Preliminary assessment of ₂₂₅Ac excretion in patients undergoing radionuclide therapy with ₂₂₅Ac-DOTA-TATE

The aim of this study was to evaluate the activity of 225 Ac in urine of patients undergoing radionuclide therapy with 225 Ac-DOTA-TATE. Activity concentration was determined in the urine samples collected within 72 hours after injection of 225 Ac-DOTA-TATE, using the ORTEC semiconductor gamma spectrometer, model TSP-DX-100T-PAC-PKG-1. Calculation of excreted activities was additionally performed based on scintig- raphy scans of patients receiving 225 Ac-DOTA-TATE. Scans were conducted 5 times for each patient: immedi- ately after injection, at 4 hours, and on the 1st, 2nd, and 3rd days after injection of the radiopharmaceutical. Absolute activity values and fractions of the injected activity were calculated based on the specific activity values. The results of the calculated activity concentration values demonstrate that maximum excretion was observed within the four hours after 225 Ac-DOTA-TATE injection. Significant differences between the two methods of determining 225 Ac activity were observed only on the third day after radiopharmaceutical injection, which allows for the simplification of future experimental work by using indirect radioactivity measurement methods for activity calculations. There were no significant differences between patient groups with different number of 225 Ac-DOTA-TATE injection, which allows for the exclusion of this parameter in the evaluation of experimental results. The results of this study represent the first published experimental data on the determi- nation of actinium excretion in patients.