Evaluation of in vitro and in vivo stability of the radiopharmaceutical [153Sm]Sm-EDTMP for biokinetics studies in bone metastases pain palliation care

The radiopharmaceutical [153Sm]Sm-EDTMP is administered for painful bone metastases with the standard dosage of 37 MBq/kg, without evaluation of patient individual characteristics. For a better dose estimate in vivo stability should be considered, because labelled and unlabelled samarium do not have the same metabolic pathway. We evaluated radiopharmaceutical in vitro stability, measuring the activity by beta and gamma spectrometry. Subsequently we verified in vivo stability on serial blood and urine samples. The percentage of the unlabelled radiopharmaceutical is high and, on the basis of radiochemical data as well as blood clearance and urine excretion, we calculated the main parameters for a preliminary biokinetic model.