p16+ Oropharyngeal Cancer Radiation Optimization Trial Reducing Elective Treatment Volumes (PROTEcT)

Inclusion Criteria: * Age 18 or older * Provide informed consent * ECOG performance status 0-2 * Histologically confirmed squamous cell carcinoma * p16-positive tumor, as determined by immunohistochemistry at local hospital * Primary tumor site in the oropharynx (includes tonsil, soft palate, base of tongue, walls of oropharynx) * Eligible for curative intent treatment. * Smokers and non-smokers are included * Tumor stage (AJCC 8th edition): T1 to T3 * Nodal stage (AJCC 8th edition): N1 to N2 * Adequate bone marrow function, hepatic, and renal function for chemotherapy (Hemoglobin \> 80 g/L; Absolute neutrophil count \>1.5x109 /L, platelets \> 100 x109/L; Bilirubin \< 35 umol/L; AST or ALT \< 3 x the upper limit of normal; serum creatinine \< 130 umol/L or creatinine clearance ≥ 50 ml/min) Exclusion Criteria: * \- Clinical, radiologic or pathologic Ib nodal involvement (including invasion into submandibular gland) * Primary cancer with extension and involvement of the oral cavity * Metastatic disease * Contraindications to radiotherapy or chemotherapy * Prior history of head and neck cancer within 5 years * Prior head and neck radiation at any time * Inability to attend full course of radiotherapy or follow-up visits * Pregnant or lactating women