[1] Univ Western Ontario, Schulich Sch Med & Dent, Dept Epidemiol & Biostat, London, ON, Canada
[2] Univ Hlth Network, Princess Margaret Canc Ctr, Radiat Med Program, Toronto, ON, Canada
[3] Univ Toronto, Dept Radiat Oncol, Toronto, ON, Canada
[4] Univ Hlth Network, Energy & Environm Dept, Toronto, ON, Canada
[5] Univ Hlth Network, Princess Margaret Canc Ctr, Dept Biostat, Toronto, ON, Canada