stable results within tolerance throughout the test periods. Radiographic contrast sensitivity ranged between 2.2% and 3.2% and spatial resolution ranged between 1.25 and 1.6 lp/mm. Over four months the CBCT images showed stable spatial linearity, scan slice geometry, contrast resolution (1%; <7 mm disk) and spatial resolution (>6 lp/cm). The HU linearity was within +/-40 HU for all measurements. By combining test methods from multiple institutions, we have developed a comprehensive, yet practical, set of QA tests for the OBI system. Use of the tests over extended periods show that the OBI system has reliable mechanical accuracy and stable image quality. Nevertheless, the tests have been useful in detecting performance deficits in the OBI system that needed recalibration. It is important that all tests are performed on a regular basis.

    View details for DOI 10.1118/1.2362872

    View details for Web of Science ID 000242250800048

    View details for PubMedID 17153422

  • Overview of image-guided radiation therapy MEDICAL DOSIMETRY Xing, L., Thorndyke, B., Schreibmann, E., Yang, Y., Li, T., Kim, G., Luxton, G., Koong, A. 2006; 31 (2): 91-112

    Abstract

    Radiation therapy has gone through a series of revolutions in the last few decades and it is now possible to produce highly conformal radiation dose distribution by using techniques such as intensity-modulated radiation therapy (IMRT). The improved dose conformity and steep dose gradients have necessitated enhanced patient localization and beam targeting techniques for radiotherapy treatments. Components affecting the reproducibility of target position during and between subsequent fractions of radiation therapy include the displacement of internal organs between fractions and internal organ motion within a fraction. Image-guided radiation therapy (IGRT) uses advanced imaging technology to better define the tumor target and is the key to reducing and ultimately eliminating the uncertainties. The purpose of this article is to summarize recent advancements in IGRT and discussed various practical issues related to the implementation of the new imaging techniques available to radiation oncology community. We introduce various new IGRT concepts and approaches, and hope to provide the reader with a comprehensive understanding of the emerging clinical IGRT technologies. Some important research topics will also be addressed.

    View details for DOI 10.1016/j.meddos.2005.12.004

    View details for Web of Science ID 000237818000002

    View details for PubMedID 16690451

  • Dosimetry and radiobiologic model comparison of IMRT and 3D conformal radiotherapy in treatment of carcinoma of the prostate INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Luxton, G., Hancock, S. L., Boyer, A. L. 2004; 59 (1): 267-284

    Abstract

    Intensity-modulated radiotherapy (IMRT) has introduced novel dosimetry that often features increased dose heterogeneity to target and normal structures. This raises questions of the biologic effects of IMRT compared to conventional treatment. We compared dosimetry and radiobiologic model predictions of tumor control probability (TCP) and normal tissue complication probability (NTCP) for prostate cancer patients planned for IMRT as opposed to standardized three-dimensional conformal radiotherapy (3DCRT).Segmented multileaf collimator IMRT treatment plans for 32 prostate cancer patients were compared to 3DCRT plans for the same patients. Twenty-two received local-field irradiation (LFI), and 10 received extended-field irradiation (EFI) that included pelvic lymph nodes. For LFI, IMRT was planned for delivery of 2 Gy minimum dose to the prostate (> or =99% volume coverage) for 35 fractions. The 3DCRT plans, characterized by more homogenous dose to the target, were designed according to a different protocol to deliver 2 Gy to the center of the prostate for 37 fractions. Mean total dose from 35 fractions of IMRT was equal to mean total dose from 37 fractions of 3DCRT. For EFI, both IMRT and 3DCRT were planned for 2 Gy per fraction to a total dose of 50 Gy to prostate and pelvic lymph nodes, followed by 2 Gy per fraction to 20 Gy to the prostate alone. Treatment dose for EFI-IMRT was defined as minimum dose to the target, whereas for EFI-3DCRT, it was defined as dose to the center of the prostate. TCP was calculated for the prostate in the linear-quadratic model for two choices of alpha/beta. NTCP was calculated with the Lyman model for organs at risk, using Kutcher-Burman dose-volume histogram reduction with Emami parameters.Dose to the prostate, expressed as mean +/- standard deviation, was 74.7 +/- 1.1 Gy for IMRT vs. 74.6 +/- 0.3 Gy for 3D for the LFI plans, and 74.8 +/- 0.6 Gy for IMRT vs. 71.5 +/- 0.6 Gy for 3D for the EFI plans. For the studied protocols, TCP was greater for IMRT than for 3D across the full range of target sensitivity, for both localized- and extended-field irradiation. For LFI, this was due to the smaller number of fractions (35 vs. 37) used for IMRT, and for EFI, this was due to the greater mean dose for IMRT, compared to 3D. For all organs, mean NTCP tended to be lower for IMRT than for 3D, although NTCP values were very small for both 3D and IMRT. Differences were statistically significant for rectum (LFI and EFI), bladder (EFI), and bowel (EFI). For both LFI and EFI, the calculated NTCPs qualitatively agreed with early published clinical data comparing genitourinary and gastrointestinal complications of IMRT and 3D. Present calculations support the hypothesis that accurately delivered IMRT for prostate cancer can limit dose to normal tissue by reducing treatment margins relative to conventional 3D planning, to allow a reduction in complication rate spanning several sensitive structures while maintaining or increasing tumor control probability.

    View details for DOI 10.1016/j.ijrobp.2004.01.024

    View details for Web of Science ID 000221047500034

    View details for PubMedID 15093924

  • Lens dose in MLC-based IMRT treatments of the head and neck INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Pawlicki, T., Luxton, G., Le, Q. T., Findley, D., Ma, C. M. 2004; 59 (1): 293-299

    Abstract

    The objectives of this work are: (1) to determine typical dose to the lens during step-and-shoot intensity modulated radiotherapy (IMRT) treatments of the head and neck, and (2) to report on the dose calculation accuracy of a commercial inverse planning system in predicting lens dose.The Corvus inverse treatment planning system (Nomos, Cranberry Township, PA) was used to plan IMRT treatments for patients with head-and-neck cancers in our clinic. Patients were treated on Varian C-series linacs (Varian, Palo Alto, CA) with 4-MV or 6-MV X-rays. A Rando phantom (Alderson Laboratories, Stamford, CT) was specially modified to accommodate 1 x 1 x 1 mm(3) thermoluminescent dosimeters at the position of the lens. The IMRT treatment plans were then delivered to the modified Rando phantom. The thermoluminescent dosimeter measurements were converted to dose and taken as an estimate of the lens dose. A total of 20 cases were used in this study (15 cases with 4 MV and 5 cases with 6 MV).Expressed as a percentage of the prescription dose, the mean dose to the left and right lens for all 4-MV cases was 9.1% (range, 2.0% to 61.3%). For the 6-MV cases, the mean dose to the left and right lens was 12.8% (range, 3.6% to 41.3%). For both the 4-MV and 6-MV cases, the case of maximum dose occurred when the IMRT treatment target included volumes superior to the level of the lens. The field size and number of monitor units did not correlate with the measured lens dose. The only factor of significance affecting lens dose was the inferior-to-superior distance of the target to the lens. For target-lens distance >/=6 mm, the maximum measured lens doses were 5.9% and 9.0% relative to the prescribed dose for the 4-MV and 6-MV beams, respectively. These data are similar to those observed in conventional head-and-neck treatments. For all cases, the difference between the dose measured and that predicted by Corvus was less than 2% and 4% of the dose prescribed to the gross tumor volume for the 4-MV and 6-MV cases, respectively.In IMRT, factors such as leaf leakage and number of monitor units play a secondary role and are not more significant than what is observed in conventional head-and-neck treatment when the lens is shielded by the collimator jaws. The target-lens distance is the parameter that affects the lens dose most strongly. For cases where the tumor is at or above the level of the lens, the lens dose can amount to an appreciable fraction of the prescription dose. To keep the lens dose to a minimum, noncoplanar beams that enter or exit into the lens should not be used.

    View details for DOI 10.1016/j.ijrobp.2004.01.019

    View details for Web of Science ID 000221047500036

    View details for PubMedID 15093926

  • Independent dosimetric calculation with inclusion of head scatter and MLC transmission for IMRT MEDICAL PHYSICS Yang, Y., Xing, L., Li, J. G., Palta, J., Chen, Y., Luxton, G., Boyer, A. 2003; 30 (11): 2937-2947

    Abstract

    Independent verification of the MU settings and dose calculation of IMRT treatment plans is an important step in the IMRT quality assurance (QA) procedure. At present, the verification is mainly based on experimental measurements, which are time consuming and labor intensive. Although a few simplified algorithms have recently been proposed for the independent dose (or MU) calculation, head scatter has not been precisely taken into account in all these investigations and the dose validation has mainly been limited to the central axis. In this work we developed an effective computer algorithm for IMRT MU and dose validation. The technique is superior to the currently available computer-based MU check systems in that (1) it takes full consideration of the head scatter and leaf transmission effects; and (2) it allows a precise dose calculation at an arbitrary spatial point instead of merely a point on the central axis. In the algorithm the dose at an arbitrary spatial point is expressed as a summation of the contributions of primary and scatter radiation from all beamlets. Each beamlet is modulated by a dynamic modulation factor (DMF), which is determined by the MLC leaf trajectories, the head scatter, the jaw positions, and the MLC leaf transmission. A three-source model was used to calculate the head scatter distribution for irregular segments shaped by MLC and the scatter dose contributions were computed using a modified Clarkson method. The system reads in MLC leaf sequence files (or RTP files) generated by the Corvus (NOMOS Corporation, Sewickley, PA) inverse planning system and then computes the doses at the desired points. The algorithm was applied to study the dose distributions of several testing intensity modulated fields and two multifield Corvus plans and the results were compared with Corvus plans and experimental measurements. The final dose calculations at most spatial points agreed with the experimental measurements to within 3% for both the specially designed testing fields and the clinical intensity modulated field. Furthermore, excellent agreement (mostly within +/- 3.0%) was also found between our independent calculation and the ion chamber measurements at both central axis and off-axis positions for the multifield Corvus IMRT plans. These results indicate that the approach is robust and valuable for routine clinical IMRT plan validation.

    View details for DOI 10.1118/1.1617391

    View details for Web of Science ID 000186596900011

    View details for PubMedID 14655941

  • Calculation of brachytherapy doses does not need TG-43 factorization. Against the proposition. Medical physics Luxton, G. 2003; 30 (6): 998-999

    View details for PubMedID 12852520

  • An image fusion study of the geometric accuracy of magnetic resonance imaging with the Leksell stereotactic localization system. Journal of applied clinical medical physics Yu, C., Petrovich, Z., Apuzzo, M. L., Luxton, G. 2001; 2 (1): 42-50

    Abstract

    A special acrylic phantom designed for both magnetic resonance imaging (MRI) and computed tomography (CT) was used to assess the geometric accuracy of MRI-based stereotactic localization with the Leksell stereotactic head frame and localizer system. The acrylic phantom was constructed in the shape of a cube, 164 mm in each dimension, with three perpendicular arrays of solid acrylic rods, 5 mm in diameter and spaced 30 mm apart within the phantom. Images from two MR scanners and a CT scanner were obtained with the same Leksell head frame placement. Using image fusion provided by the Leksell GammaPlan (LGP) software, the coordinates of the intraphantom rod positions from two MRI scanners were compared to that of CT imaging. The geometric accuracy of MR images from the Siemens scanner was greatly improved after the implementation of a special software patch provided by the manufacturer. In general, much better accuracy was achieved in the transverse plane where images were acquired. Most distortion was found around the periphery while least distortion was present in the middle and most other parts of the phantom. For most intracranial lesions undergoing stereotactic radiosurgery, accuracy of target localization can be achieved within size of a voxel, especially with the Siemens scanner. However, extra caution should be taken for imaging of peripheral lesions where the distortion is the greatest.

    View details for PubMedID 11674837

  • Application of radiosurgery principles to a target in the breast: A dosimetric study MEDICAL PHYSICS Jozsef, G., Luxton, G., Formenti, S. C. 2000; 27 (5): 1005-1010

    Abstract

    To investigate the technical and physical feasibility of using a radiosurgery-like technique to irradiate a small target within the breast with a single fraction.During diagnostic biopsy, a tantalum surgical clip is placed in the lesion identified at mammography. Transverse CT scans over the entire breast are obtained, as the patient lies prone on a special table that allows the breast to hang down. The clip is used as a reference point to define the isocenter of the radiation treatment.The clip is visible on port films taken with a 4 MV beam, allowing the isocenter to be set to its planned location. No movement of the hanging breast is visually detected. The possible beam directions are enclosed by a 220 degrees horizontal x 180 degrees vertical angular interval. Dosimetry of two "radiosurgical" examples, (A) seven fixed horizontal beams and (B) six 45 degrees arcs and a 90 degrees sagittal arc using a 4 MV x-ray beam with a 32 mm diameter collimator, are discussed. Both field arrangements produce adequate tumor coverage: the minimum target dose is 83% of the dose maximum in the fixed beam arrangement and 86% in the multiarc setup. In arrangement A the lung and other tissues external to the breast receive dose only from scattered radiation. In arrangement B the maximum lung dose is less than 5% of the dose to isocenter.From a dosimetric point of view both described techniques are feasible, and the radiosurgery-like treatment is executable.

