Postoperative Unilateral Neck Irradiation for Oral Cancer: Risk Factors for Contralateral Neck Recurrence and Implications for Patient Selection

Introduction: Postoperative irradiation is commonly used in patients with oral cancer who are at high risk of recurrence. However, the need for contralateral neck irradiation remains controversial. This study evaluated the efficacy of unilateral neck irradiation and identified risk factors for recurrence in the contralateral neck. Methods: This retrospective study included 85 patients with oral cancer (27-88 years of age; median, 65 years) who underwent postoperative unilateral neck irradiation at a single institution between 2010 and 2023. Recurrence patterns and late adverse events were analyzed. The ipsilateral neck control rate (INCR), neck control rate (NCR), progression-free survival (PFS), and overall survival (OS) were estimated using the Kaplan-Meier method. The two-year contralateral neck control rate (CNCR) was evaluated using log-rank testing and Cox proportional hazards regression. Results: The median duration of follow-up was 45 months. At two years, the rates of INCR, NCR, PFS, and OS were 85%, 77%, 69%, and 82%, respectively. Recurrence was observed in 31 (36.5%) patients, including ipsilateral recurrence in 15 (17.6%), contralateral recurrence in 11 (12.9%), and distant recurrence in 16 (18.8%), with 6 (7.1%) showing contralateral-only recurrence. No grade ≥3 late adverse events were observed. Five or more metastatic lymph nodes, ≥T2 tumors, and newly diagnosed status were significantly associated with poorer CNCR. Conclusion: Unilateral neck irradiation may be an effective strategy for selected patients with oral cancer, particularly those with fewer metastatic lymph nodes, lower T stage, or recurrent cases.