TY - JOUR
AU - Ahmed, Nada A
AB - ABSTRACT Radiation doses were determined to propose national diagnostic reference levels (NDRLs) and achievable doses (ADs) for computed tomography (CT) examinations in Sudan. Doses were estimated from retrospectively collected scan parameters for 1336 CT examinations of adult patients from 14 Sudanese hospitals using CT Expo 2.5 software. ADs and NDRLs were set at the 50th and 75th percentile of the hospital median dose distribution, respectively. The proposed CTDIvol (mGy) ADs ranged from: 10 (chest) to 64 (head), and that of the dose-length product (DLP; mGy.cm) ranged from 366 (chest) to 1225 (head). The proposed CTDIvol (mGy) NDRLs ranged from 15 kidney–ureter–bladder (KUB) to 79 (head), whereas that of the DLP (mGy.cm) ranged from 690 (chest) to 1490 (head). Current doses fell within the upper range of the doses presented in the literature emphasizing the need for implementation of the current ADs and NDRLs for CT to enhance patient protection and dose optimization in Sudan. INTRODUCTION Protecting patients from radiation exposure during computed tomography (CT) is extremely important given the high collective dose that occurs in the population as a result of radiation exposure from CT(1). Despite the concerns associated with radiation exposure, CT remains a valuable and indispensable tool for diagnosing several symptoms given its continuous evolution(1, 2). The most fundamental change has been observed in CT hardware (i.e. increased detector rows, improved X-ray tubes, detectors and so on), but software improvements have also been made (i.e. dose-reduction systems and new reconstruction algorithms), which enable more rapid image acquisition and enhanced image quality at lower dose(3). Dose surveys have been used as a tool to monitor radiation dose levels for quality assurance purposes and to compare the radiation burden that results from CT scans with that arising from other imaging modalities. The national reference doses for radiographic X-ray examinations were first proposed in the UK in 1989 following a national dose survey that was conducted in the mid-1980s(4). The International Commission on Radiological Protection (ICRP) defined the diagnostic reference levels (DRLs) in 1990 and further developed the concept in ICRP publications 73, 105 and 135(5–8). According to the ICRP, DRLs are ‘a form of investigation level, apply to an easily measured quantity, usually the absorbed dose in air, or in a tissue-equivalent material at the surface of a simple standard phantom or representative patient’(7). A DRL is an investigational level used to identify unusually high radiation doses for common imaging procedures. DRLs are suggested action levels; if a facility’s dosage exceeds these levels, the facility should review its methods and determine if acceptable image quality can be achieved at lower doses. DRLs are not dose limits, as dose limits may compromise patient care(5–9). Due to its importance, the use of DRLs is endorsed by major radiation protection professional and advisory bodies around the globe. In the UK, the Health Protection Agency—formerly the National Radiological Protection Board (NRPB)—reported a 55% reduction in the 75th percentile of patient radiation doses after 20 years of employing and educating others about DRLs and achievable doses (ADs)(9). ADs can be used with DRLs to help optimize image quality and dose. It is approximately set at the median (50th percentile) of the study dose distribution—i.e. half of the facilities produce images at lower doses and half use higher doses(4, 9). Facilities should strive to reduce patient doses below the proposed ADs. With multi-slice CT being increasingly used due to its clinical benefits, it is vital to determine the radiation absorbed dose levels in patients during these procedures, as this will help propose national diagnostic reference levels (NDRLs) for use in dose optimization. Consequently, DRLs in CT have been established in several countries around the world to reduce dose variability and promote optimization(10–16). In Sudan, several dose surveys were performed to explore radiation protection for patients across different diagnostic procedures, including radiography, interventional radiology and CT(17–19). The survey results were used for dose optimization. Our recent efforts focused on determining the radiation doses for CT using size-specific dose estimates(20, 21). As there were no NDRLs for imaging procedures in Sudan, radiation protection institutions and professionals merely rely on internationally established DRLs. In 2017, the National Assembly in Sudan passed the Nuclear and Radiological Regulatory Control Act(22). The act established the Sudanese Nuclear & Radiological Regulatory Authority (SNRRA) as an independent, national regulator on such areas as radiation safety, nuclear security, safeguards and liability. SNRRA is also responsible for adopting guidelines and dose constraints for different exposure scenarios, including proposed NDRLs for imaging procedures. As of 2016, a nationwide dose survey was initiated in Sudan, which aimed to derive ADs and NDRLs for common CT examinations. This study uses retrospectively collected CT scan parameters, as well as CT Expo software(23), to calculate volume CT dose index (CTDIvol) and dose-length product (DLP) dose metrics for adult CT examinations in Sudan. The overall object of the survey was to present evidence-based DRLs for the purpose of reducing radiation exposure among patients, while helping to identify opportunities for optimization. The presented data add additional insights into the factors that affect patient dose in CT examinations. MATERIALS AND METHODS Survey design This survey was conducted from 2017 to 2018 to collect patient scan parameters, which were used to calculate the radiation doses for 1336 adult patient examinations across 14 hospitals in Sudan. The 14 scanners included in this survey, which constituted 35% of all CT scanners in Sudan in 2017, perform ~80% of the CT scans for adult patients in the country. The remaining 20% are performed by scanners mostly distributed in distant, small towns with lower population densities. Data collected in this study are thus assumed to have provided a fairly representative picture of the CT practices performed in the country at the time. Of the 14 CT scanners, one was a single-slice, one was an eight-slice, five were 16-slice, six were 64-slice and one was a 128-slice CT unit. Adult patients aged >  17 years were studied according to anatomic region: head, paranasal sinus (PNS), chest, abdomen, pelvic, kidney–ureter–bladder (KUB) and CT urography (CTU). The individual examinations were selected and matched to the seven standard CT examinations according to the hospital classifications. As such, some overlap is expected to exist, as some hospitals carry out abdominal CTs, whereas other hospitals performed it as an abdominal–pelvic examination. Data collection CT scan parameters were retrospectively collected from the Digital Imaging and Communications in Medicine (DICOM) datasets stored by the scanners. At the end of each week, one of the authors visited the clinic to collect the information before it could be deleted. They recorded the following CT scan parameters: CT equipment-specific information (make/model/year of installation and number of slices); patient demographic data (age and gender) and CT scan parameters (kV, mA, rotation time and scan time [spiral mode], scan length [start and end of the scan region], number of slices, slice thickness, collimation and pitch). Before dose calculations, data quality checks were performed by the project supervisor—an expert in the field—to ensure sufficiently correct information was collected to enable dose calculations and interpretations. CT scan parameters and the data for at least 20 patients per procedure at each facility were collected as recommended(8). In cases where a hospital used fixed kV and mA values, data collection was confined to at least 10 patients per procedure per hospital, as the collection of additional data was not expected to provide new information. CTDIvol and DLP values were calculated using retrospectively collected patient-specific scan parameters and CT Expo 2.5 dosimetry software(23). Table 1 summarizes the distribution of the scanner manufacturers, models, facility type, year of installation and information on the use of the tube current modulation (TCM). It is important to mention that the weight information of the studied patients was not included in the DICOM header; this has precluded us from applying weight restrictions on patient dose. Table 1 Distribution of scanner manufacturers and models Hospital . Facility type . CT device (Make/Model) . Number of slices . Year of installation . The use of TCM . ANH Military Toshiba/Aquilion 64 2013 Fixed kV, and mA ZSH Private Toshiba/Aquilion 64 2011 Fixed kV, and mA MMH Military Toshiba/Aquilion 64 2013 Fixed kV, and mA OSH Military Neusoft/NeuViz 128 2016 TCM DOC Private Neusoft/NeuViz 64 2014 TCM DAH Private Philips/Brilliance 64 2014 Fixed kV, and mAs RUH Military Siemens/Emotion 16 2008 TCM YPC Private Toshiba/Aquilion 16 2011 Fixed kV, and mA NIMR Government Siemens/Emotion 16 2013 TCM Kdfan Government GE/Bright speed 16 2014 TCM PSUD Government Shimadzu 1 2010 Fixed kV, mAs Medani Government Toshiba/Axiom 16 2014 TCM Antalia Private GE/Bright speed 8 2010 Fixed kV, mAs for Head CT RCARE Private Toshiba/Aquilion 64 2012 Fixed kV, mAs for Head CT Hospital . Facility type . CT device (Make/Model) . Number of slices . Year of installation . The use of TCM . ANH Military Toshiba/Aquilion 64 2013 Fixed kV, and mA ZSH Private Toshiba/Aquilion 64 2011 Fixed kV, and mA MMH Military Toshiba/Aquilion 64 2013 Fixed kV, and mA OSH Military Neusoft/NeuViz 128 2016 TCM DOC Private Neusoft/NeuViz 64 2014 TCM DAH Private Philips/Brilliance 64 2014 Fixed kV, and mAs RUH Military Siemens/Emotion 16 2008 TCM YPC Private Toshiba/Aquilion 16 2011 Fixed kV, and mA NIMR Government Siemens/Emotion 16 2013 TCM Kdfan Government GE/Bright speed 16 2014 TCM PSUD Government Shimadzu 1 2010 Fixed kV, mAs Medani Government Toshiba/Axiom 16 2014 TCM Antalia Private GE/Bright speed 8 2010 Fixed kV, mAs for Head CT RCARE Private Toshiba/Aquilion 64 2012 Fixed kV, mAs for Head CT Open in new tab Table 1 Distribution of scanner manufacturers and models Hospital . Facility type . CT device (Make/Model) . Number of slices . Year of installation . The use of TCM . ANH Military Toshiba/Aquilion 64 2013 Fixed kV, and mA ZSH Private Toshiba/Aquilion 64 2011 Fixed kV, and mA MMH Military Toshiba/Aquilion 64 2013 Fixed kV, and mA OSH Military Neusoft/NeuViz 128 2016 TCM DOC Private Neusoft/NeuViz 64 2014 TCM DAH Private Philips/Brilliance 64 2014 Fixed kV, and mAs RUH Military Siemens/Emotion 16 2008 TCM YPC Private Toshiba/Aquilion 16 2011 Fixed kV, and mA NIMR Government Siemens/Emotion 16 2013 TCM Kdfan Government GE/Bright speed 16 2014 TCM PSUD Government Shimadzu 1 2010 Fixed kV, mAs Medani Government Toshiba/Axiom 16 2014 TCM Antalia Private GE/Bright speed 8 2010 Fixed kV, mAs for Head CT RCARE Private Toshiba/Aquilion 64 2012 Fixed kV, mAs for Head CT Hospital . Facility type . CT device (Make/Model) . Number of slices . Year of installation . The use of TCM . ANH Military Toshiba/Aquilion 64 2013 Fixed kV, and mA ZSH Private Toshiba/Aquilion 64 2011 Fixed kV, and mA MMH Military Toshiba/Aquilion 64 2013 Fixed kV, and mA OSH Military Neusoft/NeuViz 128 2016 TCM DOC Private Neusoft/NeuViz 64 2014 TCM DAH Private Philips/Brilliance 64 2014 Fixed kV, and mAs RUH Military Siemens/Emotion 16 2008 TCM YPC Private Toshiba/Aquilion 16 2011 Fixed kV, and mA NIMR Government Siemens/Emotion 16 2013 TCM Kdfan Government GE/Bright speed 16 2014 TCM PSUD Government Shimadzu 1 2010 Fixed kV, mAs Medani Government Toshiba/Axiom 16 2014 TCM Antalia Private GE/Bright speed 8 2010 Fixed kV, mAs for Head CT RCARE Private Toshiba/Aquilion 64 2012 Fixed kV, mAs for Head CT Open in new tab Dosimetry data on Neusoft/NeuViz scanners shown in Table 1 were not included in the CT Expo 2.5 software; therefore, for these two scanners, the console-displayed CTDIvol and DLP values were recorded and used in the data analysis. Dosimetry Currently, two types of quantities are used to establish DRLs in CT(24–26). They include the following: (1) weighted CT dose index (CTDIw) and volume CT dose index (CTDIvol); and (2) CT DLP. CTDIw (from which CTDIvol is deduced) is defined as air kerma which, in the diagnostic X-ray energy range, is equal to the absorbed dose in air, and hence the term used is the CT dose index