Findings on Surveillance Imaging After Preoperative Partial Breast Irradiation for Early Stage Breast Cancer

Purpose To evaluate the mammographic sequelae of preoperative accelerated partial breast irradiation (APBI) delivered via either stereotactic radiosurgery or a conventionally fractionated regimen. Methods and Materials This multicenter, retrospective study evaluated surveillance mammograms from patients enrolled in 2 prospective, preoperative APBI clinical trials. At 1 site, 31 patients with cT1N0 invasive carcinomas or low- or intermediate-grade ductal carcinoma in situ ( Results At a median follow-up of 61 months, 17 patients (55%) treated with single-dose APBI exhibited exuberant fat necrosis at the lumpectomy site. Fat necrosis was believed to be clinically palpable in 5 (16%) of these patients within the first 3 years of follow-up. Exuberant fat necrosis developed in 5 patients (20%) treated with fractionated APBI over a median 68-month follow-up period but only 2 of those patients (8%) who underwent conventional whole breast radiation therapy. Conclusions In situ tumor targeting in the preoperative setting allows relative sparing of normal tissue but results in a larger and more vigorous area of change on surveillance imaging, potentially reflecting the interaction of surgical resection with an irradiated tissue bed. High-dose stereotactic radiosurgery in particular increases the risk of developing a uniquely robust and well-demarcated pattern of fat necrosis on mammogram that may also present clinically. With many ongoing studies evaluating the preoperative treatment approach, defining the landscape of expected imaging sequelae will provide useful anticipatory guidance for clinicians and patients.