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

PurposeDetailed 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, Ga-68-PSMA-11 and F-18-DCFPyL.MethodsThis retrospective analysis included 34 patients with low tumor burden referred for PET/CT imaging with Ga-68-PSMA-11 and subsequently F-18-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 SUVpeak 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.ResultsFor 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 Ga-68-PSMA-11 in the kidneys, spleen and major salivary glands (p<0.001), while the liver exhibited slightly higher F-18-DCFPyL uptake (p=0.001, mean bias 0.791.30). The lowest solid-organ uptake variability was found in the liver (COV 21.9% for Ga-68-PSMA-11, 22.5% for F-18-DCFPyL). There was a weak correlation between F-18-DCFPyL uptake time and liver SUVpeak (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 p id=Par4 Normal tissue biodistribution patterns of Ga-68-PSMA-11 and F-18-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.