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: