The Japan Radiation Research Society Annual Meeting Abstracts
The 51st Annual Meeting of The Japan Radiation Research Society
Session ID : S2-4
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Biological responses to low dose radiation
Effect of Continuous Exposure to Very Low Dose Rates of Gamma Rays on Life Span and Neoplasia in Mice
*Ignacia _III_B. TANAKASatoshi TANAKAYoichi OGHISOFumiaki SATO
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Abstract

Late effects of low-dose and low-dose-rates of ionizing radiation are potential hazards to radiation workers and to the general public, thereby becoming a serious concern in the recent years. Using a total of 4,000 mice, we studied the late biological effects of chronic exposure to low-dose-rate radiation on life span and neoplasia. Two thousand male and 2000 female 8-week-old specific pathogen free (SPF) B6C3F1 mice were randomly divided into 4 groups, one non-irradiated (control) and three irradiated. The irradiated groups were exposed to 137Cs gamma rays at dose-rates of 21, 1.1 and 0.05 mGy day-1 for approximately 400 days with total doses equivalent to 8000, 400 and 20 mGy, respectively. All mice were kept under SPF conditions until natural death and pathological examination was performed to determine the cause of death. Statistical analyses showed that life spans of both sexes of mice irradiated with 21 mGy day-1 (P < 0.0001) and of females irradiated with 1.1 mGy day-1 (P < 0.05) were significantly shorter than those of the control group. Our results show no evidence of lengthened life span in mice chronically exposed to very low-dose-rates of gamma rays. Neoplasms accounted for >86.7% of all deaths. Compared to non-irradiated controls, incidences of lethal neoplasms were significantly increased for myeloid leukaemia and hemangiosarcomas in males, soft tissue neoplasms and malignant granulosa cell tumors in females exposed to 21 mGy day-1. The number of multiple primary neoplasms per mouse was significantly increased in mice irradiated at 21 mGy day-1. Our results suggest that life shortening in mice continuously exposed to low- dose-rate gamma rays is due to early death from a variety of neoplasms and not from increased incidence of specific lethal neoplasms. This study was performed under contract with the Aomori Prefectural Government, Japan.

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© 2008 The Japan Radiation Research Society
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