G Fastner - Department of Radiotherapy and Radio-Oncology, Landeskrankenhaus, Paracelsus Medical University,Salzburg, Austria.
R Reitsamer - Department of Special Gynecology, Landeskrankenhaus, Paracelsus Medical University, Salzburg,Austria.
T Fischer - Department of Special Gynecology, Landeskrankenhaus, Paracelsus Medical University, Salzburg,Austria.
P KOPP - Department of Radiotherapy and Radio-Oncology, Landeskrankenhaus, Paracelsus Medical University,Salzburg, Austria.

The aim of this study nonrandomized study was to compare ipsilateral breast tumor recurrence rates in patients with invasive breast cancer, who had been treated withbreast conserving surgery and whole breast irradiation (WBI) and conventional boost or intraoperative electron radiotherapy boost (IOERT). Material and Methods:378 patients were included in the study, 188 patients in group I (conventional boost) and 190 patients in group II (IOERT boost). Patients were comparable with regard toage, menopausal status, tumor size, histological type, grading and axillary lymph node status. Included were patients with invasive breast cancer pT1-2, pN0-2, M0 and breast conserving surgery with clear margins > 3 mm. 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 I and group II) received postoperative WBI of 51 – 56.1 Gy. Group I received postoperative electron boost irradiation of 12 Gy after WBI and group II received one intraoperative electron boost of 9 Gy in a single fraction during surgery before WBI. 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 7.2% (95% CI, 3.2-11%), 4.4% (95% CI, 1.5-8.0%), 14.4% (95% CI, 9.1-19.4%) and 82.4% respectively in group I and 1.6% (95% CI, 0.0-5.9%, p=0.0023), 0.5% (95% CI, 0.0-2.0%, p=0.0029), 9.5% (95% CI, 5.0-22.2%, p=0.22) and 84% respectively in group II. Conclusion: Patients treated with IOERT boost and WBI achieve excellent local control rates at 10 years and exhibit statistically significant decreased true local recurrence rates compared to patients treated with WBI and conventional electron boost.