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Planning and Delivery of Fully Dynamic Trajectory Modulated Arc Therapy On Pituitary Adenoma: Dosimetric Advantages Over Conventional Volumetric Modulated Arc Therapy

J Liang

J Liang1*, D Hristov2 , K Otto3 , S Kim1 , (1) Department of Radiation Oncology, Virginia Commonwealth University, Virginia (2) Department of Radiation Oncology, Stanford University, California (3) Department of Physics, University of British Columbia, British Columbia


TU-CD-304-2 (Tuesday, July 14, 2015) 10:15 AM - 12:15 PM Room: 304

Purpose: To assess the potential benefit of trajectory modulated arc therapy (TMAT) for treatments of small benign intracranial tumor, pituitary adenoma.

Methods: A TMAT planning platform that incorporates complex source motion trajectory involving synchronized gantry rotation with translational and rotational couch movement was used for the study. The platform couples an interactive trajectory generation tool with a VMAT algorithm that performs multi-resolution, progressive sampling MLC optimization on a user-designed trajectory. A continuous couch rotation of 160° angular span with ±20° mini gantry arcs was used to emulate a non-coplanar horizontal arc-like trajectory. Compared to conventional non-coplanar gantry arcs (60°-100° gantry rotation with couch kicks), TMAT limited the unnecessary low to medium dose spread in the anterior and posterior directions, where primary OARs (e.g., brainstem, optic chiasm, optic nerves, and lens) are in close proximity to the targeted pituitary tumor volume. For 5 standard fractionation pituitary adenoma cases (50.4Gy/28fractions), TMAT and non-coplanar VMAT plans were generated and compared under equivalent objectives/constraints. TMAT delivery was implemented and demonstrated on Varian TrueBeam via XML scripts.

Results: Both techniques showed good target coverage while OARs were able to meet the constraints on QUANTEC guidelines. Notably, TMAT decreased the dose deposition in the anterior-to-posterior direction surrounding PTV. TMAT significantly reduced the mean doses on brainstem, optic nerves, eyes and lens by 47.29%±13.17%, 28.51%±8.68%, 80.82%±8.71% and 65.38%±19.99% compared with VMAT, all p≤0.01. Percentage reductions of maximum point dose in eyes and lens were 75.68%±10.30% and 70.72%±18.62% respectively for TMAT versus VMAT, all p≤0.01. A representative isocentric TMAT pituitary plan was delivered via an XML script with 200 control points and 282 MUs.

Conclusion: Deliverable TMAT plans were achieved in developer mode in TrueBeam. TMAT was shown to be superior for pituitary adenoma irradiation in terms of OARs sparing.

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