1. Department of Biomedical Data Sciences, Leiden University Medical Center, Leiden, The Netherlands;
2. Department of Radiotherapy, Leiden University Medical Center, Leiden, The Netherlands;
3. Department of Radiotherapy, Amsterdam University Medical Centers, Amsterdam, The Netherlands;
4. Department of Radiotherapy, Haaglanden Medical Center, The Hague, The Netherlands;
5. Radiotherapy Group Deventer, Deventer, The Netherlands