SU‐E‐T‐150: Filmless Quality Assurance for Linear Accelerator with Electronic Portal Image Device

Abstract

Purpose: Our intention was to perform some machine quality assurance (QA) tests that require the use of films with electronic portal imaging device (EPID). A software tool was designed for these tasks which include Light vs Radiation Field, Isocenter Star Shot, Winston‐Lutz and MLC Picket Fence images. Methods: For Light vs Radiation Field, BB dots were placed on the tabletop to indicate the light field and double‐exposure technique was used to enhance the display of BB dots. For Table Isocenter Star Shot, a square field was used, and a steel ruler was placed on the table to show one of the major axis on the images. For Winston‐Lutz test, we placed a small steel ball at isocenter and irradiate it with a square field from various gantry angles. For MLC Picket Fence test, we used a multi‐segment MLC field to deliver six rectangular fields adjacent to each other. In addition to the composite image, the EPID also saved the image from each segment. Our software analyzed the images of all segments. Results: The ability to save multiple images without entering the treatment room greatly shortened the overall time spent. The test results of Light vs Radiation Field, Isocenter Star Shot and Winston‐Lutz from the EPID are similar to the film, except the image quality is much better on EPID images. A significant advantage of EPID is that individual image of every segment can be saved and analyzed; where as one cannot determine accurately the position errors on a composite image of film. This analysis of EPID based images facilitates easy calibration of MLC leaves Conclusions: Compared to film method, the EPID images are of higher quality and better consistency. The software we developed provides us with fast, convenient, and accurate analysis for this application.