Abstract

PurposeTo perform quality assurance of non-coplanar, volumetric-modulated arc therapy featuring continuous couch rotation (CCR-VMAT) using a C-arm linear accelerator.MethodsWe planned and delivered CCR-VMAT using the TrueBeam Developer Mode. Treatment plans were created for both a C-shaped phantom and five prostate cancer patients using seven CCR trajectories that lacked collisions; we used RayStation software (ver. 4.7) to this end. Subsequently, verification plans were generated. The mean absolute error (MAE) between the center of an MV-imaged steel ball and the radiation field was calculated using the Winston–Lutz test. The MAEs between planned and actual irradiation values were also calculated from trajectory logs. In addition, correlation coefficients (r values) among the MAEs of gantry angle, couch angle, and multi-leaf collimator (MLC) position, and mechanical parameters including gantry speed, couch speed, MLC speed, and beam output, were estimated. The dosimetric accuracies of planned and measured values were also assessed using ArcCHECK.ResultsThe MAEs ±2 standard deviations as revealed by the Winston–Lutz test for all trajectories were 0.3 ± 0.3 mm in two dimensions. The MAEs of the gantry, couch, and MLC positions calculated from all trajectory logs were within 0.04°, 0.08°, and 0.02 mm, respectively. Deviations in the couch angle (r = 0.98, p < 0.05) and MLC position (r = 0.86, p < 0.05) increased significantly with speed. The MAE of the beam output error was less than 0.01 MU. The mean gamma passing rate ± 2 SD (range) of the 3%/3 mm, 3%/1 mm, and 5%/1 mm was 98.1 ± 1.9% (95.7–99.6%), 87.2 ± 2.8% (80.2–96.7%), and 96.3 ± 2.8% (93.9–99.6%), respectively.ConclusionsCCR-VMAT delivered via the TrueBeam Developer Mode was associated with high-level geometric and mechanical accuracy, thus affording to high dosimetric accuracy. The CCR-VMAT performance was stable regardless of the trajectory chosen.

Highlights

  • Today, 4π radiotherapy is recognized as a useful therapeutic approach ensuring target-dose conformity while sparing doses to organs-at-risk (OARs)

  • The dosimetric advantages of such therapy compared with coplanar intensity-modulated radiotherapy (IMRT) and volumetricmodulated arc therapy (VMAT) have been demonstrated in planning studies for many diseased sites including the brain [1, 2], head and neck [3, 4], liver [5], lung [6], breast [7] and prostate [8]

  • CCR-VMAT delivery in the TrueBeam developer mode From 24 trajectories of Dynamic WaveArc (DWA) plans available in RayStation, seven non-coplanar arc trajectories lacking collisions were selected with the help of an in-house collision map prepared for use with TrueBeam when ArcCHECK (Sun Nuclear, Melbourne, FL, USA) was placed on the ExacTrac X-Ray 6D couch (BrainLAB) (Fig. 1)

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Summary

Introduction

4π radiotherapy is recognized as a useful therapeutic approach ensuring target-dose conformity while sparing doses to organs-at-risk (OARs). 4π radiotherapy including 4π static beam radiotherapy and 4π arc beam radiotherapy has been clinically implemented using mono-isocentric beams. In a Phase 1 trial, Yu et al showed that 4π static beam radiotherapy was feasible and safe and associated with dosimetric benefits and high-level delivery efficiency when used to treat high-grade glioma [9]. One form of 4π arc beam radiotherapy, O-ring system-specific non-coplanar VMAT, termed Dynamic WaveArc (DWA), has been clinically implemented in the Vero4DRT system (Mitsubishi Heavy Industries, Ltd., Hiroshima, Japan; and BrainLAB AG, Munich, Germany) [10, 11]. High dose conformity and high-level delivery accuracy have been reported by several investigators [12,13,14]

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