Sparing of high retropharyngeal nodal basins in patients with unilateral oropharyngeal carcinoma treated with intensity modulated radiation therapy.

PURPOSE: The introduction of intensity modulated radiotherapy (IMRT) has facilitated dose painting and sparing of uninvolved/low-risk nodal basins in head and neck cancers. In oropharynx cancer (OPC), the need for elective coverage of uninvolved high contralateral retropharyngeal (RP) nodes and the risk associated with sparing this region remain unclear. We examined outcomes of OPC patients treated with IMRT and omission of contralateral high RP coverage.

METHODS AND MATERIALS: We identified 102 OPC patients with cN0-N2b disease treated with definitive IMRT with or without concurrent chemotherapy between 2010 and 2013. The contralateral RP nodal basins superior to the vertebral level of C1 were omitted from the elective IMRT field for all patients. Of the 67 patients (66%) with p16 status available, 63 (94%) were p16+ . We used the Kaplan-Meier method to estimate overall survival, as well as freedom from local failure, regional failure, distant failure, and retropharyngeal failure.

RESULTS: The median follow-up was 26.9 months (range, 3.0-59.9 months). There were no failures in the treated ipsilateral RP nodes or the spared contralateral high RP nodes in the entire cohort. In the p16+ cohort and the entire cohort, the 2-year rates of overall survival and freedom from local, regional, distant, and retropharyngeal failure were 98.0% and 95.1%, 98.1% and 97.7%, 96.4% and 96.7%, 98.1% and 95.1%, and 100% and 100%, respectively.

CONCLUSIONS: Omission of contralateral high RP nodes in patients with p16+ OPC with unilateral disease is safe.