|Year : 2021 | Volume
| Issue : 2 | Page : 46-52
Diagnostic reference levels for head and abdominal computed tomography of adult patients in selected states in South-South Nigeria
Anwuli Christiana Tobi1, Chukwuka Emmanuel Mokobia1, Joyce Ekeme Ikubor2, Akintayo Daniel Omojola3, Maryann Etim Ekpo4, Anita Franklin Akpolile1
1 Department of Physics, Delta State University, Abraka, Nigeria
2 Department of Radiology, Faculty of Clinical Medicine, College of Health Sciences, Delta State University, Abraka, Nigeria
3 Department of Radiology, Federal Medical Centre, Medical Physics Unit, Asaba, Delta State, Ibadan, Nigeria
4 Department of Physics, University of Ibadan, Ibadan, Nigeria
|Date of Submission||01-Dec-2020|
|Date of Acceptance||15-Feb-2021|
|Date of Web Publication||07-May-2021|
Mrs. Anwuli Christiana Tobi
Department of Physics, Delta State University, Abraka
Source of Support: None, Conflict of Interest: None
Context: Diagnostic reference level (DRL) is the first step in the optimization process to manage patient dose corresponding with the medical purpose. Aim: The objective of this study was to develop local DRL for computed tomography (CT) of the head and abdomen in adult patients in four CT centers in South-South Nigeria. Materials and Methods: A prospective, cross-sectional study of 546 adult patients that underwent CT examination of the head and abdomen from 2018 to 2020 using four different CT scanners. Volume CT dose index (CTDIvol) and dose length product (DLP) of contrast and non-contrast CT examinations of the head and abdomen were collated and the 50th percentile DRL was determined and compared to other published DRLs. Results: The 50th percentile CTDIvol/DLP for non-contrast head CT examination for centers A, B, C, and D was 75.3 mGy/1776.6 mGy.cm, 21.8 mGy/457 mGy.cm, 17.4 mGy/373.6 mGy.cm, and 29.6 mGy/628.5 mGy.cm, respectively. The 50th percentile CTDIvol/DLP for contrast head CT examination for centers A, B, C, and D was 150.6 mGy/3326.2 mGy.cm, 41.4 mGy/832.4 mGy.cm, 35.6 mGy/653.6 mGy.cm, and 77.9 mGy/1458.4 mGy.cm, respectively. The 50th percentile CTDIvol/DLP for non-contrast abdomen CT examination for centers A and B was 22.8 mGy/1488.5 mGy.cm and 7.9 mGy/302.3 mGy.cm, respectively. The 50th percentile CTDIvol/DLP for contrast abdomen CT examination for centers B and C was 19.6 mGy/825.7 mGy.cm and 31.5 mGy/1555.5 mGy.cm, respectively. There was correlation between contrast and non-contrast CTDI (P = 0.003) and DLP (P = 0.025) for the head. Conclusion: Wide variations CTDIvol and DLP values were observed among the centers for similar body part CT examinations.
Keywords: Computed tomography, dose-length product, diagnostic reference level, volume computed tomography dose index
|How to cite this article:|
Tobi AC, Mokobia CE, Ikubor JE, Omojola AD, Ekpo ME, Akpolile AF. Diagnostic reference levels for head and abdominal computed tomography of adult patients in selected states in South-South Nigeria. J Radiat Cancer Res 2021;12:46-52
|How to cite this URL:|
Tobi AC, Mokobia CE, Ikubor JE, Omojola AD, Ekpo ME, Akpolile AF. Diagnostic reference levels for head and abdominal computed tomography of adult patients in selected states in South-South Nigeria. J Radiat Cancer Res [serial online] 2021 [cited 2021 Jul 29];12:46-52. Available from: https://www.journalrcr.org/text.asp?2021/12/2/46/315659
| Introduction|| |
There has been a tremendous increase in the use of computed tomography (CT) in medical imaging since its introduction. This has resulted in an increased risk of cancer from radiation exposure to the organs during CT scanning. In medical imaging, the use of reference values known as diagnostic reference levels (DRLs) is often preferred to that of dose limits. The former represent the first step in the optimization process in the management of patient dose. The introduction of DRL in clinical practices has help in the identification of irregularities in the delivery of dose to the patient. DRLs are often established for different regions from surveys of doses from varying CT imaging examinations., These indicators of imaging practice will not only provide guidance in the dose management but also ensure that appropriate doses are delivered during specific clinical examinations. The radiation metric quantities used for DRL in CT are the volume CT dose index (CTDIvol) and dose-length product (DLP). An approximate of the average dose to a cross-section of the phantom is represented by the CTDIvol. The complete radiation risk to a patient is represented by the DLP.
