Assessment of skeletal metastasis in prostate cancer staging: an intra-individual comparison of⁶⁸Ga-PSMA PET/CT,⁶⁸Ga-NODAGA-Zoledronate PET/CT, and^99mTc-MDP bone scan

Background: Zoledronate is a bisphosphonate that accumulates at sites of high bone turnover. Radiolabeled Zoledronate has been successfully demonstrated in clinical imaging of skeletal metastasis. ⁶⁸Ga-NODAGA-Zoledronate PET/CT with ⁶⁸Ga-PSMA PET/CT has, in recent times, joined ^99mTc-MDP bone scan as radionuclide options for the assessment of skeletal metastasis. Bone is a common site of prostate cancer (PCa) metastasis. We aimed to compare the diagnostic ability of ⁶⁸Ga-PSMA PET/CT, ⁶⁸Ga-NODAGA-Zoledronate PET/CT, and ^99mTc-MDP bone scan in the detection of skeletal metastases in the staging of treatment-naïve men with intermediate- to high-risk PCa.

Methods: Men with newly diagnosed adenocarcinoma of the prostate gland were prospectively recruited to undergo, within four weeks, imaging with ⁶⁸Ga-PSMA PET/CT, ⁶⁸Ga-NODAGA-Zoledronate PET/CT, and ^99mTc-MDP bone scan for the assessment of skeletal metastasis. Two experienced readers independently performed image analysis. Per patient and per lesion analyses were done and compared between imaging tests. The SUVmax of the most intense lesion was compared between ⁶⁸Ga-PSMA PET/CT and ⁶⁸Ga-NODAGA-Zoledronate PET/CT.

Results: Ten men were included with median age, Gleason score and PSA of 68.5 years (Interquartile range, IQR=63 - 74), 8 (IQR=8-9) and 119.29 ng/mL (IQR=25 - 280.58), respectively. On per-patient analysis, skeletal metastasis was detected in all patients on all three imaging tests. On a per lesion analysis, ⁶⁸Ga-PSMA PET/CT identified more lesions (n=213 skeletal metastases) compared with ⁶⁸Ga-NODAGA-Zoledronate PET/CT (n=174 skeletal metastases) and ^99mTc-MDP bone scan (n=153 skeletal metastases), p=0.355. The mean SUVmax of the most intense lesion was 20.26 ± 7.56 for ⁶⁸Ga-PSMA PET/CT compared with 14.82 ± 7.93 for ⁶⁸Ga-NODAGA-Zoledronate PET/CT, p=0.227. Conclusion: On a per-patient basis, ⁶⁸Ga-PSMA PET/CT, ⁶⁸Ga-NODAGA-Zoledronate PET/CT, and ^99mTc-MDP bone scan have a comparable performance for the detection of skeletal metastases in men with intermediate- to high-risk PCa. On a per lesion analysis, the seeming better performance of ⁶⁸Ga-PSMA PET/CT in detecting more skeletal metastases than ⁶⁸Ga-NODAGA-Zoledronate PET/CT and ^99mTc-MDP bone scan did not reach statistical significance.