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Cancer risk from radiation: reduction of dose rate lowers mammary cancer more effectively for adult rats

Update:2019年2月4日更新
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Risk of breast cancer after low dose rate radiation exposure is not well understood. The present study provides experimental evidence for dose rate and age dependencies induced by continuous γ-ray irradiation on mammary carcinogenesis. In this study, female rats were subjected to continuous or acute whole-body irradiation and the incidence of mammary cancer was monitored. When adult rats were irradiated at 60 mGy/h for a total of 4 Gy, their mammary cancer risk significantly increased relative to unirradiated rats; however, for adult rats irradiated at 3–24 mGy/h, even though they also received a total of 4 Gy, their risk did not significantly increase. A larger increase in the incidence rate of carcinoma per dose was found for the juveniles than for the adults irradiated at 6 mGy/h, whereas age did not influence the effect of acute irradiation at 30 Gy/h. Similar approaches on other organs will unveil the whole picture of age difference in the effect of low dose rate radiation.

Irradiate condition

Fig. 1.  Juvenile and adult rats were irradiated at a low dose rate. For high dose rate data, rats were irradiated at 13 weeks of age, and past data were used for rats irradiated at 3 or 7 weeks.

Result

Fig. 2.  Mammary cancer risk of juvenile and adult rats irradiated at a low dose rate (6 mGy/h, upper panels) and that of rats irradiated at a high dose rate (30 Gy/h, lower panels). *** P < 0.001, ** P < 0.01, *** P < 0.001 vs. unirradiated. Vertical bars, 95% confidence interval (upper limit in parentheses).

Reference

Tatsuhiko Imaoka, Mayumi Nishimura, Kazuhiro Daino, Ayaka Hosoki, Masaru Takabatake, Yukiko Nishimura, Toshiaki Kokubo, Takamitsu Morioka, Kazutaka Doi, Yoshiya Shimada, Shizuko Kakinuma. Prominent Dose Rate Effect and Its Age Dependence of Rat Mammary Carcinogenesis Induced by Continuous γ-Ray Exposure. Radiation Research https://doi.org/10.1667/RR15094.1