Abstract
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Objectives: To evaluate PET with 2-18F-fluoro-L-tyrosine (F-TYR) and FDG for assessing tumor grade and survival in primary brain tumors.
Methods: Data obtained in 42 consecutive patients (24 M, 18 W) were reviewed. Pathology obtained at surgery (n=18) or by biopsy (n=24) was: Astrocytoma (Gr. I, n=2; Gr II n=18; Gr III n=5; Gr IV n=6), oligoastrocytoma (Gr II n=2; Gr III n=1), oligodendroglioma (Gr II n=3, Gr III n=4) and 1 ganglioglioma Gr II. All pts were imaged prior to any treatment. PET was performed 30±10 min. (avg±SD) after injecting 307±33 MBq F-TYR. Forty pts also had FDG-PET. Tumor to cortex activity ratios (T/C) were obtained by drawing ROIs over the most active transaxial slice in the tumor and over the contralateral parietal cortex. An ROC analysis was performed to assess the optimal cut-off value for differentiating low-grade and high-grade tumors. Kaplan-Meier survival curves were established according to the median value of the activity ratios.
Results: The T/C were significantly higher with F-TYR than with FDG, especially for low-grade tumors (1.7 Vs 0.6). Both F-TYR and FDG T/C were higher (P<0.05 and <0.001, respectively) in high grade lesions, but only after excluding oligodendrogliomas, which were all active (F-TYR: 2.5; FDG: 1.2). The optimal cut-off for tumor grades was 1.98 with F-TYR (AUC 0.673) and 0.7 with FDG (AUC 0.771). Without the oligodendrogliomas, the AUC increased to 0.731 and 0.875, respectively. The median follow up was 720 days (range 166-1793). Thirteen patients deceased. According to the Kaplan-Meier survival curves, FDG uptake, but not F-TYR, was predictive of the outcome.
Conclusions: Although F-TYR allows a better tumor to background contrast in low-grade gliomas, FDG remains useful for characterizing the tumor grade and predicting the outcome.
- Society of Nuclear Medicine, Inc.