[1] Univ Toronto, Michener Inst, Toronto, ON, Canada
[2] Univ Toronto, Princess Margaret Canc Ctr, Dept Radiat Therapy, Toronto, ON, Canada
[3] Univ Toronto, Princess Margaret Canc Ctr, Dept Otolaryngol Head & Neck Surg Surg Oncol, Toronto, ON, Canada
[4] Univ Toronto, Princess Margaret Canc Ctr, Dept Biostat, Toronto, ON, Canada
[5] Univ Toronto, Princess Margaret Canc Ctr, Dept Radiat Oncol, Toronto, ON, Canada