The International Commission on Radiological Protection (ICRP) in 2007 recommends that for DRLs in medical imaging, the median value (50th percentile) for the DRL quantity from each of the centers in the survey be used as local/facility DRLs while 75th percentile of the median values obtained from each centers be used as national DRLs.
Ekpo et al. noting the absence of a recommended DRL value for CT examinations in Nigeria highlighted the need for establishing such at all levels-National, Regional and State as has been recommended by the ICRP. This absence has earlier been observed by Martin et al.
In Nigeria, in spite of the large number of examinations carried out yearly, the dose information available is grossly inadequate. Most of the dose data available are from the South-West (SW), South-East, North-Central, South-South, and Middle Belt of the country. There is no evidence of recommended data indicating the establishment of national DRLs of common CT examinations carried out in Nigeria. The study is aimed at developing local DRLs for head and abdominal CT examinations in selected centers in the South-South.
| Materials and Methods|| |
The study commenced with obtaining ethical clearance from the Health Research and Ethics Committee from the radiological centers.
This study was a prospective, cross-sectional study of 546 adult patients that underwent CT examination of the head and abdomen (contrast and non-contrast) using four different CT scanners in Edo and Delta states in the South-South region of Nigeria (two were in government based facilities while the other two were in privately owned centers) coded as A, B, C, and D, respectively.
This study evaluated CT DRLs of the head and abdomen, which are the most commonly performed CT examinations in each of the study centers. CT scanners surveyed had multi-slice capability ranging from 4 to 64 slices. Dose survey was carried out for a period of 14 months. Head CT was the most common examination done in each of the centers (84.6%), followed by CT abdomen (15.4%).
The equipment were CT scanners of the following models, Toshiba-aquillion (64 slice), General Electric (GE) Revolution ACTs (8 slice), GE light speed plus (4 slice), and GE bright speed (4 slice). Some details of the scanners are given in [Table 1].
Scan protocols for both adult head and abdomen were set at potential tube voltage of 120kvp for all centers while the tube current varied among the scanners. The slice thickness, pitch, rotation time, and scan length also varied among the centers [Table 2].
|Table 2: Technical parameters of computed tomography scanners for the different examinations|
Click here to view
Data for all CT head and abdomen examinations (contrast and non-contrast) in 546 adult patients (age 18–95 years) performed between October 2018 and March 2020 were prospectively collated from the console of each of the CT scanner in the study centers by the researchers in the presence of the radiographers during patient scan without interfering with patient care or delivery of CT service to the patient.
Data collected and recorded for each patient include patients' bio data such as age, gender and weight; scan protocol, CTDIvol, and DLP. Exposure parameters in terms of tube voltage, tube current, and rotation time were also recorded.
The minimum, maximum, standard deviation, median, mean, and 50th percentiles and 75th percentiles were analyzed for CTDIvol and DLP using the SPSS for Windows, Version 20.0 (SPSS Inc., Chicago, IL, USA). The DRL for each study center was defined at 50th percentiles of CTDIvol and DLP values. The 50th percentile of CTDIvol and DLP for each center was compared with the DRL values published by other researchers in Nigeria, Africa, European commission, United Kingdom UK, United States of America (USA), Germany, Ireland, Norway, Switzerland, India, Portugal, and Japan.
| Results|| |
546 CT examinations were carried out in this study in which the study population comprised of 269 female and 277 male adult patients in all of the centers. Center B recorded the highest number of patients, whereas center D had the least number of patients [Table 3]. The 50th/75th percentile CTDIvol and DLP for non-contrast examinations of the head in the four study centers was 75.3 mGy/75.3 mGy and 1777 mGy.cm/2115.3 mGy.cm for center A, 21.8 mGy/23 mGy and 457 mGy.cm/509.6 mGy.cm for center B, 17.4 mGy/18.5 mGy and 373.6 mGy.cm/524.8 mGy.cm for center C, 29.6 mGy/36.5 mGy and 628.5 mGy.cm/718.6 mGy.cm for center D. The 50th/75th percentile CTDIvol and DLP for contrast examinations of the head in the four study centers were 150.6 mGy/150.6 mGy and 3326.2/3703.8 mGy.cm for center A, 41.4 mGy/45.4 mGy and 832.4/926.4 mGy.cm for center B, 35.6 mGy/35.6 mGy and 704 mGy.cm for center C, 77.9 mGy/80.7 mGy and 1458.4/1769 mGy.cm for center D.
