Inter-observer Variations in FDG-PET Interpretation for Cancer Screening

Background: Diagnostic guidelines for the use of 2-(fluorine 18) fluoro-2 deoxy-D-glucose (FDG)-positron emission tomography (PET) in cancer screening have yet to be established. We assessed inter-observer variability in screening FDG-PET. Methods: Subjects comprised 40 individuals who underwent FDG-PET and computed tomography (CT) for cancer screening. To assess various patterns of FDG uptakes, three subsets of the cases were selected: ‘Cancer’, 15 cases with cancer; ‘Not malignant’, 15 cases with suspected cancer by FDG-PET who were confirmed as cancer-free; and ‘Normal’, 10 cases without remarkable FDG uptake who were confirmed as cancer-free. A total of 68 lesions made up of malignancy (n ¼ 18), benign (n ¼ 21), and physiological FDG uptake (n ¼ 29) were interpreted by six physicians. Each observer reviewed each case three times. Step 1 involved interpretation of PET images alone, Step 2 involved side-by-side reading of PET and CT images, and Step 3 involved re-evaluation of findings with the results of other screening tests. We assessed inter-observer agreement for each step. Results: Inter-observer agreement for all lesions at each step was moderate, compared to fair agreement for ‘Normal’ subjects. Inter-observer agreement of ‘Cancer’ and ‘Not malignant’ subjects in Step 1 were better than those in Step 2 and 3; however, the differences were not statistically significant. Conclusion: The interpretation of FDG-PET is adequately reproducible, while that of ‘Normal’ subjects is less reproducible. Improvement of inter-observer variability in assessing physiological FDG uptakes requires universal reporting criteria in FDG-PET. Correlative interpretation of PET, CT and other information may require standardization in subjects with suspected cancer by FDG-PET.