LI Dong-li, XU Yi-kai, WANG Quan-shi, WU Hu-bing , LI Hong-sheng

Background  18F-fluorodeoxyglucose (FDG) is the most widely used radiotracer in tumor imaging, but its use for brain gliomas and recurrence is limited by the high 18F-FDG uptake in normal brain tissue. 11C-methionine (MET) has low uptake in the normal brain tissue, providing potential advantages over 18F-FDG. The aim of the study was to investigate the diagnostic value of 11C-MET compared to 18F-FDG positron emission tomography and computed tomography (PET/CT) in patients with suspected primary and residual/recurrent gliomas.
Methods  Eighty paired PET/CT scans using 11C-MET and 18F-FDG were performed on 44 newly diagnosed patients with suspected gliomas and 36 post-operative patients with suspected residual/recurrent tumors. PET/CT results were evaluated by visual and semiquantitative analysis. The sensitivity, specificity and accuracy for detection of gliomas and residual/recurrent tumors were calculated using visual analysis. Tumor to contralateral normal gray matter (T/G) ratio was calculated for semiquantitative analysis.
Results  Final pathology of the 44 newly diagnosed patients included 26 gliomas (14 high-grade and 12 low-grade tumors) and 18 non-glioma benign lesions. Residual/recurrent gliomas were verified in 28 patients and excluded in 8/36 post-operative patients by subsequent histopathologic examination and/or clinical follow-up for more than six months. The sensitivity, specificity and accuracy of 11C-MET PET/CT were 88.5%, 83.3% and 86.4% for gliomas and 96.4%, 87.5% and 94.4% for residual/recurrent gliomas, respectively. The sensitivity, specificity and accuracy of 18F-FDG PET/CT were 50.0%, 88.9% and 65.9% for gliomas and 46.4%, 100.0% and 58.3% for residual/recurrent gliomas, respectively. 11C-MET had a higher sensitivity than 18F-FDG (83.3% vs. 33.3%, P=0.031) in low-grade gliomas, but had no significant difference in sensitivity from 18F-FDG for high-grade gliomas (92.9% vs. 64.3%, P=0.219). 11C-MET T/G uptake ratios in high-grade gliomas, low-grade gliomas and benign lesions were 1.94±0.53, 1.78±0.61 and 1.06±0.34, respectively. 18F-FDG T/G uptake ratios in high-grade gliomas, low-grade gliomas and benign lesions were 1.05±0.37, 0.66±0.14 and 0.63±0.17, respectively.
Conclusions  11C-MET PET/CT is superior to 18F-FDG PET/CT in detecting and delineating gliomas and residual/recurrent tumors, especially low-grade gliomas and residual/recurrent lesions present in gray matter, but its role in non-invasive grading of the tumors is limited.