(Tuesday, 7/31/2018) 9:30 AM - 10:00 AM
Room: Exhibit Hall | Forum 8
Purpose: To investigate quantitatively image quality and dose of radiographic proton imaging with a high MeV therapeutic beam from the MEVION-S250 proton therapy system using Gafchromic-films and computed-radiographic-plates.
Methods: Proton beams from the MEVION-S250 machine were used to perform radiographic imaging of different phantoms that include the leeds, head, pelvis and CAT phantoms. The MEVION-system provides a double scattering 250-MeV proton beam shaped with two nozzles (14,25cm diameters) and various beam ranges (5-32cm) and range modulation (2-20cm). The different objects in the leeds phantom were used to quantify image quality. Imaging quality dependence on dose was quantified using different dose levels (0.1-10MU). The leeds phantom was places upstream outside the Bragg-peak range while the imager either of films or CR-plates detector were placed downstream to measure the exiting protons.
Results: Image quality of the proton radiographic images was affected by multiple factors that include: (a) depth in phantom, (b) dose or monitor-unit (MU) from the proton imaging beam, (c) separation between the phantom and imager, (d) beam modulation and (e) beam range. Image quality of the leeds phantom improved with depth in phantom as the phantom location approached the Bragg-peak where the best positon and contrast resolutions were obtained. As dose increased, image quality improved with better signal to noise ratio particularly at the Bragg-peak. The increased separation between the leeds phantom and imaging plate led to increased scatter or bending of the proton beam which degraded quality of the proton radiographic images. Short beam ranges and wider modulations improved image quality as the phantom became closer to or within the spread-out Bragg-peak, respectively.
Conclusion: This study investigates quantitatively the dependence of image quality on different parameters including phantom depth, range and modulation. Radiographic proton images are feasible for clinical applications and have comparable image quality to kV-diagnostic photon images.
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