Assessment of Simplified Methods for Quantification of 18 F-FDHT Uptake in Patients with Metastatic Castration-Resistant Prostate Cancer

F-fluorodihydrotestosterone ( F-FDHT) PET/CT potentially provides a noninvasive method for assessment of androgen receptor expression in patients with metastatic castration-resistant prostate cancer (mCRPC). The objective of this study was to assess simplified methods for quantifying F-FDHT uptake in mCRPC patients and to assess effects of tumor perfusion on these F-FDHT uptake metrics. Seventeen mCRPC patients were included in this prospective observational multicenter study. Test and retest 30-min dynamic F-FDHT PET/CT scans with venous blood sampling were performed in 14 patients. In addition, arterial blood sampling and dynamic O-H O scans were obtained in a subset of 6 patients. Several simplified methods were assessed: Patlak plots; SUV normalized to body weight (SUV ), lean body mass (SUV ), whole blood (SUV ), parent plasma activity concentration (SUV ), area under the parent plasma curve (SUV ), and area under the whole-blood input curve (SUV ); and SUV corrected for sex hormone-binding globulin levels (SUV ). Results were correlated with parameters derived from full pharmacokinetic F-FDHT and O-H O. Finally, the repeatability of individual quantitative uptake metrics was assessed. Eighty-seven F-FDHT-avid lesions were evaluated. F-FDHT uptake was best described by an irreversible 2-tissue-compartment model. Replacing the continuous metabolite-corrected arterial plasma input function with an image-derived input function in combination with venous sample data provided similar results ( = 0.98). Patlak and SUV showed an excellent correlation ( > 0.9). SUV showed a moderate correlation to ( = 0.70, presumably due to fast F-FDHT metabolism. When calculating SUV , correlation to improved ( = 0.88). The repeatability of full kinetic modeling parameters was inferior to that of simplified methods (repeatability coefficients > 36% vs. < 28%, respectively). F-FDHT uptake showed minimal blood flow dependency. F-FDHT kinetics in mCRPC patients are best described by an irreversible 2-tissue-compartment model with blood volume parameter. SUV showed a near-perfect correlation with the irreversible 2-tissue-compartment model analysis and can be used for accurate quantification of F-FDHT uptake in whole-body PET/CT scans. In addition, SUV could potentially be used as an even simpler method to quantify F-FDHT uptake when less complex scanning protocols and accuracy are required.