Europium-154 contamination levels in Samarium-153-EDTMP for radionuclide therapy

¹⁵³Sm-EDTMP, a useful non toxic bone seeking isotope in the palliative radionuclide therapy for bone metastases, is produced by neutron activation of enriched of ¹⁵²Sm ₂O ₃ targets. During the large-scale formation of ¹⁵³Sm, however, there is a co-production of some long-lived radio nuclides, among which ¹⁵⁴Eu is a major and inevitable radionuclide impurity. The level of ¹⁵⁴Eu contamination was evaluated performing a gamma-ray spectrometry of a radiopharmaceutical sample and the urine of an administered patient. As expected, gamma-ray spectra revealed the presence of ¹⁵³Eu in all the samples. The specific activity of ¹⁵³Eu in the urine sample collected at 6 hours after injection is 21 Bq/ml and is less than 1 Bq/ml in 24 hr. The contamination levels of ¹⁵³Eu, normalized to the corresponding activity of ¹⁵³Sm, were 0.0012% in the residual and in the first urine sample and 0.0017% and 0.0031% at 30 and 54 hours after administration, respectively. The results of this study show that the level of the long-lived ¹⁵³Eu impurity is not a limitation in the metastatic bone pain palliation due to the additional radiation dose burden, but could pose a cause of concern in case of discharging.