1. Department of Radiation Oncology, Medisch Spectrum Twente, Enschede, The Netherlands,
2. Department of Epidemiology, Medisch Spectrum Twente, Enschede, The Netherlands,
3. Departement of Research Methodology, Measurement, and Data Analysis, Faculty of Behavioral Science, University of Twente, The Netherlands,
4. Laboratory for Pathology Oost Nederland, Hengelo, The Netherlands,
5. Department of Radiation Oncology, Leiden University Medical Centre, Leiden, The Netherlands, and
6. Radiotherapy Centre West, Medical Centre Haaglanden, The Hague, The Netherlands