Continuous aperture dose calculation and optimization for volumetric modulated arc therapy.

Continuous aperture dose calculation and optimization for volumetric modulated arc therapy.
Phys Med Biol. 2018 Oct 26;63(21):21NT01
Authors: Christiansen E, Heath E, Xu T
Abstract
Although VMAT delivery features continuous gantry rotation and leaf motion, dose calculation is often performed under the dual assumption of discrete apertures changing instantaneously from one discrete angle to the next. In this work, the validity of these two approximations is determined, as well as their impact on the quality of optimized plans. Further, an accurate method of fluence calculation is derived which does not use the discrete aperture approximation, but instead calculates the fluence as the multi-leaf collimator leaves sweep from one position to another. This continuous aperture fluence calculation is integrated in the VMAT optimization process using the open-source treatment planning system matRad. The three-step approach of VMAT optimization is used: fluence map optimization followed by leaf sequencing and direct aperture optimization, with variable leaf speed, gantry rotation speed, and MU rate. The benefit of the continuous aperture VMAT method over the discrete aperture method is determined by comparing the plan quality of discrete aperture and continuous aperture optimized plans, when the former is recalculated using the continuous aperture fluence calculation. Discrete aperture VMAT plans calculated at 4° spacing result in significan...

Source: Physics in Medicine and Biology - October 26, 2018 Category: Physics Authors: Christiansen E, Heath E, Xu T Tags: Phys Med Biol Source Type: research