Department of Radiation Oncology, Duke University Medical Center, Durham, NC 27707, USA.
Phys Med Biol. 2012 Oct 21;57(20):6587-600. doi: 10.1088/0031-9155/57/20/6587. Epub 2012 Sep 25.
We propose a method to incorporate independent verification of gantry angle for electronic portal imaging device (EPID)-based pre-treatment quality assurance (QA) of clinical volumetric modulated arc therapy (VMAT) plans. Gantry angle is measured using projections in the EPID of a custom phantom placed on the couch and the treatment plan is modified so as to be incident on the phantom with a portion of the beam that is collimated in the clinical plan. For our implementation, collimator and couch angles were set to zero and the inferior jaw and two most inferior multi-leaf collimator pairs were opened for the entire QA delivery. A phantom containing five gold coils was used to measure the gantry rotation through which each portal image was acquired. We performed the EPID QA for ten clinical plans and evaluated accuracy of gantry angle measurement, scatter incident on the imager due to the phantom, inter-image pixel linearity and inter- and intra-image noise. The gantry angle could be measured to within 0.0 ± 0.3° for static gantry and 0.2 ± 0.2° for arc acquisitions. Scatter due to the presence of the phantom was negligible. The procedure was shown to be feasible and adds gantry angle to the treatment planning parameters that can be verified by EPID-based pre-treatment VMAT QA.
我们提出了一种方法，将独立验证机架角度纳入电子射野影像装置（EPID）用于临床容积旋转调强弧形治疗（VMAT）计划的治疗前质量保证（QA）中。使用放置在治疗床的定制体模的 EPID 中的投影来测量机架角度，并修改治疗计划，以使部分光束以在临床计划中准直的方式入射到体模上。对于我们的实施方式，将准直器和治疗床角度设置为零，并打开下颚和两个最下面的多叶准直器对，以进行整个 QA 交付。一个包含五个金线圈的体模用于测量机架旋转，通过该旋转获取每个射野图像。我们对十个临床计划进行了 EPID QA，并评估了机架角度测量的准确性、由于体模而导致的落在成像仪上的散射、图像间像素线性度以及图像内和图像间噪声。对于静态机架，可以将机架角度测量到 0.0 ± 0.3°以内，对于弧形采集，可以测量到 0.2 ± 0.2°以内。由于体模的存在而导致的散射可以忽略不计。该程序被证明是可行的，并将机架角度添加到可以通过基于 EPID 的治疗前 VMAT QA 验证的治疗计划参数中。