    View details for Web of Science ID 000087212200021

    View details for PubMedID 10841403

  • Monitor unit calculation for an intensity modulated photon held by a simple scatter-summation algorithm PHYSICS IN MEDICINE AND BIOLOGY Xing, L., Chen, Y., Luxton, G., Li, J. G., Boyer, A. L. 2000; 45 (3): N1-N7

    Abstract

    An important issue in intensity modulated radiation therapy (IMRT) is the verification of the monitor unit (MU) calculation of the planning system using an independent procedure. Because of the intensity modulation and the dynamic nature of the delivery process, the problem becomes much more involved than that in conventional radiation therapy. In this work, a closed formula for MU calculation is derived. The approach is independent of the specific form of leaf sequence algorithms. It is straightforward to implement the procedure using a simple computer program. The approach is illustrated by a simplified example and is demonstrated by a few CORVUS (NOMOS Corporation, Sewickley, PA) treatment plans. The results indicate that it is robust and suitable for IMRT MU verification.

    View details for Web of Science ID 000085887000017

    View details for PubMedID 10730973

  • Quality assurance of beam accuracy for Leksell Gamma Unit. Journal of applied clinical medical physics Yu, C., Petrovich, Z., Luxton, G. 2000; 1 (1): 28-31

    Abstract

    For the acceptance test and annual quality assurance of the Leksell Gamma Unit, measurement of the beam accuracy, defined as a distance between mechanical and radiological isocenters, poses a challenge to medical physicists. The specification for the beam accuracy is within 0.5 mm for the 4-mm collimator helmet. In this report, we introduce a simple technique to analyze the beam accuracy by using a conventional film densitometer plus mathematical modeling. A small piece of film was placed inside the film cassette containing a sharp needle. The needle is located such that its tip is exactly positioned at the mechanical isocenter. Before exposure, the film was pierced by the needle. Density profile was measured by using a densitometer with a spatial resolution of 0.8 mm. The profile was then fitted to a model of the two Gaussian functions. One is for the radiation field profile, the other for a dip caused by the narrow hole. The difference between the centers of the two Gaussian functions defines the deviation of the beam accuracy from the mechanical center of the unit. The deviations for x, y, and z directions from one of our annual measurements are 0.032, 0.054, and 0.195 mm, respectively. The combined deviation is 0.20 mm, which is well within the specification and in excellent agreement with the results from the manufacture's laser measurement. This technique provides a simple, accurate and practical tool for measurement of the beam accuracy in the acceptance test and annual quality assurance of the Leksell Gamma Unit.

    View details for PubMedID 11674816

  • Image-guided radiosurgery for the spine and pancreas. Computer aided surgery Murphy, M. J., Adler, J. R., Bodduluri, M., Dooley, J., Forster, K., Hai, J., Le, Q., Luxton, G., Martin, D., Poen, J. 2000; 5 (4): 278-288

    Abstract

    A robotic image-guided radiosurgical system has been modified to treat extra-cranial sites using implanted fiducials and skeletal landmarks to locate the treatment targets. The system has been used to treat an artero-venous malformation in the cervical spine, a recurrent schwannoma of the thoracic spine, a metastatic adenocarcinoma of the lumbar spine, and three pancreatic cancers. During each treatment, the image guidance system monitored the position of the target site and relayed the target coordinates to the beam-pointing system at discrete intervals. The pointing system then dynamically aligned the therapy beam with the lesion, automatically compensating for shifts in target position. Breathing-related motion of the pancreas lesions was managed by coordinating beam gating with breath-holding by the patient. The system maintained alignment with the spine lesions to within +/- 0.2 mm on average, and to within +/- 1 mm for the pancreatic tumors. This experience has demonstrated the feasibility of using image-guided robotic radiosurgery outside the cranium.

    View details for PubMedID 11029160

  • Radial dose distribution, dose to water and dose rate constant for monoenergetic photon point sources from 10 keV to 2 MeV: EGS4 Monte Carlo model calculation MEDICAL PHYSICS Luxton, G., Jozsef, G. 1999; 26 (12): 2531-2538

    Abstract

    A comprehensive set of dose distributions from monoenergetic photon-emitting isotropic point sources in a medium can be used as a reference database for the dosimetry of photon emitter sources in that medium. Data of this type for water over the photon energy range from 15 keV to 2 MeV have been published based on calculations using a one-dimensional photon transport model. The present work, based on a previously published EGS4 Monte Carlo code, updates the classic data set of Berger and provides more extensive calculations than previously available. Air kerma strength per unit photon emission rate from an isotropic point emitter is obtained as a function of energy using published data for mass energy absorption coefficients. The TG-43 dose rate constant for water as a function of energy is calculated for monoenergetic photon emitters as the ratio of dose rate to water at 1 cm to air kerma strength for unit photon emission rate. Results for the radial dose distribution agree well with the data of Berger between 40 and 400 keV. For energies > or =500 keV, a previously undescribed buildup region for the radial dose function is identified. Thickness of the buildup region ranges from 1 mm at 500 keV to 8 mm at 2 MeV. Between 15 and 30 keV, the radial dose function within a few millimeters of the emitter is calculated to be 4%-5% higher than values derived from Berger's data. The maximum dose rate constant for monoenergetic photon emitters occurs at an energy of 60 keV, and has the value 1.355 cGy h(-1)U(-1), where U is the unit of air kerma strength, 1 microGy m2 h(-1). This would correspond to the maximum hypothetical dose rate constant for a brachytherapy photon source emitting photons of energy < or =2 MeV.

    View details for Web of Science ID 000084359200005

    View details for PubMedID 10619236

  • TLD dose measurement: A simplified accurate technique for the dose range from 0.5 cGy to 1000 cGy MEDICAL PHYSICS Yu, C., Luxton, G. 1999; 26 (6): 1010-1016

    Abstract

    A simplified TLD technique characterized by high precision and reproducibility of dose measurement is presented. One hundred eighty LiF TLD rods 1 mm diam x 3 mm length as obtained from the manufacturer were annealed for 1 h at 400 degrees C followed immediately by 2 h at 105 degrees C. After exposure to a dose of 1 Gy of 4 MV x rays, TLDs were annealed for 15 min at 105 degrees C, then read out. TLDs were then sorted into five groups, ranging from 26 to 50 rods each with approximately equal sensitivity after correcting for the drift in the sensitivity of the TLD reader during the readout session. Maintaining group identity, the TLDs were again annealed, irradiated and read out. Fewer than 10% of the TLDs were removed from each group because the corrected readings differed from the respective group mean by more than 3.5%. The standard deviation of the readout was approximately 1.5% within each group. The planchet heater was not flushed with nitrogen gas. Various tests were performed to assess the stability of the group sorting technique and the linearity of TLD dose response. After reannealing, five TLDs were randomly drawn from one of the presorted groups, and subjected to various dose of 4 MV radiation over the range from 0.5 to 1000 cGy. This resulted in an average readout standard deviation of 1.2%. Response per unit dose was almost flat over the range from 0.5 cGy to 100 cGy, and increased by 15% over the range from 100 cGy to 1000 cGy. TLD sensitivity was affected by the duration of the anneal, but was virtually independent of the various time delays between irradiation, prereadout anneal, and readout. The group annealing and sorting (GAS) procedure provides a simple, reliable, precise, convenient, and accurate method for TLD measurements.

    View details for Web of Science ID 000080958800019

    View details for PubMedID 10436903

  • Gamma knife radiosurgery for metastatic melanoma: An analysis of survival, outcome, and complications NEUROSURGERY Lavine, S. D., Petrovich, Z., Cohen-Gadol, A. A., Masri, L. S., Morton, D. L., O'Day, S. J., Essner, R., Zelman, V., Yu, C., Luxton, G., Apuzzo, M. L. 1999; 44 (1): 59-64

    Abstract

    Although the mainstays for treatment of metastatic brain disease have been surgery and/or external beam radiation therapy, an increasing number of patients are being referred for stereotactic radiosurgery as the primary intervention for their intracranial pathological abnormalities. The lack of efficacy and cognitive and behavioral consequences of whole brain irradiation have prompted clinicians to select patients for alternative therapies. This study analyzes the effectiveness of Leksell gamma unit therapy for metastatic melanoma to the brain.We present our experience with 59 Leksell gamma unit treatment sessions in 45 consecutive patients who presented with metastatic melanoma to the brain. Five of these procedures were performed as salvage therapy for patients who needed second radiosurgical treatment for new lesions that were remote from the previous targets and were not included in the overall analyses.The population included 78% male patients. The mean patient age was 53 years (age range, 24-80 yr). The mean time from diagnosis of primary melanoma to discovery of brain metastasis was 43 months (median, 27.5 mo; range, 1-180 mo). At the time of diagnosis of brain disease, 35.5% of the patients (16 of 45 patients) had neurological symptoms, 77.7% (35 of 45 patients) had known visceral metastases, and 11.1% (5 of 45 patients) had seizure disorders. Eighty-six percent of the lesions (80 of 93 lesions) were cortical, 12% (11 of 93 lesions) were cerebellar, 1% (1 of 93 lesions) were pontine, and 1% (1 of 93 lesions) were thalamic. Fifty-seven percent of the sessions (31 of 54 sessions) were performed for a single lesion, 24.1% (13 of 54 sessions) for two lesions, 9.2% (5 of 54 sessions) for three lesions, 7.4% (4 of 54 sessions) for four lesions, and 1.8% (1 of 54 sessions) for five lesions. The mean treatment volume was 5.6 cc, with a mean prescription of 21.6 Gy to the 56.0% mean isodose line. The median survival time of the patients in our population, using Kaplan-Meier curves, was 43 months from the time of diagnosis of primary melanoma (range, 3-180 mo) and 8 months (range, 1-20 mo) from the time of gamma knife treatment. Complications included seizures within 24 hours of the procedure in four patients, with transient nausea and vomiting in three patients, transient worsening of preprocedure paresis responsive to steroids in three patients, and increased confusion in one patient. All 45 patients were located for follow-up (mean follow-up duration, 1 yr). After gamma knife treatment, 78% of the patients (35 of 45 patients) experienced either improved or stable neurological symptomatology before death or at the time of the latest follow-up examination. There were 26 deaths (58%). The cause of death was determined to be neurological in only 2 of 45 patients (7.7%). Follow-up magnetic resonance images revealed a 97% local tumor control rate of gamma knife-treated lesions, with 28% radiographic disappearance (9 of 32 cases). Six patients developed new lesions remote from radiosurgical targets and underwent second procedures.Although metastatic melanoma to the brain continues to have a foreboding prognosis for long-term survival, gamma knife radiosurgery seems to be a relatively safe, noninvasive, palliative therapy, halting or reversing neurological progression in 77.8% of treated patients (35 of 45 patients). The survival rate matches or exceeds those previously reported for surgery and other forms of radiotherapy. Only 7.7% of the patients in our study population who died as a result of metastatic melanoma (2 of 26 patients) died as a result of neurological disease. The routine use of therapeutic level antiseizure medication is emphasized, considering the findings of our review.

    View details for Web of Science ID 000077752300029

    View details for PubMedID 9894964

  • TLD measurements of the relative output factors for the Leksell Gamma Knife STEREOTACTIC AND FUNCTIONAL NEUROSURGERY Yu, C., Luxton, G., Apuzzo, M. L., Petrovich, Z. 1999; 72: 150-158

    Abstract

    The accuracy of the output factor directly affects the accuracy of dose delivery during patient treatment. At our Gamma Knife center, annual output factor measurements have been carried out by using a high accuracy TLD technique, characterized by the group annealing and sorting (GAS) procedure. For each collimator exposure, one to five LiF Thermoluminescent Dosimeter (TLD) 1 x 1 x 1 mm3 cubes were used, depending upon the collimator size, and the process was repeated until approximately 10 TLDs had been exposed for each collimator. Transit radiation dose accumulated during the motion of the treatment couch was measured for each collimator helmet, and the result was subtracted from the uncorrected TLD dose measurements. The mean values of the output factors for the 14, 8 and 4 mm collimators from last 5 years were 0.985 ¿ 0.001, 0.948 ¿ 0.005 and 0.833 ¿ 0.007, respectively, relative to the 18 mm collimator. These measured relative output factors are virtually identical to the values recommended by the manufacturer for the 14 mm and 8 mm collimators. On the other hand, the output factor for the 4 mm collimator was approximately 4.1% larger than that recommended by the manufacturer. The significance of these findings is discussed.

    View details for Web of Science ID 000084707700020

    View details for PubMedID 10681703

  • Conformal episcleral plaque therapy INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Astrahan, M. A., Luxton, G., Pu, Q., Petrovich, Z. 1997; 39 (2): 505-519

    Abstract

    Episcleral plaque therapy (EPT) with sealed 125I sources is widely used in the treatment of choroidal melanoma. In EPT, as elsewhere in radiotherapy, concern for normal tissue tolerance has frequently been a dose-limiting factor. The concept of conformal therapy, which seeks to improve dose homogeneity within the tumor and greatly reduce the dose to uninvolved structures may provide a solution to this problem. Radioactive sources are typically distributed uniformly over the surface of an episcleral plaque and are sometimes offset slightly from the scleral surface to reduce the dose to the sclera relative to the apex and prescribed therapeutic margin at the tumor base. Nevertheless, it is not uncommon for scleral dose to exceed the dose to the apex of intermediate to tall tumors by a factor of 4 or more. The availability of low-energy sealed sources such as 125I prompted the development of gold-backed plaques to shield noninvolved periocular tissues. The concept of shielding can be extended to include collimation of individual sources. The potential advantages of individual source collimation include reduced scleral dose, more homogeneous tumor dose, and superior shielding of adjacent normal structures such as the fovea as compared to previous plaque designs.A three-dimensional treatment-planning system has been extended to design a plaque that incorporates individually collimated 125I sources. Thermoluminescent dosimetry (TLD) and radiochromic film were used to compare calculated dose-rate distributions with measured dose rates in an acrylic phantom.Calculations predict that source collimation in the form of a "slotted" gold plaque will achieve the purposes of the study. The collimating effect of the slots is demonstrated qualitatively using radiochromic film, and the accuracy of the calculation is demonstrated quantitatively with TLD.The episcleral plaque described in this report is simpler to assemble than previous plaque designs. It produces a more homogeneous dose distribution in the tumor, reduces scleral dose by up to 50% as compared to conventional designs, and significantly reduces radiation dose to uninvolved structures adjacent to the plaque.

