방사선 촬영조건에 따른 ESD 평가 모델 개선 연구

Abstract

Concerning radiation exposure in medical process, dose limit and dose constraint are not regulated as the benefit of patient is the priority. The exposure doses on patient vary widely depending upon the degree of equipment worn-out in medical facilities, equipment conditions, technical method of staff, etc. Exposure dose control methods include the actual measurement method by using the TLD (Thermoluminesence Dosimeter) and transmission ionization chamber, entrance surface dose calculation by using the equipment output measured in the air and indirect measurement based on radiography conditions. In this study, radiography equipment management degree was assessed along with equipment characteristics and conditions for each imaging part. Then the modified patient dose calculation method was used as it gives smaller errors compared with the actual dose amounts. By doing so, this study seeks to establish active response to radiographic exposure and contribute to reduced medical exposure. The modified equation herein put weight on tube voltage, inherent filter, added filter and its accompanied back scatter factor in the existing equation to calculate the entrance surface dose. As the thicker the subject’s part, the higher the tube voltage and tube current; the exponential constant in the modified equation moved up. While the index of lateral lumbar was found the highest, the index of anterior wrist was the lowest. The more the radiography conditions, the larger the deviation between actual measurement values and indirect equation values was. It was also found that, rather than the distance, increase in tube voltage by the subject’s thickness was found to have a larger effect on BSF. However, it seems necessary to use medical quality control in parallel to reduce error variables in order to get closer to ESD approximate value found under direct measurement. In addition, this study sought to establish an auto-control software based on LabVIEW capable of predicting and protecting from exposure dose in the modified and improved patient dose assessment method. ESD according to radiography conditions was displayed along with the images of each radiography part. Surface doses were displayed according to tissue weight. Based on diverse indirect equations, diagnostic reference levels were compared for assessment in this study. Accordingly, diagnostic radiography patient dose comparison would become easier and radiographic exposure control and evaluation will become more efficient. The study findings are expected to be useful in patients’ effective dose rate evaluation and dose reduction; and present a way forward in the national exposure dose control research.