1. Center for Proton Therapy, Paul Scherrer Institute, ETH Domain, 5232 Villigen, Switzerland
2. Department of Radiation Oncology, Inselspital, Bern University Hospital, University of Bern, 3012 Bern, Switzerland
3. Department of Pediatric Hematology and Oncology, University Hospital Bonn, 53127 Bonn, Germany
4. Department of Radiation Oncology, University of Zürich, 8091 Zürich, Switzerland