or, alternatively, the CT air kerma index. DLP is the integrated absorbed dose along a line parallel to the axis of rotation for the complete CT examination (DLP). In this study, CTDIvol and DLP radiation dose indices were calculated using CT Expo 2.5 Monte Carlo-based dosimetry software. This software uses Microsoft excel spreadsheets and the patient-specific scanning parameters that were collected to CTDIvol and DLP values(23). The software provides the DLP per sequence, as well as the DLP for the entire examination. Equations, as well as correction factors used in CT Expo software, were previously presented in the software documentation, as well as in the literature(18, 23, 27). CT Expo calculates the CTDIvol given information on pitch or equivalently total collimation and table feed for rotation. For head protocols (head and PNS), the software calculates CTDIvol and DLP based on 16-cm head CT phantoms. All other examinations (CTDIvol and DLP) were based on 32-cm abdominal CT phantoms. For multiple phase dose calculations using CT Expo, the average scan parameters were used to calculate the average CTDIvol per procedure, and the total DLP (the sum of DLPs for all phases) was calculated by setting the number of scan sequences used. Several methods are applied for dose measurements in CT that include the following: (1) measurements of CTDI for certain kV(17); (2) the console-displayed CTDI and DLP values(11) and (3) the software-based CT dose parameter calculations(18, 28). Although measurements of CTDI are laborious and time consuming to undertake for a nationwide survey, authors in the literature have expressed their concerns over the accuracy of the console-displayed dose data(28). Thus, it was recommended that clinicians should frequently review the accuracy of console-displayed CTDI and DLP following the acquisition of new CT scanners or after modifying the CT protocol(29). Thus, we have elected to use CT Expo software for data processing in our survey. An important feature of the CT Expo software program is that it includes scanner corrections for over-ranging and over-beaming, which increase the radiation dose by increasing the exposed area and dose profile, respectively(23, 27). DRLs and ADs Across all examinations, the NDRLs and ADs proposed in this study refer to both single and multiphase CT examination acquisitions. The ADs were set at the median (50th percentile), whereas the DRLs were set at the 75th percentile. The percentiles were determined from the distribution of hospital median values(8, 9). RESULTS In this study, six facilities were private hospitals, four were military hospitals and the remaining four were government hospitals. Of the 1336 CT examinations, there were 340 abdominal (25.4%), 327 head (24.5%), 217 chest (16.2%), 139 KUB (10.4%), 108 PNS (8.1%), 105 CTU (7.9%) and 100 pelvic CT scans (7.5%). Table 2 shows the median scan parameters and associated range for the seven CT examinations. The median age from 36 to 57 years. The median kV was in the range of 100–120. The median mAs ranged from 140 (for PNS CT scans) to 225 (for head CT scans). The median scan length ranged from 13.5 cm for PNS to 45.6 cm for abdominal CTs. The median pitch value ranged from 0.7 to 1.0. Table 2 Statistical summary (median and range) of the scan parameters across seven CT examinations Exam . Age . kV . mAs . L (cm) . Pitch . Med. . Range . Med . Range . Med . Range . Med . Range . Med. . Range . Head 49 29–68 120 100–140 225 40–601 16.0 12.1–20.2 0.8 0.3–1.8 PNS 36 26–46 120 100–140 140 100–300 13.5 10.2–20.3 0.7 0.3–1.7 Chest 54 43–72 120 100–130 150 52–200 31.9 19.1–35.8 1.0 0.5–1.6 Abd 56 40–69 120 100–120 169 45–250 45.6 38.1–66.7 1.0 0.6–1.6 Pelvis 47 26–60 120 120–120 194 68–250 31.7 26.0–45.0 0.9 0.7–1.5 KUB 46 27–58 120 100–130 183 49–253 42.9 41.0–47.0 1.0 0.6–1.5 CTU 48 33–51 120 100–120 170 49–250 42.2 28.2–46.4 0.8 0.6–1.0 Exam . Age . kV . mAs . L (cm) . Pitch . Med. . Range . Med . Range . Med . Range . Med . Range . Med. . Range . Head 49 29–68 120 100–140 225 40–601 16.0 12.1–20.2 0.8 0.3–1.8 PNS 36 26–46 120 100–140 140 100–300 13.5 10.2–20.3 0.7 0.3–1.7 Chest 54 43–72 120 100–130 150 52–200 31.9 19.1–35.8 1.0 0.5–1.6 Abd 56 40–69 120 100–120 169 45–250 45.6 38.1–66.7 1.0 0.6–1.6 Pelvis 47 26–60 120 120–120 194 68–250 31.7 26.0–45.0 0.9 0.7–1.5 KUB 46 27–58 120 100–130 183 49–253 42.9 41.0–47.0 1.0 0.6–1.5 CTU 48 33–51 120 100–120 170 49–250 42.2 28.2–46.4 0.8 0.6–1.0 Open in new tab Table 2 Statistical summary (median and range) of the scan parameters across seven CT examinations Exam . Age . kV . mAs . L (cm) . Pitch . Med. . Range . Med . Range . Med . Range . Med . Range . Med. . Range . Head 49 29–68 120 100–140 225 40–601 16.0 12.1–20.2 0.8 0.3–1.8 PNS 36 26–46 120 100–140 140 100–300 13.5 10.2–20.3 0.7 0.3–1.7 Chest 54 43–72 120 100–130 150 52–200 31.9 19.1–35.8 1.0 0.5–1.6 Abd 56 40–69 120 100–120 169 45–250 45.6 38.1–66.7 1.0 0.6–1.6 Pelvis 47 26–60 120 120–120 194 68–250 31.7 26.0–45.0 0.9 0.7–1.5 KUB 46 27–58 120 100–130 183 49–253 42.9 41.0–47.0 1.0 0.6–1.5 CTU 48 33–51 120 100–120 170 49–250 42.2 28.2–46.4 0.8 0.6–1.0 Exam . Age . kV . mAs . L (cm) . Pitch . Med. . Range . Med . Range . Med . Range . Med . Range . Med. . Range . Head 49 29–68 120 100–140 225 40–601 16.0 12.1–20.2 0.8 0.3–1.8 PNS 36 26–46 120 100–140 140 100–300 13.5 10.2–20.3 0.7 0.3–1.7 Chest 54 43–72 120 100–130 150 52–200 31.9 19.1–35.8 1.0 0.5–1.6 Abd 56 40–69 120 100–120 169 45–250 45.6 38.1–66.7 1.0 0.6–1.6 Pelvis 47 26–60 120 120–120 194 68–250 31.7 26.0–45.0 0.9 0.7–1.5 KUB 46 27–58 120 100–130 183 49–253 42.9 41.0–47.0 1.0 0.6–1.5 CTU 48 33–51 120 100–120 170 49–250 42.2 28.2–46.4 0.8 0.6–1.0 Open in new tab Table 3 presents the dose-distribution statistics associated with the scanners’ median values. The boxplot distributions of the CTDIvol (mGy) and DLP (mGy.cm) values of the examinations at different hospitals are depicted in Figures 1 and 2. Table 3 Dose-distribution statistics of the calculated scanner median values Exam . Sample size . Percentile of the dose distributions (%) . 95th percentile/ 5th percentile . Hospitals . Patients . 5 . 25 . 50 . 75 . 