1. Department of Oncology and Medical Physics, Haukeland University Hospital, Bergen, Norway
2. Department of Physics and Technology, University of Bergen, Bergen, Norway
3. Danish Centre for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark
4. Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
5. Department of Radiation Oncology, University of Florida, Jacksonville, FL, USA