Background: Our previously published proof-of-concept trial using functional imaging to select patient with human papillomavirus (HPV) oropharyngeal carcinoma (OPC) for radiation de-escalation showed promising results. Here we report the outcome of a larger validation trial using the same paradigm where select HPV+ OPC patients received a definitive dose of 30Gy concurrently with chemotherapy and were subsequently observed. Methods: The trial enrolled patients who had p16+, T0-2, N1-N2c, M0 OPC by AJCC 7th TNM. Patients were required to have resection of the primary site (negative margin not required) or core biopsy of lymph node if unknown primary. In addition to standard positron emission tomography (PET), a pre-radiation dynamic ¹⁸F-FMISO (fluoromisonidazole) PET was performed to identify hypoxia in gross nodal disease. Patients with evidence of hypoxia ( > 1.2 tumor to muscle standard uptake value on ¹⁸F-FMISO) underwent repeat¹⁸F-FMISO PET around 2 weeks into radiation. Patients without pre-radiation hypoxia or with resolution of hypoxia on ¹⁸F-FMISO PET received 30Gy with 2 cycles of concurrent chemotherapy (cisplatin 100mg/m² or carboplatin AUC 1.25 x 4 with 5-fluorouracil 2400 mg/m²). Results: From 11/2/17-1/4/21, 158 HPV+ OPC patients consented and were enrolled on trial. Patient characteristics were as follows: male (90%); ages 36-80 years; T-stage T0(26), T1(77), T2(55); N stage N1(19), N2a(15), N2b(95), N2c(29). Of the 114 patients with pre-treatment hypoxia, 24 had persistent hypoxia and received 70Gy. 128 patients were de-escalated to 30Gy and chemotherapy (86% cisplatin). 6 patients withdrew from trial [3 decided to receive standard of care; 3 refused ¹⁸F-FMISO PET]. Acute mucositis rates were 11% grade 0, 59% grade 1, and 30% grade 2, respectively. Acute xerostomia rates were 92% grade 1 and 8% grade 2, respectively. Weight loss was infrequent and only 19% complained of grade 1 and 5% complained of grade 2 weight loss. Six patients experienced grade 3 adverse events (diarrhea (2), syncope (2), vasovagal (1), dysphagia (1)). No patients required PEG tubes. With a median follow-up is 12 months (range: 2 months to 40 months), the 1-year locoregional control, distant metastasis-free overall survival rates were 94%, 100%, and 100%, respectively. Among the 30Gy de-escalated patients, none failed in the primary site. 8 patients had recurrent nodal disease underwent successful salvage surgery of which no additional therapy was given to 4 patients. Conclusions: Major de-escalation to 30Gy using patient specific treatment response based on hypoxia resolution resulted in excellent locoregional control with significant toxicity reduction. Updated results along with detailed correlative analysis will be presented. Clinical trial information: NCT03323463