Interobserver Agreement Rates on Fibroblast Activation Protein Inhibitor–Directed Molecular Imaging and Therapy

Abstract

ObjectivesFibroblast activation protein (FAP) has emerged as a novel target for FAP inhibitor (FAPI)–directed molecular imaging and endoradiotherapy (ERT). We aimed to assess the interobserver agreement rates for interpretation of 68Ga-FAPI-4 PET/CT and decision for ERT.Patients and MethodsA random order of 68Ga-FAPI-4 PET/CTs from 49 oncology patients were independently interpreted by 4 blinded readers. Per scan, visual assessment was performed, including overall scan impression, number of organ/lymph node (LN) metastases, and number of affected organs/LN regions. Moreover, a maximum of 3 target lesions, defined as largest in size and/or most intense, per organ compartment were identified, which allowed for an additional quantitative interobserver assessment of LN and organ lesions. To investigate potential reference tissues, quantification also included unaffected liver parenchyma and blood pool. Readers also had to indicate whether FAPI-directed ERT should be considered (based on intensity of uptake and widespread disease). Interobserver agreement rates were evaluated using intraclass correlation coefficients (ICCs) and interpreted according to Cicchetti (with 0.4–0.59 indicating fair, and 0.6–0.74 good, agreement).ResultsOn a visual basis, the agreement rate for an overall scan impression was fair (ICC, 0.42; 95% confidence interval [CI], 0.27–0.57). The concordance rate for number of affected LN areas was also fair (ICC, 0.59; 95% CI, 0.45–0.72), whereas the number of LN metastases, number of affected organs, and number of organ metastases achieved good agreement rates (ICC, ≥0.63). In a quantitative analysis, concordance rates for LN were good (ICC, 0.70; 0.48–0.88), but only fair for organ lesions (ICC, 0.43; 0.26–0.60). In regards to background tissues, ICCs were good for unaffected liver parenchyma (0.68; 0.54–0.79) and fair for blood pool (0.43; 0.29–0.58). When readers should decide on ERT, concordance rates were also fair (ICC, 0.59; 95% CI, 0.46–0.73).ConclusionsFor FAPI-directed molecular imaging and therapy, a fair to good interobserver agreement rate was achieved, supporting the adoption of this radiotracer for clinical routine and multicenter trials.

Impact of 68Ga-FAPI-04 PET/CT on Staging and Therapeutic Management in Patients With Digestive System Tumors

“…The need for further approval was waived by the local institutional review board due to the retrospective nature of this study (number 20210415 02). Parts of this cohort have been reported previously, 12 , 13 but without investigating effects on staging and therapeutic management.…”

“…Correction of emission data and image reconstruction were also performed. 12,13 For GCI, patients affected with PDAC or HCC received multiphasic CT and/or multiphasic MRI. One individual with PDAC received noncontrast full-dose PET/CT due to severely impaired renal function (patient 3).…”

Nanoparticles targeted to fibroblast activation protein outperform PSMA for MRI delineation of primary prostate tumours

“…In another study, 1.5T MRI guided stereotactic body RT by LINAC guided by PSMA-PET produced encouraging oncological and tolerability results in the management of oligometastatic castration sensitive prostate cancer (53). Recently, FAP-targeted PET has demonstrated fair to good interobserver agreement rates in the detection of organ and lymph node metastases across a variety of tumour types (54). There are yet to be clinical studies investigating the use of molecular MRI contrast agents in image-guided RT.…”

Associations between Normal Organs and Tumor Burden in Patients Imaged with Fibroblast Activation Protein Inhibitor-Directed Positron Emission Tomography

“…20210415 02). Parts of this cohort have been investigated previously [ 22 , 23 , 24 , 25 ], without assessing correlations between normal uptake and tumor burden.…”