Intraoperative radiation therapy is mainly used for breast tumor treatment, but has the potential due to ist very local radiation deposit to be used for other areas as well. Accelerated partial breast irradiation (APBI) is a technique that promises to overcome the logistical problems created by external beam radiation therapy (EBRT). APBI can be applied interstitial or intracavitary. Common APBI techniques include multicatheter-based brachytherapy (mostly with radioactive wires gamma emmitting Ir-192 or beta-emitting Y-90), balloon catheter approaches (e.g. balloon filled with radioactive beta-emmitting Co-55) or electronic brachytherapy systems using miniature x-ray sources (at or around 50 kV). APBI is used for fractionated radiation delivery (total of around 30 Gy) or as a boost treatment (around 10 Gy) in combination with EBRT. While some of these approaches have significantly improved the outcome and the treatment comfort many problems remain, e.g. multi-day treatments, difficult handling for the staff, treatment planning / dose distribution and lack of or inconsistent image guidance and quality control. We propose a new catheter (double-balloon) filled with gamma-emitting Rhenium liquid.