1. Departments of Otolaryngology, Head and Neck Surgery, and
2. Departments of Radiotherapy and
3. Neurosurgery, Maastricht University Medical Centre;
4. Neurosurgery, Gamma Knife Centre Tilburg, St. Elisabeth Hospital, Tilburg; and
5. Department of Epidemiology and Statistics, Maastricht University, Maastricht;
6. Department of Radiology, Isala Klinieken, Zwolle, The Netherlands