Radiation-induced Xerostomia: Evaluation with 18F-FDG PET/CT.

Objectives: To investigate the relationship between radiation dose, metabolic changes in the salivary glands assessed by 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT), and xerostomia severity in patients with head and neck cancer following radiotherapy (RT). Methods: We retrospectively analyzed 107 patients treated with intensity-modulated RT or volumetric modulated arc therapy for head and neck malignancies. Clinical xerostomia severity was evaluated at the time of post-treatment PET/CT. Mean gland doses and dose-volume parameters (V10-V50) were extracted from treatment plans. Metabolic changes were evaluated by Δmaximum standardized uptake value and Δmean standardized uptake value between pre and post treatment PET/CT scans. The relationships between clinical, dosimetric, and metabolic variables were examined. Results: Moderate-to-severe xerostomia occurred in 63.6% of patients. Both higher T and N stage were significantly associated with greater xerostomia severity (p<0.05). Patients with nodal metastases on pretreatment PET/CT demonstrated a higher prevalence of xerostomia. Dose-volume parameters (V10-V30 for parotids, V50 for submandibular glands) were significantly correlated with symptom severity. ΔSUV values were significantly associated with both mean dose and dose-volume parameters, particularly in the left parotid gland, where patients receiving >30 Gy showed markedly greater metabolic decline. Parotid glands demonstrated stronger dose-dependent metabolic changes compared with submandibular glands, consistent with their higher radiosensitivity. Conclusion: Despite the use of advanced RT techniques, xerostomia remains a frequent toxicity. 18F-FDG PET/CT reliably captured dose-dependent salivary gland impairment and reflected the impact of tumor burden on toxicity risk. These findings underscore the complementary role of PET-derived biomarkers as integrative tools for predicting salivary dysfunction beyond conventional dosimetric parameters.