Prognostic significance of intermediate and high SUVmax values and imaging timing on FDG-PET/CT after radiation therapy in HNSCC: a retrospective cohort study

Abstract

Introduction Head and neck cancer is a disease with a tendency for recurrence and metastases even after treatment. Late detection leads to poor patient outcomes. One promising diagnostic tool is FDG-PET/CT which can detect both, morphological and metabolic evidence of malignant diseases. A common measure is SUVmax, the maximum standardized uptake value in a lesion. The objective of this study is to evaluate the prognostic value of post-treatment FDG-PET/CT in patients with head and neck squamous cell carcinoma (HNSCC), focusing on the association of SUVmax and scan timing with progression-free survival (PFS). Methods This retrospective study included 84 patients with HNSCC treated with definitive radiotherapy between 2016 and 2023 at a German university hospital. All patients underwent at least one post-radiotherapy FDG-PET/CT scan. All post radiation scans that were performed before or no later than one month after documented disease progression were included for prognostic analysis. SUVmax values were categorized into three groups: (1) physiological uptake (no suspicious lesion, no SUVmax value recorded, and radiological report consistent with post-therapeutic changes), (2) intermediate uptake (SUVmax >1 but <7.5), and (3) high uptake (SUVmax ≥7.5). PET/CT timing was stratified as early (≤3 months) or delayed (>3 months) after radiotherapy. Diagnostic performance metrics and survival outcomes were analyzed. Results A total of 88 post-treatment PET/CT scans were evaluated. Mean follow up was 27.7 months. Disease progression occurred in 33 patients and 10 patients died during follow-up. SUVmax ≥7.5 was significantly associated with shorter PFS (p < 0.05). Intermediate SUVmax values also predicted increased progression risk compared to physiological uptake. The optimal diagnostic performance was achieved with delayed PET/CT (>3 months), particularly using a low SUVmax threshold (>1), which yielded high sensitivity (90.9%) and negative predictive value (88.9%). Multivariate analysis confirmed SUVmax as an independent predictor of PFS (HR: 1.21; 95% CI: 1.11-1.32; p < 0.001), alongside male sex and oral cavity primary site. Conclusion Post-treatment FDG-PET/CT is a valuable prognostic tool in HNSCC follow-up. SUVmax, especially when evaluated after three months, is predictive of disease progression. Integrating PET/CT into routine surveillance may improve risk stratification and inform tailored follow-up intensity.