Incidence of PSMA PET thyroid incidentaloma depends on analysis method and tracer

To investigate the incidences of prostate-specific membrane antigen (PSMA) thyroid incidentaloma (PTI) using different methods to define PTI, to compare the incidence of PTI among different PSMA PET tracers, and to evaluate the clinical consequences of PTI. PSMA PET/CT scans in consecutive patients with primary prostate cancer were analyzed for the presence of PTI using a structured visual (SV) analysis reporting any elevated thyroidal uptake; a semi-quantitative (SQ) analysis using a SUVmax thyroid/bloodpool (t/b) ratio ≥ 2.0 as cutoff; and an analysis of PTI incidence in the clinical reports (RV analysis). A total of 502 patients were included. The incidence of PTIs was 22% in the SV analysis, 7% in the SQ analysis, and 2% in the RV analysis. PTI incidences differed significantly from 29 to 64% (SQ, resp. SV analysis) for [${}^{18}$F]PSMA-1007, 7 to 23% for [${}^{68}$Ga]PSMA-11, 2 to 8% for [${}^{18}$F]DCFPyL, and to 0% for [${}^{18}$F]PSMA-JK-7. The majority of PTI in the SV and SQ analyses consisted of diffuse (72-83%) and/or only slightly elevated thyroidal uptake (70%). Inter-observer agreement in the SV analysis was substantial (kappa = 0.76-0.78). During follow-up (median 16.8 months), there were no thyroid-related adverse events except in three patients. The incidence of PTI varies greatly among different PSMA PET tracers and is strongly dependent on the analysis method applied. PTI may safely be restricted to focal thyroidal uptake with a SUVmax t/b ratio ≥ 2.0. The clinical pursuit of a PTI must be weighed up to the expected outcome of the underlying disease. Thyroid incidentalomas (PTIs) are recognized in PSMA PET/CT. Incidence of PTI varies greatly among PET tracers and analysis methods. Incidence of thyroid-related adverse events in PTI cases is low.