Outcomes of Technically Optimal Intraoperative Radiation Therapy with Electrons Versus Whole-Breast External Beam Radiation in Suitable Breast Cancer Patients

Abstract Purpose Intraoperative radiation therapy (IORT) with electrons is associated with higher ipsilateral breast tumor recurrence rates in early-stage breast cancer than whole-breast external beam radiation therapy (EBRT). Although limited randomized and retrospective data suggest that this approach may suit a subset of patients, its role remains uncertain. This study aimed to compare oncological outcomes between technically optimal IORT with electrons and whole-breast EBRT in suitable breast cancer patients. Methods and Materials In this single-center retrospective cohort study, patients were grouped by radiation treatment: IORT with electrons or whole-breast EBRT. Endpoints included disease-free survival (DFS), local control, and breast cancer-specific survival (BCSS). Results From January 2011 to December 2021, 204 eligible patients were reviewed (IORT, 74; EBRT, 130). The median follow-up was 5.1 years. The 5-year DFS rates were 95.61% for IORT and 98.08% for EBRT (log-rank P = 0.02). The 5-year local control rates were 98.46% for IORT and 100% (no event) for EBRT (log-rank P = 0.07). The 5-year BCSS rates were comparable: 98.61% for IORT and 100% (no event) for EBRT (log-rank P = 0.23). On univariable analysis for DFS, receipt of systemic treatment was a statistically significant protective factor (hazard ratio, 0.09; 95% CI, 0.01–0.74). Receipt of whole-breast EBRT was associated with a reduced risk of events, although this did not reach statistical significance (hazard ratio, 0.12; 95% CI, 0.02–1.01). Conclusions IORT with electrons was associated with a modest but statistically significant reduction in 5-year DFS in appropriately selected patients compared with whole-breast EBRT, while BCSS remained comparable between groups. Therefore, electron-based IORT should be approached with caution and reserved for patients who prioritize treatment convenience.