Volume 34, Issue 1, January 2024, Pages 14-22Author links open overlay panel, ,

MR-Guided Radiation Therapy (MRIgRT) has been made possible only due to the ingenuity and commitment of commercial radiation therapy system vendors. Unlike conventional linear accelerator systems, MRIgRT systems have had to overcome significant and previously untested techniques to integrate the MRI systems with the radiation therapy delivery systems. Each of these three commercial systems has developed different approaches to integrating their MR and Linac functions. Each has also decided on a different main magnetic field strength, from 0.35T to 1.5T, as well as different design philosophies for other systems, such as the patient support assembly and treatment planning workflow. This paper is intended to provide the reader with a detailed understanding of each system's configuration so that the reader can better interpret the scientific literature concerning these commercial MRIgRT systems.

Section snippetsIntroduction to the 0.35T System

The first generation 0.35T system began as a Cobalt-driven radiation therapy machine (FDA cleared in 2012 with first patient treated in 2014).1,2 To accelerate the clinical application of MRgRT, the manufacturer used 3 Cobalt heads producing a total of 600 cGy per minute total at isocenter with fresh sources rather than await the MR-Linac development. In 2016 (FDA cleared in 2017), the manufacturer successfully modified their MRgRT system to utilize a linear accelerator, leading to the

Introduction to the 0.5T System

The rotating open bi-planar linac-MR system (Alberta LMR) was developed since 2005 and has installed at the Cross Cancer Institute (CCI) and University of Alberta (UofA), Edmonton, Alberta, Canada and shown in (Fig. 4). It has been commercialized in Edmonton. The system was designed from the ground up to specifically provide MR-guidance without compromising the advantages of current image guided radiotherapy practices. The open bi-planar design allows the option of placing the radiation beam

Extensive Couch Positioning for Planned or Offset Targets

On the LMR the Kevlar couch has a longitudinal length of 260 cm. There are  three translational degrees of freedom with maximum vertical speed of 5 cm/s and maximum horizontal speeds of 15 cm/s. It offers vertical and lateral ± 23 cm which makes it unique in this sector. This allows the positioning of any target, including targets that are strongly offset, at the planned position or at the isocenter. 3D target positioning is performed when these couch motions are used in tandem with the

Introduction to the 1.5T System

This section presents a brief overview of the development of the 1.5T MRIgRT system, a radiotherapy system with integrated 1.5T MRI functionality for high precision targeting (Fig. 5). The clinical potential and its applications are beyond the scope of this work, Hall et al.24 is one of the starting points for the clinical work related to the 1.5T system.

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