1 Department of Radiation Oncology, Kliniken Maria Hilf, 41063 Mönchengladbach, Germany; Department of Radiation Oncology, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg, Germany; German Cancer Consortium Partner Site Freiburg and German Cancer Research Center, Heidelberg, Germany. Electronic address: ursula.nestle@mariahilf.de.
2 Department of Radiation Oncology, Faculty of Medicine, Medical Center, University of Freiburg, Freiburg, Germany.
3 Institute of Medical Biostatistics, Epidemiology and Informatics, University Hospital Mainz, Mainz, Germany.