The 50th/75th percentile CTDIvol and DLP for non-contrast examinations of the abdomen in centres A and B was 22.8 mGy/22.8 mGy and 1488.5 mGy.cm/1557.9 mGy.cm for center A, respectively, 7.9 mGy/8 mGy and 302.3 mGy.cm/370.4 mGy.cm for center B. The 50th/75th percentile CTDIvol and DLP for contrast examinations of the abdomen in centers B and C were 19.6 mGy/23.2 mGy and 825.7 mGy.cm/1030.3 mGy.cm for center B and 31.5 mGy/38.3 mGy and 1555.5 mGy.cm/2004.8 mGy.cm for center C.
There was no correlation between the CTDIvol at 75th percentile with age (P = 0.213), but there was correlation with CTDIvol at 50th percentile (P = 0.006), DLP at 50th percentile (P = 0.010), and DLP at 75th percentile (P = 0.017) for non-contrast head CT for center A, B, C, and D.
There was no correlation between the CTDIvol at 75th percentile with age (P = 0.341), but there was correlation with CTDIvol at 50th percentile (P = 0.010), DLP at 50th percentile (P = 0.004), and DLP at 75th percentile (P = 0.001) for contrast head CT for center A, B, C, and D [Table 4].
|Table 4: Volume computed tomography dose index and dose length product values obtained for all centers|
Click here to view
There was no difference in age (P = 0.05), CTDIvol at 50th percentile (P = 0.222), DLP at 50th percentile (P = 0.316), CTDIvol at 75th percentile (P = 0.222), and DLP at 75th percentile (P = 0.342) for non-contrast and contrast examination for the head [Table 4].
A comparison of 50th percentile DRL values of this study for non-contrast head CT with that of published DRLs in Nigeria shows that Center A has the highest dose value of CTDIvol and DLP. This is followed closely by the study in Ibadan [Table 5].
|Table 5: Comparison of diagnostic reference level values of non-contrast head computed tomography with that of published diagnostic reference levels in Nigeria|
Click here to view
The comparison of DRL values of non-contrast head CT with that of published DRLs in Africa shows that the study in Senegal had the highest CTDIvol dose value. This is followed by centers A, the study in Ghana, the study in Kenya (2016), the study in Cameroun, the study in Kenya (2010), centers D in Benin, center B in Benin, and center C in Warri, respectively. Center A recorded the highest DLP value [Table 6].
|Table 6: Comparison of diagnostic reference level values of non-contrast head computed tomography with that of published diagnostic reference levels in Africa|
Click here to view
When compared with published DRLs in other parts of the world, the CTDIvol value of center A is same with the ACR reference value alongside Norway and Portugal, while its DLP value is far higher than all the other countries [Table 7].
|Table 7: Comparison of diagnostic reference level values of non-contrast head computed tomography with that of published diagnostic reference levels in other parts of the world|
Click here to view
For contrast examination of the head, the 50th percentile values of CTDIvol and DLP obtained in centers A and D were far higher than all other published values compared in this study [Table 8].
|Table 8: Comparison of diagnostic reference level values of contrast head computed tomography with that of published diagnostic reference levels|
Click here to view
The obtained CTDIvol and DLP values from the present study are below the ACR and European commission values. Centers C and D were not considered since they do not have patient for non-contrast abdominal CT scan examination as at the time of this study [Table 9].
|Table 9: Comparison of diagnostic reference level values of non-contrast abdominal computed tomography with that of published diagnostic reference levels|
Click here to view
Centers A and B were not considered since they do not have patient for contrast abdominal CT scan examination as at the time of this study. Center C recorded a higher CTDIvol and DLP values when compared with other studies [Table 10].
|Table 10: Comparison of diagnostic reference level values of contrast abdominal computed tomography with that of published diagnostic reference levels|
Click here to view
| Discussion|| |
This study established the first local DRLs for CT head and abdomen examinations of adult patients in four radio diagnostic centers in South-South Nigeria.
