Abstract P4-10-06: 10-Years Results of Intraoperative Electron Radiotherapy (IOERT) in Boost Modality in Breast Cancer Patients Treated with Breast Conserving Surgery

Introduction: The aim of this nonrandomized study was to compare the ipsilateral breast tumor recurrence rates in patients with invasive breast cancer, who had been treated with breast conserving surgery and whole breast irradiation and conventional boost or intraoperative electron radiotherapy boost (IOERT). Patients and Methods: 378 patients were included in the study, 188 patients in group 1 (conventional boost) and 190 patients in group 2 (IOERT boost). Patients were comparable with regard to age, menopausal status, tumor size, histological type, grading and axillary lymph node status. Included were patients with invasive breast cancer pT1 and pT2, N0, N1, N2, M0, and breast conserving surgery with clear margins >3mm. Excluded were patients with DCIS only, patients with invasive breast cancers larger than pT2, patients after primary systemic therapy and patients with multicentric disease. All patients (group 1 and group 2) received postoperative whole breast irradiation of 51-56.1 Gy. Group 1 received postoperative electron boost irradiation of 12 Gy after whole breast irradiation and group 2 received one intraoperative electron boost of 9 Gy in a single fraction during surgery before whole breast irradiation. Results: The 10-years actuarial rates of ipsilateral breast tumor recurrence (IBTR), true local recurrence (TLR), distant recurrence (DR) and disease free survival (DFS) were 7.1% (95%CI, 3.2-11.0%), 4.8% (95%CI, 1.5-8.0%), 14,2% (95%CI, 9.1-19.4%) and 82.4% respectively in group1 and 2.7% (95%CI, 0.0-5.9%, P=0.062), 0.7% (95%CI, 0.0-2.0%, P=0.016), 13.6% (95%CI, 5.0-22.2%, P=0.90) and 84.0% (P= 0.76) respectively in group 2. Conclusion: Patients treated with IOERT boost and whole breast irradiation achieve excellent local control rates at 10 years and exhibit statistically significant decreased true local recurrence rates compared to patients treated with whole breast irradiation and conventional electron boost. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-10-06.