Estimation of effective dose to the patient during medical x-ray examinations from measurements of the dose-area product.

Effective dose is likely to be used as a dose index for patient exposures in diagnostic radiology. Calculation of effective dose requires estimates of doses to many organs. In the absence of such dose data it would be useful to be able to directly estimate effective dose from a quantity that can be easily measured in the x-ray room. Relationships between effective dose and each of entrance surface dose, entrance air kerma and dose-area product were studied for common radiographic projections using the organ dose data from Monte Carlo modelling performed at the National Radiological Protection Board, UK. Dose-area product proved to be the best quantity for estimating effective dose and these data are presented. For typical peak generating potentials, estimates of effective dose can be made from dose-area product using a small number of conversion coefficients. For cervical spine, chest, kidneys, abdomen, lumbar spine and pelvis AP projections, the conversion coefficient 0.21 mSv per Gy cm2 will estimate effective dose within 30% of the value obtained using specific organ doses. Conversion coefficients for lateral and PA projections of the trunk are approximately half this value. These coefficients allow the direct estimation of effective dose with sufficient accuracy for most purposes.