Radiation therapy for primary and metastatic tumors of the liver

Neutron-activated biodegradable samarium-153 acetylacetonate-poly-L-lactic acid microspheres for intraarterial radioembolization of hepatic tumors

BACKGROUND

Liver cancer is the 6^th most common cancer in the world and the 4^th most common death from cancer worldwide. Hepatic radioembolization is a minimally invasive treatment involving intraarterial administration of radioembolic microspheres.

AIM

To develop a neutron-activated, biodegradable and theranostics samarium-153 acetylacetonate (¹⁵³SmAcAc)-poly-L-lactic acid (PLLA) microsphere for intraarterial radioembolization of hepatic tumors.

METHODS

Microspheres with different concentrations of ¹⁵²SmAcAc (i.e., 100%, 150%, 175% and 200% w/w) were prepared by solvent evaporation method. The microspheres were then activated using a nuclear reactor in a neutron flux of 2 × 10¹² n/cm²/s¹, converting ¹⁵²Sm to Samarium-153 (¹⁵³Sm) via ¹⁵²Sm (n, γ) ¹⁵³Sm reaction. The SmAcAc-PLLA microspheres before and after neutron activation were characterized using scanning electron microscope, energy dispersive X-ray spectroscopy, particle size analysis, Fourier transform infrared spectroscopy, thermo-gravimetric analysis and gamma spectroscopy. The in-vitro radiolabeling efficiency was also tested in both 0.9% sodium chloride solution and human blood plasma over a duration of 550 h.

RESULTS

The SmAcAc-PLLA microspheres with different SmAcAc contents remained spherical before and after neutron activation. The mean diameter of the microspheres was about 35 µm. Specific activity achieved for ¹⁵³SmAcAc-PLLA microspheres with 100%, 150%, 175% and 200% (w/w) SmAcAc after 3 h neutron activation were 1.7 ± 0.05, 2.5 ± 0.05, 2.7 ± 0.07, and 2.8 ± 0.09 GBq/g, respectively. The activity of per microspheres were determined as 48.36 ± 1.33, 74.10 ± 1.65, 97.87 ± 2.48, and 109.83 ± 3.71 Bq for ¹⁵³SmAcAc-PLLA microspheres with 100%, 150%, 175% and 200% (w/w) SmAcAc. The energy dispersive X-ray and gamma spectrometry showed that no elemental and radioactive impurities present in the microspheres after neutron activation. Retention efficiency of ¹⁵³Sm in the SmAcAc-PLLA microspheres was excellent (approximately 99%) in both 0.9% sodium chloride solution and human blood plasma over a duration of 550 h.

CONCLUSION

The ¹⁵³SmAcAc-PLLA microsphere is potentially useful for hepatic radioembolization due to their biodegradability, favorable physicochemical characteristics and excellent radiolabeling efficiency. The synthesis of the formulation does not involve ionizing radiation and hence reducing the complication and cost of production.