Dose Area Product
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Dose area product (DAP) is a quantity used in assessing the radiation risk from diagnostic
X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
radiography Radiography is an imaging technology, imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical ("diagnostic" radiog ...
examinations and interventional procedures, like
angiography Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. Modern angiography is perfo ...
. It is defined as the
absorbed dose Absorbed dose is a dose quantity which represents the specific energy (energy per unit mass) deposited by ionizing radiation in living matter. Absorbed dose is used in the calculation of dose uptake in living tissue in both radiation protecti ...
multiplied by the area irradiated, expressed in
gray Grey (more frequent in British English) or gray (more frequent in American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning that it has no chroma. It is the color of a cloud-covered s ...
- centimetres squared (Gy·cm2 – sometimes the prefixed units dGy·cm2, mGy·cm2 or cGy·cm2 are also used). Gray (Gy) is the
SI unit The International System of Units, internationally known by the abbreviation SI (from French ), is the modern form of the metric system and the world's most widely used system of units of measurement, system of measurement. It is the only system ...
of absorbed dose of
ionizing radiation Ionizing (ionising) radiation, including Radioactive decay, nuclear radiation, consists of subatomic particles or electromagnetic waves that have enough energy per individual photon or particle to ionization, ionize atoms or molecules by detaching ...
, while the milligray (mGy) is its subunit, numerically equivalent to the
millisievert The sievert (symbol: SvPlease note there are two non-SI units that use the same Sv abbreviation: the sverdrup and svedberg.) is a derived unit in the International System of Units (SI) intended to represent the stochastic health risk of ionizing ...
(mSv) as used to quantify equivalent and effective doses for gamma (γ) and X-rays. Manufacturers of DAP meters usually calibrate them in terms of absorbed dose to air. DAP reflects not only the dose within the radiation field but also the area of tissue irradiated. Therefore, it may be a better indicator of the overall risk of inducing cancer than the dose within the field. It also has the advantage of being easily measured, with the permanent installation of a DAP meter on the X-ray set. Due to the divergence of a beam emitted from a "point source", the area irradiated (A) increases with the square of distance from the source (A ∝ d2), while radiation intensity (I) decreases according to the inverse square of distance (I ∝ 1/d2). Consequently, the product of intensity and area, and therefore DAP, is independent of distance from the source.
DICOM Digital Imaging and Communications in Medicine (DICOM) is a technical standard for the digital storage and Medical image sharing, transmission of medical images and related information. It includes a file format definition, which specifies the str ...
"X-Ray Acquisition Dose Module" metadata within each medical imaging study often includes various DAP and dose length product (DLP) parameters.


How DAP is measured

An ionization chamber is placed beyond the X-ray collimators and must intercept the entire X-ray field for an accurate reading. Different parameters of the X-ray set, such as peak voltage (kVp),
X-ray tube An X-ray tube is a vacuum tube that converts electrical input power into X-rays. The availability of this controllable source of X-rays created the field of radiography, the imaging of partly opaque objects with penetrating radiation. In contras ...
current (mA), exposure time, or the area of the field, can also be changed.
For example, a X-ray field with an entrance dose of 1 mGy will yield a 25 mGy·cm2 DAP value. When the field is increased to with the same entrance dose, the DAP increases to 100 mGy·cm2, which is four times the previous value.


Kerma Area Product

Kerma Kerma was the capital city of the Kerma culture, which was founded in present-day Sudan before 3500 BC. Kerma is one of the largest archaeological sites in ancient Nubia. It has produced decades of extensive excavations and research, including t ...
area product (KAP) is a related quantity, which for all practical radiation protection purposes is equal to dose area product. However, strictly speaking \mathrm = \mathrm \times (1-g), where ''g'' is the fraction of energy of liberated charged particles that is lost in radiative processes in the material and the dose is expressed in absorbed dose to air. The value of ''g'' for diagnostic X-rays is only a fraction of a percent. Adult
coronary angiography Coronary () may, as shorthand in English, be used to mean: * Coronary circulation, the system of arteries and veins in mammals ** Coronary artery disease ** Coronary occlusion ** A myocardial infarction, a heart attack As adjective * Referring to ...
and PCI procedures expose patients to an average DAP in the range of 20 to 106 Gy·cm2 and 44 to 143 Gy·cm2 respectively.priory.com RADIATION EXPOSURE IN THE CATH LAB – SAFETY AND PRECAUTIONS
Dr S M S Raza, MB BS, MD. First Published October 2006


See also

* Effective dose *
Equivalent dose Equivalent dose (symbol ''H'') is a dose quantity representing the stochastic health effects of low levels of ionizing radiation on the human body which represents the probability of radiation-induced cancer and genetic damage. It is derived fro ...
* Computed tomography dose index


References

{{DEFAULTSORT:Dose Area Product Radiology Medical terminology Nuclear medicine Medical physics