Intra-individual comparison of (68)Ga-PSMA-11 and (18)F-DCFPyL normal-organ biodistribution

PURPOSE: Detailed data comparing the biodistribution of PSMA radioligands is still scarce, raising concerns regarding the comparability of different compounds. We investigated differences in normal-organ biodistribution and uptake variability between the two most commonly PSMA tracers in clinical use, (68)Ga-PSMA-11 and (18)F-DCFPyL. METHODS: This retrospective analysis included 34 patients with low tumor burden referred for PET/CT imaging with (68)Ga-PSMA-11 and subsequently (18)F-DCFPyL. Images were acquired with 4 cross-calibrated PET/CT systems. Volumes of interest were placed on major salivary and lacrimal glands, liver, spleen, duodenum, kidneys, bladder, blood-pool and muscle. Normal-organ biodistribution of both tracers was then quantified as SUV(peak) and compared using paired tests, linear regression and Bland-Altman analysis. Between-patient variability was also assessed. Clinical and protocol variables were investigated for possible interference. RESULTS: For both tracers the highest uptake was found in the kidneys and bladder and low background activity was noted across all scans. In the quantitative analysis there was significantly higher uptake of (68)Ga-PSMA-11 in the kidneys, spleen and major salivary glands (p < 0.001), while the liver exhibited slightly higher (18)F-DCFPyL uptake (p = 0.001, mean bias 0.79 ± 1.30). The lowest solid-organ uptake variability was found in the liver (COV 21.9% for (68)Ga-PSMA-11, 22.5% for (18)F-DCFPyL). There was a weak correlation between (18)F-DCFPyL uptake time and liver SUV(peak) (r = 0.488, p = 0.003) and, accordingly, patients scanned at later time-points had a larger mean bias between the two tracers’ liver uptake values (0.05 vs 1.46, p = 0.001). CONCLUSION: Normal tissue biodistribution patterns of (68)Ga-PSMA-11 and (18)F-DCFPyL were similar, despite subtle differences in quantitative values. Liver uptake showed an acceptable intra-patient agreement and low inter-patient variability between the two tracers, allowing its use as a reference organ for thresholding scans in the qualitative comparison of PSMA expression using these different tracers. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s40644-019-0211-y) contains supplementary material, which is available to authorized users.