Pharmacokinetic studies of ⁶⁸Ga-labeled Bombesin (⁶⁸Ga-BZH₃) and F-18 FDG PET in patients with recurrent gliomas and comparison to grading: preliminary results.

Purpose: Dynamic PET studies with a ⁶⁸Ga-Bombesin analog, the ⁶⁸Ga-BZH₃, were performed in patients with highly suspected recurrent gliomas to investigate the effect of the receptor scintigraphy on tumor grading. Furthermore, dynamic F-18 Fluorodeoxyglucose (FDG) studies were performed for comparison.

Methods: The study consisted of 15 patients with histologically confirmed recurrent gliomas. Dynamic PET scans using ⁶⁸Ga-BZH₃ and FDG were obtained on 2 different days within 1 week. Multivariate analysis was used for the evaluation of the kinetic data. Standardized uptake values were calculated and a compartment (2-tissue) as well as a noncompartment model was used for data evaluation of both tracers.

Results: The evaluation includes 6 patients with a WHO II, 6 patients with a WHO III, and 3 patients with a WHO IV recurrent gliomas. Of the 15 patients, 10 patients demonstrated an increased ⁶⁸Ga-BZH₃ uptake visually, 3 of them with a WHO II, 4 with a WHO III, and 3 with a WHO IV tumor. Of the 15 patients, 6 patients revealed an enhanced FDG metabolism visually, 3 of them with a WHO II, and 3 with a WHO III. None of the 3 patients with WHO IV tumor demonstrated an enhanced FDG-uptake. Discriminant analysis based on a combination of FDG influx and binding potential of ⁶⁸Ga-BZH₃ best discriminated between low- and high-grade gliomas with a correct classification rate of 100%.

Conclusions: ⁶⁸Ga-BZH₃ seems to be helpful in patients with recurrent gliomas for the differentiation between low- and high-grade gliomas. Overall, the quantitative evaluation was superior to the visual analysis and the parameters of the ⁶⁸Ga-BZH₃ kinetics were more helpful than those of FDG for the differentiation between low- and high-grade gliomas.