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Non-Coplanar Volumetric-Modulated Arc Therapy Versus Proton Experiences with Planning, Quality Assurance and Delivery for Skull Base Tumors

J Syh

J Syh*, G Schimke , M Waddell , Willis-Knighton Medical Center, Shreveport, LA


SU-I-GPD-T-566 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Volumatic-modulated arc therapy (VMAT) is characterized by variable gantry rotation speed, leaf traveling speed in beam blocking device and variable dose rate during the beam delivery. The clinical experience we had with plan quality, dose delivery quality assurance with phantom measurements, and pre-treatment machine QA was a tedious process.

Methods: Photon beam of 6 MV was employed for planning and delivery using VMAT(SRS) technique for base of skull tumors. Four non-coplanar arcs were used with couch and collimator rotations. Arc beams were delivered as partial arcs when necessary to limit dose to organs at risk (OAR’s) such as the eye, lens, brainstem and optical chiasm. Proton treatment plans with multiple fields were generated using pencil beam algorithm in the same treatment planning system for each case. The same plan objectives were set as clinical goals for both planning techniques.

Results: For a VMAT(SRS) plans with non-coplanar arcs, the average gantry speed was 5.3 degree/second with optimized variable dose rate to deliver 90 control points at most if 4 degree gantry interval is selected per arc. In contrary, proton plans with either oblique beams or orthogonal beams were used for delivery. Multiple Dose Volume Histograms (DVH) for both techniques were compared.

Conclusion: An analysis of dosimetric characteristics with regards to doses to the OAR’s was demonstrated by DVH comparison. The advantages and limitations of each individual technique addressed here were not inclusive of the fundamental radio-biological principles of each.

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