Three-dimensional conformal radiotherapy with a simultaneously integrated boost-technique in early stage breast cancer: First results on local control and survival

Purpose: Purpose of our study was to report on local control, locoregional control (LRC), disease-free-survival (DFS) and overall survival (OS) in women with early stage breast cancer treated with lhe 3D-CRT Simultaneously Integrated Boost-technique (3D-CRT-SIB) as part of breast conserving radiotherapy (RT). In previous reports from our institution, the 3D-CRT-SIB was superior to the sequential boost (SB)-technique regarding unwanted excessive dose to the boost area and shorter overall treatment time. However, clinical outcome remains to be determined. Materials: The study population was composed of 482 consecutive female invasive breast cancer patients (stage I-III) treated with 3D-CRT-SIB, following breast conserving surgery, at the University Medical Center Groningen between 2005-2008. Data was collected retrospec1ively from medical files. The fractionation scheme used was 28 times 1.8 Gy to the whole ipsilateral breast and simultaneously delivered 2.3 Gy (74.5%) to the tumour bed or 2.4 Gy in case of close or focally positive resection margins. The total applied breast dose was 50.4 Gy with a dose to the boost area of 64.4 or 67.2 Gy. These schedules are biologically equivalent to 25 x 2 Gy with a sequential boost dose of 8 x 2 Gy or 10 x 2 Gy using an αβ of 10 for tumour control. Next to outcome report, we identified prognostic factors for any recurrence (LRR and metastases as first event) by using multivariate Cox regression survival analysis. Results: At diagnosis, the mean age was 57.6 (SO 10.7 years). Mean follow-up was 33.9 (SO 11.3) months. Tumours≤2 cm were observed in 363 (75.3%) patients and 149 (30.9%) patients had node positive disease. Chemotherapy was given in 178 (36.9%), hormonal therapy in 188 (39.0%) and regional RT in 26 (5.4%) women, respectively. Local control with 2 ipsilateral in-breast recurrences was 99.4% at 36 months. The 36-months LRC, DFS and OS were 99.1%, 94.9% and 99.0%, respectively. During followup, 4 women had a LRR, 20 developed distant metastases and 7 died, all of breast cancer. In muitivariate analysis, tumours larger than 2 cm (Hazard ratio (HR) 3.2: 95%-confidence interval (CI) 1.3-7.5, p=0.009) and grade II/III differentiation (HR 2.71; 95%-CI 1.15-6.39: p=0.023) were risk factors for any recurrence. Conclusions: The 3D-CRT-SIB technique In breast conservinq therapy results in excellent local control, regional control and overall survival. Longer follow-up is needed to further confirm these results.