Tumor Volume Response on Interim CT asa Prognostic Marker in Head and Neck Squamous Cell Carcinoma (HNSCC)

Background: Tumor volume dynamics during treatment are increasingly recognized as potential biomarkers in head and neck squamous cell carcinoma (HNSCC). This study aimed to evaluate the prognostic value of interim tumor volume response during chemoradiotherapy based on imaging-derived volumetry. Methods: We retrospectively analyzed interim CT scans from a prospective, multicenter phase III trial in patients with locally advanced HNSCC treated with concurrent chemoradiotherapy. The primary variable of interest was the tumor volume reduction rate (VRR) following approximately 49,6 Gy of treatment (corresponding to ~5 weeks of therapy). Volumetric data were obtained through manual segmentation, and associations with locoregional control and overall survival (OS) were assessed via uni- and multivariable analysis. Results: Patients with poor volumetric response (VRR < 30.1%) had significantly lower locoregional control and survival rates. In multivariable models, VRR emerged as an independent predictor of OS, outperforming baseline tumor volume and p16 status. Interim volume behavior enabled dynamic risk stratification regardless of HPV status or nodal category. Conclusion: Tumor shrinkage during the early phase of chemoradiotherapy is a clinically meaningful and accessible prognostic marker in HNSCC. Incorporating interim volumetric response into adaptive radiotherapy protocols may enable personalized treatment strategies by identifying poor responders for escalation and favorable responders for de-escalation.