Breast dose from magnification films in mammography

In mammography, much attention has been given to estimating breast dose from exposures made in conventional "contact" geometry, but much less attention has been given to doses from magnification geometry. Estimation based on contact film dose is difficult because the grid is removed, the geometry is different, and calculation of scatter reaching the film is complex. In this paper, exposures of Perspex blocks of standard thickness to give the same film density in both geometries are compared on 20 X-ray sets of various designs with a nominal magnification 1.8. The ratio derived between doses in each geometry is 2.2+/-0.15, giving an average magnification film dose of 5.0+/-0.3 mGy.