1987 Douglas Lea memorial lecture. Particle dosimetry in bone and the toxicity of bone-seeking radionuclides.

Consideration is given to the tissues at risk in bone and a Monte Carlo method is described which determines the absorbed dose to endosteal tissues and marrow in trabecular bone. The method synthesizes random tracks through the trabecular structures that deposit energy along a path through any given trabecular cavity. The path lengths through the trabeculae and marrow cavities are measured with a bone-scanning microscope and other bone data, such as trabecular surface areas, can also be derived. Results are given for human bones and for bones of the beagle, miniature pig and rhesus monkey. They show that, for the same radionuclide concentration, the doses to endosteal tissues and bone marrow are several times greater in animal than in human bone, and that higher doses in human bone from the Ca and Sr radionuclides are obtained if the initial deposition on bone surfaces is allowed for. Other studies show that the occurrence of osteosarcoma in the human long bones correlates well with trabecular surface area and also that, unlike the case of beta-particles from 90Sr+90Y, leukaemia is not a significant consequence of the alpha-particle doses from 226Ra in human bone or from 226Ra, 239Pu and other alpha emitters in beagle bone.