Non-coplanar trajectories to improve organ at risk sparing in volumetric modulated arc therapy for primary brain tumors. Issue 1 (October 2016)

• Record Type: Journal Article
• Authors: Smyth, Gregory; Evans, Philip M.; Bamber, Jeffrey C.; Mandeville, Henry C.; Welsh, Liam C.; Saran, Frank H.; Bedford, James L.
• Is Part Of: Radiotherapy and oncology. Volume 121:Issue 1(2016:Oct.)
• Page Start: 124
• Page End: 131
• Publication Date: 2016-10
• Subjects: VMAT -- Non-coplanar -- Trajectory -- Optimization -- Treatment planning -- Hippocampal sparing; Oncology -- Periodicals; Radiotherapy -- Periodicals; Tumors -- Periodicals; Medical Oncology -- Periodicals; Neoplasms -- radiotherapy -- Periodicals; Radiotherapy -- Periodicals; Radiothérapie -- Périodiques; Cancérologie -- Périodiques; Tumeurs -- Périodiques; Electronic journals; 616.9940642
• DOI: 10.1016/j.radonc.2016.07.014
• Languages: English
• ISSNs: 0167-8140

Abstract

Abstract: Background and purpose: To evaluate non-coplanar volumetric modulated arc radiotherapy (VMAT) trajectories for organ at risk (OAR) sparing in primary brain tumor radiotherapy. Materials and methods: Fifteen patients were planned using coplanar VMAT and compared against non-coplanar VMAT plans for three trajectory optimization techniques. A geometric heuristic technique (GH) combined beam scoring and Dijkstra's algorithm to minimize the importance-weighted sum of OAR volumes irradiated. Fluence optimization was used to perform a local search around coplanar and GH trajectories, producing fluence-based local search (FBLS) and FBLS + GH trajectories respectively. Results: GH, FBLS, and FBLS + GH trajectories reduced doses to the contralateral globe, optic nerve, hippocampus, temporal lobe, and cochlea. However, FBLS increased dose to the ipsilateral lens, optic nerve and globe. Compared to GH, FBLS + GH increased dose to the ipsilateral temporal lobe and hippocampus, contralateral optics, and the brainstem and body. GH and FBLS + GH trajectories reduced bilateral hippocampi normal tissue complication probability ( p = 0.028 and p = 0.043, respectively). All techniques reduced PTV conformity; GH and FBLS + GH trajectories reduced homogeneity but less so for FBLS + GH. Conclusions: The geometric heuristic technique best spared OARs and reduced normal tissue complication probability, however incorporating fluence information into non-coplanar trajectory optimization maintained PTV homogeneity.