Head and Neck Cancer

SS 31 - H&N 3 - Strategies to Improve Outcomes and Minimize Toxicity in Oropharyngeal Cancer

224 - High Local Control Rates of p16-Positive Squamous Cell Carcinomas of the Oropharynx Following Intensity Modulated Radiation Therapy Without a Clinical Target Volume Expansion

Tuesday, October 23
4:55 PM - 5:05 PM
Location: Room 214 A/B

High Local Control Rates of p16-Positive Squamous Cell Carcinomas of the Oropharynx Following Intensity Modulated Radiation Therapy Without a Clinical Target Volume Expansion
A. Burr1, P. M. Harari1, R. J. Kimple2, and M. E. Witek1; 1Department of Human Oncology, University of Wisconsin, Madison, WI, 2University of Wisconsin School of Medicine and Public Health, Department of Human Oncology, Madison, WI

Purpose/Objective(s): The favorable outcomes of patients with p16-positive oropharyngeal squamous cell carcinoma (OPSCC) warrant investigation of treatment techniques that maintain excellent clinical outcomes while minimizing overall toxicity. The purpose of this study was to examine local control and toxicity for patients treated with direct expansion of the gross tumor volume (GTV) to planning target volume (PTV) for their primary tumor (without a clinical target volume (CTV) expansion).

Materials/Methods: We queried our institutional database for p16-positive OPSCC treated with definitive radiation or chemoradiation using IMRT between 2002 and 2016 to a dose of 70 Gy. The GTV was defined by physical exam combined with imaging findings and expanded by 3mm to create the PTV. Imaging at the time of first failure was registered to the treatment planning scan containing target volumes in order to categorize failure patterns. In-field failures were defined if 95% of the recurrent tumor volume was contained within the 95% isodose line (IDL). Marginal failures were defined if 20-80% of the recurrent tumor extended outside of the 95% IDL and out-of-field failures were defined if greater than 80% of the recurrence was outside the 95% IDL. The Kaplan-Meier method was used to estimate overall survival and local recurrence free survival. Univariate analysis was used to identify variables associated with local control.

Results: We identified 134 p16-positive OPSCC patients meeting our search criteria. Median follow-up was 48 months (range 0.4-151.3) with a 5-year overall survival of 81.1% (95% CI: 74.1% to 88.8%). Local recurrence free survival was 91.3 % (95% CI: 86.6% to 96.4%). Ten patients (7.5% of study group) developed recurrence of the primary tumor. There were 7 in-field failures and 1 marginal failure. Two out-of-field failures were identified involving the floor of mouth and carotid sheath, respectively. There were no variables associated with local failure in univariate analysis. The median time to gastrostomy tube removal was 2.7 months from treatment completion with 9.7% of patients remaining gastrostomy tube dependent at 2 years or at time of death. Of those with long term gastrostomy tubes, 77% retained their gastrostomy tube because of disease progression and ultimately died from their disease. The rate of grade ≥2 xerostomia and dysphagia were 39% and 12% at 2 years, respectively.

Conclusion: The above represents the largest local control analysis for p16-positive OPSCC treated with IMRT planned without incorporation of a clinical target volume expansion. Despite refined target volumes and steep dose gradients associated with IMRT, excellent local control was achieved (92.5%) with less than 10% gastrostomy tube retention. These data support prospective evaluation of reduced primary tumor volume expansions in p16-positive patients.

Author Disclosure: A. Burr: None. P.M. Harari: Member; ASTRO Board of Directors. R.J. Kimple: Employee; University of Wisconsin. Research Grant; Threshold Pharmaceuticals, Peloton Therapeutics, American Cancer Society, National Institute of Health, V Foundation for Cancer Research. M.E. Witek: None.

Adam Burr, MD, PhD

Disclosure:
Employment
University of Wisconsin Hospitals and Clinics: Resident: Employee; UW Health: Resident: Employee

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