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A Winston-Lutz Test Based High Resolution Quality Assurance Protocol for Auto-Driving Couch System for Stereotactic Radiosurgery

K Li1*, (1)John R Marsh Cancer Center, (2) Associates In Medical Physics, Hagerstown, MD


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To develop a quality assurance procedure for auto-driving couch system with Winston-Lutz test.

Methods: A Varian Truebeam Linac based SRS system with 6-degree Perfect Pitch couch was employed for this study. A metal ball with 5mm diameter was initially placed at the isocenter based on the light field cross hair with a 17.5mm Cone mounted on Linac gantry. Six unit-displacements were generated in vertical, longitudinal, lateral direction, rotation, pitch and roll. And a 8-step loop was formed after driving the couch from initial position to all the designed positions and then back to the original position. And the execution of this unit displacement vector loop map was done by automatic driving couch at outside system console. For each step, a Winston-Lutz test was done with gantry rotation at 0, 90, 180, and 270 degree, with collimator rotation at 45, 90, 270 and 315 degree, and couch rotation at 45, 90, 270, and 315 degree. And the MV imager was used to collect all the images. Then DoseLab software from Mobius Medical System was applied to analyze these image sets.

Results: Given the metal ball position in this study, at each step the corresponding magnitudes in millimeter for delta x were -0.03, -0.02, -0.02, 1.15, 1.16, 1.10, 1.20 and 0.14; for delta y were -0.32, -0.42, 0.66, 0.66, 0.67, 0.48, 0.46, and -0.35; for delta z were 0.73, -0.52, -0.51, -0.53, -0.52, -0.47, -0.47, and 0.51; and in total delta displacement were 0.89, 0.88, 1.22, 1.48, 1.50, 1.37, 1.45 and 0.84.

Conclusion: Winston-Lutz test could be applied in quality assurance test for auto-driving couch system with high sensitivity. And the procedure could be simplified through composition and decomposition methods. Furthermore, this principle could be implemented in other auto-driving systems in radiotherapy


Stereotactic Radiosurgery, Quality Assurance, Localization


Education: Knowledge of methodology

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