9 March 2018 Proton radiography for relativistic proton beam therapy
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Abstract
Proton beam radiation therapy is at the forefront of modern techniques for cancer treatment, due to its high level of radiation-dose deposition accuracy. This treatment accuracy, however, is limited by the ability to position the treatment beam within the patient's anatomy. Typically, the patient's position is registered orthogonally, using X-ray imaging. However, if instead, beam's-eye-view imaging were enabled by proton radiography, dose deposition measurements could be improved with intrinsically-registered patient positioning. At a typical treatment facility, with a maximum proton energy on the order of 250 MeV, imaging capabilities are limited by the high degree of multiple-Coulomb scatter protons accumulate before exiting the patient. However, in increasing the proton energy from 250 MeV to 800 MeV, the accumulated scatter is reduced by a factor of five, and, coupled with a magnetic-lens, collimated imaging system, enables high-resolution, high-contrast imaging. Further, based on results from Geant4, the dose profile of this higher energy beam is tightly constrained, a fact which may be exploited in the future to further increase treatment accuracy. The full-width half-max of the dose-deposition kernels at 33.4 cm depth (the 250-MeV Bragg peak) are 1.56 cm for 250-MeV protons, compared with 0.52 cm for 800-MeV protons. At 1-cm downstream of this point, the 250-MeV kernel has dropped off to 32%, while the 800-MeV dose is still at 95%. An 800-MeV proton treatment plan exploiting the constrained lateral profile would utilize techniques developed for photon therapy, to deliver the dose from 360° and tightly constrain the dose, stereotactically.
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Matthew S. Freeman, Matthew S. Freeman, Michelle A. Espy, Michelle A. Espy, Per E. Magnelind, Per E. Magnelind, Fesseha G. Mariam, Fesseha G. Mariam, Frank E. Merrill, Frank E. Merrill, Dale Tupa, Dale Tupa, Carl H. Wilde, Carl H. Wilde, } "Proton radiography for relativistic proton beam therapy", Proc. SPIE 10573, Medical Imaging 2018: Physics of Medical Imaging, 105732H (9 March 2018); doi: 10.1117/12.2293928; https://doi.org/10.1117/12.2293928
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