Phase II Trial of Accelerated Partial Breast Irradiation (APBI) using Non-Invasive Image-Guided Breast Brachytherapy (NIBB)

Abstract Purpose NIBB is a novel approach to deliver 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, and therefore does not require large PTV margins. We present the primary outcomes of this prospective phase II study (XXXXX). Methods Eligible patients with early-stage breast cancer underwent NIBB APBI using a dose 34Gy in 10 fractions delivered daily or BID. Treatment was delivered using an Ir-192 HDR 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 CTCAE v3.0. Cosmesis was assessed using the NRG/RTOG scale. Ipsilateral breast tumor recurrence (IBTR) was defined as any recurrence or new primary in the treated breast. Results 40 patients underwent protocol treatment. Median patient age was 68yrs (50-92yrs). Mean tumor size was 1.1cm (0.3-3.0cm) with 62.5% invasive carcinoma and 37.5% DCIS. 39% elected to receive endocrine 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 >7cm was associated with telangiectasia, p Conclusion 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.