(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: To evaluate proton radiographic imaging using the spot scanning MEVION proton therapy system and investigate the use of proton on-board imaging as an alternative for on-board kV photon imaging systems.
Methods: Radiographic proton images of different phantoms were acquired using pencil beams from the spot scanning MEVION-proton therapy machine. A high energy of nearly 230MeV single layer proton with 3.5mm diameter spots and 2.5mm spot spacing were used to irradiate the phantoms that included different patters to evaluate image quality of the proton radiographs. The proton radiographs were acquired with high sensitivity and spatial resolution phosphorous detector plates used in computed radiography. The image quality of the proton radiographs was evaluated using different proton dose levels (0.2-2.0MU), ranges (1-32cm) and modulation (2-25cm).
Results: The range modulation of one energy layer spot scanning proton beam provided higher contrast images by setting the detector at high dose gradient of the Bragg peak. Proton radiographic images with acceptable image quality were obtained with low imaging dose levels using 0.2MU per spot of the pencil proton beam. Lower imaging dose was achieved by using proton beams with the highest proton energy of nearly 230MeV that crossed through the phantom and locating the Bragg peak at the level of the detector. The image quality improved with increasing depth of the quality assurance phantom because of shorter scatter range between the imaging objects and the detector. The increased separation between the imaging object and the detector decreased image quality because of increased proton scatter thickness before detection.
Conclusion: The use of range modulated proton pencil beams produced superior soft-tissue radiographic images with lower imaging doses in comparison with photon radiographic images. This method of proton radiographic imaging using direct therapeutic beams from proton radiotherapy machines may provide an alternative to on-board imaging with photon beams.
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