Physics, Techniques and ProceduresMid-breast dose
the radiation dose delivered to the midpoint of the breast at
mammography. Also in
mammography, the maximum radiation dose is found at the entrance skin field, i.e. on the side of
X ray tube. For a 4 cm thick breast the entrance dose is about 5 mGy, but this depends on many factors. Deeper in the breast, the amount of radiation decreases according to the
inverse square law due to the absorption by the tissues and to lesser extent due to
scattering. In general, it is possible to state that the average mid-breast dose is in the range of 30% of the entrance dose; somewhat smaller with film-screen
mammography and somewhat higher with
xeroradiography. The mid-breast dose depends strongly on a number of factors, like the imaging geometry, tissue thickness and composition, tube structure and filtration,
film screen system, possible magnification, etc.
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