Measurement of out of field doses in brain proton therapy with GATE simulations

Proton therapy as one of the radiotherapy applications, aims to treat the tumor by using the accelerated proton particle. High radiation dose distributions delivered to the tumor tissue, is characterized with Bragg curves, while the radiation in the tissues surrounding the tumor is expected to be as low as possible. In our study, proton treatment of the tumor volume placed in the brain created by GATE software was simulated. The absorbed doses in other organs created by GATE software during treatment were determined using DoseActor and TLEDoseActor algorithms. Nuclear interactions of the accelerated proton with the nucleus of the target atom make the target atom reactive and cause secondary radiation. Similar to the TLEDoseActor algorithm, NTLE algorithm was used to determine the doses caused by neutrons from these secondary radiations. With the algorithms used, out-of-field doses and secondary doses for proton beams at 250 MeV energy were determined. It is important to determine the secondary radiations caused by the interaction of the proton with the tissue and to determine the doses out of the field. These results may be helpful in determining and preventing secondary cancer formation in proton therapy in clinical applications.