1. Department of Surgery, Leiden University Medical Center, Leiden, The Netherlands
2. Department of Radiotherapy, Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital, Amsterdam
3. Department of Statistics, European Organization for Research and Treatment of Cancer Data Center, Brussels, Belgium
4. Department of Medical Statistics, Leiden University Medical Center, Leiden, The Netherlands
5. Department of Surgery, Uppsala University Hospital, Uppsala, Sweden
6. Department of Radiation Therapy, Besançon University Hospital, Besançon, France
7. Department of Radiation Therapy, University of Frankfurt, Frankfurt am Main, Germany
8. Department of Radiotherapy, Maria Sklodowska-Curie Memorial Cancer Centre, Warsaw, Poland