Comparative Study of the Influence of Anode and Filter Materials on Primary Shielding Requirements for Mammography

Abstract

Comparison of primary shielding requirements for mammography x-ray beams that are transmitted through different filter materials at equivalent thicknesses has been carried out. In this study, the primary shielding requirement is that which is additional to that provided by the compression paddle, breast tissue, grid and image receptor. Equivalent thickness is defined as the thickness of a filter material (with Z-value between 37 and 55) that will reduce either intensity or total energy or exposure of a given unfiltered incident beam by the same extent or produce equal hardening of the same unfiltered beam as a reference filter (0.03 g cm Mo). The unfiltered incident beams used are those generated by molybdenum (Mo) and tungsten (W) anodes at kVp's of 18, 20, 22,..,42. In most cases (especially for filter with Z-values greater than 42 and values of operating potential greater than 22 kVp), results show that no single thickness was found that could simultaneously match intensity, total energy, exposure, and hardening as the reference filter. There are significant disparities in the values of the additional primary shielding requirements for beams transmitted through the equivalent thicknesses. Structures of the computer software programs (MAFHAMS and MAXRAPS) used to execute the models developed for the computations of the additional primary shielding requirements for the 'equalized' beams are presented.