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British Journal of Radiology (2003) 76, 393-397
© 2003 British Institute of Radiology
doi: 10.1259/bjr/13457134
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Full Paper

Radiation doses for barium enema and barium meal examinations in Ireland: potential diagnostic reference levels

E M Carroll, BSc, MSc and P C Brennan, PhD

School of Diagnostic Imaging, University College Dublin, St. Anthony's, Herbert Avenue, Dublin 4, Ireland

Correspondence: P C Brennan


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 Conclusions
 References
 
Wide variations in patient dose for the same examinations have been demonstrated by several studies throughout Europe. By investigating patient dose, variations can be acknowledged, causal agents sought and the necessary adjustments made. Diagnostic reference levels (DRLs) provide a framework with which dose levels from individual hospitals are compared, and when exceeded, corrective actions can be taken where appropriate. This study aimed to establish DRLs for barium enema and barium meal examinations in Ireland. Measurements were recorded using a dose–area product meter in 12 hospitals representing 33% of relevant hospitals. Results demonstrated wide mean hospital dose variation, by up to a factor of 7.8 and 4.2 for barium enema and barium meal examinations, respectively. Minimum and maximum individual patient dose values varied by a factor of 45 for barium enemas and 90 for barium meal examinations. Reasons for dose variations were complex, but major factors for both examinations were fluoroscopy time, secondary radiation grid type and level of filtration. Some examination-specific factors were also noted. DRLs, established using the quantity dose–area product, were calculated to be 47 Gy cm2 for barium enemas and 17 Gy cm2 for barium meal examinations. Although the DRL value for barium meals was the same as the reference value established in the UK for that examination in 1996, the barium enema DRL in this study was 45% higher than the relevant UK value.


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 Conclusions
 References
 
Many factors influence the level of radiation doses delivered to patients undergoing medical X-ray examinations [1–4]. These can be responsible for large dose variations within and between hospitals for standard sized patients undergoing the same examination [2, 3]. It is important to identify these factors, assess the level of contribution each makes to dose variations recorded and take corrective action in a cost-effective way. This can lead to standardized and optimized radiological procedures.

Diagnostic reference levels (DRLs), mandatory under European legislation [5], facilitate standardization and optimization. By establishing relevant DRLs, following dose surveys within a particular population, practices and equipment in departments that exceed these levels can be analysed and causal agents determined [5–7]. This can lead to swift and important reduction in patient doses not only in the hospitals with dose values above reference levels, but also in hospitals where less than optimum procedures have been identified. The dose-reducing potential of introducing regular patient dose surveys and making comparisons with DRLs has been shown by the National Radiological Protection Board (NRPB). In 1992 the NRPB published reference dose values for a number of common diagnostic X-ray examinations following a dose survey in the UK between 1983 and 1985 [6]. In a subsequent survey, published in 1996 [7], reductions in patient doses of up to 40% were evident, leading to collective dose savings of 4700 man sieverts per year in the UK and lower third quartile values in the patient dose distributions on which the DRLs were based (Table 1Go). The more recent NRPB report (2002) demonstrates doses up to 20% lower than the 1996 publication [8]. This suggests that the introduction of DRLs in Ireland could lead to reduced patient dose.


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  		Table 1. Reference dose levels established by the UK 1992 study and 1995 review published in 1996 [7]

 
In Ireland, following a Health Research Board funded study, DRLs were established for plain film examinations of the chest, abdomen, pelvis and lumbar spine [3]. In that study wide variation in mean hospital doses by up to a factor of 23 and individual patient dose variations of up to a factor of 75 were shown. Although reference levels 40% lower than those established 5–10 years earlier by the UK and the CEC were demonstrated in the Irish study, the same levels were 50% higher than more recent UK values [3, 7]. This highlights the need for each country to establish their own DRLs and update them regularly.

It should be acknowledged that when DRLs are being established, particular emphasis is given to those examinations which contribute significantly to the collective population dose [6, 9]. Barium enema and barium meal examinations are two such examinations, together responsible for up to 17% of the collective dose in the UK [10]. Although reference levels have been established in the UK and Europe for these examinations, they have yet to be established in Ireland [6, 7]. This study aims to address this deficiency by establishing DRLs for barium enemas and barium meals based on the third quartile values of dose–area product (DAP) measurements. Reasons for patient dose variation will be examined and discussed.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 Conclusions
 References
 
The Dosimetry Working Party of the UK Institute of Physical Sciences in Medicine (now the Institute for Physics and Engineering in Medicine) [6] established guidelines for patient dose measurements in diagnostic radiology in 1992. These guidelines have been used in this study. A list of all hospitals using fluoroscopy units was obtained through the Radiological Protection Institute of Ireland. The list included 47 hospitals throughout the Republic of Ireland, 36 of which could be considered for this study.

