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Radium-223 dichloride is an alpha particle-emitting pharmaceutical with targeted anti-tumour effect on bone metastases with a half-life of 11,4 days.

The active moiety, the isotope radium-223 (as radium-223 dichloride) mimics calcium and targets bone, specifically areas of bone metastases, by forming complexes with the bone mineral hydroxyapatite.

The specific activity of radium-223 is 1,9 MBq (0,0514 mCi)/ng. The six-stage-decay of radium-223 to lead-207 occurs via short-lived daughters, and is accompanied by a number of alpha, beta and gamma emissions with different energies and emission probabilities. The fraction of energy emitted from radium-223 and its daughters as alpha particles is 95,3 % (energy range of 5,0 to 7,5 MeV). The emitted as beta particles is 3,6 % (average energies are 0,445 MeV and 0,492 MeV), and the fraction emitted as gamma-radiation is 1,1 % (energy range of 0,01 to 1,27 MeV).

The high linear energy transfer of alpha emitters (80 keV/micrometer) leads to a high frequency of double-strand DNA breaks in adjacent cells, resulting in a localised anti-tumour effect.

The alpha particle range from radium-223 is less than 100 micrometres (less than 10 cell diameters) which minimises damage to the surrounding normal tissue.

Radium-223 dichloride has an effect on serum bone markers studied in a phase II randomised study (bone formation markers: bone alkaline phosphatase (ALP), total ALP and procollagen I N propeptide (PINP), bone resorption markers: C- terminal crosslinking telopeptide of type I collagen(S-CTX-I) and type I collagen crosslinked C-telopeptide (ICTP)).