Intraoperative radiotherapy (IORT) as a boost during breast conserving surgery (BCS) using low kV X-rays - the first five years of experience with a novel approach

626 Background: Recently, the concept of IORT during BCS has been introduced using linear accelerators, brachytherapy or dedicated mobile IORT devices generating fast electrons or low energy X-rays. Here, we report the first 5 years of a single center experience after introduction of a novel approach to deliver IORT as a tumor bed boost during BCS for breast cancer. Methods: 155 breast cancers in 154 women (median age 63 yrs, range 30 - 83 yrs, T1/T2 = 110/45, N0/N+ = 104/51) were treated between February 2002 and December 2007 at the University Medical Center Mannheim/University of Heidelberg, in whom IORT as tumor bed boost was applied using 50 kV X rays (20 Gy, INTRABEAM, Carl Zeiss Oberkochen, additional OR time about 45 - 60 min) followed by 46 - 50 Gy external beam whole breast radiotherapy (EBRT). Chemotherapy was given before EBRT. The median interval between BCS+IORT and EBRT was 10 wks. Median follow-up was 34 mon (max 79.6 mon, 1 pt lost to f/u). Overall survival (OS), local relapse free survival (LRFS) and disease free survival (DFS) were calculated at 5 yrs using the Kaplan Meier method. 81 patients were evaluated at 3 yr f/u for normal tissue effects using the LENT SOMA scoring system. Results: Ten patients have died, 2 pts suffered from in breast relapse and 8 pts developed distant metastases yielding a 5yr OS of 87.0%, a 5yr LRFS of 98.4% and a 5 yr DFS of 73.9%. Grade 3 fibroses of the tumor bed were detected in 6% of the patients after 3 yrs. Skin toxicity was mild (teleangiectases and hyperpigmentations in 6% each). Conclusions: IORT as a tumor bed boost using the INTRABEAM system yields low recurrence and toxicity rates when followed by external beam whole breast radiotherapy. [Table: see text]