1 Division of Radiotherapy and Imaging, Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Sutton SM2 5PT, UK. Electronic address: john.yarnold@icr.ac.uk.
2 Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.
3 Division of Radiation Oncology, Tom Baker Cancer Centre, Calgary, AB, Canada.
4 Department of Radiation Oncology, Dr Bernard Verbeeten Instituut, Tilburg, Netherlands.
5 Advanced Centre for Treatment, Education and Research in Cancer, Tata Memorial Center, Mumbai, India.