Clinically evident fat necrosis in women treated with high-dose-rate brachytherapy alone for early-stage breast cancer

Purpose: To investigate the incidence of and variables associated with clin ically evident fat necrosis in women treated on a protocol of high-dose-rat e (HDR) brachytherapy alone without external-beam whole-breast irradiation for early-stage breast carcinoma. Methods and Materials: From 6/1997 until 8/1999, 30 women diagnosed with St age I or II breast carcinoma underwent surgical excision and postoperative irradiation via HDR brachytherapy implant as part of a multi-institutional clinical Phase I/II protocol. Patients eligible included those with T1, T2, N0, N1 (less than or equal to 3 nodes positive), MO tumors of nonlobular h istology with negative surgical margins, no extracapsular lymph-node extens ion, and a negative postexcision mammogram, Brachytherapy catheters were pl aced at the initial excision, re-excision, or at the time of axillary sampl ing. Direct visualization, surgical clips, ultrasound, or CT scans assisted in delineating the target volume defined as the excision cavity plus 2-cm margin. High activity Ir-192 (3-10 Ci) was used to deliver 340 cGy per frac tion, 2 fractions per day, for 5 consecutive days to a total dose of 34 Gy to the target volume. Source position and dwell times were calculated using standard volume optimization techniques. Dosimetric analyses were performe d with three-dimensional postimplant dose and volume reconstructions. The m edian follow-up of all patients was 24 months (range, 12-36 months), Results: Eight patients (crude incidence of 27%) developed clinically evide nt fat necrosis postimplant in the treated breast. Fat necrosis was determi ned by clinical presentation including pain and swelling in the treated vol ume, computed tomography, and/or biopsy. All symptomatic patients (7 of 8 c ases) were successfully treated with 3 to 12 months of conservative managem ent. Continuous variables that were found to be associated significantly wi th fat necrosis included the number of source dwell positions (p = 0.04), a nd the volume of tissue which received fractional doses of 340 cGy, 510 cGy , and 680 cGy (p = 0.03, p = 0.01, and p = 0.01, respectively). Other conti nuous variables including patient age, total excised tissue volume, tumor s ize, number of catheters, number of days the catheters were in plate, plana r separation, dose homogeneity index (DHI), and uniformity index (UI) were not significant. Discrete variables including the presence/absence of DCIS, sentinel versus full axillary nodal assessment, receptor status, presence/ absence of diabetes, and the use of chemotherapy or hormone therapy were no t found to have a significant association with the risk of fat necrosis. Conclusions: In this study of HDR brachytherapy of the breast tumor excisio n cavity plus margin, treatment was planned and delivered in accordance wit h the dosimetric parameters of the protocol resulting in a high degree of t arget volume dose homogeneity, Nonetheless, at a median follow-up of 24 mon ths, a high rate of clinically definable fat necrosis occurred. The overall implant volume as reflected in the number of source dwell positions and th e volume of breast tissue receiving fractional doses of 340, 510, and 680 c Gy were significantly associated with fat necrosis, Future dosimetric optim ization algorithms for HDR breast brachytherapy will need to include these factors to minimize the risk of fat necrosis, (C) 2001 Elsevier Science Inc .