Detection of primary prostate cancer using PSMA hybrid imaging for staging and comparison of [18F]PSMA-1007 with [68Ga]Ga-PSMA-11 PET/CT

Introduction: PSMA PET/CT hybrid imaging has proven to be a valuable method for the detection of recurrent prostate carcinoma (PCa). The goal of this study is to evaluate the performance of [¹⁸F]PSMA-1007 PET/CT (¹⁸F-PSMA) compared to [⁶⁸Ga]Ga-PSMA-11 PET/CT (⁶⁸Ga-PSMA) for the primary staging of PCa.

Methods: We retrospectively compared ¹⁸F-PSMA (52) and ⁶⁸Ga-PSMA (36) scans of 88 patients with elevated prostate specific antigen (PSA) serum levels (> 4.0 ng/mL), suspected of having primary PCa. PSMA positive lesions were compared with the histopathologic Gleason Score (GS) of prostate biopsies.

Results: Choosing an optimal cut off-level of SUV_max 8.95 by ROC analysis (AUC=0.750; 95% CI 0.590; 0.911; SD (AUC)=0.082), ¹⁸F-PSMA was able to distinguish between GS ≤7a (low- and intermediate-favourable-risk PCa) versus GS ≥7b (intermediate-unfavourable- and high-risk PCa) with a sensitivity of 62%, a specificity of 85%, a positive predictive value (PPV) of 92%, and an accuracy of 67% (p<0.001).

The ROC analysis revealed a cut off-level of SUV_max 4.75 for ¹⁸F-PSMA to distinguish between GS ≤7 versus GS ≥8 (high-risk PCa) with a sensitivity of 90%, a specificity of 52%, a PPV of 61%, and an accuracy of 63% (p<0.001).

By means of ROC analysis a SUV_max of 8.7 was found to be an optimal cut off-level for ⁶⁸Ga-PSMA (AUC=0.814; 95% CI 0.668; 0.961; SD (AUC)=0.075) to distinguish between GS ≤7a versus GS ≥7b with a sensitivity of 54%, a specificity of 91%, a PPV of 93%, and an accuracy of 66% (p<0.001).

While choosing a cut off-level of SUV_max 6.2, ⁶⁸Ga-PSMA was able to distinguish between GS ≤7 versus GS ≥8 with a sensitivity of 89%, a specificity of only 33%, a PPV of only 43%, and an accuracy of 63% (p<0.001).

Conclusions: This study demonstrates that ¹⁸F-PSMA and ⁶⁸Ga-PSMA are both suitable for the detection of primary PCa, especially in patients with high-risk PCa, with a correlation of PSMA-positive lesions with GS. However, our data reveal a higher specificity for ¹⁸F-PSMA when differentiating between PCa with low- and intermediate-risk versus high-risk, with comparable sensitivity.