The study observed that all the centers performed both contrast and non-contrast CT head scans. Center A performed only non-contrast CT abdomen examinations. Center B performed both contrast and non-contrast CT abdomen examinations. Center C performed only contrast CT abdomen examinations. Center D did not have enough patients for abdomen CT examinations. Contrast head CT examination had the highest number of patients. Different technical protocols for CT examination of the head and abdomen were observed among the centers. Although all the centers used the same tube voltage value of 120kv for all adult examinations, non-contrast CT abdomen examinations were performed in centers A and B only while contrast CT abdomen examinations were performed in only centers B and C. The present study showed no significant difference in CTDIvol for contrast and non-contrast CT scan (P = 0.220).
A one-way ANOVA test shows that there was statistically significant difference between kVp and other parameters such as image thickness (P = 0.016), pitch (P = 0.012), rotation time (P = 0.012), and scan length (P = 0.050). There was also no statistically significant difference for mAs and other parameters (P < 0.05). The study also showed that there was no statistically significant difference in kVp against mAs among the centers for the head CT.
In center A, the values of the 50th percentile CTDIvol and DLP in both head and abdomen (contrast/non-contrast) CT examinations were higher than in centers B, C, and D. The 50th percentile CTDIvol for non-contrast CT head examinations of center A was 53% higher than center B, 58% higher than center C, and 45% higher than center D. The 75th percentile CTDIvol value of non-contrast CT head examinations in center A was 52% higher than center B, 56% higher than center C and 38% higher than center D. The 50th percentile CTDIvol for contrast CT head examinations of center A was 110% higher than center B, 115% higher than center C and 73% higher than center D. The 75th percentile CTDIvol value of contrast CT head examinations in center A was 106% higher than center B, 115% higher than center C and 70% higher than center D. This study discovered that the mA protocol in center A was 1.9, 4.4, and 3.7 times higher to center B, C, and D, respectively. Another factor identified was the type of scanner and image acquisition algorithm of the CT in center A. Some studies have reported high dose with Toshiba CT product.,
The 50th percentile CTDIvol value for noncontrast CT head examinations for center A was 14% higher than the study in Nigeria, 26% higher than the study in SW, 9% higher than the study in Anambra, 37% higher than the study in Abuja, and 1% higher than the study in Ibadan.
The 50th percentile CTDIvol value for noncontrast CT head examinations for center A was 11% higher than the study in Ghana, 23% higher than the study in Cameroun, 14% lower than the study in Senegal, 24% higher than the study in Kenya (2010), and 14% higher than the study in Kenya (2016).
The 50th percentile CTDIvol value for non-contrast CT head examinations was 10% higher than the study in UK, 15% higher than the study in Europe, 10% higher than the study in Germany, 17% higher than the study in Norway, 10% higher than the study in Switzerland, 43% higher than the study in India, and 10% lower than the study in Japan. The 50th percentile CTDIvol values in center A was the same with the study in the USA, Norway, and Portugal. Centers B, C, and D have CTDIvol values below the European commission and ACR recommended values.
The 50th percentile CTDIvol in center A for contrast CT head examinations was 103% higher than the study in SW, 91% higher than the study in Europe, 108% higher than the study in Iran, 85% higher than the study in Ireland, and 84% higher than the study in France.
The 50th percentile CTDIvol obtained in center A for non-contrast abdominal CT examinations was 15% higher than center B, 13% higher than the study at SW Nigeria, 8% higher than the study in UK, 2% lower than the study at Europe, 2% lower than the study at the USA (2008), and 3% higher than the study at the USA (2017).
The 50th percentile DLP value of head CT examinations (contrast and non-contrast) in center A was far higher than that obtained in the other study centers and other compared studies.
A higher CTDI and DLP dose values for head CT examinations were observed in all the centers and published studies. This is due to the use of high dose to obtain quality images since the head is made up of high attenuating bony structures.
A large variation of dose was observed among the centers in this study for both head and abdomen CT examinations. This may be due to the different scanner types, slices, and the imaging protocols used by each center. Dose optimization is required for CT head examinations (contrast/non-contrast) in center A to reduce patient radiation exposure.
There was no statistically significant correlation between mAs and CTDIvol (P = 0.180) and DLP (P = 0.262) for center A-D for head CT at 75th percentile. A study by Xu et al. shows that there was statistically significant correlation between mAs and CTDIvol, showing that mAs can strongly affect CTDIvol. An initial assessment shows that the protocols were statistically different from a One-way ANOVA test among the four facilities. These results can be used to explain the lack of correlation that was observed and it also indicates that there was no protocol harmonization in the studied area. Patient shape and size have been shown to affect CTDIvol and DLP, respectively, it was not available in this study as most center do not keep record of patient thickness. There was no correlation between patient weight and CTDIvol (P = 0.291/P = 0.558) and DLP (P = 0.428/P = 0.544) for non-contrast and contrast head CT scans.
