Effective dose and energy imparted in diagnostic radiology

The patient effective dose, E, is an indicator of the stochastic radiation risk associated with radiographic or fluoroscopic x-ray examinations. Determining effective doses for radiologic examinations by measurement or calculation is generally very difficult. By contrast, the energy imparted, ε, to the patient may be obtained from the x-ray exposure-area product incident on the patient. As energy imparted is approximately proportional to the effective dose for any given x-ray radiographic view, the availability of E/ε ratios for common radiographic projections provides a convenient way for estimating effective doses. Ratios of E/ε were obtained for 68 projections using E and ε values obtained from published dosimetry data computed using Monte Carlo techniques on an adult anthropomorphic phantom. The average E/ε ratio for the 68 projections in adults was 17.8±1.4 mSv/J, whereas uniform whole body irradiation corresponds to 14.1 mSv/J. The major determinant of E/ε ratios was the projection employed (the body region irradiated and x-ray beam orientation), whereas the tube potential and beam filtration were of secondary importance. Adult E/ε ratios may also be used to obtain effective doses to pediatric patients undergoing x-ray examinations by application of a correction factor based on the patient mass.