British Journal of Radiology 75 (2002),652-656 © 2002 The British Institute of Radiology
Reducing dose at barium enema: radiographers do it digitally
M T Crawley, BSc, MSc
1 and
A Booth, MRCP, FRCR
2
Departments of 1 Medical Physics and 2 Radiology, Stoke Mandeville Hospital, Mandeville Road, Aylesbury, Buckinghamshire HP21 8AL, UK
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Abstract
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It has been previously shown that, whilst radiographers in our hospital can undertake barium enema examinations with the same degree of diagnostic accuracy as consultant radiologists, there was a dose penalty to the patient arising from the use of a restrictive protocol requiring radiographers to take a series of plain radiographs for reporting purposes. For the past 3 years radiographers at this hospital have worked to a new protocol that replaces all routine radiographs with digital spot films. In the present study, dose–area product (DAP) measurements for 801 barium enema examinations performed by consultant radiologists and radiographers, using the revised protocol, were analysed and compared to ascertain whether there were still significant differences in radiation dose to the patient depending on the category of staff performing the examination. All examinations were reported by a consultant radiologist. The radiologists' reports were analysed against the known outcomes to compare the diagnostic accuracy of the examination when carried out by the two categories of staff. This study shows that using a modified protocol, in which digital spot films replace the series of overcouch radiographs for reporting, our radiographers are able to perform barium enemas without dose penalty to the patient, and without compromizing diagnostic accuracy. Means with 95% confidence intervals for DAP in the two groups were 9.8 Gycm2 (9.4–10.3 Gycm2) and 10.7 Gycm2 (10.2–11.1 Gycm2) for radiographers and radiologists, respectively.
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Introduction
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Radiographers conduct barium enema examinations in many hospitals, and the examination protocol used varies according to local practice. However, radiographers are often required to take a series of plain radiographs for reporting by a radiologist. As radiation dose to the patient is protocol-dependent, this requirement has been shown to result in an elevated patient dose, over and above that given when the procedure is carried out by a consultant radiologist [1]. We have adopted an amended protocol in which all routine radiographs for reporting are replaced by a series of digital spot films. In this study, doses to patients arising from barium enema examinations conducted by radiographers according to the amended protocol were analysed and compared with patient doses for examinations conducted by consultant radiologists. Diagnostic accuracy was investigated by reviewing the radiologists' reports for all patients with colorectal carcinoma confirmed by surgery or endoscopy.
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Method
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Following training by a consultant radiologist, four radiographers worked to an amended protocol that defined the procedure to be followed for a standard barium enema and the digital spot films required for subsequent reporting. The radiographer protocol no longer includes overcouch films, with all reporting now based on digital spot films taken using an undercouch fluoroscopic tube. The radiographers' standard views are summarized in Table 1
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A patient selection system was used to allocate patients to the two staff groups, i.e. consultant radiologists and radiographers. Mobile out-patients and GP referrals were allocated to radiographer sessions, whereas in-patients, patients over 75 years of age and those with a disability were allocated to the radiologist sessions. Hence, patients pre-selected for examination by a radiologist were potentially the more difficult cases. However, the impact of patient population bias on patient dose has been assessed previously at this hospital and shown to have no significant effect on patient dose [1].
All dose–area product (DAP) data used in the study were derived from examinations carried out in the same X-ray room using the same X-ray equipment (Siemens Aktiengesellschaft, Erlangen, Germany), which comprised an undercouch fluoroscopic tube with image intensifier and a digital imaging facility. The room was also equipped with an overcouch radiographic tube though, as stated above, overcouch radiographic films no longer form part of the radiographer protocol and have also become obsolete for radiologist examinations in this Trust. Both X-ray tubes were fitted with DAP meters. All equipment was subject to routine quality control procedures, which included measurements of air kerma at the image intensifier input face and image quality assessments at monthly intervals. All measured parameters remained within local limits during the entire period of the study. The calibration of the DAP meters was checked annually over the range 60–120 kVp.
DAP values were recorded for 912 barium enemas performed during 2000. Of these 912 examinations, 251 examinations were carried out by four specially trained radiographers, 550 by seven consultant radiologists and the remaining 111 by radiology registrars. The consultant group included one associate specialist. Examinations by registrars were excluded from this particular analysis as DAP readings are expected to be higher as this group is still in training. All examinations by both consultants and radiographers were carried out according to the revised protocol, which increased the number of digital spot films and eliminated overcouch films. The 2000 data were compared to data from 1994–1996, during which time all examinations were based on the original protocol involving three routine radiographs for the radiographer studies. Our 1994–1996 data have been reported previously [1].
Data recorded for each examination in 2000 (date, type of operator [consultant radiologist or radiographer], operator and DAP) were analysed using standard software [2]. Frequency plots of the data for the two types of operator (Figure 1) showed that data were skewed. Square root, logarithmic and reciprocal transformations were applied to the data to determine which of these transformations produced the distribution closest to normality, in order that parametric tests could be applied. Data were subsequently transformed to log DAP before analysis using one-way analysis of variance for differences between operator types and between individual operators. Summary measures for the sub-groups (mean, standard deviation and 95% confidence interval for mean) were calculated on the log scales and then back-transformed (Table 2).
Diagnostic accuracy of examinations carried out by the two groups was assessed by identifying all patients with cancers confirmed by endoscopy or surgery in the population examined during 2000, and checking radiologists' reports for those patients to determine (i) accuracy of the report and (ii) whether the patient had been examined by a radiographer or radiologist. Audit of colorectal cancer demonstration rate was chosen as a measure of diagnostic accuracy as it is easily measured, is of clinical importance and is in line with the clinical effectiveness audit recommendations of the Royal College of Radiologists [3].
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Results
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Mean DAP values, with 95% confidence intervals, for the two groups were 9.8 Gycm2 (9.4–10.3 Gycm2) for radiographers and 10.7 Gycm2 (10.2–11.1 Gycm2) for radiologists. Corresponding median values were 9.7 Gycm2 and 10.7 Gycm2 for radiographers and radiologists, respectively. Under the original protocol, significant differences in DAP were observed between operator types, with an elevated DAP for radiographers when compared with radiologists. Under the revised protocol, this disparity in DAP has been removed. As might be expected the group median DAP for both staff groups was significantly reduced from the 1996 values of 22.6 Gycm2 for radiographers and 18.6 Gycm2 for radiologists. In the data for 1996 there were significant differences in DAP between individuals within both staff groups. In 2000, these differences persisted within the radiologist group, but were not observed in the radiographer group. Data for individual operators during 2000 are shown in box plots in Figure 2 and in Table 3.
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Figure 2. Dose–area product (DAP) by operator. Operators 1–7 are consultant radiologists and operators 8–11 are radiographers.
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A single overcouch radiograph was taken on only four occasions; three times by registrars and once by a consultant. This very low incidence (0.4%) of overcouch tube use supports our assertion that the requirement for radiographs is now obsolete except in extremely rare circumstances. Registrar radiographs were possibly owing to an initial reluctance to abandon a practice learnt elsewhere. The reason for the one consultant radiograph was not recorded.
Diagnostic accuracy of the examinations does not appear to be adversely affected when examinations are conducted by radiographers. These results are summarized in Table 4. Out of a total of four patients with confirmed colorectal cancer, all of whom underwent barium enema examinations in 2000, no cancers were missed.
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Discussion
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Under our original protocol for radiographer enemas, total DAP, and therefore patient dose, was significantly higher for barium enema examinations by radiographers compared with examinations by consultant radiologists, owing to the requirement placed on radiographers to take a series of plain radiographs for reporting purposes. In this study we have demonstrated that when a radiographer examination is undertaken according to our revised protocol, the disparity in dose between the two staff groups is removed. The reduction in DAP from 22.6 Gycm2 to 9.8 Gycm2 for radiographers can largely be attributed to removal of the requirement for additional radiographs for the reporting radiologist.
