Diagnostic Usefulness of 3′-Deoxy-3′-[18F]Fluorothymidine Positron Emission Tomography in Recurrent Brain Tumor

Objective: We evaluated the diagnostic usefulness of 3'-deoxy-3'[F-18]fluorothymidine (FLT) compared with 2-[F-18]fluoro-2-deoxy-Dglucose (FDG) positron emission tomography (PET) in recurrent brain tumors. Methods: Twenty patients with suspected recurrence after surgical removal of primary tumors were studied. The uptake was assessed visually and quantified by standardized uptake value (SUV) and SUV ratio of tumor to white matter, tumor to gray matter, and tumor to normal tissue. Final diagnoses were made by histopathology or clinical and radiological follow-up. Results: Of 20 lesions, 15 were recurrences. 3'-Deoxy-3'[F-18] fluorothymidine PET showed high diagnostic sensitivity (15/ 15 [100%]) and moderate specificity (3/5 [60.0%]). 2-[F-18]fluoro-2-deoxy-D-glucose PET showed moderate diagnostic sensitivity (11/15 [73.3%]) and specificity (4/5 [80%]). All of 4 recurrent tumors without FDG uptake showed FLT uptake. Tumor-to-normal tissue ratios (3.99 +/- 1.72) of recurrent tumors on FLT PET were significantly higher than tumor-to-white matter ratios (1.96 +/- 0.93) and tumor-to-gray matter ratios (1.32 +/- 0.33) on FDGPET (P < 0.001), although SUVs (0.62 +/- 0.32) of recurrent tumors on FLT PET were lower than those (2.44 +/- 1.02) on FDG PET (P < 0.001). Conclusion: 3'-Deoxy-3'-[F-18]fluorothymidine PET has a high sensitivity but a lower specificity, which has a limited role in the diagnosis of recurrent brain tumors as a complimentary tool of magnetic resonance imaging.