1 Collaboration for Cancer Outcomes Research and Evaluation, Ingham Institute for Applied Medical Research, UNSW Australia, Liverpool, NSW, Australia. Electronic address: michael.barton@sswahs.nsw.gov.au.
2 Applied Radiation Biology and Radiotherapy Section, Division of Human Health - Department of Nuclear Sciences and Applications, International Atomic Energy Agency, PO Box 100, 1400 Vienna, Austria.
3 Department of Radiation Oncology, Princess Margaret Hospital, Toronto, Ontario, Canada.