School of Mathematical and Physical Sciences, University of Newcastle, Newcastle, NSW 2308, Australia.
Phys Med Biol. 2012 Jun 21;57(12):N209-24. doi: 10.1088/0031-9155/57/12/N209. Epub 2012 May 30.
In modern radiotherapy, it is vitally important to monitor the performance of all linac components including the collimation system. In this study, a simple measurement method and accurate algorithm are introduced for investigation of the secondary and tertiary collimator sag during radiotherapy arc treatments. The method is based on cine EPID images of a ball bearing marker fixed to the gantry head and determines the jaw and MLC sag in all directions relative to the reference at zero gantry angle. Analysis was performed using different field sizes and collimator angles, different linacs and different gantry rotation directions. The accuracy of the method was tested and was less than 0.02 mm. The repeatability and reproducibility of the method was 0.005 and 0.09 mm, respectively. The setup is easy and quick and the algorithm is fast and fully automatic with sub-pixel accuracy. This method is suitable to be included in the routine quality assurance of linacs to monitor the collimator system performance.
在现代放射治疗中，监测所有直线加速器组件的性能至关重要，包括准直系统。本研究提出了一种简单的测量方法和精确的算法，用于研究放射治疗弧形治疗过程中次级和三级准直器的下垂。该方法基于安装在机架头上的球轴承标记的电影 EPID 图像，确定相对于参考位置在零机架角度下的所有方向上的机架和叶片准直器的下垂。分析使用了不同的射野大小和准直器角度、不同的直线加速器和不同的机架旋转方向进行。该方法的准确性测试结果小于 0.02 毫米。该方法的重复性和再现性分别为 0.005 毫米和 0.09 毫米。设置简单快捷，算法快速且全自动，具有亚像素精度。这种方法适合纳入直线加速器的常规质量保证中，以监测准直器系统的性能。
