Impact of preoperative MRI on long-term outcomes of breast-conserving therapy with electronic kV-intraoperative radiotherapy: A risk-stratified analysis based on ASTRO criteria.

purposePreoperative breast MRI (pMRI) in patients undergoing breast-conserving surgery (BCS) remains controversial, particularly regarding long-term oncologic outcomes. The utility of pMRI within contemporary, risk-stratified radiation therapy paradigms, using the ASTRO risk classification as a reference, is unclear. METHODS AND MATERIALS: We retrospectively analyzed 613 BCS patients at a single institution (2014-2022). Patients were stratified by pMRI status and ASTRO 2016 risk classification based on final pathology. Primary outcomes included overall recurrence, locoregional recurrence, distant metastasis, and overall survival. Cox proportional hazards regression estimated hazard ratios (HRs) and 95% confidence intervals (CIs).

resultsOverall recurrence was lower in the pMRI cohort versus non-pMRI (4.0% vs. 11.2%, p = 0.007). Among high-risk patients, pMRI was associated with reduced overall recurrence (5.3% vs. 14.6%, p = 0.009) and a trend toward lower locoregional recurrence (3.8% vs. 9.4%, p = 0.066). This benefit was observed in high-risk patients receiving standard radiotherapy (4.9% vs. 13.1%, p = 0.024) but not in those receiving non-standard radiotherapy. No significant benefit was seen in low-risk patients. Adjusted analysis identified pMRI as an independent protective factor for recurrence (HR 0.42, 95% CI 0.19-0.93, p = 0.036).

conclusionspMRI significantly reduces recurrence in high-risk BCS patients, particularly with standard radiotherapy. These findings support using ASTRO risk classification to guide selective pMRI use, prioritizing high-risk patients where precise surgical planning and target delineation yield the greatest clinical benefit.