- Email: [email protected]
Survey of paediatric imaging exposure from computed tomography examinations
Radiation Physics and Chemistry xxx (xxxx) xxxx
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Survey of paediatric imaging exposure from computed tomography examinations M. Alkhorayef Department of Radiological Sciences, College of Applied Medical Sciences, King Saud University, P.O Box 10219, Riyadh, 11433, Saudi Arabia
ARTICLE INFO
ABSTRACT
Keywords: Computed tomography Radiation exposure Patient doses Medical dosimetry Cancer risk
This study investigated the paediatric patient doses received in Saudi Arabia during CT examinations of the brain, abdomen and chest. The study includes data from a total of 59 patients from three hospitals, the mean age and age range of the paediatric cases being 5.10 (0.01–13) years, mean weight and weight range 20 (3–40) kg. The range of DLP (mGy.cm) per procedure was 113–995, 54–1244 and 30.0–190.0 for brain, abdomen and chest procedures, respectively. DRLs were proposed for all three procedures, the values being comparable with European Guidelines on Quality Criteria for Computed Tomography. The study has shown there to be a need in Saudi Arabia to refer to such criteria as well as a need for continuous training of staff in radiation dose optimisation concepts.
1. Introduction While computed tomography (CT) represents just 5% of all X-ray imaging procedures nevertheless use of the modality accounts for some 40%–67% of all medical radiation exposures. The dose from a single CT examination ranges from 1.0 mSv to 27.0 mSv (Bernier et al., 2012). Worldwide, CT contributes to in excess of 70% of the collective dose from diagnostic X-ray examinations. Thus, due to the introduction of complex procedures such as CT angiography and perfusion, patients are being exposed to higher radiation doses. Since in Saudi Arabia available patient dose data from use of diagnostic radiology is limited, further radiation dose measurements are required (Alkhorayef et al., 2019; Sulieman et al., 2018). Exposure of the general population to ionising radiation is of particular concern due to the risks associated with radiation. Protection of paediatric patients is of particular concern, the nature of the sensitive organs of the young being acknowledged, including the brains, thyroid gland and gonads, all susceptible when in the developmental stage. A specific concern is the greater risk of carcinogenesis than that for adults, the longer life expectancy of the paediatrics also meaning they have greater time for the cancer effect to manifest. In regard to diagnostic procedures, justified according to predefined criteria by qualified medical practitioners to diagnose a clinical problem and optimised, then the benefits from the clinical diagnosis are viewed to outweigh the expected radiation risk (Sulieman et al., 2011). It is especially important to make sure that CT scans in children are performed with exposure settings that are adjusted for an optimised
outcome. Such conditions imply that individually, as a result of CT radiation examination, there remains a small but nevertheless statistically significant increased risk of developing cancer (Frush et al., 2003). The International Commission on Radiological Protection (ICRP, 2007) estimated the cancer risk for the whole population per effective dose unit to be 5.5 × 10−2 Sv−1. Thus, a radiation dose of 50 mSv has a probability of three cancer incidents in 330 procedures. The probability of fatal and non-fatal cancer at doses > 100 mGy is proportionally increased with doses according to linear no threshold model. Berrington de González et al. reported that almost 29,000 of the expected cancers in the United States were possibly linked to radiation exposure from CT scans (Berrington de González et al., 2009). In another study, Sodickson et al. (2009) quantified that radiation exposure from CT procedures generated 0.7% of the total anticipated cancer incidents and 1% of total cancer mortality (Sodickson et al., 2009). Cancer risk apart, the well documented link between radiation tissue reactions due to lengthy medical exposures, skin injuries and other deterministic effects included, are a concern in regard to CT angiography and interventional radiology. Thus, while at medical imaging levels using CT tissue reaction effects do not occur in normal practice, limited cases have been reported of skin erythema and hair loss during poor CT machine settings per CT brain perfusions (ICRP, 2007). In Saudi Arabia in 2017, out of a total of 144 million visits to the hospitals and healthcare centres, 14.3 million patients were investigated with radiology in all health sectors (MoH, 2017), equating to 1 out of 10 patients. The Saudi population is estimated to be 33.4 million, thus the ratio of radiological investigations to the total
E-mail address: [email protected]. https://doi.org/10.1016/j.radphyschem.2019.04.011 Received 15 December 2018; Received in revised form 1 April 2019; Accepted 7 April 2019 Available online 26 April 2019 0969-806X/ © 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: M. Alkhorayef, Radiation Physics and Chemistry, https://doi.org/10.1016/j.radphyschem.2019.04.011
Radiation Physics and Chemistry xxx (xxxx) xxxx
M. Alkhorayef
population is 0.43. Thus, the Saudi population is exposed to high collective doses. Therefore, an accurate estimate of patient doses is recommended to avoid unnecessary exposure. The radiology departments are well equipped with advanced imaging modalities but the number of published studies is quite limited compared to the massive number of medical procedures, including CT. Of the data available for CT paediatric examinations, these include McLean et al. (2003), Verdun et al. (2008), Kritsaneepaiboon et al. (2012), Sulieman et al. (2015), Hwang et al. (2015) and Gao et al. (2018). Much more limited studies have been conducted in Saudi Arabia, including Sulieman et al. (2018), the authors noting that a CT dose optimisation protocol has yet to be implemented in many of the radiology departments. The present multicentre survey is needed in seeking to assess the level of patient exposure, with comparison made against international guidelines and diagnostic reference level (DRL). The particular objective of present study is to investigate paediatric patient doses received during certain CT examinations, also seeking to provide local DRLs for the brain, abdomen and chest.
