Host: The Japan Radiation Research Society
Co-host: City of Kitakyushu, University of Occupational and Environmental Health, Japan
Chromosomal translocation induced by acute high-dose-rate irradiation persists for a long time in human and murine lymphocytes or bone marrow cells in a dose-dependent manner, yet, chronological changes of translocation rate after the continuous low-dose-rate radiation exposure remain to be elucidated. SPF C3H/HeN female mice were continuously exposed to gamma-rays at a low-dose-rate of 20 mGy/22 hr/day from the age of 8 weeks for a maximum of about 400 days, to achieve accumulated doses of 500, 1000, 2000, 4000, 6000, and 8000 mGy. Splenocytes from irradiated and age-matched, non-irradiated mice were cultured for 48 hr in the presence of LPS, Con A, and 2-ME to obtain metaphase spreads, and translocation rates were analyzed precisely using multiplex-fluorescence in situ hybridization (M-FISH) method. They were increased linearly in irradiated mice up to 8000 mGy, depending on accumulated doses. Clones having the same translocations detectable in at least three different cells, were appeared at the dose of 4000 mGy, and rapidly increased over 6000 mGy. The dose and dose-rate effectiveness factor (DDREF) at the same dose of 500 mGy, as compared to high-dose-rate (890 mGy/min) gamma-irradiation was 2.6-4.1, depending on types of chromosome aberrations. These results are important for radiation risk assessment of cancers induced by low-dose-rate radiation exposure. This study was performed under contact with Aomori Prefecture Government, Japan.
