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SU-E-T-436: Fluence-Based Trajectory Optimization for Non-Coplanar VMAT.

Smyth, G, Evans, PM, Bamber, JC, Saran, FH, Mandeville, HC and Bedford, JL (2015) SU-E-T-436: Fluence-Based Trajectory Optimization for Non-Coplanar VMAT. Medical Physics, 42 (6).

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PURPOSE: To investigate a fluence-based trajectory optimization technique for non-coplanar VMAT for brain cancer. METHODS: Single-arc non-coplanar VMAT trajectories were determined using a heuristic technique for five patients. Organ at risk (OAR) volume intersected during raytracing was minimized for two cases: absolute volume and the sum of relative volumes weighted by OAR importance. These trajectories and coplanar VMAT formed starting points for the fluence-based optimization method. Iterative least squares optimization was performed on control points 24° apart in gantry rotation. Optimization minimized the root-mean-square (RMS) deviation of PTV dose from the prescription (relative importance 100), maximum dose to the brainstem (10), optic chiasm (5), globes (5) and optic nerves (5), plus mean dose to the lenses (5), hippocampi (3), temporal lobes (2), cochleae (1) and brain excluding other regions of interest (1). Control point couch rotations were varied in steps of up to 10° and accepted if the cost function improved. Final treatment plans were optimized with the same objectives in an in-house planning system and evaluated using a composite metric - the sum of optimization metrics weighted by importance. RESULTS: The composite metric decreased with fluence-based optimization in 14 of the 15 plans. In the remaining case its overall value, and the PTV and OAR components, were unchanged but the balance of OAR sparing differed. PTV RMS deviation was improved in 13 cases and unchanged in two. The OAR component was reduced in 13 plans. In one case the OAR component increased but the composite metric decreased - a 4 Gy increase in OAR metrics was balanced by a reduction in PTV RMS deviation from 2.8% to 2.6%. CONCLUSION: Fluence-based trajectory optimization improved plan quality as defined by the composite metric. While dose differences were case specific, fluence-based optimization improved both PTV and OAR dosimetry in 80% of cases.

Item Type: Article
Subjects : Electronic Engineering
Divisions : Faculty of Engineering and Physical Sciences > Electronic Engineering
Authors :
Smyth, G
Evans, PM
Bamber, JC
Saran, FH
Mandeville, HC
Bedford, JL
Date : June 2015
DOI : 10.1118/1.4924797
Copyright Disclaimer : © 2015 American Association of Physicists in Medicine. 4. This is the peer reviewed version of the following article: Smyth, G., Evans, P., Bamber, J., Saran, F., Mandeville, H. and Bedford, J. (2015), SU-E-T-436: Fluence-Based Trajectory Optimization for Non-Coplanar VMAT. Med. Phys., 42: 3434. which has been published in final form at 10.1118/1.4924797. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving
Uncontrolled Keywords : Optimization; Brain; Auditory system; Dosimetry; Cancer; Lenses
Depositing User : Symplectic Elements
Date Deposited : 01 Mar 2017 09:23
Last Modified : 31 Oct 2017 19:03

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