Background and objectives:

Prostate specific membrane antigen (PSMA) PET is a novel imaging modality that has been incorporated into current clinical practice at certain centres. It is currently used pre‐operatively for the detection of metastatic disease in the setting of negative lymph node staging by conventional imaging techniques. It is not yet clear whether it has a role in the description of disease in the prostate itself. The aim of this study is to evaluate the diagnostic accuracy of 68 Ga‐PSMA PET by determining whether pre‐operative PSMA PET avidity in the prostate on 68 Ga‐PSMA PET correlates with higher risk prostate cancer on histopathology and whether this in turn should influence surgical technique.

Materials and methods:

This is a prospective, multi‐centre cohort study at Monash Health. Between January 2015 and August 2016, 12 patients (mean age ± SD, 64 ± 5.2 years) were identified with biopsy‐proven intermediate to high risk prostate cancer who had undergone 68 Ga‐PSMA PET prior to radical prostatectomy. Data (demographics, histopathology of radical prostatectomy) was collated from Scanned Medical Records. Referral for 68 Ga‐PSMA PET/CT was granted by multidisciplinary team discussion. All imaging was performed at Monash Health using 68 Ga‐PSMA ligands. SUVmax was measured for each avid focus in the prostate. The histologic location and Gleason score of each specimen were compared to 68 Ga‐PSMA PET images. Statistical analysis with SPSS was performed using t‐test.

Results:

The correlation of higher risk disease (Gleason 8 and 9) on histopathology with intense avidity on 68 Ga‐PSMA PET showed a specificity and sensitivity of 75%. Furthermore, all patients with higher risk disease demonstrated more intense avidity than intermediate risk disease (Gleason 7). The correlation of the location of disease (right or left) on imaging to histopathology demonstrated a sensitivity and specificity of 70.5% and 85.7%, respectively. However, of those with higher risk disease, only 50% of 68 Ga‐PSMA PET‐avid foci correlated with the location of disease on radical prostatectomy specimen. The remaining 50% had hot spots that did not correlate to the histopathology.

Conclusion:

68 Ga‐PSMA PET is more likely to detect higher risk disease in the prostate as compared to intermediate risk disease, however the location of disease in the prostate does not necessarily correlate to that detected on histopathology. Therefore, surgical decisions regarding nerve sparing should not be altered by the 68 Ga‐PSMA PET result.