- Patients must have undergone a segmental mastectomy (SM) with a level I and ll axillary dissection or sentinel lymph node biopsy. Surgical margins at time of SM must be negative (> or = 2 mm) for both invasive carcinoma and for non-invasive ductal carcinoma. Patients who have post-operative margins which are negative but less than 2mm will be considered eligible if the surgeon states that the margin in question could not be improved.