@misc{oai:repo.qst.go.jp:00071503,
 author = {今岡, 達彦 and 西村, まゆみ and 臺野, 和広 and 細木, 彩夏 and 高畠, 賢 and ショウラー, 恵 and 小久保, 年章 and 島田, 義也 and 今岡 達彦 and 西村 まゆみ and 臺野 和広 and 細木 彩夏 and 高畠 賢 and ショウラー 恵 and 小久保 年章 and 島田 義也},
 month = {Sep},
 note = {Exposure of children to neutrons can occur during proton radiotherapy and intensity-modulated radiotherapy for treatment of childhood tumors, as these modalities emit secondary neutrons from irradiation apparatuses and within the patient body. The mammary gland is one of the susceptible organs to radiation carcinogenesis, and can be exposed to neutrons during radiotherapy for thoracic tumors. We therefore aimed to investigate the effect of neutron exposure during childhood on the risk of mammary carcinogenesis. Female Sprague-Dawley rats at 1, 3 and 7 weeks after birth (neonatal, prepubertal and postpubertal stages, respectively) were whole-body irradiated with fast neutrons, having an average energy of 2 MeV, with doses of 0.05, 0.1, 0.2, 0.5 or 1.0 Gy. Rats were observed until 90 weeks of age and the hazard ratio for mammary carcinoma development, as compared to the non-irradiated group, was calculated based on palpation records and pathological examination, using Cox’s proportional hazard model. Hazard ratios for γ-ray-induced carcinogenesis were obtained from our previous study, in which dose responses (0.2-1 Gy) were similar among the groups of rats irradiated at 1, 3 and 7 weeks after birth. Relative biological effectiveness (RBE) values were calculated based on linear fitting of the dose-hazard relationship. The effect of neutrons increased with the age at irradiation, indicating RBE values of 7, 7 and 18 for animals that were 1, 3 and 7 weeks of age, respectively. Carcinogenesis after irradiation at 1 week of age was characterized by a blunted response at 1 Gy and concomitant early cessation of the estrous cycle, implying that premature ovarian failure changed the hormonal milieu and led to attenuated cancer development. Our findings offer RBE information for use in the risk assessment of radiotherapy of childhood tumors. The unexpected observation of age-dependent RBE values necessitates further clarification of underlying mechanisms., The 60th Meeting of Radiation Research Society},
 title = {Age dependent effect of fast neutrons on rat mammary carcinogenesis},
 year = {2014}
}