Incorporation of dose-rate effects into the BIANCA biophysical model and application for space radiation risk assessment

Exposure to space radiation represents a critical issue for astronauts’ health, since it can lead to different types of effects including cancer, cataract, skin damage, damage to blood forming organs, cardiovascular diseases, CNS damage etc. Space radiation exposure is characterized by relatively low dose rates over long periods due to Galactic Cosmic Rays, plus short, higher-dose exposures in case of intense Solar Particle Events (SPE). In this framework the BIANCA biophysical model, which until now has been applied to predict cell death and chromosomal aberrations following acute exposure, was extended by integrating the Lea-Catcheside approach, which takes into account the effects of dose fractionation and dose rate; the good agreement between model predictions and proton cell survival data on fractionated irradiation (either obtained in this work, or taken from the literature) allowed validating the model for the considered scenarios. Afterwards, exploiting an interface with the FLUKA radiation transport code, BIANCA was applied to analyze the impact of dose rate for the August 1972 SPE, by calculating RBE-weighted organ doses in a human voxel phantom under different shielding conditions and for different irradiation durations. The results showed differences up to 50 % in the RBE-weighted dose between acute and protracted irradiation; such difference tends to decrease with increasing shielding. Following this work, BIANCA can now predict RBE values for cell survival taking into account not only the RBE dependence on particle type, energy and dose, but also the dependence on dose-rate. This allowed improving the accuracy in the prediction of astronauts’ Gy-equivalent doses in case of a SPE exposure.