X-ray beam energy, scatter, and radiation risk in chest radiography.

Effective doses for patients undergoing chest radiography were computed utilizing updated weighting factors, published organ doses and measured entrance doses. The effective dose decreases with beam energy (kVp) and reaches a minimum value after 100 kVp, with values when a grid is used (6.90 microSv) being 145% higher at this energy than when no grid is used (2.82 microSv). The uncertainties associated with derivation of the tissue weighting factors are shown not to affect the point at which risk is minimized. Use of the effective dose as the measure of risk does not require special treatment of the remainder tissue as with use of effective dose equivalent. The effective dose required for radiographs of constant optical density was examined to incorporate the behavior of the detector's response to energy and compare results to previous work where exit dose was held constant. The effective dose at 120 kVp with a grid (6.84 microSv) is compared to an estimate of that associated with the current kVp distribution (14.55 microSv). Since image quality is enhanced by the grid, its use in conjunction with a beam energy of 120 kVp could maximize the benefit/risk ratio in chest radiography and should be considered for universal implementation. Such adoption could reduce the population risk compared to current practice.

Rare-earth scatter fractions in chest radiography.

A beam stop technique was used to measure the densitometric scatter fractions under three regions of a humanoid chest phantom utilizing LaOBr and Gd2O2S screens. For these receptors, the scatter fractions under the lung and retrocardiac areas were 13%-36% lower than published values for CaWO4. In the mediastinal area, there was no significant difference between the CaWO4 and rare-earth phosphors. The use of grids reduces the scatter fraction in all three regions by 40%-75%. With and without a grid, radiographic contrast with Gd2O2S was measured utilizing simulated lesions placed above the lung and retrocardiac areas.