Radiobiological Risk Estimates for Space Flight Based on Long-Term Studies in Proton-Irradiated Primates

Between 1963 and 1969, 301 young rhesus monkeys were exposed to low and intermediate doses of X-rays, protons or electrons to simulate space radiation hazards; 57 control animals were incorporated in the experimental design, and both sexes were represented. The subjects have been followed for nearly 30 years, and major findings of the study include: 1) highly significant incidence of glioblastoma multiforme (high-grade astrocytoma) in male animals exposed to 55-MeV protons; 2) highly significant incidence of severe endometriosis in female subjects exposed to different radiation energies and doses; 3) development of significant late lenticular opacifications (cataracts) in monkeys 20+ years following exposures to low and intermediate doses of protons. As the animals age, abundant data are expected to provide additional insights into the late stochastic (probabilistic) and deterministic effects induced in primates by exposures to low and intermediate doses of particulate radiations. Refined space radiobiological risk estimates, based on a long-lived primate model closely resembling the human in many of its responses to ionizing radiations, will enable scientists and engineers to design spacecraft and associated hardware to maximize the short- and long-term safety of personnel participating in lengthy space missions.