    View details for Web of Science ID A1997XV96900031

    View details for PubMedID 9308957

  • Extracranial radiation doses in patients undergoing gamma knife radiosurgery NEUROSURGERY Yu, C., Luxton, G., Apuzzo, M. L., MacPherson, D. M., Petrovich, Z. 1997; 41 (3): 553-559

    Abstract

    To determine extracranial doses in patients undergoing gamma knife radiosurgery and identify component sources of the extracranial doses using phantom measurements.The lateral canthi, thyroid, sternum, and midpelvis region were monitored in 104 unselected patients during their gamma knife treatments using thermoluminescent dosimetry. Measured doses were normalized to integral dose, equivalent time (which is defined in relation to the activity of the cobalt-60 sources), and collimator size to correlate radiation doses with these parameters. A phantom was constructed from a polystyrene sphere as a model of the head adjacent to thoracic and pelvic body sections from a commercial humanoid phantom.On average, 18 minutes of equivalent time and five isocenters were required to achieve the prescribed dose coverage. The median prescribed dose was 18 Gy. For the lateral canthi, thyroid, sternum, and pelvis, the median doses were 24, 20, 21, and 4 cGy, respectively. Normalization to equivalent time and collimator size was superior to other techniques. Phantom measurements supported the results from patient measurements and further refined estimates of component doses to extracranial sites.Doses to extracranial sites ranged from 1.5% of the prescribed dose for the lateral canthi to 0.2% for the pelvis. Doses to the sternum and pelvis were proportional to the duration of irradiation. Scatter radiation contributed more than 50% of the dose to the canthi and thyroid. Leakage radiation typically contributed 80 to 90% of the dose to the sternum and pelvis. Radiation during patient couch transit contributed little to the doses at the measured extracranial sites.

    View details for Web of Science ID A1997XU97200025

    View details for PubMedID 9310971

  • Episcleral plaque thermoradiotherapy of posterior uveal melanomas AMERICAN JOURNAL OF CLINICAL ONCOLOGY-CANCER CLINICAL TRIALS Petrovich, Z., Pike, M., Astrahan, M. A., Luxton, G., Murphree, A. L., LIGGETT, P. E. 1996; 19 (2): 207-211

    Abstract

    Episcleral plaque radiotherapy is a widely applied treatment for selected patients with uveal melanomas. This treatment is well tolerated but may produce severe late radiation complications resulting in decreased visual acuity that reduces the attractiveness of conservative therapy. The purpose of this study was to access if the addition of episcleral hyperthermia decreases late radiation complications through radiation dose reduction while maintaining high incidence of local tumor control. In a 3-year period, episcleral plaque thermoradiotherapy was given to 25 patients with uveal melanoma in a Phase I study. The mean tumor height was 6.2 mm and the mean tumor basal area was 173 mm(2). The mean radiation dose given to the tumor apex was 72.2 Gy and the mean hyperthermia temperature, given once for 45 min, was 43.5 degrees C. Of the 25 patients treated, 22 (88%) showed tumor height reduction, 2 (8%) showed no change, and 1 (4%) had an increase in tumor height. At the last follow-up (range, 20-68 months; mean, 31.2 months), a 43% mean tumor height reduction was recorded (p = 0.0002). Of the 22 patients initially showing tumor regression, 2 (9%) had subsequent tumor progression. At least ambulatory vision (>5/200) was maintained by 20 (80%) patients. Severe complications, including hemorrhagic retinal detachment and a large vitreous hemorrhage, were seen in 2 (8%) patients early in this Phase I study. The treatment program was well tolerated by the study patients. Severe late treatment toxicity was sharply reduced by limiting the mean scleral temperature to < or equal to 44 degrees C. This study employing 30% lower radiation doses, showed tumor regression in the majority of patients. Longer follow-up is needed to assess long-term treatment efficacy and late treatment complications.

    View details for Web of Science ID A1996UC42300025

    View details for PubMedID 8610652

  • Stereotactic radiosurgery for primary and metastatic brain tumors CANCER INVESTIGATION Petrovich, Z., Luxton, G., Formenti, S., Jozsef, G., Zee, C. S., Apuzzo, M. L. 1996; 14 (5): 445-454

    View details for Web of Science ID A1996VH81700005

    View details for PubMedID 8816860

  • SURGERY WITH ADJUVANT IRRADIATION IN PATIENTS WITH PATHOLOGICAL STAGE-C ADENOCARCINOMA OF THE PROSTATE CANCER Petrovich, Z., Lieskovsky, G., Freeman, J., Luxton, G., Groshen, S., Formenti, S., Baert, L., Chen, S. C., Skinner, D. G. 1995; 76 (9): 1621-1628

    Abstract

    In recent years, the routine use of prostate-specific antigen (PSA) to detect cancer of the prostate (CaP) early has renewed the controversy regarding radiotherapy versus radical prostatectomy as the superior definitive treatment. Radiotherapy alone has been reported to result in a high incidence of local recurrence, whereas on the other hand surgical treatment has resulted in a high incidence of microscopic residual tumor. The purpose of this study was to review our treatment results with radical prostatectomy followed by planned courses of postoperative irradiation in patients with pathologic Stage (PS) C disease.From 1972 to 1989, 95 patients with CaP with PS C tumors were treated with radical prostatectomy and bilateral pelvic lymphadenectomy. Pathologic stage distribution was: C1 in 26 (27%), C2 in 37 (39%), and C3 in 32 (34%) patients. The median follow-up was 6 years. All 95 study patients received postoperative pelvic irradiation as the only adjuvant treatment. Radiotherapy treated volume included the prostatic fossa and its immediate vicinity. The RT dose ranged from 33 Gy to 61.8 Gy (median, 45 Gy).The overall 5- and 10-year actuarial survival rates were 94% and 73%, respectively, with the 5 and 10 year disease specific survival of 98% and 91%, respectively. Clinical and/or prostate specific antigen recurrence was 31% at 5 years and 44% at 10 years. Prostate specific antigen elevation without clinical evidence of recurrent disease was recorded in 26 (27%) patients. Seminal vesicle involvement (C3) and high Gleason's score (8-10) were the most important factors predicting recurrence. Of the 95 patients treated, 2 had pelvic recurrence alone and 1 had local and distant metastatic disease. Radiotherapy was well tolerated with no clinically important morbidity.Based on this experience, moderate dose adjuvant radiotherapy after radical prostatectomy in patients with PS C CaP is recommended.

    View details for Web of Science ID A1995TA52400018

    View details for PubMedID 8635067

  • DOSIMETRY OF INTERSTITIAL BRACHYTHERAPY SOURCES - RECOMMENDATIONS OF THE AAPM RADIATION-THERAPY COMMITTEE TASK GROUP NO 43 MEDICAL PHYSICS Nath, R., Anderson, L. L., Luxton, G., Weaver, K. A., Williamson, J. F., Meigooni, A. S. 1995; 22 (2): 209-234

    View details for Web of Science ID A1995QG79600010

    View details for PubMedID 7565352

  • SINGLE ISOCENTER TREATMENT PLANNING FOR HOMOGENEOUS DOSE DELIVERY TO NONSPHERICAL TARGETS IN MULTIARC LINEAR-ACCELERATOR RADIOSURGERY INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Luxton, G., Jozsef, G. 1995; 31 (3): 635-643

    Abstract

    Conventional radiosurgery refers to single isocenter focused beam irradiation of small intracranial targets with a single collimator. Conventional radiosurgery is characterized by spherical-shaped isodose surfaces. Nonspherical targets require a different approach to avoid exposing a large volume of nontarget brain tissue to high dose, particularly for lesions larger than 25 mm. Multiple isocenters are frequently used to treat nonspherical large targets, but multiple isocenter treatments are associated with a relative dose inhomogeneity of approximately 100% within the target volume, and may be correlated with an increased rate of complications. The feasibility of conformally treating elongated targets to an approximately homogeneous dose using a single isocenter methodology will be demonstrated.A prolate ellipsoid of revolution, 25 mm in diameter, 35 mm in length, positioned at five representative locations in a head phantom, was used as a target model. The alignment of the target was taken to be parallel in turn to each of the three principal axes of the head model (A/P, R/L, and C/C). Dose conformation is achieved by nonuniform arc weighting, selective limitation of the extent of individual arcs, and the use of different collimator apertures for the different arcs in accordance with the aperture size required to encompass the target for that arc. Treatment plans were selected based on considerations of dose-volume histograms and conformation of the 80% dose surface with the surface of the target. The goal was that the minimum target dose would not be less than 80% of the maximum dose.Practical treatment plans for which the minimum target dose exceeded 80% were obtained for the three orthogonal orientations of the target for the five target locations. Plan parameters were essentially independent of the target position, dependent only on target orientation. The 80% isodose contour surface enclosed on average 2.8 cm3 larger volume (range: 2.1-3.9 cm3) than the prescribed 11.45 cm3 target. The minimum dose to the target ranged from 80.1 to 84.5%, and the average dose to the target was 94.26%. The 80-to-50% dose volume enclosed an average of 14.8 cm3 of nontarget volume (range: 12.7-15.9 cm3). Average deviation in the principal planes of the 80% isodose lines from the surface of the target volume was 0.95 mm for the 25 mm dimension (range 0.0 to +1.9 mm) and 0.86 mm (range 0.0 to + 2.4 mm) for the 35 mm dimension.Standardized single isocenter treatment plans with the isocenter at the center of the target can achieve good conformation of the dose distribution to targets elongated along any of the principal axes, and located anywhere in the brain.

    View details for Web of Science ID A1995QG40100026

    View details for PubMedID 7852130

  • COMPARISON OF RADIATION-DOSIMETRY IN WATER AND IN SOLID PHANTOM MATERIALS FOR I-125 AND PD-103 BRACHYTHERAPY SOURCES - EGS4 MONTE-CARLO STUDY MEDICAL PHYSICS Luxton, G. 1994; 21 (12): 1989-1990

    View details for Web of Science ID A1994PY38000021

    View details for PubMedID 7700208

  • MAMMALIAN-CELL SURVIVAL STUDIES CHARACTERIZING MULTIPORT NEGATIVE PI-MESON IRRADIATION WITH THE STANFORD MEDICAL PION GENERATOR (SMPG) INTERNATIONAL JOURNAL OF HYPERTHERMIA Li, G. C., Fessenden, P., Hahn, G. M., Fisher, G., Luxton, G., Bagshaw, M. A. 1994; 10 (3): 361-370

    Abstract

    Radiobiological measurements have been made under various conditions of muliport pion irradiation using the Stanford Medical Pion Generator (SMPG). Chinese hamster cells (HA-1) were suspended in a tissue-equivalent 25% gelatin/medium solution. Hypoxic and aerobic HA-1 cells were irradiated simultaneously in a cylindrical water tank at either 4 or 16 degrees C. Irradiation at the focus of 60 converging pion beams, at a peak dose rate of 6 rads/min, gave relative biological effectiveness (RBEs) of 2.8, 1.8 and 1.4 at 50, 20 and 5% survival, respectively, and an oxygen enhancement ratio (OER) of 1.7. Plateau irradiation with crossing pion beams, at a peak dose-rate of 3 rads/min, resulted in survival values very close to those obtained with similar doses of 85 kV X-rays. Preliminary studies with large irradiation volumes in broadened pion stopping regions indicate RBEs significantly > 1 for survival > 50%. Supporting microdosimetric data with the SMPG are consistent with the radiobiological results.

    View details for Web of Science ID A1994NP47600008

    View details for PubMedID 7930802

  • COMPARISON OF RADIATION-DOSIMETRY IN WATER AND IN SOLID PHANTOM MATERIALS FOR I-125 AND PD-103 BRACHYTHERAPY SOURCES - EGS4 MONTE-CARLO STUDY MEDICAL PHYSICS Luxton, G. 1994; 21 (5): 631-641

    Abstract

    A model based on the EGS4 Monte Carlo system is developed for calculating dose rate to water from an embedded low-energy brachytherapy source, given measurement data of dose rate to water within a water-substitute solid phantom for a source of given strength. The EGS4-based model is used to calculate point source dose rate distributions per unit source strength for water and for several species of solid phantoms. As a model for the dose rate distribution to an infinitesimal water inhomogeneity embedded in the solid phantom, the Monte Carlo is used to calculate dose rate to a thin spherical shell of water contained within the solid phantom at various distances centered on the source. Comparing this distribution to that calculated for a homogeneous water phantom, one can derive correction factors to determine dose rate to homogeneous water medium from measurements with water dose-calibrated detectors within the solid phantom. These factors are calculated for polymethylmethacrylate (PMMA or acrylic), solid water (WT1), and RW-1, a material optimized for low-energy dosimetry, with photon spectra from Pd-103 and from two commercial models of I-125 seed used as input. For model 6711 I-125 seeds at 1 cm in PMMA and WT1, the calculated ratios of dose rate to water to dose rate to water in the solid phantom are 0.893 and 1.038, respectively. Applying these factors to published, apparently divergent measurements of the specific dose rate constant based on measurements in PMMA and WT1 phantoms, the specific dose rate constant inferred for the model 6711 seed are found to be in excellent agreement: 0.878 cGy h-1U-1 (1.115 cGy- cm2h-1mCi-1) from the mean of the WT1 measurements and 0.879 cGy h-1U-1 from the PMMA measurements. Among the phantoms studied for Pd-103 and I-125, measurements in RW-1 would most closely approximate those for water.

