Absorbed Dose Near Bone: A Conductivity Method of Measurement

Abstract

A method is described for measuring absorbed dose-rate directly in a thin film of solid insulating material, by means of the electrical conductivity induced in the material by X rays. The method is suitable for interface investigations, including the problem of dosage in tissue close to bone. A film of polythene 25 μ thick was used to measure the absorbed dose near a bone-fat interface for comparison with Spiers' (1949) calculations of dosage in Haversian canals. The results show general agreement, especially with the later and more comprehensive calculations (Woodard and Spiers, 1953). A discrepancy remains unresolved in that the experimental doses near bone are higher than the calculated doses at the longer wavelengths. The technique has also been used for depth dose and back-scatter measurements at 60 kV, since the conductivity system responds correctly to the softest, i.e. scattered radiation. The characteristics of induced currents in polythene are briefly described.