Furthermore, there was no statistically significant difference in the DLP and CTDIvol for head and abdomen for non-contrast examination (P = 0.761; P = 0.340). This was also same for contrast exam in center B and C (P = 0.295; P = 0.067). Since the DLP is the product of the CTDIvol and the scan length, this implies that the scan time for the head and abdomen did not affect both parameters (CTDIvol and DLP).
| Conclusion|| |
This study provides the first DRLs for head and abdominal CT examinations which are the most common CT adult examinations performed in the centers. The obtained data in this study can contribute in the development of national DRL in Nigeria.
The authors acknowledge with thanks the management and staff of the radiology department of Delta State University teaching hospital, Oghara, Lily hospital, Warri, University of Benin teaching hospital, Benin City and Raytouch diagnostic center, Benin City.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
United Nations Scientific Committee on the Effects of Atomic Radiation UNSCEAR. Sources and Effects of Ionizing Radiation. Volume II. United Nations, New York: Effects Report to the General Assembly, with Scientific Annexes; 2000.
Brenner D, Elliston C, Hall E, Berdon W. Estimated risks of radiation-induced fatal cancer from pediatric CT. AJR Am J Roentgenol 2001;176:289-96.
International Commission on Radiological Protection ICRP. The 2007 Recommendations of the International Commission on Radiological Protection. ICRP publication 103. Ann ICRP 2007;37:1-332.
Foley SJ, McEntee MF, Rainford LA. Establishment of CT diagnostic reference levels in Ireland. Br J Radiol 2012;85:1390-7.
Korir GK, Wambani JS, Korir IK, Tries MA, Boen PK. National diagnostic reference level initiative for computed tomography examinations in Kenya. Radiat Prot Dosimetry 2016;168:242-52.
Jarvinen H, Seuri R, Koresniemi M, Lajunen A, Hallinen E, Savikurki-Heikkila P, et al
. Indication-Based national diagnostic reference levels for paediatric CT. A new approach with proposed values. Prot Dosimetry 2015;165:86-90.
McCollough CH, Leng S, Yu L, Cody DD, Boone JM, McNitt-Gray MF. CT dose index and patient dose: They are not the same thing. Radiology 2011;259:311-6.
Nagel HD. Radiation Exposure in Computed Tomography. Germany: CTB Publications, d-21073 Hamburg; 2002.
Ekpo EU, Adejoh T, Akwo JD, Owujekwe CE, Modu AA, Abba M, et al
. Diagnostic reference levels for common computed tomography (CT) examinations: Results from the first Nigerian nationwide dose survey. J Radiol Prot 2018;38:525-35.
International Commission on Radiological Protection ICRP. Radiological Protection and Safety in Medicine (Report 73). Ann ICRP 1996;26:1-47.
Martin CJ, Le Heron J, Borras C, Sookpeng S, Ramirez G. Approaches to aspects of optimization of protection in diagnostic radiology in six continents. J Radio Prot 2013;33:711-34.
Akpochafor MO, Omojola AD, Adeneye SO, Ekpo V, Adedewe NA, Adedokun AR, et al
. Computed tomography dose reference level for non contrast and contrast examination in 13 CT Facilities in South-West Nigeria. Pak J Radiol 2018;28:285.
Adejoh T, Nzotta CC, Aronu ME, Dambele MY. Diagnostic reference levels for computed tomography of the head in Anambra State of Nigeria. West Afr J Radiol 2017;24:142-6. [Full text]
Abdukadir MK, Schandof C and Hasford F. Determination of computed Tomography Diagnostic Reference Levels in North-Central Nigeria. Pac J Sci Tecchnol 2016;17:341-9.
Mundi AA, Hammed S, Dlama J, Abdul- Jamiu A, Peter E, Itopa R, et al
. Diagnostic reference level for adult brain computed tomography scans: A case study of a tertiary health care center in Nigeria. J Dent Med Sci 2015;14:66.
Ogbole GI and Obed R. Radiation doses in computed Tomography: Need for optimization and application of dose reference levels in Nigeria. West Afr J Radiol 2014;21;1-6.
