Commissioning and initial stereotactic ablative radiotherapy experience with Vero

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

Characteristics and performance of the first commercial multileaf collimator for a robotic radiosurgery system

“…At this point, dynamic use of the InCise™ MLC is not implemented. Our leaf travel tests have yielded speeds that are lower than some currently available dynamic MLCs, 19,20,26 but still considered sufficient for dynamic delivery. 27 In this sense, the characteristics of the InCise™ MLC do not seem to prohibit dynamic techniques as a potential future application.…”

“…Fischer et al 17 and García-Garduño et al 18 determined penumbrae of around 2.5 mm, in a slightly different measurement setup. Sharma et al 19 found a range of 2-4 mm for 6 MV delivery modes and different field sizes, and Solberg et al 20 reported around 4.5 mm for a 10×10 cm 2 field on a gimbaled Linac. It is important to keep in mind that different exposure conditions chosen by various authors have an impact on numerical results and impede direct comparability.…”

Image-guided radiotherapy and motion management in lung cancer

“…The newer Vero® (BrainLab AG) dynamic tracking system is in clinical use in only few clinics (only two reported in literature 38,39 ). The machinery is very different from that of the CyberKnife, using a gimballed treatment head mounted on an O-ring, but the principles of the tracking monitoring and driving systems are very similar to those of the CyberKnife described above.…”

Lateral head flexion as a noncoplanar solution for ring gantry stereotactic radiosurgery

“…However, the inability to delivery noncoplanar beams or arcs may limit the ability to achieve the highly conformal plans required for high quality SRS treatment. There have been some solutions to this problem proposed before that rely on using hardware modifications using a simple gantry tilt, or a more complex solution by mounting the treatment head on gimbals . The purpose of this work is to study the feasibility of a new treatment technique that takes advantage of normal neck motion to change the head position in order to increase beam entrance angles in a ring‐gantry geometry.…”

“…There have been some solutions to this problem proposed before that rely on using hardware modifications using a simple gantry tilt, 13 or a more complex solution by mounting the treatment head on gimbals. 14,15 The purpose of this work is to study the feasibility of a new treatment technique that takes advantage of normal neck motion to change the head position in order to increase beam entrance angles in a ring-gantry geometry. The range of lateral head flexion is evaluated as a means to approximate a couch rotation.…”