ACCELERATED HEAVY-IONS AND THE LENS .9. LATE EFFECTS OF LET AND DOSE ON CELLULAR-PARAMETERS IN THE MURINE LENS

Lenses of mice irradiated with 250 MeV protons, 670 MeV/amu Ne-20, 600 MeV/amu Fe-56, 350 MeV/amu Fe-56, 600 MeV/amu Nb-93 or 593 MeV/amu La -139 ions were evaluated by analysing cytopathological indicators whic h have been implicated in the cataractogenic process. The LETs ranged from 0.39 to 953 keV/mum and the fluences from 1.31 x 10(3)/mm2 to 5.1 2 x 10(7)/mm2. The lenses were assessed 64 weeks post-irradiation in o rder to observe the late effects of LET and dose on the target cell po pulation of the lens' epithelium. Our studies showed that growth-depen dent pathological changes occurred at the cellular level as a function of dose and LET. For a given particle dose, as the LET rose, the numb er of abnormal mitotic figures, micronuclei frequency, and the disorga nization of meridional rows increased to a maximum and then reached a plateau or decreased. For particles of the same LET, the severity of m eridional rows disorganization and micronuclei frequency increased wit h increasing dose. The numbers of cells surviving at late times post-i rradiation were comparable with those of controls. In addition, the ce llular density was similarly unaffected. These observations are consis tent with the current theory of the mechanism of radiation cataractoge nesis which posits that genomic damage to the epithelial cells survivi ng the exposure is responsible for opacification.