Neutron RBE for induction of tumors with high lethality in Sprague-Dawley rats

The effectiveness of fission neutrons is compared to that of gamma rays and X rays with regard to the induction of malignancies in male Sprague-Dawley rats. The analysis is based on autopsy results, It is focused on tumors th at tend to be present in animals dying early, which is indicative of a high degree of lethality. The relative biological effectiveness (RBE) is deduce d from a comparison of the cumulative hazard functions. Different nonparame tric models-the constant relative risk model, a time shift model, and an ac celeration model-are employed in the comparison, and the resulting values o f RBE are seen to be substantially independent of the choice of model. The results are in good agreement with earlier studies of nonlethal lung tumors in the same series of experiments. At neutron doses of 20 to 60 mGy, the R BE of fission neutrons is about 50. (C) 2000 by Radiation Research Society.