A Dose Dose Rate Map of Biological Effects of Ionizing

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					                 A “Dose/Dose-Rate Map” of Biological Effects of Ionizing Radiation

                                                     Kazuo Sakai

               Low Dose Radiation Research Center, Central Research Institute of Electric Power Industry

Body of Abstract: We investigated effects of low dose/dose-rate irradiation on mice, using our low
dose-rate irradiation facilities. We found that a prolonged gamma-irradiation at around 1 mGy/hr
suppressed the appearance of skin tumors in methylcholanthrene- injected ICR and C57BL/6 mice and
delayed the appearance of radiation-induced thymic lymphomas in C57BL/6 mice. We also investigated
the effects on disease model mice. In Type II diabetic C57BL/KsJ-db/db mice, the urine glucose level
was improved in some of the mice irradiated at 0.70 mGy/hr but not in the non-irradiated control mice.
In severe autoimmune MRL-lpr/lpr mice, the immunological status was kept better in the mice
irradiated at 0.35 or 1.2 mGy/hr.?
To elucidate the mechanisms underlying these effects, we examined bio-protective functions in vivo and
in vitro after irradiation. We recognized that, under certain conditions, low dose/dose-rate irradiation
increased certain protective functions, including anti-oxidative capacity, DNA repair capacity,
apoptosis, and immune functions. These data were then plotted against the dose and dose-rate to make a
map to identify the dose and dose-rate region in which harmful effects are observed, the region in which
protective functions are increased, and the region in which no effect is observed. Certain
epidemiological data from a high background area in China were also plotted in the map. Implications
of the dose and dose-rate dependence of biological effects in radiation protection will be discussed using
the map as a base.