Entrance Surface Dose and its Correlation with Patient Parameters

Reference doses defined only for a standard patient (70 kg, 170 cm) make less sense as this standard patient will rarely be met during typical examinations. The entrance surface dose (ESD) was measured for three types of radiographic examination (lumbar spine AP and lateral and pelvis) using a small dosemeter placed at a well defined position in the radiation field. As expected, the ESD shows a significant correlation with patient diameter, with the measured mean values being smaller than a quarter of CEC reference dose levels. Therefore it is suggested that the reference dose values be reduced or defined not as an upper limit for a standard patient but for intervals of the thickness of the patient region to be examined. A suitable and easy to measure parameter to estimate patient exposure is the dose-area product.