1. Department of Radiotherapy; University Hospital of Münster; Münster Germany
2. Center for Radiotherapy Rheine/Osnabrück; Osnabrück Germany
3. Western German Proton Therapy Center; University Hospital of Essen; Essen Germany
4. Center for Proton Radiation Therapy; Paul Scherrer Institute; Villigen Switzerland
5. Department of Radiotherapy; Clinic Augsburg; Augsburg Germany
6. Department of Radiotherapy; University Hospital of Homburg/Saar; Homburg/Saar Germany
7. Department of Radiotherapy; University Hospital of Leipzig; Leipzig Germany
8. Department of Radiotherapy; University Hospital of Aachen; Aachen Germany
9. Department of Radiotherapy; University Hospital of Frankfurt; Frankfurt Germany
10. Institute of Biostatistics and Clinical Research (IBKF); University of Münster; Münster Germany