Omitting Elective Irradiation of the Contralateral Retropharyngeal Nodes in Oropharyngeal Squamous Cell Carcinoma Treated with Intensity-modulated Radiotherapy

Introduction: The use of intensity-modulated radiation therapy (IMRT) in head and neck cancers has allowed for selective sparing of low-risk or uninvolved lymph nodes. In oropharyngeal cancers, the benefits and risks of omitting contralateral retropharyngeal lymph nodes (RPLN) remain uncertain. This study examines the outcomes of elective coverage of contralateral RPLN in oropharyngeal cancer treated with definitive IMRT. Methods: We analyzed 54 patients with newly diagnosed unilateral tonsil or base of tongue squamous cell carcinoma with at most unilateral neck involvement (cN0-N2b) and no RPLN involvement. These patients had no prior head and neck irradiation and were treated with definitive radiotherapy or chemoradiotherapy between 2012 and 2017. Cumulative incidences of local/regional/distant failure were estimated using competing risks methodology, and overall survival (OS) was estimated using the Kaplan-Meier method. Results: All patients received elective nodal coverage to the ipsilateral RPLN, and 38 (62%) patients did not receive elective treatment of the contralateral RPLN. There were no significant differences in baseline characteristics. There were no contralateral RPLN failures observed. When comparing patients who received contralateral RP treatment with those who did not, there were no significant differences in two-year local failure (23% vs. 9%, p = 0.09), regional failure (18% vs. 4%, p = 0.12), or distant failure (15% vs. 9%, p = 0.62). Two-year OS was 89%. Mean parotid dose was not significantly lower after sparing vs. treating the contralateral RPLN (median 25.6 vs. 32.7 Gy, p = 0.15). Conclusions: The omission of contralateral RPLN irradiation in tonsil or tongue base carcinomas with unilateral neck involvement is safe without compromising disease control.