Estimation of doses to patients from "complex" conventional X-ray examinations

Patient and staff doses for some complex x-ray examinations

The aim of this study was to measure patient and staff doses simultaneously for some complex x-ray examinations. Measurements of dose-area product (DAP) and entrance skin dose (ESD) were carried out in a sample of 107 adult patients who underwent different x-ray examinations such as double contrast barium enema (DCBE), single contrast barium enema (SCBE), barium swallow, endoscopic retrograde cholangiopancreatography (ERCP) and percutaneous transhepatic cholangiography (PTC), and various orthopaedic surgical procedures. Dose measurements were made separately for each projection, and DAP, thermoluminescent dosimetry (TLD), film dosimetry and tube output measurement techniques were used. Staff doses were measured simultaneously with patient doses for these examinations, with the exception of barium procedures. The measured mean DAP values were found to be 8.33, 90.24, 79.96 Gy cm(2) for barium swallow, SCBE and DCBE procedures with the fluoroscopy times of 3.1, 4.43 and 5.86 min, respectively. The calculated mean DAP was 26.33 Gy cm(2) for diagnostic and 89.76 Gy cm(2) therapeutic ERCP examinations with the average fluoroscopy times of 1.9 and 5.06 min respectively. Similarly, the calculated mean DAP was 97.53 Gy cm(2) with a corresponding fluoroscopy time of 6.1 min for PTC studies. The calculated mean entrance skin dose (ESD) was 172 mGy for the orthopaedic surgical studies. Maximum skin doses were measured as 324, 891, 1218, 750, 819 and 1397 mGy for barium swallow, SCBE, DCBE, ERCP, PTC and orthopaedic surgical procedures, respectively. The high number of radiographs taken during barium enema examinations, and the high x-ray outputs of the fluoroscopic units used in ERCP, were the main reasons for high doses, and some corrective actions were immediately taken.

Effective doses in radiology and diagnostic nuclear medicine: a catalog

Medical uses of radiation have grown very rapidly over the past decade, and, as of 2007, medical uses represent the largest source of exposure to the U.S. population. Most physicians have difficulty assessing the magnitude of exposure or potential risk. Effective dose provides an approximate indicator of potential detriment from ionizing radiation and should be used as one parameter in evaluating the appropriateness of examinations involving ionizing radiation. The purpose of this review is to provide a compilation of effective doses for radiologic and nuclear medicine procedures. Standard radiographic examinations have average effective doses that vary by over a factor of 1000 (0.01-10 mSv). Computed tomographic examinations tend to be in a more narrow range but have relatively high average effective doses (approximately 2-20 mSv), and average effective doses for interventional procedures usually range from 5-70 mSv. Average effective dose for most nuclear medicine procedures varies between 0.3 and 20 mSv. These doses can be compared with the average annual effective dose from background radiation of about 3 mSv.

Radiation doses from small-bowel follow-through and abdominopelvic MDCT in Crohn's disease

OBJECTIVE

The purpose of our study was to compare organ and effective doses for small-bowel follow-through (SBFT) and abdominopelvic MDCT in adults with Crohn's disease, to retrospectively evaluate the number of radiographic examinations performed for Crohn's disease indications, and to identify those patients undergoing serial examinations to better delineate the use of radiology in the diagnosis and clinical management of Crohn's disease.

MATERIALS AND METHODS

Using an anthropomorphic phantom and metal-oxide semiconductor field-effect transistor (MOSFET) dosimeters, specific organ doses were measured for 5 minutes of continuous fluoroscopy (kVp, 120; mA, 0.6) of each of the following: right lower quadrant, central abdomen, and pelvis. Effective doses were determined based on International Commission on Radiological Protection (ICRP) 60 weighting factors. Organ and effective doses were determined for abdominal and pelvic 16-MDCT: detector configuration, 16 x 0.625 mm; pitch, 1.75; 17.5 mm per rotation; rotation time, 0.5 second; 140 kVp; 340 mA. Electronic records were reviewed to determine the number of patients imaged for Crohn's disease indications and the number of studies per patient.

