Comparison of PET imaging with a 68Ga-labelled PSMA ligand and 18F-choline-based PET/CT for the diagnosis of recurrent prostate cancer

Positron emission tomography (PET) with choline tracers has found widespread use for the diagnosis of prostate cancer (PC). However, choline metabolism is not increased in a considerable number of cases, whereas prostate-specific membrane antigen (PSMA) is overexpressed in most PCs. Therefore, a Ga-68-labelled PSMA ligand could be superior to choline tracers by obtaining a high contrast. The aim of this study was to compare such a novel tracer with standard choline-based PET/CT. Thirty-seven patients with biochemical relapse of PC [mean prostate-specific antigen (PSA) 11.1 +/- 24.1 ng/ml, range 0.01-116] were retrospectively analysed after F-18-fluoromethylcholine and Ga-68-PSMA PET/CT within a time window of 30 days. Radiotracer uptake that was visually considered as PC was semi-quantitatively analysed by measuring the maximum standardized uptake values (SUVmax) of the scans acquired 1 h after injection of Ga-68-PSMA complex solution (median 132 MBq, range 59-263 MBq) and F-18-fluoromethylcholine (median 237 MBq, range 114-374 MBq), respectively. In addition, tumour to background ratios were calculated. A total of 78 lesions characteristic for PC were detected in 32 patients using Ga-68-PSMA PET/CT and 56 lesions were detected in 26 patients using choline PET/CT. The higher detection rate in Ga-68-PSMA PET/CT was statistically significant (p = 0.04). In five patients no lesion was found with both methods. All lesions detected by F-18-fluoromethylcholine PET/CT were also seen by Ga-68-PSMA PET/CT. In Ga-68-PSMA PET/CT SUVmax was clearly (> 10 %) higher in 62 of 78 lesions (79.1 %) and the tumour to background ratio was clearly (> 10 %) higher in 74 of 78 lesions (94.9 %) when compared to F-18-fluoromethylcholine PET/CT. Ga-68-PSMA PET/CT can detect lesions characteristic for PC with improved contrast when compared to standard F-18-fluoromethylcholine PET/CT, especially at low PSA levels.