1 Division Medical Radiation Physics, Department of Radiation Oncology, Medical University of Vienna/AKH Wien, Austria.
2 Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
3 Division of Cancer Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, The Christie NHS Foundation Trust, United Kingdom; Nuffield Department of Population Health, University of Oxford, United Kingdom.
4 German Cancer Research Center (DKFZ), Heidelberg, Germany.