Survival and diseases in C57BL 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 of 1287 animals were used in the experiments. Survival of irradiated animals was reduced significantly only in the mice receiving the highest doses (1 Gy neutrons, 3 Gy X rays ). Mice exposed to the lowest doses (0.125 Gy neutrons, 0.5 Gy X rays) lived significantly longer than controls, apparently reflecting a reduction in non-neoplastic lung and liver diseases. All malignant tumors increased significantly from (and including) doses of 0.5 Gy neutrons and 1 Gy X rays. Hepatocellular carcinoma was the principal contributor to the increase in tumor incidence, at least after exposure to neutrons. No significant increase in hepatocellular carcinoma was seen in 21-day-old mice exposed to X rays. An increase, especially after 3 Gy X rays, was also observed for all leukemias. Controls in the present study lived significantly longer than those in our earlier studies of irradiated adult mice, making a direct comparison of the radiation-induced effects in adult and infant mice difficult. Based on percentage life shortening, it appears that exposure during infancy does not shorten total survival or survival from cancer much more than exposure of adults, although such exposure, especially to neutrons, causes more hepatocellular carcinoma. Due to the nonlinearity 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 or a linear-quadratic function, an RBE from 5 to 8 is obtained. No RBE can be estimated for hepatocellular carcinoma in mice of an age of 21 days because exposure to X rays does not seem to cause this tumor at that age

Effect of X rays alone or combined with diethylnitrosamine on tumor induction in infant mouse liver.

The possible combined effects of the initiator diethylnitrosamine (DEN) with X rays on cancer induction in C57BL/Cnb mouse liver were evaluated. Four groups of infant mice were treated as follows: with DEN alone, with X rays alone, with DEN + X rays, and with X rays + DEN. Mice in each group were killed at 10-week intervals over 70 weeks. The following parameters were measured: body weight, liver weight, number and size of macroscopic liver lesions, and number and total surface of the different types of microscopic liver lesions. The number of induced liver foci and carcinomas was found to depend essentially on the dose of DEN. X irradiation did not produce any combined effect on the induction of foci and carcinomas when given 7 days before or after DEN administration

Effect of neutrons alone or combined with diethylnitrosamine on tumor induction in the livers of infant C57BL mice.

The possible combined effects of the initiator diethylnitrosamine (DEN)+neutrons on the induction of foci, adenomas and carcinomas in the livers of C57BL/Cnb mice were evaluated. Four groups of infant mice were treated as follows: DEN alone, neutrons alone, DEN followed by neutrons and neutrons followed by DEN. Ten mice in each group were killed at 10-week intervals over 70 weeks. The following parameters were measured: body weight, liver weight, number and size of superficial macroscopic liver lesions, and number and total surface area of the different types of microscopic liver lesions. The rate of appearance of foci increased significantly at different times when a dose of 0.125 Gy of neutrons was administered 7 days before or after a dose of 1.25 micrograms of DEN. No significant differences were observed in the total surface area of foci and/or adenomas and carcinomas when increasing doses of neutrons were given 7 days before or after the administration of 1.25 and 2.5 micrograms of DEN