Diagnostic Value of (11)C-Methionine (MET) and (18)F-Fluorothymidine (FLT) Positron Emission Tomography in Recurrent High-Grade Gliomas; Differentiation from Treatment-Induced Tissue Necrosis

We retrospectively evaluated the usefulness of combined measurement of L-methyl-[(11)C]methionine (MET) and 3'-deoxy-3'-[(18)F]fluorothymidine (FLT) positron emission tomography (PET) in the differential diagnosis between recurrent gliomas and necrotic lesions. Twenty-one patients with high-grade glioma, previously treated with surgery and radiotherapy with chemotherapy and first radiological suspicion of recurrence were enrolled. The uptake was assessed by the maximum standardized uptake value (SUVmax) and lesion-to-normal tissue count density ratio (L/N ratio). Of the 21 lesions, 15 were diagnosed recurrent gliomas and six were necrotic lesions. The average SUVmax was not significantly different between recurrent gliomas and necrotic lesions on either MET-PET or FLT-PET. The average L/N ratio of recurrent gliomas (3.36 ± 1.06) was significantly higher than that of necrotic lesions (2.18 ± 0.66) on MET-PET (p < 0.01) and the average L/N ratio of recurrent gliomas (7.01 ± 2.26) was also significantly higher than that of necrotic lesions (4.60 ± 1.23) on FLT-PET (p < 0.01). ROC curve analysis showed that the areas under the curves were high but not different between MET- and FLT-PET. PET studies using MET and FLT are useful in the differentiation of recurrent glioma from treatment-induced necrotic lesion. However, there is no complementary information in the differentiation with simultaneous measurements of MET- and FLT-PET.