95 . CTDIvol (mGy)  Head 14 327 31.11 52.48 63.5 79.06 94.19 3.0  PNS 9 108 13.30 15.70 27.80 78.90 79.75 6.0  Chest 12 217 5.91 7.34 9.90 20.94 47.73 8.1  Abdomen 14 340 5.78 8.45 13.42 32.60 49.42 8.6  Pelvis 8 100 6.17 7.03 12.00 20.30 31.86 5.2  KUB 10 139 6.66 7.31 10.65 15.10 18.01 2.7  CTU 7 105 6.89 11.93 19.10 41.95 60.10 8.7 DLP (mGy.cm)  Head 14 327 565 960 1225 1490 2043 3.6  PNS 9 108 201 313 618 1363 1535.1 7.6  Chest 12 217 164 243 366 690 1711 10.4  Abdomen 14 340 253 358 722 1271 2300 9.1  Pelvis 8 100 225 309 600 838 959 4.3  KUB 10 139 299 337 511 816 910 3.0  CTU 7 105 356 566 850 1589 2267 6.4 Exam . Sample size . Percentile of the dose distributions (%) . 95th percentile/ 5th percentile . Hospitals . Patients . 5 . 25 . 50 . 75 . 95 . CTDIvol (mGy)  Head 14 327 31.11 52.48 63.5 79.06 94.19 3.0  PNS 9 108 13.30 15.70 27.80 78.90 79.75 6.0  Chest 12 217 5.91 7.34 9.90 20.94 47.73 8.1  Abdomen 14 340 5.78 8.45 13.42 32.60 49.42 8.6  Pelvis 8 100 6.17 7.03 12.00 20.30 31.86 5.2  KUB 10 139 6.66 7.31 10.65 15.10 18.01 2.7  CTU 7 105 6.89 11.93 19.10 41.95 60.10 8.7 DLP (mGy.cm)  Head 14 327 565 960 1225 1490 2043 3.6  PNS 9 108 201 313 618 1363 1535.1 7.6  Chest 12 217 164 243 366 690 1711 10.4  Abdomen 14 340 253 358 722 1271 2300 9.1  Pelvis 8 100 225 309 600 838 959 4.3  KUB 10 139 299 337 511 816 910 3.0  CTU 7 105 356 566 850 1589 2267 6.4 CTDIvol and DLP of the head protocols (head and PNS) are referenced to the 16 cm PMMA phantom; all other values are referenced to the 32-cm body phantom. Open in new tab Table 3 Dose-distribution statistics of the calculated scanner median values Exam . Sample size . Percentile of the dose distributions (%) . 95th percentile/ 5th percentile . Hospitals . Patients . 5 . 25 . 50 . 75 . 95 . CTDIvol (mGy)  Head 14 327 31.11 52.48 63.5 79.06 94.19 3.0  PNS 9 108 13.30 15.70 27.80 78.90 79.75 6.0  Chest 12 217 5.91 7.34 9.90 20.94 47.73 8.1  Abdomen 14 340 5.78 8.45 13.42 32.60 49.42 8.6  Pelvis 8 100 6.17 7.03 12.00 20.30 31.86 5.2  KUB 10 139 6.66 7.31 10.65 15.10 18.01 2.7  CTU 7 105 6.89 11.93 19.10 41.95 60.10 8.7 DLP (mGy.cm)  Head 14 327 565 960 1225 1490 2043 3.6  PNS 9 108 201 313 618 1363 1535.1 7.6  Chest 12 217 164 243 366 690 1711 10.4  Abdomen 14 340 253 358 722 1271 2300 9.1  Pelvis 8 100 225 309 600 838 959 4.3  KUB 10 139 299 337 511 816 910 3.0  CTU 7 105 356 566 850 1589 2267 6.4 Exam . Sample size . Percentile of the dose distributions (%) . 95th percentile/ 5th percentile . Hospitals . Patients . 5 . 25 . 50 . 75 . 95 . CTDIvol (mGy)  Head 14 327 31.11 52.48 63.5 79.06 94.19 3.0  PNS 9 108 13.30 15.70 27.80 78.90 79.75 6.0  Chest 12 217 5.91 7.34 9.90 20.94 47.73 8.1  Abdomen 14 340 5.78 8.45 13.42 32.60 49.42 8.6  Pelvis 8 100 6.17 7.03 12.00 20.30 31.86 5.2  KUB 10 139 6.66 7.31 10.65 15.10 18.01 2.7  CTU 7 105 6.89 11.93 19.10 41.95 60.10 8.7 DLP (mGy.cm)  Head 14 327 565 960 1225 1490 2043 3.6  PNS 9 108 201 313 618 1363 1535.1 7.6  Chest 12 217 164 243 366 690 1711 10.4  Abdomen 14 340 253 358 722 1271 2300 9.1  Pelvis 8 100 225 309 600 838 959 4.3  KUB 10 139 299 337 511 816 910 3.0  CTU 7 105 356 566 850 1589 2267 6.4 CTDIvol and DLP of the head protocols (head and PNS) are referenced to the 16 cm PMMA phantom; all other values are referenced to the 32-cm body phantom. Open in new tab Figure 1 Open in new tabDownload slide Boxplot of CTDIvol distribution for seven helical CT examinations in Sudan. Figure 1 Open in new tabDownload slide Boxplot of CTDIvol distribution for seven helical CT examinations in Sudan. Figure 2 Open in new tabDownload slide Boxplot of DLP distribution for seven helical CT examinations in Sudan. Figure 2 Open in new tabDownload slide Boxplot of DLP distribution for seven helical CT examinations in Sudan. As shown in Table 2, the proposed CTDIvol (mGy) ADs ranged from: 10 (chest) to 64 (head), and that of the DLP (mGy.cm) ranged from 366 (chest) to 1225 (head). The proposed CTDIvol (mGy) NDRLs ranged from 15 (KUB) to 79 (head), while that of the DLP (mGy.cm) ranged from 690 (chest) to 1490 (head). The interquartile range (IQR) of the CTDIvol values varied from 7.8 mGy for KUB to 63.2 mGy for PNS CT. The IQR of the DLP values varied from 447 mGy.cm for chest CT scans to 1050 mGy.cm for PNS CT scans. The IQRs exceeded the established ADs for the PNS, chest, abdominal and CTU CT scans for the DLP values. For CTDIvol, the IQRs exceeded the established ADs for the PNS, chest, abdominal, pelvic and CTU CT scans. Further, dose variability is expressed as the ratio at the 95th percentile to the 5th percentile. As shown in Table 3, the ratio of the CTDIvol values at the 95th percentile to the 5th percentile varied from 2.7 (KUB) to 8.7 (CTU), whereas the ratio of the DLP values at the 95th percentile to the 5th percentile varied from 3.0 (KUB) to 10.4 (Chest). DISCUSSION Possibility for dose optimization Our results showed wide variations in the radiation dose delivered by CT examinations that were performed for several body regions across different centers. The dose variability presented here provides clear evidence for the notion that dose optimization is possible without unduly affecting the quality of diagnostic information. The following scan parameters influenced patient dose to varying degrees: tube voltage, mean tube current, tube current–time product, scan coverage and pitch factor(30). The influence of these parameters on patient dose, as demonstrated in this study, is elaborated below. As shown in Table 2, with the exception of abdominal CT, most hospitals in Sudan used a median kV of 120. Using lower kV values could be considered an option for dose reduction. For example, previous research has indicated that reducing the kVp from 120 to 100 reportedly resulted in a dose reduction of 33%, while further reducing the value to 80 kVp could reduce the dose by 65%(31). In the current study, a significant number of CT scanners used protocols with fixed kV and mA values for the same procedure (Table 1). The small variations seen in the total mA values observed were related to both the table speed between rotations, as well as the number of scan sequences. There were only six multi-slice CT units, with less than half utilizing the TCM feature. Conversely, some were using procedure-specific protocols provided by the vendors. The fact that most hospitals use fixed protocols and do not use the TCM feature has serious implications for patient dose, as demonstrated in this study (Table 4). TCM automatically increases the mA in those