    View details for Web of Science ID A1994NM42600001

    View details for PubMedID 7935197

  • STEREOTACTIC RADIOSURGERY - PRINCIPLES AND COMPARISON OF TREATMENT METHODS NEUROSURGERY Luxton, G., Petrovich, Z., Jozsef, G., Nedzi, L. A., Apuzzo, M. L. 1993; 32 (2): 241-259

    Abstract

    Methods of stereotactic radiosurgery are reviewed and compared with respect to technical factors and published clinical results. Heavy-ion beams, the Leksell cobalt-60 gamma knife, and the conventional linear accelerator (linac) are compared with respect to dosimetry, radiobiology, treatment planning, cost, staffing requirements, and ease of use. Clinical results on the efficacy of treatment of arteriovenous malformations are tabulated, and other applications of radiosurgery are described. It is concluded that although there are dosimetric and radiobiological advantages to charged-particle beams that may ultimately prove critical in the application of radiosurgery to large (> 30 mm) lesions, these advantages have not yet demonstrated clinical effect. On the other hand, equally excellent clinical results are obtained for small lesions with photon beams--the gamma knife and the linac. There are only minor differences between gamma and x-ray beam dose distributions for small, spherical-shaped targets. Mechanical precision is superior for the gamma knife as compared with the linac. The superior mechanical precision is of limited importance for most clinical targets, because inaccuracy of cranial target localization based on radiological imaging is greater than the typical linac imprecision of +/- 1 mm. Treatment planning for the linac is not standardized, but existing systems are based on well-known algorithms. The linac allows flexible, ready access to individualized beam control, without intrinsic field size limitations. Thus, it is more readily possible to achieve homogeneous dose distributions for nonspherical targets with one or more dimensions greater than 25 mm, as compared with that achieved with the gamma unit.(ABSTRACT TRUNCATED AT 250 WORDS)

    View details for Web of Science ID A1993KL52000014

    View details for PubMedID 8437663

  • RADIONECROSIS SECONDARY TO INTERSTITIAL BRACHYTHERAPY - CORRELATION OF MAGNETIC-RESONANCE-IMAGING AND HISTOPATHOLOGY NEUROSURGERY Oppenheimer, J. H., Levy, M. L., Sinha, U., Elkadi, H., Apuzzo, M. L., Luxton, G., Petrovich, Z., Zee, C. S., Miller, C. A. 1992; 31 (2): 336-343

    Abstract

    Radiation-induced tissue damage in the central nervous system is a well-known complication of interstitial brachytherapy for brain tumors, yet imaging correlates have historically been based upon computed tomographic scans. We now present magnetic resonance imaging (MRI) to correlate radiation changes after interstitial brachytherapy with the histopathology. The central nervous system of a 38-year-old man with a left frontal cerebral glioma diagnosed by stereotactic biopsy was treated with interstitial brachytherapy (iridium-192, 47 Gy), followed by limited-field irradiation (45 Gy). With progressive deterioration, a second biopsy demonstrated radiation changes. Despite aggressive medical management, the patient died 9 months after completion of radiation therapy. Postmortem evaluation compared MRI scans of the intact, fixed brain with the histopathology. Axial sections (10 mm) obtained by MRI scan and autopsy brain slices were cut in the identical plane. Neuroimaging and histopathological findings of the lesion correlated within 2 to 3 mm resolution. In the peripheral white matter, MRI scan did not indicate the extent of radiation effect histologically. We suggest that MRI has limited utility in assessing the extent of impact of radiation on surrounding brain.

    View details for Web of Science ID A1992JJ52000020

    View details for PubMedID 1513439

  • EPISCLERAL PLAQUE RADIOTHERAPY IN THE TREATMENT OF UVEAL MELANOMAS INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Petrovich, Z., Luxton, G., Langholz, B., Astrahan, M. A., LIGGETT, P. E. 1992; 24 (2): 247-251

    Abstract

    During an 8-year period, 85 patients with uveal melanomas were treated with episcleral plaque radiotherapy (EPRT). The T-stage was: T1-3 (4%), T2-29 (34%) and T3-53 (62%). The mean tumor elevation was 6.1 mm. Radiation dose was prescribed at the tumor apex and at D5mm. The mean D5mm dose was 150.1 Gy (range 70.5-430 Gy) and the mean dose at the apex was 102.6 Gy (range 29.8-200 Gy). Useful vision (greater than 5/200) was maintained in 73% of patients. The 5-year actuarial survival was 88%. Metastatic disease developed in 9 (11%) patients, 6 of whom died of their disease. Basal tumor dimensions were important factors predicting metastatic disease, p = 0.002. A decrease in tumor evaluation was seen in 82%. There was a much lower incidence of decrease in tumor radial and circumferential dimensions, 47.5 and 46%, respectively, p less than 0.001. Treatment complications were common (56%), particularly in patients with large tumors (72%), p = 0.04. The incidence of complications was higher in patients treated prior to 1988 as compared to those who were treated more recently (67 vs 35%, p = 0.010). There were 13 (15%) patients who had enucleation. This included 12 treated before 1986 and 1 patient treated subsequently (46 vs 2%, p less than 0.001). In a univariate analysis, tumor height and radiation dose at D5mm were important factors predicting enucleation, p = 0.004. In a multivariate analysis, however, the most important factor predicting enucleation was treatment administration prior to 1986, p less than 0.001). A sharp decrease in the incidence of severe complications, including enucleation, as seen after 1985, is likely due to a major effort in treatment optimization.

    View details for Web of Science ID A1992JP78400009

    View details for PubMedID 1526863

  • EPISCLERAL PLAQUE THERMORADIOTHERAPY IN PATIENTS WITH CHOROIDAL MELANOMA INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Petrovich, Z., Astrahan, M. A., Luxton, G., Green, R., Langholz, B., Liggett, P. 1992; 23 (3): 599-603

    Abstract

    From 1988 to 1991, 21 patients with uveal melanoma were treated in a Phase I study with episcleral plaque radiotherapy (EPRT). This irradiation was combined with localized current field episcleral hyperthermia (LCFHT). Tumor stage was: T3 = 15 (71%) and T2 = 6 (29%). Follow-up ranged from 2 to 42 months (mean 9.2 months). EPRT was given using custom built I-125 gold plaques. Radiation doses to the tumor apex ranged from 13 to 123 Gy (mean dose 70.0 Gy) given at a mean dose rate of 55 cGy/hr. LCFHT was given with 500 KHz frequency for 45 min immediately before EPRT. The temperature was controlled on the scleral surface using four thermocouples. T mean ranged from 42.5 degrees C to 45 degrees C +/- 0.5 degrees C (mean 43.4 degrees C). The study patients showed rapid tumor necrosis. A 25% mean decrease of apical tumor dimension was noted, p = 0.0007. At least ambulatory vision (greater than 5/200) was maintained by 17/21 (81%) patients. Visual acuity was seen to improve greater than 6 months post-plaque therapy in 10 (48%) study patients. This was following an intermediate decrease in visual acuity. Severe complications, including large hemorrhagic retinal detachment and large vitreous hemorrhage, were seen in two (9.5%) of the early study patients. A mean scleral temperature reduction to less than or equal to 44 degrees C +/- 0.5 degrees C resulted in good treatment tolerance and a lack of serious complications in subsequently treated patients. A Phase II prospective randomized trial comparing LCFHT with 60 versus 80 Gy EPRT dose to the tumor apex is currently being activated for patients with choroidal melanoma.

    View details for Web of Science ID A1992JA07400016

    View details for PubMedID 1612961

  • ALGORITHM FOR DOSIMETRY OF MULTIARC LINEAR-ACCELERATOR STEREOTAXIC RADIOSURGERY MEDICAL PHYSICS Luxton, G., Jozsef, G., Astrahan, M. A. 1991; 18 (6): 1211-1221

    Abstract

    Treatment planning for multiarc radiosurgery is an inherently complex three-dimensional dosimetry problem. Characteristics of small-field x-ray beams suggest that major simplification of the dose computation algorithm is possible without significant loss of accuracy compared to calculations based on large-field algorithms. The simplification makes it practical to efficiently implement accurate multiplanar dosimetry calculations on a desktop computer. An algorithm is described that is based on data from fixed-beam tissue-maximum-ratio (TMR) and profile measurements at isocenter. The profile for each fixed beam is scaled geometrically according to distance from the x-ray source. Beam broadening due to scatter is taken into account by a simple formula that interpolates the full width at half maximum (FWHM) between profiles at isocenter at different depths in phantom. TMR and profile data for two representative small-field collimators (10- and 25-mm projected diameter) were obtained by TLD and film measurements in a phantom. The accuracy of the calculational method and the associated computer program were verified by TLD and film measurements of noncoplanar multiarc irradiations from these collimators on a 4-MV linear accelerator. Comparison of film measurements in two orthogonal planes showed close agreement with calculations in the shape of the dose distribution. Maximal separation of measured and calculated 90%, 80%, and 50% isodose curves was less than or equal to 0.5 mm for all planes and collimators. All TLD and film measurements of dose to isocenter agreed with calculations to within 2%.

    View details for Web of Science ID A1991GQ08500019

    View details for PubMedID 1753906

  • RADIOTHERAPY FOLLOWING RADICAL PROSTATECTOMY IN PATIENTS WITH ADENOCARCINOMA OF THE PROSTATE INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Petrovich, Z., Lieskovsky, G., Langholz, B., Luxton, G., Jozsef, G., Skinner, D. G. 1991; 21 (4): 949-954

    Abstract

    From 1973 to 1986, 160 patients with adenocarcinoma localized to the prostate were treated with radical prostatectomy and pelvic lymphadenectomy. In 78 (49%) patients more advanced stage of disease was found at surgery and they received local pelvic irradiation (RT). This consisted of 45 Gy for microscopic and 55 Gy for macroscopic residual disease. RT was given at 1.8 Gy a day, using the four-field "box" technique with the 23 MV X ray beam. Pelvic lymph node metastases were found in 28 (36%) patients who, in addition to RT, received systemic therapy: 20 with cyclophosphamide alone, 4 combined with 5-Fluorouracil, and 4 patients received DES. The 5- and 10-year overall actuarial survival was 95 and 77%, respectively, and the 5- and 10-year disease-free survival was 58 and 43%, respectively. Recurrent tumor was found in 34 (44%) patients. Of these 34 patients, 32 (94%) had distant metastatic tumor and 2 (6%) had local recurrence in the pelvis. The presence of metastatic disease in pelvic lymph nodes had clinical significance since it influenced disease-free survival and the incidence of tumor recurrence. The 10-year disease-free survival for the 50 patients with no lymph node metastases was 51%, as compared to 28% for the 28 patients with such metastases, p = 0.001. Similarly, recurrent tumor was found in 28% of the former and 68% of the latter patients, p = 0.002. Other important parameters predicting recurrence were: clinical stage, p = 0.018, histological grade, p = 0.013, and Gleason's grade, p = 0.002. This treatment program was very well tolerated and of low toxicity. There was no surgical mortality. Surgical complications were seen in 10 (13%) patients including: minor in 5 and major in 5. At 1 year, 77% of the patients remained continent, while 10% had mild stress incontinence. Of the remaining 13% only 3 (4%) patients had severe incontinence (greater than 5 pads daily). RT toxicity was mild with 38% experiencing diarrhea. Severe toxicity was seen in 2 (3%) patients who, early in the study, developed scrotal and lower extremity edema. Severe chemotherapy complications were seen in 1 (4%) patient who had severe neutropenic sepsis. Postoperative radiotherapy is a well tolerated, safe and effective treatment in patients who have microscopic or macroscopic residual tumor following radical prostatectomy.

    View details for Web of Science ID A1991GJ63200009

    View details for PubMedID 1917624

  • TREATMENT RESULTS OF STEREOTAXIC INTERSTITIAL BRACHYTHERAPY FOR PRIMARY AND METASTATIC BRAIN-TUMORS INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Lucas, G. L., Luxton, G., Cohen, D., Petrovich, Z., Langholz, B., Apuzzo, M. L., Sapozink, M. D. 1991; 21 (3): 715-721

    Abstract

    A total of 41 stereotactic interstitial brain implants in 39 patients were performed for recurrence after teletherapy (recurrence implant), or as part of initial treatment in conjunction with teletherapy (primary implant). Implanted tumors consisted of malignant gliomas (33), other primary brain tumors (3), and single metastatic lesions (3). All patients were temporarily implanted with Ir-192 using a coaxial catheter afterloading system; two patients were implanted twice. Survival post-implant for glioblastoma multiforme (GBM), 13 patients, was 10 months whether implanted primarily or for recurrence. Mean time to recurrence, measured from initiation of teletherapy to implantation, was 10 months. Twenty patients with anaplastic astrocytoma (AA) had a median survival post-implant of 23 months for primary implants (7 patients) and 11 months for recurrence implants (13 patients). Mean time to recurrence, measured from initiation of teletherapy to implantation, was 19 months. Three patients (9%) of the evaluable group required reoperation for symptomatic mass effect, all with initial diagnosis of AA. Survival for this subgroup was 14, 22, and 32 months post-implantation. Using stereotactic techniques, interstitial brachytherapy of brain tumors was technically feasible with negligible acute morbidity and mortality, and appeared to offer limited prolongation of control for a subset of patients with recurrent malignant gliomas. The role of this modality in primary treatment for malignant gliomas needs to be further defined by prospectively randomized trials.

