Trial of Individualized Adaptive RT in HPV-related High Risk Oropharynx Cancer

Inclusion Criteria: * Patients must have pathologically confirmed, locally/regionally advanced p16+ squamous cell carcinoma of the oropharynx referred for definitive chemo-RT * AJCC 8 Stage III (cT4 or N3) * ECOG 0-1 performance status within two weeks of enrollment * Pre-treatment laboratory criteria within four weeks of enrolment: WBC \> 3500/ul, granulocyte \> 1500/ul. Platelet count \> 100,000/ul. Total Bilirubin \< 1.5 X ULN. AST and ALT \< 2.5 X ULN. Estimated Creatinine clearance \>30cc/min * Patients must be able to receive protocol chemotherapy in the judgment of the treating Medical Oncologist * Age \>18 * All patients must be informed of the investigational nature of this study and given written informed consent in accordance with institutional and federal guidelines. * Women of childbearing potential and male participants must agree to use a medically effective means of birth control throughout their participation in the treatment phase of the study. Exclusion Criteria: * Pregnancy or women of childbearing potential and men who are sexually active and not willing/able to use medically acceptable forms of contraception; this exclusion is necessary because the treatment involved in this study may be significantly teratogenic. * Patients should have no contraindications to having a contrast enhanced MRI scan. These contraindications will be assessed at the time of enrollment using the guidelines set up and in clinical use by the Institutional Standard Practice. * Patients should have no contraindications to having a contrast enhanced PET scan. These contraindications will be assessed at the time of enrollment using the guidelines set up and in clinical use by the Institutional Standard Practice. * Prior invasive malignancy (except non-melanomatous skin cancer) unless disease free for a minimum of 3 years (For example, carcinoma in situ of the breast, oral cavity, or cervix are all permissible). * Any prior therapy for the study cancer; note that prior chemotherapy for a different cancer is allowable if \> 3 years prior to study;