This is a single-arm, phase II study to establish the safety of reducing radiation dose in selected HPV-Associated OPSCC patients receiving adjuvant radiation after TORS and neck dissection. This protocol also allows for sparing of the primary resection bed, in appropriate patients, as previously published by our group and found to be safe and effective.

This is a single-arm Phase II non-inferiority study of adjuvant radiation for locally-advanced HPV-Associated oropharyngeal squamous cell carcinoma. Patients with pT0-T3, N0-N1, M0 disease (per AJCC 8th Edition), detectable pre-operative and undetectable postoperative ctHPVDNA will be eligible. Patients will have undergone TORS primary site resection and neck dissection. Patients will undergo adjuvant RT +/- guideline-indicated chemotherapy. The neck and the primary site will be considered separately.

The primary objective of the study will be to determine the 2-year locoregional control (LRC) rate. Secondary objectives include measures of toxicity (as measured by CTCAE, version 5.0), patient-reported QOL (as measured by the MDASI and MDADI questionnaire), progression-free survival, metastasis-free survival, and overall survival. Differences between patients treated with IMRT and proton therapy in terms of toxicity and QOL will serve as another secondary objective.

Inclusion Criteria:

• Patients ≥ 18 years old
• Histologically confirmed diagnosis of squamous cell carcinoma of the oropharynx, p16-positive on immunohistochemistry or HPV-positive by In-Situ Hybridization
• Pathologic T0 (unknown primary), T1, T2, or T3 disease (per AJCC 8th Ed)
• Pathologic N0-N1 disease (per AJCC 8th Ed)
• Preoperative plasma ctHPVDNA of ≥ 50 copies/mL
• Undetectable postoperative plasma ctHPVDNA
• ECOG Performance Status 0-1

Exclusion Criteria:

• Prior external beam radiation therapy to the head and neck
• Presence of T4 disease
• ≥ 5 positive lymph nodes (which is pathologic N2 disease, per AJCC 8th edition)
• Presence of distant metastatic disease
• Uncontrolled inter-current 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.