High-dose single-fraction IMRT versus fractionated external beam radiotherapy for patients with spinal bone metastases: study protocol for a randomized controlled trial - Rief, Harald; Sterzing, Florian; Katayama, Sonja; Bruckner, Thomas; Rieken, Stefan; Bostel, Tilman; Förster, Robert; Schlampp, Ingmar; Wolf, Robert; Debus, Jürgen (Trials, 2015)