British Journal of Radiology 74 (2001),162-165 © 2001 The British Institute of Radiology
Reduction of radiation dose to patients undergoing barium enema by dose audit
S K Yu1,
Y K Cheung2,
T L Chan2,
C M Kung2 and
M K Yuen2
1 Medical Physics Division
2 Department of Diagnostic Radiology, Tuen Mun Hospital, N.T., Hong Kong
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Abstract
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Nowadays, new fluoroscopic machines are usually equipped with a dose–area product (DAP) meter for dose measurement. In our hospital, DAP meters have been used in the Diagnostic Radiology Department for dose audit since June 1997. Demographic patient data, name of radiologist, fluoroscopic duration and DAP readings of every case were recorded by radiographers. In early 1999, questionnaires were distributed to radiologists who had performed fluoroscopic examinations during the auditing period. 23 radiologists with varying years of experience completed the questionnaire and their practice was analysed. Since familiarization with the examination technique would affect radiologists' practice, these radiologists were divided into two groups for analysis. Radiologists with less than 3 years of experience were grouped together as junior radiologists, whilst others were grouped as senior radiologists. Results of the questionnaire indicated that radiologists generally found DAP meters useful for dose evaluation in the process of technique refinement. Radiologists aware of being under continuous surveillance of their practice showed significant reduction of doses (junior radiologists 25%, p<0.005; senior radiologists 36%, p<0.05) and fluoroscopic times (junior radiologists 36%, p<0.001; senior radiologists 18%, p<0.05) compared with radiologists who were unaware that they were under surveillance but with similar radiological experience. This effect is believed to be because of increased awareness of radiation dose through audit. In addition, this "audit effect" may also affect junior radiologists in decision-making regarding the number of radiographs (p<0.05), but no effect was found for senior radiologists (p>0.5).
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Introduction
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Radiation dose measurement in diagnostic radiology is the corner-stone for setting good practice standards as well as optimizing radiation protection to both staff and patients. Radiation dose measurements allow assessment of dose to organs and the associated risk from X-ray exposure, thus providing a means to compare diagnostic techniques or X-ray equipment.
Fluoroscopic examinations, including interventional procedures, contribute a relatively large portion of radiation dose to patients among radiological procedures. They also contribute a large fraction of the genetically significant dose, since the abdominal region is the area frequently examined under fluoroscopy. Fluoroscopy is operator-dependent; considerable variation of exposure delivered by different radiologists for the same type of examination has been reported [1]. The various techniques adopted by different radiologists are believed to be of paramount significance in explaining the wide range of radiation doses, which vary by as much as three orders of magnitude [2]. Similar findings have also been reported for interventional radiology [3, 4]. In Britain, evidence shows that unnecessary diagnostic irradiation may be responsible for 100–250 deaths from cancer annually [5]. Patient dose audit and dose reduction are therefore of prime importance.
Recently, there has been evidence that dose reduction could be achieved by increasing staff awareness of radiation dose [6, 7]. Similarly, greater dose reduction may be achieved by ensuring the radiologist is aware that his/her fluoroscopic practice is continuously under surveillance. We call this the "audit effect".
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Methods and materials
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In the Diagnostic Radiology Department of Tuen Mun Hopsital, Hong Kong, patient dose from fluoroscopic examinations has been monitored continuously in an audit programme since June 1997. All fluoroscopic examinations were performed with a fluoroscopic unit (TRIDOROS 512MP; Siemens, Erlangen, Germany) equipped with a Diamentor meter (PTW, Freiberg, Germany). For each X-ray tube, an optical transparent flat-plate ionization chamber was attached to the light beam/diaphragm housing. The Diamentor meter recorded both the fluoroscopic and the radiographic exposures independently, and was periodically calibrated and checked by the Medical Physics Division.
Patient doses were estimated indirectly by measuring dose–area product (DAP) in units of cGy cm2. For each examination, radiographers were required to record the DAP, screening time and patient demographic data, whilst the radiologists' names were recorded in a separate attendance book. Reports on dose, with the radiologists' names masked, were made quarterly and posted in the radiologist duty room. These reports described the performance of all radiologists in terms of DAP and screening time in each quarter year.
In early 1999, all radiologists who had performed fluoroscopic examinations during the auditing period were requested to fill in a questionnaire regarding the following points:
- Years of experience being a radiologist (including trainee).
- Whether they noticed the existence of the DAP meter.
- Whether they knew the function and purpose of the DAP meter.
- Would they be more aware of radiation exposure to patient?
- Would they try to reduce radiation exposure if they knew that they were being monitored?
- Would they check the DAP results after they finished an examination?
- Would they agree that dose monitoring helped them to refine their techniques?
- Whether they found any inconvenience during the monitoring procedures.
23 radiologists with varying years of experience, ranging from radiology trainees with less than 1 year of experience to consultant radiologists with more than 10 years of experience, completed the questionnaire and their practice was analysed in this study. Since the complexity of the examination could significantly affect radiation dose to the patient and the required fluoroscopic time, to minimize this effect we limited our study to only one type of fluoroscopic examination, the barium enema, which was performed using the same fluoroscopy machine and room. In addition, the duty roster of radiologists in that room was set in a cyclic basis, regardless of rank and seniority, so that the case complexity assigned to each radiologist was randomized.
