18F-FLT uptake can be used to monitor the biological response of esophageal SCC and normal tissue to RT. Increased uptake of 18F-FLT following treatment interruptions may reflect accelerated repopulation. 18F-FLT PET may have advantages compared to 18F-FDG PET in differentiating inflammation from tumor. 18F-FLT PET may help oncologists predict treatment response as early as one week after the beginning of treatment and estimate clonogenic repopulation during RT. 18F-FETNIM PET can depict hypoxia in esophageal SCC. Prior to CCRT, tumor hypoxia demonstrates spatial variability in different days, though overall 18F-FETNIM uptake remains similar. Baseline SUVmax may be predictive of treatment response.