Dose-rate effects and dose and dose-rate effectiveness factor on frequencies of chromosome aberrations in splenic lymphocytes from mice continuously exposed to low-dose-rate gamma-radiation

Dose-rate effects on chromosome aberrations in the low-dose-rate range have not been evaluated previously. The incidences of chromosome aberrations were analysed in splenic lymphocytes from female specific pathogen-free (SPF) C3H mice that were continuously irradiated with low- or medium-dose-rate (LDR, MDR) 137Cs γ rays from 56 days of age to evaluate the dose-rate effects. The dose-response relationship for the frequency of dicentric chromosome aberration at each dose rate (400 mGy 22h day, 20 mGy 22h day and 1 mGy 22h day) was obtained using age-adjusted multiple linear regression analysis assuming that the relationship can be represented by a linear or linear quadratic model and a test for the difference between the irradiated group and the non-irradiated group. Values of the linear term, shown as the slope, decreased as the dose rate was reduced from 400 mGy 22h day (18.2 mGy h−1) to 1 mGy 22h day (0.045 mGy h−1), indicating a positive dose-rate effect in the dose-rate region. The incidences of dicentric chromosomes and translocation for LDR (20 mGy day−1) were compared with those for HDR (890 mGy min−1) irradiation at each total dose to obtain the dose and dose-rate effectiveness factor (DDREF). The DDREFs were 4.5 for dicentrics and 2.3 for translocations at a total dose of 100 mGy based on the chromosome aberration rate. These results will be useful for estimating the risk of LDR radiation exposure and radiation protection.