[CR (Computed Radiography)].

Abstract

Several recent studies have a questionnaire survey of many hospitals regarding the radiation exposure conditions of X-ray examinations. From the survey result the entrance surface doses (first quartile, median, third quartile and mean values) have calculated by using the Numerical Dose Determination (NDD) method. The calculated result for all types of examinations showed that the median values were lower than the mean values, whereas the median values of the results were lower than those in the NRPB 21 in England. The mean values of the results were lower than those in the NRPB 21 in England. The mean values were lower than IAEA guidance levels. The results have indicated that the medical exposure dose (entrance surface dose) is lower with Computed Radiography (CR) than with the Screen/Film (S/F) system except the case of chest radiography. In the case of chest radiography (adult patients) by CR exposure set-up using a lower voltage and high mAs than the S?F method, the entrance surface doses were 150 % of the median value for the overall examination and 160 % of the median value for orthochromatic S/F systems. A difference in patient dose among hospitals using CR system was also found. Mean entrance 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 that showed higher doses of third quartile than above mentioned, dose differences of a quartile were distributed 2 to 10 times higher than mean exposure doses. Mori et al. propose guidance levels are lower than IAEA guidance levels of entrance surface doses for examinations carried out in Japanese institutions as the 3rd quartile of the dose distributions. Therefore the quality control of tube voltage, tube current and mAs and a regular measurement of exposure for X-ray units are required.