Department of Radiological Technology, Ehime University Hospital, Ehime, Japan.
Graduate School of Advanced Technology and Science, Tokushima University, Tokushima, Japan.
J Appl Clin Med Phys. 2021 Jul;22(7):66-76. doi: 10.1002/acm2.13260. Epub 2021 May 5.
Volumetric-modulated arc therapy (VMAT) requires highly accurate control of multileaf collimator (MLC) movement, rotation speed of linear accelerator gantry, and monitor units during irradiation. Pretreatment validation and monitoring of these factors during irradiation are necessary for appropriate VMAT treatment. Recently, a gantry mounted transmission detector "Delta Discover® (D4D)" was developed to detect errors in delivering doses and dose distribution immediately after treatment. In this study, the performance of D4D was evaluated. Simulation plans, in which the MLC position was displaced by 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mm from the clinically used original plans, were created for ten patients who received VMAT treatment for prostate cancer. Dose deviation (DD), distance-to-agreement (DTA), and gamma index analysis (GA) for each plan were evaluated by D4D. These results were compared to the results (DD, DTA and GA) measured by Delta Phantom + (D4P). We compared the deviations between the planned and measured values of the MLC stop positions A-side and B-side in five clinical cases of prostate VMAT during treatment and measured the GA values. For D4D, when the acceptable errors for DD, DTA, and GA were determined to be ≤3%, ≤2 mm, and ≤3%/2 mm, respectively, the minimum detectable errors in the MLC position were 2.0, 1.5, and 1.5 mm based on DD, DTA, and GA respectively. The corresponding minimum detectable MLC position errors were 2.0, 1.0, and 1.5 mm, respectively, for D4P. The deviation between the planned and measured position of MLC stopping point of prostate VMAT during treatment was stable at an average of -0.09 ± 0.05 mm, and all GA values were above 99.86%. In terms of delivering doses and dose distribution of VMAT, error detectability of D4D was comparable to that of D4P. The transmission-type detector "D4D" is thus suitable for detecting delivery errors during irradiation.
容积旋转调强弧形治疗（VMAT）需要在照射过程中对多叶准直器（MLC）运动、直线加速器旋转速度和监视器单位进行高度精确的控制。在 VMAT 治疗中，需要对这些因素进行预处理验证和照射过程中的监测。最近，开发了一种安装在旋转架上的传输探测器“Delta Discover®（D4D）”，用于在治疗后立即检测剂量和剂量分布的传递误差。在这项研究中，评估了 D4D 的性能。为接受前列腺癌 VMAT 治疗的 10 名患者创建了模拟计划，其中 MLC 位置从临床使用的原始计划中偏移了 0.5、1.0、1.5、2.0、2.5 和 3.0 毫米。通过 D4D 评估了每个计划的剂量偏差（DD）、符合度距离（DTA）和伽马指数分析（GA）。将这些结果与通过 Delta Phantom +（D4P）测量的结果（DD、DTA 和 GA）进行了比较。我们比较了五个前列腺 VMAT 治疗过程中计划和测量的 MLC 停止位置 A 侧和 B 侧的偏差，并测量了 GA 值。对于 D4D，当确定 DD、DTA 和 GA 的可接受误差分别为≤3%、≤2mm 和≤3%/2mm 时，基于 DD、DTA 和 GA，MLC 位置的最小可检测误差分别为 2.0、1.5 和 1.5mm。对于 D4P，相应的最小可检测 MLC 位置误差分别为 2.0、1.0 和 1.5mm。在治疗过程中前列腺 VMAT 的 MLC 停止点的计划和测量位置之间的偏差稳定在平均-0.09±0.05mm，所有 GA 值均高于 99.86%。在 VMAT 的剂量和剂量分布方面，D4D 的误差检测能力与 D4P 相当。因此，传输式探测器“D4D”适用于检测照射过程中的输送误差。
