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Original Research |
1 Tanzania Atomic Energy Commission, Arusha, Tanzania.
2 Sudan Atomic Energy Commission, Khartoum, Sudan.
3 King Abdul Aziz City for Science and Technology, Riyadh, Saudi Arabia.
4 Dubai Hospital, Dubai, United Arab Emirates.
5 University of Sarajevo, Sarajevo, Bosnia and Herzegovina.
6 Vinca Institute of Nuclear Sciences, Belgrade, Serbia.
7 Centre Régional d'Études Nucléaires de Kinshasa (CREN-K),
Kinshasa, Democratic Republic of the Congo.
8 Chulalongkorn Hospital, Bangkok, Thailand.
9 Clinical Centre Banja Luka, Banja Luka, Bosnia and Herzegovina.
10 Radiotherapy and Nuclear Medicine Department, Parirenyatwa Group of Hospitals,
Harare, Zimbabwe.
11 Institut National des Sciences et Techniques Nucléaires, Antananarivo,
Madagascar.
12 International Atomic Energy Agency, Wagramer Strasse 5, A-1400, Vienna,
Austria.
13 Atomic Energy Organization of Iran, Tehran, Iran.
14 Ghana Atomic Energy Commission, Accra, Ghana.
Received August 19, 2007;
accepted after revision January 3, 2008.
This work was undertaken as part of technical cooperation projects under
grants. of the International Atomic Energy Agency, RAF/9/033 (Africa),
RAS/9/9034 and 9040 (Asia), and RER/9/079 and 080 (Europe).
Abstract
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SUBJECTS AND METHODS. In this multinational prospective study, image quality and patient radiation doses were surveyed in 12 countries in Africa, Asia, and Eastern Europe, covering 45 hospitals. The rate of unsatisfactory images and image quality grade were noted, and causes for poor image quality were investigated. The entrance surface doses for adult patients were determined in terms of the entrance surface air kerma on the basis of X-ray tube output measurements and X-ray exposure parameters. Comparison of dose levels with diagnostic reference levels was performed.
RESULTS. The fraction of images rated as poor was as high as 53%. The image quality improved up to 16 percentage points in Africa, 13 in Asia, and 22 in Eastern Europe after implementation of a quality control (QC) program. Patient doses varied by a factor of up to 88, although the majority of doses were below diagnostic reference levels. The mean entrance surface air kerma values in mGy were 0.33 (chest, posteroanterior), 4.07 (lumbar spine, anteroposterior), 8.53 (lumbar spine, lateral), 3.64 (abdomen, anteroposterior), 3.68 (pelvis, anteroposterior), and 2.41 (skull, anteroposterior). Patient doses were found to be similar to doses in developed countries and patient dose reductions ranging from 1.4% to 85% were achieved.
CONCLUSION. Poor image quality constitutes a major source of unnecessary radiation to patients in developing countries. Comparison with other surveys indicates that patient dose levels in these countries are not higher than those in developed countries.
Keywords: patient doses • quality assurance • radiation protection • radiation safety • radiography
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However, two concerns remain from the radiation protection point of view. The first concern is poor image quality produced in radiographic examinations. It is increasingly recognized that there is a tremendous amount of waste of resources, particularly in develop ing countries, because images of poor quality have been reported in earlier studies to be as much as 15-40% of all images [3-5]. Poor-quality images result in unnecessary radiation exposure to patients through repeated radio graphic examinations, loss of diagnostic information, and increased social costs in addition to the economic costs of health care.
The International Basic Safety Standards (commonly known as BSS) developed by the International Atomic Energy Agency (IAEA) with cosponsorship of the Food and Agriculture Organisation of the United Nations (FAO), the International Labor Organization (ILO), the Nuclear Energy Agency of the Organisation for Economic Cooperation and Development (OECD/NEA), the Pan American Health Organization (PAHO), and the World Health Organization (WHO) require attention to image quality by considering corrective actions if such exposures do not provide useful diagnostic information and do not yield medical benefits to patients [6]. Similar recommendations are provided by other international and national bodies such as the International Commission on Radiological Protection (ICRP), the United States' Nationwide Evaluation of X-ray Trends (NEXT) program, the United Kingdom's National Radiological Protection Board (NRPB), and the Commission of European Communities (CEC) [7-10].
