Updates to astronaut radiation limits: radiation risks for never-smokers

Area of Science:

• Radiation epidemiology
• Space medicine
• Risk assessment

Background:

• Recent epidemiological assessments of atomic bomb survivors (Life Span Study - LSS) provide updated radiation risk data.
• Current National Aeronautics and Space Administration (NASA) astronaut dose limits are based on older National Council on Radiation Protection and Measurements (NCRP) reports (2000).
• Older models utilized mortality risk transfer, while newer analyses focus on incidence-based risk transfer.

Purpose of the Study:

• To compare recent LSS epidemiological findings with earlier NCRP risk projections.
• To evaluate the impact of using incidence-based risk transfer and a healthy worker (never-smoker) population on astronaut dose limits.
• To recommend updated age- and gender-specific dose limits for astronauts.

Main Methods:

• Tissue-specific, incidence-based risk transfer from LSS data to a U.S. population.
• Adjustment of cancer rates to exclude smoking effects for a never-smoker reference population.
• Application of a mixture model (equal weights for additive and multiplicative transfer) to estimate radiation risks.

Main Results:

• Incidence-based risk transfer leads to higher projected risk and reduced dose limits for older astronauts (>40 years) compared to mortality-based models.
• Radiation risks for lung and total cancer are estimated to be 20% lower for males and 30% lower for females among never-smokers compared to the general U.S. population.
• The analysis highlights significant uncertainties in risk projections that could be reduced by improving transfer models.

Conclusions:

• Updated epidemiological data and incidence-based risk transfer necessitate revised astronaut dose limits.
• Considering a healthy never-smoker population reduces estimated radiation risks compared to the average U.S. population.
• Refined risk transfer models, incorporating cancer initiation and promotion, are crucial for reducing uncertainties in radiation exposure risk assessment for astronauts.