|Year : 2018 | Volume
| Issue : 1 | Page : 54-59
Diagnostic reference levels for mammography examinations in North Eastern Nigeria
Dlama Zira Joseph1, Christian Chukwuemeka Nzotta2, Joseph Dimas Skam3, Mohammed Sani Umar4, Dambele Y Musa5
1 Department of Radiology, Abubakar Tafawa Balewa University Teaching Hospital, Bauchi, Nigeria
2 Department of Radiography and Radiological Sciences, Nnamdi Azikiwe University, Awka, Anambra, Nigeria
3 Department of Radiology, Federal Medical Centre, Katsina State, Nigeria
4 Department of Radiology, Aminu Kano Teaching Hospital, Kano, Nigeria
5 Department of Radiography, Bayero University Kano, Kano, Nigeria
|Date of Web Publication||2-Jul-2018|
Dlama Zira Joseph
Department of Radiology, Abubakar Tafawa Balewa University Teaching Hospital, Bauchi
Source of Support: None, Conflict of Interest: None
Background: Diagnostic reference levels (DRLs) plays an important role in health-care delivery and radiation safety of patients. This study was carried out as part of a comprehensive project to establish DRLs for the radiological examinations for the first time in North Eastern Nigeria. Objective of the Study: The aim is to establish DRL for mammography examination in North Eastern Nigeria and to compare it with other established works. Materials and Methods: This study is a prospective cross-sectional study conducted in two university teaching hospitals in North Eastern Nigeria. Sixty patients were recruited for the study. Thermoluminescent dosimeter (TLD) chips were exposed for craniocaudal (CC) and mediolateral examinations to record the entrance skin dose (ESD). TLD readings were obtained at the Center for Energy Research and Training Zaria, Kaduna State, Nigeria. Dance formula was used to convert ESD to mean glandular dose (MGD). Student's t-test was used to determine the relationship between the mean ESD obtained in the two centers and Pearson's correlation was used to determine the relationship between the MGD and anthropotechnical parameters. Statistical significance was set at P < 0.05. Results: The total MGD for this study was 0.31 ± 0.05 mGy and 0.69 ± 0.11 mGy for CC and mediolateral oblique (MLO), respectively. DRL was 0.63 mGy and 1.04 mGy for CC and MLO, respectively. There was no statistically significant relationship (P > 0.05) between the MGD and anthropotechnical parameters. The DRL in this work were higher when compared with international established work. Conclusion: There is need for optimization of our radiology practice in North Eastern Nigeria and most centers in Nigeria.
Keywords: Diagnostic reference levels, entrance skin dose, mammography, mean glandular dose, thermoluminescent dosimeter
|How to cite this article:|
Joseph DZ, Nzotta CC, Skam JD, Umar MS, Musa DY. Diagnostic reference levels for mammography examinations in North Eastern Nigeria. Afr J Med Health Sci 2018;17:54-9
|How to cite this URL:|
Joseph DZ, Nzotta CC, Skam JD, Umar MS, Musa DY. Diagnostic reference levels for mammography examinations in North Eastern Nigeria. Afr J Med Health Sci [serial online] 2018 [cited 2019 Feb 22];17:54-9. Available from: http://www.ajmhs.org/text.asp?2018/17/1/54/235738
| Introduction|| |
Diagnostic reference levels (DRLs) are suggested radiation dose levels of the radiographic investigations above which a facility should review its methods and determine if acceptable image quality can be achieved at lower doses. The imperativeness of establishing DRLs for mammography is important because it forms a comprehensive, concise, and powerful tool for optimizing radiation protection of patients. DRLs are values which are usually easy to measure and have a direct link with patient doses. They are, therefore, established to aid efficient dose management and to optimize patient doses. DRLs are beginning to be a well-defined tool for dose optimization in many countries. There has been number of approaches to DRLs use for medical imaging; however, detailed inter- and intra-hospital variations for the same examinations are recommended by international organizations.
