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 hematologic function within 30 days prior to registration, defined as follows: * White Blood Count (WBC) \>/= 2 K/mcL * Absolute neutrophil count (ANC) ≥ 1,000 cells/mm3 * Platelets ≥ 100,000 cells/mm3 * Hemoglobin ≥ 8.0 g/dl; Note: The use of transfusion or other intervention to achieve Hgb ≥ 8.0 g/dl is acceptable * Adequate renal function within 30 days prior to registration, defined as follows: * Serum creatinine ≤ 1.5 mg/dl or creatinine clearance (CC) ≥ 50 ml/min determined by 24-hour collection or estimated by Cockcroft-Gault formula CCr male = \[(140 - age) x (wt in kg)\] \[(Serum Cr mg/dl) x (72)\] CCr female = 0.85 x (CrCl male) * Adequate hepatic function within 30 days prior to registration, defined as follows: * Bilirubin ≤ 2 mg/dl * AST or ALT ≤ 3 x the upper limit of normal * Negative serum pregnancy test within 14 days prior to registration for women of childbearing potential * The subject must provide study-specific informed consent prior to study entry Exclusion Criteria: * Subjects with prior head and neck radiation therapy * Subjects with simultaneous primary cancers outside of the oropharynx * Note: Exceptions can be made for patients with simultaneous primaries outside the oropharynx if determined by the PI/Co-PI the patient can proceed with protocol activities * Prior invasive malignancy (except non-melanomatous skin cancer) unless disease free for 3 years or if cure rate from treatment at 5 years to be 90% or greater * Prior systemic chemotherapy for the study cancer; note that prior chemotherapy for a different cancer is allowable * No particle therapy such as but not limited to proton therapy is allowed in Cohort A. For Cohort B, this exclusion is removed. * Severe, active co-morbidity defined as follows: * Unstable angina and/or congestive heart failure requiring hospitalization within the last 6 months * Transmural myocardial infarction within the last 6 months * Acute bacterial or fungal infection requiring intravenous antibiotics at the time of registration * Chronic Obstructive Pulmonary Disease exacerbation or other respiratory illness requiring hospitalization or precluding study therapy within 30 days of registration * Hepatic Insufficiency resulting in clinical jaundice and/or coagulation defects