Radiochemical Quality Control Methods for Radium-223 and Thorium-227 Radiotherapies.

Background: The majority of radiopharmaceuticals for use in disease detection and targeted treatment undergo a single radioactive transition (decay) to reach a stable ground state. Complex emitters, which produce a series of daughter radionuclides, are emerging as novel radiopharmaceuticals. The need for validation of chemical and radiopurity with such agents using common quality control instrumentation is an area of active investigation. Here, we demonstrate novel methods to characterize 227 Th and 223 Ra. Materials and Methods: A radio-TLC scanner and a gamma counter, two common and widely accessible technologies, as well as a solid-state alpha particle spectral imaging camera were evaluated for their ability to characterize and distinguish 227 Th and 223 Ra. We verified these results through purity evaluation of a novel 227 Th-labeled protein construct. Results: The gamma counter and alpha camera distinguished 227 Th from 223 Ra, enabling rapid and quantitative determination of radionuclidic purity. The radio-TLC showed limited ability to describe purity, although use under alpha particle-specific settings enhanced resolution. All three methods were able to distinguish a pure from impure 227 Th-labeled protein. Conclusions: The presented quality control evaluation for 227 Th and 223 Ra on three different instruments can be applied to both research and clinical settings as new alpha particle therapies are developed.