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treatment with bevacizumab and irinotecan predicted treatment-related effect, depending on the rate of the
response to the treatment and correlated with overall tracer uptake by tumor. Employment of imaging amino
survival. [12] Similar predictive value of FDG-PET was acid transport may prove to have an important clinical
reported with other therapies in glioma patients. [36] role in the management of brain tumor patients since
FDG PET compared to MRI scans with and without it may result in changes in therapeutic management. [62]
contrast enhancement had much higher specificity
(97% vs. 23%) for detection of recurrence in 90 glioma For example, application of O-(2-(18)F-fluoroethyl)-
patients clinically suspicious of tumor growth. [13] L-tyrosine (FET) PET/CT in newly diagnosed brain
tumors could predict their biologic behavior in most
OTHER POSITRON EMISSION TOMOGRAPHY of the cases. [48,52,63] FET represents an artificial amino
TRACERS AND COMPARISON WITH acid not incorporates into proteins but transports into
(18)F-FLURODEOXYGLUCOSE active glioma cells. [46] FET-PET may be more accurate
than FDG-PET for differentiation of malignant gliomas
During the last several years, new PET tracers from low-grade gliomas, [64,65] by their low FET uptake
have been developed for a wide range of biological on PET in the low-grade tumors. [66,67] Thus, in a study
targets [Table 2]. [37] of 88 patients with an intracerebral lesion observed by
MRI, FET PET was performed, followed by biopsy in
PET of amino acid transport and metabolism could be 60 patients. The sensitivity of FET PET for high-grade
a reliable method in assessing a metabolic response tumors (WHO III-IV) was reported 94% and for low-
after treatment of a tumor or in establishing a grade tumors (WHO I-II) 68%. However, there were

Table 2: Other PET tracers for patients with gliomas
Tracer Mechanism No. of Untreated or Advantages Disadvantages
studies recurrent glioma
AMT [38] Amino acid PET tracer not 1 Recurrent AMT PET could False positive results
incorporated into proteins but differentiate between can occur in cortical
transported into gliomas via the tumor and XRT necrosis dysplasia with
kynurenine pathway epileptic focus [39]
MET PET [40] MET is transported by the LAT1 5 Upfront [15] MET uptake correlated Short
amino acid transporter into Recurrent [41-44] with prognosis [15] half-life (20 min)
glioma and is incorporated into MET PET could requiring on site
proteins [41] differentiate between production; MET
tumor and XRT may accumulate in
necrosis [40,42] brain abscesses or
Correlate with OS and inflammation [45]
outcome [43,44]
FET PET FET is an artificial amino acid 5 Upfront [47,48] FET PET could Rare false positive
transported into active glioma Recurrent [49-51] differentiate glioma from in granulomatous
cells but incorporated into nonneoplastic tissue conditions and
proteins [46] FET PET distinguished reactive astogliosis
[52]
active tumor from or false negative
radiation necrosis; [50,51] cases [53]
dynamic FET uptake
could differentiate
between high and low
grade tumors [49]
FDOPA PET: l-DOPA is the precursor of 2 Upfront [55] Correlation of FDOPA Diagnostic
(18)F-FDOPA dopamine and is transported Recurrent [55,56] uptake, tumor usefulness mostly
physiologically into the brain proliferation and grade in upfront gliomas;
and abnormally into the brain Diagnostic accuracy of limited data
tumors [54] recurrence similar to
MRI [56]
FLT PET [57,58] FLT is an analog of 2 Upfront [57] FLT PET could FLT may accumulate
deoxythymidine, which is Recurrent [58] differentiate between in benign
composed of deoxyribose and high and low grade lesions with BBB
the pyrimidine base thymine and tumors disruption [45]
phosphorylated by thymidine FLT-PET responses
kinase 1 during DNA synthesis [59] correlated with OS
CHO: During glioma cell proliferation 1 Various brain Higher uptake in It may also
(18)F‑fluoromethylcholine choline is trapped into the cells lesions (tumors or malignant tumors accumulate in
to produce phosphatidylcholine, nontumors) various inflammatory
a necessary constituent of the processes [61]
plasma membrane [60]
PET: Positron emission tomography; MRI: Magnetic resonance imaging; XRT: Radiation therapy; BBB: Blood brain barrier; MET: (11)C-methionine;
AMT: Alpha-(11)C-methyl-l-tryptophan; FDG: (18)F-flurodeoxyglucose; FET: O-(2-(18)F-fluoroethyl)-l-tyrosine; FDOPA: (18)F-FDOPA; FLT: 3’-fluoro-3’ deoxythymidine;
PFS: Progression-free survival; OS: Overall survival

Neuroimmunol Neuroinflammation | Volume 1 | Issue 3 | December 2014 109