Survival and diseases in C57 BL mice exposed to X rays or 3.1 MeV neutrons at an age of 7 or 21 days

Survival and causes of mortality were studied in 7 or 21 day old male C57BL/Cnb mice exposed to 0.5, 1 or 3 Gy of 250 kVp X rays or 0.125, 0.25, 0.5 or 1 Gy of accelerator neutrons (modal energy 3.1 MeV). A total 1287 animals were used in the experiments. Survival of irradiated animals were used in the experiments. Survival of irradiated animals is reduced significantly only in the highest dose groups (1 Gy neutrons, 3 Gy X rays). All malignant tumors increase significantly from (and including) doses of 0.5 Gy neutrons and 1 Gy X rays. Hepatocellular carcinoma is the principal contributor to the increase in tumor incidence, at least after neutron exposure. No significant increase in hepatocellular carcinoma is seen for 21 old mice exposed to X rays. An increase, especially after 3 Gy of X rays is also observed for all leukemias. Based on percentage life shortening, it appears that exposure during infancy does not shorten total survival from cancer much more than that of adults although such exposure, especially that to neutrons, causes more hepatocellular carcinoma. Due to the non-linearity of the dose-effect relationships, it is difficult to calculate the RBE of neutrons. For survival time at higher doses an RBE of about 3 is obtained. When the incidence of all malignant tumors and of hepatocellular cancer is fitted to a linear-quadratic function an approximate RBE from 5 to 8 is obtained. (authors)