Table 2 The mean values and standard deviation of the demographic data. Parameter
Age (Year)
Height (cm)
Weight (kg)
Average Max Min Median SD
5.10 13 0.01 3.9 4.8
79.2 140 25 8.5 40.1
20 40 3 7 18.5
Table 3 CT Patient dose values for paediatric CT brain. Parameter
Average ± sd
Minimum
Maximum
Tube voltage (kVp) Tube current-time product (mAs) Slice thickness Pitch
120 241.5 ± 45 1.8 ± 1.4 0.4
120 91 1 0.4
120 478 5 0.4
the field of view, with use being made of a tissue equivalent phantom, the yield being multiplied by exposure to absorbed dose conversion factor.
2. Materials and methods 2.1. Patient dose measurements
CTDI =
Radiation doses per CT brain, abdomen and chest procedure were assessed in three hospitals for a total of 59 paediatric patients, the clinical procedures having been justified by qualified physicians. The Ethics and Research Committee approved the study and consent was obtained for all patients prior to examination. The different CT systems used, with detectors ranging between 16 and 128, have been identified in Table 1. The clinical indications included trauma, pneumonia and abdominal disorders. The mean age and age range was 5.10 (0.01–13) years, with mean weight and weight range of 20 (3–40) kg. Significant variation was noticed between patient age and weight (Table 2). The image acquisition parameters that were used are presented in Table 3. The dose measurements for each whole procedure comprised volume CT dose index (CTDIvol (mGy) per single slice and the dose length product (DLP, mGy.cm). Accurate measurement of standard patient size has been important, allowing comparison with other studies. The study, originally designed for adults as well as paediatric patients, has been exclusively conducted herein for paediatric cases. The actual scan parameters used for a number of individual standard patients were recorded during routine examinations. Patient demographic data were collected, e.g., age (years), gender, weight (kg) and height (cm). Record was also made of image acquisition parameters: tube potential (kVp), tube current (mA), exposure time (s), slice thickness (mm). Organ equivalent and effective doses were assessed using normalised DLP values (mGy.cm) published by the ImPACT group (ImPACT, 2011).
CTDIw =
installation
Detected Type
A B C
Philips Siemens Siemens
Brilliance Light speed SOMATOM Definition
2004 2008 2014
16 64 20
1 CTDIcenter + CTDIperiphery 3
CTDIvol =
equation 2
CTDIw pitch
equation 3
To calculate the patient dose per whole procedure, CTDIvol is multiplied by the scan length to obtain the DLP, as illustrated in equation (4)
DLP (mGy . cm) = CTDIvol
scan length
equation 4
DLP (mGy.cm) was used to calculate the effective dose (H) using software provided by the National Radiological Protection Board, (NRPB-SR250, 1996), now part of Public Health England). The risk (RT) of cancer probability per CT procedure was calculated by multiplying the effective dose (E) by the risk factor (R) (ICRP, 2007). 3. Results While the same 120 kVp tube voltage has been used in all three hospitals, the tube current-time product (mAs) showed wide variation, of up to five times. This variation can increase the uncertainty of dose measurement and effective dose estimation since patient weight can be expected to increase with age. Patient doses in the three hospitals are presented in Table 4. In general, the variations in dose are due to differences that include the number of scans, tube current and repeated scans. Measured patient doses in terms of DLP (mGy.cm) for all patients are shown in Table 4. Patient effective doses per procedure are presented in Fig. 1. The estimated effective dose from the abdomen procedure is observed to be greater than that for the chest and brain procedure. In paediatric patients all organs are in close vicinity, thus a small field size, may expose large number of sensitive organs.
