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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Purpose
The aim of this study was to clear any specific LETs cause change in skin reaction. We irradiated mice feet with mono-energetic and SOBP carbon ions, to obtain dose response of early skin reaction at different LETs.
Materials and methods
Mice
C3H/HeMsNrsf female mice aged 4 months old were used for this study. The animals were produced and maintained in specific pathogen-free (SPF) facilities.
Irradiation
The mice right hind legs received daily fractionated irradiation ranged from single to 6 fractions. Carbon ions (12C6+) were accelerated by the HIMAC synchrotron to 290 MeV/u. Irradiation was conducted using horizontal carbon-ion beams with a dose rate of ~3 Gy/min. We chose the LETs at entrance of plateau (20keV/μm) and the SOBP (proximal:40keV/μm, middle:45keV/μm, distal:60keV/μm, distal-end:80keV/μm). The reference beam was 137Cs γ-rays with a dose rate of 1.2 Gy/min.
Skin reaction
Skin reaction of the irradiated legs were scored every other day, between the14th and 35th post irradiation days. Our scoring scale consisted of 7 steps, ranging from 0.5 to 3.5.(1) The skin score analyzed a result by the method that described by Ando.(2) The Fe-plot proposed Douglas and Fowler was used as a multifraction linear quadratic model. A plot between the reciprocal of the isoeffect dose and the dose per fraction resulted in a straight line.
Results
Required isoeffect total dose increased linearly with the fraction numbers on a semi-logarithmic chart at LET 20- 60keV/µm SOBP beam. The isoeffect total dose decreased with increase of the LET. However, no increases of isoeffect total dose were observed at few fractionations at 80keV/µm. (data not shown) Using an Fe-plot, we analyzed the isoeffect total dose to evaluate the dependence on Carbon beam, or γ-ray. When I irradiate it by γ-ray, an Fe-plot shows linearly. But, irradiated by Carbon beam, an Fe-plot bent at low fractions. (Fig.1)
Conclusion
The LQ-model based Fe-plot could not fit skin reaction at few fractions at high-LET.
Fractionated Irradiation of Carbon Beam and the Isoeffect Dose on Acute Reaction of Skin
