The Absorption of Radiation in Bone

It is usual to calcitlate absorbed dose in any biological material by multiplying the exposure dose by a conversion factor (rads per roentgen) appropriate to the material and the quality of the radiation absorbed. Using the conventional conversion factor for bone in this way tells nothing of the dose received by soft tissue included in the bone structure. This dose is related to the dose in bone but depends largely on the relation between the range of the secondary electrons produced in bone and the size of the cavity containing the soft tissue. Similarly, the dose in soft tissue near a bone surface will be dependent on the range of these same secondary electrons and therefore on the energy of the radiation producing them. Spiers calculated the ionization produced within cavities of various sizes and at various distances from an interface for a number of qualities of radiation. These values have been used to estimate conversion factors which lead to a milch more realistic assessment of the dose in or near bone. At lower energies where the absorption in bone and the dose in soft tissue in bone lies between the dose in bone and the dose in soft tissue remote from bone. In the megawltage region, where the absorbed dose in hone is less than that in soft tissue. the dose in the soft tissue in bone is about 10% higher than that in soft tissue remote from hone.