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Visibility of Radiographic Imaging with a Proton Beam From the MEVION-S250 Therapy System and Quantitative Evaluation of Image Quality and Dose

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G Wright

G Wright*, S Ahmad , O Algan , T Herman , I Ali , Oklahoma Univ. Health Science Ctr., Oklahoma City, OK


SU-I-GPD-J-81 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate quantitatively image quality and dose of proton radiographic images using a beam from the MEVION-S250 proton therapy machine.

Methods: A proton beams was used in radiographic imaging of different phantoms from the MEVION-S250 machine which has two nozzle sizes: 14 cm and 25 cm diameters and different beam ranges (5-32 cm) and range modulation (2-20cm). The high and low contrast resolution objects in the leeds phantom were used to quantify image quality. Imaging with the proton beams occurred outside the Bragg peak close to the proximal edge which was then compared with radiographic images of the leeds phantom imaged with kV photon beams from an on-board-imager mounted on a TrueBeam-linac. The radographic images from proton and photon imaging beams were detected with XR-QA2-Gafchromic films that have high sensitivity and dose range 0.1-20cGy.

Results: The different objects of the leeds phantom were visible on the XR-QA2 Gafchromic-film imaged with different proton beams. Image quality of these radiographs depended on the range and range modulations of the MeV proton beam. The signal-to-noise ratio decreased by 8% with increasing depth in the phantom (15cm) and the strips broadening in the position resolution objects increased with increasing depth. The imaging dose increased (60%) with increasing range (5-20cm) of the proton imaging beam. Smaller range modulation provided better image quality due to increased scattering and deflection of the protons with phantom depth. The imaging dose from the proton beam deposited in the leeds phantom was 30% less than the dose in the corresponding radiographs with kV-photon beams.

Conclusion: Radiographic imaging with the proton beam from the therapeutic MEVION-S250 system is visible. Image quality depends on the depth and range modulation used in the proton imaging beam. Radiographic imaging with proton beam may provide alternative technique for on-board image guidance with proton therapy.

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