Purpose: Given the good correlation between PSMA expression and intraglandular tumour aggressiveness based on immunohistochemistry, there is increasing interest in 68Ga-PSMA-11 PET/MRI for staging prostate cancer (PCA). Therefore, accurate knowledge of prostate anatomy as well as normal distribution of PSMA within the prostate gland is becoming essential. The aim of this study was to investigate the physiological intraprostatic distribution of 68Ga-PSMA-11.
Methods: We retrospectively analysed all patients who underwent a staging 68Ga-PSMA-11 PET/MRI scan between June 2016 and January 2018 for high-risk PCA, underwent radical prostatectomy in our institution, and gave written consent for further data analysis. In each patient, standardized volumes of interest (VOIs) were placed bilaterally in the central, transition and peripheral zones within the zonal anatomy according to T2 weighted sequences in the axial and coronal planes. VOIs were only placed if they were safely within healthy tissue without spillover from the PCA. SUVmax and SUVmean were determined and their differences among the regions were assessed using the Wilcoxon signed-ranks test.
Results: Of 283 consecutive patients scanned with 68Ga-PSMA-11 PET/MR, 31 were analysed. A total of 133 VOIs were placed, 46 in the central zone, 41 in the transition zone and 46 in the peripheral zone. Differences in SUVmax between the central zone (mean 3.9 ± 0.58) and transition zone (mean 3.2 ± 0.59) and between the central zone and peripheral zone (mean 2.7 ± 0.54) were statistically significant (both p < 0.001).
Conclusion: Our results suggest that higher 68Ga-PSMA-11 accumulation in the central zone than in the transition and peripheral zones is normal, and leads to a pattern resembling "Mickey Mouse ears" on 68Ga-PSMA-11 PET. This pattern could be helpful in avoiding false-positive interpretations of PET scans.
Keywords: False-positive; Normal distribution; PET/MR; Prostate cancer; Staging.