[A study of entrance surface dose with CR and film/screen systems, and analysis of the X-ray conditions for chest radiography].

Several previous studies have indicated that the medical exposure dose(entrance surface dose) is lower with Computed Radiography(CR) than with the Film/Screen(F/S) system. We conducted a questionnaire survey of 1,297 hospitals regarding the radiation exposure conditions of X-ray examinations. From the survey results, we calculated the entrance surface dose(first quartile, median, third quartile, and mean) using the NDD calculation method. In the case of chest radiography(adult patients) by CR, the entrance surface dose was 150% of the median value for the overall examination and 160% of the median value for orthochromatic screen systems. The CR exposure set-up using a lower voltage and higher mAs than the F/S method was found to result in a high entrance surface dose. We also found a difference in patient dose among hospitals using CR. Mean surface dose in CR system was 0.12 mGy in a quartile, 0.19 mGy in the middle and 0.27 mGy in the third quartile. Among the hospitals which showed higher doses of third quatile them above mentioned, dose differences of a quartile were distributed 2 to 10 times higher them mean exposure doses.