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

Abstract

Purpose: 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 68Ga-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. Methods: 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 18F-fluoromethylcholine and 68Ga-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 68Ga-PSMA complex solution (median 132 MBq, range 59-263 MBq) and 18F-fluoromethylcholine (median 237 MBq, range 114-374 MBq), respectively. In addition, tumour to background ratios were calculated. Results: A total of 78 lesions characteristic for PC were detected in 32 patients using 68Ga-PSMA PET/CT and 56 lesions were detected in 26 patients using choline PET/CT. The higher detection rate in 68Ga-PSMA PET/CT was statistically significant (p = 0.04). In five patients no lesion was found with both methods. All lesions detected by 18F-fluoromethylcholine PET/CT were also seen by 68Ga-PSMA PET/CT. In 68Ga-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 18F-fluoromethylcholine PET/CT. Conclusion: 68Ga-PSMA PET/CT can detect lesions characteristic for PC with improved contrast when compared to standard 18F- fluoromethylcholine PET/CT, especially at low PSA levels. © 2013 The Author(s).