Interobserver Agreement of Qualitative Analysis and Tumor Delineation of 18F-Fluoromisonidazole and 3′-Deoxy-3′-18F-Fluorothymidine PET Images in Lung Cancer

ters were, respectively, 0.59 for 18 F-FDG, 0.43 for 18 F-FMISO, and 0.44 for 18 F-FLT using the 5-level scale; the values were 0.81 for 18 F-FDG and0.77for both 18 F-FMISOand 18 F-FLTusingthe2-levelscale.The mean overlap and mean k between observers were 0.13 and 0.19, respectively, for 18 F-FMISO and 0.2 and 0.3, respectively, for 18 FFLT. The segmentation methods yielded significantly different volumes for 18 F-FMISO and 18 F-FLT (P , 0.001). In comparison with physicians, the best method found was 1.5 · maximum SUV (SUVmax) of the aorta for 18 F-FMISO and 1.3 · SUVmax of the muscle for 18 F-FLT. The methods using the SUV of 1.4 and the method using1.5 ·theSUVmaxoftheaorta couldbe usedfor 18 F-FMISOand 18 F-FLT. Moreover,for 18 F-FLT,2othermethods(adaptivethresholdbasedon 1.5 or 1.6 · muscle SUVmax) could be used. Conclusion: The reproducibilityofthevisualanalysesof 18 F-FMISOand 18 F-FLTPET/CT images was demonstrated using a 2-level scale across 18 centers, but the interobserver agreement was low for the 18 F-FMISO and 18 FFLT volume measurements. Our data support the use of a fixed threshold (1.4) or an adaptive threshold using the aorta background to delineate the volume of increased 18F-FMISO or 18F-FLT uptake. With respect to the low tumor-on-background ratio of these tracers, we suggest the use of a fixed threshold (1.4).