Dosimetric Effects of Gantry Angular Acceleration and Deceleration in Volumetric Modulated Radiation Therapy

Abstract

Preliminary studies have shown that Volumetric modulated radiation therapy (VMAT) is a promising and competitive radiation treatment modality and could replace conventional intensity modulated radiation therapy (IMRT) for certain disease sites. Contrast to direct aperture optimization (DAO) adopted in intensity modulated arc therapy (IMAT), where MLC apertures are pre-defined and are not included in optimization, VMAT optimizes both MLC apertures and monitor unit (MU) weights. In addition, VMAT uses a much higher gantry angle sampling frequency to better model the continuously moving source. Thus, a desirable dose distribution can be achieved through MLC aperture modulation, dose rate modulation, and gantry angular speed modulation. Unlike conventional rotational techniques, in which the gantry rotates at a uniform angular speed from one segment to the next during treatment, VMAT requires the gantry to accelerate and decelerate frequently to deliver a given angular dose rate (MU/degree). This could potentially become a source of dosimetric error and compromise the plan quality. In this study, we investigated the dosimetric effects of gantry angular acceleration and deceleration in VMAT. Here, we report our initial results of the study. As far as we know, this is the first study of this kind on VMAT and RapidArc in the field.