68 Ga-PSMA PET/CT Imaging Predicting Intraprostatic Tumor Extent, Extracapsular Extension and Seminal Vesicle Invasion Prior to Radical Prostatectomy in Patients with Prostate Cancer.

PURPOSE: 68 Ga-labeled prostate-specific membrane antigen (PSMA) ligand positron emission tomography/computed tomography (PET/CT) has shown promising results in patients with biochemical recurrence after primary therapy for prostate cancer. In this study, we evaluated the usefulness of PSMA I&T (imaging and therapy) PET/CT prior to radical prostatectomy.

METHODS: The study population consisted of 21 patients with prostate cancer who underwent 68 Ga-PSMA I&T PET/CT before either open or laparoscopic radical prostatectomy. Intraprostatic tumor extent, extracapsular extension (ECE) and seminal vesicle invasion (SVI) were assessed on the PET/CT scans. Tracer uptake was quantified in terms of standardized uptake values (SUVs). Imaging findings were correlated with final whole-gland histopathology.

RESULTS: Of the 21 patients, two had T stage 2b disease, nine stage 2c, six stage 3a and four stage 3b. The median Gleason score was 7. The SUVmean of the primary tumors was 9.5 ± 8.8. SUVmean was higher in tumors with ECE than in organ-confined tumors (13.8 ± 11.0 vs. 5.6 ± 3.2, p  = 0.029). Peak tracer uptake was significantly positively correlated with Gleason score ( r s  = 0.49, p  = 0.025). Sensitivity, specificity, positive predictive value and negative predictive value were, respectively, 94.7%, 75.0%, 97.3% and 60.0% for tumor infiltration of an individual prostate lobe, 75.0%, 100.0%, 100.0% and 97.4% for SVI, and 90.0%, 90.9%, 90.0% and 90.9% for ECE, using an angulated contour of the prostate as the criterion. Tumor volume derived from 68 Ga-PSMA I&T PET/CT was significantly correlated with preoperative prostate-specific antigen value ( r p  = 0.75, p  < 0.001) and tumor volume on histopathology ( r p  = 0.45, p  = 0.039).

CONCLUSIONS: 68 Ga-PSMA I&T PET/CT prior to radical prostatectomy can contribute to presurgical local staging of prostate cancer. In this pilot study, 68 Ga-PSMA I&T PET/CT showed promising results for prediction of lobe infiltration, ECE and SVI.