Selective Adjuvant Therapy for HPV-mediated Oropharynx SCCs Based on Residual Circulating Tumor DNA Levels (SAVAL)

Inclusion Criteria 1. Is there pathologically (histologically or cytologically) proven diagnosis of p16+ squamous cell carcinoma (including the histological variants papillary squamous cell carcinoma and basaloid squamous cell carcinoma) of the oropharynx or p16+ squamous cell carcinoma unknown primary? Note: specimen from cervical lymph nodes with a well-defined primary site documented clinically or radiologically is acceptable; in patients with carcinoma of unknown primary this will be sufficient for pathologic confirmation without a clinically or radiographically defined primary site. 2. Does the patient have clinical stage T0-3, N0-N1, and M0 disease (AJCC 8th edition) as defined by physical examination and appropriate imaging (PET/CT preferred, CT neck with IV contrast with CT chest without contrast as recommended alternative to PET/CT) with imaging within 60 days of enrollment? 3. Has the patient completed a ctDNA evaluation with results demonstrating positive ctDNA levels prior to surgery either in blood or on biopsy tissue? 4. Upon multi-disciplinary review, is the patient a candidate for TORS based on evaluation by ear, nose, throat (ENT) and review at multi-disciplinary tumor board? 5. Was a general history and physical examination performed by a radiation oncologist, medical oncologist, or head and neck surgeon within 60 days prior to registration? 6. Was the patient's Zubrod Performance Status 0-1 within 30 days prior to registration? 7. Is the patient ≥ 18 years of age? 8. If a woman of child-bearing potential or sexually active male, is the patient willing to use effective contraception throughout their participation in the treatment phase of the study and at least 180 days following the last study treatment. 9. Did the patient provide study specific informed consent prior to study entry, including consent for mandatory submission of tissue for required p16 review? Exclusion Criteria 1. Does the patient have cancer considered to be from an oral cavity site (oral tongue, floor mouth, alveolar ridge, buccal or lip), nasopharynx, hypopharynx, or larynx? 2. Does the patient have distant metastasis? 3. Does the patient have prior invasive malignancy (except non-melanomatous skin cancer and low/intermediate risk prostate cancer) unless disease free for a minimum of 3 years? 4. Did the patient have prior systemic chemotherapy for the study cancer (prior chemotherapy for a different cancer is allowable)? 5. Did the patient have prior radiotherapy to the region of the study cancer that would result in overlap of radiation therapy fields? 6. Did the patient have prior cancer related surgeries of the head and neck excluding superficial removal of cutaneous skin malignancies? 7. Does the patient have any co-morbid condition or concern that may interfere with follow up per experimental arm? 8. Does the patient have an active drug or alcohol dependency that in the opinion of the investigator would limit compliance with study requirements? 9. Is the patient pregnant or nursing (an exception will be made for nursing patients that are not receiving chemotherapy)?