1. Department of Internal Medicine, University Medical Center Groningen, The Netherlands.
2. Radiotherapeutic Institution Friesland, Leeuwarden, The Netherlands.
3. Department of Epidemiology, University Medical Center Groningen, The Netherlands.
4. Department of Radiotherapy, MAASTRO Clinic, Maastricht, The Netherlands.
5. Department of Radiotherapy, University Medical Center Nijmegen, The Netherlands.
6. Department of Medical Oncology, University Medical Center Groningen, The Netherlands.