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Review
. 2022 Aug 12;11(16):4730.
doi: 10.3390/jcm11164730.

History of Technological Advancements towards MR-Linac: The Future of Image-Guided Radiotherapy

Nikhil Rammohan  1 , James W Randall  1 , Poonam Yadav  1
Affiliations
Review

History of Technological Advancements towards MR-Linac: The Future of Image-Guided Radiotherapy

Nikhil Rammohan et al. J Clin Med. .

Abstract

Image-guided radiotherapy (IGRT) enables optimal tumor targeting and sparing of organs-at-risk, which ultimately results in improved outcomes for patients. Magnetic resonance imaging (MRI) revolutionized diagnostic imaging with its superior soft tissue contrast, high spatiotemporal resolution, and freedom from ionizing radiation exposure. Over the past few years there has been burgeoning interest in MR-guided radiotherapy (MRgRT) to overcome current challenges in X-ray-based IGRT, including but not limited to, suboptimal soft tissue contrast, lack of efficient daily adaptation, and incremental exposure to ionizing radiation. In this review, we present an overview of the technologic advancements in IGRT that led to MRI-linear accelerator (MRL) integration. Our report is organized in three parts: (1) a historical timeline tracing the origins of radiotherapy and evolution of IGRT, (2) currently available MRL technology, and (3) future directions and aspirations for MRL applications.

Keywords: IGRT; MRgRT; adaptive therapy; image-guided radiotherapy; linear accelerator; magnetic resonance; radiotherapy.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Registration of cone beam CT obtained in treatment position on treatment machine to planning CT scan for abdominal RT in three dimensions: (a) coronal, (b) axial, and (c) sagittal slices each illustrate the registration between the CT scans used on the treatment machine to ensure alignment.
Figure 2
Figure 2
Step and Shoot IMRT with tangential approach used for treating breast cancer. Note the interdigitation of the MLCs that are used to modulate dose received with each treatment segment or configuration of leaves.
Figure 3
Figure 3
Inverse Planning IMRT used to create a more complex treatment plan for a head and neck case. Note the highly conformal dose distribution (left) panel and the multiple beams (right) panel, each with a unique MLC configuration, as can be noted on yellow beam.
Figure 4
Figure 4
Volumetric modulated arc therapy treatment technique illustrated in (left) two dimensions and (right) three dimensions. Note the sweeping, continuous arc motion around the patient.
Figure 5
Figure 5
ViewRay MRIdian MRL model that replaced the initial tri-cobalt design in 2017.
Figure 6
Figure 6
Adapted radiotherapy plan on ViewRay MRIdian for abdominal target. (a) The predicted plan was found to have inadequate target coverage and/or OAR sparing (blue color) and (b) was adapted to produce the reoptimized plan. Note the change in dose to stomach on the axial slice.
See this image and copyright information in PMC

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