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A Method to Improve Accuracy and Workflow of Single Isocenter Volumetric Modulated Arc Therapy (VMAT) for Frame-Based Radiosurgery of Multiple Metastases

K Ahn

K Ahn1, 2*, M Malin2 , K Yenice2 , N Ozturk1, 2 , B Smith1 , K Slavin1 , M Koshy1, 2 , B Aydogan1, 2 , (1) University of Illinois at Chicago, Chicago, IL, (2) The University of Chicago, Chicago, IL


SU-I-GPD-T-621 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Single-isocenter volumetric modulated arc therapy (VMAT) techniques can provide comparable SRS plan quality with improved delivery efficiency for treating multiple metastases. Nevertheless, planning is time consuming and verification of frame-based setup and delivery accuracy, especially at non-coplanar angles, can be challenging. We investigated the feasibility of a single-isocenter VMAT technique with a special focus on improving treatment workflow as well as setup and delivery verification for frame-based SRS of multiple metastases.

Methods: We developed a preplanning protocol for RapidArc (Varian Medical Systems) that uses pretreatment MR images for contouring and dose calculations. Preplans based on the MRI dataset were saved as template and used to generate comparable treatment plans using the CT image set taken on the day of treatment after frame placement. Delivery accuracy of non-coplanar arcs was evaluated by two different localization methods: 1) Integrated Calypso surface beacon with the OBI kV-imaging, 2) Stereoscopic in-room kV-imaging (Brainlab ExacTrac). Dosimetric and spatial delivery accuracy was validated with Gafchromic EBT3 film (Ashland) embedded in a Lucy phantom (Standard Imaging).

Results: Treatment goals set at the MRI preplanning phase were achieved in the final plans with a considerable reduction of planning time (ranging from 2 to 4 fold) on the day of delivery. Both MR and CT based plans achieved tumor prescription dose coverage of 99% with conformity indices < 1.2, and less than 10% variation in 12-Gy isodose volume for tumors of 1 cc – 7 cc volume. Film analysis confirmed 3%-1mm gamma passing rates > 95% using both localization methods.

Conclusion: We devised a practical approach to improve plan quality, treatment day workflow and delivery accuracy of frame-based non-coplanar single-isocenter RapidArc SRS treatment. This approach allows for efficient planning and accurate delivery of SRS for multiple metastasis with appropriate quality checks and verification on the day of procedure.

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