RT Journal Article SR Electronic T1 Reproducibility and Repeatability of Semiquantitative 18F-Fluorodihydrotestosterone Uptake Metrics in Castration-Resistant Prostate Cancer Metastases: A Prospective Multicenter Study JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 1516 OP 1523 DO 10.2967/jnumed.117.206490 VO 59 IS 10 A1 Hebert Alberto Vargas A1 Gem M. Kramer A1 Andrew M. Scott A1 Andrew Weickhardt A1 Andreas A. Meier A1 Nicole Parada A1 Bradley J. Beattie A1 John L. Humm A1 Kevin D. Staton A1 Pat B. Zanzonico A1 Serge K. Lyashchenko A1 Jason S. Lewis A1 Maqsood Yaqub A1 Ramon E. Sosa A1 Alfons J. van den Eertwegh A1 Ian D. Davis A1 Uwe Ackermann A1 Kunthi Pathmaraj A1 Robert C. Schuit A1 Albert D. Windhorst A1 Sue Chua A1 Wolfgang A. Weber A1 Steven M. Larson A1 Howard I. Scher A1 Adriaan A. Lammertsma A1 Otto S. Hoekstra A1 Michael J. Morris YR 2018 UL http://jnm.snmjournals.org/content/59/10/1516.abstract AB 18F-fluorodihydrotestosterone (18F-FDHT) is a radiolabeled analog of the androgen receptor’s primary ligand that is currently being credentialed as a biomarker for prognosis, response, and pharmacodynamic effects of new therapeutics. As part of the biomarker qualification process, we prospectively assessed its reproducibility and repeatability in men with metastatic castration-resistant prostate cancer. Methods: We conducted a prospective multiinstitutional study of metastatic castration-resistant prostate cancer patients undergoing 2 (test/retest) 18F-FDHT PET/CT scans on 2 consecutive days. Two independent readers evaluated all examinations and recorded SUVs, androgen receptor–positive tumor volumes, and total lesion uptake for the most avid lesion detected in each of 32 predefined anatomic regions. The relative absolute difference and reproducibility coefficient (RC) of each metric were calculated between the test and retest scans. Linear regression analyses, intraclass correlation coefficients (ICCs), and Bland–Altman plots were used to evaluate repeatability of 18F-FDHT metrics. The coefficient of variation and ICC were used to assess interobserver reproducibility. Results: Twenty-seven patients with 140 18F-FDHT–avid regions were included. The best repeatability among 18F-FDHT uptake metrics was found for SUV metrics (SUVmax, SUVmean, and SUVpeak), with no significant differences in repeatability among them. Correlations between the test and retest scans were strong for all SUV metrics (R2 ≥ 0.92; ICC ≥ 0.97). The RCs of the SUV metrics ranged from 21.3% (SUVpeak) to 24.6% (SUVmax). The test and retest androgen receptor–positive tumor volumes and TLU, respectively, were highly correlated (R2 and ICC ≥ 0.97), although variability was significantly higher than that for SUV (RCs > 46.4%). The prostate-specific antigen levels, Gleason score, weight, and age did not affect repeatability, nor did total injected activity, uptake measurement time, or differences in uptake time between the 2 scans. Including the most avid lesion per patient, the 5 most avid lesions per patient, only lesions 4.2 mL or more, only lesions with an SUV of 4 g/mL or more, or normalizing of SUV to area under the parent plasma activity concentration–time curve did not significantly affect repeatability. All metrics showed high interobserver reproducibility (ICC > 0.98; coefficient of variation < 0.2%–10.8%). Conclusion: Uptake metrics derived from 18F-FDHT PET/CT show high repeatability and interobserver reproducibility.