RESULTS

The highest fluoroscopic organ doses were as follows: in the right lower quadrant, right kidney (0.78 cGy) and marrow (0.66 cGy); in the central abdomen, kidneys (1.5 and 1.6 cGy) and marrow (0.76 cGy); and in the pelvis, marrow (0.67-0.95 cGy). Effective doses for the right lower quadrant, central abdomen, and pelvis were 1.37, 2.02, and 3.83 mSv, respectively. For MDCT, the highest organ doses were to the liver (2.95-3.33 cGy). The effective dose for abdominopelvic MDCT was 16.1 mSv. Three hundred seventy-three patients underwent imaging for Crohn's disease. The average number of SBFT and CT examinations was 1.8 and 2.3, respectively. Thirty-four (9%) of 373 patients underwent more than five CT examinations and 11 (3%) had more than 10.

CONCLUSION

Organ and effective doses are up to five times higher with MDCT than with SBFT. Crohn's disease is more frequently imaged with CT. For a subset of patients who undergo numerous CT examinations, efforts should be made to minimize the number of CT examinations, decrease the CT dose, or consider MR enterography.

Estimation of radiographic doses in a case-control study of acute myelogenous leukemia

Radiation exposure from dental and medical radiography is inherently difficult to estimate. Because no single resource is available for this type of data, gathering the information needed to estimate exposure in epidemiologic studies is a labor-intensive, imprecise process. For a case-control study of adult-onset acute myelogenous leukemia in Los Angeles County and radiography, a database was created of estimates of dose to the red bone marrow for each radiographic procedure reported by subjects in interviews and recorded in subjects' medical records. Resources used included the medical literature as well as personal communications with radiology experts. Dose estimates for each procedure based on this database are reported. Methods and complications are contrasted with a past effort to estimate dose from dental radiography for a case-control study of parotid gland tumors. Among the more difficult aspects of medical radiography dose estimation are the wide variety of examinations performed, the continually-changing environment of diagnostic imaging, and the number of variables that contribute to the delivered dose to an individual from a specific imaging procedure.

Dosimetric aspects of a national survey of diagnostic and interventional radiology in Switzerland

The effective dose delivered to the patient was determined, by modeling, for 257 types of examinations covering the different modalities of diagnostic and interventional radiology. The basic operational dosimetric quantities considered were obtained from the parameters of the examinations on the basis of dosimetric models. These models required a precise characterization of each examination. The operational dosimetric quantities were converted into doses to organs and effective doses using appropriate conversion factors. The determination of the collective effective dose to the Swiss population requires a number of corrections to account for the variability of several parameters: sensitivity of the detection system, age, gender, and build of the patient. The use of various dosimetric models is illustrated in this paper for a limited number of examination types covering the different radiological modalities, for which the established typical effective doses are given. With regard to individual doses, the study indicated that the average effective doses per type of examination can be classified into three levels: (a) the weakly irradiating examinations (less than 0.1 mSv), which represent 78% of the examinations and 4% of the collective dose, (b) the moderately irradiating examinations (between 0.1 mSv and 10 mSv), which represent 21% of the examinations and 72% of the collective dose, (c) the strongly irradiating examinations (more than 10 mSv), which represent 1% of the examinations and 24% of the collective dose.

Differences in effective dose estimation from dose-area product and entrance surface dose measurements in intravenous urography

In this study, measurements of dose-area product (DAP) and entrance surface dose (ESD) were carried out in a sample of 25 adult patients who underwent intravenous urography (IVU). These measured quantities were used to estimate the effective dose E from the IVU examination, a quantity closely correlated to radiation risk. Estimating E involves the use of conversion coefficients that have been determined for specific X-ray views in a mathematical phantom. These are obtained under conditions which are not usually met in clinical practice. As a result, the E estimates using the two different measurable quantities can be quite different. Analysis of the calculation procedure suggests that the E estimate using the DAP measurements, in addition to being more practical, could be more accurate than using ESD measurements, as DAP is sensitive to the X-ray field size settings. Furthermore, it is shown that in the absence of the appropriate equipment, a reliable E estimate can be obtained from the ESD calculated using the exposure data for each X-ray view.

