68Ga-Citrate PET of Healthy Men: Whole-Body Biodistribution Kinetics and Radiation Dose Estimates

68Ga-citrate has one of the simplest chemical structures of all 68Ga-radiopharmaceuticals, and its clinical use is justified by the proven medical applications using its isotope-labeled compound 67Ga-citrate. To support broader application of 68Ga-citrate in medical diag-nosis, further research is needed to gain clinical data from healthy volunteers. In this work, we studied the biodistribution of 68Ga-citrate and subsequent radiation exposure from it in healthy men. Methods: 68Ga-citrate was prepared with an acetone-based radiolabeling pro-cedure compliant with good manufacturing practices. Six healthy men (age 41 +/- 12 y, mean +/- SD) underwent sequential whole-body PET/ CT scans after an injection of 204 +/- 8 MBq of 68Ga-citrate. Serial arte-rialized venous blood samples were collected during PET imaging, and the radioactivity concentration was measured with a y-counter. Urinary voids were collected and measured. The MIRD bladder -void-ing model with a 3.5-h voiding interval was used. A model using a 70-kg adult man and the MIRD schema was used to estimate ab-sorbed doses in target organs and effective doses. Calculations were performed using OLINDA/EXM software, version 2.0. Results: Radio-activity clearance from the blood was slow, and relatively high radioac-tivity concentrations were observed over the whole of the 3-h measuring period. Although radioactivity excretion via urine was rather slow (biologic half-time, 69 +/- 24 h), the highest decay-corrected con-centrations in urinary bladder contents were measured at the 90-and 180-min time points. Moderate concentrations were also seen in kid-neys, liver, and spleen. The source organs showing the largest resi-dence times were muscle, liver, lung, and heart contents. The heart wall received the highest absorbed dose, 0.077 +/- 0.008 mSv/MBq. The mean effective dose (International Commission on Radiologi-cal Protection publication 103) was 0.021 +/- 0.001 mSv/MBq. Conclusion: PET imaging with 68Ga-citrate is associated with modest radiation exposure. A 200-MBq injection of 68Ga-citrate results in an effective radiation dose of 4.2 mSv, which is in the same range as other 68Ga-labeled tracers. This suggests the feasibility of clinical studies using 68Ga-citrate imaging in humans and the possi-bility of performing multiple scans in the same subjects across the course of a year.