Journal Article Age Modifies the Effect of 2-MeV Fast Neutrons on Rat Mammary Carcinogenesis

Imaoka, Tatsuhiko  ,  Nishimura, Mayumi  ,  Daino, Kazuhiro  ,  Hosoki, Ayaka  ,  Takabatake, Masaru  ,  Kokubo, Toshiaki  ,  Doi, Kazutaka  ,  Showler, Kaye  ,  Nishimura, Yukiko  ,  Moriyama, Hitomi  ,  Morioka, Takamitsu  ,  Shimada, Yoshiya  ,  Kakinuma, Shizuko

188 ( 4 )  , pp.419 - 425 , 2017-10 , Radiation Research Society
ISSN:0033-7587
Description
The relative biological effectiveness (RBE) of neutrons depends on their physical nature (e.g., energy) and the biological context (e.g., endpoints, materials). From the perspective of radiological protection, age is an important biological context that influences radiation-related cancer risk, but very few studies have addressed its potential impact on neutron effects. We therefore investigated the influence of age on the effect of accelerator-generated fast neutrons (mean energy, ~2 MeV) in an animal model of breast carcinogenesis. Female Sprague-Dawley rats at 1, 3, and 7 weeks of age were irradiated with fast neutrons at absorbed doses of 0.0485–0.97 Gy. All animals were kept under specific pathogen–free conditions and screened weekly for mammary tumors by palpation until they were 90 weeks old. Tumors were diagnosed based on histology. Mathematical modeling was used to analyze mammary cancer incidence, collectively using data from this study and a previously reported experiment on 137Cs γ rays. The results indicate that neutron irradiation elevated the risk of palpable mammary carcinoma with a linear dose response, the slope of which depended on age at the time of irradiation. The RBE of neutron irradiation was 7.5 ± 3.4, 9.3 ± 3.5, and 26.1 ± 8.9 (mean ± SE) for animals treated at 1, 3, and 7 weeks of age, respectively. Our results indicate that animal age is an important factor influencing the effect of fast neutrons on breast cancer risk.

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