Room: Exhibit Hall | Forum 6
Purpose: A prototype for an on-board imager using high-energy MeV proton beam was developed and tested. The proton radiograph dependence on the different parameters of the therapeutic proton beam such as dose, depth, modulation and range was evaluated using Gafchromic-films and computed-radiography.
Methods: Radiographic images were acquired using energetic 250MeV proton beams from the MEVION-S250 machine. The proton beam was utilized to irradiate different phantoms that include the Leeds, head, pelvis and CAT-phantoms. The testing objects in Leeds phantom were used to evaluate image quality of the proton radiographs similar to photon imaging quality evaluation. Different beam parameters were investigated that include: (a) depth in phantom (0-15cm), (b) dose or monitor units (0.1-10MU) from the proton imaging beam, (c) separation between the phantom and imager (1-11cm), (d) beam modulation (0-15cm) and (e) beam range (5-32cm).
Results: The image quality of proton radiographs improved with depth in phantom because of increased proton dose deposition with depth. The best image quality was obtained at the Bragg peak where most proton dose was deposited. It also improved with increasing proton imaging dose which provided better signal-to-noise ratio. The separation between the imaging detector and Leeds phantom degraded image quality of the proton radiographs which was due to increased beam scatter through the medium before reaching the detector. Proton beams with the least modulation provided best image quality. The increased beam range improved image quality. The dose deposited by proton beams before the Bragg peak was smaller than doses deposited by diagnostic kV-photons.
Conclusion: This study proved feasibility of on-board radiographic imaging with high-energy MeV-proton beam. Proton radiographs had higher contrast for soft tissues in comparison with photon radiographs which showed usually enhanced bone anatomy. On-board proton imaging has potential clinical application for patient setup and tumor localization using proton image-guided radiation therapy.