Inkoom S, Schandorf C, Boadu M, Emi-Reynolds G, A Nkansah. Adult medical x-ray assessments for computed tomography procedures in Ghana – A review. J Appl Sci Technol 2014;19;1-9.
Moifo B, Roger J, Tapouh M, Guena MNT, Ndah TN, Samba RN, et al
. Diagnostic Reference Levels of Adults CT-Scan Imaging in Cameroon: A Pilot Study of Four Commonest CT-Protocols in Five Radiology Departments Doses from Computed Tomography (CT) Examinations in the UK – 2011 Review. Open J Med Imaging 2017;7:1-8.
Diagne M, Gning F, Dieng MM, Gueye L. Preliminary Diagnostic Reference Levels of Adult CT at Aristide Ledantec National Hospital 23rd
WiN Global Conference: Women in Nuclear meet Atoms for Peace. Programme Abstr INIS 2015;48:150.
Wambani JS, Korir GK, Onditi EG, Korir IK. A survey of computed tomography imaging techniques and patient dose in Kenya. East Afr Med J 2010;87:400-7.
Shrimpton PC, Hillier MC, Lewis MA, Dunn M. National survey of doses from CT in the UK: 2003. Br J Radiol 2006;79:968-80.
European Commision (EC). Diagnostic Reference Levels in Thirty-six European countries.European Union, Luxembourg Radiation Protection 180:2014.
American College of Radiology (ACR). ACR practice guideline for diagnostic reference levels in medical X-ray imaging. ACR practice guideline. Resolution 3, Virgina, United States:ACR;2008.
Brix G, Nagel HD, Stamm G, Veit R, Lechel U, Griebel J, et al
. Radiation exposure in multi-slice versus single-slice spiral CT: Results of a nationwide survey. Eur Radiol 2003;13:1979-91.
Friberg EG, Widmark A, Ryste Hauge IH. National Collection of Local Diagnostic Reference Levels in Norway and Their Role in Optimization of X-Ray Examinations. Østerås, Norway: Norwegian Radiation Protection Authority; 2009. p. 8.
Treier R, Aroua A, Bochud F, Samara E, Verdum FR, Stuessi A, et al
. Diagnostic reference levels in computed tomography in Switzerland. In: Dossel O, Schlegel WC, editors. World Congress on Medical Physics and Biomedical Engineering. Vol. 25. September 7-12, Munich Germany: IFMBE Proceedings; 2009.
Saravanakumar A, Vaideki K, Govindarajan KN, Jayakumar S. Establishment of diagnostic reference levels in computed tomography for select procedures in Pudhuchery, India. J Med Phys 2014;39:50-5.
] [Full text]
Santos J, Foley S, Paulo G, McEntee MF, Rainford L. The establishment of computed tomography diagnostic reference levels in Portugal. Radiat Prot Dosimetry 2014;158:307-17.
Fukushima Y, Tsushima Y, Takei H, Taketomi-Takahashi A, Otake H, Endo K. Diagnostic reference level of computed tomography (CT) in Japan. Radiat Prot Dosimetry 2012;151:51-7.
Najafi M, Deevband MR, Ahmadi M, Kardan MR. Establishment of diagnostic reference levels for common multi-detector computed tomography examinations in Iran. Australas Phys Eng Sci Med 2015;38:603-9.
French Republic, Order of 24 0ctober 2011 relating to diagnostic reference levels in radiology and nuclear medicine. Official Journal of the French Republic of January 14, 2012, Text 22 of 147, NOR: ETSP1129093A.
Kanal KM, Butler PF, Sengupta D, Bhargavan-Chatfield M, Coombs LP, Morin RL. U.S. diagnostic reference levels and achievable doses for 10 adult CT examinations. Radiology 2017;284:120-33.
Elmahdi A, Abuzaid MM, Babikir E, Sulieman A. Radiation dose associated with multi-detector 64-slice computed tomography brain examinations in Khartoum State, Sudan. Pol J Radiol 2017;82:603-6.
Smith-Bindman R, Wang Y, Chu P, Chung R, Einstein AJ, Balcombe J, et al
. International variation in radiation dose for computed tomography examinations: Prospective cohort study. BMJ 2019;364:k4931. doi: 10.1136/bmj.k4931.
Xu J, He X, Xiao H, Xu J. Comparative study of volume computed tomography dose index and size-specific dose estimate head in computed tomography examination for adult patients based on the mode of automatic tube current modulation. Med Sci Monit 2019;25:71-6.
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10]