A Single-arm Phase II Study of Post-Transoral Robotic Surgery (TORS) Alone to the Primary Tumor Site and Selective Neck Dissection (SND) Followed by Adjuvant Radiation Therapy (+/- Chemotherapy) to the Regional Nodes for Advanced Stage, Human Papilloma Virus (HPV) Positive, Oropharyngeal Cancer

Inclusion Criteria: * Patients 18 years or older Histologically confirmed diagnosis of squamous cell carcinoma of the oropharynx, stage IVa, p16-positive on immunohistochemistry Pathologic T1 or T2 disease, resected with negative margins ( 2mm) Pathologic N2a, N2b, or N2c disease ECOG Performance Status 0-1 * Patients must sign an informed consent document that indicates they are aware of the investigational nature of the treatment in this protocol as well as the potential risks and benefits - - - Ability to understand and the willingness to provide written informed consent Exclusion Criteria * Prior radiation therapy to the head and neck Prior chemotherapy within the past 5 years Presence of T3 or T4 disease Presence of close (2 mm) or positive margins PNI on TORS resection of the primary cancer Presence of N0 or N1 disease in neck dissection Presence of distant metastatic (M1) disease * Uncontrolled intercurrent illness including, but not limited to, symptomatic congestive heart failure, unstable angina pectoris, connective tissue disease or psychiatric illness/social situations that would limit compliance with study requirements.