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Session: Therapy General ePoster Viewing [Return to Session]

Independent Evaluation of MPC Using Winston-Lutz Test

W Luo*, M Halfman, University of Kentucky, Lexington, KY


PO-GePV-T-303 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: The Varian Machine Performance Check (MPC) system is a QA tool used to quickly test the functions and performance of the Varian TrueBeam and Halcyon. This study was to evaluate MPC with geometry test independently using the Winston-Lutz test.

Methods: MPC was performed on the Varian TrueBeam using an IsoCal phantom sitting on the six-degree-freedom treatment couch. Beam isocenter size/location, Isocenter coincidence, collimator rotation offset, gantry position accuracy, couch accuracy, MLC leaf position (inner leaves), and Jaw position are checked by MPC. The Winston-Lutz test (WL) was conducted with a 10x10x10cm3 plastic cube. A small metal ball (BB) sits in the center of the cube. The cube was set on the couch with the BB located at the isocenter. The WL results were analyzed using the Pylinac Winston-Lutz program.

Results: MPC performed six tests with the IsoCal phantom aligned with the isocenter, and three tests with the IsoCal phantom off the isocenter. Correspondingly, nine WL tests were performed. The average isocenter diameter measured by WL was 0.33 mm, and 0.35 mm by MPC with the IsoCal phantom aligne with the isocenter, and the difference was 0.02 mm. With the phantom off isocenter, the isocenter diameter was 0.32 mm in average for both WL and MPC.

Conclusion: MPC tests of the isocenter and couch are highly accurate. The accuracy of tests are not affected by phantom setup uncertainty and thus reliable. It is comparable with WL test in accuracy for isocenter test and also a convenient and efficient tool for SRS/SBRT QA.



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