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Dynamic Wave Arc Trajectory Verification Using KV X-Ray Fluoroscopy

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M BURGHELEA*, K Poels , T Depuydt , K Tournel , D Verellen , M De Ridder , Universitair Ziekenhuis Brussel, Jette, Brussel


SU-E-T-140 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:Purpose: This study investigates the geometric accuracy of simultaneous Gantry/Ring rotation during Dynamic Wave Arc (DWA) delivery.
Methods: The Vero SBRT system consists of a 6MV LINAC mounted on an O-ring gantry that can rotate around the vertical axis (±60⁰), similar to couch rotation on C-arm gantries. To provide CBCT and fluoroscopy imaging functionalities, two orthogonal kV imaging units are attached to the O-ring at -45⁰/+45⁰ from the beam axis.
Dynamic Wave Arc maximizes Vero’s motion capabilities by employing synchronized gantry and ring motion on a complex non-coplanar trajectory in combination with aperture based optimized MLC segments.
Four wave arc trajectories (T1-4) were delivered using a cubic phantom with a configuration of five lead beads. O-ring gantry position information was retrieved through continuous dual-source kV X-ray image acquisition during DWA. An in-house algorithm read in the image set, extracted the projected marker positions and determined the angulation through reconstruction of the beam source position. The geometric error was quantified as the distance between the independently detected positions from kV-images and reference trajectory derived from the treatment plan in the Ring-Gantry space.
Results: The average displacement between the 3D gantry/ring positions reconstructed from the fluoroscopy images and the reference trajectory was 0.346 mm (SD 0,171) for T1. A mean offset of 0.348 mm (SD 0,182) and 0.357 mm (SD 0.194) was observed for trajectory T2(2segmens) and T3(4segments), respectively. The saw shape T4 presented a mean geometric error of 0.363 (SD 0.156). The overall systematic error of 0.350 was caused by the difference between planned reference trajectory created by linear interpolation between CP, and the machine delivery following a spline curve.
Conclusion: An independent geometric QA approach has been developed for DWA delivery verification, successfully applied on diverse trajectories and disclosed that the Vero system is capable of accurately follow complex trajectories.

Funding Support, Disclosures, and Conflict of Interest: The first author is financially sustained by Brainlab AG (Feldkirchen, Germany). This collaborative work was supported by the Flemish government through the Hercules foundation and the Fonds voor Wetenschappelijk Onderzoek Vlaanderen Grants G.0486.06 and G.0412.08.

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