Biological Effects of High-Energy Neutrons Measured In Vivo Using aVertebrate Model

摘要

Interaction of solar protons and galactic cosmic radiation withthe atmosphere and other materials produces high-energysecondary neutrons from below 1 to 1000 MeV and higher.Although secondary neutrons may provide an appreciablecomponent of the radiation dose equivalent received by spaceand high-altitude air travelers, the biological effects remainpoorly defined, particularly in vivo in intact organisms. Here wedescribe the acute response of Japanese medaka (Oryziaslatipes) embryos to a beam of high-energy spallation neutronsthat mimics the energy spectrum of secondary neutronsencountered aboard spacecraft and high-altitude aircraft. Todetermine RBE, embryos were exposed to 0-0.5 Gy of high-energy neutron radiation or 0-15 Gy of reference y radiation.The radiation response was measured by imaging apoptotic cellsin situ in defined volumes of the embryo, an assay that provides aquantifiable, linear dose response. The slope of the dose responsein the developing head, relative to reference y radiation,indicates an RBE of 24.9 (95% CI 13.6-40.7). A higher RBEof 48.1 (95% CI 30.0-66.4) was obtained based on overallsurvival. A separate analysis of apoptosis in muscle showed anoverall nonlinear response, with the greatest effects at doses ofless than 0.3 Gy. Results of this experiment indicate thatmedaka are a useful model for investigating biological damageassociated with high-energy neutron exposure.