68Ga-Pentixafor PET/CT for In Vivo Imaging of CXCR4 Receptors in Glioma Demonstrating a Potential for Response Assessment to Radiochemotherapy: Preliminary Results

Purpose : The aim of this study was to evaluate the diagnostic potential of Ga-68-pentixafor PET/CT for in vivo CXCR4 receptors imaging in glioma and its possible role in response assessment to radiochemotherapy (R-CT). Methods : Nineteen (12 men, 7 women) patients with glioblastoma multiforme (GBM) underwent Ga-68-pentixafor PET/CT, contrast-enhanced MR, and MR spectroscopy. Patients were divided in to 2 groups, that is, group I was the presurgical (n = 9) group in which the scanning was done before surgery, and PET findings were correlated with CXCR4 receptors' density. The group II was the postsurgical (n = 10) group in which the scanning was done before and after R-CT and used for treatment response evaluation. The quantitative analysis of Ga-68-pentixafor PET/CT evaluated the mean SUVmax, SUVmean, SUVpeak, and T/B values. MR spectroscopy data evaluated the ratios of tumor metabolites (choline, NAA, creatine). Results : Ga-68-Pentixafor uptake was noted in all (n = 19) the patients. In the group I, the mean SUVmax, SUVmean, SUVpeak, and T/B values were found to be 4.5 +/- 1.6, 0.60 +/- 0.26, 1.95 +/- 0.8, and 6.9 +/- 4.6, respectively. A significant correlation (P < 0.005) was found between SUVmean and choline/NAA ratio. Immunohistochemistry performed in 7/9 showed CXCR4 receptors' positivity (intensity 3(+); stained cells >50.0%). In the group II, the mean SUVmax at baseline was 4.6 +/- 2.1 and did not differ (4.4 +/- 1.6) significantly from the value noted at post-R-CT follow-up PET/CT imaging. At 6 months' clinical follow-up, 4 patients showed stable disease. SUVmax and T/B ratios at follow-up imaging were lower (3.70 +/- 0.90, 2.64 +/- 1.35) than the corresponding values (4.40 +/- 2.8; 2.91 +/- 0.93) noted at baseline. Six (6/10) patients showed disease progression, and the mean SUVmax, and T/B ratio in these patients were significantly (P < 0.05) higher than the corresponding values at baseline and also higher than that noted in the stable patients. Conclusions : Ga-68-Pentixafor PET/CT can be used for in vivo mapping of CXCR4 receptors in GBM. The technique after validation in a large cohort of patients may have added diagnostic value for the early detection of GBM recurrence and for treatment response evaluation.