Assessment of Simplified Methods for Quantification of 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-HO 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-HO. 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.