Purpose: To report outcomes for breast-conserving therapy using adjuvant accelerated partial breast irradiation with interstitial multicatheter brachytherapy by a cooperative group of institutions.
Methods: From 1992 to 2013, a total of 1356 patients were treated with breast-conserving surgery and adjuvant accelerated partial breast irradiation using interstitial multicatheter brachytherapy. A total of 1131 patients had >1 year of data available to assess oncologic and cosmesis outcomes. Median age was 59 years old (range 22-90 years). Histologies treated included 1005 (73 %) invasive ductal carcinoma and 240 (18 %) ductal carcinoma-in situ. T stages were 18 % Tis, 75 % T1, and 8 % ≥T2. Nodal status was 73 % N0 and 6 % N1a. Estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 was positive in 83, 70, and 6 %, respectively. Cox multivariate analysis for local control was performed using histology, age, estrogen receptor status, tumor size, grade, margin, and nodal status.
Results: The mean (SD) follow-up was 6.9 years (4.3). The 10-year actuarial risk (95 % confidence interval) of an ipsilateral breast tumor recurrence was 7.6 % (5.6-10.1). Other 10-year actuarial risks (95 % confidence interval) were regional failure 2.3 % (1.4-3.7), distant metastasis 3.8 % (2.5-5.7), cause-specific survival 96.3 % (94.2-97.6), overall survival 86.5 (83.0-89.3), and new contralateral cancers 4.6 % (3.0-6.9). On multivariate analysis, high grade (hazard ratio 2.81) and positive margin status (hazard ratio 18.42) were the only two significant variables associated with an increased risk of local recurrence. Physician-reported cosmesis was excellent/good in 84 % (98 of 116) of patients with >5 years of follow-up.
Conclusions: This is the largest report of outcomes with interstitial breast brachytherapy. This treatment resulted in excellent long-term local control and cosmesis outcomes.