First-in-human evaluation of [F-18]CETO: a novel tracer for adrenocortical tumours

Purpose [C-11]Metomidate positron emission tomography (PET) is currently used for staging of adrenocortical carcinoma and for lateralization in primary aldosteronism (PA). Due to the short half-life of carbon-11 and a high non-specific liver uptake of [C-11]metomidate there is a need for improved adrenal imaging methods. In a previous pre-clinical study para-chloro-2-[F-18]fluoroethyletomidate has been proven to be a specific adrenal tracer. The objective is to perform a first evaluation of para-chloro-2-[F-18]fluoroethyletomidate positron emission computed tomography ([F-18]CETO-PET/CT) in patients with adrenal tumours and healthy volunteers. Methods Fifteen patients underwent [F-18]CETO-PET/CT. Five healthy volunteers were recruited for test-retest analysis and three out of the five underwent additional [O-15]water PET/CT to measure adrenal blood flow. Arterial blood sampling and tracer metabolite analysis was performed. The kinetics of [F-18]CETO were assessed and simplified quantitative methods were validated by comparison to outcome measures of tracer kinetic analysis. Results Uptake of [F-18]CETO was low in the liver and high in adrenals. Initial metabolization was rapid, followed by a plateau. The kinetics of [F-18]CETO in healthy adrenals and all adrenal pathologies, except for adrenocortical carcinoma, were best described by an irreversible single-tissue compartment model. Standardized uptake values (SUV) correlated well with the uptake rate constant K-1. Both K-1 and SUV were highly correlated to adrenal blood flow in healthy controls. Repeatability coefficients of K-1, SUV65-70, and SUV120 were 25, 22, and 17%. Conclusions High adrenal uptake combined with a low unspecific liver uptake suggests that F-18]CETO is a suitable tracer for adrenal imaging. Adrenal SUV, based on a whole-body scan at 1 h p.i., correlated well with the net uptake rate K-i.