The standard postoperative radiotherapy after breast-conserving surgery (BCS) is percutaneous irradiation of the entire breast to a total dose of 50 Gy, usually followed by a tumor bed boost.Due to the increased detection of small breast cancers, it is necessary to consider modifications of the existing therapeutic practice, e.g.by using intraoperative radiotherapy (IORT).Intrabeam(R) (Carl Zeiss, Oberkochen/Germany) is an innovative mobile device for IORT including a miniature radiation source generating isotropic low energy X-ray energies to 50kV maximum.Using a spherical applicator, a single high radiation dose of 20 Gy is administered to the turnour bed in the operating room immediately after wide tumor resection.Preliminary data suggest that IORT given as tumour bed boost with Intrabeam after BCS could be a reliable alternative to conventional postoperative boost radiation by accurate dose delivery without geographical miss and by enabling smaller treatment volumes, complete skin-sparing and reducing postoperative radiation time by 7-10 days.The first 5 years of experience of our institution in 154 breast cancer patients treated between 2002 and 2007 using low energy X-rays followed by 46-50 Gy external beam radiotherapy (EBRT) of the whole breast with a median follow up of 34 months shows a low local recurrence rate of 1.5% in 5 years and low toxicity rates.Pilot studies show that targeted IORT of the tumour bed might alter the cytokine and growth factor expression patterns in the surgical wound and abrogate their stimulatory effect on cancer cell growth and motility.