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 and Radiological Science and Technology.
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The NFSa fibrosarcomas, transplanted in the right hind legs of syngeneic C3H male mice and grew to reach 8 mm in diameter, were irradiated with various LET of carbon ions. Equal doses were daily delivered for up to 6 days. Growth delay by 15 days here designated TGD15 was calculated from the tumor regrowth curve, and used as the isoeffect dose. Skin of the right hind legs was also irradiated with carbon ions. Skin reaction scores for each group were plotted against dose, and the isoeffect dose to produce score 3.0 was calculated. The RBE of carbon ions relative to Cs-137 g rays depended on the LET and the number of fractions. The RBE(skin) ranged from 1.4 to 1.7 for 20 keV/mm, from 1.5 to 2.3 for 40 keV/mm and from 2.5 to 2.9 for 80 keV/mm, respectively. The RBE(tumor) ranged from 1.3 to 1.5 for 20 keV/mm, from 1.8 to 2.3 for 40 keV/mm and from 2.4 to 3.0 for 80 keV/mm, respectively. When the therapeutic gain was designated the quotient of RBE(tumor) divided by RBE(skin), the therapeutic gain for 42 keV/mm was larger than that for 77 keV/mm whereas the therapeutic gain for 20 keV/mm was unity or less. The RBE of carbon ions depended on dose such that the RBE deceased with an increase of dose. The dose dependence of RBE for 20 keV/mm was same between the skin reaction and the tumor growth delay. However, the dose dependence of RBE for 42 and 77 keV/mm was more prominent for the skin reaction than the tumor growth delay, suggesting that a large dose per fraction would be appropriate for carbon-ion therapy.
重粒子線による治療効果比に関する研究
