Three-Year Outcomes of a Canadian Multicenter Study of Accelerated Partial Breast Irradiation Using Conformal Radiation Therapy

Purpose: To report 3-year toxicity, cosmesis, and efficacy of a multicenter study of external beam, accelerated partial breast irradiation (APBI) for early-stage breast cancer. Methods and Materials: Between March 2005 and August 2006, 127 women aged ≥40 years with ductal carcinoma in situ or node-negative invasive breast cancer ≤3 cm in diameter, treated with breast-conserving surgery achieving negative margins, were accrued to a prospective study involving five Canadian cancer centers. Women meeting predefined dose constraints were treated with APBI using 3 to 5 photon beams, delivering 35 to 38.5 Gy in 10 fractions, twice a day, over 1 week. Patients were assessed for treatment-related toxicities, cosmesis, and efficacy before APBI and at specified time points for as long as 3 years after APBI. Results: 104 women had planning computed tomography scans showing visible seromas, met dosimetric constraints, and were treated with APBI to doses of 35 Gy (n = 9), 36 Gy (n = 33), or 38.5 Gy (n = 62). Eighty-seven patients were evaluated with minimum 3-year follow-up after APBI. Radiation dermatitis, breast edema, breast induration, and fatigue decreased from baseline levels or stabilized by the 3-year follow-up. Hypopigmentation, hyperpigmentation, breast pain, and telangiectasia slightly increased from baseline levels. Most toxicities at 3 years were Grade 1. Only 1 patient had a Grade 3 toxicity with telangiectasia in a skin fold inside the 95% isodose. Cosmesis was good to excellent in 86% (89/104) of women at baseline and 82% (70/85) at 3 years. The 3-year disease-free survival was 97%, with only one local recurrence that occurred in a different quadrant away from the treated site and two distant recurrences. Conclusions: At 3 years, toxicity and cosmesis were acceptable, and local control and disease-free survival were excellent, supporting continued accrual to randomized APBI trials.