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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 - 2 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 ized' beams are presented.

In the estimation of additional shielding requirements for primary beam apart from that provided by patient and hardware in the x-ray beam, there is the need to distinguish between attenuation and hardening properties of materials in comparison. In this work, numerical comparison of attenuation and hardening properties of phantom (Lucite, soft tissue, water) and hardware (aluminum and steel) materials with those of lead have been carried out. Results presented show that the shielding affordable by lead attenuation equivalent thicknesses (LAE) and lead hardening equivalent thicknesses (LHE) is not strictly equivalent to that affordable by thicknesses of substitutes (phantom materials, aluminum and steel) when there are differences in attenuation and hardening properties. Even though beams through LAE that are not "exact" have equal exposure values, the half value layers are higher than those through thicknesses of lead substitutes. Example calculations show that the use of lead thickness (LAE) that are not "exact" to account for the shielding afforded by the thickness of the patient (water phantom) produces lesser reduction of the primary radiation level in the area indicated for shielding. The "exact" LAE that will reduce the primary radiation level equally as the patient and radiographic table may be higher by close to 20% or more of that which is not "exact."

In this work, numerical models are presented for the determination of additional shielding requirements apart from that afforded by patient and hardware devices (grid, cassette, cassette holder, and x-ray table) for diagnostic x-ray primary beams. The models provide an opportunity for the incorporation of appropriate transmission factors obtained by integration of incident radiation energy distribution and workload spectra for clinically realistic condition of varying thicknesses of patient. It was found that as a result of significant differences in the attenuation and hardening properties of water (which was used to represent patient) and lead, lead exposure attenuation equivalent thicknesses do not transmit beam of equivalent penetrating power (though of equivalent exposure) as corresponding patient thicknesses. Sample results are presented which show that ignoring these significant differences will result in underestimation of shielding afforded by patient and hardware devices in practice; thus installing in addition more thickness of lead than necessary. For different incident beam qualities (kVp), obtaining exposure attenuation equivalence of varying thicknesses of patients and hardware in terms of lead is a nontrivial phenomenon.

Present interest is in the shielding of diagnostic X-ray units. Numerical comparison has been made of the attenuation and hardening properties of lead and some particular alternative materials: steel, plate glass and gypsum wallboard. Results show, for particular choices of thickness, that lead and steel can be made to provide closely similar attenuation and spectral hardening, values of lead attenuation equivalent (LAE) and lead hardening equivalent (LHE) thicknesses being nearly the same. Significant differences in the attenuation and hardening properties of lead are found in comparison with plate glass and gypsum wallboard. LAE produces better matching of exposure for lead-plate glass and lead-gypsum wallboard than LHE.

Shielding requirements for mammography when considerations are to be given to attenuation by compression paddle, breast tissue, grid and image receptor (intervening materials) has been investigated. By matching of the attenuation and hardening properties, comparisons are made between shielding afforded by breast tissue materials (water, Lucite and 50%–50% adipose-glandular tissue) and some materials considered for shielding diagnostic x-ray beams, namely lead, steel and gypsum wallboard. Results show that significant differences exist between the thickness required to produce equal attenuation and that required to produce equal hardening of a given incident beam. While attenuation equivalent thickness produces equal exposure, it does not produce equal hardening. For shielding purposes, equivalence in exposure reduction without equivalence in penetrating power of an emerging beam does not amount to equivalence in shielding affordable by two different materials. Presented are models and results of sample calculations of additional shielding requirements apart from that provided by intervening materials. The shielding requirements for the integrated beam emerging from intervening materials are different from those for the integrated beam emerging from materials (lead/steel/gypsum wallboard) with attenuation equivalent thicknesses of these intervening materials.

The mass attenuation and energy-absorption coefficients (radiation interaction data), which are widely used in the shielding and dosimetry of X-rays used for medical diagnostic and orthovoltage therapeutic procedures, are strongly dependent on the energy of photons, elements and percentage by weight of elements in body tissues and substitutes. Significant disparities exist in the values of percentage by weight of elements reported in literature for body tissues and substitutes for individuals of different ages, genders and states of health. Often, interested parties are in need of these radiation interaction data for body tissues or substitutes with percentage by weight of elements and intermediate energies that are not tabulated in literature. To provide for the use of more precise values of these radiation interaction data, parameters and computer programs, MUA_T and MUEN_T are presented for the computation of mass attenuation and energy-absorption coefficients for body tissues and substitutes of arbitrary percentage-by-weight elemental composition and photon energy ranging between 1 keV (or k-edge) and 400 keV. Results are presented, which show that the values of mass attenuation and energy-absorption coefficients obtained from computer programs are in good agreement with those reported in literature.