18F FET PET
Indications
18F-FET PET may provide additional diagnostic information compared to standard MRI in neuro-oncology 1).
The addition of 18F FET PET to MRI helped discriminate tumor from non-tumor lesions in the largest consecutive cohort of pediatric CNS tumor patients 2)
18F–FET PET may be useful in the differential diagnosis between brain tumors and non-neoplastic lesions and between low-grade and high-grade gliomas. Integration of 18F-FET PET into surgical planning allows better delineation of the extent of resection beyond margins visible with standard MRI. For biopsy planning, 18F-FET PET is particularly useful in identifying malignant foci within non-contrast-enhancing gliomas. 18F-FET PET may improve the radiation therapy planning in patients with gliomas. This metabolic imaging method may be useful to evaluate treatment response in patients with gliomas and it improves the differential diagnosis between brain tumours recurrence and post-treatment changes. 18F-FET PET may provide useful prognostic information in high-grade gliomas.
For quantification of standard PET-derived parameters such as the tumor-to-background ratio, the background activity is assessed using a region of interest (ROI) or volume of interest (VOI) in unaffected brain tissue. However, there is no standardized approach regarding the assessment of the background reference 3).
(18)F-Fluoroethyl-l-thyrosine (FET) is a positron emission tomography (PET) radiopharmaceutical applicable for widespread use because of its long half-life radionuclide.
Fluoroethyl Tyrosine Positron Emission Tomography for patients with gliomas undergoing multimodal treatment or various forms of irradiation is a powerful tool to improve the differential diagnosis 4).
FET PET reliably distinguishes between post-therapeutic benign lesions and tumour recurrence after initial treatment of low- and high-grade gliomas 5).
Maps of (18)FET uptake kinetics strongly correlated with histopathology in suspected grade II gliomas. Anaplastic foci can be accurately identified, and this finding has implications for prognostic evaluation and treatment planning 6).
Dynamic 18F-FET PET in suspected WHO grade II gliomas defines distinct biological subgroups with different clinical courses 7).
In low grade gliomas 5 aminolevulinic acid fluorescence is the exception and FET PET is more sensitive. High grade areas in diffuse gliomas with anaplastic foci usually fluoresce, if they are FET PET positive. As a result, FET PET appears valuable for pre-operative identification of anaplastic foci and hot spots are strongly predictive for ALA-derived fluorescence, which highlight anaplastic foci during resection 8).
Age, tumor volume, and Fluoroethyl Tyrosine Positron Emission Tomography uptake are factors predicting 5-ALA-induced fluorescence in gliomas without typical glioblastoma imaging features. Fluorescence was associated with an increased Ki67/MIB-1 index and high-grade pathology. Whether fluorescence in grade II gliomas identifies a subtype with worse prognosis remains to be determined 9).