In a patient with otherwise favorable DCIS and a focally positive margin who refuses reexcision, is APBI an appropriate treatment option?  

Typically speaking, with positive margin, we always discuss re-excision (if possible and if the surgeon thinks it’s a true positive margin). If the patient refuses, with positive margin, I would offer her whole breast and a boost, I would not favor APBI. 

With partial breast brachytherapy, the dose at the surface of the device (the lumpectomy cavity margins) is about 230% of the prescribed dose. Hence, it is likely to be by far more effective in eradicating any positive surgical margin.