We have modified a 120 kVp GE microCT scanner to allow it to deliver conformal radiation beams to small animals, in a manner similar to clinical radiotherapy. To accomplish this, a microCT-compatible variable-aperture collimator and 2D motion stage have been developed. Preliminary evaluation of this system has demonstrated that we can achieve dose rates as high as 3 Gy/minute and beam sizes as small as 1 mm, with beam penetration suitable for small animal targets. By using a series of radially convergent beams, therapeutic radiation doses may be delivered to confined tissue volumes while sparing surrounding normal tissues. MicroCT images of live subjects can be acquired on this system at spatial resolutions down to 50 um, which may then be used to plan radiation treatments using software described below. Monte Carlo models of this system have been constructed to facilitate accurate dosimetric simulations. By developing an inherently image-guided radiotherapy system, we can merge images from multiple modalities for use in planning and evaluating radiation therapies. This unit is now operational and is being applied as a tool to study tumor radiobiology.

Current research projects in this area include:

• Design of device control software for micro-CT based radiotherapy
• Development of Monte Carlo simulation methods for small animal kilovoltage radiotherapy
• Development of inverse planning methods
• Engineering and evaluation of immobilization methods for small animal multimodal imaging and therapy
• Investigation of intensity-modulation methods

Recent publications:

• Bazalova M, Nelson G, Noll JM, Graves EE. Modality comparison for small animal radiotherapy: a simulation study. Medical Physics 2013. [In press]
• Bazalova M, Nelson G, Noll JM, Graves EE. The Importance of Tissue Segmentation for Dose Calculations for Kilovoltage Radiation Therapy. Medical Physics 2011; 38:3039-3049.
• Nelson GS, Perez J, Vilalta M, Graves E.  Facilitating multimodal preclinical imaging studies in mice by using an immobilization bed. Comparative Medicine 2011; 61:499-504.
• Motomura AR, Bazalova M, Zhou H, Keall PJ, Graves EE>. Investigation of the effects of treatment planning variables in small animal radiotherapy dose distributions.  Medical Physics 2010; 37:590-599.
• Zhou H, Xu J, Rodriguez M, van den Haak F, Zhu X, Xian Y, Nelson G, Jogani R, Keall PJ, Graves EE.  Development of a MicroCT-Based Image-Guided 3D Conformal Radiotherapy System for Small Animals.  International Journal of Radiation Oncology Biology Physics 2010; 78:297-305.
• Zhou H, Keall PJ, Graves EE.  A Bone Composition Model for Monte Carlo X-Ray Transport Simulations. Medical Physics 2009; 36:1008-1018.
• Rodriguez M, Zhou H, Keall P, Graves E.  Commissioning of a Novel MicroCT/RT System for Small Animal Conformal Radiotherapy.  Physics in Medicine and Biology 2009; 54:3727-3740.
• Bazalova M, Zhou H, Keall PJ, Graves EE. Kilovoltage beam Monte Carlo dose calculations in sub-millimeter voxels for small animal radiotherapy.  Medical Physics 2009; 36:4991-4999.
• Graves EE, Zhou H, Chatterjee R, Keall PJ, Gambhir SS, Contag CH, Boyer AL.  Design and Evaluation of a Variable Aperture Collimator for Conformal Radiotherapy of Small Animals Using a MicroCT Scanner. Medical Physics 2007, 34: 4359-4367.