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Marshall, Jakob

University of British Columbia

Trajectory volumetric modulated arc therapy (VMAT) is an emerging technique in high precision radiation therapy. Trajectory VMAT permits modulated radiation treatment delivery using dynamic rotation of the treatment couch and linear accelerator gantry. The couch and gantry angles combine to alter the orientation of radiation beams incident on the patient deeming particularly useful for avoidance of organs at risk (OAR) while maintaining treatment coverage of the tumour. Trajectory VMAT treatment plans require optimization of the beam orientations (trajectory) and radiation modulation along the trajectory. A framework and algorithm for optimizing trajectory VMAT treatment plans is presented. The framework first optimizes the trajectory around the patient before incorporating modulation of the radiation beam using VMAT optimization. The trajectory optimization step relies on a dosimetric beam scoring map, termed the 4Pi intensity map, to rank beam orientations. The 4Pi intensity map characterizes the dosimetric contribution of each feasible beam orientation to the optimal solution with beams at each point on the 4Pi sphere. The 4Pi intensity map is shown to rank beam orientations based on their ability to treat the target volume and avoid OAR and healthy tissue exposure. Using Dijkstra’s shortest path algorithm, 3700 trajectories (with differing start and end points of the trajectory) are generated using the 4Pi intensity map. Each trajectory is re-optimized and evaluated on its dosimetric quality with the best trajectory taken as optimal. Optimization of the radiation modulation along the trajectory is performed using VMAT optimization to obtain the optimal trajectory VMAT treatment plan. The 4Pi intensity map was shown to encode the information provided by a geometric overlap map, a map used for trajectory optimization in the literature [1-3]. Trajectory VMAT treatment plans created with the developed framework were assessed on six patients with single brain lesions finding comparable or superior dosimetric quality to coplanar VMAT treatment plans optimized in the Eclipse treatment planning system. In total, the developed trajectory optimization framework presents an efficient pre-processing step to VMAT optimization to permit trajectory VMAT treatment planning in hopes of generating high quality treatment plans to improve patient outcomes.

Text

2022-08-12

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/82350

Medical Physics

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/