(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: HyperArcᵀᴹ (Varian Medical Systems, Palo Alto, CA) is a planning and delivery system for VMAT SRS featuring a highly automated workflow. We report plan characteristics and quality assurance results for the first patient cohort treated in the Americas.
Methods: The cohort contained 23 plans and 62 targets, 11 single-target plans and 12 having 2 to 13 targets. The plans used a 10 MV flattening filter free beam and a multileaf collimator having 2.5 mm central and 5 mm peripheral leaf width. Dose was calculated on a 1 mm grid using the Analytical Anisotropic Algorithm version 13.6. The RTOG conformity index was calculated for each target. The Paddick gradient index and mean brain dose were calculated for each plan. Quality assurance was done for the smallest and largest targets using radiochromic film (EBT-XD, Ashland Chemical, Covington, KY) in an acrylic phantom. The phantom was positioned using image guidance. The film was registered to the treatment plan to obtain the residual geometric error and the film-to-plan ratio and gamma with criteria 1%/1mm were calculated.
Results: The median equivalent target diameter and CI were 7.6 mm (2.5 to 33.9) and 1.25 (0.98 to 3.24), respectively. CI was target size dependent, having median 1.10 (1.51) for equivalent diameter greater (less) than 7.6 mm. Median brain mean dose was 2.4% (1.3% to 9.7%) for single target plans and 10.5% (3.6% to 14.8%) for multitarget plans. The median gradient index was 4.00 (2.75 to 16.87). The median offset between film and plan was 0.28 mm (0.04 to 0.63). The mean film-to-plan dose ratio was 1.010 (0.968 to 1.050). The median fraction of pixels having gamma>1 was 2.4% (0.0% to 24.7%). Median beam-on to beam-off time was 3.0 minutes (2.3 to 18.0).
Conclusion: HyperArcᵀᴹ produces high quality VMAT SRS plans that are accurately and efficiently delivered.
Funding Support, Disclosures, and Conflict of Interest: UAB receives research funding from Varian Medical Systems. R Popple has received speaking honoraria from Varian Medical Systems.
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