    View details for Web of Science ID A1991GC63200024

    View details for PubMedID 1651307

  • MANAGEMENT OF CARCINOMA OF THE ESOPHAGUS - THE ROLE OF RADIOTHERAPY AMERICAN JOURNAL OF CLINICAL ONCOLOGY-CANCER CLINICAL TRIALS Petrovich, Z., Langholz, B., Formenti, S., Luxton, G., Astrahan, M. 1991; 14 (1): 80-86

    Abstract

    This is an analysis of treatment results over a 23-year period in 241 patients with carcinoma of the esophagus. The treatment for unresectable patients was external beam radiotherapy (EBRT) alone (mean dose 55 Gy) in 137 (57%) combined with brachytherapy (mean dose 50 + 40 Gy) in 46 (19%), and chemotherapy alone in 3 (1%) patients. In the 55 resectable patients, treatment was resection alone in 9 (4%), and combined with radiotherapy (mean dose 43 Gy) in 46 (19%) patients. The 1-, 2-, and 5-year survival for the 241 patients was 36, 15, and 5%, respectively (median 38 weeks). The 5-year survival was 18% for radiotherapy (RT)-surgery (S) patients, 11% for EBRT with brachytherapy, 2% for EBRT alone, and 0% for patients who had S alone, p less than 0.001. Survival correlated well with initial performance status, treatment, stage of disease, tumor size, radiation dose, and degree of response, p less than 0.001, but not with tumor location in the esophagus and patients' race and sex, p = 0.44. Serious complications occurred in 5 (2%) patients treated with RT alone and in 4 (7%) patients treated with S alone or combined with RT. The leading cause of death was persistent or recurrent tumor in the chest found in 39% patients.

    View details for Web of Science ID A1991EV47900018

    View details for PubMedID 1702923

  • OPTIMIZATION OF I-125 OPHTHALMIC PLAQUE BRACHYTHERAPY MEDICAL PHYSICS Astrahan, M. A., Luxton, G., Jozsef, G., LIGGETT, P. E., Petrovich, Z. 1990; 17 (6): 1053-1057

    Abstract

    Episcleral plaques containing 125I sources are often used in the treatment of ocular melanoma. Within four years post-treatment, however, the majority of patients experience some visual loss due to radiation retinopathy. The high incidence of late complications suggests that careful treatment optimization may lead to improved outcome. The goal of optimization would be to reduce the magnitude of vision-limiting complications without compromising tumor control. We have developed a three-dimensional computer model for ophthalmic plaque therapy which permits us to explore the potential of various optimization strategies. One simple strategy which shows promise is to maximize the ratio of dose to the tumor apex (T) compared to dose to the macula (M). By modifying the parameters of source location, activity distribution, source orientation, and shielding we find that the calculated T:M ratio can be varied by a factor of 2 for a common plaque design and posterior tumor location. Margins and dose to the tumor volume remain essentially unchanged.

    View details for Web of Science ID A1990EJ43100013

    View details for PubMedID 2280735

  • COMMENTS ON DOSIMETRIC CONSIDERATION ON MULTIPLE ARC STEREOTAXIC RADIOTHERAPY RADIOTHERAPY AND ONCOLOGY Jozsef, G., Luxton, G. 1990; 19 (1): 90-91

    View details for Web of Science ID A1990EB47000009

    View details for PubMedID 2122497

  • EPISCLERAL RADIOACTIVE PLAQUE THERAPY - INITIAL CLINICAL-EXPERIENCE WITH 56 PATIENTS AMERICAN JOURNAL OF CLINICAL ONCOLOGY-CANCER CLINICAL TRIALS LEAN, E. K., Cohen, D. M., LIGGETT, P. E., Luxton, G., Langholz, B., Lau, R., Astrahan, M. A., HYDEN, E. C., Petrovich, Z. 1990; 13 (3): 185-190

    Abstract

    Between 1983 and 1987, 56 patients with choroidal melanoma were treated at the University of Southern California with episcleral plaque (RPT). There were 29 female and 27 male patients, with a mean age of 59 years. Tumor stage at diagnosis was T2 in 18 (32%) and T3 in 38 (68%) patients. The tumor height ranged from 2.9 to 15 mm (mean 6.8 mm). Radial dimensions ranged from 5 to 25 mm (mean 13.2 mm), and circumference ranged from 7 to 23 mm (mean 12.3 mm). Most (77%) patients had posteriorly located tumors, including 18% that were juxtapapillary. Custom-designed gold plaques were utilized in this study. Radioactive isotopes used were 125I for 26 procedures or 192Ir for 31 procedures. A total of 56 patients were treated, with one patient having two procedures. Radiation doses at the tumor apex ranged from 29.8 to 165.4 Gy (mean 94.5 Gy), with the dose at 5-mm depth ranging from 70.5 to 430 Gy (mean 161.5 Gy). Follow-up ranged from 29 to 57 months (mean 39 months). The overall 4-year survival was 96%, with a 91% incidence of free-of-disease progression at 4 years. The majority (84%) of patients experienced a decrease in tumor height, with 27 (48%) patients having greater than 50% decrease. Increase in tumor height was noted in 5 (9%) and no change in 4 (7%) patients. Useful vision (greater than 5/200) was observed in 59% of patients, including 21% who had improved vision. Metastatic tumor occurred in 5 (9%) patients, with a mean time to metastases of 14 months. There was a good correlation between radial tumor dimension and metastatic disease, p less than 0.001. Treatment complications were observed in 34 (61%) patients, with cataract and retinopathy being the most common. Enucleation was performed in 11 (20%) patients, with a mean time to enucleation of 14.5 months. Causative factors for enucleation were treatment complications in 6 and tumor progression in 5 patients. Enucleations were required primarily in patients with tumors greater than 8 mm in height (p = 0.009). Improved RPT techniques with three-dimensional dosimetry are needed to reduce the overall incidence of treatment complications. Adjuvant hyperthermia is being investigated in an attempt to improve tumor control in patients with larger tumors.

    View details for Web of Science ID A1990DF25600001

    View details for PubMedID 2346123

  • MEASUREMENT OF DOSE-RATE FROM EXPOSURE-CALIBRATED I-125 SEEDS INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Luxton, G., Astrahan, M. A., Findley, D. O., Petrovich, Z. 1990; 18 (5): 1199-1207

    Abstract

    Dose rate in water 1 cm transverse to an 125I seed calibrated for air kerma strength is not well established; 125I dosimetry calculations are, however, based on this constant. The specific dose constant was obtained from a series of dose rate measurements using thermoluminescent dosimetry (TLD) in a rigid geometry, full scatter acrylic phantom for individual model 6711 seeds. With a statistical precision of approximately +/- .5%, the dose rate to an infinitesimal mass of water located in acrylic at a perpendicular distance of 1 cm from the seed was found to be 0.977 cGy/h per microGy-m2/h of air kerma strength. Dose rate in a water phantom was calculated using a model that takes into account differences in both attenuation and scatter between water and acrylic. The specific dose constant in water was determined to be 0.932 (1.184 cGy-cm2/mCi-h, for the conventional exposure rate constant of 1.45 R cm2/mCi-h). This value is 7.5% less than dose rate in water from an unattenuated point source, and 9.7% less than the value commonly used for dosimetry calculations. The results suggest that most clinical 125I dosimetry estimates to date should be reconsidered for a possible reduction by about 10%. Relative scatter attenuation factors at 3 and 5 mm are also presented.

    View details for Web of Science ID A1990DH04300028

    View details for PubMedID 2347727

  • AN INTERACTIVE TREATMENT PLANNING SYSTEM FOR OPHTHALMIC PLAQUE RADIOTHERAPY INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Astrahan, M. A., Luxton, G., Jozsef, G., KAMPP, T. D., LIGGETT, P. E., Sapozink, M. D., Petrovich, Z. 1990; 18 (3): 679-687

    Abstract

    Brachytherapy using removable episcleral plaques containing sealed radioisotope sources is being studied as an alternative to enucleation in the treatment of choroidal melanoma and other tumors of the eye. Encouraging early results have been reported, but late complications which lead to loss of vision continue to be a problem. A randomized national study, the Collaborative Ocular Melanoma Study (COMS) is currently in progress to evaluate the procedure. The COMS specified isotope is 125I. Precise dosimetric calculations near the plaque may correlate strongly with complications and could also be used to optimize isotope loading patterns in the plaques. A microcomputer based treatment planning system has been developed for ophthalmic plaque brachytherapy. The program incorporates an interactive, 3-dimensional, solid-surface, color-graphic interface. The program currently supports 125I and 192Ir seeds which are treated as anisotropic line sources. Collimation effects related to plaque structure are accounted for, permitting detailed study of shielding effectiveness near the lip of a plaque. A dose distribution matrix may be calculated in any subregion of a transverse, sagittal, or coronal planar cross section of the eye, in any plane transecting the plaque and crossing the eye diametrically, or on a spherical surface within or surrounding the eye. Spherical surfaces may be displayed as 3-dimensional perspective projections or as funduscopic diagrams. Isodose contours are interpolated from the dose matrix. A pointer is also available to explicitly calculate and display dose at any location on the dosimetry surface. An interactive editing capability allows new plaque designs to be rapidly added to the system.

    View details for Web of Science ID A1990CZ51100026

    View details for PubMedID 2318702

  • Treatment of T3 primary malignant melanoma of the choroid with episcleral radioactive plaque. Endocurietherapy Hyperthermia Oncology Petrovich Z, Liggett PE, Lean E, LangholzB, Luxton G, Palmer D, Astrahan MA 1990; 6 (1): 11-17
  • Radioactive plaque therapy in the management of primary malignant ocular melanoma: An overview. Endocurietherapy Hyperthermia Oncology Petrovich Z, Liggett PE, Luxton G, Lean E, Langholz B, Astrahan M 1990; 6: 131-141
  • SURGICAL THERAPY AND RADIOTHERAPY FOR CARCINOMA OF THE ESOPHAGUS - TREATMENT RESULTS IN 195 PATIENTS JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Petrovich, Z., Lam, K., Langholz, B., Formenti, S., Luxton, G., Tildon, T. 1989; 98 (4): 614-617

    Abstract

    Between 1963 and 1986, 195 patients with carcinoma of the esophagus were seen in the Department of Radiation Oncology at the University of Southern California School of Medicine. Of these 195 patients, 137 had unresectable or inoperable tumors and received radiotherapy. A combination of radiotherapy and surgical therapy was used in 46 patients, 9 patients were treated with surgery alone, and three with chemotherapy alone. Among the nonsurgical patients, 13 scored less than 50 on the Karnofsky scale, 25 had distant metastases, and 69 lost more than 10% of their body weight. The majority (94%) had squamous cell carcinoma and a few (6%) had adenocarcinoma. Fifty percent had middle esophageal lesions, 30% had lower lesions, and 20% had upper esophageal lesions. Stage I was diagnosed in 13%, II in 27%, III in 29%, and IV in 27%; the disease was not staged in 5%. The 5-year actuarial survival rate for all patients was 4% (median 32 weeks). The 5-year survival rate of the 46 patients with combination therapy was 18%, and it was 2% for the remaining 149 patients (p less than 0.001). These figures are independent of stage of disease. The 2-year survival rate by stage was as follows: I, 25%; II, 21%; III, 5%; and IV, 0% (p less than 0.001). Complete response was obtained in 18% and partial response in 41%. Complete response was dependent on the tumor stage. It was 40% for stage I disease, 23% for stage II, 11% for stage III, and 6% for stage IV disease. Similarly, a larger percentage (39%) of the 46 patients with combination surgical/radiation therapy had a complete response than of patients treated by either radiotherapy alone (n = 137, 12%) or surgery alone (n = 9, 11%). Complete response and initial performance status were important factors influencing survival (p less than 0.001). Surgery with adjuvant irradiation offered a better survival rate than radiotherapy or surgery used as single modalities. Treatment results for patients with advanced carcinoma of the esophagus remain poor.

