Bio

Academic Appointments


Honors & Awards


  • 3rd Place, John R. Cameron Young Investigator Award, AAPM (2008)

Professional Education


  • DABR, The American Board of Radiology, Therapeutic Medical Physics (2011)
  • Residency, Stanford University, Medical Physics (2010)
  • PhD, Wake Forest University, Medical Physics (2008)
  • MS, Wake Forest University, Medical Imaging (2005)
  • BS, University of North Carolina at Chapel Hill, Applied Science (2001)

Research & Scholarship

Current Research and Scholarly Interests


My current research is focused on evaluating and improving linac-based stereotactic body radiation therapy (SBRT) treatment planning and delivery techniques, predicting dosimetric indices in prospective plans through automated data mining, and developing new approaches for planning and delivering prone partial breast irradiation.

Publications

Journal Articles


  • Dosimetric Analysis of Organs at Risk During Expiratory Gating in Stereotactic Body Radiation Therapy for Pancreatic Cancer INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Taniguchi, C. M., Murphy, J. D., Eclov, N., Atwood, T. F., Phd, K. N., Christman-Skieller, C., Mok, E., Xing, L., Koong, A. C., Chang, D. T. 2013; 85 (4): 1090-1095

    Abstract

    To determine how the respiratory phase impacts dose to normal organs during stereotactic body radiation therapy (SBRT) for pancreatic cancer.Eighteen consecutive patients with locally advanced, unresectable pancreatic adenocarcinoma treated with SBRT were included in this study. On the treatment planning 4-dimensional computed tomography (CT) scan, the planning target volume (PTV), defined as the gross tumor volume plus 3-mm margin, the duodenum, and the stomach were contoured on the end-expiration (CTexp) and end-inspiration (CTinsp) phases for each patient. A separate treatment plan was constructed for both phases with the dose prescription of 33 Gy in 5 fractions with 95% coverage of the PTV by the 100% isodose line. The dose-volume histogram (DVH) endpoints, volume of duodenum that received 20 Gy (V20), V25, and V30 and maximum dose to 5 cc of contoured organ (D5cc), D1cc, and D0.1cc, were evaluated.Dosimetric parameters for the duodenum, including V25, V30, D1cc, and D0.1cc improved by planning on the CTexp compared to those on the CTinsp. There was a statistically significant overlap of the PTV with the duodenum but not the stomach during the CTinsp compared to the CTexp (0.38 ± 0.17 cc vs 0.01 ± 0.01 cc, P=.048). A larger expansion of the PTV, in accordance with a Danish phase 2 trial, showed even more overlapping volume of duodenum on the CTinsp compared to that on the CTexp (5.5 ± 0.9 cc vs 3.0 ± 0.8 cc, P=.0003) but no statistical difference for any stomach dosimetric DVH parameter.Dose to the duodenum was higher when treating on the inspiratory than on the expiratory phase. These data suggest that expiratory gating may be preferable to inspiratory breath-hold and free breathing strategies for minimizing risk of toxicity.

    View details for DOI 10.1016/j.ijrobp.2012.07.2366

    View details for Web of Science ID 000315809300047

  • RADIOTHERAPY DOSE PERTURBATION OF ESOPHAGEAL STENTS EXAMINED IN AN EXPERIMENTAL MODEL INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS Atwood, T. F., Hsu, A., Ogara, M. M., Luba, D. G., Tamler, B. J., Disario, J. A., Maxim, P. G. 2012; 82 (5): 1659-1664

    Abstract

    To investigate the radiotherapy dose perturbations caused by esophageal stents in patients undergoing external beam treatments for esophageal cancer.Four esophageal stents were examined (three metallic stents: WallFlex, Ultraflex, and Alveolus; one nonmetallic stent with limited radiopaque markers for visualization: Polyflex). All experiments were performed in a liquid water phantom with a custom acrylic stent holder. Radiochromic film was used to measure the dose distributions adjacent to the stents at locations proximal and distal to the radiation source. The stents were placed in an air-filled cavity to simulate the esophagus. Treatment plans were created and delivered for photon energies of 6 and 15 MV, and data analysis was performed on uniform regions of interest, according to the size and geometric placement of the films, to quantify the dose perturbations.The three metallic stents produced the largest dose perturbations with distinct patterns of "hot" spots (increased dose) measured proximal to the radiation source (up to 15.4%) and both "cold" (decreased dose) and hot spots measured distal to the radiation source (range, -6.1%-5.8%). The polymeric Polyflex stent produced similar dose perturbations when the radiopaque markers were examined (range, -7.6%-15.4%). However, when the radiopaque markers were excluded from the analysis, the Polyflex stent produced significantly smaller dose perturbations, with maximum hot spots of 7.3% and cold spots of -3.2%.The dose perturbations caused by esophageal stents during the treatment of esophageal cancer using external beam radiotherapy should be understood. These perturbations will result in hot and cold spots in the esophageal mucosa, with varying magnitudes depending on the stent. The nonmetallic Polyflex stent appears to be the most suitable for patients undergoing radiotherapy, but further studies are necessary to determine the clinical significance of the dose perturbations.

