Dose area product (DAP) is a quantity used in assessing the radiation risk from diagnostic X-ray examinations and interventional procedures. It is defined as the

absorbed dose Absorbed dose is a dose quantity which is the measure of the energy deposited in matter by ionizing radiation per unit mass. Absorbed dose is used in the calculation of dose uptake in living tissue in both radiation protection (reduction of harmf ...

multiplied by the area irradiated, expressed in

gray Grey (more common in British English) or gray (more common in American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning literally that it is "without color", because it can be composed o ...

- centimetres squared (Gy·cm² – sometimes the prefixed units mGy·cm² or cGy·cm² are also used). 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 advantages 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.

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), tube current (mA), exposure time, or the area of the field, can also be changed.
For example, a 5 cm × 5 cm X-ray field with an entrance dose of 1 mGy will yield a 25 mGy·cm² DAP value. When the field is increased to 10 cm × 10 cm 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 located in present-day Sudan at least 5,500 years ago. Kerma is one of the largest archaeological sites in ancient Nubia. It has produced decades of extensive excavations and research, in ...

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

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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

References

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