The effect of escalating the boost dose for patients with involved resection margin after breast-conserving surgery

BACKGROUND: This study aims to investigate the impact of boost dose escalation on ipsilateral breast tumor recurrence (IBTR) in breast cancer patients with involved resection margins following breast-conserving surgery. METHODS: Between January 1998 and December 2010, 192 patients were treated with a boost dose of over 10 Gy for involved resection margins. We retrospectively analyzed outcomes in 192 patients who underwent whole breast irradiation of 50.4 Gy followed by a median boost dose of 15.0 Gy (range, 12–16 Gy). Boost doses of 12.5 Gy and 15 Gy were delivered to patients with carcinoma in situ and invasive carcinoma, respectively, at the positive margins. We evaluated the impact of the boost dose on the IBTR rate. RESULTS: Median follow-up duration was 6.7 years (0.4–15.6 years). The 5-year cumulative risk of IBTR as a first event was 5.0%. IBTR occurred as a first recurrence in 13 of 192 patients. In-boost-field recurrences were found in 11 patients (85%). Five patients (39%) experienced out-of boost field recurrences, and three experienced both types of recurrences. In multivariate analysis, age (<40 years), pT stage, and positive radial resection margin were prognostic factors for IBTR (P = 0.029, P = 0.024 and P = 0.035, respectively). CONCLUSIONS: A median boost dose of 15 Gy might be insufficient in patients younger than 40 years, with tumor size greater than 2 cm, or with involved radial resection margins. On the other hand, in cases of positive superficial or deep margins, dose-escalated boost or re-excision may not be necessary.