Commissioning and initial stereotactic ablative radiotherapy experience with Vero

Timothy D Solberg,Ezequiel Ramirez,Ryan D Foster,Paul M Medin,Chuxiong Ding,John Yordy

doi:10.1120/jacmp.v15i2.4685

Timothy D Solberg, Ezequiel Ramirez + Show 4 more

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https://doi.org/10.1120/jacmp.v15i2.4685

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Abstract

The purpose of this study is to describe the comprehensive commissioning process and initial clinical performance of the Vero linear accelerator, a new radiotherapy device recently installed at UT Southwestern Medical Center specifically developed for delivery of image‐guided stereotactic ablative radiotherapy (SABR). The Vero system utilizes a ring gantry to integrate a beam delivery platform with image guidance systems. The ring is capable of rotating ± 60° about the vertical axis to facilitate noncoplanar beam arrangements ideal for SABR delivery. The beam delivery platform consists of a 6 MV C‐band linac with a 60 leaf MLC projecting a maximum field size of 15×15 cm2 at isocenter. The Vero planning and delivery systems support a range of treatment techniques, including fixed beam conformal, dynamic conformal arcs, fixed gantry IMRT in either SMLC (step‐and‐shoot) or DMLC (dynamic) delivery, and hybrid arcs, which combines dynamic conformal arcs and fixed beam IMRT delivery. The accelerator and treatment head are mounted on a gimbal mechanism that allows the linac and MLC to pivot in two dimensions for tumor tracking. Two orthogonal kV imaging subsystems built into the ring facilitate both stereoscopic and volumetric (CBCT) image guidance. The system is also equipped with an always‐active electronic portal imaging device (EPID). We present our commissioning process and initial clinical experience focusing on SABR applications with the Vero, including: (1) beam data acquisition; (2) dosimetric commissioning of the treatment planning system, including evaluation of a Monte Carlo algorithm in a specially‐designed anthropomorphic thorax phantom; (3) validation using the Radiological Physics Center thorax, head and neck (IMRT), and spine credentialing phantoms; (4) end‐to‐end evaluation of IGRT localization accuracy; (5) ongoing system performance, including isocenter stability; and (6) clinical SABR applications.PACS number: 87.53.Ly

Highlights

206 Solberg et al.: stereotactic body radiation therapy (SBRT) experience with Vero applied in a number of extracranial disease sites
In this work we describe the clinical commissioning of the Vero system for stereotactic ablative radiotherapy (SABR) applications, using key AAPM and ASTRO documents to guide the process.[13,14] We focus on beam data acquisition and dosimetric commissioning of the treatment planning system and end-to-end evaluation of IGRT localization capabilities
Vero PDD are similar to that of another commercial unit routinely used for SABR, the Novalis Tx, which has a PDD of 85.9% at 5 cm depth for a 10 × 10 cm2 field relative to 86.2% for the Vero.[35]. The Vero reference PDD (100 cm source-to-surface distances (SSD), 10 × 10 cm2 field size, 10 cm depth) is 66.7%

Summary

Introduction

206 Solberg et al.: SBRT experience with Vero applied in a number of extracranial disease sites. Stereotactic ablative radiotherapy (SABR) holds significant potential for improving tumor control rates across a range of locations and histologies. SABR requires the use of technology at a standard above that routinely considered necessary for conformal radiotherapy and IMRT applications.[12,13,14] the processes often involve a number of disparate, but interconnected, elements including: immobilization, motion management, image guidance, small field dosimetry, and dose calculation through complex heterogeneities. In July 2011, a Vero linear accelerator (BrainLAB AG, Feldkirchen, Germany) was installed at the University of Texas Southwestern Medical Center to support our stereotactic ablative radiotherapy (SABR) programs.

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