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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To reduce errors in the carbon beam distribution between the treatment planning system and the actual situation, we evaluated the geometrical accuracy, volume accuracy, water equivalent length (WEL), and treatment planning, and compared the evaluation results of axial and helical scan methods with various scan parameters. The results indicated that both scan methods show good geometrical accuracy for thin slice thickness, but for thick slice images it is easier to understand the phantom as a sphere from the helical as compared with the axial scan. Treatment planning with thin slice thickness provided accurate dose distribution for both scan methods, and the dose distribution on the treatment planning system was almost the same as that in the actual situation. Not all institutes, however, can obtain thin slice CT images, and some used thick-slice CT images in planning. For the axial scan, such thick slice images induced differences in the dose distribution between treatment planning and the actual situation. The helical scan with a small reconstructed increment reduced these differences even with relatively thick CT images. To achieve a more accurate dose distribution, radiation therapy planning should be performed using thin slice thickness for both scan methods or the helical scan with a small reconstructed increment. Although we reached this conclusion using the carbon beam, it may also be applied to proton beam therapy.
Physical evaluation of multidetector-row computed tomography (MDCT) scan methods and conditions for improvement of carbon beam distribution
