Janssen NNY, et al. - This study was performed with the aim to retrospectively compare the use of a single or multiple ¹²⁵I seeds in radioactive seed localization (RSL) to enable breast conserving surgery (BCS) in patients with extensive ductal carcinoma in situ (eDCIS). In this patient group, it was observed that multiple-seed RSL enabled bracketing of large areas of DCIS, with the potential to decrease the high rate of positive resection margins.