1. Department of Radiation Oncology, University Medical Center Utrecht, 3508 GA , The Netherlands
2. Department of Radiation Oncology, Gustave Roussy Campus , Villejuif 94 800, France
3. Department of Oncology, University College London Hospitals NHS Foundation Trust , London NW1 2PB, United Kingdom
4. Department of Radiation Oncology, University Hospital Heidelberg , Heidelberg 69120, Germany
5. Institut Claudius Regaud, Institut Universitaire du Cancer de Toulouse-Oncopole, Toulouse NeuroImaging Center, Université de Toulouse, Inserm, UPS, Toulouse 31100 , France
6. Danish Centre for Particle Therapy, Aarhus University Hospital , Aarhus DK-8200, Denmark
7. The Christie NHS Foundation Trust and Division of Cancer Sciences, University of Manchester, Manchester Cancer Research Centre, Manchester Academic Health Science Centre , Manchester M20 4BX, United Kingdom
8. Princess Maxima Center for Pediatric Oncology , Utrecht 3582CS, The Netherlands