TSPO Imaging in Glioblastoma Multiforme: A Direct Comparison Between 123I-CLINDE SPECT, 18F-FET PET, and Gadolinium-Enhanced MR Imaging.

Abstract

Here we compare translocator protein (TSPO) imaging using 6-chloro-2-(4'-(123)I-iodophenyl)-3-(N,N-diethyl)-imidazo[1,2-a]pyridine-3-acetamide SPECT ((123)I-CLINDE) and amino acid transport imaging using O-(2-(18)F-fluoroethyl)-l-tyrosine PET ((18)F-FET) and investigate whether (123)I-CLINDE is superior to (18)F-FET in predicting progression of glioblastoma multiforme (GBM) at follow-up. Three patients with World Health Organization grade IV GBM were scanned with (123)I-CLINDE SPECT, (18)F-FET PET, and gadolinium-enhanced MR imaging. Molecular imaging data were compared with follow-up gadolinium-enhanced MR images or contrast-enhanced CT scans. The percentage overlap between volumes of interest (VOIs) of increased (18)F-FET uptake and (123)I-CLINDE binding was variable (12%-42%). The percentage overlap of MR imaging baseline VOIs was greater for (18)F-FET (79%-93%) than (123)I-CLINDE (15%-30%). In contrast, VOIs of increased contrast enhancement at follow-up compared with baseline overlapped to a greater extent with baseline (123)I-CLINDE VOIs than (18)F-FET VOIs (21% vs. 8% and 72% vs. 55%). Our preliminary results suggest that TSPO brain imaging in GBM may be a useful tool for predicting tumor progression at follow-up and may be less susceptible to changes in blood-brain barrier permeability than (18)F-FET. Larger studies are warranted to test the clinical potential of TSPO imaging in GBM, including presurgical planning and radiotherapy.