1. Department of Radiation Oncology; University Hospital Zurich; Zurich Switzerland
2. Department of Radiation Oncology; Leopoldina Hospital Schweinfurt; Schweinfurt Germany
3. Cancer Research UK/Medical Research Council Oxford Institute for Radiation Oncology, Gray Laboratories; University of Oxford; Oxford United Kingdom
4. Department of Radiation Oncology; Netherlands Cancer Institute; Amsterdam the Netherlands
5. Department of Radiotherapy; Royal Marsden NHS Foundation Trust/Institute of Cancer Research; Sutton United Kingdom
6. Department of Radiation Oncology; University Hospital Würzburg; Würzburg Germany