Phase 2 Trial of Accelerated Partial Breast Irradiation (APBI) Using Noninvasive Image Guided Breast Brachytherapy (NIBB).

ABSTRACT

PURPOSE: Noninvasive image guided breast brachytherapy (NIBB) is a novel approach to delivery of accelerated partial breast irradiation (APBI) that may hold advantages over established techniques. NIBB is not invasive but maintains a high level of precision by using breast immobilization via breast compression and image guidance; it therefore does not require large planning tumor volume margins. We present the primary outcomes of this prospective phase 2 study (BrUOG Br-251). METHODS AND MATERIALS Eligible patients with early-stage breast cancer underwent NIBB APBI using a dose 34 Gy in 10 fractions delivered daily or twice a day. Treatment was delivered using an Ir-192 high-dose-rate source via specialized applicators. Two orthogonal treatment axes were used for each fraction. The primary endpoints were late toxicity and cosmesis assessed at 2 and 5 years. Toxicity was assessed using the National Cancer Institute Common Terminology Criteria for Adverse Events v3.0. Cosmesis was assessed using the NRG/Radiation Therapy Oncology Group scale. Ipsilateral breast tumor recurrence was defined as any recurrence or new primary in the treated breast. RESULTS: Forty patients underwent protocol treatment. Median patient age was 68 years (50-92 years). Mean tumor size was 1.1 cm (0.3-3.0 cm). Among the cohort, 62.5% had invasive carcinoma and 37.5% had ductal carcinoma in situ. Thirty-nine percent elected to receive hormone therapy. No grade ≥3 late toxicities were observed at any time point. Grade 2 toxicity was 5% and 10% at 2 and 5 years, respectively. Telangiectasia grade 1 and 2 occurred in 27.5% and 5%, respectively. Breast separation of >7 cm was associated with telangiectasia (P < .01). The rate of good to excellent cosmetic outcome was 95% at 2 years and 100% at 5 years. With a median follow-up of 68 months, the actuarial 5-year freedom from ipsilateral breast tumor recurrence was 93.3% (±4.8%), and overall survival was 93.7% (±4.4%). CONCLUSIONS: NIBB to deliver APBI is well tolerated with a low incidence of significant late toxicity and has favorable cosmetic outcomes. Continued evaluation of the NIBB APBI technique in a larger cohort is warranted.