Hirashima Hideaki, Miyabe Yuki, Nakamura Mitsuhiro, Mukumoto Nobutaka, Mizowaki Takashi, Hiraoka Masahiro
Department of Radiation Oncology and Image-applied therapy, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
J Appl Clin Med Phys. 2018 May;19(3):234-242. doi: 10.1002/acm2.12324. Epub 2018 Apr 6.
The purpose of this study was to develop a simple verification method for the routine quality assurance (QA) of Dynamic WaveArc (DWA) irradiation using electronic portal imaging device (EPID) images and log data analysis. First, an automatic calibration method utilizing the outermost multileaf collimator (MLC) slits was developed to correct the misalignment between the center of the EPID and the beam axis. Moreover, to verify the detection accuracy of the MLC position according to the EPID images, various positions of the MLC with intentional errors in the range 0.1-1 mm were assessed. Second, to validate the geometric accuracy during DWA irradiation, tests were designed in consideration of three indices. Test 1 evaluated the accuracy of the MLC position. Test 2 assessed dose output consistency with variable dose rate (160-400 MU/min), gantry speed (2.2-6°/s), and ring speed (0.5-2.7°/s). Test 3 validated dose output consistency with variable values of the above parameters plus MLC speed (1.6-4.2 cm/s). All tests were delivered to the EPID and compared with those obtained using a stationary radiation beam with a 0° gantry angle. Irradiation log data were recorded simultaneously. The 0.1-mm intentional error on the MLC position could be detected by the EPID, which is smaller than the EPID pixel size. In Test 1, the MLC slit widths agreed within 0.20 mm of their exposed values. The averaged root-mean-square error (RMSE) of the dose outputs was less than 0.8% in Test 2 and Test 3. Using log data analysis in Test 3, the RMSE between the planned and recorded data was 0.1 mm, 0.12°, and 0.07° for the MLC position, gantry angle, and ring angle, respectively. The proposed method is useful for routine QA of the accuracy of DWA.
本研究的目的是开发一种简单的验证方法，用于利用电子射野影像装置（EPID）图像和日志数据分析对动态弧形调强放疗（DWA）照射进行常规质量保证（QA）。首先，开发了一种利用最外层多叶准直器（MLC）狭缝的自动校准方法，以校正EPID中心与射束轴之间的对准误差。此外，为了根据EPID图像验证MLC位置的检测精度，评估了MLC在0.1-1毫米范围内故意设置误差的各种位置。其次，为了验证DWA照射期间的几何精度，考虑三个指标设计了测试。测试1评估了MLC位置的精度。测试2评估了在可变剂量率（160-400MU/分钟）、机架速度（2.2-6°/秒）和环形速度（0.5-2.7°/秒）下的剂量输出一致性。测试3验证了在上述参数加上MLC速度（1.6-4.2厘米/秒）的可变值下的剂量输出一致性。所有测试均输送至EPID，并与使用0°机架角度的固定辐射射束获得的测试结果进行比较。同时记录照射日志数据。EPID能够检测到MLC位置上0.1毫米的故意误差，该误差小于EPID像素尺寸。在测试1中，MLC狭缝宽度与其曝光值的偏差在0.20毫米以内。在测试2和测试3中，剂量输出的平均均方根误差（RMSE）小于0.8%。在测试3中使用日志数据分析，对于MLC位置、机架角度和环形角度，计划数据与记录数据之间的RMSE分别为0.1毫米、0.12°和0.07°。所提出的方法对于DWA精度的常规QA很有用。
