Clinical phase I/II trial to investigate preoperative dose-escalated intensity-modulated radiation therapy (IMRT) and intraoperative radiation therapy (IORT) in patients with retroperitoneal soft tissue sarcoma: interim analysis - Röder, Falk; Bischof, Marc; Ulrich, Alexis; Habl, Gregor; Uhl, Matthias; Huber, Peter E.; Nikoghosyan, Anna; Alldinger, Ingo; Hensley, Frank W.; Debus, Jürgen (BMC cancer, 2014)