Clinical outcomes with the MammoSite radiation therapy system: results of a prospective trial

The purpose of this study was to report the treatment-induced adverse events and cosmetic and treatment outcomes of accelerated partial breast irradiation (APBI) delivered with the MammoSite radiation therapy system (RTS) in breast cancer patients undergoing breast-conserving therapy (BCT).

This is a prospective clinical trial that was approved by the institutional review board. The study included female breast cancer patients undergoing breast-conserving therapy in the form of surgery and APBI delivered with the MammoSite RTS. Patients and tumor characteristics, treatment-induced acute adverse events based on the Common Toxicity Criteria for Adverse Events (CTCAE) version 2.0, chronic AEs according to Radiation Therapy Oncology Group (RTOG) scale, treatment outcomes (including local control, disease-free survival, and overall survival), and cosmetic outcomes are reported.

The study included 36 eligible patients treated consecutively in our institution between November 2003 and August 2009. The age range was 45-83 years. A total of 29 patients had invasive disease (median size 1.1 cm), while 7 patients had in situ disease only (median size 0.8 cm). The skin distance in most of the patients (91.7 %) was ≥1 cm; only three patients (8.3 %) had skin distance <1 cm. The median balloon diameter was 5 cm (range 4-6 cm). At a median follow-up of 42 months (range 4-65 months), local control, disease-free survival, and overall survival were 100 %. None of the patients experienced any grade 3 or 4 toxicities; 16.7 and 5.6 % of the patients had late grade 2 fibrosis and telangiectasia, respectively. At last follow-up, cosmetic outcome was rated as good or excellent in 94 % of the patients.

APBI delivered with the MammoSite RTS is a feasible, tolerable, and effective treatment modality. Multicenter, randomized, controlled clinical trials with a larger number of patients are required for verification.