Technical note: potentially higher patient radiation doses using digital equipment for barium studies

Dose audit and evaluation of work practices during barium procedures using digital radiography techniques

Effective dose and organ doses during barium procedures performed using digital radiography machines were estimated and the related work practices were evaluated. Measured values of dose area product (DAP) were used for the calculation of effective doses. One hundred and thirty eight patients undergoing barium procedures were included in the study. The use of additional 0.2 mm copper filter during barium procedures effectively reduced patient doses. The effective dose during barium swallow procedure varied from 0.03 mSv to 3.5 mSv; during barium meal it varied from 0.18 mSv to 2.62 mSv; and during barium enema it varied from 0.56 mSv to 4.24 mSv. Dose auditing was done on the basis of patient doses, imaging techniques and image quality. Selection of optimized exposure factors imparted lower dose to patients during barium procedures.

Computed Tomographic Colonography (CTC): Possibilities and Limitations of Clinical Application in Colorectal Polyps and Cancer

Colorectal cancer is the second leading cause of cancer-related deaths in Europe and the United States. Most colorectal cancers develop from adenomatous polyps over a number of years. Early detection of polyps eliminates the risk of subsequent carcinomas.

Computed tomographic (CT) colonography is a diagnostic technique detecting colorectal neoplasms. With the introduction of multidetector-row computed tomography (MD-CT), CT colonography (CTC) has gained influence as a new diagnostic tool in early detection of colonic pathologies by acquiring volumetric CT data sets of the abdomen. This volumetric data is analyzed using CTC workstations, which provide an interactive display of 2D and 3D images of the colon. In several studies, CTC revealed a high accuracy (sensitivity/patient: 83–100% and specificity/patient: 93–100%) in detecting pathological colonic changes. Furthermore, CTC is an excellent diagnostic technique for the evaluation of patients with incomplete conventional colonoscopy and allows the assessment of extracolonic abdominal and pelvic organs.

In this article, the status of CT colonography as a method of detecting colonic polyps and colorectal carcinomas using single- and multidetector-row CT will be reviewed.

The effect of equipment set up on patient radiation dose in conventional and CT angiography of the renal arteries

Patient radiation dose in angiography of the renal arteries was assessed and optimized after installing new radiological equipment. In three separate studies (n=50, 25 and 20) patient exposure was monitored in detail. For the first study default factory settings were used, for the second the number of digital subtraction angiography (DSA) images was halved and the X-ray beam filtering during fluoroscopy was increased, and for the third study filtering during DSA was increased as well. Standard projections were derived and used in Monte Carlo simulations to derive dose conversion coefficients to calculate effective dose from the dose-area product (DAP). Dose conversion coefficients were also calculated for CT angiography (CTA). Using default factory settings on the new angiography system, DAP, number of images and effective dose were much higher than on the replaced unit. For the studies given above, DAP was reduced from 144 Gy cm(2) to 65 Gy cm(2) to 32 Gy cm(2), and effective dose from 22 mSv to 11 mSv to 9.1 mSv, respectively. Effective dose due to CTA was 5.2 mSv. It is concluded that modern angiography systems, resulting in high customer satisfaction, may readily cause much higher patient exposure than older systems. These doses may also be much higher than necessary. Optimization before putting such systems into use is absolutely essential. Internationally accepted recommendations for image quality and technique factors in angiography would be of great help.

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.

Entrance skin dose estimates derived from dose-area product measurements in interventional radiological procedures

Patient skin doses resulting from interventional radiological procedures have the potential to exceed threshold doses for deterministic effects such as erythema and epilation. If the irradiation geometry is known, the entrance skin dose can be estimated from the measured dose-area product. For each of 10 non-coronary interventional procedures, a nominal geometry was identified. From a previous survey of patient dose-area products, the entrance skin doses were estimated under the assumption that all procedures were performed with the nominal geometry specific to it. An analysis of the uncertainties in these doses caused by realistic deviations from the nominal geometry was also performed and it was shown that the estimated entrance skin dose values are at least to within 40%, and generally to within about 30%, of those actually received. For example, the median estimated entrance skin doses for the posteroanterior and lateral projections of cerebral angiography were 100 and 110 mGy. respectively, and for hepatic angiography 425 mGy. The largest entrance skin dose estimate for a single projection was for the angiography component of a CT arterial portography procedure at 670 mGy. Comparisons between entrance skin dose estimates obtained from this study are made with data from other interventional radiology patient dose surveys.

