Positron emission tomography (PET) is a proven accurate modality used for the detection of active malignant tumors. The performance of PET in detecting bony metastases, however, has not been adequately investigated.
Purpose: The aim of this study was to compare the performance of bone and 2-deoxy-2-[18F]fluoro-D-glucose (FDG) PET scans in evaluating bony metastases from lung cancer.
Procedure: This retrospective study evaluated 85 patients with lung cancer who underwent both FDG-PET and bone scans within three weeks of each other for initial staging or restaging. The number and sites of bony lesions on FDG-PET and bone scans were correlated. Concordant lesions between the two modalities were considered to be positive for malignancy; discordant lesions were compared with X-rays, computed tomography (CT), magnetic resonance imaging (MRI), and/or follow-up findings. The mean follow-up interval was 7.9 months.
Results: Bone scans were positive for lesions in 24 patients and negative in 61 patients while FDG-PET was positive for bony lesions in 17 patients and negative in 65 patients. FDG-PET was indeterminate for rib involvement in three patients having an underlying lung cancer, whom were evaluated separately. A total of 88 and 41 bony lesions were identified on bone scans and FDG-PET, respectively. Correlation of bone scans with other imaging modalities and clinical follow-up findings revealed a sensitivity, specificity, positive and negative predictive value of 81%, 78%, 34%, and 93%, respectively and for FDG-PET 73% (P=0.81), 88% (P=0.03), 46% (P=0.5,) and 97% (P=0.04), respectively. Using bone scans, 10 patients were correctly diagnosed with bony metastases, 54 were correctly diagnosed free of bony metastases, 17 patients were falsely diagnosed with metastases, and metastases were missed in one patient. Using FDG-PET scans, eight patients were correctly diagnosed with bony metastases, 66 were correctly diagnosed free of bony metastases, seven patients were falsely diagnosed with metastases, and one patient had metastases which were missed. Of the three patients with lung cancer close to the chest wall in whom FDG-PET was indeterminate for rib involvement, the bone scans were truly positive for rib involvement in two of them, and truly negative in the remaining patient.
Conclusions: FDG-PET scans demonstrated significantly higher specificity and negative predictive values than bone scans for evaluating bony metastases from lung cancer. On the other hand, bone scans are more sensitive with higher positive predictive values than FDG-PET scans, but the differences were not statistically significant.