Efficiency of 18F-FDG and 99mTc-depreotide SPECT in the diagnosis of malignancy of solitary pulmonary nodules

Purpose: The purpose of the study was to compare F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET) and Tc-99m-depreotide single-photon emission computed tomography (SPECT) in the diagnosis of malignancy of solitary pulmonary nodules (SPNs). Methods: Twenty-eight patients without any history of cancer and presenting an SPN (0.8 - 3 cm in size) underwent FDG PET and depreotide SPECT. Depreotide SPECT and FDG PET were performed on a double-head gamma camera and a dedicated PET scanner respectively. Twenty-five out of 28 lesions were removed by thoracotomy or assessed by biopsy ( n= 1) and histologically examined. A strategy of serial CT scanning was adopted in the three remaining patients. Results: Histological findings revealed 18 malignant nodules and seven benign lesions. Stability over a 2-year period indicated a benign process in the remaining three cases. Both techniques yielded true positive results in 15 of the 18 cancers. FDG PET identified two additional adenocarcinomas not detected by depreotide SPECT. A carcinoid tumour not visualised on FDG PET was identified by depreotide SPECT. Seven of the ten benign lesions did not reveal tracer uptake on either depreotide SPECT or FDG PET. Both techniques showed false positive results for the same two lesions. One more false positive was seen on FDG PET. FDG PET and depreotide SPECT had a sensitivity of 94.4% and 88.9% respectively; this difference was not significant. In our experience, depreotide SPECT and FDG PET are equally sensitive (92.3%) for large (> 1.5 cm) and equally specific (85.7%) for small ( up to 1.5 cm) SPNs suspicious for malignancy. Conclusion: This study showed F-18-FDG PET to be more sensitive than Tc-99m-depreotide SPECT in the diagnosis of malignancy of SPNs. However, the combination of both techniques may provide additional accuracy.