Abstract
Dose-rate-effects on chromosome aberrations at low dose rate region has no been evaluated. Incidences of chromosome aberrations were analyzed in splenic lymphocytes from female SPF C3H mice continuously irradiated with low- or medium-dose-rate (LDR, MDR) of Cs 134 gamma-rays from 56 days of age to evaluate the dose-rate effects. Dose response relationship of dicentrics chromosome aberration frequencies was obtained at each dose rate (400 mGy/22h/day, 200 mGy/22h/day, 20 mGy/22h/day and 1 mGy/22h/day) using age-adjusted multiple liner regression analysis and a test for difference between radiation group and non-irradiated group on the assumption that the relationship is shown by a linear or a linear quadratic model. Values of the linear term, which are shown as slope, were decreased with reduction of dose rates from 400 mGy/day(18.2 mGy/h) to 1 mGy/day(0.045 mGy/h), indicating positive dose-rate-effects. Incidences of dicentric chromosomes at LDR (20 mGy/day) were compared with those in HDR(890 mGy/min) irradiation at each total dose to obtain dose and dose-rate effectiveness factor (DDREF). Incidence of translocation detected by M-FISH method in irradiated mice at 20 mGy/day was also used for obtaining DDREF. Dose and dose-rate effectiveness factor (DDREF) were obtained to be 4.5 for dicentrics and 2.3 for translocations using chromosome aberration rate. These results will be a useful for risk estimation of LDR radiation exposure. This study was performed under contract with the Aomori Prefectural Government, Japan.
