RecruitingRadiation therapyTreatment De-Escalation for Favorable Prognosis Human Papilloma Virus (HPV) or p16-Positive Oropharyngeal Cancer Receiving Definitive RadiotherapyThe current standard treatment option for Human Papillomavirus (HPV) or p16-positive oropharyngeal cancer is full-dose radiation combined with chemotherapy. Results with chemotherapy combined with full-dose radiation therapy leads to high rates of cure; this has called into question whether therapy can be decreased in intensity since both chemotherapy and radiation have long-term side effects. One approach to decrease intensity of treatment is to give radiation alone (excluding chemotherapy) and to decrease radiation therapy dose. The investigator believes that omitting chemotherapy and decreasing radiation dose both to tumor and the regions of the head and neck at highest risk of potential spread, may have no significant impact on the cancer recurring while potentially leading to fewer long-term side effects.