Space radiation risks for astronauts on multiple International Space Station missions

Area of Science:

• Space Medicine
• Radiation Oncology
• Astrobiology

Background:

• Space radiation exposure poses significant mortality and morbidity risks for astronauts.
• NASA's acceptable risk limit for cancer fatality is 3%, using upper 95% confidence levels (CL) for risk assessment.
• Evaluating the probability of causation (PC) between past radiation exposure and cancer diagnosis is crucial.

Purpose of the Study:

• To predict age- and sex-specific cancer risks and life-loss for astronauts on ISS missions.
• To estimate the probability of causation (PC) for cancer diagnoses post-mission.
• To assess radiation risks under different solar cycle conditions and mission durations.

Main Methods:

• Utilized risk projection models with uncertainty estimates for ISS mission scenarios.
• Calculated cancer risks, expected years of life-loss, and probability of causation (PC).
• Modeled risks considering high and low linear energy transfer (LET) radiation, increased tumor lethality, and circulatory diseases.

Main Results:

• Risk projections are within NASA standards for missions ≤1 year.
• Exceedances of the 3% risk of exposure-induced death (REID) upper 95% CL occur by 18-24 months during solar minimum.
• Median PC and upper 95% CIs exceed 50% for several cancers in longer missions or near solar minimum.

Conclusions:

• Current mission lengths are acceptable for most astronauts, but risks increase significantly for longer durations, especially during solar minimum.
• Increased tumor lethality and circulatory disease risks could further limit mission durations.
• Further research is needed to accurately evaluate risks from high LET radiation and other factors.