GLUCOSE CONSUMPTION AND METHIONINE UPTAKE IN LOW-GRADE GLIOMAS AFTER I-125 BRACHYTHERAPY

We investigated whether 2-[F-18]-fluoro-2-deoxy-D-glucose (FDG) and ca rbon-11 methionine are suitable tracers to monitor the effects of ther apy for low-grade gliomas. Ten patients with low-grade glioma without previous treatment were studied with FDG positron emission tomography. Additionally, L-[methyl-C-11]methionine uptake was measured in five s ubjects before and 1 year after computerized tomography (CT)-guided st ereotactic and computer-assisted implantation of iodine-125 seeds. All scans were 3D-matched to CT, isodose volumes were determined, and cha nges in glucose metabolism and methionine uptake were evaluated in tum our and brain tissue as a function of radiation dose. After 1 year glu cose metabolism was not significantly altered up to a radiation dose o f 300 Gy, whereas methionine uptake showed a significant dose-dependen t de crease. Higher rates of decline were found in tumours with high b asal methionine incorporation activity before therapy. These data sugg est that measurement of methionine uptake is more suitable than measur ement of FDG uptake for monitoring therapeutic effects in low-grade gl iomas.