Absorption, distribution and excretion of intravenously injected 68Ge/68Ga generator eluate in healthy rats, and estimation of human radiation dosimetry

Abstract

Abstract Background This study evaluated the absorption, distribution, and excretion of Gallium-68 (68Ga) radionuclide after a single intravenous (i.v.) injection of 68Ge/68Ga generator eluate in healthy rats. Additionally, human radiation doses were estimated from the rat data. Methods Twenty-one female and 21 male Sprague-Dawley rats were i.v. injected with 47 ± 4 MBq of 68Ge/68Ga generator eluate, and the radioactivity of excised organs was measured using a gamma counter at 5, 30, 60, 120, or 180 min afterwards (n = 3–7 for each time point). The radioactivity concentration and plasma pharmacokinetic parameters were calculated. Subsequently, the estimates for human radiation dosimetry were determined. Additionally, 4 female and 5 male rats were positron emission tomography (PET) imaged for in vivo visualization of biodistribution. Results 68Ga radioactivity was cleared relatively slowly from blood circulation and excreted into the urine, with some retention in the liver and spleen. Notably, the 68Ga radioactivity in female genital organs, i.e., the uterus and ovaries, was considerable higher compared with male genitals. Extrapolating from the female and male rat 68Ga data, the estimated effective dose was 0.0308 mSv/MBq for a 57-kg woman and 0.0191 mSv/MBq for a 70-kg man. Conclusions The estimated human radiation burden of the 68Ge/68Ga generator eluate was slightly higher for females and similar for males as compared with somatostatin receptor ligands 68Ga-DOTANOC, 68Ga-DOTATOC, and 68Ga-DOTATATE, which is probably due to the retention in the liver and spleen. Our results revealed some differences between female and male rat data, which, at least in part, may be explained by the small sample size.