Mammography is an X-ray examination of the breast usually done for breast cancer screening and accompanied by further development of both invasive and noninvasive radiological technique used for establishing the diagnosis of palpable and nonpalpable lesions. The major projection for X-ray mammography includes craniocaudal (CC) and mediolateral obliques view. There are two types of patients on whom mammograms are performed: Symptomatic women in the clinic and asymptomatic women in breast screening programs. The standard investigations used for breast imaging are X-ray mammography and real-time ultrasonography with Doppler interrogation, magnetic resonance imaging, scintimammography, and digital mammography. High-quality mammography requires good and functional equipment with highly skilled and well-trained radiographers. Breast cancer causes almost half a million deaths in the world per year but early detection has been demonstrated to reduce mortality by up to 30%.,,
The International Commission on Radiological Protection (ICRP) introduced DRLs in their 1996 publication 73 as a parameter to be used for quality control, comparison of dose levels, optimization, and limiting variations in dose among diagnostic imaging centers., The methods through which the DRLs are established become important when trying to establish international comparisons as radiation dose measurements are required.,
Measuring radiation dose to the breast has been performed using a variety of approaches including air kerma, entrance skin dose (ESD), mid-breast dose, total energy transmitted to the breast, and the mean glandular dose (MGD). The average dose absorbed by the glandular tissue was found to be the most effective way of measuring absorbed dose of the breast because the mammary glands are most sensitive to ionizing radiation and to have the highest risk of developing radiation-induced carcinogenesis. MGD is the recommended metric used by many authorities such as ICRP, United States National Council on Radiation Protection and Measurements, the British Institute of Physics and Engineering in Medicine, the European Council Protocol and International Atomic Energy Agency (IAEA).,
Dose to glandular tissue of the breast cannot be directly measured using X-ray examination but can be assessed with certain standard assumptions that depend on breast characteristics and X-ray spectra., MGD represents the effective dose absorbed by the breast and it is calculated from conversion factors that have been established, such factors relate MGD to entrance surface dose (ESD) and allows for a wide and flexible range of X-ray spectra, breast thickness, and glandularity.,
So many countries have established DRLs for mammography examination, but many others are yet to do so. It is, therefore, imperative to establish for our region. The aim of this study was to establish DRLs for mammography examination in North Eastern Nigeria and to compare it with other established work.
| Materials and Methods|| |
This study is a prospective, cross-sectional study carried out in the Radiology Departments of two University Teaching Hospitals located in North Eastern part of Nigeria referred to as Hospital A and Hospital B. Sixty patients were recruited for the study. The data, in this study, were collected from October 2015 to January 2016. The centers were chosen because they met the eligibility criteria for the study; having all the imaging modalities for the study and Nigerian Nuclear Regulatory Authority's Requirement for Authorization and Practice (Licensing) involving ionizing radiation.
Mammography machine: For Hospital A, the machine was manufactured by Planmed OY, Helsinki Finland in April 2008, while that of Hospital B was manufactured by Halogic Inco-operation, USA in July 2012. Their kilovolts peak (kVp) and mass (mAs) range are 20–35 and 10–500 for Hospital A, and 20–40 and 10–400 for Hospital B, respectively. The inherent filtration for both hospitals was 30 μM molybdenum, 0.5 mmAl, and 25 μM rhodium.
Mediolateral oblique (MLO) and CC views were considered. The patient breast was positioned on the support paddle with compression in place. The machine uses automatic exposure control; it therefore provides the exposure factors to be used automatically namely kVp, mAs, anode/filter combination according to the breast granularity and thickness. The machine also provides the compressed breast thickness before exposure is made. The parameters were recorded for each patient, and the compressed breast thickness was measured using flexible meter rule. Thermoluminescent dosimeters (TLDs) were placed at the upper inner quadrant of the breast before any compression was made for both the CC and MLO views of both breasts. Two TLDs were exposed for each patient. The exposed TLDs were labeled for proper identification and kept in black nylon away from radiation.
In line with Helsinki Declaration, (1964) ethical approval was obtained from the research ethics committee of the Faculty of Health Science and Technology, Nnamdi Azikiwe University Nnewi Campus and from each hospital under study. Informed consent form interpreted in Hausa language was filled by each (volunteer, patient) participant in compliance with the Human Research Ethics Guidelines for patients who do not understand English language. The first author/researcher also underwent web-based training by National Health Institute on Research Ethics, United States, involving humans for adequate knowledge on research procedures and guidelines involving humans.
Dose determination for mammography
After the TLDs were read by the TLD reader, the value obtained by the control TLD reading was subtracted from the value of the actual TLD to get the value of the entrance surface dose (ESD).
To get the MGD the conversion factors derived by Dance et al. (2000) was used to calculate the MGD.
