RecruitingRadiation therapyRadiotherapy Dose De-escalation in HPV-Associated Cancers of the OropharynxThe purpose of this study is to use intra-treatment 18FDG-PET/CT during definitive radiation therapy for human papillomavirus (HPV)-related oropharyngeal cancer (OPC) as an imaging biomarker to identify and select patients with a favorable response for chemoradiation dose de-escalation. This study will prospectively evaluate the clinical outcomes for patients undergoing dose de-escalation.