TQ08-Quality assurance of multileaf collimator leaf (MLC) using radiographic film and/or electronic portal image device (EPID)

Lei Xing

Department of Radiation Oncology,

Stanford University, Stanford, CA 94305-5847

The success of an IMRT treatment critically depends on the positioning accuracy of the MLC leaves for both step-and-shoot and dynamic deliveries. In this talk, I will summarize the commonly used MLC quality assurance (QA) procedure for IMRT. In particular, I will describe the methods and tools used for checking the accuracy of MLC leaf positions.  In addition to the conventional film-based approach, I will talk about a novel EPID-based technique, with which it is now possible to quantitatively detect an error of ~0.3mm in any leaf at any location within the 40X40cm field. Different from the commonly used edge-searching approach, which detect a potential leaf displacement purely based on the gray scale change of the acquired image at the edge of a leaf end, the new technique utilizes the fact that the integral signal in small region of interest (ROI) is a more sensitive and reliable indicator of the displacements of the MLC leaves above the area. I point out that the relation between the integral signal and the leaf displacement (including the adjacent leaf errors) can be pre-established and used subsequently as a quantitative means for detecting possible leaf positional errors:

TQ08-使用放射胶片和电子射野影像装置的多叶光栅（MLC）质量保证

Lei Xing

Department of Radiation Oncology,

Stanford University, Stanford, CA 94305-5847

无论是静态还是动态，调强治疗的成功都依赖于MLC叶片的定位精确度。下面我要总结在调强放疗中的常用MLC质量保证程序。我还要详细介绍用于检测MLC叶片定位精确度的方法和工具。除了传统的基于胶片的方法，我会介绍一种新的基于电子射野影像装置的技术，使用它可以在40×40cm射野内的任意叶片位置探测到0.3mm左右的误差。与常用的边缘寻找方法不同，它完全通过在叶片边缘采集的图像的灰度的改变来探测潜在的偏移，新技术的原理是在小的感兴趣区域（ROI）内的积今信号是MLC叶片位置偏移的更敏感、更可靠的指示器。我要指出的是积分信号和叶片位置偏移（包括相邻叶片误差）之间的关系能够被预先设定且作为一个定量的工具，用于随后的可能的叶片位置误差的探测。