The MGD was calculated using this formula:
MGD = K × g × C × s
Where K = ESD
g = ESD to MGD conversion factor on the assumption that the entire breast has a glandularity 50%.
C = Conversion factor for difference in breast composition other than 50% glandularity.
s = conversion factor for different X-ray spectrum which can be due to different anode/filter combination, for example, Mo/Mo, Mo/Rh.
Data were obtained and saved on a computer Microsoft Excel Spreadsheet and categorized for each examination and imaging modality, respectively. It was independently checked by a statistician and two senior radiographers. Statistical Package for the Social Sciences (SPSS, IBM, Chicago, USA) version 21.0 was used to analyze the mean and standard deviation of the anthropometric variables, technical parameters, and radiation dose received. Seventy-fifth percentile or (3rd quartile) value of the total mean of the examinations and/or procedures were obtained at 95% confidence interval. Using Kolmogorov–Smirnov to test for normality of data distribution, it was verified that, for 95% of confidence level, there was a normal distribution. Therefore, we used a parametric test that was suitable for the set of data and analysis. Pearson's correlation was used to determine the relationship between radiation dose and breast thickness while Student's t-test was used to compare the MGD for the two hospitals. Statistical significance was set at P < 0.05.
| Results|| |
[Table 1] shows mean and standard deviation of the ESD, MGD, and DRLs for mammography examination. The mean ESD for CC and MLO are 0.50 ± 9.48 mGy and 0.70 ± 0.74 mGy for Hospital A, 0.31 ± 0.05 mGy and 0.69 ± 0.11 mGy for Hospital B. The total mean and standard deviation for both hospitals were 0.48 ± 0.69 mGy and 0.68 ± 0.40 mGy for CC and MLO, respectively. The MGD for CC and MLO are 0.31 ± 0.05 and 0.69 ± 0.11 mGy. The DRL for CC and MLO are 0.63 mGy and 1.04 mGy.
|Table 1: Mean glandular dose received and 75 percentile (diagnostic reference levels) for mammography examination|
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[Table 2] shows the relationship between Mean glandular doses received by patients and anthropometric parameters for mammography. There was no statistical significant relationship (P< 0.05) relationship between mean glandular dose examinations for Cranio-caudal, and medio-lateral oblique examinations with compressed breast thickness, weight, height and body mass index (BMI) head computed tomography (CT), and abdominal CT. However, chest CT showed statistical significant relationship (P< 0.05) with weight and height.
|Table 2: The relationship between mean glandular dose received by patients and anthropometric parameters for mammography examination|
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[Table 3], CC view and MLO, showed no statistically significant differences (P > 0.05) with technical parameters.
|Table 3: Relationship between doses received by patients during radiographic examination and technical parameters|
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[Table 4] shows the t-test comparison of radiation dose and some technical parameters for mammography examination between Hospitals A and B. Detailed result from table shows that when the mean doses for the hospitals were compared; there was no statistically significant relationship (P > 0.05) between mAs, kVp, and MGD for the hospitals.
|Table 4: Comparison of patient's mean glandular dose and technical parameters for mammography examination between Hospital A and Hospital B|
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[Table 5] shows comparison of established DRLs for mammography examination with that of the European Commission, United Kingdom, and Australia. The DRL for Australian Radiation Protection and Nuclear Safety Agency (ARPANSA), EC, UK, and this work were 0.88 mGy, 2.0 mGy, 2.0 mGy, and 0.63 mGy for CC view. DRL for MLO was 1.30 mGy, 2.0 mGy, 2.1 mGy, and 1.04 mGy for ARPANSA, EC, UK, and present work, respectively. The DRL values for mammography, in this study, are higher compared to that of ARPANSA, UK, and European Commission, respectively.
|Table 5: Comparison of diagnostic reference levels for mammography in this work with European Commission, United Kingdom, and Australian radiation protection and nuclear safety agency diagnostic reference levels|
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| Discussion|| |
This study established DRLs for the radiological examination in two selected university teaching hospitals in North Eastern Nigeria. The hospitals studied were divided into two A and B, respectively. There are three university teaching hospitals in North Eastern Nigeria as at the time of the study. However, Hospitals A and B were chosen because they met the inclusion criteria for the study having the necessary functional imaging facility (mammography). A total of sixty patients participated in this study.
