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British Journal of Radiology (2004) 77, 864-868
© 2004 British Institute of Radiology
doi: 10.1259/bjr/99143061
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A review of factors affecting patient doses for barium enemas and meals

C J Martin, PhD, FIPEM, FIOP

Health Physics, Department of Clinical Physics & Bio-Engineering, West House, Gartnavel Royal Hospital, Glasgow G12 0XH, UK


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 Conclusions
 References
 
A study of patient doses for barium enema and meal examinations has been carried out for hospitals in the West of Scotland to assess the impact of dose reduction facilities on new X-ray equipment. Dose–area product (DAP) information has been collected on examinations for groups of patients at 20 hospitals and results reviewed together with data on equipment performance measurements. Median DAPs for barium enemas and meals were 15.7 Gy cm2 and 4.8 Gy cm2, respectively, and effective doses estimated from the results are 3.5±0.7 mSv and 1.5±0.5 mSv, respectively. These doses are lower than those reported in earlier studies and in previous surveys in the West of Scotland. The reduction in dose is linked primarily to the low dose facilities available on newer X-ray equipment, such as low dose pulsed fluoroscopy, digital imaging facilities and use of copper filtration. Use of the image intensifier for decubitus images on C-arm units employed for barium enemas also gives a significantly lower dose. Equipment with copper filtration had the lowest doses. The reduction in effective dose will be significantly less than the reduction in DAP for units in which a copper filter is included and the adoption of lower diagnostic reference levels is proposed for units with this facility. It is important that the operators are aware of the low dose imaging options on their equipment in order that techniques can be fully optimized.


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 Conclusions
 References
 
Barium examinations of the gastrointestinal system make up about 16% of the collective dose from radiology examinations in the UK [1]. Periodic review of the techniques used and the doses received by patients has allowed the consequences of developments in equipment and practices to be evaluated [2–9]. The present review was undertaken to assess the impact of dose reduction facilities incorporated into fluoroscopic X-ray equipment in the last 5 years.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 Conclusions
 References
 
A study was undertaken of doses for barium enemas performed in 20 hospitals and for barium meals in eight hospitals in the West and Borders of Scotland, as part of a triennial survey programme. Information was recorded on patient weight, screening time, numbers of images and dose–area product (DAP) for groups of between 10 and 50 procedures. Mean results were determined for each hospital from data for patients with weights between 50 kg and 90 kg, with mean weights of 70±5 kg. Questionnaires were completed, giving the fluoroscopic dose settings, pulsing regimens and imaging options most frequently used for barium enemas, together with exposure factors for decubitus films. Information was also collected on the proportion of barium enema examinations performed by radiographers. X-ray equipment performance tests and DAP meter calibrations are carried out annually using Keithley Triad systems, with calibrations traceable to a national standard. The tests include measurements of phantom entrance surface dose (ESD) rate for fluoroscopy and ESD for fluorographic imaging options, made with an ionization chamber placed on 150 mm, 200 mm and 250 mm thick water phantoms for a wide range of settings [10]. The degree of association between mean DAPs for each hospital and equipment performance and operator technique factors, which could be directly related to dose, was examined by determining the correlation coefficients. Comparisons were also made with a study of barium enema doses carried out for 11 of the same hospitals in 1994. Calculations of relative ESDs from X-ray beams of different quality were made using X-ray spectra software [11] with simulations designed to give similar doses at the image receptor after passage through 200 mm of soft tissue. ESD to effective dose conversion coefficients derived for pelvis radiographs from Monte Carlo software [12] were applied in order to assess relative effective doses with different tube potential and filtration options. This software was also used to compare ESD with effective dose conversion coefficients with and without additional copper filtration.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 Conclusions
 References
 
