Faculty of Engineering, Division of Quantum Science and Engineering, Research Group of Applied Quantum Beam, Laboratory of Quantum Beam Science and Medical Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan.
Department of Radiology, Niigata University Medical and Dental Hospital, Niigata 951-8520, Japan.
Phys Med Biol. 2020 Dec 18;65(23):235046. doi: 10.1088/1361-6560/abae09.
To achieve an accurate stopping power ratio (SPR) prediction in particle therapy treatment planning, we previously proposed a simple conversion to the SPR from dual-energy (DE) computed tomography (CT) data via electron density and effective atomic number (Z ) calibration (DEEDZ-SPR). This study was conducted to carry out an initial implementation of the DEEDZ-SPR conversion method with a clinical treatment planning system (TPS; VQA, Hitachi Ltd., Tokyo) for proton beam therapy. Consequently, this paper presents a proton therapy plan for an anthropomorphic phantom to evaluate the stability of the dose calculations obtained by the DEEDZ-SPR conversion against the variation of the calibration phantom size. Dual-energy x-ray CT images were acquired using a dual-source CT (DSCT) scanner. A single-energy CT (SECT) scan using the same DSCT scanner was also performed to compare the DEEDZ-SPR conversion with the SECT-based SPR (SECT-SPR) conversion. The scanner-specific parameters necessary for the SPR calibration were obtained from the CT images of tissue substitutes in a calibration phantom. Two calibration phantoms with different sizes (a 33 cm diameter phantom and an 18 cm diameter phantom) were used for the SPR calibrations to investigate the beam-hardening effect on dosimetric uncertainties. Each set of calibrated SPR data was applied to the proton therapy plan designed using the VQA TPS with a pencil beam algorithm for the anthropomorphic phantom. The treatment plans with the SECT-SPR conversion exhibited discrepancies between the dose distributions and the dose-volume histograms (DVHs) of the 33 cm and 18 cm phantom calibrations. In contrast, the corresponding dose distributions and the DVHs obtained using the DEEDZ-SPR conversion method coincided almost perfectly with each other. The DEEDZ-SPR conversion appears to be a promising method for providing proton dose plans that are stable against the size variations of the calibration phantom and the patient.
为了在粒子治疗计划中实现准确的停止功率比（SPR）预测，我们之前提出了一种通过电子密度和有效原子数（Z）校准（DEEDZ-SPR）将 SPR 从双能（DE）计算机断层扫描（CT）数据转换的简单方法。本研究旨在首次将 DEEDZ-SPR 转换方法与临床治疗计划系统（TPS；VQA，日立有限公司，东京）一起用于质子束治疗。因此，本文提出了一种用于人体模型的质子治疗计划，以评估通过 DEEDZ-SPR 转换获得的剂量计算在校准体模尺寸变化时的稳定性。使用双源 CT（DSCT）扫描仪获取双能 X 射线 CT 图像。还使用相同的 DSCT 扫描仪进行了单次能量 CT（SECT）扫描，以比较 DEEDZ-SPR 转换与基于 SECT 的 SPR（SECT-SPR）转换。SPR 校准所需的特定于扫描仪的参数是从校准体模中的组织替代品的 CT 图像中获得的。使用两个不同尺寸的校准体模（直径为 33 cm 的体模和直径为 18 cm 的体模）进行 SPR 校准，以研究束硬化效应对剂量不确定性的影响。使用 VQA TPS 设计的铅笔束算法为人体模型设计的每个质子治疗计划都应用了一组校准的 SPR 数据。使用 SECT-SPR 转换的治疗计划显示出 33 cm 和 18 cm 体模校准的剂量分布和剂量体积直方图（DVH）之间的差异。相比之下，使用 DEEDZ-SPR 转换方法获得的相应剂量分布和 DVH 几乎完全吻合。DEEDZ-SPR 转换似乎是一种很有前途的方法，可以提供对校准体模和患者尺寸变化稳定的质子剂量计划。
