University of Toronto - Department of Radiation Oncology, University of Toronto - Department of Biostatistics, Cleveland Clinic - Department of Radiation Oncology, Mayo Clinic - Department of Radiation Oncology, Maastricht University - Department of Radiation Oncology (MAASTRO), University of Toronto - Princess Margaret Cancer Centre, University of Toronto - Princess Margaret Cancer Centre, University of Toronto - Princess Margaret Cancer Centre, Cleveland Clinic - Imaging Institute, Cleveland Clinic - Imaging Institute, Cleveland Clinic - Department of Radiation Oncology, Cleveland Clinic - Department of Radiation Oncology, Mayo Clinic - Department of Radiology, Mayo Clinic - Department of Radiation Oncology, Mayo Clinic Hospital - Phoenix - Department of Otolaryngology-Head and Neck Surgery, Maastricht University - Department of Radiology and Nuclear Medicine, Maastricht University - Department of Radiology and Nuclear Medicine, Maastricht University - GROW School for Oncology and Developmental Biology, Creighton University - Department of Surgery, Memorial Sloan Kettering Cancer Center, University of Toronto - Department of Biostatistics and University of Toronto