MR-guided RAdiotherapy to Breast With Dose Escalation to regionaL Lymph NodEs

MR imaging has the potential to improve both the localisation of pan-LN treatments and the subsequent treatment delivery using MR-linac technology. The MIRABELLE study will apply the MR sequences developed in LN-negative volunteers/patients to the context of node-positive breast cancer patients with the aim of reducing the delineated nodal volume thereby facilitating dose-escalation to involved LNs. The benefit of using MRI for LN localisation as compared to conventional CT imaging will be investigated by determining whether a higher dose can be delivered using MRI- as compared to CT-based delineation. Any increase in dose will be deemed a success as this has potential to improve tumour control. In addition, inter-observer errors in outlining will be explored to investigate whether these are reduced using MRI. Reduced inter-observer errors would result in smaller margins for error such that less normal tissue could be irradiated.