The Netherlands Cancer Institute, Department of Radiation Oncology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
The Netherlands Cancer Institute, Department of Radiation Oncology, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
Phys Med. 2018 Oct;54:137-145. doi: 10.1016/j.ejmp.2018.10.005. Epub 2018 Oct 11.
To investigate the effectiveness of an EPID-based 3D transit dosimetry system in detecting deliberately introduced errors during VMAT delivery.
An Alderson phantom was irradiated using four VMAT treatment plans (one prostate, two head-and-neck and one lung case) in which delivery, thickness and setup errors were introduced. EPID measurements were performed to reconstruct 3D dose distributions of "error" plans, which were compared with "no-error" plans using the mean gamma (γ), near-maximum gamma (γ) and the difference in isocenter dose (ΔD) as metrics.
Out of a total of 42 serious errors, the number of errors detected was 33 (79%), and 27 out of 30 (90%) if setup errors are not included. The system was able to pick up errors of 5 mm movement of a leaf bank, a wrong collimator rotation angle and a wrong photon beam energy. A change in phantom thickness of 1 cm was detected for all cases, while only for the head-and-neck plans a 2 cm horizontal and vertical shift of the phantom were alerted. A single leaf error of 5 mm could be detected for the lung plan only.
Although performed for a limited number of cases and error types, this study shows that EPID-based 3D transit dosimetry is able to detect a number of serious errors in dose delivery, leaf bank position and patient thickness during VMAT delivery. Errors in patient setup and single leaf position can only be detected in specific cases.
研究基于 EPID 的 3D 剂量传递测量系统在检测调强放疗（VMAT）过程中故意引入的误差的有效性。
使用四个 VMAT 治疗计划（一个前列腺、两个头颈部和一个肺部病例）对 Alderson 体模进行照射，在这些计划中引入了传输、厚度和设置误差。进行 EPID 测量以重建“误差”计划的 3D 剂量分布，并使用平均伽马（γ）、近最大伽马（γ）和等中心剂量差异（ΔD）作为指标，将其与“无误差”计划进行比较。
在总共 42 个严重误差中，检测到的误差数量为 33 个（79%），如果不包括设置误差，则有 27 个（90%）。该系统能够检测到叶栅 5mm 运动、准直器旋转角度错误和光子束能量错误等误差。所有病例均能检测到 1cm 的体模厚度变化，而仅对头颈部计划会提示 2cm 的水平和垂直体模移位。对于肺部计划，仅能检测到单个叶栅 5mm 的误差。
尽管该研究仅针对有限数量的病例和误差类型进行，但表明基于 EPID 的 3D 剂量传递测量系统能够检测到 VMAT 传输过程中剂量传输、叶栅位置和患者厚度的一些严重误差。患者设置和单个叶栅位置的误差仅在特定情况下才能检测到。
