Life-shortening and disease incidence in mice after exposure to gamma rays or high-energy neutrons.
Male C57Bl/Cnb and BALB/c mice were exposed to single and fractionated d(50) + Be neutrons or 137Cs gamma rays at 12 weeks of age and were followed for life-shortening and disease incidence as ascertained by autopsy and histological examinations at the time of spontaneous death. Fractionation schedules used were 10 exposures at 24-h intervals and 8 exposures at 3-h intervals for gamma rays, and 8 exposures at 3-h intervals for neutrons. The data were analyzed by the Kaplan-Meier procedure using as criteria causes of death and possible causes of death. Individual groups were compared by a modified Wilcoxon test according to Hoel and Walburg (J. Natl. Cancer Inst. 49, 361-372 (1972)). No significant difference was found in C57Bl/Cnb and BALB/c male mice between a single gamma-ray exposure and a single neutron exposure. Gamma-ray fractionation was clearly less effective in reducing survival time than a single exposure. In contrast, fractionation of neutrons was slightly, although not significantly, more effective in reducing survival time than a single exposure. The relative biological effectiveness (RBE) for life-shortening for d(50)-Be neutrons compared to gamma rays is of the order of 1 to 2 for a single exposure to neutrons and between 2 and 3 for fractionated neutrons compared to a single exposure to gamma rays. Neutron irradiation caused somewhat more cancer than gamma irradiation, and the RBE for cancer induction may be higher, probably between 2 and 3 in the range of 1 to 3 Gy, although the present data do not allow a more precise assessment.
Université Catholique de Louvain, Brussels, Belgium.
J R
JR
Maisin
A
A
Wambersie
G B
GB
Gerber
G
G
Mattelin
M
M
Lambiet-Collier
B
B
De Coster
J
J
Gueulette
D000818:Animals; D002588:Cesium Radioisotopes; D005720:Gamma Rays; D008017:Life Expectancy; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009017:Morbidity; D009502:Neutrons; D011833:Radiation Injuries, Experimental / Q000503:physiopathology*
D002588:Cesium Radioisotopes