Determination of human absorbed dose from [153Sm]-Samarium maltolate based on distribution data in rats

Background: Therapeutic radiopharmaceuticals are designed to deliver high doses of radiation to selected target organs with an aim of minimizing unwanted radiation to surrounding healthy tissue. Due to the potential of targeted radiotherapy to treat a wide range of malignant conditions, [153Sm]-samarium maltolate was developed for possible therapeutic applications. Materials and Methods: The organ radiation-absorbed doses have been evaluated for human based on animal data. After intravenous administration of 153Sm-Mal to four groups of rats, they were sacrificed at exact time intervals and the percentage of injected dose per gram of each organ was calculated by direct counting from rat data. Then S values for 153Sm by using specific absorbed fractions were calculated. By taking advantage of the formulation that Medical Internal Radiation Dose suggests, radiation-absorbed doses for all organs were calculated and extrapolated from rat to human. Results: From rat data, it is estimated that a 185-MBq injection of 153Sm-Mal into a human might result in the highest absorbed dose in the lymphoma tissues (liver 176.3, lungs 68, spleen 66.8 and sternum 19 mGy), especially in liver respect to the other tissues. Conclusion: These results suggest 153Sm-Mal as an efficiently new therapeutic agent in order to overcome possible lymphatic malignancies.