The authors retrospectively analyzed the data obtained in patients who had undergone l-[methyl-11C] methionine (MET)—positron emission tomography (PET) studies to clarify the relationship between MET uptake and tumor biological features and to discuss the clinical usefulness of MET-PET studies.
One hundred ninety-four patients with cerebral glioma or suspected glioma underwent PET scanning 20 minutes after injection of MET, whose uptake into the tumor was expressed as a ratio to contralateral healthy brain tissue (T/N ratio). Analyses were performed to determine how MET uptake correlated with tumor pathological features and prognosis. The T/N ratios before and after various treatments were also examined.
There were significant differences in the T/N ratio among the nonneoplastic lesions, low-grade gliomas, and malignant gliomas. Furthermore, there were significant correlations between patient survival and pretreatment T/N ratios. Among patients with malignant gliomas, a significant difference in survival was observed between cases with and without postoperative tumor remnant based on elevated MET uptake. The MET uptake was heterogeneous even among the homogeneous tumor areas demonstrated on MR imaging. Malignant pathological features were detected in the areas with the highest MET uptake. The effectiveness of radiotherapy or chemotherapy was expressed as a significantly decreased T/N ratio in some of the tumor types.
The ability of MET-PET to reflect the biological nature of gliomas makes it an excellent method for monitoring active tumor tissue, and treatments based on its findings should provide a powerful clinical protocol in the course of glioma therapy.