The mean deviation of the bony structures was 1.4, 1.6, and 0.9 mm in the transversal plane of the thoracic spine, the lumbar spine, and the pelvis, respectively (Herfarth et al. 2000c;Lohr et al. 1999).This system is used in Heidelberg for stereotactic fractionated treatment of paraspinal tumors, prostate cancer, and for pelvic chordomas or chondrosarcomas (Herfarth et al. 2000c; Lohr et al. 1999; Milker-Zabel et al. 2003; Thilmann et al.2002).