Comparison of 4′-[methyl-11C]thiothymidine (11C-4DST) and 3′-deoxy-3′-[18F]fluorothymidine (18F-FLT) PET/CT in human brain glioma imaging

Abstract

Methods: Twenty patients with primary and recurrent brain gliomas underwent 18F-FLT and 11C-4DST PET scans. The uptake values in the tumors were evaluated using the maximum standardized uptake value (SUVmax), the tumor-to-normal tissue uptake (T/N) ratio, and the tumor-to-blood uptake (T/B) ratio. These values were compared among different glioma grades. Correlation between the Ki-67 labeling index and the uptake values of 11C-4DST and 18F-FLT in the tumor was evaluated using linear regression analysis. The relationship between the individual 18F-FLT and 11C-4DST uptake values in the tumors was also examined. Background: 3′-deoxy-3′-[18F]fluorothymidine (18F-FLT) has been used to evaluate tumor malignancy and cell proliferation in human brain gliomas. However, 18F-FLT has several limitations in clinical use. Recently, 11C-labeled thymidine analogue, 4′-[methyl-11C]thiothymidine (11C-4DST), became available as an in vivo cell proliferation positron emission tomography (PET) tracer. The present study was conducted to evaluate the usefulness of 11C-4DST PET in the diagnosis of human brain gliomas by comparing with the images of 18F-FLT PET. Results: 11C-4DST uptake was significantly higher than that of 18F-FLT in the normal brain. The uptake values of 11C-4DST in the tumor were similar to those of 18F-FLT resulting in better visualization with 18F-FLT. No significant differences in the uptake values of 18F-FLT and 11C-4DST were noted among different glioma grades. Linear regression analysis showed a significant correlation between the Ki-67 labeling index and the T/N ratio of 11C-4DST (r = 0.50, P < 0.05) and 18F-FLT (r = 0.50, P < 0.05). Significant correlations were also found between the Ki-67 labeling index and the T/B ratio of 11C-4DST (r = 0.52, P < 0.05) and 18F-FLT (r = 0.55, P < 0.05). A highly significant correlation was observed between the individual T/N ratio of 11C-4DST and 18F-FLT in the tumor (r = 0.79, P = 0.0001). Conclusions: The present study demonstrates that 11C-4DST is useful for the imaging of human brain gliomas with PET. A relatively higher background uptake of 11C-4DST in the normal brain compared to 18F-FLT limits the detection of low-tracer-uptake tumors. Moreover, no superiority was found in 11C-4DST over 18F-FLT in the evaluation of cell proliferation.