Comparison of 60-MeV Protons and 300-kVp X-Rays for Induction of Lens Opacities in RF Mice

In a study of the relative biological effectiveness (RBE) of protons for late somatic effects in mammals, 8-week-old RF female mice either received whole-body 60-MeV proton or 300-kVp x-radiation in single graded doses up to 400 rads or were sham exposed. In a smaller preceding study of cataract induced by lower energy protons (35 and 55 MeV), mice were exposed to high intensity beams of up to 2000 rads of protons or x-rays directed largely to the eye or head region. Animals in both groups were examined with the slit lamp for lens changes at appropriate intervals up to one year or more after treatment. Results show that the RBE of 35-60-MeV protons is one for induction of lens opacities; that is, low-LET (linear-energy-transfer-) particulate and low-LET electromagnetic radiations have the same cataractogenic effectiveness.