Effects of Heavy Ions on Rabbit Tissues: Cataractogenesis

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Abstract
As part of an investigation of the responses of optic and proximate tissues to heavy-ion irradiation, the lenses of New Zealand white rabbits were exposed to the Bragg plateau regions of 530 MeV/amu Ar ions and 365 MeV/amu Ne ions and also to 60Co γ-photons. The linear energy transfers (LET∞s) for the radiations were 90 ± 5, 35 ± 3, and 0·3 keV/μm, respectively. After irradiation, lenticular opacities were monitored through their incipient and/or clinical stages (≤5 years) by slit-lamp biomicroscopy and scored with subjective, but well-defined, indices. Cataractogenesis, which progressed according to the model proposed by Rubin and Casarett (1968), was modified by radiation quality in the following ways. (1) The rate of development of the early (acute) stage increased with the LET∞ of the incident radiation; (2) at the intermediate (plateau) stage, the values for the relative biological effectiveness (r.b.e.) of the heavy ions were similar to those reported for proliferating cells in culture; (3) for a given intermediate level, the onset of late cataractogenesis occurred earlier the higher the LET∞ of the radiation involved. As with alopecia, the r.b.e.s for cataractogenesis varied with post-irradiation time.

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