The second concern is the significant variation in dose levels to patients of similar size undergoing the same type of radiographic examination. In 1982, ICRP stated that the dose to patients from a given type of examination may vary between hospitals by a factor of 2 to 10 [11]. Experience from various national surveys has shown even larger variation in patient doses for the same examinations—to a factor of 20 or more in different hospitals or even in different rooms in the same hospital [12-14]. In this regard, the standards require the establishment of diagnostic reference levels or guidance levels for medical exposure by appropriate professional bodies in consultation with national health and regulatory authorities [7-10].
There is growing evidence that comparison of dose values with diagnostic reference levels has led to a decrease in patient doses [12-19], and therefore the use of this optimization tool should be widely promoted. In addressing the two aforementioned concerns, establishment of a quality assurance (QA) program focusing on image quality and patient dose seems a logical step forward. QA in radiology has unfortunately been dominated by testing of radiographic equipment, and the evaluation of image quality and patient dose has not received due attention. The complete quality cycle has to be considered, with feedback mechanisms for rectification of malfunctions and of operator performance, to ensure the desirable diagnostic confidence with the lowest possible radiation dose to the patient.
Numerous surveys on the frequency of radiographic examinations, associated patient doses, and comparison with diagnostic reference levels have been reported at the national level [9, 13, 14, 16-19], and the examples cited here are not exhaustive. In some cases, studies have been extended to include optimization, in which dose reduction measures have been identified and their effectiveness shown. However, there is still an absence of information on national practices from a large number of countries, particularly those in the least-developed regions of the world. In addition, the important issue of the quality of radiographic images related to the established patient dose levels is hardly addressed in most reported studies. The focus of reported national surveys has primarily been on dose assessment, and information on image quality is practically nonexistent in such surveys. It is well understood that the dose levels to patients undergoing diagnostic radiographic examinations are, in principle, determined by the required quality of images and the extent of investigation necessary to meet specific clinical objectives [10]. Therefore, there is a lack of information in a multinational setting on the status of the quality of radiographic images and the associated radiation doses to patients undergoing radiographic examinations.
In a project launched by the IAEA in different regions of the world, an attempt has been made to survey image quality and patient dose in the most common radiographic examinations and to compare assessed doses to diagnostic reference levels. The main objective of the project was to introduce a QA program for optimization of radiologic protection in radiography in participating countries so as to fulfill BSS requirements. The project was started in the latter part of 2005 as a prospective study and focused on developing countries. The details of this project can be found online at rpop.iaea.org/RPoP/RPoP/content/InformationFor/MemberStates/1_RegionalProjects/index.htm. This article presents the initial project results on image quality assessment, typical dose levels to patients undergoing the most common radio graphic examinations, and comparison with diagnostic reference levels for 12 participating countries in Africa, Asia, and Eastern Europe. On the basis of the results, the potential for optimization of radiographic examinations is then evaluated.
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General
The project was implemented in two phases from August 2005 to December
2006, each phase covering the assessment of both image quality and patient
dose. Participating countries were requested to identify hospitals and
radiography rooms that were to be enrolled in the project. The participants
were encouraged to select at least two radiography rooms per hospital so as to
point out any important interroom differences in patient doses and image
quality. The work in phase 1 involved assessment of the baseline data by
scoring image quality and identification of the causes for poor image quality
for a 2-week period. Along with image quality assessment, dose assessment (see
Patient Dose Assessment section) for at least 10 adult patients per selected
radiographic projection was also performed. Before beginning phase 2 of the
survey, quality control (QC) tests were performed to identify equipment
malfunctions and to apply appropriate corrective actions based on image
quality assessment and equipment performance.
