Monte-carlo simulations for proton-beam-induced prompt radiations in biological tissue

In this paper, we report on a feasibility study for proton-induced prompt radiations and for the potential application to proton therapy. A GEANT4 simulation program was used to perform a Monte-Carlo study to obtain energy spectra and vertex profiles for prompt photons and neutrons induced in human tissue during irradiation with therepeutic proton beams. The simulation results show that prompt photons with energies larger than 3 MeV tend to show a close spatial correlation with the Bragg curve of dose delivery. On the other hand, the contribution of photon emissions induced by various charged particles and neutrons is relatively large in the low-energy region of the prompt-photon spectra. The photons in the energy range lower than 3 MeV are broadly distributed over the tissue volume and show a relatively poor spatial correlation with the dose profile of the proton beam. The Monte-Carlo analysis for the prompt neutrons shows that the spatial correlation with the dose profile decreases as the proton-beam energy increases.