Institute of Medicine, University of Tsukuba, Tsukuba, Japan.
Proton Medical Research Center, University of Tsukuba Hospital, Tsukuba, Japan.
In Vivo. 2024 Sep-Oct;38(5):2478-2483. doi: 10.21873/invivo.13718.
BACKGROUND/AIM: Passive scattering proton beam therapy (PSPT) is performed by taking actual measurements of all pre-designated fields in a treatment plan followed by appropriate adjustments to the prescribed dose. For this reason, it is necessary to ensure precision management of the measurements (patient-specific calibration) in the administration of a planned dose. Therefore, this study investigated the impact on dose distribution in treatment planning when the patient calibration point differs from the normalized point in a treatment plan.
A total of 16 cases were selected, where the patient calibration point and normalized point did not match, and the normalized point used in the treatment plan was changed to the patient calibration point using a treatment planning system (VQA ver. 2.01, HITACHI). At this point, the displacement of the relative dose at the isocenter was estimated as an error owing to the difference compared to the patient calibration point.
Overall, the error was within the range of ±1.5%, with the exception of orbit cases. Calibrated points also tended to be lower than the normalized points in the treatment plan. In terms of treatment sites, a greater deviation was observed for head cases. Cases with a large deviation in sites other than the head were attributed to poor flatness within the radiation field owing to a narrower opening of the patient collimator.
Dose measurement errors in PSPT due to differing calibration points were generally within ±1.5%, with higher deviations observed in head treatments because of complex structures and narrow collimator openings. A γ analysis for significant deviations showed a 98.7% passing rate, suggesting limited overall impact. It is important to select stable calibration points in dosimetry to ensure high precision in dose administration, particularly in complex treatment areas.
背景/目的：被动散射质子束治疗（PSPT）是通过对治疗计划中的所有预定射野进行实际测量，并对规定剂量进行适当调整来完成的。因此，有必要确保在给予计划剂量时对测量（患者特异性校准）进行精确管理。因此，本研究探讨了在治疗计划中患者校准点与计划中的归一化点不同的情况下，对剂量分布的影响。
共选择了 16 例患者，患者校准点与归一化点不匹配，使用治疗计划系统（HITACHI 的 VQA ver. 2.01）将计划中的归一化点更改为患者校准点。此时，由于与患者校准点的差异，将在等中心点的相对剂量的位移估计为误差。
总体而言，误差在±1.5%的范围内，除了眼眶病例。校准点也倾向于低于计划中的归一化点。就治疗部位而言，头部病例的偏差较大。头部以外部位的偏差较大的病例归因于由于患者准直器开口较窄而导致辐射场内的平坦度较差。
由于校准点不同，PSPT 中的剂量测量误差通常在±1.5%以内，由于结构复杂和准直器开口较窄，头部治疗的偏差较大。对于显著偏差的γ分析显示 98.7%的通过率，表明总体影响有限。在剂量学中选择稳定的校准点对于确保剂量给予的高精度非常重要，特别是在复杂的治疗区域。
