Variations in measured patient entrance exposure for selected x-ray procedures

It has been proposed that single skin entrance exposure values be recommended for specific radiographic examinations. Numerous factors, however, contribute to large excursions in the measured skin entrance exposure (ESE) received by patients even in idealized conditions. Excluding the obvious effects of generator miscalibration, suboptimal film processing, film/screen spectral mismatches, et cetera, large variations in ESE are observed, even though clinically satisfactory radiographs are obtained. In particular, variations in ESE can be attributed to: selection of the film/screen combination, use of grids, patient thickness and tissue composition, kVp settings and the filtration employed. Data were taken at our institution for several representative examinations under various conditions. Lithium Fluoride TLD ribbons were placed on a series of patients undergoing PA and Lateral chest radiographs and PA abdomen radiographs with barium for Upper GI series. The patient ESE data observed at our institution, together with data taken with an anthropomorphic phantom will be presented. These data will be used to demonstrate that although a single ESE guideline may be appropriate under a specific set of conditions, a single value may be either too restrictive for a slower system or excessive for a faster system.