Mean DAP results for barium enemas at each hospital are displayed in Figure 1Go with the component from decubitus images indicated, together with other views taken with a separate X-ray tube. Mean DAP results for barium meals are shown in Figure 2Go. The median DAP for barium enemas for all the hospitals in the study was 15.7 Gy cm2 (range 4.4–30.4 Gy cm2), of which 4.1 Gy cm2 (range 0.9–10.5 Gy cm2) was for decubitus images, while that for barium meals was 4.8 Gy cm2 (range 2.0–13.7 Gy cm2). The median screening times were 1.9 min (range 1.1–4.0 min) for barium enemas and 2.2 min (range 1.1–2.8 min) for barium meals, and the median total numbers of images recorded were 12.2 (range 4.1–23.3) for barium enemas and 11.8 (range 5.9–24.5) for barium meals. Detailed data on equipment and technique factors for barium enemas performed in individual hospitals are given in Table 1Go. DAP values on newer equipment were less, because of the lower fluoroscopic patient ESD rates, options for pulsed fluoroscopy and lower dose digital imaging facilities with the newer equipment, rather than any significant increase in the dose rates with the age of the equipment. Among the 14 units over 5 years old, the increase in fluoroscopic image intensifier dose rate since installation was less than 10% for eight units, 10–20% for three units and 20–30% for the remaining three units. The correlations between DAPs and equipment related dose factors (DAP correlation coefficients: patient entrance dose rate 0.51, patient entrance dose per image 0.68) were higher than with operator technique factors (DAP correlation coefficients: screening time 0.43, number of images 0.37). Results for barium enemas in 11 hospitals were compared with data for the same hospitals from a survey in 1994. The median DAP for the 1994 survey was 26 Gy cm2 (range 9.3–48.9 Gy cm2) compared with 16.3 Gy cm2 (range 4.3–30.4 Gy cm2) for the same 11 hospitals in the present survey. However, median screening times were within 1% in the two studies and the median number of images taken was significantly less in the 1994 study (9 compared with 13.4). New X-ray equipment had been installed in nine of the 11 hospitals in the intervening period.



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  		Figure 1. Distribution of dose–area products (DAPs) for barium enemas in 20 hospitals in the West of Scotland with data recorded in Table 1Go in ascending order of recorded DAP. The components from fluoroscopy and fluorography with the undercouch X-ray tube, and for decubitus imaging are included separately. For units A and G where decubitus images were recorded using the image intensifier and the same X-ray tube as the rest of the examination, an estimate has been made of the component for decubitus images.

 


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  		Figure 2. Distribution of dose–area products (DAPs) for barium meals in eight hospitals in the West of Scotland for groups of between 11 and 30 patients.

 

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  		Table 1. Mean data for barium enema examinations studied and information on equipment options employed

 
The survey of practices in the West of Scotland showed that about 54% of barium enemas were performed by radiographers. The proportions of examinations undertaken by radiographers in different hospitals are summarized in Table 2Go. Barium enemas in hospitals where there were less than 500 examinations per year were all performed by one group, usually radiologists, while in hospitals with larger numbers, combinations of radiologists and radiographers or all radiographers were used. The median DAP for the fluoroscopy tube for hospitals where radiographers performed the majority of examinations was 8.3 Gy cm2 (range 1.9–14.6 Gy cm2) as compared with 10.1 Gy cm2 (range 4.4–26.8 Gy cm2) for hospitals where radiologists performed the majority. The screening times for hospitals where radiographers performed more examinations were significantly shorter with a median time of 1.7 min (range 1.1–2.6 min) compared with 2.5 min (range 2.1–12.7 min) for hospitals where the majority were performed by radiologists. The numbers of images recorded were similar with a median number of 9.5 (range 5.5–12.2) in the hospitals using more radiographers and 10.1 (range 2.1–12.7) in those using more radiologists. C-arm units were excluded from this analysis because of the larger numbers of images recorded, which included a number of decubitus images (see discussion). However, these values are influenced by radiologists performing all the examinations in several hospitals with older units and by the involvement of radiologists in larger teaching hospitals, where trainees carry out examinations under supervision.


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  		Table 2. Performance of barium enema examinations by radiographers

 

   Discussion
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 Abstract
 Introduction
 Methods
 Results
 Discussion
Conclusions
 References
 
All but one of the results from this study were below the local diagnostic reference levels (DRLs) of 13 Gy cm2 for meals and 31 Gy cm2 for enemas, based on national recommendations from the National Radiological Protection Board [3]. The unit which gave a dose above the DRL is now no longer in use. Factors contributing to larger doses were higher fluoroscopic entrance dose rates (units K, L and R), higher dose rates for imaging with the undercouch tube (units R, S and T), longer screening times on older units (M, P and T) and the lack of any fluorographic imaging facility (unit R). Doses for decubitus and other films were also comparatively high in some departments (E, N, Q and S). These areas were highlighted for attention in reports to individual hospitals.