parts of the body with the greatest attenuation and decreases it in those body parts with lower attenuation(31). This prevents smaller patients from being subjected to higher doses, and it further prevents the need for repeated CT scans among obese patients. The mAs values in this study were higher than those reported in previous studies, particularly for head CT scans. The pitch value used in most cases was below unity (range: 0.7–1.0), which is known to result high patient doses. The use of a pitch value above unity resolves the issues associated with overlapping helical sections, resulting in lower patient doses. However, this may also lead to reduced image quality, particularly for thin reconstructed slices; thus, the use of higher pitch values needs to be balanced with the imaging requirements. The use of fixed and high mA values, in addition to lower pitch values, is among the factors responsible for the elevated dose levels observed in this study(30, 31). Table 4 Comparison of median achievable doses (AD) with those reported in the literature Country . Head . PNS . Chest . Abdomen . Pelvis . KUB . CTU . Reference . CTDIvol (mGy)  USA 49.0 — 10.0 — 13.0 — — (11)  Canada 71.7 — 9.5 — 12.8 — — (12)  South Korea 56.8 — 5.5 6.6 6.6 — — (13)  Japan 70.0 — 10.0 13.7 13.7 — — (14)  California 50.0 25.0 12.0 12.0 — — — (31)  Switzerland 42.0 15.0 6.0 10.0 10.0 — — (32)  Sudan 63.5 27.8 9.9 13.4 12.0 10.7 19.1 This study DLP (mGy.cm)  USA 849 — 347 — 657 — — (11)  Canada 1044 — 362 — 609 — — (12)  South Korea 993 — 227 334 334 — — (13)  Japan 1097 — 400 650 650 — — (14)  California 960 400 550 960 — — — (30)  Switzerland 750 240 210 470 470 — — (32)  Sudan 1225 618 366 722 600 511 850 This study Country . Head . PNS . Chest . Abdomen . Pelvis . KUB . CTU . Reference . CTDIvol (mGy)  USA 49.0 — 10.0 — 13.0 — — (11)  Canada 71.7 — 9.5 — 12.8 — — (12)  South Korea 56.8 — 5.5 6.6 6.6 — — (13)  Japan 70.0 — 10.0 13.7 13.7 — — (14)  California 50.0 25.0 12.0 12.0 — — — (31)  Switzerland 42.0 15.0 6.0 10.0 10.0 — — (32)  Sudan 63.5 27.8 9.9 13.4 12.0 10.7 19.1 This study DLP (mGy.cm)  USA 849 — 347 — 657 — — (11)  Canada 1044 — 362 — 609 — — (12)  South Korea 993 — 227 334 334 — — (13)  Japan 1097 — 400 650 650 — — (14)  California 960 400 550 960 — — — (30)  Switzerland 750 240 210 470 470 — — (32)  Sudan 1225 618 366 722 600 511 850 This study Open in new tab Table 4 Comparison of median achievable doses (AD) with those reported in the literature Country . Head . PNS . Chest . Abdomen . Pelvis . KUB . CTU . Reference . CTDIvol (mGy)  USA 49.0 — 10.0 — 13.0 — — (11)  Canada 71.7 — 9.5 — 12.8 — — (12)  South Korea 56.8 — 5.5 6.6 6.6 — — (13)  Japan 70.0 — 10.0 13.7 13.7 — — (14)  California 50.0 25.0 12.0 12.0 — — — (31)  Switzerland 42.0 15.0 6.0 10.0 10.0 — — (32)  Sudan 63.5 27.8 9.9 13.4 12.0 10.7 19.1 This study DLP (mGy.cm)  USA 849 — 347 — 657 — — (11)  Canada 1044 — 362 — 609 — — (12)  South Korea 993 — 227 334 334 — — (13)  Japan 1097 — 400 650 650 — — (14)  California 960 400 550 960 — — — (30)  Switzerland 750 240 210 470 470 — — (32)  Sudan 1225 618 366 722 600 511 850 This study Country . Head . PNS . Chest . Abdomen . Pelvis . KUB . CTU . Reference . CTDIvol (mGy)  USA 49.0 — 10.0 — 13.0 — — (11)  Canada 71.7 — 9.5 — 12.8 — — (12)  South Korea 56.8 — 5.5 6.6 6.6 — — (13)  Japan 70.0 — 10.0 13.7 13.7 — — (14)  California 50.0 25.0 12.0 12.0 — — — (31)  Switzerland 42.0 15.0 6.0 10.0 10.0 — — (32)  Sudan 63.5 27.8 9.9 13.4 12.0 10.7 19.1 This study DLP (mGy.cm)  USA 849 — 347 — 657 — — (11)  Canada 1044 — 362 — 609 — — (12)  South Korea 993 — 227 334 334 — — (13)  Japan 1097 — 400 650 650 — — (14)  California 960 400 550 960 — — — (30)  Switzerland 750 240 210 470 470 — — (32)  Sudan 1225 618 366 722 600 511 850 This study Open in new tab Concerning the effect of CT technology on radiation dose, the participating centers were equipped with CT units that featured a number of slices per rotation, ranging from 1 to 128. Although the evolution of CT generations is accompanied by dose optimization features that reduces the dose of radiation, one key discovery that was made during the course of this study was that the highest radiation doses came from the Toshiba/Aquilion 64 systems. This arose given that these systems use fixed kV and mA values during the scan, irrespective of patient size, implying that dose optimization techniques were not implemented at these centers. Excluding these systems, we observed that CT models with a higher number of detectors in a given row are associated with lower doses; however, this is inconsistent across all centers. This finding suggests that there may be a lack of awareness about the need to train staff on the use of CT dose-optimization features. Further, there is also a need to acquire advanced CT systems featuring more detector rows, which would help ensure that lower radiation doses reach the patient. Comparison with the literature The ADs derived from the results of this radiation-dose study were compared with those presented in the literature, as shown in Table 4(10–16, 31–33). Excluding the figure reported in Canada, the current CTDIvol AD for head CT was higher than the associated values reported in the literature. The CTDIvol ADs for the remaining examinations are comparable to those in the literature. The DLP ADs for head CT are higher than the results presented in the literature. For abdominal CT, the values are comparable to those reported in other countries, with the exception of the dose value presented in California, which is higher (Table 4). Table 5 compares the proposed DRLs with those of the literature(10–16, 32–34). Excluding the dose values reported in Canada and Japan, the current CTDIvol DRLs for head CT are higher than the corresponding values reported in the literature. When comparing our calculated CTDIvol DRLs with the international data, we found that chest, abdominal and pelvic CT scans featured radiation doses that were comparable to what was reported in Egypt; however, the values are higher than those presented in the literature. A similar pattern is shown for DLP, where the DRLs values from this study fall in the upper range of the values presented internationally. Table 5 Comparison of the proposed DRLs with those reported in the literature . Weight (kg) . Head . Chest . Abdomen . Pelvis . Reference . CTDIvol (mGy)  EC — 60.0 10.0 25.0 (10)  USA — 56.0 13.0 16.0 16.0 (11)  Canada 50–90 79.1 14.1 18.1 18.1 (12)  South Korea 47–87 63.7 7.3 9.7 — (13)  Japan — 85.5 14.3 18.2 18.2 (14)  Australia 70 ± 5 kg 60.0 15.0 15.0 — (15)  Egypt 39–133 30.4 22.3 30.5 31.0 (16)  California — 62.0 17.0 17.0 — (30)  UK — 60.0 12.0 15.0 15.0 (31)  Switzerland 60–85 51.0 7.0 11.0 11.0 (32)  Sudan — 79.0 20.0 32.0 20.0 This study DLP (mGy.cm)  EC — 1000 400 800 550 (10)  USA — 962 469 781 781 (11)  Canada 50–90 1302 521 874 874 (12)  South Korea 47–87 1120 297 472 (13)  Japan — 1360 543 871 871 (14)  Australia 70 ± 5 kg 1000 450 700 — (15)  Egypt 39–133 1359 420.8 1423.3 1323.0 (16)  California — 1300 830 1460 (30)  UK — 970 610 745 745 (31)  Switzerland 60–85 890 250 540 540 (32)  Sudan — 1490 690 1271 838 This study . Weight (kg) . Head . Chest . Abdomen . Pelvis . Reference . CTDIvol (mGy)  EC — 60.0 10.0 25.0 (10)  USA — 56.0 13.0 16.0 16.0 (11)  Canada 50–90 79.1 14.1 18.1 18.1 (12)  South Korea 47–87 63.7 7.3 9.7 — (13)  Japan — 85.5 14.3 18.2 18.2 (14)  Australia 70 ± 5 kg 60.0 15.0 15.0 — (15)  Egypt 39–133 30.4 22.3 30.5 31.0 (16)  California — 62.0 17.0 17.0 — (30)  UK — 60.0 12.0 15.0 15.0 (31)  Switzerland 60–85 51.0 7.0 11.0 11.0 (32)  Sudan — 79.0 20.0 32.0 20.0 This study DLP (mGy.cm)  EC — 1000 400 800 550 (10)  USA — 962 469 781 781 (11)  Canada 50–90 1302 521 874 874 (12)  South Korea 47–87 1120 297 472 (13)  Japan — 1360 543 871 871 (14)  Australia 70 ± 5 kg 1000 450 700 — (15)  Egypt 39–133 1359 420.8 1423.3 1323.0 (16)  California — 1300 830 1460 (30)  UK — 970 610 745 745 (31)  Switzerland 60–85 890 250 540 540 (32)  Sudan — 1490 690 1271 838 This study Open in new tab Table 5 Comparison of the proposed DRLs with those reported in the literature . Weight (kg) . Head . Chest . Abdomen . Pelvis . Reference . CTDIvol (mGy)  EC — 60.0 10.0 25.0 (10)  USA — 56.0 13.0 16.0 16.0 (11)  Canada 50–90 79.1 14.1 18.1 18.1 (12)  South Korea 47–87 63.7 7.3 9.7 — (13)  Japan — 85.5 14.3 18.2 18.2 (14)  Australia 70 ± 5 kg 60.0 15.0 15.0 — (15)  Egypt 39–133 30.4 22.3 30.5 31.0 (16)  California — 62.0 17.0 17.0 — (30)  UK — 60.0 12.0 15.0 15.0 (31)  Switzerland 60–85 51.0 7.0 11.0 11.0 (32)  Sudan — 79.0 20.0 32.0 20.0 This study DLP (mGy.cm)  EC — 1000 400 800 550 (10)  USA — 962 469 781 781 (11)  Canada 50–90 1302 521 874 874 (12)  South Korea 47–87 1120 297 472 (13)  Japan — 1360 543 871 871 (14)  Australia 70 ± 5 kg 1000 450 700 — (15)  Egypt 39–133 1359 420.8 1423.3 1323.0 (16)  California — 1300 830 1460 (30)  UK — 970 610 745 745 (31)  Switzerland 60–85 890 250 540 540 (32)  Sudan — 1490 690 1271 838 This study . Weight (kg) . Head . Chest . Abdomen . Pelvis . Reference . CTDIvol (mGy)  EC — 60.0 10.0 25.0 (10)  USA — 56.0 13.0 16.0 16.0 (11)  Canada 50–90 79.1 14.1 18.1 18.1 (12)  South Korea 47–87 63.7 7.3 9.7 — (13)  Japan — 85.5 14.3 18.2 18.2 (14)  Australia 70 ± 5 kg 60.0 15.0 15.0 — (15)  Egypt 39–133 30.4 22.3 30.5 31.0 (16)  California — 62.0 17.0 17.0 — (30)  UK — 60.0 12.0 15.0 15.0 (31)  Switzerland 60–85 51.0 7.0 11.0 11.0 (32)  Sudan — 79.0 20.0 32.0 20.0 This study DLP (mGy.cm)  EC — 1000 400 800 550 (10)  USA — 962 469 781 781 (11)  Canada 50–90 1302 521 874 874 (12)  South Korea 47–87 1120 297 472 (13)  Japan — 1360 543 871 871 (14)  Australia 70 ± 5 kg 1000 450 700 — (15)  Egypt 39–133 1359 420.8 1423.3 1323.0 (16)  California — 1300 830 1460 (30)  UK — 970 610 745 745 (31)  Switzerland 60–85 890 250 540 540 (32)  Sudan — 1490 690 1271 838 This study Open in new tab The common finding identified throughout the course of this study is that most of the reported doses fell within the upper range of the doses presented in the international literature. For example, the doses observed for this study were higher than those presented in a Korean study(13). Upon taking a closer look at the scanning parameters used in the Korean study, we found that the highest value of 223.1 mA was used for head CT, which is higher than the mA values in the current study (range: 40–601 mA; median: 225 mA; Table 2), which clearly explains why high doses were observed in this study. Some of the differences in doses presented in Tables 4 and 5 are related to the fact that the currently proposed ADs and NDRLs for Sudan are determined from the CT dose data of single and multiphase CT combined, whereas some data in these tables were obtained from single-phase CT examinations (Switzerland) and multiphase CT examinations (Canada and Korea). When comparing the current results with those of the previous dose survey conducted in Sudan in 2011(17), we observed that the increased number of multi-slice CT scans and the use of enhanced technology (as represented by the number of detector rows) have not been accompanied by lower radiation doses. For example, the CTDIvol values reported in Sudan in 2011 for head, chest, abdominal and pelvic CT were as follows: 65.5, 11.5, 11.6 and 11.0 mGy, respectively. These values are very close to our current corresponding dose values of 63.5, 9.90, 13.4 and 12.0 mGy, respectively. However, this is not the case for the DLP values obtained in this study, which are higher than the corresponding values presented in our previous study conducted in Sudan in 2011 (Figure 3). These differences in radiation doses are mainly due to the fact that in this study, we had both single and multiphase CT examinations, whereas in 2011, only single-phase CT examinations were studied. Some dose value increases are expected given the use of the CT Expo software, which incorporates increased scan lengths due to scanner over-beaming and over-ranging. Figure 3 Open in new tabDownload slide Current DLP ADs for four CT examinations compared with the corresponding values reported in the 2011 survey in Sudan. Figure 3 Open in new tabDownload slide Current DLP ADs for four CT examinations compared with the corresponding values reported in the 2011 survey in Sudan. General points and limitations During our study, we noticed that some of the technologists in Sudan required additional training and experience. Under no circumstance did we find that the operating technologist understood the meaning of common CT dose descriptors (CTDIvol and DLP). Our current efforts aimed to propose ADs and NDRLs as a first step towards achieving dose optimization with the