Preliminary Results in 173 Breast Cancer Patients Treated with Post-Lumpectomy MammoSite Single-Lumen Brachytherapy or Multi-Catheter Brachytherapy.

The objective of this study was to report our single-institution results with MammoSite and multi-catheter brachytherapy. Between February 2003 and January 2009, 173 women with unifocal pathological Tis, T1, or T2 (up to 30 mm), N0 or N1 carcinomas of the breast were treated with post-lumpectomy brachytherapy to 34 Gy in 10 fractions over 5-10 days. We treated 137 patients with MammoSite single-lumen balloon brachytherapy, and 36 patients with multi-catheter brachytherapy. Patients with small and/or nonspherical lumpectomy cavities were usually treated with multi-catheter brachytherapy using 4-12 interstitial catheters. Median follow-up was 33 months. Three-year ipsilateral breast tumor control, disease-free, and overall survival rates for MammoSite brachytherapy were 100%, 100%, and 99%, respectively. Similar rates were obtained with multi-catheter brachytherapy. Minimum distances from the planning target volume for plan evaluation to a rib were 10 ± 8 mm (mean ± standard deviation) and 8 ± 4 mm (mean ± standard deviation) for MammoSite brachytherapy and multi-catheter brachytherapy, respectively (p = 0.48). Maximum rib doses were 101 ± 14% (mean ± standard deviation) and 74 ± 10% (mean ± standard deviation) of the prescribed dose for MammoSite brachytherapy and multi-catheter brachytherapy, respectively (p = 0.001). Multi-catheter brachytherapy results in more conformal radiation dose delivery and a significantly lower rib dose than MammoSite single-lumen brachytherapy. Long-term follow-up is needed to determine if the delivery of a lower radiation dose to the ribs will translate into a lower incidence of rib pain and fractures.