Title: Suppression of carcinogenic processes in mice by chronic low dose rate gamma-irradiation

Authors: Kazuo Sakai, Yuko Hoshi, Takaharu Nomura, Takeshi Oda, Toshiyasu Iwasaki, Kazuko Fujita, Takeshi Yamada, Hiroshi Tanooka

Addresses: Low Dose Radiation Research Center, Central Research Institute of Electric Power Industry, 2-11-1, Iwad Kita, Komae, Tokyo 201-8511, Japan. Low Dose Radiation Research Center, Central Research Institute of Electric Power Industry, 2-11-1, Iwad Kita, Komae, Tokyo 201-8511, Japan. Low Dose Radiation Research Center, Central Research Institute of Electric Power Industry, 2-11-1, Iwad Kita, Komae, Tokyo 201-8511, Japan. Low Dose Radiation Research Center, Central Research Institute of Electric Power Industry, 2-11-1, Iwad Kita, Komae, Tokyo 201-8511, Japan. Low Dose Radiation Research Center, Central Research Institute of Electric Power Industry, 2-11-1, Iwad Kita, Komae, Tokyo 201-8511, Japan. Low Dose Radiation Research Center, Central Research Institute of Electric Power Industry, 2-11-1, Iwad Kita, Komae, Tokyo 201-8511, Japan. Low Dose Radiation Research Center, Central Research Institute of Electric Power Industry, 2-11-1, Iwad Kita, Komae, Tokyo 201-8511, Japan. Low Dose Radiation Research Center, Central Research Institute of Electric Power Industry, 2-11-1, Iwad Kita, Komae, Tokyo 201-8511, Japan

Abstract: Effects of low dose rate radiation on the process of carcinogenesis induced by a chemical carcinogen were examined. ICR female mice, 35 or 36 mice for each group, were kept and exposed to ¹³⁷Cs gamma-rays in the long-term low dose rate irradiation facility at the Central Research Institute of Electric Power Industry at a dose rate of 0.3, 0.96, or 2.5 mGy/h. Thirty-five days later, the mice were injected in the groin with 0.5 mg of 20-methylcholanthrene (MC) dissolved in olive oil, and irradiation was continued. Tumours started to appear 2 months after MC injection. Cumulative tumour incidences after 216 days following MC injection were 94% in the mice irradiated at 0.3 mGy/h, 76% at 0.95 mGy/h, 89% at 0.30 mGy/h, and 94% in non-irradiated control mice. The difference between the tumour incidence in the control mice and that in the mice irradiated at 0.95 mGy/h was statistically significant. These results indicate the suppressive effect of low dose rate irradiation on the process of tumour induction initiated by MC with an optimum dose rate of approximately 1 mGy/h.

Keywords: gamma irradiation; low dose rate; suppression of carcinogenesis; skin tumour; mouse.

DOI: 10.1504/IJLR.2003.003485

International Journal of Low Radiation, 2003 Vol.1 No.1, pp.142 - 146

Published online: 11 Sep 2003 *

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