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two false-positive cases with postischemic lesions. A demonstrated that FDG-PET was a superior test to
[52]
study on differences in the dynamics of FET uptake in in vivo predict histologic grade of the tumor compared
gliomas could differentiate between recurrent high and with MET PET [Table 1]. [14] However, in respect to the
[49]
low-grade tumors. In another study, it was shown that low-grade gliomas, MET PET appears to better correlate
an FET-PET with a receiver-operating-characteristic with overall prognosis and survival rather than FDG
curve analysis, a mean tumor-to-brain ratio of 2.5 PET or conventional MRI, suggesting that both tracers
was highly specific for tumor rather than nontumor may be complementary during evaluation of gliomas
tissue. [47] In 10 patients with recurrent glioma treated before or after therapies. [15] Similar results in another
with a combination of bevacizumab and irinotecan study suggested that both FDG and MET PET provide
FET PET could predict treatment failure, thus provided useful complementary information assisting surgeons
additional information from that obtained by MRI to determine the extent of the surgical resection. [16] In
response assessment based on RANO criteria. [50] A a recent study of 35 patients with suspected recurrent
meta-analysis of 13 studies with 462 newly diagnosed gliomas FDG PET and MET PET were performed
untreated patients with primary brain tumors indicated during the same day and correlated with subsequent
that FET-PET may be an excellent tool for differentiating histopathology or MRI/modified Rankin scale and
tumor for non tumoral lesions. [48] clinical follow-up. The results of this study suggested
that MET PET should be preferred over FDG PET when
Another PET tracers that may be employed for evaluation available since it demonstrated higher sensitivity for
of brain tumors are (18)F-labeled fluoromethylcholine detection of recurrence (94.7% vs. 81.2%) and the same
(18F-FCho) [60] and (11)C-methionine (MET) specificity. [21] However, one study found that neither
PET. [31,40,50] MET-PET may aid in the differential diagnosis FDG PET or MET PET add any additional information
of tumor recurrence versus radiation necrosis although over the conventional MRI regarding prognosis of
its specificity and sensitivity have been reported both patients with malignant gliomas. [22] A meta-analysis of
as 75%. [42] In patients with glioma, clinical stability 26 heterogeneous studies about several PET tracers for
induced by temozolomide chemotherapy correlated diagnosing recurrent gliomas found that FDG-PET had
to a decline or stability of tumor MET uptake on a summary sensitivity of 0.77 and specificity of 0.78
PET. [43] Furthermore, although the standard MET PET for any glioma histology, and MET PET had a summary
did not correlate with survival, a voxel-wise parametric sensitivity of 0.70 and specificity of 0.93 for high-grade
response map analysis of MET PET correlated with glioma. Data were limited for FET and 3’-deoxy-3’-[18F]
OS in 14 patients with recurrent malignant gliomas fluorothymidine (FLT) PET. The authors concluded
treated with specific immunotherapy targeting that apart from FDG and MET PET that seem to have
the Wilms tumor 1gene product. [44] The short half- utility during evaluation of glioma recurrence, further
life (20 min) of (11)C limits its use of MET PET to studies using direct comparisons between PET tracers
institutions with an onsite cyclotron. A comparison and imaging modalities are needed. [23]
of MET PET with FET-PET (half-life of 120 min) in
29 patients with recurrent gliomas showed that both DOPA: 3,4-dihydroxy-6-(18)F-fluoro-l-phenylalanine
tracers differentiated tumor tissue and treatment-related (FDOPA) PET tested in a 59 glioma patients (22 with
changes with high sensitivity and specificity suggesting new untreated gliomas and 37 with recurrent tumors)
that FET PET could be used in places where an onsite showed that FDOPA uptake was higher in high-grade
cyclotron is unavailable. [68] FET PET may provide more than in low-grade tumors in newly diagnosed, but
accurate information in respect of treatment response not recurrent tumors, suggesting that its usefulness
or failure compared with response assessment based as a noninvasive tumor grading procedure can be
on conventional MRI and RANO criteria, [69] and could only in previously untreated tumors. [55] In recurrent
reliably distinguish between posttherapeutic treatment gliomas, FDOPA was able to diagnose the recurrence
related effects and tumor recurrence independently on with a sensitivity of 100% and specificity of 85.7%
the employed treatment modality. [51] in contrast to 47.6% and 100% of FDG PET. [20] In that
study, the analysis showed superiority of FDOPA PET
In addition, there is evidence that FET PET in the compared with FDG-PET to diagnose recurrence in
management of patients with recurrent glioma treated low-grade tumors but no statistical difference in high-
with a combination of bevacizumab and irinotecan grade gliomas. [20]
may be cost-effective since it can prevent overtreatment
and additional costs, as well as potential side effects Comparison of FDOPA PET with contrast enhancing
to patients. [70] MRI scan for detection of tumor recurrence in 35 glioma
patients revealed that although both examinations
A comparison study between FDG-PET and MET PET in had high sensitivity (100% vs. 92.3%), FDOPA PET
59 patients with either untreated or recurrent gliomas had much higher specificity (88.9% vs. 44.4%) than

110 Neuroimmunol Neuroinflammation | Volume 1 | Issue 3 | December 2014