Glandular breast dose for monoenergetic and high-energy X-ray beams: Monte Carlo assessment

To extend the utility of normalized glandular dose (DgN) calculations to higher x-ray energies (up to 120 keV) and to provide the tools for investigators to calculate DgN values for arbitrary mammographic and x-ray spectra.

Validated Monte Carlo methods were used to assess DgN values. One million x-ray photons (1-120 keV, in 1-keV increments) were input to a semicircular breast geometry of thicknesses from 2 to 12 cm and breast compositions from 0% to 100% glandular. DgN values for monoenergetic (1-120 keV) x-ray beams, polyenergetic (40-120 kV, tungsten anode) x-ray spectra, and polyenergetic mammographic spectra were computed. Skin thicknesses of 4-5 mm were used.

The calculated DgN values were in agreement within approximately 1%-6% with previously published data, depending on breast composition. DgN tables were constructed for a variety of x-ray tube anode-filter combinations, including molybdenum anode-molybdenum filter, molybdenum anode-rhodium filter, rhodium anode-rhodium filter, tungsten anode-rhodium filter, tungsten anode-palladium filter, and tungsten anode-silver filter. DgN values also were graphed for monoenergetic beams to 120 keV and for general diagnostic x-ray beams to 120 kV.

The tables and graphs may be useful for optimizing mammographic procedures. The higher energy data may be useful for investigations of the potential of dual-energy mammography or for calculation of dose in general diagnostic or computed tomographic procedures.