Fetus dose calculation during proton therapy of pregnant phantoms using MCNPX and MCNP6.2 codes

Radiotherapy of pregnant cancer patients is not common, but when applied accurate assessment the fetus dose required, especially since treatment planning systems are able and do allow out-of-field doses. Proton therapy significantly reduces doses, such as to fetus, compared photon radiotherapy techniques could be promising for patients. Within this study Monte Carlo calculations performed on three different computational phantoms representing women, all in second trimester pregnancy. Simplified proton beam women brain was modelled, total equivalent (normalized per target dose) calculated. Between MCNPX MCNP6.2 code versions we observed up 6% difference. In work 3 groups participated variation between 8% 12% MCNP6.2, respectively. Depending phantom used fetal 0.4 0.8 {\mu}Sv/Gy. Major contribution came from neutrons, with only 20% coming photons, while other particles have negligible contributions. Results differ by factor two, were used, due geometrical anatomical characteristics mother position.