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Creating Plans with the Benefits of the Conformal Arc Technique in the RayStation Treatment Planning System

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N Staley

N Staley*, D Pearson , University of Toledo, Toledo, OH


SU-I-GPD-T-561 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To establish a robust procedure for planning conformal arc-like plans in the RayStation treatment planning system (TPS) using VMAT optimization and to combine the dose gradient benefits of the conformal arc technique with the varying dose rates of VMAT.

Methods: Seven conformal arc SRS brain or SBRT lung patient plans created in Pinnacle³ were exported along with their dose distributions to the RayStation TPS. Using the same beam arrangements as the Pinnacle³ plans, combinations of VMAT optimization objectives and settings were used with the goal of reproducing the original conformal arc plans by forcing the MLC to take the shape of the PTV volumes while mimicking their PTV coverage and maximum point doses.

Results: A suitable procedure for optimizing conformal arc plans was established using two optimization objectives while making use of RayStation’s ability to limit MU and maximum delivery time per beam. The first objective was minimum dose to a contracted ROI based on the highest level PTV that acted like a conformal arc block, and the second was dose fall-off using the external ROI. Using this set of starting parameters, these objectives were adjusted over multiple optimizations to produce plans with dose distributions very similar to conformal arc plans. Gradient index values and maximum point doses were comparable between both plan sets. Paddick conformity index values were better for most RayStation plans due to slight modulation of the dose remaining after optimization.

Conclusion: The procedure was able to produce conformal arc-like plans for a variety of PTV shapes, sizes, and locations. The procedure allows users to make use of RayStation’s rapid optimization and dose calculation, allowing them to quickly produce feasible plans. Additionally, these plans benefit from both the steep dose fall-off of conformal arc plans and the highly conformal nature of VMAT plans.

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