1. Department of Radiation Oncology; Hospital Universitario Cruces/Biocruces Health Research Institute; Barakaldo Spain
2. Department of Radiation Oncology; Hospital Duran i Reynals; Barcelona Spain
3. Department of Radiation Oncology; Hospital de Castellón; Castelló Spain
4. Department of Radiation Oncology; Hospital Meixoeiro; Vigo Spain
5. Department of Radiation Oncology; Hospital Virgen Del Rocío; Sevilla Spain
6. Department of Radiation Oncology; Hospital Virgen Macarena; Sevilla Spain
7. Department of Radiation Oncology; Hospital San Chinarro; Madrid Spain
8. Bioinformatics and Statistics Department; Hospital Universitario Cruces/Biocruces Heatlh Research Institute; Barakaldo Spain
9. Department of Radiation Oncology; University of Lübeck; Lübeck Germany