Performance of 18 F-FAPI PET/CT in assessing glioblastoma before radiotherapy: a pilot study

Abstract

Background We aimed to determine the performance of 18 F-FAPI PET/CT used for preprocedural assessment of glioblastoma before radiotherapy. Methods Twelve glioblastoma patients having undergone incomplete surgical resection or biopsy were examined with 18 F-FAPI PET/CT and MRI scanning before radiotherapy. All patients had confirmed tumor residues according to findings of histopathological and/or long-term clinical and radiological follow-ups. Lesion characterization data, including SUVmax and tumor-to-background ratio (TBR) on PET/CT were attained. PET/CT and MRI findings were compared in terms of number of lesions. The correlation between immunohistochemistry, molecular expression, and PET/CT parameters was also evaluated. Results 18 F-FAPI PET/CT detected 16 FAPI-avid out of 23 lesions in 12 patients described on MRI. MRI was statistically different from 18 F-FAPI PET/CT for lesion detection according to the exact McNemar statistical test (P = 0.0156). The SUVmax and TBR of the glioblastomas was 7.08 ± 3.55 and 19.95 ± 13.22, respectively. The sensitivity and positive predictive value (PPV) of 18 F-FAPI PET were 69.6% and 100%, respectively. Neither the Ki-67 index nor the molecular expression was correlated with the FAPI-PET/CT parameters. Conclusion 18 F-FAPI PET/CT detects glioblastomas at a lower rate than MRI. However, the 100% PPV of the examination may make it useful for differentiating controversial lesions detected on MRI. The 18 F-FAPI-avid lesions are displayed more clearly probably due to a higher TBR. 18 F-FAPI PET/CT imaging might find application in glioblastoma biopsy and radiotherapy planning.

FAPI PET/CT Imaging—An Updated Review

“…Ki-67 index and molecular expression profile did not show any significant correlation with FAPI PET/CT parameters. Despite a moderate sensitivity (69.6%), the excellent positive predictive value (PPV) (100%) of FAPI PET/CT may help when MRI findings are equivocal and can potentially guide biopsy site selection [87]. High TBRs allow the application of FAPI PET/CT (using either [ 68 Ga]Ga-FAPI-02 or [ 68 Ga]Ga-FAPI-04) for RT planning in glioblastoma patients as demonstrated by Windisch et al in a pilot study.…”

Clinical applications of fibroblast activation protein‐targeted theranostics in oncologic and nononcologic disease: Current status and future directions

“…Yao et al evaluated 18 F-FAPI PET/computed tomography (CT) and MRI before radiotherapy in patients with residual glioblastoma after surgery. Despite a lower lesion detection rate (69.6%) than MRI, the positive predictive value (PPV) of 18 F-FAPI PET/CT was 100%, suggesting that it is useful for differentiating controversial lesions detected on MRI [19]. Standard treatment of high-grade glioblastomas is maximal resection followed by radiotherapy.…”

PET Agents for Primary Brain Tumor Imaging

“…Fibroblasts are not present in brain (tumors); however, it does appear that there are FAP-positive cells such as FAP-positive foci of neoplastic cells in gliomas and FAP-positive vessels in glial tumors, and FAP seems to be overexpressed in most glioblastomas. Neither agent crosses the BBB, so uptake in clinical practice will reflect at least BBB permeability, possibly combined with FAP overexpression (164). One advantage is that FAPI agents have low background activity in the brain parenchyma (165).…”