Low dose neutron late effects: Cataractogenesis. Final progress report, April 1, 1992--March 31, 1993

Abstract

The work is formulated to resolve the uncertainty regarding the relative biological effectiveness (RBE) of low dose neutron radiation. The study exploits the fact that cataractogenesis is sensitive to the inverse dose-rate effect as has been observed with heavy ions and was an endpoint considered in the follow-up of the A-bomb survivors. The neutron radiations were initiated at the Radiological Research Accelerator facility (RARAF) of the Nevis Laboratory of Columbia University. Four week old ({+-} 1 day) rats were divided into eight dose groups each receiving single or fractionated total doses of 0.2, 1.0, 5.0 and 25.0 cGy of monoenergetic 435 keV neutrons. Special restraining jigs insured that the eye, at the midpoint of the lens, received the appropriate energy and dose with a relative error of {+-} 5%. The fractionation regimen consisted of four exposures, each administered at three hour ({+-} 1 minute) intervals. The neutron irradiated groups were compared to rats irradiated with 250 kVp X-rays in doses ranging from 0.5 to 7 Gy. The animals were examined on a biweekly basis utilizing conventional slit-lamp biomicroscopy and the Scheimpflug Slit Lamp Imaging System (Zeiss). The follow-ups, which proceeded for over 2 years, are now complete. This proved essentialmore » inasmuch as given the extremely low doses which were utilized, clinically detectable opacities were not anticipated until a significant fraction of the life span has lapsed. The results have exceeded all expectations.« less