Clinical Medicine - Contd . RADIATION AND THE STRUCTURE OF BONE

Whenever the body is irradiated, for diagnostic or therapeutic purposes, a considerable amount of bone and bone marrow is inevitably included in the field of the radiation beam. Furthermore, many of the radioisotopes used clinically become incorporated in bone, sometimes to a high degree. The physical consideration of this irradiation of bone is complex because (a) the increased radiation absorption in bone, compared with that in soft tissues, depends markedly on radiation energy, (b) the deposition of radioisotopes in bone is frequently very non-uniform and (c) the ionizing particles (secondary electrons released by X-rays and oc and 3 particles from radioisotopes) which distribute the radiation energy within bone, have ranges which are of the same order of magnitude as the dimensions of the microscopic structures of the bone anatomy. Three facets of studies relating to bone will be described, two of which are also of interest outside the immediate field of radiology.