Abstract: Background and purpose:  ¹⁸ F-FLT is a proliferative radiotracer. This study aimed to evaluate the prognostic value of functional molecular image of  ¹⁸ F-FLT PET/CT taken before and in the process of radiotherapy. Methods: Patients with newly diagnosed esophageal squamous cell carcinoma (ESCC) were enrolled in the study. All patients received radiotherapy/chemoradiotherapy. The planned dose was 61.2 Gy and 1.8 Gy per fraction respectively. The concurrent chemotherapy was platinum, paclitaxel or fluoropyrimidine based. Patients were examined by PET with  ¹⁸ F-fluoro-30-deoxy-30-L-fluorothymidine (FLT) at baseline and 4 weeks after treatment initiation. The overall survival (OS) and progression-free survival (PFS) were followed up. The SUV maximum (SUV _max ) of primary tumor and positive nodes were recorded. PET/CT findings were analyzed for the correlation with clinical response of patients and survival. Results: Thirty-nine patients were enrolled in the study, among whom 25 patients completed two planned PET/CT. Patients with SUV max-N ≥5.00 had worse OS (P=0.002) and PFS (P=0.01) than those with SUV _max-N <5.00. The SUV _max of both primary tumor and lymph nodes significantly decreased in the interim scan compared to the baseline scan in FLT PET/CT, but the relationship between the change of SUV _max and prognosis seemed to be weak. Conclusion: Baseline SUV _max of lymph node on  ¹⁸ F-FLT PET/CT had prognostic value in patients with esophageal cancer undergoing radiotherapy/radiochemotherapy. The decrease of SUV _max of tumor after 4 weeks’ radiotherapy couldn’t predict prognosis properly.

Key words:  ¹⁸ F-FLT PET/CT, Esophageal squamous cell cancer, Radiochemotherapy, Survival