    View details for Web of Science ID A1989AU11400019

    View details for PubMedID 2796368

  • DEEP REGIONAL HYPERTHERMIA OF THE LIVER - A CLINICAL-STUDY OF 49 PATIENTS AMERICAN JOURNAL OF CLINICAL ONCOLOGY-CANCER CLINICAL TRIALS Petrovich, Z., Langholz, B., Kapp, D. S., Emami, B., Oleson, J. R., Luxton, G., Astrahan, M. 1989; 12 (5): 378-383

    Abstract

    From 1981 to 1986, six medical centers participated in feasibility studies of radiofrequency deep regional hyperthermia (HT) in the treatment of hepatic metastases. A total of 49 patients, 32 men and 17 women, were treated with an annular phased array. Colon was the primary site in 74% of the patients, and adenocarcinoma was the diagnosis in 80%. More than one half of the patients had been treated previously. This included chemotherapy (CT) in 17 patients and radiotherapy (RT) in 10 patients, with a mean RT dose of 24 Gy. Upper abdominal pain was the dominant presenting symptom in 53% of patients. In the study, treatment was administered as follows: 14 (28%) patients received HT alone, 17 (35%) received HT + RT, 14 (28%) received HT + CT, and 4 (8%) received HT + RT + CT. A total of 157 HT treatments was administered at a mean frequency of 55 MHz and a mean power of 780 watts. The number of HT sessions ranged from 1 to 8, with a mean of 3.2 treatments per patient. Temperature was monitored continuously throughout each treatment session. The treatment aim was to reach and maintain a temperature of 42.5 degrees C for 30 min. In practice, owing to the difficulty in reaching this temperature, an equivalent (lower) temperature from 40 to 42 degrees C was used, extending the duration of treatment sessions to 45-60 min. Thermal dose was defined as the number of minutes at 42.5 degrees C or its equivalent. In 21 (43%) patients, a temperature less than 40 degrees C was obtained and thermal dose = 0. Thermal dose was less than or equal to 50 in 17 (35%) patients, greater than 50 less than or equal to 100 in 7 (14%), and greater than 100 in 4 (8%). RT was given at a daily dose of 1.8 Gy to a total of less than 20 Gy in 14 patients, greater than 20 less than or equal to 30 Gy in 6, and greater than 30 Gy in 1. CT consisted of 5-Fluorouracil by way of Hepatic Artery Infusion (HAI) in 9 patients, i.v. cisplatin in 5, and doxorubicin HAI in 3. Objective tumor regression (CR + PR) was seen in 6 (12%) patients. An additional 10 (20%) patients had less than 50% greater than 25% tumor regression, and 10 (20%) had complete or partial pain relief. The median duration of CR and PR was 26 weeks.(ABSTRACT TRUNCATED AT 400 WORDS)

    View details for Web of Science ID A1989AU35300003

    View details for PubMedID 2801598

  • INTERSTITIAL THERMORADIOTHERAPY FOR RECURRENT HEAD AND NECK-CANCER AMERICAN JOURNAL OF OTOLARYNGOLOGY Petrovich, Z., Lam, K., Langholz, B., Astrahan, M., Luxton, G., Rice, D. 1989; 10 (4): 257-260

    Abstract

    From 1985 to 1987, 22 head and neck sites in 20 patients with recurrent tumors were treated with interstitial thermoradiotherapy (ITRT). The sites treated were 15 neck (68%), four tongue (18%), two parotid (9%), and one buccal mucosa (4%). Squamous cell carcinoma was diagnosed in 21 sites and adenocarcinoma in the other. All patients had prior radiotherapy (RT), including 15 who underwent a combination of RT and surgery. Interstitial RT with iridium 192 (mean dose, 40 Gy) was combined with interstitial microwave hyperthermia (mean thermal dose, 90 units). Complete response (CR) was obtained in 15 (68%) sites and partial response (PR) in seven (32%) sites. There were no local recurrences in the 15 CR patients during a period of observation of up to 30 months. Of the seven PR patients, one had radical neck dissection and is free of tumor after 28 months. Tumor volume was an important factor influencing CR (P less than .001), whereas RT and thermal dose were not (P = .3). Of the 20 patients treated, 19 experienced major subjective benefit. Serious complications occurred in two patients: one had localized soft tissue necrosis, the other had aspiration pneumonia. ITRT was well-tolerated by patients despite prior aggressive therapy. High objective response rate and low toxicity demonstrate the value of this treatment combination in the management of patients with postradiation recurrence of head and neck tumors.

    View details for Web of Science ID A1989AF65400005

    View details for PubMedID 2764238

  • INTERSTITIAL MICROWAVE HYPERTHERMIA COMBINED WITH IR-192 RADIOTHERAPY FOR RECURRENT TUMORS AMERICAN JOURNAL OF CLINICAL ONCOLOGY-CANCER CLINICAL TRIALS Petrovich, Z., Langholz, B., Lam, K., Luxton, G., Cohen, D., Jepson, J., Astrahan, M. 1989; 12 (3): 264-268

    Abstract

    From 1985 through 1987, 44 tumors in 39 patients with recurrent cancer were treated with interstitial microwave hyperthermia (HT) combined with interstitial 192Ir radiotherapy (RT). All patients had unresectable and previously treated tumors (mean RT dose 57.6 Gy). Diagnoses were squamous cell carcinoma in 27 (62%), adenocarcinoma in 11 (25%), melanoma in 5 (11%), and soft tissue sarcoma in 1 (2%) site. Interstitial RT dose was from 25 to 50 Gy (mean 38.3 Gy). The first HT session was scheduled immediately before the loading of 192Ir, and the second was scheduled following its removal. Each session lasted 45-60 min at therapeutic temperature (42.5 degrees C). Complete response (CR) was obtained in 28 (64%) sites and partial response (PR) in 15 (34%) sites. None of the CR patients had local recurrence. Tumor volume was the most important factor influencing CR (p less than 0.001). The treated site, radiation dose, and thermal dose were not significant factors for CR (p = 0.03). The overall median survival was 39 weeks, with a 2-year survival of 22%. The treatment was well tolerated, with two patients developing focal skin necrosis.

    View details for Web of Science ID A1989U959200017

    View details for PubMedID 2658541

  • MICROWAVE APPLICATOR FOR TRANS-URETHRAL HYPERTHERMIA OF BENIGN PROSTATIC HYPERPLASIA INTERNATIONAL JOURNAL OF HYPERTHERMIA Astrahan, M. A., Sapozink, M. D., Cohen, D., Luxton, G., KAMPP, T. D., Boyd, S., Petrovich, Z. 1989; 5 (3): 283-296

    Abstract

    An applicator for heating the prostate gland using a transurethral approach is described. This technique uses three microwave antennas and a thermometry sensor attached to the outer surface of a balloon (Foley) type urological catheter. Each microwave antenna also includes a built-in thermistor to control temperature and balance power. The balloon catheter assures rapid and reproducible localization of the antennas in the prostatic urethra. The two-dimensional SAR and steady-state temperature distributions surrounding the applicator in tissue equivalent phantom are reported. Longitudinal temperature distributions measured in situ at the applicator-urethral interface and the longitudinal and radial temperature distributions measured in normal canine prostate are presented and discussed. The technique appears to be capable of elevating temperature to greater than 42 degrees C in a cylindrically symmetrical volume up to 5 cm length and 0.5 cm radial penetration surrounding the applicator.

    View details for Web of Science ID A1989T958100001

    View details for PubMedID 2470840

  • A TECHNIQUE FOR COMBINING MICROWAVE HYPERTHERMIA WITH INTRALUMINAL BRACHYTHERAPY OF THE ESOPHAGUS INTERNATIONAL JOURNAL OF HYPERTHERMIA Astrahan, M. A., Sapozink, M. D., Luxton, G., KAMPP, T. D., Petrovich, Z. 1989; 5 (1): 37-51

    Abstract

    A technique for combining microwave hyperthermia with 192Ir brachytherapy for the treatment of oesophageal carcinoma is described. This approach uses an intraluminal afterloading applicator and up to six microwave antennae to deliver both hyperthermia and brachytherapy, with minimal modification of the existing procedure for brachytherapy alone. Each microwave antenna includes a built-in thermistor to control temperature and balance power. Longitudinal temperature distributions were measured in situ from within the applicator, and at the applicator-tissue interface in vivo. Two-dimensional SAR and steady-state temperature distributions measured in muscle-equivalent phantom are presented and discussed. The technique appears to be capable of elevating tissue temperature to greater than 42 degrees C in a radially symmetric volume of length greater than 5 cm, with radial penetration of 0.5 cm. The clinical technique is relatively simple and well tolerated.

    View details for Web of Science ID A1989R515700004

    View details for PubMedID 2921533

  • The importance of brachytherapy in the treatment of patients with unresectable carcinoma of the esophagus. Endocurietherapy Hyperthermia Oncology Petrovich Z, Langholz B, Lam K, Formenti S, Luxton G, Astrahan M, Tildon TLangholz B, Lam K, Formenti S, Luxton G, Astrahan M, Tildon T 1989; 5: 201-208
  • THE ACCURACY OF TEMPERATURE-MEASUREMENT FROM WITHIN AN INTERSTITIAL MICROWAVE ANTENNA INTERNATIONAL JOURNAL OF HYPERTHERMIA Astrahan, M. A., Luxton, G., Sapozink, M. D., Petrovich, Z. 1988; 4 (6): 593-607

    Abstract

    Temperature measurement from within microwave interstitial antennas is a promising new development for hyperthermia. These antennas could enable the development of multipoint temperature regulation, leading to improved control of temperature distributions and therefore more effective hyperthermia treatments. In the complex environment of an antenna within a plastic catheter, measured temperatures were found to differ from the estimated local tissue temperature by up to 8 degrees C. In the design evaluated in this report the primary source of this error appears to be self-heating distal to the antenna junction, particularly in the outer copper conductor. The magnitude of self-heating is directly proportional to applied microwave power. Catheter wall thickness, tissue perfusion, and longitudinal temperature gradient also influence the measured temperature.

    View details for Web of Science ID A1988P585000002

    View details for PubMedID 3171255

  • EXTERNAL BEAM AND INTRALUMINAL RADIOTHERAPY IN THE TREATMENT OF CARCINOMA OF THE ESOPHAGUS JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY HYDEN, E. C., Langholz, B., TILDEN, T., Lam, K., Luxton, G., Astrahan, M., Jepson, J., Petrovich, Z. 1988; 96 (2): 237-241

    Abstract

    During a 10-year period, 46 patients with unresectable or inoperable carcinoma of the esophagus were treated with teletherapy-brachytherapy combination at the University of Southern California School of Medicine. Stage distribution was as follows: stage I, 5 (11%) patients; stage II, 23 (50%) patients; stage III, six (13%) patients; and stage IV, 12 (26%) patients. Thirteen patients were treated for recurrent disease, including 11 patients initially treated with teletherapy and two who had had surgical resection. Radiotherapy was given by teletherapy in 33 and brachytherapy in all 46 patients. An average tumor dose was 50 Gy with teletherapy and 20 Gy per application with brachytherapy. There were 25 patients who had more than one brachytherapy application. The 5-year actuarial survival rate for 28 patients with stage I or II disease was 12%, with a median of 13 months. This compared with no 5-year survivals and a median survival of 10 months for the 18 patients with stage III or IV disease. Failure at the primary site was seen in 16 (35%) patients. Complete response was seen in 20%, partial response in 76%, and no response in 4%. Treatment was well tolerated. Complications included esophageal stenosis in two patients and tracheoesophageal fistula in one. Teletherapy-brachytherapy combination is an effective treatment in the management of unresectable or inoperable carcinoma of the esophagus.

    View details for Web of Science ID A1988P709400007

    View details for PubMedID 3398546

  • DOSIMETRIC CALCULATIONS AND MEASUREMENTS OF GOLD PLAQUE OPHTHALMIC IRRADIATORS USING IR-192 AND I-125 SEEDS INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Luxton, G., Astrahan, M. A., LIGGETT, P. E., NEBLETT, D. L., Cohen, D. M., Petrovich, Z. 1988; 15 (1): 167-176

    Abstract

    The dosimetry of ophthalmic plaques designed to hold iridium-192 or iodine-125 seeds is investigated experimentally and by means of a computer model. A phantom for thermoluminescent dosimetry (TLD) which permits measurements to within 2 mm of the plaque surface is described. TLD data are compared with model calculations that take into account the active length of the seeds, anisotropy of dose distribution from single seeds, and scatter within the phantom. An isotropic point source calculational model is accurate for clinical calculations, particularly at depths greater than 5 mm. Relative central axis dose measurements for 125I in a gold plaque are also in agreement with the model. Comparisons of 192Ir, 125I and 60Co plaques are presented. The relative advantages of using these isotopes in eye plaques are discussed.

    View details for Web of Science ID A1988P408400023

    View details for PubMedID 3391814

  • BACKSCATTER MEASUREMENTS FROM A SINGLE SEED OF I125 FOR OPHTHALMIC PLAQUE DOSIMETRY MEDICAL PHYSICS Luxton, G., Astrahan, M. A., Petrovich, Z. 1988; 15 (3): 397-400

    Abstract

    To determine the dosimetric effect of a gold plaque applicator used in 125I ophthalmic irradiation, relative dose rates at points 2-18 mm transverse to the axis of a single seed of 125I were measured in an acrylic phantom under three different measurement conditions. The detectors were 1-mm diameter X 3-mm length LiF thermoluminescent dosimeters (TLD's). Conditions corresponded to the following: (i) full scatter, (ii) the presence of an ophthalmic gold plaque, and (iii) no scatter material on the side of the seed opposite to the TLD's. The dose rate with the gold plaque is less than that with full scatter phantom. There is no significant decrease in dose rate at 2.2 mm from the seed. Dose rate is significantly reduced at greater distances. The does rate decrease ranges from 4% at 5 mm to 10% at 18 mm. The 125I seed in the gold plaque gives 3%-5% higher dose rate than in the absence of backscatter material.

