An investigation on patient dose in screen-film diagnostic radiology in Lhasa City, Xizang Autonomous Region, China

Abstract

This study aimed to investigate patient dose in diagnostic screen-film radiographic examinations in the city of Lhasa, China. Seven out of the twenty-six hospitals registered with the Lhasa Health Bureau were included in the investigation. The entrance surface air Kerma (ESAK) of seven conventional screen-film radiology X-ray equipment in these hospitals was measured with a QA dosimeter in September 2012. The X-ray examinations were divided into three categories: PA (posterior-anterior) chest, upper/lower limb, and AP (anterior-posterior) lumbar spine. For each category, ESAKs were calculated and analyzed. The mean ESAK was 0.6 mGy for PA chest, 0.3 mGy for upper/lower limb, and 1.8 mGy for AP lumbar spine. In addition, the mean ESAK value recorded for PA chest X-ray examinations exceeded the corresponding value recommended by the International Atomic Energy Agency (0.4 mGy).

Keywords

radiation dosage / radiology / radiation protection / radiography/statistics & numerical data

Introduction

Humans worldwide are exposed to ionizing radiation from various sources, and the largest artificial source of exposure is from medical uses of radiation [1]. Although various kinds of man-made radiation are used for medical purposes, diagnostic radiology is the major contributor to man-made exposures in China.

Investigations on patient radiation dose from medical X-ray examinations have been performed in Europe [2-4]. In Africa, Eastern Europe, and Asia, several surveys have been published on the patient radiation dose from radiographic procedures [5,6]. The current study is the first to evaluate the technical condition of radiographic examinations of screen-film radiography (SFR) in Lhasa, capital city of Xizang Autonomous Region, China. No systematic records of patient exposure were found in Lhasa. In addition, no established diagnostic reference levels (DRLs) exist in the Xizang Autonomous Region.

Materials and methods

Apart from the city region, seven counties belong to Lhasa. About 280 000 people live in the city, and another 270 000 people live in the seven counties. Approximately 26 hospitals exist in the Lhasa area, and 19 of them are distributed in the city region; only one hospital exists in each of the seven counties. About four hospitals with a volume of over 300 outpatients per day exist. All of these large-volume hospitals are distributed in the city region. Furthermore, 19 of these 26 hospitals are sponsored and managed by the government, and the rest are supported by private sources.

This study analyzed the data of 7 out of 26 hospitals registered in the Lhasa City Bureau of Health. Seven different models of radiographic equipment in the hospitals were chosen for investigation. Six of the radiographic setups were conventional SFR equipment, and only one of them was the computed radiography (CR) system adapted from an SFR unit. Tables 1 to 3 show the proportion of various kinds of hospitals in the statistical population and our sample. Tables 1 to 3 indicate that the sample hospitals had similar proportion in hospital scale, attribution, and geographic distribution to the statistical population. Questionnaires about the technical conditions of radiographic procedure were filled out by the equipment technicians. Table 5 shows the details of the technical parameters used in sample equipments.

The radiographic procedures were divided into three categories, i.e., PA chest, upper/lower limb, and AP lumbar spine, because most of the technicians in sampling hospitals follow this classification to determine exposure parameters.

Patient dose for X-ray procedures was measured in September 2012. Measurements were performed on the exposure parameters of adult patients with a mean weight of 70 kg to estimate the typical dose to an average patient. A total of 21 measurements (three categories in seven equipment pieces) were performed. A QA dosimeter (model: Barracuda; RTI Corporation, Sweden) was used for the measurements, and this dosimeter was calibrated in the traceable Secondary Standard Dosimetry Laboratory at the Shanghai Institute of Measurement and Testing Technology.

The entrance surface air Kerma (ESAK) for radiographic examinations is given by

(1)ESAK=Ka,i^{°}\times {}^{°}B{,}^{[\mathrm{4}]}

where K_a,i is the incident air Kerma for each category, and B is the backscatter factor. An appropriate backscatter factor is multiplied to obtain the ESAK value [7].

Each ESAK value of the three categories of radiographic procedures was calculated according to Eq. (1). K_a,i was derived from the measurement result. In the measurement procedure, the detector was placed on the central axis of the x-ray beam at the same distance from the focus with the focus skin distance (FSD) recorded and exposures were performed under the conditions used in the radiographic procedures.

Results

Table 4 summarizes the median, 25%, and 75% mean values with the standard deviation and dose range of ESAK for the sampled radiographic equipment. The final column gives the International Atomic Energy Agency (IAEA) recommendation values [8]. Table 5 shows the technical parameters selected for the various examination types. The results of ESAK calculation and FSD are given in the last column.

Discussion

Table 4 shows that the mean ESAK values of the conventional screen-film radiographic procedure are below the IAEA recommendations, except that for PA chest. The results also showed that the ESAK of patients in Lhasa was similar to the results of Daryoush’s report on Isfahan in 2006 [9] and 2012 [10]. The entrance surface dose (ESD) results of chest PA are 0.7 mGy and 0.74 mGy, respectively. Milatovic [11] revealed that the patient dose in diagnostic radiology in Montenegro and the mean value of ESAK in PA chest is about 0.9 mGy. Kim [5] reported that the patient dose in diagnostic radiology in Korea in 2007 and the mean value of ESD of PA chest in Korea are about 0.21 mGy. Surveys in Syria [12] and Lithuania [13] have also shown the effects of interference. Among these surveys, the most impressive one is that involving the National Patient Dose Database in the UK, which is supported by their Health Protection Agency [2,14,15]. Patient doses are reported every 5 years, and the reports show the patient dose level of diagnostic radiological procedure and the trend of patient dose in the UK. The latest report shows that the mean value of ESD of PA chest is about 0.12 mGy in the UK [14], which is far less than the mean value of PA chest in this survey.

Another factor is the significant variations in radiological practice. The typical technical parameters used varied across a wide range. The tube voltage range of PA chest was from 52 kV to 80 kV, and the mA·s product had an even more enormous diversity. This wide variety can explain the variations in patient dose. This situation is probably caused by the use of a low-kilovolt technique, the lack or improper adjustment of automatic exposure control systems, and inadequate staff training.

Considering these results and to optimize the protection of patients, quality control programs need to be performed to reach dose conditions that are as low as reasonably achievable. These programs can avoid considerable cost and high patient doses.

Efforts must be made to further lower patient doses while securing image quality. Furthermore, relevant education and training of technicians in radiology sections is urgently needed in the hospitals in Lhasa City. The findings of this survey can be used as a baseline upon which future dose measurements may be compared.

This survey investigated the technical conditions of radiography in the Xizang Autonomous Region of China. Data from 26% of the hospitals in the Lhasa area were analyzed in this survey. ESAKs of three radiographic categories were measured and calculated. However, a limitation of the survey is that CT scan, dental radiology, and mammography were not included in the survey. Further studies are projected toward two directions. One is to investigate other diagnostic procedures such as CT, dental radiology, and mammography. The other is to investigate the entire Xizang population to gather more reliable information on patient dose in the Xizang Autonomous Region.

Conclusions

Results of the patient doses in conventional SFR in Lhasa are presented. The dose of patients undergoing common radiology examination in Lhasa was found to be below the IAEA recommendation level, except for the PA chest category. Efforts including relevant staff training and education need to be made to further lower patient dose while securing image quality.

References

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