Survey On Dose Reference Levels For Some Common Types Of X-ray Photography

Objective Diagnostic X-rays are used so extensively in medicine that they represent by far the largest man-made source of public exposure to ionizing radiation. After humans’ positive development and utilization, X-ray is found to be a double-edged sword and more attention should be paid to the radiation protection problem. Timely grasping dose level status and situation for patients of performing medical X-ray diagnosis examinations can provide the basis for establishing diagnosis reference or guidance levels (DRLs) and radiation protection measures. Conventional method of obtaining dose levels in census is accurate but time-consuming and manpower intensive. There is a certain uncertainty of doing dose levels survey by using estimation model but it is relatively convenient. The guidance levels have not been updated within last ten years in our country. Local reference levels were also not been established according to actual situations. In this research, DRLs are aimed to be acquired by directly measuring and calculating by using mathematical model. Learning from foreign experience, DRLs of three common types of medical X-ray photography in Shanghai are established, which provide methods and data for related research.Methods To achieve the main purpose above, this research was carried out in the following three aspects.1) Through the analysis of medical exposure application frequency and its development trend in Shanghai, major types of medical diagnostic X-ray photography were obtained. Based on the strict quality control of the data, thermoluminescence dosimeter (TLD) were used to measure the entrance surface doses (ESDs) of a total of1726adult patients performing chest posteroanterior (PA), chest lateral (LAT) and lumbar lateral X-ray photography.2) Based on the dose estimation model developed by our research group, experimental surveys were adopted to compare the difference between TLD measurements entrance surface dose (ESDTLD) and calculated ESD (ESDc). The estimation model was applied to the investigation of this study to calculate the entrance surface dose and then do the result analysis. What’s more, the uncertainty of the estimation model was evaluated.3) Based the method of establishing DRL and combined with DRL’s situation and development trend at home and abroad, the values of DRLs for doses achieved by directly measuring and calculating using mathematical model were analyzed and compared. According to local conditions, DRLs of the three common types for performing medical X-ray photography in Shanghai were tried to be established.Results According to diagnosis frequency and single ESD for X ray photography in Shanghai, three common types of chest posteroanterior (PA), chest lateral (LAT) and lumbar lateral projection were selected to do detailed study. In this research, ESDs of1726adults performing the three types of X-ray photography in Shanghai showed a big difference between each. The mean values of ESD were0.23mGy,0.57mGy,4.48mGy, respectively. The changing trend combined well with the foreign investigation results on the ESD values and the main exposure parameters (mAs and kVp). Verification test showed that the mean relative deviation between the three types of TLD measurements entrance surface dose (ESDTLD) and calculated ESD (ESDC) values were1.9%,5.1%,1.7%, respectively. So, the estimation model could be used to do the assessment of dose levels. In this survey, the relative deviation of the mean values of ESD for the three different types of photography between the estimated and the measured were13.0%,12.3%,3.3%, respectively. A paired t-test showed no statistically significant difference. What’s more, in different countries or regions, the time of establishing DRLs and DRL categories were different. And the DRLs showed a decreasing trend. The75%of mean ESDTLD values by each equipment for the patients performing medical X-ray diagnosis radiography in Shanghai were0.32mGy,0.75mGy,6.84mGy, respectively; the75%of mean ESDc values were0.28mGy,0.81mGy, and6.92mGy, respectively. They were all less than the current national guidance levels.Conclusions This estimate model established by our research team could be used to evaluate the levels of entrance surface does for medical X-ray diagnosis photography. Doses for patients performing medical X-ray diagnosis photography were dropping down continuously. This study proposed to0.30mGy,1.0mGy,8.0mGy respectively as the diagnostic reference levels for chest posteroanterior, chest lateral, lumbar lateral projection performing X-ray photography.