10-Year follow-up of 621 patients treated using high-dose rate brachytherapy as ambulatory boost technique in conservative breast cancer treatment.

PURPOSE: Breast conserving treatment, consisting of lumpectomy followed by whole-breast irradiation, is considered the standard of care in early-stage breast cancer. Randomized studies have reported that delivering boost doses to tumor bed improves local control rates, particularly in young women. This study sought to evaluate local control and cosmetic results of delivering boost doses using a high-dose-rate (HDR) brachytherapy (HDRBT) in breast cancer conservative treatment.

METHODS: We included 621 T1-T2, N0-N1 breast cancer patients who underwent lumpectomy, external irradiation (44Gy over 5weeks), and a boost dose of two fractions of 5Gy to the tumor bed by means of HDR iridium brachytherapy. Implantation was performed during the lumpectomy or 2-3weeks after external irradiation. Population characteristics were as follows: pTis=11.6%; pT1=63.4%; pT2=25.0%; median tumor size=1.5cm; histology: ductal carcinoma in situ (DCIS): 72 (11.6%); infiltrative ductal carcinoma (IDC): 471 (75.8%); other: 78 (12.6%). For IDCs, the surgical margins were positive in 38cases (6.2%) and an extensive intraductal component was present in 254 cases.

RESULTS: With a median follow-up of 10.3years, 47 local relapses were observed (10-year local relapse rate: 7.4%). Small-volume implantation (V100<45cc) and ductal carcinoma in situ histology both significantly correlated with local relapse. The 10-year overall survival was 91%. Cosmetic results were evaluated in 264patients, proving excellent in 58 (22%), good in 153 (58%), fair in 40 (15%), and poor in 13 (5%).

CONCLUSIONS: Small implant volume and ductal carcinoma in situ histology significantly correlated with local relapse following HDR brachytherapy dose boost in breast cancer conservative treatment. Modern image-guided breast brachytherapy techniques using surgical clips as a guide may decrease potential treatment targeting errors, consequently improving local control without increasing toxicity.