Intraoperative radiotherapy vs. multicatheter brachytherapy as accelerated partial-breast irradiation: a secondary analysis of two multicenter prospective cohorts.

AIM: The aim of this study is to compare for the first time the IBTR rates observed among early breast cancer patients treated either by multi-catheter brachytherapy or IORT in two prospective multicenter cohorts. Secondary objectives included, regional and distant relapse rates, mastectomy-, disease-, and cause-specific free survival, and overall survival. MATERIALS AND METHODS: Two multicenter prospective studies of partial-breast irradiation were ongoing at the University Hospitals of Las Palmas province. A province-wide prospective cohort was established to evaluate interstitial brachytherapy in patients undergoing breast-conserving treatment. This cohort comprised 182 women treated between 2008 and 2017 across all university-affiliated hospitals in Las Palmas. A second prospective multicenter investigation assessed the use of intraoperative radiotherapy (IORT) as exclusive partial-breast irradiation. This study included 312 patients treated between January 2013 and December 2022 by three surgical teams operating at the academic university hospitals of the Las Palmas province. RESULTS: Two out of the 182 patients of the Brachytherapy cohort developed a local recurrence (LR) during the first 5 years of follow-up. The actuarial IBTR risk at 5 years was 1.1% (95% CI: 0.3-1.9). During the follow-up, three out of the 312 patients of the IORT cohort developed a local recurrence (LR). The actuarial IBTR risk at 5 years was 1.0% (95% CI 0.4-1.6). These differences were not statistically significant (p=0.885). CONCLUSION: In our opinion, this secondary analysis of two prospective multicenter cohorts may offer new information regarding the role of interventional APBI in early breast cancer patients, stratified by the GEC-ESTRO risk groups.