@article{oai:repo.qst.go.jp:00046500,
 author = {Imaoka, Tatsuhiko and Nishimura, Mayumi and Daino, Kazuhiro and Kokubo, Toshiaki and Doi, Kazutaka and Iizuka, Daisuke and Nishimura, Yukiko and Okutani, Tomomi and Takabatake, Masaru and Kakinuma, Shizuko and Shimada, Yoshiya and 今岡 達彦 and 西村 まゆみ and 臺野 和広 and 小久保 年章 and 土居 主尚 and 飯塚 大輔 and 西村 由希子 and 奥谷 倫未 and 高畠 賢 and 柿沼 志津子 and 島田 義也},
 issue = {4},
 journal = {International Journal of Radiation Oncology Biology Physics},
 month = {Oct},
 note = {Purpose: The risk of developing secondary cancer after radiotherapy, especially after treatment of childhood cancers, remains a matter of concern. The high biological effects of carbon-ion radiation have enabled powerful radiotherapy, yet the approach is commonly restricted to the treatment of adults. Susceptibility of the fetus to particle radiation-induced cancer is also unclear. The present study is aimed to investigate the effect of carbon-ion irradiation in childhood on breast carcinogenesis.
Methods and Materials: We irradiated female Sprague-Dawley rats of various ages (embryonic days 3, 13 and 17, and 1, 3, 7 and 15 weeks after birth) with 137Cs gamma rays or a 290-MeV/u monoenergetic carbon-ion beam (linear energy transfer, 13 keV/um). All animals were screened weekly for mammary carcinoma by palpation until they were 90 weeks old. 
Results: Irradiation of fetal and mature (15-week-old) rats with either radiation source at a dose of 0.2 or 1 Gy did not substantially increase the hazard ratio compared to the non-irradiated group. Dose responses (0.2-2.0 Gy) to gamma rays were similar among the groups of rats irradiated 1, 3 and 7 weeks after birth. The effect of carbon ions increased along with the age at the time of irradiation, indicating relative biological effectiveness values of 0.2 [-0.3, 0.7], 1.3 [1.0, 1.6] and 2.8 [1.8, 3.9] (mean and 95% confidence interval) for animals that were 1, 3 and 7 weeks of age, respectively. 
Conclusions: Our findings imply that carbon-ion therapy may be associated with a risk of secondary breast cancer in humans, the extent of which may depend on the age of the patient at the time of irradiation.},
 pages = {1134--1140},
 title = {Influence of age on the relative biological effectiveness of carbon ion radiation for induction of rat mammary carcinoma.},
 volume = {85},
 year = {2012}
}