[1] Univ Toronto, Princess Margaret Canc Ctr, Dept Radiat Oncol, Toronto, ON M4N 3M5, Canada
[2] Univ Toronto, Sunnybrook Hlth Sci Ctr, Dept Radiat Oncol, Toronto, ON M4N 3M5, Canada
[3] Univ Toronto, Sunnybrook Res Inst, Dept Surg, Orthopaed Biomech Lab, Toronto, ON M4N 3M5, Canada
[4] Univ Toronto, Toronto Western Hosp, Div Neurosurg, Toronto, ON M4N 3M5, Canada
[5] Univ Toronto, Toronto Western Hosp, Spinal Program, Toronto, ON M4N 3M5, Canada
[6] Univ Calif San Francisco, Dept Radiat Oncol, San Francisco, CA USA