Gastrointestinal fluoroscopy: patient dose and methods for its reduction.

The aim of this study was to demonstrate a method which could be used to identify factors which contribute to the radiation exposure to patients from fluoroscopy during contrast examinations of the gastro-intestinal tract. Measurements of exposure made at the level of the X-ray tube collimator were extrapolated to obtain entrance exposure at the centre of the field and used as an index of the integral dose to the patient. Such data have heretofore been unavailable. The population studied included 65 patients ranging in age from 1 month to 21 years. In an initial study, median entrance exposure at the field centre for barium swallow examinations ranged from 0.98 to 1.7 mC/kg (3.8 to 6.6 R); barium meal: 1.9-5.7 mC/kg (7.4-22 R); barium meal with small bowel: 1.4-7.7 mC/kg (5.3-30 R); barium enema: 0.93-7.7 mC/kg (3.6-41 R). Gonadal dose, measured in males, ranged from undetectable to 0.71 mGy (71 mrad). The presence of contrast medium in the fluoroscopic field increased the exposure from a single 100 mm spot film, taken with automatic exposure control, by a factor of up to 16, and fluoroscopic exposure rate, using automatic brightness control, by a factor of 2 or more. We recommend modifications in the operation and design of fluoroscopic equipment, especially when fitted with brightness and exposure controls, for the reduction of patient exposure. Implementation of two modifications, a high/low dose switch, and a variable aperture iris diaphragm, reduced patient exposure from 1.4 to 3.4 times.