Evaluation of dose area product vs. patient dose in diagnostic X-ray units

Dose Area Product (DAP) meters which measure in units of [Gy*m2], are widely used in radiology, fluoroscopy and interventional cardiology X-ray units. However, assessment of the radiological hazard to the patient undergoing a given diagnostic procedure cannot be readily obtained from the measured value of DAP. We also developed simple relationships between Entrance Surface Dose (ESD) and the DAP value measured in air, for different collimator field sizes and patient thickness. To establish these relationships, measurements were performed in a water phantom using high-sensitive thermoluminescent detectors (LiF:Mg,Cu,P) calibrated in terms of Kerma in water. Using these relationships developed for a given X-ray unit, calculations of ESD (in mGy) could be performed on the basis of DAP by the X-Ray unit software itself, if the X-ray unit could also evaluate the Focus-to-Skin Distance (FID), e.g. by ultra-sound techniques.