When attempting to establish national DRLs which are relevant to all hospitals in a country, it is important to sample as many hospitals as possible. Owing to the limited number of DAP meters available, measurements across all hospitals were not concurrent. The number of measurements within each hospital was therefore limited so that all data were obtained within a reasonable time period, facilitating realistic and relevant interhospital comparisons. A random sample of 12 hospitals was selected, representing 33% of the hospitals suitable for this study. This was felt to provide a strong sample size, comparable with the NRPB 1996 publication where 25% of the relevant UK hospitals were sampled [7]. All 12 hospitals were sent letters explaining the purpose of the study and requesting the department's approval. These letters were followed up 1 week later by a phone-call. All superintendent radiographers agreed to participate in the study. Once all 12 departments had agreed to take part in the study, ethical approval was sought. For hospitals without an ethics committee, approval was sought from the Chief Executive Officer or in some cases, from the radiology director.

The UK National Protocol for Patient Dose Measurements in Diagnostic Radiology [6] recommends a minimum of 10 adult patients per examination per hospital. These guidelines were followed for this study. Both sexes were included. The UK National Protocol [6] and the European Guidelines [9] recommend that the mean weight of the sample lies within ±5 kg of 70 kg and this guideline was followed in this work. Patients outside 70 kg±20 kg (50 kg–90 kg) were excluded from the study [6, 7, 9]. The examinations chosen for this study were barium enemas and barium meals.

A DAP meter was used to measure radiation dose throughout the investigation. Some hospitals had their own DAP meter and this was calibrated shortly before any measurements were taken [6]. Those hospitals without DAP meters had one installed by the authors (VacuDAP 2001, J M Dolan & Co. Limited, Dun Laoghaire, Dublin) which was calibrated before any measurements were recorded. A DAP meter is the recommended dosimeter for fluoroscopic examinations [1, 6, 11–13].

Radiographers were required to complete a form after each examination [6, 7]. Details recorded included grade of radiologist, patient's gender, height, weight, date of birth, method of recording images, number of images, average kVp and fluoroscopy time. Whether the patient had a failed colonoscopy examination prior to the barium enema was also recorded. A second form, providing details about equipment type, waveform, filtration, secondary radiation grid, X-ray couch, automatic exposure control and quality assurance programmes in operation was completed by the superintendent radiographer.

In a study of this nature, it is useful to identify key agents that are responsible for variation in patient dose. This facilitates corrective procedures so that high dose hospitals can reduce doses to or below reference levels. A stepwise regression method was used for this purpose and selected independent variables relating to procedural and technical factors as predictors for the dependent variable—radiation dose.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 Conclusions
 References
 
The DAP was recorded for a total of 281 patients in 12 hospitals (Tables 2Go and 3Go). Mean hospital DAP variation factors of 7.8 and 4.2 and individual patient DAP variation factors of 45 and 90 were noted for barium enemas and barium meals, respectively (Tables 2, Go3, Go4Go).


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  		Table 2. Minimum, mean and maximum dose–area product (DAP) values for barium enema examinations

 

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  		Table 3. Minimum, mean and maximum dose–area product (DAP) values for barium meal examinations

 

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  		Table 4. Minimum, mean and maximum dose–area product values of all individual patients for barium enema and barium meal examinations. (All figures have been rounded off to one decimal point)

 
For barium enemas a seven variable regression model was demonstrated as the best explanation of the variance in dose demonstrated. In decreasing importance these variables were fluoroscopic time, film number, level of filtration, grid material (fluoroscopic), grid ratio (radiographic), a failed colonoscopy previous to the barium examination and grid ratio (fluoroscopic). This model explained 70% of the barium enema dose variation. A four variable regression model best explained the variation in doses for barium meals. In decreasing order, the variables included in this model were fluoroscopic time, patient weight, grid ratio (fluoroscopic) and filtration and these accounted for 53% of the barium meal dose variation.

