DOSIS: a Monte Carlo simulation program for dose related studies in mammography

Dosimetric studies in mammography are addressed by means of a Monte Carlo simulation program. The core of this program (DOSIS: dosimetry simulation studies) is a simulation model developed using FORTRAN 90, enriched with a graphical user interface developed in MS Visual Basic. User defined mammographic technique parameters affecting breast dose are imported to the simulation model and the produced results are provided by means of both absolute (surface dose, exposure at detector plane) and relative quantities (percentage depth dose, isodose curves). The program functionality has been demonstrated in the evaluation of various mammographic examination techniques. Specifically, the influence of tube voltage and filtration on the surface dose and the exposure at detector plane has been studied utilizing a water phantom. Increase of tube voltage from 25 to 30 kVp for a Mo/Mo system resulted in a 42% decrease of the surface dose for a thick breast (6 cm), without changing the exposure at the detector plane. Use of 1.02 mm Al filter for a W anode system operating at 30 kVp resulted in a 19.1% decrease of the surface dose delivered to a 5 cm water equivalent breast. Overall, W/Al systems appear to have improved dosimetric performance, resulting up to a 65% decrease of surface dose compared to Mo/Mo systems, for identical exposures at the detector plane and breast thicknesses.