1. Department of Radiation Oncology, Cruces University Hospital/Biocruces Bizkaia Health Research Institute, Vizcaya, Spain
2. Department of Surgery, Radiology and Physical Medicine of the University of the Basque Country (UPV/EHU), Leioa, Vizcaya, Spain
3. Department of Radiation Oncology, Instituto Catalan de Oncología, Avinguda de la Gran vía de l'Hospitalet, 199-203, 08907 L'Hospitalet de Llobregat, Barcelona, Spain
4. Department of Bioinformatics and Statistics, Cruces University Hospital/Biocruces Health Research Institute, Barakaldo, Spain
5. Department of Radiation Oncology, Hospital Virgen Del Rocío, Av Manuel Siurot, Sevilla, Spain