The dose area product (DAP) or kerma area product (KAP) is a method of radiation dose monitoring used in radiographic and fluoroscopic studies. It provides one indication of the radiation dose received by a patient and is the measurement used in dose audits (such as comparing Diagnostic reference levels).
It is calculated as the product of dose and beam area (Gy.cm2), and is measured using an ionization chamber placed between the x-ray tube/collimator set up and the patient (which in theory is independent of its position in the beam). The dose area product can be divided by the area of exposure (in cm2) to give the incident accumulated exposure (air kerma) at that site. The dose area product is linked to a patients stochastic risk.
The cumulative air kerma can be used as an indication of the dose received by the skin. The peak skin dose is be calculated using the dose area product (or more accurately the interventional reference point kerma), taking into account further factors such as backscatter and overlapping projections. The peak skin dose gives an estimation of deterministic risk (i.e. tissue reactions).
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