Production of Sm-153 with high specific activity for targeted radionuclide therapy

Aim/Introduction: Samarium-153 (153Sm) poses a high potential for targeted radionuclide therapy because of its favorable decay characteristics. 153Sm has a half-life of 1.93 d, decays into a stable daughter nuclide (153Eu) and emits β- particles (E = 705 keV (30%), 635 keV (50%)) which are suitable for therapy. 153Sm also emits γ photons (103 keV (28%)) with characteristics that also allow SPECT imaging, making 153Sm a high-potential theranostic radioisotope. However, the full potential of 153Sm in nuclear medicine is currently not being exploited because of the limited specific activity available as a result of the carrier added production method. Therefore, in this work, a new production method was developed to produce 153Sm with high specific activity, suitable for radiolabeling. Materials and Methods: 153Sm as efficiently produced via neutron irradiation of a highly enriched 152Sm target (98.7% enriched, σth = 206 b) in the BR2 reactor at SCK CEN. Irradiated target materials were shipped to CERN MEDICIS, where 153Sm was isolated from the 152Sm target via mass separation (MS) in combination with laser resonance enhanced ionization to drastically increase the specific activity. Further radiochemical purification steps were developed at SCK CEN to recover the 153Sm from the MS target to yield a solution ready for radiolabeling. Gamma spectrometry and inductively coupled plasma mass spectrometry (ICP-MS) were used to characterize the produced 153SmCl3. Proof of concept radiolabeling studies were performed with multiple concentrations of p-SCN-Bn-DOTA to confirm the quality of the produced 153SmCl3. results: The production process of high specific activity (HSA) 153Sm was found efficient, yielding 153Sm with a specific activity of 1.87 TBq/mg at end of purification. An overall mass separation efficiency of 4.5% was reached on average. The radiochemical process following the mass separation was found to be highly efficient, reaching an overall recovery rate of 84%. The HSA 153SmCl3 was produced with a very high radiochemical (98.9 ± 0.24%.) and radionuclidic purity (>99.99%). Radiolabeling with the produced HSA 153Sm was efficient, even at low concentrations of p-SCN-Bn-DOTA. Conclusion: In this proof-of-concept study, we demonstrated the potential to combine neutron irradiation with mass separation to supply high specific activity 153Sm. Using this process, 153SmCl3 suitable for radiolabeling, was produced with a very high specific activity allowing application of 153Sm in targeted radionuclide therapy. Further studies to incorporate 153Sm in radiopharmaceuticals for targeted radionuclide therapy are ongoing.