The radio-europium impurities in [153Sm]-EDTMP production: a review of isolation methods

Dosimetric implications of the potential radionuclidic impurities in 153Sm-DOTMP

Thehuman internal dosimetry of the radionuclidic impurities of samarium-153 in a new bone-seeking radiopharmaceutical, ¹⁵³Sm-1,4,7,10tetraazacyclododecanetetramethylenephosponic acid (¹⁵³Sm-DOTMP), has been estimated from preclinical data. The effective dose from the impurities in lower-specific-activity ¹⁵³Sm is less than 17% of the effective dose from pure Sm-153. It has a background-equivalent radiation time for a dosage of 37 MBq/kg of less than one-half year.

[Evaluation of radionuclide impurities in several radiopharmaceuticals]

PURPOSE

Revisions to German radiation protection laws have resulted in updated limit values, which could affect the unrestricted release of waste produced by nuclear medicine therapy. In addition, signs of long-lived concomitant nuclides in ¹⁵³Sm and ²²³Ra radiopharmaceuticals have been seen in the past. Therefore, the goal of this article was to analyze the radionuclidic purity of selected radiopharmaceuticals.

METHOD

48 samples from 12 different radiopharmaceuticals were examined. A high purity germanium semiconductor detector (HPGe detector) was used for the qualitative and quantitative evaluation of concomitant nuclides.

RESULTS

Various europium isotopes were identified in ⁹⁰Y-citrate, ¹⁵³Sm-Quadramet, ¹⁶⁶Ho-QuiremSpheres, and ¹⁶⁹Er-erbium citrate, with the greatest amount being found in ¹⁵³Sm (7.0 ppm (¹⁵²Eu), 8.4 ppm (¹⁵⁴Eu), and 2.1 ppm (¹⁵⁵Eu)). ¹⁶⁹Yb was the most significant impurity in ¹⁶⁹Er (513 ppm). In the case of ¹⁷⁷Lu radiopharmaceuticals, there was a significant difference in the ^177mLu content (0.8 ppm vs. 0.0024 ppm) between two different manufacturers. No concomitant nuclides could be found within the detection limits in the case of ⁹⁰Y spheres, ²²³Ra, and ²²⁵Ac.

CONCLUSION

The limit values for unrestricted release are exceeded manyfold in the case of the identified concomitant nuclides. As a result, alternative release procedures (extension of the decay time, specific release, release in the individual case) or transfer to collection facilities must be considered. Technical methods for reducing or preventing impurities could also be a possible solution. Consequences for patient radiation exposure were able to be ruled out.

Development of neutron-activated samarium-153-loaded polystyrene microspheres as a potential theranostic agent for hepatic radioembolization

PURPOSE

Hepatic radioembolization is an effective minimally invasive treatment for primary and metastatic liver cancers. Yttrium-90 [90Y]-labelled resin or glass beads are typically used as the radioembolic agent for this treatment; however, these are not readily available in many countries. In this study, novel samarium-153 oxide-loaded polystyrene ([153Sm]Sm2O3-PS) microspheres were developed as a potential alternative to 90Y microspheres for hepatic radioembolization.

METHODS

The [152Sm]Sm2O3-PS microspheres were synthesized using solid-in-oil-in-water solvent evaporation. The microspheres underwent neutron activation using a 1 MW open-pool research reactor to produce radioactive [153Sm]Sm2O3-PS microspheres via 152Sm(n,γ)153Sm reaction. Physicochemical characterization, gamma spectroscopy and in-vitro radionuclide retention efficiency were carried out to evaluate the properties and stability of the microspheres before and after neutron activation.

RESULTS

The [153Sm]Sm2O3-PS microspheres achieved specific activity of 5.04 ± 0.52 GBq·g-1 after a 6 h neutron activation. Scanning electron microscopy and particle size analysis showed that the microspheres remained spherical with an average diameter of ~33 μm before and after neutron activation. No long half-life radionuclide and elemental impurities were found in the samples. The radionuclide retention efficiencies of the [153Sm]Sm2O3-PS microspheres at 550 h were 99.64 ± 0.07 and 98.76 ± 1.10% when tested in saline solution and human blood plasma, respectively.

CONCLUSIONS

A neutron-activated [153Sm]Sm2O3-PS microsphere formulation was successfully developed for potential application as a theranostic agent for liver radioembolization. The microspheres achieved suitable physical properties for radioembolization and demonstrated high radionuclide retention efficiency in saline solution and human blood plasma.