    View details for Web of Science ID A1988P076600018

    View details for PubMedID 3405144

  • INTERSTITIAL THERMORADIOTHERAPY FOR RECURRENT OR PERSISTENT TUMORS INTERNATIONAL JOURNAL OF HYPERTHERMIA Lam, K., Astrahan, M., Langholz, B., Jepson, J., Cohen, D., Luxton, G., Petrovich, Z. 1988; 4 (3): 259-266

    Abstract

    Between 1984 and 1986, 31 sites in 27 patients with biopsy proven tumours were treated with a combination of interstitial microwave hyperthermia (HT) and iridium 192 implants (RT). The 31 sites treated included fifteen (48 per cent) head and neck, six (20 per cent) breast, four (13 per cent) vagina and cervix, and six (20 per cent) others. All patients had prior surgery, RT, or chemotherapy. Of the 31 sites treated, 19 (61 per cent) had complete response (CR) with no recurrence in the volume treated. Additionally, eight patients remained free of tumour from 3 to 24 months. Partial response (PR) was seen in 11 (36 per cent) sites while one (3 per cent) had lesser degree tumour regression. Tumour control rate correlated well with the dose of radiation, p = 0.02, and tumour volume, p = 0.02, but not with thermal dose. Treatment complications of significance occurred in one (3 per cent) site, which developed soft tissue necrosis. This study again has demonstrated the effectiveness of RT-HT combination in treatment of recurrent tumours.

    View details for Web of Science ID A1988N035200003

    View details for PubMedID 3385222

  • TREATMENT OF CARCINOMA OF THE SKIN WITH BONE AND OR CARTILAGE INVOLVEMENT AMERICAN JOURNAL OF CLINICAL ONCOLOGY-CANCER CLINICAL TRIALS Petrovich, Z., KUISK, H., Langholz, B., Luxton, G., Petrovich, M., CHAK, L., Rice, D. 1988; 11 (2): 110-113

    Abstract

    From 1956 to 1978, 23 patients with stage T4 carcinoma of the skin of the head and neck were treated with radiotherapy (RT). There were nine patients with cancer of the skin of the nose, eight with tumors of the pinna, and six with lesions of the eyelids. Basal cell carcinoma (BCC) was seen in 61%, squamous cell carcinoma (SCC) in 26%, and 13% of patients had tumors with BCC and SCC features. The majority of patients had large tumors. Less than one-third of patients had smaller lesions, whereas three patients had intermediate-size tumors (greater than 2 cm to less than or equal to 5 cm). Of the 23 patients treated, nine had prior surgical therapy and recurrent or persistent tumor. The remaining 14 patients had no prior therapy. RT was given up to an average total dose of 55 Gy. The 5-year actuarial tumor control rate was 80%. Of the 23 patients treated, four had recurrent tumors. There were no recurrences among the 14 BCC patients, whereas there were four recurrences among the nine SCC and mixed histology patients. Of the four patients who had tumor recurrence, one was salvaged by subsequent radical surgery and three died of their tumor. No serious complications were observed in this group of 23 patients. There was no cartilage, bone, or soft-tissue necrosis noted. RT is a good treatment option and it may be treatment of choice in patients with BCC and SCC of the skin with cartilage or bone involvement. It provides an excellent chance of tumor control, good cosmesis, preservation of function, and a low incidence of complications.

    View details for Web of Science ID A1988M902300004

    View details for PubMedID 3358361

  • Intraluminal thermoradiotherapy with teletherapy for carcinoma of the esophagus. Endocurietherapy Hyperthermia Oncology Petrovich Z, Astrahan M, Lam K, Tildon T, Luxton G, Jepson J 1988; 4: 155-161
  • A 500-kHz localized current field hyperthermia system for use with ophthalmic plaque radiotherapy. Recent results in cancer research. Fortschritte der Krebsforschung. Progrès dans les recherches sur le cancer Astrahan, M., Liggett, P., Petrovich, Z., Luxton, G. 1988; 107: 93-98

    View details for PubMedID 3375565

  • Interstitial radiotherapy combined with interstitial hyperthermia in the management of recurrent tumors. Recent results in cancer research. Fortschritte der Krebsforschung. Progrès dans les recherches sur le cancer Petrovich, Z., Lam, K., Astrahan, M., Luxton, G., Langholz, B. 1988; 107: 136-140

    Abstract

    During a 2-year period 31 sites in 27 patients with recurrent, previously treated tumors received a combination of interstitial 192Ir radiation (RT) with microwave hyperthermia (HT). Head and neck sites were treated most frequently (48%), with breast and vagina each representing about 20% of sites. Complete response (CR) with no local recurrence was obtained in 61%, partial response (PR) in 11 (36%), and one (3%) had less than 50% tumor regression. Of these patients, nine had no evidence of tumor following HT-RT therapy, 8/18 in the CR group and 1/11 in the PR group. Significant factors influencing CR were: radiation dose, tumor volume and duration of tumor control following the initial therapy (p less than 0.02). Treated site, histology and thermal dose were not significant factors influencing tumor regression. Complications of significance developed in one patient who had local skin necrosis. Interstitial HT-RT combination provides an effective palliative therapy for recurrent and/or persistent tumors. Randomized trials are necessary to assess the effectiveness of this combination as a component part of primary management of selected tumors.

    View details for PubMedID 2453899

  • OUTPUT FACTOR CONSTITUENTS OF A HIGH-ENERGY PHOTON-BEAM MEDICAL PHYSICS Luxton, G., Astrahan, M. A. 1988; 15 (1): 88-91

    Abstract

    Measurements designed to separate primary and various scatter components of central axis dose of the highest energy photon beam of the CGR Saturne 25 linear accelerator are described. This beam has an unusually large output variation with field size. The measurements are performed both in air and in a water phantom, with and without an aperture external to the collimator system. Results are presented in the form of relative output factors for different field sizes due to (i) flattening filter scatter, (ii) water phantom scatter, (iii) collimator backscatter into the monitor chamber, and (iv) collimator forward scatter onto the central axis. It is found that the flattening filter is the single largest scatter component, but that each of the other factors is significant in determining the output dose per monitor unit as a function of field size.

    View details for Web of Science ID A1988M106600018

    View details for PubMedID 3127668

  • CHARACTERISTICS OF THE HIGH-ENERGY PHOTON-BEAM OF A 25-MEV ACCELERATOR MEDICAL PHYSICS Luxton, G., Astrahan, M. A. 1988; 15 (1): 82-87

    Abstract

    The CGR Saturne 25 is an isocentrically mounted standing wave medical linear accelerator that produces dual-energy photon beams and a scanned electron beam with six selectable energies between 4 and 25 MeV. The highest energy photon beam is nominally referred to as 23 MV. For this beam the mean energy of the accelerated electron beam on the 1.3 radiation length (4 mm) tungsten x-ray target is found to be approximately 21 MeV, with the energy acceptance stated to be +/- 5%. The electron beam traverses a 270 degrees bending magnet upstream of the x-ray production target. The resulting bremsstrahlung beam passes through a combination steel and lead flattening filter, 4-cm maximum thickness. Dosimetric data for the 23-MV beam are presented with respect to rectangular field output factor, depth of maximum dose as a function of field size, surface and buildup dose, central axis percent depth dose, tissue-phantom ratios, beam profile, applicability of inverse square, and block transmission. Some data are also presented on the effect of different flattening filter designs on apparent beam energy.

    View details for Web of Science ID A1988M106600017

    View details for PubMedID 3127667

  • TREATMENT RESULTS AND PATTERNS OF FAILURE IN 646 PATIENTS WITH CARCINOMA OF THE EYELIDS, PINNA, AND NOSE AMERICAN JOURNAL OF SURGERY Petrovich, Z., KUISK, H., Langholz, B., Astrahan, M., Luxton, G., CHAK, L., Rice, D. 1987; 154 (4): 447-450

    Abstract

    From 1956 to 1978, 646 patients were treated with radiotherapy for carcinoma of the nose (350 patients, 54 percent), eyelids (159 patients, 25 percent), pinna (93 patients, 14 percent), and skin adjacent to the lip (44 patients, 7 percent). The histologic distribution was 72 percent basal cell carcinoma, 18 percent squamous cell carcinoma, and 10 percent mixed basal and squamous cell features. Tumors less than 2 cm in diameter were found in 602 patients (93 percent), whereas 44 patients (7 percent) had larger tumors. Tumor involvement of cartilage and bone was seen in 23 patients at the time of diagnosis. The 5, 10, and 20 year control rates were 99 percent, 98 percent, and 98 percent, respectively, for 502 tumors less than 2 cm in diameter. This compared favorably with control rates of 92 percent at 5 years and 79 percent at 10 years for tumors from 2 to 5 cm in diameter and 60 percent at 5 years and 53 percent at 8 years for 12 patients with massive tumors (p less than 0.0001). The histologic characteristics of the lesion had a strong influence on tumor control (p less than 0.02). Of the patients with cartilage or bone invasion, tumor was controlled in 19 (83 percent). Of these 19 patients, 11 had no evidence of disease for 3 years or more. Of all 646 patients treated, failure was seen in 60 (9 percent). It correlated well with the size of the lesion, being 7 percent for tumors of less than 2 cm and 50 percent for tumors of greater than 5 cm. Of the 60 patients in whom treatment failed, 48 (80 percent) had prior definitive therapy. Radiotherapy was an efficient modality to control operative failures; however, it was not as efficient at control in patients in whom previous radiotherapy failed. Operation was the treatment of choice to salvage patients in whom radiotherapy failed. Of the patients in whom retreatment failed, 10 were known to have died from skin cancer, and an additional 6 patients were presumed to have died from the cancer. This study has demonstrated a good control rate and good cosmetic results for small tumors of the eyelids, pinna, and nose. In addition, a good control rate was obtained in patients with cartilage and bone involvement. Treatment of massive tumors should involve planned operative resection with adjuvant radiotherapy.

    View details for Web of Science ID A1987K368200022

    View details for PubMedID 3661851

  • A 500 KHZ LOCALIZED CURRENT FIELD HYPERTHERMIA SYSTEM FOR USE WITH OPHTHALMIC PLAQUE RADIOTHERAPY INTERNATIONAL JOURNAL OF HYPERTHERMIA Astrahan, M., Liggett, P., Petrovich, Z., Luxton, G. 1987; 3 (5): 423-432

    Abstract

    Ophthalmic plaque radiotherapy has been demonstrated to be a useful alternative to enucleation in the treatment of small choroidal melanomas. The prognosis for tumours larger than 8 mm in height, however, continues to be poor. Treatment complications limit the radiation dose which may be delivered to these larger tumours. Hyperthermia has been shown to enhance the effectiveness of radiotherapy for many tumours, particularly malignant melanoma. The use of hyperthermia in conjunction with plaque radiotherapy may improve local tumour control for larger choroidal melanomas, allowing patients to maintain useful vision. We have developed an instrument which enables the combination of localized current field hyperthermia with radiotherapy using an episcleral plaque. The system is simple and inexpensive. We have measured temperature distributions in tissue-like phantoms, in excised bovine eyes, and in vivo in normal rabbits. In each of the cases studied, temperature varied by less than 1 degree C within 3 mm of, and across the concave surface of the plaque. At distances greater than 3 mm, the temperature gradient was approximately -0.3 degree C per millimetre.

    View details for Web of Science ID A1987K256400003

    View details for PubMedID 3681042

  • REGIONAL HYPERTHERMIA WITH BSD-1000 ANNULAR PHASED-ARRAY IN THE MANAGEMENT OF RECURRENT DEEP SEATED MALIGNANT-TUMORS STRAHLENTHERAPIE UND ONKOLOGIE Petrovich, Z., Emami, B., Astrahan, M., Langholz, B., Luxton, G. 1987; 163 (7): 430-433

    View details for Web of Science ID A1987J212600007

    View details for PubMedID 3616899

  • Interstitial radiobrachytherapy of malignant cerebral neoplasms: rationale, methodology, prospects. Neurological research Apuzzo, M. L., Petrovich, Z., Luxton, G., JEPSON, J. H., Cohen, D., Breeze, R. E. 1987; 9 (2): 91-100

    Abstract

    The local use of radionuclides in the management of neoplastic processes was initially considered over 80 yr ago and has enjoyed increasing enthusiasm in the treatment of somatic and central nervous system tumours during the past 30 yr. The marriage of complex neuroimaging techniques and modern stereotactic devices has markedly enhanced the technical precision of interstitial radiobrachytherapy of malignant cerebral neoplasms. In applying these techniques, it is imperative to achieve an optimal placement of radionuclide sources in order to develop a geometrically homogenous, controlled distribution of radiation. Critical considerations include determination of tumour volume and contour, and development of a homogenous dose rate (dependent upon multiple sources at varying intensity) that will not only effect tumour cell kill but do this without excessive production of radionecrosis which necessitates craniotomy because of mass. Using the Brown-Roberts-Wells (BRW) stereotactic guidance system and an image-defined, volumetrically determined target, implants of multiple iridium 192(192Ir) sources were used to establish appropriate isodose envelopes. A methodology for achieving the described objectives is detailed as it applies to a variety of malignant intracerebral neoplasms (glioblastoma multiforme, malignant astrocytoma, malignant mixed glioma, primary cerebral lymphoma, metastatic carcinoma and malignant pineal region tumours). Technical realization of precision implantation relying upon imaging data may be acheived with this method with satisfactory responses that are dependent upon histological tumour type and the morphology of the tumour distribution as related to the image. Early and late complications related to the surgical technique and radionuclide applications were less than 5%. Although encouraging, these techniques require further definition and greater data accrual before uniform application outside major medical centres can be justified. It is anticipated that improvement in results with intrinsic gliomas and other invasive neoplasms will be realized with further definition of tumour boundaries by tract biopsy techniques and concurrent utilization of hyperthermia and brain protective methods.

