Estimated human absorbed dose for 68Ga-ECC based on mice data : comparison with 67Ga-ECC

Objective: Nowadays, the efficacies of 68Ga-based tracers are comparable to that of 18F-based agents and have stimulated researchers to investigate the potential of 68Ga-based positron emission tomography (PET) imaging agents. In this study, the human absorbed dose of 68Ga labeled with ethylenecysteamine cysteine 68Ga-ECC and 67Ga-ECC was estimated based on biodistribution data in mice by the medical internal radiation dose (MIRD) method. Methods: For biodistribution of 67Ga/68Ga-ECC, three mice were killed by CO2 asphyxiation at each selected times after injection (15, 30, 45, 60, 120 min for 68Ga-ECC and 0.5, 2 and 48 h for 67Ga-ECC), and then the tissue (heart, lung, brain, intestine, skin, stomach, kidneys, liver, muscle and bone) was removed. Results: 68Ga-ECC as a new PET renal imaging agent was prepared with radiochemical purity of >97 % in less than 30 min. The biodistribution data for 68Ga-ECC showed that the most of the activity extracted from the urinary tract very fast. Comparison between human absorbed dose estimation for these two agents indicated that the absorbed dose of the most organs after injection of 67Ga-ECC is approximately tenfold higher than the amount after 68Ga-ECC injection. Conclusion: The results showed that 68Ga-ECC is a more appropriate agent rather than 67Ga-ECC and generally can be a good candidate for PET renal imaging applications.