Table 2 presents the main
corrective measures applied to improve the image quality. Awareness of
improving image quality and of dose reduction strategies created as QA
components was introduced to the radiology personnel on the basis of data from
image quality analysis. Finally, in phase 2, reassessment of the image quality
and patient doses for the same types of examination as in phase 1 was
performed for another 2 weeks.
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Image Quality Assessment
Image quality assessment in the selected 2-week period was performed in
both phases as described in the previous section and involved all radiographic
examinations. The CEC quality criteria for diagnostic radiographic images
[10] were supplied to the
participating centers for use by experienced radiologists in image quality
assessment. The use of quality criteria in this survey was mainly intended to
reduce interobserver variability by guiding radiologists on how to grade the
quality of radiographic images. The quality criteria were expected to be in
the minds of radiologists and were not used for image grading on any specific
criterion basis. Instead, each radiographic image was graded as A, B, or C
[4,
5]. Grade A images were those
clearly accepted by reporting radiologists without any remark or reservation.
Grade B included all images that were accepted with some remarks or
reservations. Grade C images were those that should be rejected. In addition
to this analysis, the participating centers were re quested to document the
main causes for B- or C-graded images, such as overexposure or under exposure,
artifacts, field-size misplacement, processing problems, or any other problems
[3-5].
Patient Dose Assessment
The patient dose assessment was also done in two phases as it was for image
quality assessment. It involved the most common seven radiographic
projections: chest, posteroanterior; lumbar spine, anteroposterior; lumbar
spine, lateral; abdomen, anteroposterior; pelvis, anteroposterior; skull,
anteroposterior; and skull, posteroanterior. The quantity used was the
entrance surface air kerma, which is the quantity currently recommended for
patient dose assessment and for comparing patient dose levels with diagnostic
reference levels in general radiography
[20].
Survey of X-Ray Exposure Parameters of Adult Patients
Before patient dose assessment, information on X-ray exposure parameters
(kVp, mAs) and geometric parameters (X-ray tube focus-film distance [FFD],
X-ray tube focus-skin distance [FSD], and film size) used in radiographic
examinations of adult patients of average body mass for selected radiographic
projections was collected. At least 10 patients were included for each
radiographic projection. A weight restriction criterion of 70 ± 10 kg
was applied as recommended
[21,
22]. The surveyed X-ray
exposure parameters were used later to estimate patient doses through a
three-step protocol: X-ray tube output measurements, incident kerma
measurements, and entrance surface air kerma calculations.
X-ray tube output measurements—For X-ray tube output measurements, the appropriate dosimeter (diode or ionization chamber) was connected to an electrometer and placed on a low scattering material (polystyrene [Styrofoam, Dow Chemical] or cardboard) on a patient support setup in the vertical position. The dosimeter was positioned in the central beam axis at a preferable X-ray tube focal spot-detector distance of 50 cm. The radiation field size at focal spot-detector distance was set to just cover the dosimeter to avoid the possible influence of scatter radiation to the dosimeter. The typical field size was 10 x 10 cm, and the tube potential was set at 50 kVp and any mAs value (depending on convenient tube load conditions). A radiographic exposure was made and the dosimeter reading recorded. This step was repeated once more at the same kVp and mAs settings and the average dosimeter reading determined. The X-ray tube output was determined as the ratio of average dosimeter reading (in air kerma) to the tube current-time product used for tube voltages 50-120 kVp in steps of 10 kVp. The values of the X-ray tube output per mAs were plotted against the tube potential and the resulting curve was fitted using a power function.
Incident air kerma and entrance surface air kerma estimations—The incident air kerma for each adult patient undergoing a particular radiographic examination was determined by the product of the X-ray tube output value (derived from the output per mAs-kVp curve corrected for the inverse distance effects between the patient's distance from the X-ray focus and the distance at output measurements) and the actual mAs used in the radiographic examination [20]. The entrance surface air kerma value was then calculated by multiplying incident air kerma to the patient's surface by the appropriate backscatter factor (BSF), which depends on the tube potential, total filtration, and radiation field size [20].
