Evaluation of the Applicability of External X-ray Radiation to Stimulate the Autoradiolysis Processes in Therapeutic Radiopharmaceuticals (Exemplified by [153Sm]Sm-PSMA-617 and [177Lu]Lu-PSMA-617)

The paper presents the results of a study on the radiolytic degradation of vector molecules in radiopharmaceuticals, caused by ionizing radiation from the radionuclide used in the preparations, in comparison with the equal dose of external X-ray irradiation. The dose factors for therapeutic radionuclides samarium-153 and lutetium-177 in aqueous solutions were estimated in geometry simulating the finished dosage form of radiopharmaceuticals (standard injection vial ) both by computational methods (in silico) and applying chemical dosimetry. Irradiation with external X-ray source to doses formed in volume of therapeutic radiopharmaceuticals with given radioactivity concentration was performed on an LNK-268 X-ray unit. Using the [ 153 Sm]Sm-PSMA-617 and [ 177 Lu]Lu-PSMA-617 radiopharmaceuticals as an instance, we compared the degree of radiolytic degradation and the profiles of radiolytic impurities formed as a result of both external X-ray irradiation and autoradiolysis. Qualitative coincidence of the impurity profiles formed in both cases was noted. It has been shown that external X-ray radiation can be used to simulate the autoradiolysis processes of radiopharmaceuticals if additional corrections are made for the type of radiation and dose rate.