[1] Princess Margaret Hosp, Dept Med Oncol, Toronto, ON M5G 2M9, Canada
[2] Princess Margaret Hosp, Dept Biostat, Toronto, ON M5G 2M9, Canada
[3] Princess Margaret Hosp, Dept Radiat Oncol, Toronto, ON M5G 2M9, Canada
[4] Univ Toronto, Toronto Hosp, Toronto, ON, Canada
[5] Univ Toronto, Program Clin Epidemiol & Hlth Serv Res, Toronto, ON, Canada
[6] McMaster Univ, Dept Clin Epidemiol & Biostat, Hamilton, ON, Canada
[7] Tom Baker Canc Ctr, Calgary, AB, Canada
[8] Hamilton Reg Canc Ctr, Hamilton, ON L8V 1C3, Canada
[9] Virginia Commonwealth Univ, Med Coll Virginia, Massey Canc Ctr, Richmond, VA 23298 USA