Intraoperative versus external beam boost for breast cancer: A matched-pair analysis.

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1120 Background: After breast conserving surgery, radiotherapy leads to a better overall survival. In addition to whole breast radiotherapy (WBRT) a boost to the tumor bed leads to a better local control. The tumor bed boost is usually added after WBRT or can be done intraoperative (IORT). Belletti et al. (Clin Cancer Res., 2008) described positive effects, an antitumoral effect and modulation of microenvironment after IORT with 50kV x-rays. A matched pair analysis was performed to investigate the impact of IORT boost on overall survival compared to standard external beam boost. Methods: Between 2002 – 2009, 370 patients were treated for breast cancer with WBRT + boost (external beam (EBRT) boost n = 146, IORT boost n =224). A matched pair analysis (1:1 propensity score matching for age, TNM, grading, hormonal treatment and chemotherapy) for overall survival and local recurrence free survival could be done for 53 pairs. All patients underwent breast conserving surgery and WBRT with 46-50Gy. 53 patients received an EBRT boost with 16Gy (2Gy/fraction, dedicated linear accelerator) and 53 patients received an IORT boost with 20Gy (INTRABEAM system, 50kV x-rays). Median follow-up was 6 months (range, 1-77 months) for the EBRT boost patients and 56 months (range, 2-97 months) for IORT boost patients. Kaplan Meier estimates were performed for overall survival and local recurrence free survival. Results: IORT boost patients had a longer follow-up than EBRT boost patients. Despite the difference in follow-up times, there was a strong trend towards better overall survival after IORT boost (90.2% vs. 62.3%, p = 0.375). One local recurrence was present in each group (EBRT boost after 15 months, local recurrence free survival 95%; IORT boost after 12 months, local recurrence free survival 98.1%). Conclusions: IORT given as a boost seems to have a positive impact on overall survival in breast cancer patients after breast conserving surgery. To identify such an effect a prospective randomized trial should be conducted.

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