Risk-adapted whole-breast irradiation following perioperative multicatheter partial-breast brachytherapy: Clinical outcomes and cumulative dose analysis.

PURPOSE: Multicatheter interstitial brachytherapy for partial breast irradiation can be initiated immediately after surgery through intraoperative catheter implantation. Although the perioperative partial-breast brachytherapy (pPBB) enables a convenient single-stage breast-conserving therapy, subsequent whole-breast irradiation (WBI) may be required on the final pathology. This study evaluated clinical outcomes and dosimetric parameters in patients receiving sequential WBI. METHODS: Consecutive patients undergoing pPBB between 2010 and 2025 were analyzed. pPBB dose was delivered at 32 Gy/8 fr. or 25.2 Gy/4 fr. High-risk patients received subsequent WBI. Outcomes and toxicities were compared with those of patients receiving pPBB alone. Cumulative OAR doses were evaluated. RESULTS: Among 922 patients treated with pPBB, 26 (2.8%) subsequently received WBI. At a median follow-up of 7.2 years, 5-year rates of local-relapse-free, disease-free, and breast cancer-specific survival in the WBI after pPBB versus pPBB alone cohorts were 100% versus 98.1% (p = 0.75), 95.2% versus 97.0% (p = 0.80), and 95.2% versus 99.7% (p = 0.96), respectively. No serious adverse events were reported. The cumulative doses to OARs remained within tolerance limits. CONCLUSIONS: Risk-adapted WBI after pPBB was associated with acceptable oncologic outcomes and toxicity. This strategy appears feasible for patients who require treatment escalation after pPBB because of high-risk pathological features.