量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum Science and Technology.
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Background: There are insufficient data at present on cancer risk after exposure of heavy ions, to the fetal and childhood periods. Using animal models, we studied the age-at-exposure effects of heavy ions on cancer induction and lifespan shortening for radiation protection for fetuses and children.
\nMaterials and Methods: Fifty female and male B6C3F1 mice per group were exposed to gamma rays (137Cs) or carbon ions (13 keV/µm) at various ages from fetal to mature adulthood periods. Mouse ages at the time of irradiation included pre-implantation (3 days post-conception (dpc)), major organogenesis (13 dpc), late fetal (17 dpc), neonatal (1 week after birth), infantile (3 weeks), young adulthood (7 weeks) and mature adulthood stages (15 weeks). The doses ranged between 0.2 and 4 Gy for gamma rays and 0.2 and 2 Gy for carbon ions. The mice were observed until moribund and their lifespan and the developed cancers were analyzed.
\nResults and Discussion: Our study indicated that female mice appeared to be more susceptible to radiation-induced lifespan shortening than male mice. Effect of gamma-rays on lifespan shortening was more manifested when irradiated at neonatal than adult stage. Surprisingly, irradiation with gamma rays at the late fetal stage had little influence on lifespan shortening compared to infant and adulthood exposures. On the other hand, carbon ions were more potent in reducing lifespan than gamma rays when female neonatal mice were exposed. When carbon ions were exposed, however, fetuses were as susceptible as infants. The results on the lifespan shortening suggest a larger RBE of carbon ions for fetuses than later stages. The RBE of carbon ions for reducing the tumor-free survival rate was ~1.0 for fetuses, suggesting that RBE of 13keV/µm carbon for cancer induction is 1.0 ~ 1.5 irrespective of age-at-exposure.
Lifespan shortening after exposure of mice at fetal, childhood and adulthood periods to gamma-rays and carbon ions
