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Secondary MU Calculation for a New Jawless Double-Stacked Halcyon Machine Using a Virtual MLC Model

W Zou*, S Anamalayil , T Li , C Kennedy , R Scheuermann , T Zhu , L Dong , University of Pennsylvania, Philadelphia, PA


(Monday, 7/30/2018) 1:15 PM - 1:45 PM

Room: Exhibit Hall | Forum 7

Purpose: The Varian Halcyon machine uses a double-stacked MLC design which composes of two sets of MLC banks. However, most commercially available secondary MU verification systems only accept plans with one MLC bank. We developed a plan converter to adapt the Halcyon plans to an open jaw plan with one composite “virtual� MLC bank to be used in RadCalc software for secondary MU verification. The goal of this study is to validate this approach for secondary MU calculation.

Methods: The DLG and transmission factor of the double MLC banks were first characterized and built into the RadCalc beam model. A Matlab GUI application was developed to convert the Halcyon plans to DICOM open jaw plans with one MLC set of 116 leafs of 5 mm width with composite control points. The same composite MLC banks were setup in the RadCalc. Nine Halcyon plans defined in TG119 including IMRT and Arc plans calculated on phantoms were first used to verify the workflow. The patient Halcyon plans were then converted and imported to RadCalc for the secondary MU verifications.

Results: The TG119 verifications with 9 plans showed great agreement between the secondary MU and Eclipse calculation. The per field MU difference was -0.82±2.78%, and total point dose difference was 1.29±1.05%. 20 IMRT patients and 20 Arc therapy patients second MU verification results were randomly selected from our treatments since last October. The field MU difference was 0.87±3.87% and 0.62±2.40%, the dose calculation difference was for 1.94±0.88% and 0.66±0.95% for IMRT and Arc therapy respectively.

Conclusion: We have successfully implemented a Halcyon plan converter to adapt the jawless double-stacked MLC Halcyon plan to a plan with open jaw and one MLC bank which is compatible to the RadCalc software. This important second check for Halcyon plans was conveniently integrated into the clinical workflow.


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