The mean DAP for decubitus films for the 13 hospitals using film/screen combinations was 5.6±3.0 Gy cm2, which was slightly greater than the mean of 4.6±2.4 Gy cm2 for the five hospitals using computed radiography (CR), while the median DAPs for film and CR were similar at 4.26 Gy cm2 and 4.28 Gy cm2, respectively. This was because a few hospitals using film had relatively high DAPs. C-arm systems were employed in hospitals A and G and the decubitus images were recorded using the image intensifier (Table 1Go). Unit A, which had the lowest DAP of all, was installed 2 years before this study, while unit G had the second lowest DAP among units over 6 years old. Usually the whole of the colon could not be recorded on one image with the intensifiers, so four decubitus images, and occasionally eight, were taken instead of two. As a result larger numbers of images were recorded with these two units (Table 1Go). Observations of a few examinations at hospital A indicated that the DAPs for the decubitus images were 0.7–1 Gy cm2, which were considerably lower than those for radiographs recorded either with film or CR. This made up 15–25% of the examination DAP, of which about 60% was from positioning under fluoroscopic control. An additional advantage of C-arm units was a shortening of examination times, because the patient did not have to be moved to another location for the decubitus images. The disadvantage of a narrower patient couch was not considered to present a major problem.

Four units (A, B, C and E) incorporated 0.2 mm thick copper filters into the fluoroscopy tube and these gave among the lowest DAP values (Figures 1 and 2GoGo). Hardening of the beam with copper filters will reduce the DAP more than the effective dose. Introduction of 0.2 mm copper filters into 80–100 kVp X-ray beams, filtered by 2.5–3 mm of aluminium, will reduce the DAP and ESD by 44–50%, but the effective dose by only 12–22%. The reduction in effective dose when a copper filter is used is lower for posteroanterior (PA) than for anteroposterior (AP) projections because radiosensitive organs such as the colon lie closer to the anterior surface. Thus the reduction in DAP results for units with copper filtration cannot be linked directly to the reduction in effective dose. ESD to effective dose conversion coefficients for adult pelvis projections have been derived using Monte Carlo software [12] and ratios of coefficients for units with and without additional 0.2 mm copper filters are given in Table 3Go. Relative values for conversion coefficients derived for similar projections for 15 year olds were within 1–6% of these values [13]. Multiplication of the DAP by a factor of 1.6 would give an indication of the relative magnitudes of the effective doses for examinations where the PA projections were predominant for units with and without an additional 0.2 mm copper filter. The effective doses for these units are lower, but differences from other units are less dramatic than the low DAP results suggest.


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  		Table 3. Ratio of conversion coefficient (effective dose/entrance surface dose) with a 0.2 mm copper filter divided by the conversion coefficient without copper filtration [12]

 
The West of Scotland has adopted a policy of applying the same DRLs for all hospitals. Since DAP results for individual hospitals extended to close to the local DRLs, these were not revised at this time. However, a reduction of 20% would only exclude one unit for barium meals and one for barium enemas and all units less than 8 years old recorded mean DAPs less than 50% of the DRLs. Since the conversion coefficients between effective dose and DAP are significantly greater for X-ray beams filtered by copper, it may be appropriate to adopt local DRLs which are lower by a factor of 1.6 for units which incorporate a 0.2 mm copper filter, say 8 Gy cm2 and 20 Gy cm2 for barium meals and barium enemas, respectively.

Effective doses
The DAP values for barium procedures in the UK have continued to fall and so the accepted values for effective dose (2.5 mSv for barium meals and 7.2 mSv for barium enemas [2]) may no longer be representative of UK practice. Conversion coefficients to enable effective doses to be derived depend on the radiological projections chosen as well as tube potential for each part of the procedure. The studies of barium meal examinations that have been performed give values for conversion coefficient between 0.175 mSv Gy–1 cm–2 and 0.205 mSv Gy–1 cm–2 [4, 14, 15] and a factor of 0.2 mSv Gy–1 cm–2 is recommended [14]. A factor of 0.2 mSv Gy–1 cm–2 was therefore applied to the DAP results from individual hospitals, with an additional factor of 1.6 incorporated for units with copper filtration, as described above. This gave a mean value for effective dose of 1.5 mSv for barium meals with a range of 0.7–2.7 mSv.

