Neutron Carcinogenesis: Dose and Dose-Rate Effects in BALB/c Mice

The influence of dose and dose rate on the tumorigenicity of neutrons was investigated in female BALB/c mice exposed to various doses of neutrons at dose rates of 5 and 25 rad/min or 1 rad/day. The tumors that were most sensitive to induction after neutron exposures included malignant lung adenocarcinomas, mammary adenocarcinomas, and ovarian tumors. For these three tumor types, increased incidences were observed after as little as 5-10 rad of neutrons delivered at a high dose rate. However, after low-dose-rate neutron exposures, different dose-response relationships were observed. Neutron irradiation at low dose rates was less effective than at high dose rates in inducing ovarian tumors at all doses tested. For malignant lung tumors and mammary tumors, on the other hand, the data suggested that the low dose rate was less effective than the high dose rate at low total doses, but more effective at high total doses.