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  • Title: Influence of age on the relative biological effectiveness of carbon ion radiation for induction of rat mammary carcinoma.
    Author: Imaoka T, Nishimura M, Daino K, Kokubo T, Doi K, Iizuka D, Nishimura Y, Okutani T, Takabatake M, Kakinuma S, Shimada Y.
    Journal: Int J Radiat Oncol Biol Phys; 2013 Mar 15; 85(4):1134-40. PubMed ID: 23084769.
    Abstract:
    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 (137)Cs γ rays or a 290-MeV/u monoenergetic carbonion beam (linear energy transfer, 13 keV/μm). 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 with the nonirradiated group. Dose responses (0.2-2.0 Gy) to γ 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 carbonion 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.
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