Department of Radiation Oncology, Chiba Cancer Center, 666-2 Nitona-chou, Chuo-ku, Chiba, Japan.
Graduate School of Human Health Sciences, Tokyo Metropolitan University, 7-2-10 Higashiogu, Arakawa-ku, Tokyo, Japan.
J Appl Clin Med Phys. 2019 Aug;20(8):98-104. doi: 10.1002/acm2.12683. Epub 2019 Jul 29.
Respiratory-gated volumetric modulated arc therapy (gated VMAT) involves further complexities to the dose delivery process because the gantry rotation must repeatedly stop and restart according to the gating signals. In previous studies, the gantry rotation performances were evaluated by the difference between the plan and the machine log. However, several reports pointed out that log analysis does not sufficiently replicate the machine performance. In this report, a measurement-based quality assurance of the relation between the gantry angle and gate-on or gate-off using triggered kilovoltage imaging and a cylinder phantom with 16 ball bearings is proposed. For the analysis, an in-house program that estimates and corrects the phantom offset was developed. The gantry angle in static and gated arc delivery was compared between the machine log and the proposed method. The gantry was set every 5 deg through its full motion range in static delivery, and rotated at three speeds (2, 4 and 6 deg s ) with different gating intervals (1.5 or 3.0 s) in gated arc delivery. The mean and standard deviation of the angular differences between the log and the proposed method was -0.05 deg ± 0.12 deg in static delivery. The mean of the angular difference was within ±0.10 deg and the largest difference was 0.41 deg in gated arc delivery. The log records the output of the encoder so that miscalibration and mechanical sagging will be disregarded. However, the proposed method will help the users to detect the mechanical issues due to the repeated gantry stops and restarts in gated VMAT.
呼吸门控容积旋转调强放疗（ gated VMAT ）为剂量输送过程增加了更多复杂性，因为旋转机架必须根据门控信号反复停止和重新启动。在以前的研究中，通过计划与机器日志之间的差值来评估旋转机架的旋转性能。然而，有几项报告指出，日志分析不能充分复制机器性能。在本报告中，提出了一种使用触发千伏成像和具有 16 个球轴承的圆柱体模体来测量门控时机架角度与通/断之间关系的质量保证方法。为了进行分析，开发了一种估算并校正模体偏移的内部程序。比较了机器日志和提出的方法在静态和门控弧形输送中的机架角度。在静态输送中，机架每 5 度设置一次，通过其全运动范围，在门控弧形输送中，以 2 、 4 和 6 度每秒的速度旋转，并具有不同的门控间隔（ 1.5 或 3.0 秒）。在静态输送中，日志和提出的方法之间的角度差的平均值和标准偏差为-0.05 度±0.12 度。在门控弧形输送中，角度差的平均值在±0.10 度以内，最大差值为 0.41 度。日志记录编码器的输出，因此不会忽略校准错误和机械下垂。然而，提出的方法将有助于用户检测由于 gated VMAT 中旋转机架的反复停止和重新启动而导致的机械问题。
