Measured

induced more cancers than were found (Bailer, 1977). Although more careful analysis of theradiation dose and associated risks estimates has negated this hypothesis, mammographyradiation doses are of concern and are routinely monitored. The magnitude of the absorbedradiation dose to the breast from mammography X-ray beams forms an important part ofthequality control of the mammographic examination since it gives an indication of theperformance of the mammographic imaging system as well as an estimated risk to the patient.Breast cancer almost always arises in the glandular tissue of the breast. As a result, the meanor average radiation absorbed dose of the glandular tissue is the preferred measure of theradiation risk associated with mammography (NCRP, 1986; Rosenstein et a!., 1985). Themean glandular (MGD) dose is the quantity also recommended by International Commissionon Radiological Protection (ICRP, 1991) and is used by many national protocols, such as theEuropean Protocol (CEC, 1996).Mammographic dosimetry is primarily to assess the risk of radiation-induced carcinogenesisin mammographic examinations. Breast dose assessment has therefore been recommended tobe included in every mammographic quality assurance programme by some national protocolsand institutions such as the European Protocol, using the mean glandular dose (MGD) as therisk assessment parameter since the glandular tissue is the most vulnerable of the breast tissues(European Protocol (CEC, 1996), the British Institute of Physical Sciences in Medicine(IPSM, 1989), and the International Commission on Radiological Protection (ICRP, 1991)).Measurements of the mean glandular dose from mammography have been carried out by anumber ofinvestigators using a variety ofmammographic techniques.II