Estimation of effective dose—Estimation of the effective dose (E) per radiographic projection was derived from the mean entrance surface air kerma by applying the appropriate entrance surface dose-to-effective dose (E/ESD) conversion coefficients, assuming similarity in the X-ray spectra used in this study and those under which the coefficients were derived [12, 23].
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The results of the image quality assessment for participating countries in Asia are presented in Table 4. Poor-quality images ranged from 7% (307/4,516) to 55% (649/1,172) before implementation of the QC program. The analysis of results indicates that the image quality improved by 7 to 13 percentage points in different countries.
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In Eastern Europe, poor-quality images ranged from 8% (58/710) to 41% (91/220) before implementation of the QC program (Table 5). In that region, the image quality improved by 1 to 22 percentage points.
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Table 6 presents the overall image quality improvements in the participating countries in Africa, Asia, and Eastern Europe. Two countries (Bangladesh and Saudi Arabia) that have not yet submitted data on image quality assessment after implementation of the QC program were not included in the overall analysis. The image quality improved by 6 (Africa), 10 (Asia), and 7 (Eastern Europe) percentage points.
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Entrance Surface Air Kerma
The results of mean entrance surface air kerma to adult patients undergoing
radiographic examinations in various participating countries before
implementation of the QC program are presented in Tables
7,
8 and
9. The diagnostic reference
levels recommended by the IAEA in terms of entrance surface dose
[24] are also indicated.
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For participating countries in Africa (Table 7), the entrance surface air kerma varied by factors of 3 (chest, posteroanterior), 21 (lumbar spine, anteroposterior), 7 (lumbar spine, lateral), 34 (abdomen, anteroposterior), 70 (pelvis, anteroposterior), and 3.7 (skull, anteroposterior). Taking into account the type of film-screen combination speed in use (Table 1), many entrance surface air kerma values were of the order of the diagnostic reference levels or well below the diagnostic reference levels. Exceptions were observed for some chest, posteroanterior; abdomen, anteroposterior; pelvis, anteroposterior; and skull, anteroposterior radiographic examinations.
For participating centers in Asia (Table 8), the entrance surface air kerma varied by factors of 2.5 (chest, posteroanterior), 6.5 (lumbar spine, anteroposterior), 2.6 (lumbar spine, lateral), 2.3 (abdomen, anteroposterior), 3.8 (pelvis, anteroposterior), and 7 (skull, anteroposterior). Comparing the entrance surface air kerma values to diagnostic reference levels, it is seen that most values were well below the diagnostic reference levels for the 400 film-screen combination speed in use with few exceptions.
For participating centers in Eastern Europe (Table 9), the entrance surface air kerma varied by factors of 13 (chest, posteroanterior), 3 (lumbar spine, antero posterior), 2.7 (lumbar spine, lateral), 4.8 (abdomen, anteroposterior), and 4 (pelvis, anteroposterior). For skull radiographic examinations, anteroposterior projections were performed in one country, whereas posteroanterior projections were per formed in another. The entrance surface air kerma values for two countries were below the diagnostic reference levels for all radiographic exam inations, whereas in the third country, some entrance surface air kerma values (chest, posteroanterior; lumbar spine, anteroposterior), were above or nearly equal to the diagnostic reference levels. The mean entrance surface air kerma values in mGy were 0.33 (chest, posteroanterior), 4.07 (lumbar spine, antero posterior), 8.53 (lumbar spine, lateral), 3.64 (abdomen, anteroposterior), 3.68 (pelvis, anteroposterior), and 2.41 (skull, antero posterior). In all three regions, the entrance surface air kerma varied by a factor of 13 (chest, posteroanterior), 25 (lumbar spine, antero posterior), 7 (lumbar spine, lateral), 34 (abdomen, anteroposterior), 88 (pelvis, anteroposterior), and 7 (skull, anteroposterior).
