Optimal Timing of Prostate Specific Membrane Antigen Positron Emission Tomography/Computerized Tomography for Biochemical Recurrence after Radical Prostatectomy

Abstract

Purpose: We developed a model predicting the probability of detecting prostate cancer recurrence outside the prostatic fossa on prostate specific membrane antigen positron emission tomography/computerized tomography in patients with biochemical recurrence after radical prostatectomy.

Materials and methods: We retrospectively included 419 consecutive patients with biochemical recurrence (prostate specific antigen less than 2.0 ng/ml) after radical prostatectomy who underwent ⁶⁸Ga-prostate specific membrane antigen-11 positron emission tomography/computerized tomography to guide salvage therapy. Patients receiving androgen deprivation therapy between radical prostatectomy and prostate specific membrane antigen positron emission tomography/computerized tomography were excluded from the study. We used multivariable logistic regression to assess predictors for the detection of prostate cancer recurrence outside the prostatic fossa on prostate specific membrane antigen positron emission tomography/computerized tomography. We minimized overfitting of the model and used decision curve analysis to determine clinical utility.

Results: Median prostate specific antigen at scanning was 0.40 ng/ml (IQR 0.30-0.70). Overall 174 (42%) patients had prostate cancer recurrence outside the prostatic fossa. Prostate specific antigen at time of scanning, and grade group, N stage and surgical margin status at radical prostatectomy specimen were significant predictors for detecting prostate cancer recurrence outside the prostatic fossa. The bootstrapped AUC of this model was 0.75 (IQR 0.73-0.77). The decision curve analysis showed a net benefit by a model based probability from 16%. Limitations include the retrospective design and the missing histological correlation of positive lesions.

Conclusions: Next to the prostate specific antigen at time of scanning, grade group, N stage and surgical margin status at radical prostatectomy specimen are significant predictors for detecting prostate cancer recurrence outside the prostatic fossa on prostate specific membrane antigen positron emission tomography/computerized tomography. The presented model is implemented in a dashboard to assist clinicians in determining the optimal time to perform ⁶⁸Ga-prostate specific membrane antigen-11 positron emission tomography/computerized tomography in patients with biochemical recurrence after radical prostatectomy.

Keywords: 68Ga-PSMA; prostatectomy; prostatic neoplasms; recurrence; salvage therapy.