Proposed reference dose levels were established at the level of the third quartile of mean DAP values from all hospitals. This is in line with previous work [6] and allows direct comparison of this study's findings with data derived from other studies. The reference levels were shown to be 47 Gy cm2 for barium enema examinations (Figure 1Go) and 17 Gy cm2 for barium meal examinations (Figure 2Go).



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  		Figure 1. Mean dose–area product (DAP) values in Gy cm2 for all hospitals and the reference dose value (indicated by the horizontal line) for barium enema examinations.

 


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  		Figure 2. Mean dose–area product (DAP) values in Gy cm2 for all hospitals and reference dose level (indicated by the horizontal line) for barium meal examinations.

 

   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
Conclusions
 References
 
In this work, large individual patient dose variations were identified with variation factors of 45 and 90 for barium enema and barium meal examinations, respectively. Mean hospital dose values for this study differed by up to a factor of 7.8 and 4.2 for barium enema and barium meal examinations, respectively. The variation factors established in this study are typical of values established in other countries [1, 2, 4, 14].

As previously mentioned a minimum of 10 patients per examination for each department is recommended. Not all hospitals were able to comply. This was mostly due to the time restriction on the study and the lack of DAP meters available. It was felt that the maximum amount of time possible had been provided to each hospital and maximum data in the time-scale of this study had been collected. The authors stress that results for hospitals with patient numbers below the recommended NRPB level should be treated with an element of caution.

Due to the multifactoral causes of radiation dose variation, it is difficult to pinpoint specific causal agents. The stepwise regression analysis, however, demonstrated that fluoroscopy time variation was an important factor for both examinations. Individual screening times for this study varied from a factor of 14 for barium enema examinations to 31 for barium meal examinations. Examples of the time-dependent-dose relationship is often demonstrated when individual hospital data are analysed (Figures 3, 4GoGo). Hospital 4 demonstrated the lowest mean DAP values for both examinations and had the lowest mean screening time for barium meals and one of the lowest times for barium enema examinations, whilst a number of the hospitals with DAP values above the third quartile had some of the longest screening times, with hospital 8 for barium enemas being the exception. A screening time/dose relationship is well established in the literature [1, 2, 14].



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  		Figure 3. Mean hospital fluoroscopic time for barium enema examinations.

 


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  		Figure 4. Mean hospital fluoroscopy time for barium meal examinations.

 
The number of images was seen to be an important factor in the dose variation demonstrated for barium enema but not for barium meal examinations. This difference between examinations is most likely due to the number of radiographic projections taken after barium enemas, which does not usually happen with barium meal examinations. It is useful to note that some of the additional dose relating to the post-fluoroscopic images during the barium enema examination may be offset by using a lower ratio secondary radiation grid as this was shown to be a causal agent for some of the dose variation seen with this examination.

The type of secondary radiation grid used during fluoroscopy was also shown to be important for both examinations. Hospitals 10 and 11 (both digital hospitals) used carbon fibre material in the grid construction and although these hospitals had the highest grid ratios at 70:1 and 36:1, respectively, for the barium meal and enema examinations, doses for these hospitals are below the third quartile value. It was also of some concern to note that, although published recommendations on required values for filtration are clear [15], a number of hospitals appeared to be operating below appropriate levels.

A number of variables explored in this study were not identified by the stepwise regression as key factors responsible for dose variation. The absence of some are surprising, particularly the type of image acquisition system and the average energy of the beam. It must be emphasised that although only a limited number of factors were identified in the statistical analysis used in this study, other possible influences on radiation dose variation should not be ignored. In addition it is important to acknowledge that not all possible variables were included in this work and the influence of others such as grid factor, patient positioning, image quality and the use of double contrast techniques should be considered for future, similar investigations.

From the results of this study it is proposed to establish national DRLs for Ireland for barium enema examinations at 47 Gy cm2 and for barium meal examinations at 17 Gy cm2. These are considerably lower than the 1992 NRPB levels which lie at 60 Gy cm2 for barium enemas and 25 Gy cm2 for barium meal examinations [6]. When compared with the NRPB third quartile values of 1995 [7], although the barium meal reference dose level in this study at 17 Gy cm2 is very close to the NRPB figure, the barium enema reference dose level at 47 Gy cm2 is over 45% higher. This highlights the importance of individual countries establishing their own reference dose levels rather than relying on data gathered elsewhere. Although immediate investigations and corrective action must be taken for those hospitals with doses consistently above the DRL values, it is important that all departments do not view DRLs as optimum levels, but continually strive to reduce radiation dose whilst maintaining image quality. This study has attempted to identify important factors which may help departments and it is hoped that in a follow-up study in 3–5 years significant dose reductions will be evident in Ireland as was the case in the UK [7, 8].


