TU-FG-201-02: Is Weekly MLC QA Necessary? Two Year EPID-Based Weekly MLC QA Experience at the University of Maryland

Abstract

Purpose: Appropriate MLC QA is important to assure treatment accuracy. In addition to the TG-142 recommended picket fence test, our institution performs four MLC tests on a weekly basis. The purpose of this study was to evaluate the clinical necessity of our weekly MLC QA program after a two-year run. Methods: Our Weekly MLC QA tests: 1) MLC positioning; 2) Interdigitation for testing hard MLC motion; 3) Picket fence at static gantry angle; 4) Leaf-end leakage and 5) dose match between a VMAT plan and the same plan with static-gantry-sliding window. For this study, a total of 794 Weekly MLC QA plans using EPID systems (3878 in total) for 10 machines from June 2014 to February 2016 were analyzed. Failure Mode Effect Analysis (FMEA) was performed with five failure modes. For each failure mode, a risk probability number (RPN) was calculated for a Weekly MLC QA (Monthly + Weekly) and for a Monthly MLC QA Only scheme. The probability of occurrence was evaluated from the Weekly QA experience. Results: Total number of failures for 794 cases were 24 (0.23%, for MLC Position test, 0.11% for Interdigitation test, 0.11% for Picket Fence Test, 0% for Leaf end Leakage test and 2.5% for VMAT test). The QA goal was to maintain the RPN score < 125. The RPN scores for the Monthly MLC QA Only ranged from 144–180, while those with Weekly (Monthly + Weekly) MLC QA decreased to 96–120. Conclusion: The Weekly MLC QA decreased the RPN numbers to the desired level (RPN<125), while those from the program of Monthly QA only were found to be higher or borderline. This objectively proves the clinical necessity for comprehensive weekly MLC QA.