Audit in action: significant reduction of double-contrast barium enema screening time with no loss of examination quality

Radiation dose measurement in gastrointestinal studies

Barium studies investigations (barium swallow, barium meal and barium enema) are the basic routine radiological examination, where barium sulphate suspension is introduced to enhance image contrast of gastrointestinal tracts. The aim of this study was to quantify the patients' radiation doses during barium studies and to estimate the organ equivalent dose and effective dose with those procedures. A total of 33 investigations of barium studies were measured by using thermoluminescence dosemeters. The result showed that the patient entrance surface doses were 12.6 ± 10, 44.5 ± 49 and 35.7 ± 50 mGy for barium swallow, barium meal, follow through and enema, respectively. Effective doses were 0.2, 0.35 and 1.4 mSv per procedure for barium swallow, meal and enema respectively. Radiation doses were comparable with the previous studies. A written protocol for each procedure will reduce the inter-operator variations and will help to reduce unnecessary exposure.

Barium enema: use of increased copper filtration to optimize dose and image quality

The purpose of this study was to determine and validate the optimum copper filtration for adult double contrast barium enema examinations. Entrance surface dose rates to polymethyl methacrylate slabs and corresponding image intensifier input kermas, were measured for various added copper filters. Image contrast was assessed using a Leeds TO.10 test object. Copper filter thickness of 0.3 mm was chosen, as this reduced entrance surface dose rate by 56%, without substantially degrading image contrast due to kV and mA saturation. 20 sets of clinical films taken with each of 0.3 mm copper, 0.1 mm copper and no copper were reviewed following randomization, by a specialist gastrointestinal radiologist. Each set of digital spot and conventional films was allocated a score for each of three regions of the bowel, on a scale of 0-3 for perceived barium coating. The Kruskal-Wallis test showed no significant difference in perceived coating between the three groups (Digital spot: sigmoid colon p=0.207, splenic flexure p=0.103, hepatic flexure p=0.894. Screen-film: left colon p=0.803, right colon p=0.487, transverse colon p=0.905). All examinations but one were classified as diagnostic. The remaining one was classified indeterminate, due to poor distension of the colon. On adding 0.3 mm copper filtration, the mean dose-area product per examination was reduced by 57%, from 17.7 Gy cm(2) to 7.6 Gy cm(2). The estimated reduction in effective dose was 11%, from 3.0 mSv to 2.7 mSv. X-ray tube loading increased by 30%, but this caused no overheating with our local examination protocol and schedule. Additional filtration of 0.3 mm copper for adult double contrast barium enemas has now been implemented in routine clinical use at our hospital.

Patient and occupational dosimetry in double contrast barium enema examinations

A new and relatively simple method is presented to distribute total dose-area product (DAP) over a number of projections that model exposure during double contrast barium enema (DCBE) examinations. In addition, hitherto unavailable entrance and effective doses to the physician performing the DCBE examination have been determined. DAP, fluoroscopy time, number of images as well as some patient data were collected for 150 DCBE examinations. For a subset of 50 examinations, the distribution of DAP over 12 hypothetical but representative projections was estimated by measuring the entrance dose in the centre of each of these projections during the complete procedure. Effective dose to the patient was obtained using DAP to effective dose conversion coefficients calculated for each of the 12 projections. Exposure of the worker was quantified by measuring the entrance dose at the forehead, neck, arms, right hand and legs. The sex-averaged effective dose to the patient per examination was 6.4+/-2.1 mSv (mean+/-SD; n=50) and the corresponding DAP was 44+/-22 Gy cm(2). The effective dose to the worker per examination was 0.52 microGy (n=50), whereas the highest entrance dose of 30+/-25 microGy was found for the right arm. The proposed method for deriving the distribution of total DAP over a set of representative projections is much less time consuming than visual observation of patient exposure, whilst accuracy seems acceptable. Entrance and effective doses per examination for workers in DCBE examinations are very low. For a normal workload, doses remain far below the legally established dose limits.

Patient dose from barium procedures

The objective of this work was to estimate patient doses (dose-area product, organ dose, effective dose and entrance surface dose) for barium procedures. A total of 175 procedures, in 175 patients, for five different examination categories was analysed. Dose-area product was determined using a transmission ionization chamber. Organ dose and effective dose were assessed using a knowledge of the examination and the software. For all patients, the contribution of fluoroscopy to the total dose was greater than that from radiography. Dose-area product from double contrast barium enema, enteroclysis and intestinal tract procedures was higher than that obtained for the other procedures. The average effective dose was 1.04 mSv and 13.99 mSv for oesophageal tract and enteroclysis examinations, respectively. Entrance surface dose in the oesophageal tract was 16 mGy, 10 times lower than for the other four procedures. Patient dose reduction in barium procedures may be achieved by improved training of resident radiologists, senior radiologists and other specialists in radiation protection.

