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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The National Institute of Radiological Sciences (NIRS) has extensively studied passive carbon-ion radiotherapy for cancer treatment with some positive outcomes. These successful results allow the patients to live for a longer time and younger patients to receive the radiotherapy. The incidence of secondary malignance as a result of the radiotherapy in these patients is of great concern to us. Especially, the assessment of the secondary neutrons inevitably produced within the patient and beam line devices in the carbon-ion radiotherapy is very important due to the potency of their biological effect. Our previous study showed that the secondary neutron exposure in normal tissues far from the target volume in carbon-ion radiotherapy is lower than that in proton radiotherapy, and is equal to or less than that in photon radiotherapy based on the measurement of the ambient dose equivalents at the patient position. [1] However, it is considered to be non-negligible in the estimation of the secondary cancer risk. Distributions of the absorbed dose and the biological effectiveness in the patient are required for assessing the risk. Such investigations are often performed using Monte Carlo calculations,[2] because it is very difficult to obtain them experimentally. However, the experimental verification of the calculations has to be done for the accurate assessment. In this study, in-air and in-water lineal energy distributions were measured by using a commercial tissue equivalent proportional counter (TEPC) at Heavy Ion Medical Accelerator in Chiba (HIMAC) treatment room. Based on the lineal energy distributions, we could obtain the in-air and in-water absorbed doses and quality factors. TEPC dosimetry can not discriminate the information of neutrons and other radiations when using TEPC only, but can provide biologically relevant information. These measured data should be useful for the secondary cancer risk assessment based on experimental data and the verification of Monte Carlo calculation.
MEASUREMENT OF IN-AIR AND IN-WATER ABSORBED DOSES AND QUALITY FACTORS OUTSIDE OF THE IRRADIATION FIELD IN PASSIVE CARBON-ION RADIOTHERAPY
