Failure patterns after definitive radiotherapy with elective neck irradiation ≤ 40 Gy for head and neck cancer: a multi-institutional study

To evaluate the efficacy and patterns of failure after definitive radiotherapy (RT) using an elective nodal irradiation (ENI) dose of ≤40 Gy for head and neck cancer. We retrospectively analyzed 290 patients with stage I-IV oropharyngeal cancer (OPC), hypopharyngeal cancer (HPC), or laryngeal cancer (LYC) who underwent definitive RT with an ENI dose of ≤40 Gy at three institutions between 2008 and 2024. A total of 278 patients received 40 Gy of ENI, whereas ENI was omitted in 12 patients (ENI-omission). The study endpoints included patterns of failure, local control (LC), regional control (RC), progression-free survival (PFS) and overall survival (OS). With a median follow-up of 35 months among surviving patients, the 2-year LC, RC, PFS and OS rates were 79.8%, 91.2%, 63.1% and 79.8%, respectively. Regional recurrence within the ENI field occurred in only four patients (1.4%), including no patients in the ENI-omission group and four in the 40-Gy ENI group. Only one patient experienced an isolated ENI field recurrence. In the multivariable analysis, advanced N category, systemic therapy and prescribed dose were associated with OS. Advanced N category was also an independent predictor of both RC and PFS. Definitive RT using an ENI dose of ≤40 Gy achieved favorable oncologic outcomes with low incidence of regional recurrence within the ENI field. These findings support the feasibility of an ENI dose of ≤40 Gy while maintaining enough elective nodal control.