[Table 1] shows mean and standard deviation of the ESD, MGD and DRLs for the mammography examination. The mean ESD for CC and MLO are 0.50 ± 9.48 mGy and 0.70 ± 0.74 mGy for Hospital A, 0.31 ± 0.05 mGy and 0.69 ± 0.11 mGy for Hospital B. The total mean and standard deviation for both hospitals were 0.48 ± 0.69 mGy and 0.68 ± 0.40 mGy for CC and MLO respectively. The MGD for CC and MLO are 0.31 ± 0.05 and 0.69 ± 0.11 mGy. The DRL for CC and MLO are 0.63 mGy and 1.04 mGy. The use of different breast imaging technique in patient's dose management is increasing due to technology advancement, availability of radiological equipment, and health-care cost-cutting measures., The mean dose in general mammography examination was found to be larger than the values reported in the studies done in India and Sudan. In the study, the mean number of runs and images per examination category were comparable. The uniformity trend in radiographic imaging technique for most examination in this study is also supportive for the potential for standardization of anatomical related imaging techniques and protocols.
The results of the MGD estimated from this study shows that dose from mammography is lower when compared with the result obtained from another work on the MGD s for women undergoing mammography breast screening. The value obtained from his work was 0.26–2.26 mGy for the MLO Views and 0.08–5.30 mGy. The difference was probably due to the difference in tube output and the use of film screen combination of which some center were using digital mammography. However, this study agrees with another study which discovered that over 90 of patients had MGD values <2.5 mGy which is below the guidance level of 3 mGy. The value of MGD obtained from this work is also significantly lower than that of another study that calculates the MGD assessment for phantoms' and patients in which the phantom gave the MGD of 1.9 mGy. When MGD is supplemented by a patient dose survey, the average MGD per image was 2.8 mGy for CC and 4.3 mGy for the MLO. Differences may be due to differences in tube output and breast granularity.,
[Table 2] shows the relationship between doses received by patients and anthropometric parameters for the mammography examination. There was no statistically significant relationship (P > 0.05) between the dose and compressed breast thickness, weight, height, and BMI.
[Table 3] shows the relationship between doses received by patients and anthropometric parameters for the mammography examination. There was no statistically significant (P > 0.05) relationship between MGD and technical parameters. Although breast thickness is not the only factor to have an effect on MGD, it is the most consistently reported. Other factors that affect MGD are not consistently reported., Other factors reported include kVp, target filter combination, HVL, mAs 6. The lack of documented protocol and etiquette in establishing DRLs in Nigeria and other countries makes it difficult to come up with a guideline and recommendations on DRL for mammography.,
[Table 4] shows the t-test comparison of radiation dose and some technical parameters for mammography examination between Hospital A and B. Detailed result from table shows that when the mean doses for the hospitals were compared there was no statistically significant relationship (P > 0.05) between mAs, kVp, and MGD for the hospitals. This corroborates with another study done by Lourenco et al., 2013, sponsored by European Society of Radiologist which indicated that there is no statistically significant relationship between two hospitals (P = 0.090).
[Table 5] shows a comparison of established DRLs for the mammography examination with that of the European Commission, United Kingdom, and Australia. The DRL for ARPANSA, EC, UK, and this work were 0.88 mGy, 2.0 mGy, 2.0 mGy, and 0.63 mGy for CC view. DRL for MLO was 1.30 mGy, 2.0 mGy, 2.1 mGy, and 1.04 mGy for ARPANSA, EC, UK, and the present work, respectively. The DRL values for mammography in this study are higher compared to that of ARPANSA, UK, and European Commission, respectively. The higher DRL encountered might have arisen from differences in sample sizes as well as the inherent variations in patient radiation dose values for different types of examination. The higher dose values in this present study suggest the need for patient dose optimization and this agrees with another study. DRLs for mammography have been established across the world, and variable methods and techniques were used. However, an internationally accepted protocol that includes dose measurement method, conversion factor compressed breast thickness for patients or phantoms and DRL percentile needs to be established before important useful and accurate international comparison can be made.
| Conclusion|| |
This present study established DRLs for mammography examinations in North Eastern Nigeria. The DRL values for mammography in this study are higher compared to that of ARPANSA, UK, and the European Commission. This study has an educational and regulatory function to the radiology community, and furthermore, provides a benchmark to assist any statutory organization to establish DRLs for diagnostic radiology practices in Nigeria, Africa, and the world entirely.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]