Bone tumors can develop when breast cancer (in women) and prostate cancer (in men) spread to the skeleton (imaged as dark spots). Radium-223 helps treat these tumors and relieve the intense pain that they cause.
Radium-223 is an isotope of radium, chemically identical to natural radium-226 that is common, in small amounts, to most rocks and soils in the earth. The short physical half-life of radium-223 (11 days), and its short-lived cascade of four alpha-emitting daughter products, make radium-223 useful for treating bone cancer metastases in the skeleton that result from advanced prostate and breast cancer. Radium-223 appears to be more effective in a cancer treatment setting than other bone-pain-palliation agents because the alpha particles are highly efficient in cell-killing. In contrast to beta-emitting radionuclides, the alpha particles from Ra-223 and daughters do not completely traverse marrow space, leading to a comparative reduction in marrow toxicity*.
Radium-223 may also have exciting new applications in radioimmunotherapy of cancer. Our Laboratory is developing new, nontoxic nanoparticle constructs for delivering atoms of Ra-223 with each antibody molecule directed to cell-surface antigen binding sites on cancer cells. The four alpha particles emitted by decay of each atom of Ra-223 in its decay chain to stable lead-207 can be highly effective against cancer cells. The short path length of each alpha particle (about 50 micrometers) implies that cancer cells will be effectively irradiated while normal adjacent tissues will be largely spared. Radium-223 may be one of the most important agents available for targeting cancer cell metastases associated with advanced cancer forms.
At Pacific Northwest National Laboratory, we have developed new methods for separating highly pure Ra-223 from mixtures that also contain actinium-227 and thorium-227. Those having interest in obtaining Ra-223 for research should contact the National Isotope Development Center at Oak Ridge National Laboratory.
*Henriksen G., Fisher D.R., Roeske J.C., Bruland Ø.S., and Larsen R.H. "Targeting of Osseous Sites with Alpha Emitting 223Ra: Comparison with the Beta Emitter 89Sr in Mice." J. Nucl. Med. 44: 252-259; 2003.