1178 - Locoregional Control and Dosimetry after Standard-Dose vs. Reduced-Dose Elective Nodal Chemoradiotherapy for HPV-Associated Oropharyngeal Carcinoma
Presenter(s)
M. Bian1, S. R. Campbell2, P. E. Clark3, R. W. Davis2, D. LaHurd4, K. Burkitt3, T. A. Sussman5, J. L. Geiger6, D. Bottalico7, J. Ku7, B. Prendes7, J. Scharpf8, E. Lamarre7, S. A. Koyfman2, N. M. Woody2, and J. A. Miller2; 1Case Western Reserve University School of Medicine, Cleveland, OH, 2Department of Radiation Oncology, Cleveland Clinic Foundation, Cleveland, OH, 3Cleveland Clinic, Cleveland, OH, 4Department of Radiation Oncology, Taussig Cancer Center, Cleveland Clinic, Cleveland, OH, 5Department of Hematology and Medical Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH, 6Department of Hematology and Medical Oncology, Taussig Cancer Center, Cleveland Clinic, Cleveland, OH, 7Department of Head and Neck Surgery, Integrated Surgical Institute, Cleveland Clinic, Cleveland, OH, 8Department of Otolaryngology, Head and Neck Institute, Cleveland Clinic, Cleveland, OH
Purpose/Objective(s): The optimal elective nodal irradiation (ENI) dose for Human Papillomavirus (HPV)-associated oropharyngeal carcinoma (OPC) has not been defined and is extrapolated from HPV-negative mucosal carcinomas. Isolated locoregional recurrences in electively irradiated regions is uncommon. Furthermore, ENI contributes to acute and late morbidity and may interfere with anti-tumoral immunity. We sought to compare locoregional control and dosimetry between patients treated with 30Gy versus 54Gy ENI (EQD2). We hypothesized that locoregional control would be similar.
Materials/Methods: We conducted a retrospective observational cohort study including patients with newly diagnosed AJCC8 stage I-III HPV+ OPC treated with definitive platinum-based photon chemoradiotherapy to 70 Gy in 35 fractions from 2021-2025. Patients who underwent resection or were treated with induction chemotherapy were excluded. After 09/2023, our institutional standard for ENI in this population changed from 56 Gy in 35 fractions (54Gy EQD2, integrated boost) to 30 Gy in 15 fractions (sequential boost) based on prior studies.
Results: One hundred forty-five patients were included (67 [30Gy ENI], 78 [54Gy ENI]). Pre-treatment patient and tumor characteristics were similar. A greater proportion of subjects treated with 54Gy smoked at least 10 pack-years (55 vs. 33%). Most patients had stage I disease (58 [30Gy] vs. 68% [54Gy]). Median radiotherapy duration was 49 days in both cohorts. Weekly cisplatin was administered in 84% vs. 47% (p<0.01) among patients treated with 30Gy vs 54Gy ENI. Feeding tube placement <90 days from end of treatment was 12% for both groups. Median follow-up was 12 months for 30Gy versus 45 months for 54Gy.
12-month local, regional, distant failure-free and overall survival were similar between 30Gy and 54Gy cohorts (LFFS [97 vs 99%, p=0.4], RFFS [99 vs 99%, p=0.6], DFFS [100 vs 98%, p=0.2], OS [98 vs 99%, p=0.8]). No isolated nodal recurrences occurred in the 30Gy group—two patients treated with 30Gy ENI developed synchronous local and regional nodal recurrences within the 70Gy volume. Median absolute lymphocyte counts were not statistically significantly different three months after chemoradiotherapy (880/mL [30Gy] vs. 780/mL [54Gy], p=0.09). Compared with patients treated with 54Gy ENI, significant (p<0.01) reductions in mean doses to the pharyngeal constrictors (10%), supraglottis (14%), contralateral parotid (28%), contralateral submandibular gland (30%), and glottis (34%) were observed with 30Gy ENI. There were no statistically significant reductions in dose to oral cavity or ipsilateral parotid gland.Conclusion: No isolated nodal recurrences were observed in a consecutive cohort of patients treated with definitive chemoradiotherapy to 70 Gy in 35 fractions with 30Gy ENI, predominantly with concurrent weekly cisplatin. Additional follow-up is required to assess whether long-term disease control, lymphocyte recovery, or late toxicity differ between these two approaches.