1 Aarhus University Hospital, Department of Oncology, Denmark.
2 Medical University of Vienna, Comprehensive Cancer Center, Department of Radiation Oncology, Austria.
3 Gustave Roussy Cancer Campus Grand Paris, Department of Radiation Oncology, Villejuif, France.
4 University Medical Center Utrecht, Department of Radiotherapy, The Netherlands.
5 Department of Radiation Oncology, University Hospital Gasthuisberg, Leuven, Belgium.
6 Medical University of Vienna, Comprehensive Cancer Center, Department of Radiation Oncology, Austria. Electronic address: richard.poetter@akhwien.at.