1. Department of Radiation Oncology, Massachusetts General Hospital/Harvard Medical School, Boston, MA, USA
2. Center for Proton Therapy, Paul Scherrer Institute, Villigen, Switzerland
3. Department of Physics, ETH Zürich, Zürich, Switzerland
4. Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany
5. OncoRay - National Center for Radiation Research in Oncology, Dresden, Germany