Accelerated partial breast irradiation: An update on published Level I evidence

Multiple adjuvant radiation therapy options currently exist for women following breast-conserving surgery including standard fractionated whole breast irradiation (WBI), accelerated whole breast irradiation (AWBI), and accelerated partial breast irradiation (APBI). The recent publication of several randomized trials comparing APBI to standard WBI provides Level I evidence supporting APBI. The purpose of this review is to summarize the Level I data supporting APBI in an effort to provide guidance when to offer this treatment approach vs. standard WBI, AWBI, or excision alone and to address questions related to its application. Four contemporary trials with over 2000 patients comparing APBI and WBI have been published and demonstrate no differences in the rates of local/regional recurrence or survival though long-term followup is limited to one study. In addition, reductions in the rates of acute and chronic toxicity and improvements in cosmetic outcome were noted in two of these trials (the University of Florence and the Hungarian Phase III trials, respectively). When contrasting other treatment approaches to APBI, patients treated in studies using AWBI have many comparable clinical and pathologic characteristics, whereas studies investigating endocrine therapy alone (surgery with no adjuvant radiation therapy) have much "lower risk" patients based on clinical, pathologic, and treatment-related criteria. Although significant Level I evidence now exists supporting the use of APBI as an alternative to WBI in selected patients undergoing breast-conserving therapy, additional data are needed to (1) help further refine patient selection criteria, (2) better clarify the optimal partial breast irradiation target and technique for each clinical setting, (3) determine when AWBI, standard WBI, or excision alone may be more appropriate, and (4) investigate if further reductions in fractionation schedules are possible.