Overall numbers of barium enemas are lower than those previously reported following the introduction of a rectal bleeding clinic and the use of CT with oral contrast or CT pneumocolon, according to clinical need. Of the remaining patients destined for barium enema, although the more difficult cases were pre-selected for radiologist examination, we previously reported that we were unable to demonstrate any influence of patient selection bias on patient dose. Further, given that more of the older, and potentially more difficult, group of patients are now examined by CT, the proportion of difficult examinations in the radiologist group is likely to be lower than before.
Diagnostic accuracy, as measured by detection and incidence of colorectal cancer, was not compromized. Although follow-up for our patient cohort is acknowledged to be short, the practice of reporting from digital films has been in place for radiologist enemas since the installation of the digital screening room in 1994. Hence our experience with digital spot film reporting supports the findings of our short-term follow-up. Diagnostic accuracy of radiographer enemas has been confirmed elsewhere for follow-up periods of 2 years and 5 years [4, 5]. Also it has been shown by Mannion et al [6], using the more sensitive indicator of polyp detection, that diagnostic accuracy is not compromized when barium enemas are conducted by radiographers.
There was also a significant reduction (approximately 40%) in DAP delivered by radiologists between the years 1996 and 2000, which is again largely attributable to the fact that radiologists had likewise abandoned the practice of taking plain radiographs. Other factors contributing to overall reduction in group DAP values in both staff groups were alterations in technique regarding positioning of the explorator before screening at the start of the examination, removal of the grid whilst screening in the barium (reducing DAP by an estimated 2–3 Gycm2), and greater awareness and use of collimation.
There were highly significant differences in DAP between some individuals for radiologists (p<0.01), but not for radiographers. The lowest DAP readings, which were achieved by Radiologist 3, were principally owing to use of a technique that pays close attention to collimation. These factors indicate that there may be scope for alteration in technique for some individual operators.
It has been shown that an approximate estimate of effective dose to the patient can be derived using a conversion factor of around 0.15 mSv Gy-1cm2 for the undercouch component of a barium enema examination [7, 8]. Therefore, using mean values the effective dose to a patient from a barium enema study at this hospital is now approximately 1.5 mSv for a radiographer-based study and 1.6 mSv for a radiologist-based study. For comparison, using the original protocol, the approximate effective dose associated with a radiographer examination was 3.1 mSv, and 2.3 mSv for a radiologist examination.
Approximately 250 patients per year will undergo barium enema examination in line with the revised protocol by a radiographer in our hospital. As individual patient dose has been halved, this represents a collective effective dose saving of approximately 0.4 man Sv per year, in addition to the dose saving of 0.4 man Sv achieved by radiologists (based on 0.7 mSv saved per patient and approximately 550 patients being examined per year with the revised protocol.
To summarize, by using a revised clinical protocol for barium enema examinations in which a series of digital spot films replaces the radiographs taken for reporting purposes, radiographers worked as consistently and with the same diagnostic yield as consultant radiologists. Furthermore, the revised protocol has enabled both staff groups to significantly reduce patient dose.
Received for publication January 2, 2002.
Revision received April 16, 2002.
Accepted for publication May 3, 2002.
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References
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- Connolly DJ, Traill ZC, Reid HS, Copley SJ, Nolan DJ. The double contrast barium enema: a retrospective single centre audit of the detection of colorectal carcinomas. Clin Radiol 2002;57:29–32.[Medline]
- Law RL, Longstaffe AJ, Slack N. A retrospective 5-year study on the accuracy of the barium enema examination performed by radiographers. Clin Radiol 1999;54:80–4.[Medline]
- Mannion AJ, Bewell J, Langan C, Robertson M, Chapman AH. A Barium enema training programme for radiographers: a pilot study. Clin Radiol 1995;50:715–9.[Medline]
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Abstract
Introduction
) and radiographers (
).