Accelerated heavy particles and the lens II. Cytopathological changes.

To assess more fully the risk to normal tissue exposed to accelerated heavy particles in the space program and during radiotherapy on earth, the cytopathological effects of a variety of doses of accelerated (570 MeV/amu) Argon (40Ar) ions on the rat lens were investigated. Time-course analyses of lenses exposed to a 1 Gy (100 rad)-dose revealed that the effects of the particles on mitotic index, nuclear fragmentation, and meridional row (MR) cytoarchitecture were qualitatively similar to those caused by 185 kVp x-rays. The effects of dose on the lens epithelium was also examined at 67 wk post-irradiation. The mitotic index returned to normal levels by that time; however, the biological effectiveness (RBE) of 40Ar relative to x-rays, in causing MR disorganization, increased with decreasing dose and closely resembled the RBE for cataractogenesis. The RBE data are consonant with the view that radiation cataracts are the result of damage to the lens epithelial population, which is later expressed as aberrant differentiation during fibergenesis.