[Evaluation of radionuclide impurities in several radiopharmaceuticals]

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.

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.

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.

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.