Comparison of 18F-fluoroethylo-L-thyrosine PET/CT and MR in the diagnosis of primary brain tumors referred to radiation therapy
Abstract
BACKGROUND: The diagnostic efficacy of 18F-FDG-PET imaging in brain tumors is markedly reduced due to high glucose metabolism in normal brain tissue. This requires further research for more sensitive and specific tracers. 18F-fluoroethylo-L-thyrosine (18F-FET) is an interesting PET radiotracer, which shows promising results in patients with brain tumors. The aim of this study was to compare 18F-fluoroethylo-L-thyrosine PET/CT and MRI in the diagnosis of primary brain tumors referred to radiation therapy.
MATERIAL AND METHODS: Thirteen patients (5M, 8F) with mean age of 56y ± 13 and histologically confirmed primary braintumors were investigated. The MRI scans were performed on MRI 1.5T scanner with FSE, DWI method, T1, T2 and FLAIR sequence. The examination was performed using brain protocol for 35 minutes and prior to PET imaging. The PET scans were performed 20–40 min after intravenous injection of 160 MBq of 18F-FET. Scans were acquired on Gemini TF PET/CT scanner using 3D brain imaging protocol for 10 minutes acquisition time. The reconstructed PET images were evaluated on a dedicated EBW workstation with Time-of-Flight reconstruction algorithms. On reconstructed images, the tumor borders were drawn using dedicated software, based on various threshold values and tumor borders and volumes were calculated on each nuclear image and compared with the volume calculated on the diagnostic MRI. For statistical analysis the t-test was used.
RESULTS: 18F-FET-PET imaging in total showed more abnormal lesions that MRI; however, the difference was not significant (p > 0.05). There were two patients with lesions detected only on the MRI study and 4 patients with abnormal tracer uptake within the brain in 18F-FET study with no correlation in the MRI study. 18F-FET-PET method showed 30 lesions in 11 patients with mean SUVmax value of 2.33 (range from 1.6 to 3.5). Based on 70% threshold cutoff value, the mean volume of brain focus was calculated on at 31.15 ± 26.89 mm3 and was in concordance with mean lesion volume measured on the MRI scan 31.51 ± 34.97 mm3. For radiation planning purposes other threshold values, as well as gradient based methods were evaluated on 18F-FET-PET imaging.
CONCLUSION: PET/CT imaging with 18F-fluoroethylo-L-thyrosine is complementary to MRI in the diagnosis of primary brain tumors referred to radiation therapy.
Keywords: Radiotherapybrain tumorpositron emission tomography18F-fluoroethylo-L-thyrosinemagnetic resonance.
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