Risk-adapted Therapy in HPV+ Oropharyngeal Cancer Using Circulating Tumor (ct)HPV DNA Profile - The ReACT Study

This research study involves HPV DNA testing (a blood test that measures the levels of DNA from the human papillomavirus in the bloodstream which investigator think sheds from the cancer itself), radiation therapy, and chemotherapy for some participants. The research study procedures includes: screening for eligibility, and study treatments including evaluations and follow-up visits. The names of the test and treatments involved in this study are: * NavDx® HPV ctDNA testing (HPV blood test) * Radiation therapy: Radiation therapy alone or combined with chemotherapy is considered a standard treatment for this disease. The investigators are researching the effectiveness of reducing the radiation doses and, in some cases, also reducing the chemotherapy dose for certain participants with favorable clinical characteristics and with certain HPV blood test results. * Chemotherapy: Cisplatin, or Carboplatin and Paclitaxel (not all participants receive any or all of these agents) * Study treatment will for up to 7 weeks and participants will be followed for 5 years from the beginning of the study. * It is expected that about 145 people will take part in this research study. The HPV ctDNA levels will be measured using a blood test called NavDx®, which will be provided free of charge from the company NAVERIS. ctDNA testing refers to circulating tumor (ct)DNA or measuring DNA fragments floating in the bloodstream that are released from the cancer cells. This testing has shown promise in early detection of cancer recurrence in several solid tumor types (including colorectal, urothelial, and breast cancer). Additionally, recent studies have shown a connection between baseline ctDNA levels and disease risk. The U.S. Food and Drug Administration (FDA) has not approved NavDx® as a method for guiding treatment decision-making, but this is an important part of this research study. While the NavDx® assay is investigational, it is performed in a Clinical Laboratory Improvement Amendment (CLIA) certified clinical laboratory and is currently available as a clinical tool for measuring HPV ctDNA levels in some cancer patients. CLIA regulations include federal standards applicable to all United States facilities or sites that test human specimens for health assessment or to diagnose, prevent, or treat disease This research study is a Phase II clinical trial. Phase II clinical trials test the safety and effectiveness of an investigational intervention to learn whether the intervention works in treating a specific disease. "Investigational" means that the intervention is being studied. Radiation therapy alone or combined with chemotherapy is considered a standard treatment for this disease. The investigators are researching the effectiveness of reducing the radiation doses and, in some cases, also reducing the chemotherapy dose for certain participants with favorable clinical characteristics and with certain HPV blood test results.