A study carried out previously by the author in five hospitals established conversion coefficients for the undercouch and decibitus components of a barium enema, as a function of tube potential [4]. However, other studies have given a range of conversion coefficients for the whole examination from 0.15 to 0.3 [14–18]. The range is linked partly to the different projections and their contributions to the DAP and partly to the tube potentials used. Mean values for coefficients from the various studies are plotted against tube potential in Figure 3Go. An adjustment to a 70 kg individual was used where a weight-dependent factor was included [18]. Two curves for the conversion factor which are close to the limits of the range for the coefficients are also plotted; one from the author's earlier study [4], assuming that one-third of the DAP results from decubitus films, and the second for PA pelvis [19] to represent the PA projections within a barium enema. Effective doses were calculated for the fluoroscopy tube using both these relationships. The coefficients chosen were linked to the tube potential selected by the fluoroscopy autodose rate control for a 250 mm thick water phantom, as tube potentials selected during examinations had not been recorded. An additional factor of 1.6 was again applied to allow for copper filtration. Effective doses for the decubitus images were derived separately for the 18 units where a second X-ray tube was used. In each case the mean coefficient for pelvis AP and PA projections at the tube potential was used [14, 19]. The two methods gave mean effective doses of 2.8 mSv (range 0.7–4.0 mSv) and 4.2 mSv (range 1.5–7.2 mSv). The mean effective dose/DAP coefficients for the whole examination for the two methods were 0.19 mSv Gy–1 cm–2 and 0.27 mSv Gy–1 cm–2. A realistic estimate of the mean effective dose for barium enemas from this study is therefore considered to be 3.5±0.7 mSv.



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  		Figure 3. Plot of mean values for dose–area product (DAP) to effective dose (ED) conversion factors derived from different studies; Hart and Wall 1994 [14] x , Gelijns et al 1997 [16] {square}, Ruiz-Cruces et al 2000 [15] +, Kemerink et al 2001 [17] {triangleup}, Lampinen and Rannikko 1999 [18] {diamondsuit}, together with factors related to tube potential from Martin and Hunter 1994 [4] (solid line), and for a posteroanterior (PA) pelvis projection from Hart et al 1996 [13] (dashed line).

 
In order that doses for fluoroscopic examinations are kept to a minimum, it is important that X-ray equipment includes appropriate dose saving facilities and that requirements are included in specifications for new equipment. It is also important that operators are aware of the dose characteristics for the options available on their equipment. When new equipment is installed, techniques should be optimized in order to ensure that the necessary diagnostic information is obtained with the minimum radiation dose. Decisions should be made about which views are necessary and the level of image quality required [20]. Low dose techniques should be used whenever the image quality is acceptable and diagnosis is not compromised. Different options may be appropriate for different parts of an examination. For example, with pulsed fluoroscopy, the rate of pulsing might be kept at 1 pulse s–1 during some phases of an examination and increased to 3 pulse s–1 or 7.5 pulse s–1 when required. For imaging, lower dose fluoroscopy "frame grabs" may be used during parts of examinations such as the filling phase in barium enemas. Physicists involved in testing the equipment should be able to advise on the dose consequences of the different options, so close collaboration between radiologists, radiographers and physicists is important in achieving optimization. Finally, techniques should be reviewed periodically to determine whether further improvements can be made.


   Conclusions
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conclusions
References
 
Results of a patient dose survey have shown that doses for barium procedures are continuing to decrease. The mean effective dose for barium meals was estimated to be 1.5±0.5 mSv and that for barium enemas 3.5±0.7 mSv. The reduction is linked to the low dose facilities available on newer equipment. Decubitus films contribute a substantial proportion of the dose for barium enema examinations and the ability to use the image intensifier in C-arm units gives a substantial dose advantage. Copper filtration is significant in lowering the DAP, but can give a false impression of the reduction in effective dose. The awareness of operators about the dose consequences of options available on their equipment is important in ensuring that full optimization is achieved.


