[C-methionine PET in assessment of brain lesions in patients with glial tumors after combined treatment]. / PÉT s S-metioninom v otsenke porazhenii golovnogo mozga u bol'nykh s glial'nymi opukholiami posle kombinirovannogo lecheniia.

Positron emission tomography (PET) with amino acid-based radiopharmaceuticals is considered as an effective method to diagnose continued growth of cerebral gliomas, but the variability of 11C-methionine uptake by brain lesions of different genesis after combined treatment still remains poorly understood. The aim of this study was to explore the information value of 11C-methionine PET in delimitating progression of cerebral gliomas and stable disease and to assess the risk of tumor recurrence at different values of the 11C-methionine uptake index. MATERIAL AND METHODS: We performed a retrospective analysis of the results of 11C-methionine PET or PET/CT in 324 patients suspected for continued growth of cerebral tumor based on magnetic resonance imaging (MRI) findings. A quantitative analysis of the results included calculation of the 11C-methionine uptake index (UI). RESULTS: A ROC analysis revealed that the specificity of PET in the diagnosis of continued tumor growth (CTG) was 98%, and the sensitivity was 71% for a UI of more than 1.9. We found that 98% of lesions with a negative level of RP uptake were related to radiation brain lesions (RBLs) or residual tumors combined with radiation pathomorphims. The UI in a range of 1.2-1.6 in 75% of lesions characterized a stable disease, but 25.5% of the lesions represented continued glioma growth. The proportion of recurrences increased to 40% in a UI range of 1.6-1.9, and 95.5% of brain lesions with a UI of more than 1.9 were tumor recurrences. Therefore, high 11C-methionine uptake with the UI above 1.9 in brain lesions characterized by radiological signs of disease progression is a highly specific indicator of CTG; however, the UI may significantly vary during tumor growth, and a substantial fraction of recurrent gliomas may have lower radiopharmaceutical uptake. In the case of borderline UI values, early dynamic control or complementary additional MRI or CT techniques should be used.

[PET using 11C-methionine in recognition of pseudoprogression in cerebral glioma after combined treatment].

The purpose of the study was to evaluate the value of PET using 11C-methionine (PET-Met) for distinction between true glioma progression and pseudoprogression (PsPr). 72 patients with treated cerebral glioma investigated by PET-Met were identified from prospective database. Entry criteria included new or progressive MR imaging enhancing lesions within first 6 months after irradiation and definite final diagnosis on the basis of the pathological study (n=17) or clinical-radiological follow-up on an average 16 months. PET examinations were assessed by visual inspection and calculating 11C-methionine uptake index (UI). Results. Pseudoprogression was defined as early radiological progression with subsequent regress or stabilization, without salvage therapy. 42 patients were considered to exhibit PsPr and 30 patients had true glioma progression. In PsPr group PET scans were either negative (n=6) or slightly increased tracer uptake (UI range 1.2-2.14) was seen in the site of contrast-enhanced lesion. The UI was 1.48±0.39 (mean±SD). In comparison with pretreatment PET 15 patients showed decrease 11C-methionine uptake on an average by 26%. In recurrence group PET-Met showed abnormal high focal 11C-methionine uptake in the lesion. The UI was 2.54±0.84 (range 1.54-5.4). An UI threshold value of greater than 1.9 optimized differentiation between glioma progression and PsPr with sensitivity of 83.5% and specificity of 97.0%. Conclusion. Metabolic characteristics of PsPr included negative tracer accumulation or slightly increased 11C-methionine uptake in the contrast-enhancing lesion with UI less than 1.9.