Testing the Safety of Giving a Standard Dose of Radiation Over a Shorter Period of Time for Patients Who Had Surgery for Intermediate-Risk Head and Neck Cancer

Inclusion Criteria: * Pathologically (histologically) proven diagnosis of squamous cell carcinoma (including variants such as verrucous carcinoma, spindle cell carcinoma, carcinoma NOS, etc.) of the head/neck (oral cavity, oropharynx or larynx); Note: Hypopharynx primaries are excluded because these patients have both a poor prognosis and high likelihood of post- radiation complications. * Clinical stage I-IVA squamous cell carcinoma of the oral cavity, oropharynx or larynx (AJCC 8th edition), including no distant metastases. * General history and physical examination prior to registration; * Chest X-ray (at a minimum) or chest CT scan (with or without contrast) or PET/CT of chest (with or without contrast) prior to registration. * Total resection of the patient's cancer (i.e. no residual disease after total resection of the patient's cancer). * One or more indications for postoperative radiotherapy, based upon pathologic findings: * Perineural invasion; * Lymphovascular invasion; * Single lymph node ≥ 3 cm or ≥ 2 lymph nodes (no extracapsular Extension); * Close margin(s) of resection (close margins defined as cancer extending to within 5 mm of a surgical margin); * Pathologically confirmed T3 or T4a primary tumor; * T2 oral cavity cancer with ≥ 5 mm depth of invasion. * Zubrod Performance Status 0-1. * Age 18-80. * Negative pregnancy test within 14 days prior to registration for participants who may become pregnant. * Patients with a prior or concurrent m…