Treatment failure pattern of oropharyngeal cancer, especially for the aspect of retropharyngeal lymph node.

Abstract

e18565 Background: In radiotherapy for head and neck cancer, it is very important to define the appropriate treatment volumes that determine the treatment outcome and toxicity. We examined the feasibility of omitting elective retropharyngeal (RP) nodal irradiation in oropharyngeal cancer. Methods: We performed a retrospective review from 2009 to 2016; 197 patients with oropharyngeal squamous cell carcinomas were treated with definitive or postoperative radiation therapy at the Seoul National University Hospital or Seoul National University Bundang Hospital. Of these patients, 151 patients (76%) were treated ipsilateral RP nodal areas up to the upper edge of C1 vertebral body, while the other 46 patients (24%) were not. We reviewed patterns of failures, disease free survival, and patient-reported chronic xerostomia status in each patient group. Results: During follow-up period, 2 patient developed RP nodal recurrences (4-108 months, median =46 months). There was no significant between-group difference in disease free survival, with a rate of 80.7% in the high RP nodal-irradiation group and 87.2% in the RP nodal spared group (P=0.17). Patients in the high RP nodal-irradiation group had higher mean ipsilateral parotid gland dose (median 28.7±7.5 Gy vs. 21.3±7.6 Gy, P<0.001) and higher rates of chronic xerostomia (72.2% vs. 58.7%, P=0.030). Conclusions: Only 2 patients with omission of high RP node irradiation developed high RP node failure, and no significant difference in DFS was shown. Omission of high RP nodal irradiation resulted in reduced ipsilateral parotid gland dose, consequently with less chronic xerostomia.