Use of FET PET in glioblastoma patients undergoing neurooncological treatment including tumour-treating fields: initial experience.

We present our first clinical experience with O-(2-18F-fluoroethyl)-L-tyrosine (FET) PET in patients with high-grade glioma treated with various neurooncological therapies including tumour-treating fields (TTFields) for the differentiation of tumour progression from treatment-related changes.

We retrospectively assessed 12 patients (mean age 51 ± 12 years, range 33-72 years) with high-grade glioma (11 glioblastomas, 1 gliosarcoma) in whom the treatment regimen included TTFields and who had undergone FET PET scans for differentiation of tumour progression from treatment-related changes. Mean and maximum tumour-to-brain ratios (TBRmean, TBRmax) were calculated. The definitive diagnosis (tumour progression or posttherapeutic changes) was confirmed either by histopathology (4 of 12 patients) or on clinical follow-up.

In all nine patients with confirmed tumour progression, the corresponding FET PET showed increased uptake (TBRmax 3.5 ± 0.6, TBRmean 2.7 ± 0.7). In one of these nine patients, FET PET was consistent with treatment-related changes, whereas standard MRI showed a newly diagnosed contrast-enhancing lesion. In two patients treated solely with TTFields without any other concurrent neurooncological therapy, serial FET PET revealed a decrease in metabolic activity over a follow-up of 6 months or no FET uptake without any signs of tumour progression or residual tumour on conventional MRI.

FET PET may add valuable information in monitoring therapy in individual patients with high-grade glioma undergoing neurooncological treatment including TTFields.