Patient specific doses used to analyse the optimum dose delivery in barium enema examinations

The exposure and geometrical data for 89 barium enema examination patients were recorded manually in five hospitals in Finland. From the recorded data, organ and primary exit doses as well as effective individual doses were calculated for each patient using the ODS-60 program, which is capable of adjusting the calculation phantom according to a patient's size and sex. The mean (and standard deviation, SD) and median effective individual doses for the patients were 9.3 (5.7) and 6.8 mSv, respectively. Conversion functions from dose-area product to relevant organ doses and to effective individual dose were presented as a function of patient sex and weight. Mean primary exit dose values were calculated for each exposure. These were used to compare a theoretically justified exposure control (EC) function with the function of the automatic exposure (rate) control, AEC (AERC), at different hospitals. According to the analysis of primary exit doses, the implementation of the EC was far from optimum. With EC function proposed in this study the SD of effective individual doses to patients could be lowered considerably.

Dose reduction in double contrast barium enema by use of low fluoroscopic current

Under standard conditions double contrast barium enema (DCBE) was carried out on a selected patient cohort using either standard (1.5 mA) or low (0.5 mA) fluoroscopic current. A statistically significant (p < or = 0.01) reduction in total dose was achieved by use of low screening current. This reduction was of the order of 40%. Fluoroscopic image quality was analysed both objectively and subjectively, and was found not to be significantly degraded when the lower current was used. On blinded evaluation all examinations were found to be of diagnostic quality. The use of low fluoroscopic current results in a reduction in patient dose, without compromising fluoroscopic image quality or diagnostic standard of the examination. Low fluoroscopic current technique has been adopted as the standard in our department.

Measurement of patient entrance surface dose rates for fluoroscopic x-ray units

Measurements of patient entrance surface dose rate provide valuable data for interpreting results from dose-area product studies on fluoroscopic x-ray equipment. Methods for measurement of entrance surface dose rate with backscatter and incident dose rate without backscatter have been investigated. Entrance surface dose rate is measured with an ionization chamber in contact with a tissue-equivalent phantom. Backscattered radiation contributes 27-45% to the measurement and is affected by field size and chamber position. Incident dose rate measured using a copper phantom provides an alternative approach. Consistent relationships between thicknesses of Perspex and copper giving similar incident dose rates under automatic gain control have been established for different tube potentials with and without a grid. This allows measurements of incident dose rate made using copper to be linked to corresponding thicknesses of tissue-equivalent material. Since only a few millimetres of copper are required, contributions from backscatter can be minimized and transport of phantoms is simplified. Incident dose can be related to dose-area product and entrance surface dose derived using backscatter factors. Such measurements play a valuable role in interpreting patient dose data and recommending options to reduce patient dose.

Reduction of patient doses from barium meal and barium enema examinations through changes in equipment factors

A study of patient doses for barium meal and barium enema examinations has been made for X-ray departments throughout Grampian Region. Dose-area products are substantially less than UK reference levels. Contributions from fluoroscopy and radiography varied significantly between different units, with fluoroscopy making up 35-92% of the mean doses for barium meals and 24-57% for barium enemas. Equipment related factors had a greater influence on patient doses than radiologists' techniques. The gain of the image intensifier and the exposure factors selected by the automatic exposure control (AEC) were the most important factors determining doses for fluoroscopy. Changes in kV/mA factors selected by the AEC have allowed reductions of 20-50% to be made in effective dose from fluoroscopy with some units. The method used for recording images was the major influence on radiographic doses. Digital spot images or fluorographic films taken from the intensifier gave only 10-20% of the dose with a film/screen system and are recommended where the image quality is satisfactory for the application. Changes in film/screen systems have given worthwhile reductions in radiographic doses. If all factors are optimized, mean doses for barium examinations could be reduced to 20% of current reference levels.

Estimation of effective dose from dose-area product measurements for barium meals and barium enemas

The International Commission on Radiological Protection has recommended the use of a new dose quantity "effective dose". The doses to 22 organs of the human body are required for a formal calculation of this quantity. This paper shows that a quick estimate of the effective dose received by a patient from a barium meal or a barium enema can be made by multiplying the measured dose-area product for the complete examination by an appropriate conversion coefficient. Despite the varied techniques used for barium examinations, such an estimate is unlikely to be in error by more than 25%.