Amount of radiation absorbed by a breast during mammography
In
mammography, mean glandular dose (MGD) is a quantity used to describe the
absorbed dose of
radiation to the
breast. It is based on a measurement of
air kerma and conversion factors. MGD can be calculated from measurements made with
poly(methyl methacrylate) (PMMA) blocks. It is often used to compare typical doses to patients between different centres or internationally, and is the preferred measure of the potential risk from mammography.[1][2][3]
Calculation
MGD can be calculated from a measured incident air kerma at the top of the breast, , as follows:[4]
converts from incident air kerma to MGD, with a glandularity of 50%, based on breast thickness and
HVL. corrects for glandularity other than 50%, depending on the breast thickness and HVL, with two versions for ages 50–64 and 40–49. corrects for the x-ray
spectra in use with a table of target/
filter combinations.[4][5]
Applications
MGD is typically used to define limits on mammography exposures by national and international organisations such as the
European Union and
International Atomic Energy Agency, at <2.5
milligray (mGy) per exposure to a standard breast (4.5 cm PMMA).[6]
In routine quality assurance testing of mammographic equipment, MGD measurements for a range of effective breast thicknesses with PMMA, and from real patient exposures, is widely recommended.[2]
References
^Yaffe, Marlin J.; Barnes, Gary T.; Conway, Burton J.; Haus, Arthur G.; Karellas, Andrew; Kimme-Smith, Carolyn; Paul Lin, Pei-Jan; Mawdsley, Gordon; Rauch, Phillip; Rothenberg, Lawrence N. (1990).
Equipment requirements and quality control for mammography. New York, NY: American Association of Physics in Medicine.
ISBN978-0-883188-07-1.
^Dance, D R; Skinner, C L; Young, K C; Beckett, J R; Kotre, C J (1 November 2000). "Additional factors for the estimation of mean glandular breast dose using the UK mammography dosimetry protocol". Physics in Medicine and Biology. 45 (11): 3225–3240.
Bibcode:
2000PMB....45.3225D.
doi:
10.1088/0031-9155/45/11/308.
PMID11098900.