Major De-escalation to 30 Gy for Select Human Papillomavirus Associated Oropharyngeal Carcinoma

Inclusion Criteria: \- Cohort A: Pathologically (histologically or cytologically) proven diagnosis of HPV associated squamous cell carcinoma of the oropharynx (tonsil, base of tongue, or oropharyngeal walls) from surgical resection or excisional biopsy regardless of margin status. * Squamous cell carcinoma of the neck of unknown primary is allowed with excision biopsy of a lymph node (or core biopsy) and consent from the PI or co-PIs * Cohort B: Pathologically (histologically or cytologically) proven diagnosis of HPV associated squamous cell carcinoma of the oropharynx (tonsil, base of tongue, or oropharyngeal walls). Surgical removal of primary site is no longer required. * Squamous cell carcinoma of the neck of unknown primary is allowed with excision biopsy of a lymph node (or core biopsy) and consent from the PI or co-PIs * Subjects must have clinically or radiographically evident measurable disease at nodal stations. * Clinical stage T1-2, N1-2c without evidence of distant metastasis based on FDG PET/CT. * Patients who have squamous cell carcinoma of the neck of unknown primary, and thus, are T0, are allowed with excision biopsy of a lymph node (or core biopsy) or consent from the PI or co-PI * CT or MRI of the neck with and without contrast Note: A CT scan of neck and/or a PET/CT performed for the purposes of radiation planning may serve as planning tools. * ECOG Performance Status of 0-2 or Karnopsky Performance Status \>/= 50 * Age ≥ 18 * Adequate h…