    View details for DOI 10.1016/j.ijrobp.2011.02.020

    View details for Web of Science ID 000301891300031

    View details for PubMedID 21514064

  • Gamma Knife (TM) Radiosurgery Treatment Planning for Small Animals using High-Resolution 7T Micro-magnetic Resonance Imaging RADIATION RESEARCH Wiant, D., Atwood, T. F., Olson, J., Papagikos, M., Forbes, M. E., Riddle, D. R., Bourland, J. D. 2009; 172 (5): 625-631

    Abstract

    Gamma Knife stereotactic radiosurgery is capable of providing small, high gradient dose distributions to a target with a high level of precision, which makes it an excellent choice for studies of focal irradiations with small animals. However, the Gamma Knife stereotactic radiosurgery process makes use of a human-sized fiducial marker system that requires a field of view of at least 200 mm(2) to relate computed tomography and magnetic resonance images to the Gamma Knife treatment planning software. Thus the Gamma Knife fiducial marker system is five to six times larger than a typical small animal subject. The required large field of view limits the spatial resolution and structural detail available in the animal treatment planning image set. In response to this challenge we have developed a custom-designed stereotactic jig and miniature fiducial marking system that allow small bore high-resolution micro-imaging techniques, such as 7T MR and micro-CT, to be used for treatment planning of Gamma Knife stereotactic radiosurgery focal irradiation of small animals.

    View details for DOI 10.1667/RR1614.1

    View details for Web of Science ID 000271521800012

    View details for PubMedID 19883231

  • Quantitative in vivo proton MR spectroscopic evaluation of the irradiated rat brain JOURNAL OF MAGNETIC RESONANCE IMAGING Atwood, T., Robbins, M. E., Zhu, J. 2007; 26 (6): 1590-1595

    Abstract

    To investigate if in vivo localized proton magnetic resonance spectroscopy (MRS) can detect putative metabolic changes in the irradiated rat brain and quantitatively measure brain metabolite changes in this model.A total of 20 adult male Fischer 344 rats were exposed to a fractionated regimen of whole brain irradiation (WBI) (total 45 Gy, given as five Gy fractions, twice per week for 4.5 weeks); 10 control rats received sham irradiation. A total of 52 weeks after WBI, all animals were subjected to high-resolution MRI and in vivo proton MRS to determine structural and brain metabolite changes. Brain metabolites were measured by using single-voxel MRS. Quantitative analysis of detectable metabolites was performed by using the spectral analysis method, LCModel.Significant differences in brain metabolite concentrations were detected in rat brains irradiated with a clinically relevant fractionated radiotherapy regimen in 52 weeks, in comparison to age-matched sham-irradiated rats.These findings indicate that quantitative in vivo MRS may serve as a sensitive imaging tool to noninvasively detect neurochemical changes in the irradiated brain.

    View details for DOI 10.1002/jmri.21095

    View details for Web of Science ID 000252012100028

    View details for PubMedID 17968883

  • Quantitative magnetic resonance spectroscopy reveals a potential relationship between radiation-induced changes in rat brain metabolites and cognitive impairment RADIATION RESEARCH Atwood, T., Payne, V. S., Zhao, W., Brown, W. R., Wheeler, K. T., Zhu, j., Robbins, M. E. 2007; 168 (5): 574-581

    Abstract

    To test the efficacy of magnetic resonance spectroscopy (MRS) in identifying radiation-induced brain injury, adult male Fischer 344 rats received fractionated whole-brain irradiation (40 or 45 Gy given in 5-Gy fractions twice a week for 4 or 4.5 weeks, respectively); control rats received sham irradiation. Twelve and 52 weeks after whole-brain irradiation, rats were subjected to high-resolution MRI and proton MRS. No apparent lesions or changes in T(1)- or T(2)-weighted images were noted at either time. This is in agreement with no gross changes being found in histological sections from rats 50 weeks postirradiation. Analysis of the MR spectra obtained 12 weeks after fractionated whole-brain irradiation also failed to show any significant differences (P > 0.1) in the concentration of brain metabolites between the whole-brain-irradiated and sham-irradiated rats. In contrast, analysis of the MR spectra obtained 52 weeks postirradiation revealed significant differences between the irradiated and sham-irradiated rats in the concentrations of several brain metabolites, including increases in the NAA/tCr (P < 0.005) and Glx/tCr (P < 0.001) ratios and a decrease in the mI/tCr ratio (P < 0.01). Although the cognitive function of these rats measured by the object recognition test was not significantly different (P > 0.1) between the irradiated and sham-irradiated rats at 14 weeks postirradiation, it was significantly different (P < 0.02) at 54 weeks postirradiation. These findings suggest that MRS may be a sensitive, noninvasive tool to detect changes in radiation-induced brain metabolites that may be associated with the radiation-induced cognitive impairments observed after prolonged fractionated whole-brain irradiation.

    View details for Web of Science ID 000250596200008

    View details for PubMedID 17973545

Stanford Medicine Resources: