Tumorigenic action of beta, proton, electron and alpha radiation in rat skin. Progress report, August 1, 1975--July 31, 1976

The carcinogenic effect of ionizing radiation on rat skin was studied in an attempt to learn more about radiation carcinogenesis, especially how various parameters of the irradiation, such as dose distribution within the tissue and dose rate, affect the yield of tumors. It was found that when the dose was localized to a small region of skin, the tumor yield was reduced and the magnitude of the reduction indicated that the region of reduced response might extend about 150 μ into the irradiated zone. The proliferative state of the hair follicles at the time of irradiation had relatively little effect on tumor induction although old animals are less susceptible than young or newborn animals. The penetration requirement of at least 0.3 mm for producing tumors suggests that the hair follicle germ cells could be the oncogenic targets. The recovery rate for tumor induction measured by split-dose exposure protocols was 4 hours for electrons. Proton radiation exhibited nearly complete recovery at 24 hours PI. UVL promotion of electron induced tumors did not significantly alter tumor yields. Radioresistance to tumor induction appears to increase with age