1. Department of Radiation Oncology, Catalan Institute of Oncology, L'Hospitalet de Llobregat, Barcelona, Spain
2. Medical Physics Department, Umberto I Hospital, Mestre, Italy
3. Department of Radiation Oncology, ERESA. Hospital General Universitario, Valencia, Spain
4. Euskal Herriko Univesitatea, Spain
5. Catalan Institute of Oncology, L'Hospitalet de Llobregat, Barcelona, Spain