Monte Carlo simulation of 6-MV dynamic wave VMAT deliveries by Vero4DRT linear accelerator using EGSnrc moving sources.

Maryam Rostamzadeh,Roberto Fedrigo,Alanah Mary Bergman,Ante Mestrovic,Yoshitomo Ishihara,Mitsuhiro Nakamura,Ermias Gete,I Antoniu Popescu

doi:10.1002/acm2.13090

Abstract

The commissioning and benchmark of a Monte Carlo (MC) model of the 6‐MV Brainlab‐Mitsubishi Vero4DRT linear accelerator for the purpose of quality assurance of clinical dynamic wave arc (DWA) treatment plans is reported. Open‐source MC applications based on EGSnrc particle transport codes are used to simulate the medical linear accelerator head components. Complex radiotherapy irradiations can be simulated in a single MC run using a shared library format combined with BEAMnrc “source20.” Electron energy tuning is achieved by comparing measured vs simulated percentage depth doses (PDDs) for MLC‐defined field sizes in a water phantom. Electron spot size tuning is achieved by comparing measured and simulated inplane and crossplane beam profiles. DWA treatment plans generated from RayStation (RaySearch) treatment planning system (TPS) are simulated on voxelized (2.5 mm3) patient CT datasets. Planning target volume (PTV) and organs at risk (OAR) dose–volume histograms (DVHs) are compared to TPS‐calculated doses for clinically deliverable dynamic volumetric modulated arc therapy (VMAT) trajectories. MC simulations with an electron beam energy of 5.9 MeV and spot size FWHM of 1.9 mm had the closest agreement with measurement. DWA beam deliveries simulated on patient CT datasets results in DVH agreement with TPS‐calculated doses. PTV coverage agreed within 0.1% and OAR max doses (to 0.035 cc volume) agreed within 1 Gy. This MC model can be used as an independent dose calculation from the TPS and as a quality assurance tool for complex, dynamic radiotherapy treatment deliveries. Full patient CT treatment simulations are performed in a single Monte Carlo run in 23 min. Simulations are run in parallel using the Condor High‐Throughput Computing software1 on a cluster of eight servers. Each server has two physical processors (Intel Xeon CPU E5‐2650 0 @2.00 GHz), with 8 cores per CPU and two threads per core for 256 calculation nodes.

Highlights

The Brainlab‐Mitsubishi Vero4DRT platform (Brainlab AG, Munich, Germany) is a 6‐MV‐medical linear accelerator with an O‐ring gantry design.[1,2,3,4] It has two axes of beam rotation; longitudinal — achieved with an O‐ring gantry, and vertical — achieved with a floor‐ring rotation (Fig. 1).Unlike conventional linear accelerators, noncoplanar beam angles are achieved without moving the patient couch
The Vero4DRT has a unique clinical delivery mode called dynamic wave arc (DWA) which employs noncoplanar volumetric modulated arc therapy (VMAT) trajectories created by enabling simultaneous motion of the gantry and floor ring about the two axes of rotation.[5,6,7]
The goal of this study is to further develop the Ishihara et al Vero4DRT static beam linac model and introduce dynamic motions into the simulation to allow for efficient dose calculations on patient CT sets of the DWA beam delivery delivered by the Vero4DRT

Summary

Introduction

The Brainlab‐Mitsubishi Vero4DRT platform (Brainlab AG, Munich, Germany) is a 6‐MV‐medical linear accelerator with an O‐ring gantry design.[1,2,3,4] It has two axes of beam rotation; longitudinal — achieved with an O‐ring gantry, and vertical — achieved with a floor‐ring rotation (Fig. 1).Unlike conventional linear accelerators, noncoplanar beam angles are achieved without moving the patient couch (the unit moves around a stationary patient). The Brainlab‐Mitsubishi Vero4DRT platform (Brainlab AG, Munich, Germany) is a 6‐MV‐medical linear accelerator with an O‐ring gantry design.[1,2,3,4] It has two axes of beam rotation; longitudinal — achieved with an O‐ring gantry, and vertical — achieved with a floor‐ring rotation (Fig. 1). The Vero4DRT has a unique clinical delivery mode called dynamic wave arc (DWA) which employs noncoplanar VMAT trajectories created by enabling simultaneous motion of the gantry and floor ring about the two axes of rotation.[5,6,7] The unit is equipped with integrated, dual‐orthogonal kV image guidance systems (ExacTrac, Brainlab, Munich, Germany) and is cone‐beam CT (CBCT) capable. This MLC has 30 pairs of 5 mm width (at isocenter) tungsten leaves.[8]

Objectives

Methods

Results

Conclusion