抄録
The suppression of Methylcholantholene(MC)-induced tumor by low dose-rate gamma irradiation has been reported in 44th annal meeting. However, it's not known how the low dose-rate radiation suppressed the appearance of MC-induced tumor. Here, we investigated the fluctuations of TD50 values in irradiated mice at low dose-rates to elucidate the mechanism of the suppressive effects. Irradiations were performed with Cs-137 gamma-rays at 1.0 mGy/hr or 0.30 mGy/hr for 1-8 weeks before tumor cell injection. Mice were injected with an appropriate number of cells prepared from MC-induced tumor. The results indicate that TD50 values in mice irradiated at 1.0 mGy/hr for 1-3 weeks were almost 1.5 times higher than in non-irradiated mice, and higher TD50 value was also shown in mice irradiated at 0.30 mGy/hr for 1-5 weeks. The change in TD50 values is considered to be reflected tumor immunological conditions; therefore, the results obtained in the present study may suggest that the low dose-rate radiation enhances tumor immunological capacity in the irradiated mice. [J Radiat Res 44:390 (2003)]
