A Study of Lens Opacification for a Mars Mission

Risk assessment in an environment of mixed radiation quality has been addressed in the past by use of the experimental parameter “relative biological effectiveness” (RBE) or the related “quality factor” (Q), which is defined for purposes of radiation protection. Herein, an alternative method, which is based on risk-related cross sections, is used to estimate risks of “stationary” cataracts caused by radiation exposures during extended missions in deep space. Estimates of the even more important risk of late degenerative cataractogenesis are made on the basis of the limited data available. Data on lenticular opacification in the New Zealand white rabbit, an animal model from which such results can be extrapolated to humans, are analyzed by the Langley cosmic ray shielding code (HZETRN) to generate estimates of stationary cataract formation resulting from a Mars mission. The effects of the composition of shielding material and the relationship between risk and linear energy transfer (LET) are given, and the effects of target fragmentation on the risk coefficients are evaluated explicitly. The needs for further experimental lens opacification studies are discussed.