Advancing space radiation risk assessment for deep space missions

To assess the risks posed by space radiation, the dose equivalent, defined as the integral of the measured absorbed dose and the radiation quality factor (Q), is currently employed. The Q is closely related to cancer risk estimation, as it reflects the relative biological effectiveness of radiation. These relationships have been investigated using several biological endpoints in anticipation of future space missions. The International Commission on Radiological Protection (ICRP) addressed radiation exposure in space using Q, as detailed in ICRP Publication 123. Currently, the Q-LET relationship established in ICRP Publication 60 for general dose assessment on the ground is applied in space dosimetry. However, a Q value that takes track structure into account has been developed to evaluate radiation risks associated with specific biological effects. For future deep space missions, a more practical Q value specifically adapted to the characteristics of space radiation may be required for accurate dose assessment. This special issue explores new frontiers in space radiation risk assessment by integrating recent advances in physical and biological research, including microdosimetry and studies of inter- and intra-cellular responses.