Clinical Nuclear Medicine

Imaging of gliomas remains challenging. The aim of the study was to assess the feasibility of using ⁶⁸Ga-PSMA-11 PET/CT for imaging gliomas.

Fifteen patients with glioma from 2 centers were included in the study. Ten patients were treated cases of glioblastoma with suspected recurrence. Two patients were sent for assessing the nature (primary lesion/metastasis) of space-occupying lesion in the brain; 3 patients were imaged immediately after surgery and before radiotherapy. Target-to-background ratios (TBR) for the brain lesions were calculated using contralateral cerebellar uptake as background.

Among the 10 cases with suspected recurrence, scan was positive in 9, subsequent surgery was done, and histopathology proved it to be true recurrence. In the scan-negative case on follow-up, no evidence of disease could be made clinically or radiologically. Among the other cases the presence or absence of disease could be unequivocally identified on the ⁶⁸Ga-PSMA-11 brain scan and correlated with the histopathology or other imaging. Apart from the visual assessment quantitative assessment of the lesions with TBR also showed a significantly high TBR value for those with true disease compared with those with no disease.

In the evaluation of gliomas, ⁶⁸Ga-PSMA-11 PET/CT brain imaging is a potentially useful imaging tool. The use of ⁶⁸Ga-PSMA-11 brain PET/CT in evaluation of recurrent glioma seems promising. Absence of physiological uptake of ⁶⁸Ga-PSMA-11 in the normal brain parenchyma results in high TBR values and consequently better visualization of glioma lesions.

Glioblastoma multiforme (GBM) is the most common and most aggressive primary tumor of the brain. After initial therapy and total resection of GBM, 80% to 90% of recurrences occur at the surgical margins. Currently, limited data are available in the literature on the possible use of ⁶⁸Ga–prostate-specific membrane antigen (PSMA-11) for diagnosis of recurrence in GBM patients. The aim was to assess the feasibility and potential of ⁶⁸Ga-PSMA-11 PET/CT as a diagnostic procedure in patients with histologically confirmed of GBM and suspected recurrent disease on MRI.

No radiopharmaceutical-related adverse events were noted. Characterization of recurrent disease with MRI included T2-weighted fast spin-echo images, fluid-attenuated inversion recovery and diffusion-weighted imaging sequences, and gadolinium enhanced T1-weighted images. Visual interpretation of PET showed increased accumulation of ⁶⁸Ga-PSMA-11 in recurrent lesion detected by T1 contrast enhanced and diffusion-weighted imaging images in all patients with a median SUVmax of the tumor of 6.5 and an SUVmean of 3.5. The median tumor-to-background brain ratio and tumor-to-liver ratio obtained from ⁶⁸Ga-PSMA-11 PET/CT were 96.7 and 0.8, respectively.

The extremely low background uptake in normal brain tissue and consequently high tumor-to-brain ratio make ⁶⁸Ga-PSMA-11 PET/CT highly promising for diagnosis of recurrent disease in GBM patients. Although PSMA expression in recurrent GBM also opens a potential way for targeted peptide therapy with α/β-emitters as well as for prediction of treatment with antiangiogenic agents, the low tumor-to-liver ratio observed in the majority of patients in this study suggests a limited role of radiolabeled PSMA ligands for targeted radionuclide therapy of recurrent GBM.