Detection of long-lived europium-152 in samarium-153-lexidronam

Samarium-153-lexidronam is a radiopharmaceutical used for pain palliation therapy in patients suffering from multilocular bone metastases. The postinjection residual of four pharmaceutical vials of 153Sm-lexidronam and one patient were investigated for contamination with other isotopes using high-resolution gamma spectroscopy. In the spectra besides the already known contaminants europium-154, 155Eu and 156Eu, europium-152 was discovered in vitro and also in vivo. 152Eu disintegrates with a half-life of 13.5 years emitting a multitude of high energy photons. Due to these properties, it does not only affect radioactive waste management regarding e.g. the disposal of the postinjection residual, but also poses an additional dose burden to the patient and to third persons. In the postinjection residual a mean activity concentration of 10.4±1.1 kBq europium-152 per GBq 153Sm was detected. 62 days after isotope application, 15.8±4.0 kBq of 152Eu were found within the patient. The lifetime effective dose to the patient from the europium impurities was determined using a multicompartment model. For 152Eu the effective dose was 2.1 mSv/GBq 153Sm-lexidronam and the total effective dose from all impurities was 6.1 mSv/GBq 153Sm-lexidronam. The total absorbed dose to third persons caused by the europium impurities was estimated as 0.6 mGy/GBq 153Sm-lexidronam.