Dose estimation for astronauts using adult mesh-type reference computational phantoms

Astronaut radiation exposure in low Earth orbit is strongly affected by orbital radiation environment, shielding condition, and radiation quality. In this study, a Geant4-based Monte Carlo model coupled with the adult male mesh-type reference computational phantom of the International Commission on Radiological Protection (ICRP) was developed to estimate organ doses for astronauts in the Chinese Space Station (CSS) orbit. Proton and electron spectra from the Earth's radiation belts (ERB) were calculated using AP9/AE9, and solar-minimum galactic cosmic ray (GCR) spectra were generated using CREME96. Organ absorbed dose, $Q(L)$-based organ dose equivalent and effective dose equivalent were calculated for two representative exposure scenarios: extravehicular activity (EVA) with spacesuit-equivalent shielding and intravehicular activity (IVA) with spacecraft shielding. The calculated effective dose equivalent rates in the CSS orbit were 1006 μSv d-1 during EVA and 571 μSv d-1 during IVA. ERB protons were the dominant contributor to organ absorbed dose and effective dose equivalent under both shielding conditions. ERB electrons contributed mainly to superficial tissues during EVA and were almost completely attenuated under IVA conditions. After spacecraft shielding, GCRs became more important for dose-equivalent-based quantities because of their high penetration capability and high-LET components. The calculation method was evaluated by additional ISS-orbit simulations and comparison with MATROSHKA measurements and previous PHITS calculations. Good agreement was obtained for IVA exposure, whereas larger deviations during EVA were mainly associated with simplified local shielding geometry and the sensitivity of superficial tissue doses to low-energy ERB particles. The comparison between CSS and ISS orbits showed that astronaut dose levels cannot be inferred from orbital altitude alone, because different orbital inclinations lead to different ERB and GCR spectra. The present results provide organ-specific dose data for astronauts in the CSS orbit and support radiation protection assessment for future long-duration missions.