Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Medical Biophysics

Supervisor

Eugene Wong

Abstract

External beam radiotherapy has become technically sophisticated with image guided radiation therapy (IGRT) and intensity modulated radiation therapy (IMRT). These technologies allow for precise delivery of radiation to geometric targets in cancer patients. However, many questions remain on how to best define targets based on biological information, such as functional imaging, and how to combine radiation with other cancer therapies. To help answer these questions, small animal preclinical studies are needed to generate data to inform clinical trials. However, the precise radiation delivery capabilities of IGRT and IMRT have not been available in the preclinical labs. To enable translational experiments and to address the lack of preclinical radiotherapy technology, a commercial micro-CT was first developed into an image-guided conformal radiotherapy system in this thesis. Computerized asymmetric jaws were constructed, implemented and characterized for the system. A Monte Carlo dose calculation package was successfully configured for the system and verified with film measurements. Respiratory gated imaging and radiotherapy was demonstrated with a phantom and in animals. Secondly, accurate radiation dosimetry reduces uncertainties in preclinical experiments. To achieve accurate dose calculations in the kilovoltage x-ray range where photoelectric effects and Compton scattering dominate, knowledge of material composition and density is needed. Dual energy micro-CT was optimized (including choice of x-ray beam peak voltages, filtrations, and duration) and evaluated for the purpose of characterizing materials. Dual energy CT techniques developed for clinical scanners were adapted and examined for micro-CT. A set of micro-CT phantoms consisting of 11 plastic materials and solutions that spanned a relevant range of compositions was designed and constructed. Initial experiments found beam-hardening image artefacts limited accurate measurements. By switching to a more sensitive detector, x-ray spectra with additional beam filtration were possible and resulted in reduced beam-hardening effects. This improved dual energy micro-CT measurement accuracy of material composition and density. In conclusion, a small animal image-guided conformal radiotherapy system was developed and commissioned for preclinical studies. Dual energy micro-CT was demonstrated as a method to characterize materials to improve kilovoltage dose calculation. This integrated micro-CT based small animal image-guided radiation platform has enabled numerous pre-clinical studies.

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