A novel compound 6D‐offset simulating phantom and quality assurance program for stereotactic image‐guided radiation therapy system

Dennis Yuen‐Kan Ngar,Wai‐Sang Poon,Michael Koon‐Ming Kam,Anthony Tak‐Cheung Chan,Michael Lok‐Man Cheung

doi:10.1120/jacmp.v14i6.4297

Dennis Yuen‐Kan Ngar, Wai‐Sang Poon + Show 3 more

Open Access

https://doi.org/10.1120/jacmp.v14i6.4297

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Abstract

A comprehensive quality assurance (QA) device cum program was developed for the commissioning and routine testing of the 6D IGRT systems. In this article, both the new QA system and the BrainLAB IGRT system which was added onto a Varian Clinac were evaluated. A novel compound 6D‐offset simulating phantom was designed and fabricated in the Prince of Wales Hospital (PWH), Hong Kong. The QA program generated random compound 6D‐offset values. The 6D phantom was simply set up and shifted accordingly. The BrainLAB ExacTrac X‐ray IGRT system detected the offsets and then corrected the phantom position automatically through the robotic couch. Routine QA works facilitated data analyses of the detection errors, the correction errors, and the correlations. Fifty sets of data acquired in 2011 in PWH were thoroughly analyzed. The 6D component detection errors and correction errors of the IGRT system were all within ±1mm and ±1° individually. Translational and rotational scalar resultant errors were found to be 0.50±0.27mmand0.54±0.23°, respectively. Most individual component errors were shown to be independent of their original offset values. The system characteristics were locally established. The BrainLAB 6D IGRT system added onto a regular linac is sufficiently precise for stereotactic RT This new QA methodology is competent to assure the IGRT system overall integrity. Annual grand analyses are recommended to check local system consistency and for external cross‐comparison. The target expansion policy of 1.5 mm 3D margin from CTV to PTV is confirmed for this IGRT system currently in PWH.PACS numbers: 87.53.Ly, 87.55.Gh, 87.55.Qr, 87.56.Fc

Highlights

101 Ngar et al.: Compound 6D phantom for Image-guided radiation therapy (IGRT) Quality assurance (QA) set up according to external surface marks such as skin marks and shell marks
BrainLAB ExacTrac X-ray system and the Novalis Linac system (BrainLAB AG) with built-in IGRT function claimed submillimeter accuracy and the static target positioning error of which had been reviewed over the past ten years.[3,4,8,9,10,11,12,13,14,15] One of the purposes of this paper is to investigate independently the accuracy of an add-on BrainLAB ExacTrac IGRT and Robotic 6D patient positioning system with the Varian iX linear accelerator installed in our center (Fig. 1)
Numerical data and statistical analyses According to the QA program and Fig. 9, 50 sets of compound random 6D offsets were generated, detected, and corrected on the 6D phantom and the IGRT system in one year, together with 25 sets of neutral configuration detection

Summary

Introduction

101 Ngar et al.: Compound 6D phantom for IGRT QA set up according to external surface marks such as skin marks and shell marks. Real-time images for IGRT can be obtained by two fixed oblique stereoscopic X-ray with flat-panel receivers, or by the built-in On-Board Imager moving isocentrically. The latter can even form 3D images through the cone-beam CT function. The CyberKnife system (Accuray Inc., Sunnyvale, CA) incorporates a 6D patient setup device

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