    View details for PubMedID 2886948

  • CARCINOMA OF THE LIP AND SELECTED SITES OF HEAD AND NECK SKIN - A CLINICAL-STUDY OF 896 PATIENTS RADIOTHERAPY AND ONCOLOGY Petrovich, Z., Parker, R. G., Luxton, G., KUISK, H., Jepson, J. 1987; 8 (1): 11-17

    Abstract

    During a period of over 20 years, 896 patients were treated with radiation in Wadsworth Medical Center, Los Angeles, for carcinoma of the lip and selected sites of skin of the head and neck. Basal cell carcinoma (BCC) was found in 467 (52%) patients, squamous cell carcinoma (SCC) in 362 (40%), and the remaining 67 (8%) had tumors with mixed basal and squamous cell features. BCC was the most common tumor (72%) among the 646 skin cancer patients while SCC predominated (99%) among the 250 lip cancer patients. Tumor control correlated well with the size of the lesion, p less than 0.0001. Histology of the lesion also had a significant (p = 0.021) influence on the tumor control rate, which was the highest among the BCC patients when compared with SCC or mixed cell patients. This study has again demonstrated the effectiveness of radiotherapy in controlling small and intermediate size epithelial tumors of the skin and lip. Additionally, irradiation, if administered properly, results in excellent cosmesis and a low incidence of treatment complications. Severe complications of radiotherapy reported in the literature took place at the beginning of this century and are no longer pertinent in the practice of modern radiation oncology. Larger lesions remain a challenge to radiation or surgical dermato-oncologists. A lack of tumor control in such lesions frequently results in a death of patient.

    View details for Web of Science ID A1987F864400002

    View details for PubMedID 3809597

  • Thermometry characteristics of the BSD interstitial hyperthermia applicator Endocurietherapy Hyperthermia Oncology Astrahan MA, Luxton G, Petrovich Z 1987; 3: 153-160
  • Ionizing and nonionizing radiation treatment of malignant cerebral gliomas: specialized approaches. Clinical neurosurgery Apuzzo, M. L., JEPSON, J. H., Luxton, G., Little, F. M. 1983; 31: 470-496

    View details for PubMedID 6388947

  • Microdosimetry of multiport irradiation with the Stanford medical pion generator Radiation Research Luxton G, Fessenden P, Zeman HD 1981; 85 (2): 238-256
  • MICRODOSIMETRY OF MULTIPORT IRRADIATION WITH THE STANFORD MEDICAL PION GENERATOR RADIATION RESEARCH Luxton, G., Fessenden, P., Zeman, H. D. 1981; 85 (2): 238-256
  • MICRODOSIMETRIC MEASUREMENTS OF PRE-THERAPEUTIC HEAVY-ION BEAMS RADIATION RESEARCH Luxton, G., Fessenden, P., Hoffmann, W. 1979; 79 (2): 256-272

    View details for Web of Science ID A1979HK72900004

    View details for PubMedID 113845

  • INITIAL PERFORMANCE OF STANFORD MEDICAL PION GENERATOR RADIOLOGY PISTENMA, D. A., Fessenden, P., Boyd, D. P., Luxton, G., Taber, R., Bagshaw, M. A. 1977; 122 (2): 527-529

    Abstract

    A novel, cylindrical geometry, superconducting pion channel has been constructed at Stanford. It can simultaneously deliver up to 60 radially converging pion beams of the same mean momentum but with individually variable momentum spread (0.0-4.3%). Virtually no tuning of the pion beam is required Preliminary tests have demonstrated many of the performance characteristics which facilitate the treatment of selected human tumors.

    View details for Web of Science ID A1977CT87700056

    View details for PubMedID 834908

  • INTRODUCTION TO USE OF NEGATIVE PI-MESONS IN RADIATION-THERAPY - RUTHERFORD 1964, REVISITED INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Bagshaw, M. A., Li, G. C., PISTENMA, D. A., Fessenden, P., Luxton, G., HOFFMANN, W. W. 1977; 3: 287-292

    View details for Web of Science ID A1977EW81600048

    View details for PubMedID 149099

  • Inelastic muon-proton scattering: multiplicity distributions and prong cross sections Physical Review D Del Papa C, Dorfan D, Flatté SM, Heusch CA, Lieberman B, Luxton G, Meyer H, Moss L, Schalk T, Seiden A, Bunnell K, Duong-van M, Mozley R, Odian A, Villa F, Wang LC 1976; 13: 2934-2943
  • np charge-exchange scattering from 60 to 300 GeV/c Physical Review Letters Barton HR Jr, Reay NW, Reibel K, Shaevitz MH, Stanton NR, Abolins MA, Brindza P, Matthews JAJ, Sidwell RA, Edwards KW, Luxton G, Kitching, P 1976; 37: 1656-1659
  • High-statistics study of ? production Physical Review Letters Shaevitz MH, Reay NW, Reibel K, Stanton NR, Edwards KW, Luxton G, Abolins MA, Sidwell RA, Dankowych JA, Luste GJ, Martin JF, Prentice JD 1976; 36 (1): 8-11
  • Differential cross sections for ?-p ->?n at 6.0 GeV/c Physical Review Letters Shaevitz MH, Reay NW, Reibel K, Stanton NR, Edwards KW, Luxton G, Abolins MA, Sidwell RA, Dankowych JA, Luste GJ, Martin JF, Prentice JD 1976; 36 (1): 5-8
  • Search for narrow two-body enhancements at Fermilab Physical Review Letters Abolins MA, Cardimona D, Matthews JAJ, Sidwell RA, Barton HR Jr., Reay NW, Reibel K, Stanton N, Edwards KW, Luxton G 1976; 37: 417-420
  • Hadron multiplicities structure functions - a comparison of muoproduction with photoproduction and e+e- annihilation Physical Review Letters Bunnell K, Duong-Van M, Mozley R, Odian A, Villa F, Wang LC, del Papa C, Dorfan D, Flatté SM, Heusch CA, Lieberman B, Luxton G, Meyer H, Moss L, Schalk T, Seiden A 1976; 36: 772-774
  • Some features of np charge-exchange scattering between 60 and 300 GeV/c Physical Review Letters Barton HR Jr, Reay NW, Reibel K, Shaevitz M, Stanton NR, Abolins MA, Brindza P, Matthews JAJ, Sidwell RA, Edwards KW, Luxton G, Kitching P 1976; 37: 1659-1662
  • Design of a tagged photon-electron beam facility for NAL Nuclear Instruments and Methods Halliwell C, Biggs PJ, Busza W, Chen M, Nash T, Murphy F, Luxton G, Prentice JD 1972; 102: 51-59
  • Kinematics of production processes at high energy and the Regge Pole hypothesis Physical Review D Luxton G 1970; 2: 1926-1934

Conference Proceedings


  • Dosimetric comparison of three photon radiosurgery techniques for an elongated ellipsoid target Yu, C., Luxton, G., Jozsef, G., Apuzzo, M. L., Petrovich, Z. ELSEVIER SCIENCE INC. 1999: 817-826

    Abstract

    To examine the dosimetric differences among three radiosurgery techniques: gamma knife, linac multiple arcs, and conformally-shaped static fields.A simulated target was taken to be a prolate ellipsoid, 25 mm in diameter, 35 mm in length, centrally located in a three-dimensional (3D) model of a patient head taken from MR images. Single isocenter linac treatment plans were developed, 9 portals for the static shaped field technique, and a 7-arc plan for the multiple arc method. A total of 13 isocenters with 3 different collimators were used in the gamma knife plan.At dose levels from 25% to 50% of the reference dose, multiple arc and shaped-field plans treated a greater volume than the gamma knife plan. The linac plans, however, delivered the dose more homogeneously across the target volume as compared to the gamma knife plan. For the dose levels between 50-100%, the shaped fields and gamma knife plan have a similar dose distribution, and treated slightly less volume than the multiple arc plan.For a target of limited volume and essentially any shape, one can obtain closely conformal dosimetry with the gamma knife. For a regular-shaped target, the single isocenter multiple arc technique gives a more homogenous dose distribution within the target. Static shaped fields offer an alternative radiosurgery technique, with dosimetry similar to the multiple arc method, applicable to targets of any shape.

    View details for Web of Science ID 000082983000040

    View details for PubMedID 10524439

  • Gamma unit facility: Concept genesis, architectural design and practical realization LeMay, D. R., Chen, T. C., Petrovich, Z., Luxton, G., Zelman, V., Zee, C. S., Green, J., Apuzzo, M. L. KARGER. 1996: 41-49

    Abstract

    The physical creation of a gamma unit facility requires the development of a broad-perspective multidisciplinary plan. The primary goal is radiosurgical treatment of intracranial lesions in a functional environment. The practical realization of a facility optimally designed for patient treatment is dependent on factors which include the facility setting, architectural goals, radiation safety requirements, and patient and medical team needs. This necessitates combined intellectual resources from neurosurgery, radiation oncology and physics, anesthesia, radiology, nursing, administration, and architectural and engineering teams. We undertook the development of a gamma unit facility which optimized the ergonomics and efficiency of patient evaluation, care and treatment, given the instrument requirements. This general plan based on our experience can be used for the development of other gamma unit facilities.

    View details for Web of Science ID A1996VQ77000009

    View details for PubMedID 8938932

  • Mechanical malfunction of the Leksell Gamma Knife during patient treatment Luxton, G., Yu, C., Petrovich, Z., Zelman, V., Zee, C. S., Machovec, D. J., LeMay, D., Apuzzo, M. L. KARGER. 1996: 35-40

    Abstract

    During the course of a patient treatment with a North American U-type gamma unit, the remote hydraulic valve controlling the direction of couch motion failed to change state. The couch, helmet and patient remained in treatment position after the expiration of treatment time for one of the target shots. No unusual equipment warning indications had been observed prior to the malfunction. The gamma unit was new, having been used to treat approximately 20 patients since it had begun to be used clinically 11 weeks previously. This specific situation was not addressed in our posted Emergency Procedures, which dealt explicitly with loss of electrical power, and loss of hydraulic pressure. In the present case, the hydraulic gauges indicated full pressure. After attempts to disengage the patient remotely proved unsuccessful, personnel entered the room. The table clutch at the foot of the couch was operated to disengage the couch/helmet assembly from its docked position. While this was not mentioned in our emergency procedures, the act had the effect of causing the cobalt-60 sources to be misaligned with the collimator apertures, thereby immediately terminating the patient treatment. This also had the unanticipated effect of substantially reducing radiation leakage exposure rate next to the couch near the tunnel opening. The patient was released from the helmet trunnions using a manufacturer-supplied long-handled special Allen key. The key was used conventionally, to release the trunnion locking mechanism, and also unconventionally to force a separation of a trunnion from the docking slot on the patient head frame. The patient was then removed from the tunnel by sliding out the pad on which she was lying. Anesthesiology personnel accompanied the patient out of the room. The unit functioned properly upon the replacement of the valve by manufacturer service personnel the next day. The patient returned for completion of treatment 1 week later. There were only minor changes to the overall patient dosimetry as a result of the malfunction. Personnel exposures were very low. The malfunction was reported to State authorities, who conducted an investigation, that was in turn followed up by an investigation by the Nuclear Regulatory Commission.

    View details for Web of Science ID A1996VQ77000008

    View details for PubMedID 8938931

  • TREATMENT OF UTERINE SARCOMAS ECHT, G., Jepson, J., Steel, J., Langholz, B., Luxton, G., Hernandez, W., Astrahan, M., Petrovich, Z. WILEY-LISS. 1990: 35-39

    Abstract

    During a 21-year period, 66 patients with uterine sarcomas were treated at California Medical Center. Histological diagnoses were mixed mesodermal sarcoma in 32 patients (48%), leiomyosarcoma in 24 (36%), and endometrial stromal sarcoma in 10 (15%) patients. The majority of patients (73%) had Stage I tumors. The treatment consisted of surgery alone in 27 (41%), surgery in combination with radiation therapy in 36 (55%), and radiation therapy alone in three (4%) patients. The overall 1-, 2-, and 5-year actuarial survival was 74%, 57%, and 38%, respectively. The 1-, 2-, and 5-year actuarial survival for the 27 surgery alone patients was 73%, 50%, and 25%, which compared with 75%, 61%, and 44% for the 36 surgery plus radiation therapy patients (P = 0.12). The disease-free survival was better for the surgery plus radiation therapy patients, as compared with the surgery alone group (38% vs. 18% at 5 years, P = 0.081). The 5-year survival by histology was 70% for the 10 endometrial stromal sarcoma patients, 40% for the 24 leiomyosarcoma patients, and 23% for the 32 mesodermal sarcoma patients (P = 0.064). As expected, survival depended on the stage of disease (P less than 0.0001). Treatment failure was observed in 35 (53%) patients, which included 9 (14%) with failure in the pelvis. There was no difference in the incidence of failure among patients in the three treatment groups and also in the three histologic groups. There was, however, a significant difference in the incidence of pelvic failure between surgery alone and surgery plus radiation therapy patients. In the 27 surgery alone patients, nine (33%) relapsed in the pelvis, whereas none of the 36 surgery plus radiation therapy patients had locoregional failure, P less than 0.0001. Adjuvant radiation therapy is an important treatment in the management of patients with sarcoma of the uterus.

    View details for Web of Science ID A1990DK33100007

    View details for PubMedID 2354406

  • DOSIMETRY OF STANFORD PION RADIOTHERAPY PROJECT Fessenden, P., Luxton, G., PISTENMA, D., Boyd, D. IOP PUBLISHING LTD. 1977: 152-152

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