Assessing the frequency and accuracy of morphologic changes of focal bone lesions on [Ga]Ga-PSMA-11 PET/CT in prostate cancer.

[BACKGROUND] In [F]F-PSMA-1007 PET imaging, focal bone uptake without morphological correlate (MC) on CT, is often classified as benign. In [Ga]Ga-PSMA-11, intense focal uptake without MC in a classical location is considered suspicious. The prevalence of focal bone uptake with or without MC on [Ga]Ga-PSMA-11 PET/CT remains unclear.

[METHODS] This single-center, retrospective study included patients who underwent a [Ga]Ga-PSMA-11 PET/CT scan for initial staging or biochemical recurrence (BCR) of prostate cancer between 04/16 - 11/21, with written informed consent for use of clinical data and adequate follow-up. For each patient with focal PSMA accumulation in the bones, up to three of these lesions were scored based on PSMA-RADS 2.0 and a clinical interpretation of suspicion for malignancy including clinical information was provided. In addition, MC on CT were assessed. A composite reference standard including imaging and clinical follow-up data was used.

[RESULTS] Out of 824 patients, 323 met eligibility criteria, with 101 showing PSMA-positive bone lesions. 176 lesions were included, 25% of 61 in the staging cohort had no MC, of which 73% were malignant. In the BCR group, 52% of 115 lesions were without MC, of which 48% were malignant. The sensitivity/specificity reached with PSMA-RADS 2.0, and MC on CT was 100%/100%and 78%/36% for staging, and 83%/100% and 60%/72% for BCR, respectively.

[CONCLUSION] Focal [Ga]Ga-PSMA-11 positive lesions without MC on CT are frequent, especially on scans for BCR, with the majority being malignant. Considering PSMA-RADS 4 lesions on [Ga]Ga-PSMA-11 on staging exams, significantly improves the accuracy. Incorporating clinical information and considering PSMA-RADS 3B can further improve the sensitivity for BCR scans.