1. Department of Statistical Sciences, University of Toronto, Toronto, Canada
2. Department of Biostatistics, University of Florida, Gainesville, Florida, USA
3. Department of Pediatrics, Vanderbilt University, Nashville, Tennessee, USA
4. Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, New York, USA
5. Department of Radiation Oncology, University of Toronto, Toronto, Canada