11C-methionine (MET) and 18F-fluorothymidine (FLT) PET in patients with newly diagnosed glioma

The purpose of this prospective study was to clarify the individual and combined role of l-methyl-11C-methionine-positron emission tomography (MET-PET) and 3′-deoxy-3′-[18F]fluorothymidine (FLT)-PET in tumor detection, noninvasive grading, and assessment of the cellular proliferation rate in newly diagnosed histologically verified gliomas of different grades. Forty-one patients with newly diagnosed gliomas were investigated with MET-PET before surgery. Eighteen patients were also examined with FLT-PET. MET and FLT uptakes were assessed by standardized uptake value of the tumor showing the maximum uptake (SUVmax), and the ratio to uptake in the normal brain parenchyma (T/N ratio). All tumors were graded by the WHO grading system using surgical specimens, and the proliferation activity of the tumors were determined by measuring the Ki-67 index obtained by immunohistochemical staining. On semiquantitative analysis, MET exhibited a slightly higher sensitivity (87.8%) in tumor detection than FLT (83.3%), and both tracers were 100% sensitive for malignant gliomas. Low-grade gliomas that were false negative on MET-PET also were false negative on FLT-PET. Although the difference of MET SUVmax and T/N ratio between grades II and IV gliomas was statistically significant (P