Effective Dose
Table 10 presents typical
effective doses estimated for adult patients across different countries before
implementing a QC program. The effective dose varied by factors of up to 13
(chest, posteroanterior), 111 (lumbar spine, anteroposterior), 17 (lumbar
spine, lateral), 154 (abdomen, anteroposterior), 72 (pelvis, anteroposterior),
and 7 (skull, anteroposterior). It can be seen that the effective doses are
similar to values reported by UNSCEAR and NRPB
[1,
23].
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Patient Dose Reductions
Table 11 presents the
entrance surface air kerma reductions for patients undergoing the most common
radiographic examinations as a result of implementing a QC program in some
participating countries. The achieved entrance surface air kerma reductions
ranged from 25% to 85% (chest, posteroanterior), 7% to 49% (lumbar spine,
anteroposterior), 1% to 39% (lumbar spine, lateral), 4% to 31% (abdomen,
anteroposterior), 7% to 23% (pelvis, anteroposterior), and 6% to 35% (skull,
antero posterior or posteroanterior). It is interesting to note that all
images associated with the dose reductions were used for reporting according
to the radiologists. This suggests that the quality of the radiographic images
was not adversely affected by dose reduction measures. However, in a few
cases, entrance surface air kerma values increased slightly after
implementation of the QC program: 17% (chest, posteroanterior), 6% (lumbar
spine, lateral), and 7% (skull, anteroposterior). The entrance surface air
kerma increment is probably attributable to measures aimed at improving the
image quality.
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Comparison with Results from Other Patient Dose Surveys
Assuming that the entrance surface air kerma is approximately equal to the
entrance surface dose (ESD) in diagnostic radiology, the comparison
of entrance surface air kerma values of this study after QC program and
entrance surface dose values in various countries is presented in
Table 12. With few exceptions,
the majority of entrance surface air kerma values are similar to the entrance
surface dose values reported recently in other countries
[9,
14,
25-28].
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The results of image quality assessment have shown a high frequency of poor-quality radiographs (grade B and C images combined) across participating hospitals in Africa, Asia, and Eastern Europe. The observed high percentage of poor image quality is likely due to an absent or in effective QA program at hospitals that participated in this survey. This view is supported by the results of the second phase on image quality assessment, in which image quality improvements were observed in terms of increase in the percentage of grade A images. The overall image quality improvement across the countries of Africa, Asia, and Eastern Europe (Table 6) is also encouraging because of QC actions.
The dose levels to patients have been analyzed in terms of mean entrance surface air kerma values and large variations have been observed. Large dose variations are a common feature in most wide-scale surveys [10, 12]. In a United Kingdom (U.K.) 2000 national survey, the variations expressed in terms of maximum-to-minimum ratio (max/min) ranged from 52 to 283 [12]. In this respect, the variations in our study are smaller, probably because of the smaller number of hospitals (45) in the study (against 371 hospitals in the U.K. national survey). It is seen that lower entrance surface air kerma variations were observed in Asian and Eastern European countries than in Africa. Entrance surface air kerma variations could be attributed to different levels of training in radiology, the choice of radiographic technique, the film-screen combination type in use, the status of QA program implementation, human physique, and, importantly, the status of implementation of radiation protection standards.
The European Directive [31] and its mandatory compliance by member states play an important role in the European setting. A similar mechanism existing in the United States through different state regulations also has a positive impact on the status of radiation protection of patients [32]. The influence of film-screen combination speed on entrance surface air kerma variations in this study was also likely to be significant because of the different film-screen combination speed classes that were in use across most hospitals studied. In a survey conducted in the United Kingdom in the 1980s, it was concluded that film-screen speed was an overriding cause of variations in patient doses for any simple radiographic examination [33]. Various approaches on how to relate film-screen combination speed classes to diagnostic reference levels are available in the literature. However, in a U.K. survey, diagnostic reference levels are stated irrespective of the film-screen combination speed class, although the survey indicates the percentage use of different film-screen combination speed classes in practice [9].
