Estimation of human effective absorbed dose of 67Ga–cDTPA–gonadorelin based on biodistribution rat data

OBJECTIVEIn this investigation, we estimated the effective absorbed dose of radiation into human organs, after an intravenous administration of gallium-67 (Ga)-labeled gonadorelin, one of the gonadotropin-releasing hormone (GnRH) agonists, using biodistribution data from injected normal rats. METHODSFive rats were killed at exact time intervals (0.25, 0.5, 1, 2, 4, 24, and 48 h post injections) and the percentage of injected dose per gram of each organ was measured by direct counting from rat data. The Medical Internal Radiation Dose formulation was applied to extrapolate from rat to human and to project the absorbed radiation dose for various organs in humans. RESULTSFrom rat data we estimated that a 185-MBq injection of Ga–cDTPA–GnRH into the humans might result in an estimated absorbed dose of 5.26 mGy in the whole body with the highest effective absorbed dose was in the lungs (2.73 mSv), and the organs that received the next highest doses were the bladder wall (1.59 mSv), liver (0.80 mSv), and bone marrow (0.52 mSv). CONCLUSIONThe biodistribution of Ga–cDTPA–GnRH in rats showed high breast uptake and low muscle and blood uptake. These results suggest that it should be possible to perform early imaging of the breast anomalies and GnRH receptors indicating potential malignant lesions.