1. Department of Radiation Oncology, Nova Scotia Cancer Centre, Halifax, NS B3H 1V7, Canada
2. Department of Radiation Oncology, Dalhousie University, Halifax, NS B3H 1V7, Canada
3. Department of Surgery, BC Cancer - Vancouver, Vancouver, BC V5Z 4E6, Canada
4. Department of Radiation Oncology, Princess Margaret Cancer Centre, Toronto, ON M5T 1W6, Canada
5. Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA
6. Department of Medicine, University of Florida Health Cancer Center, Gainesville, FL 32610, USA