Dosimetric comparability validation of small animal photon and neutron irradiations

Abstract Crew members on missions beyond low-earth orbit receive considerable radiation doses, but the effects and relative biological effectiveness of many relevant types of irradiation, including neutrons with energies of hundreds of MeV, largely remain under-investigated. Such small animal irradiations can only be compared to respective photon irradiations if comparable doses can simultaneously be delivered to a variety of organs during both irradiations, despite the different underlying dose deposition patterns. To evaluate the dosimetric comparability of upcoming small animal neutron and photon irradiations, experimental depth-dose measurements were performed at the TRIUMF neutron facility and the British Columbia Cancer Research Centre, using a neutron beam with energies of up to 450 MeV and a Cs-137 irradiator. The MOBY digital mouse phantom was used to perform Monte Carlo simulations of neutron and photon animal irradiations. Evaluated metrics included the ratio between the dose delivered to a variety of different organs (including lungs, brain, and heart) during neutron and photon irradiation. A sensitivity analysis including a variety of animal parameters (tissue elemental compositions and mass densities, animal size, and animal orientation) was performed, and the statistical significance ( p < 0.05) of the dosimetric impact of uncertainties in simulation parameters was analyzed. During nominal simulations, differences in organ doses during neutron and photon irradiation were