Comparison of (18)F-FET PET and 5-ALA fluorescence in cerebral gliomas

The aim of the study was to compare presurgical (18)F-fluoroethyl-L: -tyrosine ((18)F-FET) uptake and Gd-diethylenetriaminepentaacetic acid (DTPA) enhancement on MRI (Gd) with intraoperative 5-aminolevulinic acid (5-ALA) fluorescence in cerebral gliomas.

(18)F-FET positron emission tomography (PET) was performed in 30 patients with brain lesions suggestive of diffuse WHO grade II or III gliomas on MRI. PET and MRI data were coregistered to guide neuronavigated biopsies before resection. After oral application of 5-ALA, 38 neuronavigated biopsies were taken from predefined tumour areas that were positive or negative for (18)F-FET or Gd and checked for 5-ALA fluorescence. (18)F-FET uptake with a mean tumour to brain ratio ≥1.6 was rated as positive.

Of 38 biopsies, 21 corresponded to high-grade glioma tissue (HGG) of WHO grade III (n = 19) or IV (n = 2) and 17 biopsies to low-grade glioma tissue (LGG) of WHO grade II. In biopsies corresponding to HGG, (18)F-FET PET was positive in 86% (18/21), but 5-ALA and Gd in only 57% (12/21). A mismatch between Gd and 5-ALA was observed in 6 of 21 cases of HGG biopsy samples (3 Gd-positive/5-ALA-negative and 3 Gd-negative/5-ALA-positive). In biopsies corresponding to LGG, (18)F-FET was positive in 41% (7/17), while 5-ALA and Gd were negative in all but one instance. All tumour areas with 5-ALA fluorescence were positive on (18)F-FET PET.

There are differences between (18)F-FET and 5-ALA uptake in cerebral gliomas owing to a limited sensitivity of 5-ALA to detect tumour tissue especially in LGG. (18)F-FET PET is more sensitive to detect glioma tissue than 5-ALA fluorescence and should be considered as an additional tool in resection planning.