FAPI PET/CT Prospective Interobserver Agreement

Fibroblast activation protein (FAP) is expressed by many cancer-associated fibroblasts, having a pivotal role in many desmoplastic tumor histotypes (sarcoma, pancreatic cancer, colorectal cancer). 68Ga-FAPI inhibitor (FAPI) is a promising novel molecular imaging tracer for positron emission tomography with computed tomography (PET/CT), with favorable initial results in different tumor entities. Compared to 18F-FDG, 68Ga-FAPI PET/CT shows a similar biodistribution, with less background tracer uptake in the brain, oral mucosa and liver, thus making this tracer potentially suitable to detect tumor lesions in these regions.

Moreover, the FAPI ligand contains a DOTA peptide which makes it appropriate also for therapeutic options if linked with 177Lutetium or 90Yttrium.

There is an increasing number of trials aimed to assess the efficacy and the clinical impact of 68Ga-FAPI PET/CT. Therefore, the inter-observer agreement and variability with 68Ga-FAPI PET/CT need to be established.

Inclusion criteria

Nuclear medicine physicians or radiologists with a prior experience with 68Ga-FAPI PET/CT from high-volume centers (Essen, Germany; Bologna, Italy; Los Angeles, USA; Munich, Germany, Münster, Germany ) will be prospectively recruited as research observers. Each observer will be asked to report the number of previous clinical 68Ga-FAPI PET/CT scans and then will be classified on the basis of the experience in these three groups:

• Low experience (< 30 prior 68Ga-FAPI PET/CT studies);
• Intermediate experience (30 to 300 studies);
• High experience (> 300 studies) At least three observers will be needed for each group.

Exclusion criteria

No prior PET/CT experience.