Three dimensional dose verification of VMAT plans using the Octavius 4D dosimetric system

Sankar Arumugam,Aitang Xing,David Thwaites,Lois Holloway,Tony Young

doi:10.1088/1742-6596/573/1/012081

Abstract

The Octavius 4D dosimetric system generates a 3D dose matrix based on a measured planar dose and user supplied Percentage Depth Dose (PDD) data. The accuracy of 3D dose matrices reconstructed by the Octavius 4D dosimetric system was systematically studied for an open static field, an open arc field and clinical VMAT plans. The Octavius reconstructed 3D dose matrices were compared with the Treatment Planning System (TPS) calculated 3D dose matrices using 3D gamma (γ) analysis with 2%/2mm and 3%/3mm tolerance criteria. The larger detector size in the 2D detector array of the Octavius system resulted in failed voxels in the high dose gradient regions. For the open arc fields mean (1σ) γ pass rates of 84.5(8.9) % and 94.2(4.5) % were observed with 2%/2mm and 3%/3mm tolerance criteria respectively and for clinical VMAT plans mean (1σ) γ pass rates of 86.8(3.5) % and 96.7(1.4) % were observed.

Highlights

Modern radiotherapy techniques are highly complex and Volumetric Modulated Arc Therapy (VMAT) follows the same trend [1, 2]
The accuracy of 3D dose matrices reconstructed by the Octavius 4D dosimetric system was systematically studied for an open static field, an open arc field and clinical VMAT plans
In this work we present the validation of the Octavius 4D system for the dosimetric validation of VMAT plans with an ElektaSynergy linac

Summary

Introduction

Modern radiotherapy techniques are highly complex and Volumetric Modulated Arc Therapy (VMAT) follows the same trend [1, 2]. Three dimensional dose verification of VMAT plans is recommended to ensure the dosimetric accuracy of treatment delivery [3]. Gel dosimeters offer high resolution 3D information of delivered dose [4, 5]. Octavius 4D (PTW, Freiburg, Germany), is one such system that provides measured 3D dose matrices of the VMAT plans. In their work the synchrony of the Octavius 4D rotational unit with Linac gantry was tested for discrete gantry angles. In this work we present the validation of the Octavius 4D system for the dosimetric validation of VMAT plans with an ElektaSynergy linac. We tested the synchrony of the Octavius 4D rotational unit with linac gantry throughout arc delivery at six different gantry speeds including minimum and maximum speed of the gantry.

Octavius 4D dosimetric system

Results and Discussion

Conclusion