   Acknowledgments
 
The author would like to thank all Superintendent Radiographers and Radiographers who supplied information to enable the study to be undertaken. He would also like to thank Mr R Corrigall and Mr A Aitken for analysis of the dose data and technical staff and physicists within Health Physics for carrying out the performance tests.

Received for publication November 28, 2003. Revision received May 19, 2004. Accepted for publication June 1, 2004.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conclusions
 References
 

  1. United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and effects of ionising radiation. Volume I Sources. United Nations: New York, 2000.
  2. Hart D, Hillier MV, Wall BF, Shrimpton PC. Doses to patients from medical X-ray examinations in the UK: 1995 Review. NRPB – R289 National Radiological Protection Board. Chilton: NRPB, 1996.
  3. 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. Chilton: NRPB, 2002.
  4. Martin CJ, Hunter S. Reduction of patient doses from barium meal and barium enema examinations through changes in equipment factors. Br J Radiol 1994;67:1196–205.[Abstract/Free Full Text]
  5. Broadhead DA, Chapple C-L, Faulkner K. The impact of digital imaging on patient doses during barium studies. Br J Radiol 1995;68:992–6.[Abstract/Free Full Text]
  6. Warren-Forward HM, Haddaway MJ, Temperton DH, et al. Dose-area product readings for fluoroscopy and plain film examinations, including an analysis of the source of variation for barium enema examinations. Br J Radiol 1998;71:961–7.[Abstract]
  7. Hetherington J, Chapple CL, Rawlings DJ. Radiation dose and diagnosticity of barium enema examinations by radiographers and radiologists: a comparative study. Br J Radiol 1998;71:1219–21.[Medline]
  8. Crawley MT, Boothe A. Reducing dose at barium enema: radiographers do it digitally. Br J Radiol 2002;75:652–6.[Abstract/Free Full Text]
  9. Carroll EM, Brennan PC. Radiation doses for barium enema and barium meal examinations in Ireland: potential diagnostic reference levels. Br J Radiol 2003;76:393–7.[Abstract/Free Full Text]
  10. Martin CJ, Sutton DG, Workman A, Shaw AJ, Temperton D. Protocol for measurement of patient entrance surface dose rates for fluoroscopic X-ray equipment. Br J Radiol 1998;71:1283–7.[Abstract]
  11. Institute of Physics and Engineering in Medicine. Catalogue of Diagnostic X-ray Spectra and other Data. IPEM Report No.78. IPEM:York, 1997.
  12. Tapiovaara M, Lakkisto M, Servomaa A. PCXMC – A PC-based Monte Carlo program for calculating patient doses in medical examinations, Finnish Centre for Radiation Protection and nuclear Safety (STUK), Helsinki, 1997.
  13. Hart D, Jones DG, Wall BF. Coefficients for estimating effective doses from paediatric examinations. NRPB – R279 National Radiological Protection Board. Chilton: NRPB, 1996.
  14. Hart D, Wall BF. Estimation of effective dose from dose-area product measurements for barium meals and barium enemas. Br J Radiol 1994;67:485–9.[Abstract/Free Full Text]
  15. Ruiz-Cruces R, Ruiz F, Perez-Martinez M, et al. Patient dose from barium procedures. Br J Radiol 2000;73:742–51.
  16. Geleijns J, Broerse JJ, Chandie-Shaw MP, et al. Patient dose due to colon examination: dose assessment and results from a survey in the Netherlands. Radiology 1996;204:553–9.
  17. Kemerink GJ, Borstlap ACW, Frantzen MJ, Schultz FW, Zoetelief J, van Engelshoven JMA. Patient and occupational dosimetry in double contrast barium enema examinations. Br J Radiol 2001;74:420–8.
  18. Lampinen JS, Rannikko S. Patient specific doses used to analyse the optimum dose delivery in barium enema examinations. Br J Radiol 1999;72:1185–95.[Abstract]
  19. Hart D, Jones DG, Wall BF. Estimation of effective dose in diagnostic radiology from entrance surface dose and dose-area product measurements. NRPB – R262 National Radiological Protection Board. Chilton: NRPB, 1994.
  20. Corbett RH. The influence of radiologist's technique on patient dose in barium studies. Proc 10th Int Cong IRPA, 2000.



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