Dose-response relationship for induction of ovarian tumors in mice irradiated during prenatal, early postnatal and elder periods.

Female B6C3F1 mice were irradiated at day 17 prenatal period, day 0, 7, 35, 105, 240, 365 and 550 postnatal period with doses of 0.10 to 5.70 Gy gamma rays from (137)Cs. All mice were allowed to live through their entire life spans under a specific-pathogen free condition. The excess relative risk for prevalence at the time of death of ovarian tumors was used as a comprehensive measure of radiation effect. The excess relative risks at 1 Gy were estimated for all irradiated groups based on the dose-response relationships and compared to each other. A marked increase in susceptibility was found during the age between day 17 prenatal and day 0 postnatal period. A drastic decrease in susceptibility was observed during the period between day 105 and day 240. The shape of the dose-response curve was downward concave in mice irradiated at day 0, 7, 35 or 105 postnatal period, whereas, the downward curvature of dose-response was not observed in mice irradiated at day 17 prenatal period, day 240, 365 or 550 postnatal period. It has become obvious that mice of the early postnatal, pre-puberty and young adult periods are highly susceptible to induction of ovarian tumors by gamma rays.