1. Department of Medical Physics, Aarhus University Hospital, Aarhus, Denmark;
2. Department of Radiation, Medicine and Applied Sciences, University of California San Diego, San Diego, CA, USA;
3. Department of Radiation Oncology, Aarhus University Hospital, Aarhus, Denmark;
4. Danish Center for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark;
5. Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York City, NY, USA