aim of promoting patient protection during CT scans. In addition, there is the need to train CT technologists and other professionals on how to use multi-slice CT dose optimization features, such as TCM and organ dose modulation (ODM), while encouraging the use of dose-tracking software for the management of CT doses. The current study has several limitations. First, according to the ICRP, in order to establish NDRLs, at least 30% of facilities should be included in the study(8). Thus, 12–20 of the 40 facilities available in Sudan need to be included to establish NDRLs. For PNS, pelvic, KUB and CTU scans, the number of facilities was lower than recommended. The 14 scanners included in this study perform ~80% of all scans in Sudan; therefore, despite the small number of hospitals covered in this study, the sample is sufficiently representative of clinical practice across the country. This enables us to draw meaningful conclusions on ADs and DRLs. Another important limitation is that weight restrictions were not imposed on the sample included in this study; as such, a larger sample size may be required beyond the normally recommended 20 patients per procedure per CT device. Although dose information for average-sized patients is recommended to establish DRLs, several authors have used the data and dose information provided by the HIS or dose registry software to establish ADs and DRLs(11). In fact, the use of DICOM and HIS dose information is encouraged and widely used for dose management in CT scans. Even though there were difficulties associated with the manual data-collection process, the low frequency of certain procedures in some CT units represented one of the several obstacles faced during the study. CONCLUSION Dose metrics for common CT scan protocols in Sudan were calculated using patient-specific scan parameters and the CT Expo 2.5 dosimetry software. ADs and DRLs are proposed for head, PNS, chest, abdominal, pelvic, KUB and CTU CT examinations of adult patients. The presented data were analyzed to provide insights into the factors that affect patient radiation doses resulting from CT scans. The variability in patient doses suggests the possibility of dose optimization without jeopardizing diagnostic information quality. Based on the evidence, various optimizations were recommended, including the use of TCM and the application of a vendor-specific dose optimization feature provided by modern CT technology. In general, current doses fell within the upper range of the doses presented in the literature emphasizing the need for implementation of the current ADs and NDRLs for CT to enhance patient protection and dose optimization in Sudan and promote dose optimization both nationally and globally. ACKNOWLEDGMENT The authors are grateful to the hospitals involved in this study for their assistance and collaboration in data collection. FUNDING This project received funding from the Government of Sudan though the Sudan Atomic Energy Commission. CONFLICT OF INTERESTS The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. References 1. United Nations Scientific Committee on the Effects of Atomic Radiation . UNSCEAR 2008 . Sources and effects of ionizing radiation ( 2008 ). Annex A: Medical radiation exposures; pp: 1–204. OpenURL Placeholder Text WorldCat 2. Anam , C. , Adhianto , D., Sutanto , H., Adi , K., Ali , M. H., Rae , W. I. D., Fujibuchi , T. and Dougherty , G. Comparison of central, peripheral, and weighted size-specific dose in CT . J. Xray Sci. Technol. 28 , 695 – 708 ( 2020 ). https://doi.org/10.3233/XST-200667. Google Scholar PubMed OpenURL Placeholder Text WorldCat 3. Valentine , J. International Commission on Radiation Protection. Managing patient dose in multi-detector computed tomography (MDCT) . ICRP Publication 102 , 1 – 79 ( 2007 ). Google Scholar OpenURL Placeholder Text WorldCat 4. Shrimpton , P. C. , Jones , D. G., Hillier , M. C., Wall , B. F., Le Heron , J. C. and Faulkner , K. Survey of CT Practice in the UK. Part 2. Dosimetric Aspects . ( Chilton, UK : National Radiological Protection Board ) ( 1991 ) Report NRPB-R249 . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC 5. International Commission on Radiological Protection . The 1990 Recommendations of the International Commission on Radiological Protection. ICRP Publication 60, Ann. ICRP 21 . ( Oxford, UK : Pergamon Press ) ( 1991 ). Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC 6. International Commission on Radiological Protection . Radiological Protection and Safety in Medicine . ( Bethesda, MD : ICRP Report 26 Publication 73 ) ( 1996 ). Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC 7. International Commission on Radiological Protection (ICRP) . Radiological Protection in Medicine . ICRP Publication 105. Ann. ICRP 37 ( 6 ), (London, UK: SAGE Publications Ltd) ( 2007 ). Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC 8. International Commission on Radiological Protection (ICRP) . ICRP publication 135: diagnostic reference levels in medical imaging . Ann. ICRP 46 ( 1 ), 1 – 144 ( 2017 ). Crossref Search ADS WorldCat 9. National Council on Radiation Protection and Measurement Diagnostic . Reference Levels and Achievable Doses in Medical and Dental Imaging: Recommendations for the United States . ( Bethesda, MD : NCRP Report #172 ) ( 2012 ). Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC 10. European Commission (EC) . Diagnostic Reference Levels in Thirty-Six European Countries Part 2/2 Radiation protection No. 180 . ( Luxembourg : Publications Office of the European Union ) ( 2014 ). Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC 11. Kanal , K. M. , Butler , P. F., Sengupta , D., Bhargavan-Chatfield , M., Coombs , L. P. and Morin , R. L. US diagnostic reference levels and achievable doses for 10 adult CT examinations . Radiology 284 ( 1 ), 120 – 133 ( 2017 ). Google Scholar Crossref Search ADS PubMed WorldCat 12. Health Canada 2016 Canadian Computed Tomography Survey: National Diagnostic Reference Levels ( Canada : Health Canada ) www.healthycanadians.gc.ca/publications/security-securite/canadian-computed-tomography-survey-2016-sondage-canadien-tomodensitometrie/alt/cctsurvey-sondage-ct-eng.pdf. Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC 13. Kim , J. S. , Lee , S. K., Kim , S. K., Yoo , S. M., Kim , J. M. and Yoon , S. W. National diagnostic reference levels and achievable doses for 13 adult CT protocols and a paediatric head ct protocol: national survey of Korean hospitals . Radiat. Prot. Dosimetry 187 ( 2 ), 220 – 229 ( 2019 ). Google Scholar Crossref Search ADS PubMed WorldCat 14. Matsunaga , Y. , Chida , K., Kondo , Y., Kobayashi , K., Kobayashi , M., Minami , K., Suzuki , S. and Asada , Y. Diagnostic reference levels and achievable doses for common computed tomography examinations: results from the Japanese nationwide dose survey . Br. J. Radiol. 92 ( 1094 ), 20180290 ( 2019 ). Google Scholar Crossref Search ADS PubMed WorldCat 15. Hayton , A. , Wallace , A., Marks , P., Edmonds , K., Tingey , D. and Johnston , P. Australian diagnostic reference levels for multi detector computed tomography . Australas. Phys. Eng. Sci. Med. 36 ( 1 ), 19 – 26 ( 2013 ). Google Scholar Crossref Search ADS PubMed WorldCat 16. Salama , D. H. , Vassileva , J., Mahdaly , G., Shawki , M., Salama , A., Gilley , D. and Rehani , M. M. Establishing national diagnostic reference levels (DRLs) for computed tomography in Egypt . Phys. Med. 39 , 16 – 24 ( 2017 Jul 1 ) reference levels for interventional cardiology. Physica medica. 2018; (54):42-8 . Google Scholar Crossref Search ADS WorldCat 17. Suliman , I. I. , Abdalla , S. E., Ahmed , N. A., Galal , M. A. and Salih , I. Survey of computed tomography technique and radiation dose in Sudanese hospitals . Eur. J. Radiol. 80 ( 3 ), e544 – e551 ( 2011 ). Google Scholar Crossref Search ADS PubMed WorldCat 18. Suliman , I. I. , Khamis , H. M., Ombada , T. H., Alzimami , K., Alkhorayef , M. and Sulieman , A. Radiation exposure during paediatric CT in Sudan: CT dose, organ and effective doses . Radiat. Prot. Dosimetry 167 ( 4 ), 513 – 518 ( 2015 ). Google Scholar Crossref Search ADS PubMed WorldCat 19. Suliman , I. I. and Abdelgadir , A. H. Patient radiation doses in intraoral and panoramic X-ray examinations in Sudan . Phys. Med. 46 , 148 – 152 ( 2018 ). Google Scholar Crossref Search ADS PubMed WorldCat 20. Bashier , E. H. and Suliman , I. I. Multi-slice CT examinations of adult patients at Sudanese hospitals: radiation exposure based on size-specific dose estimates (SSDE) . Radiol. Med. 123 ( 6 ), 424 – 431 ( 2018 ). Google Scholar Crossref Search ADS PubMed WorldCat 21. Bashier , E. H. and Suliman , I. I. Radiation dose determination in abdominal CT examinations of children at Sudanese hospitals using size-specific dose estimates . Radiat. Prot. Dosimetry 183 ( 4 ), 444 – 449 ( 2019 ). Google Scholar Crossref Search ADS WorldCat 22. Gibreel , H. E. , Ahmed , M. M., Sam , A. K. and Suliman , I. I. Evaluation of Sudan Nuclear and Radiological Regulatory control act (2017) in light of IAEA safety standards . Prog. Nucl. Energ. 115 , 158 – 168 ( 2019 ). Google Scholar Crossref Search ADS WorldCat 23. Stamm , G. and Nagel , H. D. CT-Expoein neuartiges Programm zur Dosisevaluierung in der CT . Fortschr Rontgenstr 174 , 1570 – 1576 ( 2002 ). Google Scholar Crossref Search ADS WorldCat 24. International Commission on Radiation Measurements and Units . Patient Dosimetry for X-Rays Used in Medical Imaging . ( Bethesda, MD : ICRU report No. 74, ICRU ) ( 2006 ). Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC 25. International Atomic Energy Agency . Dosimetry in Diagnostic Radiology: an International Code of Practice . ( IAEA ) ( 2007 ) IAEATRSNo 457 . Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC 26. Commission for European Community (CEC) . European Guidelines on Quality Criteria for Computed Tomography . EC report EUR16262 EN. ( Luxembourg: Office for EC Publication ) ( 1999 ). Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC 27. Brix , G. , Lechel , U., Veit , R., Truckenbrodt , R., Stamm , G., Coppenrath , E. M., Griebel , J. and Nagel , H. D. Assessment of a theoretical formalism for dose estimation in CT: an anthropomorphic phantom study . Eur. Radiol. 14 ( 7 ), 1275 – 1284 ( 2004 ). Google Scholar Crossref Search ADS PubMed WorldCat 28. Almohiy , H. M. , Hussein , K. I., Alqahtani , M. S., Rawashdeh , M., Elshiekh , E., Alshahrani , M. M., Saad , M., Foley , S. and Saade , C. Development of a computational tool for estimating computed tomography dose parameters . J. Xray Sci. Technol., 2020 28 ( 6 ), 1025 – 1035 ( 2020 ). 10.3233/XST-200731 . Google Scholar Crossref Search ADS WorldCat 29. Huda , W. and Mettler , F. A. Volume CT dose index and dose-length product displayed during CT: what good are they? Radiology 258 ( 1 ), 236 – 242 ( 2011 ). Google Scholar Crossref Search ADS PubMed WorldCat 30. McCollough , C. H. , Primak , A. N., Braun , N., Kofler , J., Yu , L. and Christner , J. Strategies for reducing radiation dose in CT . Radiol. Clin. 47 ( 1 ), 27 – 40 ( 2009 Jan 1 ). Google Scholar Crossref Search ADS WorldCat 31. Raman , S. P. , Mahesh , M., Blasko , R. V. and Fishman , E. K. CT scan parameters and radiation dose: practical advice for radiologists . J. Am. Coll. Radiol. 10 ( 11 ), 840 – 846 ( 2013 ). Google Scholar Crossref Search ADS PubMed WorldCat 32. Smith-Bindman , R. et al. Radiation doses in consecutive CT examinations from five University of California Medical Centers . Radiology 277 ( 1 ), 134 – 141 ( 2015 ). Google Scholar Crossref Search ADS PubMed WorldCat 33. Shrimpton , P. C. , Hillier , M. C., Meeson , S. and Golding , S. J. Doses from Computed Tomography (CT) Examinations in the UK–2011 Review . PHE-CRCE-013, 2014. ( London, UK: Public Health England ) ( 2014 ). Google Scholar Google Preview OpenURL Placeholder Text WorldCat COPAC 34. Aberle , C. , Ryckx , N., Treier , R. and Schindera , S. Update of national diagnostic reference levels for adult CT in Switzerland and assessment of radiation dose reduction since 2010 . Eur. Radiol. 30 ( 3 ), 1690 – 1700 ( 2020 ). Google Scholar Crossref Search ADS PubMed WorldCat © The Author(s) 2021. Published by Oxford University Press. All rights reserved. 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TI - NATIONAL DIAGNOSTIC REFERENCE LEVELS AND ACHIEVABLE DOSES FOR STANDARD CT EXAMINATIONS IN SUDAN
JF - Radiation Protection Dosimetry
DO - 10.1093/rpd/ncab123
DA - 2021-11-03
UR - https://www.deepdyve.com/lp/oxford-university-press/national-diagnostic-reference-levels-and-achievable-doses-for-standard-0Mk2fL5CXv
SP - 1
EP - 9
VL - 196
IS - 1-2
DP - DeepDyve
ER -