Familiarization with the barium enema technique may also affect radiologist performance, so the radiologists were divided into two groups for analysis. Radiologists with less than 3 years of experience were grouped together as junior radiologists, whilst the others were grouped as senior radiologists. For each group of radiologists, two subgroups were defined. Radiologists with awareness of both the existence of the DAP meter and its function belonged to subgroup A; the others belonged to subgroup B. The distribution of junior and senior radiologists, their average years of experience and the total number of barium enemas performed in each group and subgroup are listed in Table 1
. Answers to the questions in the questionnaire are listed in Table 2 for subgroups A and B.
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Table 1. Number of radiologists, average years of experience and total number of barium enemas performed for each group and subgroup
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Results
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As shown in Tables 3 and 4, average fluoroscopic times were shorter for subgroup A (junior 213±157 s; senior 174±88 s) compared with subgroup B (junior 334±215 s; senior 212±160 s), and the differences in the average times between subgroups A and B were statistically significant (junior p<0.001; senior p=0.0467). Similarly, DAP readings from fluoroscopy were also found to be reduced significantly (junior p=0.018; senior p=0.022) for subgroup A (junior 999±871 cGy cm2; senior 702±881 cGy cm2) compared with subgroup B (junior 1339±1183 cGy cm2; senior 1110±1350 cGy cm2).
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Table 3. Average dose–area product (DAP) readings and fluoroscopic screening times for each radiologist group and subgroup
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Table 4. p-values of independent samples two-tailed t-test comparing the results of average dose–area product (DAP) readings and the screening times between subgroups A and Ba for each radiologist group
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Thus, the knowledge of being monitored led to an increased awareness of radiation and shorter fluoroscopic times, resulting in lower radiation doses. As expected, this "audit effect" was more pronounced for the junior radiologists (36%) than the senior radiologists (18%) in terms of fluoroscopic time shortening. Reduction of fluoroscopic DAP was found to be higher for senior radiologists (36%) than junior radiologists (25%).
In addition, the "audit effect" might also affect decision-making regarding the numbers of radiographs taken during an examination for junior radiologists (DAP from radiography: subgroup A 612±526 cGy cm2; subgroup B 773±536 cGy cm2; p=0.024). No effect was found for the senior radiologists (DAP from radiography: subgroup A 663±478 cGy cm2; subgroup B 694±758 cGy cm2; p=0.751).
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Discussion
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DAP has been regarded as an effective means for measuring radiation dose in the radiological field. All our radiologists in various subspecialties have learnt the principles. However, the DAP device is rarely seen. This might be owing to the lack of resources in our territory, or to some other reasons such that we rarely had such devices for dose measurement until recently. Moreover, it was observed that radiologists were more attentive to clinical than technical aspects. Therefore, we believe our work would be useful in increasing awareness of radiologists to radiation dose monitoring, particularly in fluoroscopic examinations.
In 1993, Hough et al [6] found that reduction of radiation dose to staff could be achieved by wearing audible radiation monitors during fluoroscopic procedures. Shortening of fluoroscopic screening time was also reported using the Hawthorne effect [7], which is the phenomenon of altered performance behaviour resulting from the knowledge of being part of an experimental study [8]. Both methods work under the same principle, that is to increase staff awareness of radiation.
In this study, significant reduction of fluoroscopic time and radiation dose was achieved by continuous dose monitoring. This reduction could not be explained by familiarization with the barium enema technique, since radiologists in each subgroup had similar average experience. From the results of the questionnaire, most of the junior radiologists (yes/sometimes 56%/33%) and about half of the senior radiologists (yes/sometimes 36%/21%) would have been more aware of radiation if they had realized the existence and the function of the DAP machine. Similarly, most of the junior radiologists (yes/sometimes 67%/22%) and some of the senior radiologists (yes/sometimes=29%/14%) would have tried to reduce radiation exposure during an examination. Therefore, the observed reduction in radiation doses and fluoroscopic times were most probably owing to the "audit effect". In other words, ensuring that radiologists know that their practice is under surveillance increases their awareness of radiation and leads to dose reduction. It is not shown in this study whether the diagnostic accuracy of examinations will be influenced by the "audit effect", but this seems unlikely.
In addition, it was observed that most radiologists (junior, yes/sometimes 11%/78%; senior, yes/sometimes 21%/50%) would check the DAP results after performing each fluoroscopic examination if the machine was available, despite the fact that they did not know how the device operates. Only one of the radiologists disagreed that dose monitoring could help refine fluoroscopic techniques, and no radiologist found any inconvenience during the monitoring procedures.
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Conclusion
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Continuous dose monitoring increases radiologists' awareness of radiation, which in turn reduces fluoroscopic times and radiation doses ("audit effect"). DAP is convenient and informative to radiologists. However, more work is necessary to publicize the use of DAP monitoring because some radiologists may still not be fully aware of its existence and function.
Received for publication November 15, 1999.
Revision received July 14, 2000.
Accepted for publication September 25, 2000.
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Abstract
Introduction