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.

Lung dose calculations at kilovoltage x-ray energies using a model-based treatment planning system

The determination of the dose to organs from diagnostic x rays has become important because of reports of radiation injury to patients from fluoroscopically guided interventional procedures. We have modified a convolution/superposition-based treatment planning system to compute the dose distribution for kilovoltage beams. We computed lung doses using this system and compared them to those calculated using the CDI3 organ dose calculation program. We also computed average lung doses from a simulated radiofrequency ablation procedure and compared our results to published doses for a similar procedure. Doses calculated using this system were an average of 20% lower for AP beams and 7% higher for PA beams than those obtained using CDI3. The ratio of the average dose to the lungs to the skin dose from the simulated ablation procedure ranged from 25% higher to 15% lower than that determined by other authors. Our results show that a treatment planning system designed for use in the megavoltage energy range can be used for calculating organ doses in the diagnostic energy range. Our doses compare well with those previously reported. Differences are partly due to variations in experimental techniques. Using a three-dimensional (3-D) treatment planning system to calculate dose also allows us to generate dose volume histograms (DVH) and compute normal tissue complication probabilities (NTCP) for diagnostic procedures.

Patient doses from barium meal and barium enema examinations and potential for reduction through proper set-up of equipment

Patient doses for barium meal and barium enema examinations, performed at two Greek hospitals, were measured using a dose-area product meter. The results were analysed to obtain the contributions of fluoroscopy and radiography to the dose as well as a number of other dose related parameters for each examination. The doses observed are within the range of values reported by other authors and comply with the dose reference levels (DRLs), proposed from relevant surveys in the UK and The Netherlands. However, comparison between the two hospitals revealed significant differences in the contributions to dose from the various parts of the examinations. To determine the reasons for these differences, measurements of dose related parameters were made using a Plexiglas phantom and standard clinical X-ray machine settings. Factors contributing to increased dose delivery were determined and recommendations have been made concerning ways in which doses might be reduced in each hospital, without degradation of the diagnostic quality of these examinations.

The average dose-area product at intravenous urography in 205 adults

The intravenous urography (IVU) is the most important and most frequently performed radiological examination in urology. This prospective study determined the dose-area product as a measurement of radiation dose in 205 adult patients undergoing IVU. Average dose-area product was 1017 cGy cm2. An average 3.7 radiographs were obtained per patient. Tomographic views were required in only 8.8% of cases. Radiation dose is dependent not only on the number and size of the obtained radiographs, but on the physical constitution of the patient. The dose-area products measured show a clear relationship to the body weight of the patient.

Patient doses in hysterosalpingography

The results of a survey of doses imparted on 41 patients undergoing hysterosalpingography is presented. Dosimetric evaluations were carried out by measuring both the dose-area product using a transmission ionization type chamber, and the entrance surface dose using thermoluminiscent dosimeters. As a result, a local reference dose value was obtained for this examination. Correlations between the dose-area product and the entrance surface dose data were analysed and compared in order to find the most appropriate dosimetric procedure. The median dose-area product obtained was 713 cGy cm2 (range 247 cGy cm2-1623 cGy cm2). Ovarian doses were also calculated, and a median value of 4.6 mGy was obtained for the whole examination. Effective doses were estimated with a median value of 3.1 mSv, and a range of 1.0 mSv-8.1 mSv.

Accidental embryo irradiation during barium enema examinations. An estimation of absorbed dose

RATIONALE AND OBJECTIVES

To investigate the possibility of an embryo to receive a dose of more than 10 cGy, the threshold of malformations induction in embryos reported by the International Commission on Radiological Protection, during barium enema examinations.

METHODS

Thermoluminescent dosimeters were placed in a phantom to calculate the depth-to-skin conversion coefficient needed for dose estimation at the average embryo depth in patients. Barium enema examinations were performed in 20 women of childbearing age with diagnostic problems demanding longer fluoroscopy times. Doses at 6 cm, the average embryo depth, were determined by measurements at the patients' skin followed by dose calculation at the site of interest.

RESULTS

The range of doses estimated at embryo depth for patients was 1.9 to 8.1 cGy. The dose always exceeded 5 cGy when fluoroscopy time was longer than 7 minutes.

CONCLUSION

The dose at the embryo depth never exceeded 10 cGy. This study indicates that fluoroscopy time should not exceed 7 minutes in childbearing-age female patients undergoing barium enema examinations.

Comparison of absorbed radiation doses in barium and air enema reduction of intussusception: a phantom study

OBJECTIVE

We assessed the relative radiation load in patients undergoing hydrostatic and pneumatic reduction of childhood intussusception.

MATERIALS AND METHODS

In a phantom study we simulated two situations occurring during reduction of intussusception. The absorbed radiation dose was measured at several positions in the phantom using either barium sulphate (BaSO4) or air in the simulated reduction, combined with either automatic exposure control (AEC) or constant exposure rate (CER) at fluoroscopy. From these values the mean absorbed dose was calculated for different depth compartments within the phantom.

RESULTS

In the barium study the mean absorbed dose averaged over the total irradiated volume was 14-23 % lower when CER was used instead of AEC; in the air study the dose was 35-43 % lower when AEC was used instead of CER. The combination of air and AEC provided the lowest mean absorbed dose in the tissue. The barium enema created a low-radiation zone, which might be utilized for protecting radiation sensitive tissue.

CONCLUSION

The use of BaSO4 or air in reduction of intussusception requires the proper combination with CER and AEC, respectively, to minimize the radiation load to the patient; the lowest radiation load is obtained by using air and AEC.

Effective dose to patients due to fluoroscopic screening in barium meal examinations: comparison between free and restricted X-ray beams

Four complete barium meal (BM) fluoroscopic examinations were digitised as sequences of 160 x 128 pixel, 8 bit images, at a rate of about 100 per min using a computer frame-grabber system and were recorded on disk for processing. The images were latter replayed and, using a suitable program, were superimposed in a new picture so that anatomic details coincided. At the same time, two more pictures were created by summing the radiation fields corresponding to the images grabbed, one with open diaphragms at 26 x 22 cm field size and one with simulated closed diaphragms at 7 x 11 cm. The average effective dose rate delivered to the patient during fluoroscopic screening was calculated for a hermaphrodite mathematical phantom and was found to be 0.21 mSv/min and 0.005 mSv/min, respectively, if either technique had been used exclusively. The average effective dose delivered to the patients with the actual techniques used in the 4 BM examinations recorded was 0.394 mSv. Data from these examinations was extrapolated to a sample group of 122 BM examinations, performed during a 9-week period, for which total exposure duration was known. The average effective dose calculated for fluoroscopy was shown to be negligible, particularly if only the 'closed' diaphragm technique was used, when compared to the estimated average effective dose of about 8.6 mSv delivered by the radiographs made during each examination.

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%.

Evolution of diagnostic radiology in a big hospital during a 5 year period, and the derived collective dose

An analysis is presented of the trends in the annual number of radiological examinations and in the average effective dose equivalent for each type of examination in a big Spanish hospital. Annual frequencies for each type of examination, annual average effective dose equivalent values for each study group, and the contribution of each examination group to the collective dose are presented. Also, sex and age distributions for several important examinations are given, and their impact on the collective dose is reviewed.