1. Radboud Institute for Health Sciences, Radboud university medical center, Nijmegen, The Netherlands
2. Orthopaedic Research Laboratory, Radboud Institute for Health Sciences, Radboud university medical center, Nijmegen, The Netherlands and Laboratory of Biomechanical Engineering, Enschede, The Netherlands
3. Radiotherapeutic Institute Friesland, Leeuwarden, The Netherlands
4. Department of Radiotherapy, Leiden University Medical Center, Leiden, The Netherlands