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Review
. 2022 Jul 13;11(14):4044.
doi: 10.3390/jcm11144044.

Towards Accurate and Precise Image-Guided Radiotherapy: Clinical Applications of the MR-Linac

James W Randall  1 , Nikhil Rammohan  1 , Indra J Das  1 , Poonam Yadav  1
Affiliations
Review

Towards Accurate and Precise Image-Guided Radiotherapy: Clinical Applications of the MR-Linac

James W Randall et al. J Clin Med. .

Abstract

Advances in image-guided radiotherapy have brought about improved oncologic outcomes and reduced toxicity. The next generation of image guidance in the form of magnetic resonance imaging (MRI) will improve visualization of tumors and make radiation treatment adaptation possible. In this review, we discuss the role that MRI plays in radiotherapy, with a focus on the integration of MRI with the linear accelerator. The MR linear accelerator (MR-Linac) will provide real-time imaging, help assess motion management, and provide online adaptive therapy. Potential advantages and the current state of these MR-Linacs are highlighted, with a discussion of six different clinical scenarios, leading into a discussion on the future role of these machines in clinical workflows.

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
The 30 Gy (yellow) isodose lines are displayed for original, predicted, and adapted plans, with PTV in red and stomach in brown. Clinically set constraint (0.03 cc < 30 Gy) achieved by the adapted plan (c) was comparable to the original plan (a), however the dose constraint for the predicted dose (b) was not met due to changes in stomach volume and positioning.
Figure 2
Figure 2
(a) Sagittal MR view of the pelvis with delineation of bowel and bladder volumes across multiple treatments using an MR-guided linear accelerator. (b) Dose volume histograms showing variability in received dose to the bladder (top) and rectum (bottom) across daily treatments depending on position and indicated by different line colors.
Figure 3
Figure 3
Comparison of different imaging modalities for the soft tissues of the abdomen. (a) Axial CBCT imaging of the liver taken on a conventional linear accelerator. (b) Axial CT slice of the abdomen used for planning with each organ of a similar electron density. (c) Axial slice of the abdomen acquired with 0.35 T MRI. (d) Axial slice of the abdomen using 1.5 T MRI. Lesion identification is much easier on both 0.35 and 1.5 T MRI images compared to CT and CBCT scans.
Figure 3
Figure 3
Comparison of different imaging modalities for the soft tissues of the abdomen. (a) Axial CBCT imaging of the liver taken on a conventional linear accelerator. (b) Axial CT slice of the abdomen used for planning with each organ of a similar electron density. (c) Axial slice of the abdomen acquired with 0.35 T MRI. (d) Axial slice of the abdomen using 1.5 T MRI. Lesion identification is much easier on both 0.35 and 1.5 T MRI images compared to CT and CBCT scans.
Figure 4
Figure 4
Treatment response assessment on serial MR images during a course of radiotherapy, with images moving chronologically from left to right. Note the visual reduction in gross tumor volume (pink) and overall reduction subsequently expanded target volume (red), as well as the freely mobile target in the abdominal cavity across multiple weeks.
See this image and copyright information in PMC

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