CyberKnife Stereotactic Body Radiotherapy for Reirradiation of Recurrent or Metastatic Head and Neck Squamous Cell Carcinoma: Outcomes and Prognostic Factors

Background Stereotactic body radiotherapy (SBRT) is used for reirradiation in recurrent or metastatic head and neck squamous cell carcinoma (RM‐HNSCC), but prognostic factors remain unclear. Methods We retrospectively analyzed 36 RM‐HNSCC patients treated with CyberKnife‐SBRT (2009–2022). Endpoints: local control (LC) and overall survival (OS), estimated using Kaplan–Meier and Cox regression. Results Median follow‐up was 8.5 months, median OS was 9.6 months, with 1‐ and 2‐year OS rates of 43.5% and 34.2%. One‐ and 2‐year LC rates were 55.1% and 34.5%, with median time‐to‐recurrence of 14.1 months. On multivariable analysis, smoking > 30 pack‐years predicted worse LC (HR 5.68; 95% CI, 1.42–22.70; p = 0.014), while former/never smoking predicted improved OS (HR 0.26; 95% CI, 0.08–0.82; p = 0.022). Gross tumor volume > 37.0 cm 3 predicted worse LC (log‐rank p = 0.044) and OS ( p = 0.003) on univariate analysis. Conclusions Smoking history independently predicted LC and OS; larger tumor volume was associated with worse outcomes and may inform patient selection for SBRT reirradiation.