Dose-area product-meter
One of the most important quality assurance procedures is to evaluate the doses delivered to patients who undergo x-ray examinations. International and national legislation requires that patient doses are monitored and checked. The purpose of such monitoring is to promote optimization of radiological procedures with respect to patient dose and image quality by detecting unplanned changes in dose levels or when local or national diagnostic reference levels are exceeded.
This film shows how to measure patient dose s with dose-area product-meter, DAP.
The DAP-meter is a real-time patient dose monitoring system for auditing patient doses. Technical data from each exposure and for every examination type can be collected. The DAP-chamber can be retrofit in existing equipment. The chamber is attached to the collimator assembly of the x-ray device. In new devices the DAP-meter system can be a part of the equipment and the data can be collected from the display or workstation.
The DAP itself should be the subject of a quality control program. You can read more about it in the other paragraph of this course.
You must daily ensure that the DAP- display remains on zero after warm up period. A good practice is to make daily check up exposure with large field and compare the daily results with each other and reference value.
According to international regulations patient doses must regularly be calculated and compared with international or national reference values. Individual patient doses is not a good indicator for comparison against reference levels. Dose distributions acquired over time and involving many patients to average out effects due to variables such as patient size, examination complexity and operator technique provide a more suitable indicator.
A good practice is to measure dose-area product from 10 most recently examined patients and for the most common examinations for at least every three years. Of course you must measure doses when radiation exposure circumstances have changed, which means exchange in xray procedures or equipments.
For example you could collect DAP-data from chest pa and lateral projections of 10 patients. When doing this, patients’ average weight should be comparable to those of reference value group.
Usually the reference weight is about 70 kg. In this case a good range of weights would be 65 to 75 kg.
It means that you take at least 10 patients about 55 kg to 85 kg so that average is 70 kg.

You must use calibration factor before you can compare your values with the reference value. Go and see the part: ‘Calibration of DAP-meter’.
After you have collected the data you must compare the average with the reference value.
Reference value for chest pa and lateral projections is 0,4 Gy cm
2
. You can use the patient dose average value of international regulations (Euratom, ICPR 62) or those of your national protocol.
Radiographer can daily use this DAP-protocol to optimize patient doses and to register doses to patient documents for auditing purposes.
DAP-measuring is not recommended for pediatric procedures, because the patient dose is often below 10 mGy.cm2
DAP-measure can be used in common imaging procedures, fluoroscopy and ortopantomography
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Calibration of DAP-meter before measurements of doses
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Evaluation of the doses delivered to patients o every 3 years, or when radiation exposure circumstances have changed o most common x-ray examinations, chest, lumbal spine… o at least 10 patients for each examination
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Calibration factor
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National reference values
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Dap value is not applicable for examinations with low radiation exposure such as pediatric, small bones…