Risk Adapted De-Intensification of Radio-Chemotherapy for Oropharyngeal Squamous Cell Carcinoma

Participants will receive either 70 gray (Gy), 60 Gy, or 50 Gy of radiation based on the following criteria: 70 Gy: Pretreatment level of plasma circulating free HPV DNA (cfHPV DNA) ≤ 3 copies/mL 60 Gy: Tumor tissue positive for HPV subtype other than 16 OR Pretreatment level of cfHPV DNA 4-99 copies/mL OR Pretreatment level of cfHPV DNA ≥ 100 copies/mL AND \<95% decrease in the level cfHPV DNA by the end of week 4 of radiation therapy 50 Gy: Tumor tissue positive for HPV subtype 16, pretreatment level of cfHPV DNA ≥ 100 copies/mL, AND ≥ 95% decrease in the level cfHPV DNA by the end of week 4 of radiation therapy

All participants will receive 40 mg/m2 of cisplatin intravenously over 60 minutes weekly during radiation therapy. If cisplatin is not recommended by the treating medical oncologist or is not tolerated, it is permissible to switch to an alternative chemotherapy regimen per institutional practice, but chemotherapy should not be discontinued unless mandated by the patient's condition.