Cataract production in mice by heavy charged argon, neon, and carbon particles

The cataractogenic potential in mice of heavy charged particles from the Bevalac was examined in relation to dose, linear energy transfer (LET), and time following exposure. BALB/c X C57/b1(6) (CB6F1) mice were exposed to graded single doses (0.05-0.9 Gy) of 570-MeV 40Ar, 425-MeV 20Ne, or 400-MeV 12C particles in the plateau portion of the Bragg curve. Lenses were examined by slit lamp biomicroscopy over a 21-month period. The cataract severity was scored subjectively on a scale of 0 to 4 and compared to the opacities induced by 225-kVp X rays. Both the onset and density of the lens opacities were related to dose, and opacification progressed throughout the entire period of observation. In terms of degree of opacification and rates of onset and progression, the cataractogenic response to 40Ar particles was greater than to either 20Ne or 12C particles. Discrimination between the effects of 20Ne and 12C was possible only at the higher doses employed (0.6 and 0.9 Gy) and only at some observation times. Based on average cataract density at the several observation times, the relative biological effectiveness (RBE) of 40Ar particles is estimated to be 3 to 5 over a cataract score range of about 1.5-3.0 (0.15-0.9 Gy). The RBE for 20Ne and 12C particles is probably somewhat greater than 1.0. The consistency of replicate lens examinations and challenges of the subjective scoring system are discussed.