# MR-Guided Radiotherapy in Oesophageal Cancer: From Principles to Practice—A Narrative Review

## TL;DR

MR-guided radiotherapy (MRgRT) improves precision in treating oesophageal cancer by using MRI to better visualize tumors and adjust treatment in real time.

## Contribution

This paper reviews the application of MR-guided radiotherapy in oesophageal cancer, emphasizing its potential for adaptive treatment and response monitoring.

## Key findings

- MRgRT enables real-time tumor visualization and motion tracking during treatment.
- Functional MRI sequences provide new ways to monitor tumor response.
- MRgRT reduces radiation dose to critical organs like the heart and lungs.

## Abstract

Oesophageal cancer is an aggressive disease with poor survival despite advances in combined chemotherapy, radiotherapy, and surgery. Radiotherapy plays a crucial role, but its precision is limited by the inability of conventional imaging such as computed tomography (CT) and positron emission tomography (PET) to clearly visualise the tumour and surrounding organs. Magnetic resonance imaging (MRI) provides excellent soft-tissue detail and can be integrated directly with a radiotherapy system, known as MR-guided radiotherapy (MRgRT). This technology enables daily imaging of the tumour during treatment, real-time motion tracking, and on-the-spot plan adjustments to account for anatomical changes. It also offers new ways to monitor tumour response using functional MRI sequences that reflect biological activity. While early clinical studies demonstrate improved accuracy and reduced radiation to the heart and lungs, wider adoption will depend on overcoming technical, workflow, and access challenges. MRgRT represents a promising step toward personalised, adaptive radiotherapy for oesophageal cancer.

Oesophageal cancer remains a significant global health burden with poor survival outcomes despite multimodal treatment. Recent advances in magnetic resonance imaging (MRI) have opened opportunities to improve radiotherapy delivery. This review examines the role of MRI and MR-guided radiotherapy (MRgRT) in oesophageal cancer, focusing on applications in staging, treatment planning, and response assessment, with particular emphasis on magnetic resonance linear accelerator (MR-Linac)-based delivery. Compared to computed tomography (CT), MRI offers superior soft-tissue contrast, enabling more accurate tumour delineation and the potential for reduced treatment margins. Real-time MR imaging during treatment can facilitate motion management, while daily adaptive planning can accommodate anatomical changes throughout the treatment course. Functional MRI sequences, including diffusion-weighted and dynamic contrast-enhanced imaging, offer quantitative data for treatment response monitoring. Early clinical and dosimetric studies demonstrate that MRgRT can significantly reduce radiation dose to critical organs while maintaining target coverage. However, clinical evidence for MRgRT in oesophageal cancer is limited to small early-phase studies, with no phase II/III trials demonstrating improvements in survival, toxicity, or patient-reported outcomes. Long-term clinical benefits and cost-effectiveness remain unproven, highlighting the need for prospective outcome-focused studies to define the role for MRgRT within multimodality treatment pathways.