The objective of this study was to develop a clinical nomogram to predict gallium-68 prostate-specific membrane antigen positron emission tomography/computed tomography (68Ga-PSMA-11-PET/CT) positivity in different clinical settings of PSA failure.

Seven hundred three (n = 703) prostate cancer (PCa) patients with confirmed PSA failure after radical therapy were enrolled. Patients were stratified according to different clinical settings (first-time biochemical recurrence [BCR]: group 1; BCR after salvage therapy: group 2; biochemical persistence after radical prostatectomy [BCP]: group 3; advanced-stage PCa before second-line systemic therapies: group 4). First, we assessed 68Ga-PSMA-11-PET/CT positivity rate. Second, multivariable logistic regression analyses were used to determine predictors of positive scan. Third, regression-based coefficients were used to develop a nomogram predicting positive 68Ga-PSMA-11-PET/CT result and 200 bootstrap resamples were used for internal validation. Fourth, receiver operating characteristic (ROC) analysis was used to identify the most informative nomogram’s derived cutoff. Decision curve analysis (DCA) was implemented to quantify nomogram’s clinical benefit.

68Ga-PSMA-11-PET/CT overall positivity rate was 51.2%, while it was 40.3% in group 1, 54% in group 2, 60.5% in group 3, and 86.9% in group 4 (p < 0.001). At multivariable analyses, ISUP grade, PSA, PSA doubling time, and clinical setting were independent predictors of a positive scan (all p ≤ 0.04). A nomogram based on covariates included in the multivariate model demonstrated a bootstrap-corrected accuracy of 82%. The nomogram-derived best cutoff value was 40%. In DCA, the nomogram revealed clinical net benefit of > 10%.

This novel nomogram proved its good accuracy in predicting a positive scan, with values ≥ 40% providing the most informative cutoff in counselling patients to 68Ga-PSMA-11-PET/CT. This tool might be important as a guide to clinicians in the best use of PSMA-based PET imaging.

European journal of nuclear medicine and molecular imaging. 2019 Sep 06 [Epub ahead of print]

Francesco Ceci, Lorenzo Bianchi, Marco Borghesi, Giulia Polverari, Andrea Farolfi, Alberto Briganti, Riccardo Schiavina, Eugenio Brunocilla, Paolo Castellucci, Stefano Fanti

Metropolitan Nuclear Medicine, S.Orsola-Malpighi Hospital, University of Bologna, Bologna, Italy. ., Department of Experimental, Diagnostic and Specialty Medicine (DIMES), Cardio-Nephro-Thoracic Sciences Doctorate, University of Bologna, Bologna, Italy., Metropolitan Nuclear Medicine, S.Orsola-Malpighi Hospital, University of Bologna, Bologna, Italy., Unit of Urology/Division of Oncology, Urological Research Institute, IRCCS San Raffaele Hospital, Milan, Italy.