Applicability of MRI-only technique in external beam radiotherapy: Dosimetric evaluation, IGRT, and quality assurance...

Magnetic Resonance Imaging (MRI) provides superior soft tissue contrast compared to planning Computed Tomography (pCT). Although pCT remains the standard method in radiotherapy planning due to its provision of electron density information required for dose calculations, the MRI-only technique can replace pCT by generating synthetic CTs (sCTs) that supply the necessary density data.

A systematic literature review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The literature search was performed in April 2025 across the PubMed, Scopus, and Web of Science databases, applying inclusion and exclusion criteria defined using the PICOS model. The included studies were assessed using the "Appraising the Evidence: Reviewing Disparate Data Systematically" tool, and extracted data were synthesised in a narrative summary table.

A total of 41 studies were included, covering different anatomical regions. The studies reported non-significant differences in dose-volume histograms (DVH) between sCT and CT. Gamma analysis conformity evaluations showed pass rates >87.4 %. The deviations across various image registrations remained <2 mm for translational displacements and <1.2° for rotations. Discrepancies between sCT-CT and sCT-Cone Beam CT were ≤1 %.

The MRI-only technique proved to be feasible for use in the central nervous system and pelvic regions, both in terms of dosimetry and image-guided verification. In head and neck oncology, the focus was exclusively on dosimetric planning. Further studies are required to validate and expand the applicability of this technique to other anatomical sites.

These findings reinforce the applicability and versatility of the MRI-only approach across multiple anatomical regions and therapeutic contexts, highlighting its potential to improve patient comfort and streamline clinical workflows.