External Validation of Two Nomograms Developed for 68Ga-PSMA-11 Applied to the Prostate-specific Membrane Antigen Tracer 18F-DCFPyl: Is Prediction of the Optimal Timing of Salvage Therapy Feasible?

Two nomograms have been developed to predict the outcome of positron emission tomography (PET)/computed tomography (CT) imaging with68Ga-labeled ligands for prostate-specific membrane antigen (68Ga-PSMA) for patients with rising prostate-specific antigen after radical prostatectomy (RP). These nomograms quantify the ability of PSMA PET/CT to detect prostate cancer recurrences, and therefore provide critical information in determining the optimal timing for PSMA PET/CT in guiding salvage therapies. We validated the ability of these nomograms to accurately predict PET/CT outcome using another ligand tracer, 18F-DCFPyL. The external validation cohort consisted of 157 men from the Prostate Cancer Network Netherlands who underwent 18F-DCFPyL PET/CT to guide salvage therapies after RP. The nomogram of Rauscher et al (predicting a positive scan) showed accurate prediction of 50-80% (discrimination 0.68, 95% confidence interval [CI] 0.59-0.76). The nomogram of Luiting et al (predicting recurrence outside the prostatic fossa) showed accurate prediction for predicted probability values between 15% and 65%, with a small degree of overestimation for predicted probability values between 30% and 50% (discrimination 0.74, 95% CI 0.28-1.24). According to calibration curves, discrimination results, and decision curve analysis, we conclude that clinicians can use these 68Ga-PSMA-based nomograms to predict 18F-DCFPyL PET/CT outcome. These nomograms improve shared decision-making in determining the optimal time to initiate PSMA PET/CT-guided salvage therapies.

Prediction tools developed for prostate scans (positron emission tomography, PET) using one type of radioactive tracer (chemicals labeled with gallium-68) are also accurate in predicting scan findings with another tracer (a chemical labeled with fluorine-18). Our study confirms that these tools can be used to guide decisions on the timing of treatments for prostate cancer recurrence.

European urology open science. 2021 Apr 29*** epublish ***

Henk B Luiting, Sebastiaan Remmers, Dennie Meijer, André N Vis, Maarten Donswijk, Daniela E Oprea-Lager, Louise Emmett, Isabel Rauscher, Henk G Van der Poel, Monique J Roobol, Pim J van Leeuwen

Department of Urology, Erasmus University Medical Center, Rotterdam, The Netherlands., Department of Urology, Amsterdam University Medical Center, VU University, Prostate Cancer Network Netherlands, Amsterdam, The Netherlands., Department of Nuclear Medicine, The Netherlands Cancer Institute, Amsterdam, The Netherlands., Department of Radiology & Nuclear Medicine, Amsterdam University Medical Center, VU University, Cancer Center Amsterdam, Amsterdam, The Netherlands., Department of Theranostics and Nuclear Medicine, St Vincent's Hospital, Sydney, Australia., Department of Nuclear Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany., Department of Urology, The Netherlands Cancer Institute, Prostate Cancer Network Netherlands, Amsterdam, The Netherlands.