| Summary: | Radioembolization shows great potential as a treatment for intermediate- and advanced-stage liver cancer. However, the choices of radioembolic agents are currently limited, and hence the treatment is relatively costly compared to other approaches. In this study, a facile preparation method was developed to produce samarium carbonate-polymethacrylate [<sup>152</sup>Sm<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>-PMA] microspheres as neutron activatable radioembolic microspheres for hepatic radioembolization. The developed microspheres emits both therapeutic beta and diagnostic gamma radiations for post-procedural imaging. The <sup>152</sup>Sm<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>-PMA microspheres were produced from commercially available PMA microspheres through the in situ formation of <sup>152</sup>Sm<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub> within the pores of the PMA microspheres. Physicochemical characterization, gamma spectrometry and radionuclide retention assay were performed to evaluate the performance and stability of the developed microspheres. The mean diameter of the developed microspheres was determined as 29.30 ± 0.18 µm. The scanning electron microscopic images show that the spherical and smooth morphology of the microspheres remained after neutron activation. The <sup>153</sup>Sm was successful incorporated into the microspheres with no elemental and radionuclide impurities produced after neutron activation, as indicated by the energy dispersive X-ray analysis and gamma spectrometry. Fourier transform infrared spectroscopy confirmed that there was no alteration to the chemical groups of the microspheres after neutron activation. After 18 h of neutron activation, the microspheres produced an activity of 4.40 ± 0.08 GBq.g<sup>−1</sup>. The retention of <sup>153</sup>Sm on the microspheres was greatly improved to greater than 98% over 120 h when compared to conventionally radiolabeling method at ~85%. The <sup>153</sup>Sm<sub>2</sub>(CO<sub>3</sub>)<sub>3</sub>-PMA microspheres achieved suitable physicochemical properties as theragnostic agent for hepatic radioembolization and demonstrated high radionuclide purity and <sup>153</sup>Sm retention efficiency in human blood plasma.
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