Scatter/primary in mammography: Monte Carlo validation

The purpose of this investigation was to compare and validate the performan ce of the SIERRA Monte Carlo simulation routines for the analysis of the sc atter to primary ratio (SPR) in the mammography setting. Two Monte Carlo si mulation methods were addressed, the direct method was a straightforward an d geometrically accurate simulation procedure, and the convolution method u ses idealized geometry (monoenergetic, normally incident delta function inp ut to the scattering medium) to produce scatter point spread functions (PSF s). The PSFs were weighted by the x-ray spectrum of interest and convolved with the held of view to estimate SPR values. The SPR results of both Monte Carlo procedures were extensively compared to five published sources, incl uding Monte-Carlo-derived and physically measured SPR assessments. The dire ct method demonstrated an overall agreement with the literature of 3.7% acc uracy (N = 5), and the convolution method demonstrated an average of 7.1% a ccuracy (N = 14). The comparisons were made over a range of parameters whic h included field of view, phantom thickness, x-ray energy, and phantom comp osition. Limitations of the beam stop method were also discussed. The resul ts suggest that the SIERRA Monte Carlo routines produce accurate SPR calcul ations and may be useful for a more comprehensive study of scatter in mammo graphy. (C) 2000 American Association of Physicists in Medicine. [S0094-240 5(00)01808-3].