Vicini FA, Cecchini RS, White JR, et al. - In this randomized, phase 3, equivalence trial done in 154 clinical centers in the USA, Canada, Ireland, and Israel, adult women (> 18 years) with early-stage breast cancer who had had lumpectomy with negative (ie, no detectable cancer cells) surgical margins were randomized using a biased-coin-based minimization algorithm to receive either whole-breast irradiation (whole-breast irradiation group) or accelerated partial breast irradiation (APBI)(APBI group) in order to examine whether APBI gave equivalent local tumor control following lumpectomy in comparison with whole-breast irradiation. In controlling ipsilateral breast-tumor recurrence (IBTR) for breast-conserving therapy, APBI could not meet the criteria for equivalence to whole-breast irradiation. This trial had broad eligibility criteria, resulting in a large, heterogeneous pool of individuals and adequate power to identify treatment equivalence, however, it was not meant to examine equality in patient subgroups or outcomes from various APBI techniques. For an individual with early-stage breast cancer, findings aid in whole-breast irradiation after lumpectomy, nevertheless, with an absolute variation of less than 1% in the 10-year cumulative incidence of IBTR, APBI could be an acceptable choice for some women.