1. Department of Radiotherapy and Oncology; J. W. Goethe University; Frankfurt am Main Germany
2. Department of Radiation Oncology; Otto von Guericke University; Magdeburg Germany
3. Institute for Radiotherapy; Hirslanden Medical Center; Aarau Switzerland
4. Department of Otorhinolaryngology; J. W. Goethe University; Frankfurt am Main Germany
5. Department of Medical Physics and Engineering; Sana Klinikum Offenbach; Offenbach am Main Germany