@misc{oai:repo.qst.go.jp:00070516,
 author = {Imaoka, Tatsuhiko and Nishimura, Mayumi and Daino, Kazuhiro and Iizuka, Daisuke and Kokubo, Toshiaki and Nishimura, Yukiko and Okutani, Tomomi and Takabatake, Masaru and Kakinuma, Shizuko and Takabatake, Takashi and Shang, Yi and Shimada, Yoshiya and 今岡 達彦 and 西村 まゆみ and 臺野 和広 and 飯塚 大輔 and 小久保 年章 and 西村 由希子 and 奥谷 倫未 and 高畠 賢 and 柿沼 志津子 and 高畠 貴志 and 尚 奕 and 島田 義也},
 month = {Sep},
 note = {Background: The risk of developing secondary cancer after radiotherapy, especially after the treatment of childhood cancers, has been a matter of great concern. Epidemiologic studies have suggested that the breast is one of the most susceptible organs to radiation-induced carcinogenesis. However, little information is available on the effect of carbon ion radiation on breast carcinogenesis in children. 
Method: Female Jcl:SD Sprague-Dawley rats were whole body–irradiated with 1 Gy of Cs-137 g rays or a monoenergetic carbon ion beam (290 MeV/u, having LET of ~13 keV/mm) at various ages from the embryonic stage to adulthood. Neonatal, juvenile and young adult rats (1, 3 and 7 weeks of age, respectively) were irradiated with g rays or monoenergetic carbon ions at various doses between 0.2 and 2 Gy. The rats were observed until 90 weeks of age. Kaplan-Meier curves of the time until mammary carcinoma palpation were analyzed by the logrank method to calculate hazard ratios. 
Results: The hazard ratio for mammary carcinoma development tended to increase in groups of rats irradiated with 1 Gy of either g rays or carbon ions at ages between 1 and 7 postnatal weeks; irradiation of fetal rats with either radiation did not increase the ratio. Irradiation of neonatal rats at 2 Gy led to early cessation of regular estrous cycling. Dose responses of g rays were similar among the groups of rats irradiated at 1, 3 and 7 weeks of age. The effect of heavy ions tended to increase along with the age at the time of irradiation, indicating RBE values of 0.2, 1.2 and 2.5 for irradiation at 1, 3 and 7 weeks of age, respectively. 
Conclusion: The carcinogenic effect of carbon ion irradiation on mammary gland depends on the age at the time of exposure., 14th International Congress of Radiation Research},
 title = {Mammary carcinogenesis after exposure of fetal, neonatal, juvenile and adult rats to gamma rays and carbon ions},
 year = {2011}
}