A Comparative Analysis of Water-Equivalent Path Length of Tissue Samples using a Fast Monolithic Proton Radiography System

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DeFillippo, Greg James
Wang, C.-K. Chris
Erickson, Anna S.
Pankuch, Mark
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Proton therapy has emerged over the past forty years as a clinically viable form of radiation oncology. With low entry dose, a rise to a sharp maximum, and a steep fall-off to zero dose after the "Bragg Peak", proton therapy has proven itself useful particularly with cancers in regions close to sensitive normal tissue. However, proton therapy treatment plans are still produced on x-ray CT scans. Due to fundamentally different natures of interaction, x-ray scans must undergo a conversion to translate Hounsfield Units (HU) to relative stopping power (RSP). This conversion can be inaccurate by up to 4%, and is currently the greatest cause of uncertainty in proton therapy. While there exist several ways around this, directly measuring RSP with proton imaging is the most accurate solution. ProtonVDA, in conjunction with Northern Illinois University, has produced a prototypical proton radiograph and CT scanner compatible with clinical pencil beam scanning (PBS) gantries. In this presentation, I demonstrate recent work on animal tissue samples using this scanner, including pork shoulder, pork ribs, and an in-tact pig head. A comparative analysis of RSP between x-ray CT and proton CT images of these samples is presented, along with sample pencil beam spots measured in the RayStation treatment program.
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