   Conclusions
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conclusions
References
 
This study has demonstrated wide variation in radiation dose for barium enema and barium meal examinations in Ireland. Individual patient dose varied by factors of 45 and 90 and mean hospital dose varied by factors of 7.8 and 4.2 for barium enema and barium meal examinations, respectively.

Main factors contributing to patient dose variation for both examinations were fluoroscopic time, secondary radiation grid type and level of filtration with some examination-specific factors being noted.

DRLs were established at the level of the third quartile value resulting in the values 47 Gy cm2 for barium enemas and 17 Gy cm2 for barium meal examinations. Although the DRL value for barium meals was the same as the reference value established in the UK in 1996 for that examination, the barium enema DRL in this study was 45% higher than the relevant UK value highlighting the need for each European Union country to establish their own levels.


   Acknowledgments
 
The authors would like to take this opportunity to thank all the superintendent radiographers and radiographers involved in the study. Thanks are also due to Dr Michael Casey, Principal Medical Physicist, Professor Lee, Consultant Radiologist and Professor Leslie Daly, Epidemiologist and Statistician.


   Footnotes
 
This study was funded by the Irish Health Research Board. Back

Received for publication November 21, 2001. Revision received March 29, 2003. Accepted for publication April 8, 2003.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conclusions
 References
 

  1. Warren-Forward HM, Haddaway MJ, Temperton DH, McCall IW. Dose-area product readings for fluoroscopic and plain film examinations, including an analysis of the source of variation for barium enema examinations. Br J Radiol 1998;71:961–7.[Abstract]
  2. Contento G, Malisan MR, Padovani R, et al. A comparison of diagnostic radiology practice and patient exposure in Britain, France and Italy. Br J Radiol 1988;61:143–52.[Abstract]
  3. Johnston DA, Brennan PC. Reference dose levels for patients undergoing common diagnostic X-ray examinations in Irish hospitals. Br J Radiol 2000;73:396–402.[Abstract]
  4. Ng K-H, Rassiah P, Wang HB, et al. Doses to patients in routine X-ray examinations in Malaysia. Br J Radiol 1998;71:654–60.[Abstract]
  5. Council Directive 97/43/Euratom. Health protection of individuals against the dangers of ionizing radiation in relation to medical exposure, and repealing Directive 84/466/Euratom 16260EN. The European Commission, 1997.
  6. Institute of Physical Sciences in Medicine, National Radiological Protection Board and the College of Radiographers, National protocol for patient dose measurements in diagnostic radiology. Chilton, Didcot: NRPB 1992.
  7. Hart D, Hillier MC, Wall BF, Shrimpton PC, Bungay D. Doses to patients from medical X-ray examinations in the UK - 1995 Review. NRPB - R289/ National Radiological Protection Board, 1996.
  8. Hart D, Hillier MV, Wall BF. Doses to patients from medical X-Ray examinations in the UK: 2000 Review. NRPB – W14/ National Radiological Protection Board, 2002.
  9. CEC, European guidelines on quality criteria for diagnostic radiographic images. EUR 16260EN. The European Commission, 1996.
  10. National Radiological Protection Board, Radiation Exposure of the UK Population from Medical and Dental X-ray Examinations, NRPB-W4, National Radiological Protection Board, Oxon, 2002.
  11. Faulkner K, et al. An international intercomparison of dose-area product meters. Radiat Prot Dosim 1992;43:131–4.[Abstract]
  12. Faulkner K, Corbett RH. Reference doses and quality in medical imaging. Br J Radiol 1998;71:1001–2.[Medline]
  13. Wright DJ, Ramsdale ML. The use of national and locally set reference dose levels in a regional programme for dose reduction in diagnostic radiology. Radiat Prot Dosim 1998;80:193–207.
  14. Ruiz-Cruces R, Ruiz F, Perez-Martinez M, Lopez J, Tort Ausina I, Diez de los Rios A. Patient dose from barium procedures. Br J Radiol 2000;73:752–61.[Abstract]
  15. S.I. No. 250 of 1998. European Community (Radiological and Nuclear Medicine Installations) Regulations, 1998.



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