As with most clinical situations with limited data, individualized decision-making is key. Based on small series, I do not generally offer RT post mastectomy for DCIS if it is close. If it is clearly involved after reviewing with the pathologist, I would discuss with the surgeon and patient taking i...

I agree with @Bruce G. Haffty that I would not for a "close" margin. The few times I've encountered an actual positive margin, it's usually a patient status-post skin-sparing mastectomy and immediate TE-based reconstruction, and they've got no idea where the "anterior" positive margin would be ...

The recent retrospective data suggest the risk of recurrence is low for patients with DCIS and close margin at mastectomy and we would recommend observationChilds et al., PMID 22975615Chan et al., PMID 20646871 

Based on a study reported by Abi-Raad et al., on Int J Radiat Oncol Biol Phys, 2011. For women with breast cancer women following mastectomy and the patient has three or more risk factors, the total LRR rate at 10 years is 19.7%. The risk factors are: positive LVI, close or positive margin (the...