Purpose
To develop a model predicting the probability of detecting prostate cancer (PCa) recurrence outside the prostatic fossa on PSMA PET/CT in patients with biochemical recurrence (BCR) after radical prostatectomy (RP).
Materials and Methods
We retrospectively included 419 consecutive patients with BCR (PSA<2.0 ng/ml) after RP who underwent 68Ga-PSMA-11 PET/CT to guide salvage therapy. Patients receiving androgen deprivation therapy between RP and PSMA PET/CT were excluded. We used multivariable logistic regression to assess predictors for the detection of PCa recurrence outside the prostatic fossa on PSMA PET/CT. We minimalized overfitting of the model and used decision curve analysis (DCA) to determine clinical utility.
Results
Median PSA at time of scanning was 0.40 (interquartile range 0.30-0.70) ng/ml. 174 (42%) patients had PCa recurrence outside the prostatic fossa. PSA at time of scanning, and grade group, N-stage and surgical margin status at RP specimen were significant predictors for detecting PCa recurrence outside the prostatic fossa. The bootstrapped AUC of this model was 0.75 (interquartile range 0.73–0.77). The DCA 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 PSA value at time of scanning, grade group, N-stage and surgical margin status at RP specimen are significant predictors for detecting PCa recurrence outside the prostatic fossa on PSMA PET/CT. The presented model is implemented in a dashboard to assist clinicians in determining the optimal moment to perform 68Ga-PSMA PET/CT in patients with BCR after RP.