NON-RADIOACTIVE ELEMENTS FOR PROMPT GAMMA ENHANCEMENT IN PROTON THERAPY

Intensity modulated proton beam scanning therapy allows for highly conformal dose distribution and better sparing of organ-at-risk compared to conventional photon radiotherapy, thanks to the characteristic dose deposition at depth, the Bragg Peak (BP), of protons as a function of depth and energy. However, proton range uncertainties lead to extended clinical margins, at the expense of treatment quality. Prompt Gamma (PG) rays emitted during non- elastic interactions of proton with the matter have been proposed for in-vivo proton range tracking. Nevertheless, poor PG statistics downgrade the potential of the clinical implementation of the proposed techniques. We study the insertion of the nonradioactive elements 19F, 17O, 127I in a tumor area to enhance the PG production of 4.44 MeV (P1) and 6.15 MeV (P2) PG rays emitted during proton irradiation, both correlated with the distal fall-off of the BP. We developed a novel Monte Carlo (MC) model using the TOPAS MC package. With this model, we simulated incident proton beams with energies of 75 MeV, 100 MeV and 200 MeV in co-centric cylindrical phantoms. The outer cylinder (scorer) was filled with water and the inner cylinder (simulating a tumor region inside water-equivalent body) was filled with water containing 0.1%–20% weight fractions of each of the tested elements.