Role of boost radiotherapy for local control of pure ductal carcinoma in situ after breast-conserving surgery: a multicenter, retrospective study of 622 patients

Purpose To evaluate the effect of boost radiotherapy on ipsilateral breast tumor recurrence (IBTR) for ductal carcinoma in situ (DCIS) after breast-conserving surgery and whole breast radiotherapy (WBRT) with or without boost. Methods and materials Retrospective, multicentre study of 622 patients (624 tumors) diagnosed with pure DCIS from 1993–2011. Results Most tumors (377/624; 60.4%) received a boost. At a median follow-up of 8.8 years, IBTR occurred in 64 cases (10.3%). A higher percentage of patients with risk factors for IBTR received a boost ( p 20 mm, HR 2.10, 95% CI 1.14–3.88), re-excision (HR 1.76, 95% CI 1.04–2.96), and tamoxifen (HR 2.03, 95% CI 1.12–3.70). Boost dose > 16 Gy had a protective effect (HR 0.39, 95% CI 0.187–0.824). Multivariate analyses confirmed the independent associations between IBTR and 11–20 mm ( p = 0.02) and > 20 mm ( p = 0.009) tumours, and re-excision ( p = 0.006). On the margin-stratified multivariate analysis, tamoxifen was a poor prognostic factor in the close/positive margin subgroup (HR 4.28 95% CI 1.23–14.88), while the highest boost dose ( > 16 Gy) had a significant positive effect (HR 0.34, 95% CI 0.13–0.86) in the negative margin subgroup. Conclusions Radiotherapy boost did not improve the risk of IBTR. Boost radiotherapy was more common in patients with high-risk disease. Tumor size and re-excision were significant independent prognostic factors.