Changes in the mouse lens caused by 600 MeV/amu accelerated iron ions

The lenses of mice were evaluated by slit-lamp biomicroscopy and cytopathological analysis following doses of 600 MeV/amμ iron ions ranging from 0.05 to 1.6 Gy. The examinations were conducted at 5, 10 and 16 months post-irrdiation. Cataracts were present in all irradiated animals although the severities were dose- and time-dependent. The degree of opacification observed in the .05 Gy dose group indicated that the threshold dose for cataractogenesis must be significantly lower. Furthermore, when compared to results from previous low-LET radiation studies in the mouse lens a relatively high RBE is suggested for iron ions. In addition to the overt loss of transparency, histopathological analyses revealed a strong dose dependence for a number of endpoints. These included micronucleation, interphase death, and meridional row disorganization. Previous studies have shown that X-ray cataracts and meridional row disorganization correlate quantitatively. Taken together, the microscopic changes support the view that the mechanism of heavy ion induced cataractogenesis is the same as that for cataracts caused by low-LET radiation. The damage incurred in the lens by heavy particles while quantitatively dissimilar is qualitatively indistinguishable from that caused by X-rays