Frequency of PET-positive benign findings on PSMA-ligand PET/CT: matched-pair comparison of 68Ga-PSMA-11 and 18F-PSMA-1007

Ziel/Aim:

The ¹⁸F labeled PSMA ligand ¹⁸F-PSMA-1007 is increasingly used for imaging of prostate cancer with PET/CT. The purpose of this study was to assess if the frequency of PET-positive benign findings on ¹⁸F-PSMA-1007 differs from ⁶⁸Ga-PSMA-11.

Methodik/Methods:

Patients with biochemical recurrent prostate cancer after radical prostatectomy who underwent ¹⁸F-PSMA-1007 PET/CT (n = 102) were matched with ⁶⁸Ga-PSMA-11PET/CT on the basis of clinical parameters (Gleason score, PSA-values, T- and N-stage, antihormonal treatment). Both ⁶⁸Ga-PSMA-11 and ¹⁸F-PSMA-1007 PET/CTs (total n = 204) were reviewed by one nuclear medicine physician. After identification of all PSMA-ligand PET findings lesions suspicious for recurrent PC were differentiated from probably benign lesions based on known pitfalls of ⁶⁸Ga-PSMA-11 studies, clinical history and CT findings.

Ergebnisse/Results:

⁶⁸Ga-PSMA-11 PET and ¹⁸F-PSMA-1007 PET revealed 178 and 369 PSMA positive lesions, respectively. On ⁶⁸Ga-PSMA-11 PET, 70.8% of those lesions were rated as suspicious for recurrent PC, while on ¹⁸F-PSMA-1007 PET only 33.6% were rated as suspicious. The 52 probably benign lesions on ⁶⁸Ga-PSMA-11 PET (mean SUV_max 4.5 ± 1.0, range 2.8 – 7.5) included unspecific (e.g. inguinal and axillary) lymph nodes in 42% (n = 22), ganglia in 29% (n = 15), bone lesions (e.g. fractures, degenerative changes) in 22% (n = 11),' and other lesions in 8% (n = 4). On¹⁸F-PSMA-1007 PET 245 probably benign lesions were noted, almost 5-times as many as for ⁶⁸Ga-PSMA-11 PET. There mean SUV_max, 6.0 ± 4.2 (range 3.0 – 42.7) was higher than of the benign lesions seen on ⁶⁸Ga-PSMA-11 PET (p = 0.00003). The benign lesions on ¹⁸F-PSMA-1007 PET included ganglia in 43% (n = 105), unspecific lymph nodes in 31% (n = 76), bone lesions in 20% (n = 51), and other lesions in 5% (n = 13).

Schlussfolgerungen/Conclusions:

¹⁸F-PSMA-1007 PET visualizes a considerably larger number of probably benign lesions than ⁶⁸Ga-PSMA-11 PET. In order to avoid false positive results it is important to carefully review corresponding CT findings and be aware of the various benign causes for focal PSMA-ligand uptake.