The CEC guideline recommends the 400 film-screen combination speed class, but its diagnostic reference levels are not based on the recommended image receptors [10]. The IAEA gives diagnostic reference levels in terms of guidance levels for the 200 film-screen combination speed class and states that the corresponding values for the 400 and 600 film-screen speed classes are half and one third, respectively, of guidance levels for the 200 film-screen combination speed classes [6]. Another approach is found in the United States, where different entrance surface exposure limits are indicated in state regulations for common medical projections depending on the film-screen speed class [32]. The differences in dealing with film-screen combination speed classes in patient dose surveys indicate the need to have a consensus for better harmonization.
Determination of patient doses or entrance surface air kerma values and their comparison with diagnostic reference levels are an important part of the optimization process in diagnostic radiology. A comparison of average dose levels from a specified imaging procedure with diagnostic reference levels should identify unusually high or low doses for the particular procedure. Results from this survey have shown that most entrance surface air kerma values in participating countries in Africa, Asia, and Eastern Europe were well below the diagnostic reference levels recommended by the IAEA [6]. Except for a few cases, the dose values obtained under this study were also below the diagnostic reference levels recommended in the U.K. and European communities [9, 10]. A similar situation is also observed with respect to some recommended diagnostic reference levels in the United States [14]. However, experience elsewhere [21] has shown that there is little correlation between patient dose and image quality, and thus the entrance surface air kerma results cannot be directly related to the image quality status discussed earlier. Comparison of entrance surface air kerma values under this study and others (Table 12) has largely shown comparable doses. Therefore, the common assumption or opinion that radiation doses to patients in developing countries are always higher than those in developed countries is not correct.
The results of effective dose estimates have reconfirmed that radiation risk to patients in conventional radiography is smaller in comparison with that in other radiographic imaging techniques such as CT or interventional procedures. Despite this situation, the observed dose variations could mean unjustified risk to patients undergoing similar types of radiographic examinations. The potential for dose reduction without affecting the quality of radiographic images in this study has also been noted. This clearly indicates the positive aspects of QA program implementation and the adherence to general principles associated with good imaging performance. It is understood that the central requirement of these principles of good imaging is the proper functioning of radiology staff members—not limited to equipment testing and QC checks, as commonly perceived.
In conclusion, the survey of image quality and patient dose levels in representative centers in some African, Asian, and Eastern European countries has been presented. It has been seen that variations in patient dose can be large to the extent of attracting suspicion as to the necessity of such dose levels (if too high) or the status of image quality (if too low). Nevertheless, the magnitudes of patient doses in developing countries are not higher than doses in developed countries and in some cases are actually lower. The application of diagnostic reference levels has been shown to have the potential for dose reductions without adversely affecting the image quality. The additional advantage of dose reduction can be an increased X-ray tube life, although there are limited data to support this assumption [14]. The experience from this study should form a basis to strengthen QA programs where they exist and establish such programs where they do not yet exist. Such QA programs are necessary to ensure that appropriate radiation exposure is delivered to the image receptor to produce an image quality that is adequate for the diagnostic task. The potential for increased awareness of such a need for optimization is one of the positive impacts of this study in reducing unnecessary patient doses without compromising the image quality.
Acknowledgments
The authors thank their respective governments for their nomination to
participate in the project. Only one principal contributor from each
participating team in a country has been included as an author, whereas many
members were involved in the project. The authors express their gratitude to
all members of the team for their cooperation and understanding. Except for
the first author, all authors' names have been arranged alphabetically by
family name. Thanks are due to the participants from Bangladesh (A. M. M.
Shariful Alam) and Armenia (K. Stepanyan) for providing data on image quality
assessment.
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