Dose-area product readings for fluoroscopic and plain film examinations, including an analysis of the source of variation for barium enema examinations

This paper contains the results of an investigation undertaken between 1994 and 1996 using dose-area product (DAP) meters for monitoring radiation doses from six types of simple examinations and seven types of complex examinations. Mean hospital DAP levels have been compared with National Reference Levels (NRL), with most departments producing levels lower than NRLs. DAP readings have allowed the proposal of provisional Reference Levels (RL) to be set for simple and complex examinations. The results were also compared with recently published data from the National Radiological Protection Board (NRPB), highlighting those hospitals which need to make changes in radiographic technique. The study of DAP reference doses also confirms that dose levels for complex investigations are clearly related to technique, in terms of screening time and number of films. Although the use of increased screening tube kilovoltage may be relevant, the overall effect is small. The results suggest that there is still a need to optimize the protocols for these examinations. The use of digital equipment has been shown to have a complex effect on dose, particularly in the case of investigations involving both films and fluoroscopy.

A study of patient radiation doses in interventional radiological procedures

Patient radiation doses received during interventional radiological procedures can be significant. To aid in the establishment of reference dose levels, a patient dose survey has been conducted of such procedures. A total of 288 non-coronary procedures (177 classified as diagnostic and 111 as therapeutic) were accrued into the study. For each procedure, the fluoroscopy screening time and the fluoroscopic and digital radiographic dose-area products were recorded in a computer database. For example, median dose-area product values (due to fluoroscopy and digital radiography combined) of 24.2, 27.9, 69.6 and 74.7 Gy cm2 were obtained for nephrostomy, biliary stent removal/insertion, cerebral angiography and percutaneous transhepatic cholangiography procedures. While the effective dose is not an accurate measure of patient risk, it is convenient for comparing the radiological risks associated with various procedures. Effective doses were estimated from the total dose-area products. The respective median estimated effective dose values for the four procedures noted above were 3.9, 4.5, 7.0 and 12.0 mSv. While an infrequently performed procedure at this institution (n = 4 during this survey), the transjugular intrahepatic portosystemic shunt (TIPS) procedure had the greatest median dose-area product and effective dose values: 347 Gy cm2 and 55.5 mSv, respectively. Excluding the extreme case of TIPS, it was found that among commonly-performed procedures, those that are categorized as therapeutic do not necessarily present a statistically significant greater radiation risk than those which are diagnostic. Comparisons between dose-area product values obtained from this study are made with data from other interventional radiology patient dose surveys and reasons for some differences noted are discussed.

Efficacy and feasibility of breast shielding during abdominal fluoroscopic examinations

RATIONALE AND OBJECTIVES

The purpose was to measure radiation exposure to the breasts during abdominal fluoroscopic examinations and evaluate the efficacy of breast shielding with a leaded vest.

MATERIALS AND METHODS

Sixty-six women underwent routine abdominal fluoroscopic examinations. During the examinations one breast was covered with a leaded shield. Radiation doses to both breasts were measured with a thermoluminescent dosimeter. The amount of radiation at the skin of the shielded breast was then compared with that at the skin of the nonshielded breast.

RESULTS

Radiation exposure to the breasts varied substantially with the type of examination being performed and with the individual patient. The average radiation level at the skin of the unshielded breast was 119 mR (range, 0-6,320 mR), compared with 59.6 mR (range, 0-1,640 mR) at the shielded breast. The average reduction in radiation exposure was 50% with shielding.

CONCLUSION

Although the average level of radiation exposure to the breast during abdominal fluoroscopic examinations is generally low, use of a leaded vest can further reduce radiation to the breast for different types of examinations.

Optimization of patient radiation dose through development of specifications for purchase of X-ray equipment

X-ray equipment characteristics and performance have an important influence on radiation doses to patients. In order that these factors can be taken into consideration when X-ray equipment is purchased, dose related requirements need to be included in specifications and additional dose information requested from manufacturers. Dose factors include techniques that directly reduce exposure; use of low attenuation materials; provision of flexibility in choice of exposure parameters; and availability of data for dose assessment. If a standard format can be developed, this should enable manufacturers to supply this information. Specifications for different types of X-ray equipment and lists of dose information to be requested from manufacturers have been prepared by the Scottish Radiation Protection Advisers' Group for use in hospitals throughout Scotland. It is hoped that this will allow patient dose to be taken into account when X-ray equipment is purchased.