3’-Deoxy-3’-[¹⁸F]-fluorothymidine PET/CT in early determination of prognosis in patients with esophageal squamous cell cancer

The purpose of this work was to investigate the prognostic value of response analysis using early 3’-deoxy-3’-[¹⁸F]-fluorothymidine (¹⁸F-FLT) PET/CT in esophageal squamous cancer patients and make a comparison with [¹⁸F]-fluorodeoxyglucose (¹⁸F-FDG) PET/CT.

For 34 patients with esophageal squamous cell cancer, both ¹⁸F-FLT PET/CT and ¹⁸F-FDG PET/CT scans were performed at baseline (pre), 4 weeks after the start of radiotherapy or chemoradiotherapy (interim), and 2 weeks after therapy completion (final). SUV_max1, SUV_max2, and SUV_max3 represent SUV_max (SUV: standard uptake values) measured on the pre, interim, and final scans, respectively. GTV_FLT-PET and GTV_FDG-PET (GTV: gross tumor volume) were measured on the pre and interim scans. ΔSUV/ΔGTV represents the fractional changes of SUV_max/GTV between two different time points. PET parameters were evaluated for correlations with outcome.

Regarding ¹⁸F-FLT PET/CT, according to receiver operating characteristic (ROC) curve analysis, parameters for predicting 2-year progression-free survival (PFS) and locoregional control (LRC) showed the highest area under curve (AUC) on interim ¹⁸F-FLT PET/CT scans (ΔSUV12, AUC of 0.812 for PFS, 0.775 for LRC, with a cutoff of 60 %; P = 0.008), compared with the parameters on pre and final scans. Patients with a ΔSUV12 greater than 60 %, who were defined as interim PET-negative group, were associated with better 2-year PFS and LRC than the interim PET-positive group (PFS: 70.6 % vs. 35.2 %, P = 0.025; LRC: 84.2 % vs 52.9, P = 0.046). In terms of ¹⁸F-FDG PET/CT, ΔSUV13 on the final 18F-FDG PET/CT scan demonstrated better prediction (AUC of 0.812 for PFS, 0.807 for LRC, with a cutoff of 75 %; P = 0.016) than the parameters on pre and interim scans. An SUV_max decrease ≥ 75 % on the final ¹⁸F-FDG PET/CT scan was associated with better clinical outcome (PFS: 73.3 % vs. 36.8 %, P = 0.022; LRC: 86.7 % vs 52.6, P = 0.029). These correlations were most prominent in the subgroup of patients treated with chemoradiotherapy.

Early interim ¹⁸F-FLT PET/CT is a significant predictor of 2-year PFS and LRC, which is correlated better with early responses and late outcomes than interim ¹⁸F-FDG PET/CT in esophageal squamous cancer patients.