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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[Purpose] In the QST hospital, carbon ion radiotherapy (CIRT) using spot-scanning was started in 2011. In order to check each individual CIRT treatment plan and its treatment delivery, the scanning system and its treatment planning system require dosimetric patient-specific Quality Assurance (PQA) before CIRT. We report results of PQA in half year of 2017.
[Methods] For the PQA, all the planned beams are recalculated on a water phantom with treatment planning software. The recalculated dose distributions are compared with the measured distributions using a 2D ionization chamber array at three depth, including 95% area of prescription dose. These are evaluated using 3%/3 mm gamma criteria with a pass threshold of 90%. We analyzed PQA results for about 1500 shots from September 2017 to March 2018, evaluated the pass rate for 10 disease sites with various target volume, energy and measurement depth.
[Results] The pass rate for prostate, head and neck, and bone and soft tissue were 95.9%, 99.3%, and 91.5%, respectively. 95.9% of lung plans with low energy beam passed. Overall, 95% of the measured beams for all shots passed the gamma criteria, and were consistent with the plan. Although the rest of 5% failed the criteria, there were no dependence of measurements depth and disease sites in these failures.
[Conclusion] The results of the PQA in the second half of FY2017 was analyzed. The overall quality assurance measurement passing rate was 95% for the gamma index criteria of 3%/3 mm. It was obvious that there was no disease sites or target dependency in these pass rates. Therefore, we could ensure the safety of the CIRT treatment plans.
Evaluation of Patient-specific Quality Assurance for Spot-Scanning Carbon Ion Radiotherapy
