Analysis of diagnosing lung cancer in patients with idiopathic interstitial pneumonia by CT and ¹⁸F-FDG-PET/CT

Objective: Idiopathic interstitial pneumonia (IIP) is often complicated by lung cancer. Lung cancer may be often indistinguishable from inflammation on computed tomography (CT). Design: We examined the comparison of usefulness between CT and ¹⁸F-fluorodeoxyglucose positron emission tomography/CT (¹⁸F-FDG-PET/CT) in those lesions. Materials and Methods: Subjects were 75 patients with IIP who were suspected of having lung cancer and underwent ¹⁸FFDG- PET/CT over a 5-year period. Fifty-four patients were diagnosed with lung cancer, including 5 patients with synchronous double lung cancer, and 21 with other disease. The relationship between the interpretation of CT and ¹⁸F-FDG-PET/CT by certified radiological specialists and final diagnosis was analyzed. Results: For the interpretation of CT, sensitivity was 81.4% and specificity 76.2%, while that for ¹⁸F-FDG-PET/CT was 88.1% and 90.5%, respectively. Of 59 lung cancer lesions, 52 (88.1%) were interpreted as "definitive lung cancer" and 58 (98.3%) as "suspected or definitive lung cancer" on either CT or ¹⁸F-FDG-PET/CT. One lesion was missed by both modalities. Conclusion: In diagnosing lung cancer associated with IIP, high sensitivities were shown in both ¹⁸F-FDG-PET/CT and CT. However, some lesions were erroneously diagnosed on CT. When lung cancer was suspected clinically, ¹⁸F-FDG- PET/CT should be considered, because ¹⁸F-FDG-PET/CT is non-invasive and shows high specificity.