Selective Avoidance of Nodal VolumEs at Minimal Risk (GCC 20110)

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 (tonsil or base of tongue)? Note: Cytologic diagnosis from a cervical lymph node (from a paraffin block, not from smears) is sufficient in the presence of clinical evidence of a primary tumor in the oropharynx. Clinical evidence should be documented, may consist of palpation, imaging, or endoscopic evaluation, and should be sufficient to estimate the size of the primary (for T stage). 2. Does the patient require elective contralateral radiotherapy in the definitive or adjuvant setting (i.e. base of tongue primary or tonsil with base of tongue invasion, soft palate invasion, or medialized as defined by \> 1/3 of the distance from the tonsil to the midline of the soft palate? 3. Does the patient have clinical stage T1-4, N0, N1 or N3, 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)? 4. 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? 5. Was the patient's Zubrod Performance Status 0-1 within 30 days prior to registration? 6. Is the patient ≥ 18 years of age? 7. For women of childbearing potential, was a serum pregnancy test completed within 2 weeks of initiation or radiotherapy? 8. If yes, was the serum pregnancy test negative? 9. 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. 10. 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 a carcinoma of the neck of unknown primary origin? 3. Does the patient have distant metastasis? 4. Does the patient have prior invasive malignancy (except non-melanomatous skin cancer) unless disease free for a minimum of 3 years? 5. Did the patient have prior systemic chemotherapy for the study cancer (prior chemotherapy for a different cancer is allowable)? 6. Did the patient have prior radiotherapy to the region of the study cancer that would result in overlap of radiation therapy fields? 7. Did the patient have prior surgery of the head and neck excluding superficial removal of cutaneous skin malignancies? 8. Is the patient homeless? 9. Does the patient have an active drug or alcohol dependency? 10. Is the patient pregnant or nursing (an exception will be made for nursing patients that are not receiving chemotherapy)? 11. Radiographic evidence of contralateral nodal disease as described below. 1) Max standardized uptake value (SUV) greater than 3.0, or 2) Short-axis diameter is \> 1.5 cm for level II nodes, \> 0.8 cm for retropharyngeal node, or \> 1.0 cm for level III, IV, or V, or 3) Central necrosis or heterogeneous enhancement