Abstract
BackgroundThe aim of this study was to investigate the dosimetric quality in volumetric modulated arc therapy (VMAT) plans with optimal collimator angles that can represent the outline of multiple brain targets.MethodsTwenty patients with multiple target volumes in the brain cases were selected retrospectively. To better represent the outline of the multiple brain targets, four conformal arc plans were generated for each patient using one full arc with four collimator settings. The optimal collimator angles calculated from the integrated multi-leaf collimator (MLC) aperture that had the smallest aperture size for certain collimator settings of the conformal arc plan were selected. VMAT plans with the optimal collimator angles with angular sections of 40° and 60° (Colli-VMAT (40°), Colli-VMAT (60°)) were generated, followed by evaluation of field sizes, dose-volumetric parameters and total monitor units (MUs).ResultsPatient-averaged values of field sizes for Colli-VMAT (40°) (111.5 cm2) were lowest and 1.3 times smaller than those for Std-VMAT (143.6 cm2). Colli-VMAT plans improved sparing of most normal organs but for brain stem and left parotid gland. For the total MUs, the averaged values obtained with the Colli-VMAT (40°) (390 ± 148 MU) were smaller than those obtained with the Std-VMAT (472 ± 235 MU).ConclusionsThe Colli-VMAT plans with smaller angular sections could be suitable in the clinic for multiple brain targets as well as for irregularly shaped targets. Determination of the optimal collimator rotation generally showed good normal tissue sparing and MU reduction for multiple brain targets.
Highlights
The aim of this study was to investigate the dosimetric quality in volumetric modulated arc therapy (VMAT) plans with optimal collimator angles that can represent the outline of multiple brain targets
Planning studies have consistently demonstrated that VMAT plans show equivalent dosimetric plan quality and usually reduce monitor unit (MU) usage compared to intensity-modulated radiation therapy (IMRT) [3,4,5]
Conformal arc plans generated with four collimator settings suggested in this study were adopted to calculate the optimal collimator angles in the VMAT plans, and the results of this study showed a noticeable improvement for the dosimetric plan quality and reduction of the total MUs as compared to Colli-VMATPre plans
Summary
The aim of this study was to investigate the dosimetric quality in volumetric modulated arc therapy (VMAT) plans with optimal collimator angles that can represent the outline of multiple brain targets. Planning studies have consistently demonstrated that VMAT plans show equivalent dosimetric plan quality and usually reduce monitor unit (MU) usage compared to intensity-modulated radiation therapy (IMRT) [3,4,5]. Because of these reasons, VMAT has been widely used for various treatment sites clinically [6,7,8,9,10,11]. In EclipseTM (Varian Medical Systems, Palo Alto, CA), the recommended collimator angles for VMAT plan optimization are collimator rotations of 10° (350°) and 30° (330°) for most cases [13]
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