Table 1 CT machines. model
equation 1
CTDIvol is calculated using the following equation (3)
In CT procedures, the X-ray tube rotates around the patient, the dose being distributed homogeneously. To calculate the CTDIvol (mGy), DLP (mGy.cm) and Effective Dose (mSv) use has been made of equation (1). CTDI is the overall radiation deposited energy absorbed per slice (collimation). CTDI(mGy) is extrapolated from the CTDI100 (C/kg) measurement using an ionisation chamber of length 100 mm at the centre of
manufacture
D (Z ) dz
whereD(Z) = Profile of radiation exposure along z axis.N = slices number.T = slice thickness (mm) or the width of the tomographic volume. Because X-rays are absorbed linearly inside the body across the radiation field, the peripheral tissues receive greater doses than the tissues and organs in the centre during 360° X-ray tube rotation around the patient. Thus the appropriate weighting is taken into account using equation (2).
2.2. CT dose descriptors and measurement
Hospital
1 NT
2
Radiation Physics and Chemistry xxx (xxxx) xxxx
M. Alkhorayef
Table 4 Paediatric radiation doses (mGy.cm) during brain, chest, abdomen. CT Procedures
Hospital
Min
Median
Mean
3rd quartile
Max
Brain
A B C A B C A B C
113.0 115.0 118.0 72.0 54.0 60.0 33.6 30.0 42.6
280.0 290.0 310.0 310.0 92.8 280.5 49.2 36.0 55.7
300 ± 117 328.8 ± 225 350 ± 117 340.8 ± 200 94.5 ± 31 295.1 ± 230 62.5 ± 71 73.1 ± 78 80.4 ± 80
397.5 323.0 419.5 330.0 122.7 350.5 69.3 76.1 86.5
492.0 995.0 502.0 1014.0 138.0 1244.0 140.1 190.5 160.6
Abdomen Chest
4. Discussion
comparisons between different procedures are possible with different imaging modalities. In this study, the mean effective dose also showed wide variation (Fig. 2). Because the conversion factors and software used are the same, the difference is mainly due to a difference in DLP. Fig. 1 shows the radiation dose to patients in the three hospitals, no consistent trend in patient doses being found. Fig. 2 shows a comparison with previous studies, the dose being lower compared to previous published results. DRLs can be used to verify the practices for typical examinations for a group of standardised patients. This is done in order to ensure that the dose will not be exceeded in normal practice without adequate justification (ICRP, 2000). For paediatric CT procedures, and to the best of our knowledge, no previous proposal for DRLs has been made, either at the national or international level, Thus, based on ICRP recommendations, a third quartile value of the median value can be used as the DRL. Thus the proposal, one a local basis, is for the adoption of 380, 270 and 80 mGy cm for CT brain, abdomen and chest respectively.
CT scanning is recognised to be a high radiation dose modality when compared to other diagnostic X-ray techniques. Since its launch into clinical practice more than 30 years ago, CT scanner technology has developed and its use has become more widespread, with commensurate concerns over patient radiation doses. The introduction of multislice scanners has focused further attention on this issue and it is generally believed that it will lead to higher patient doses. Incidents resulting in tissue reactions have been reported by Rehani (2015). In this study a total of 59 paediatric patients undergoing different CT modalities have been studied, the patient doses resulting from different CT technologies, ranging from 16 to 64 slices. The results of this study show wide variations in patient dose among different hospitals in terms of DLP and CTDIvol. The patients were scanned with routine protocols adopted by the operator, use being made of 120 kVp and mAs in the range 91–478, as shown in Table 3, and with the pitch (0.4) or less than unity. These parameters produced the radiation values represented in Table 4, showing values of DLP ranging between 113 mGy cm to 995 mGy cm for brain procedures. The abdomen doses were found to be greater compared to the brain and chest CT examinations (Table 4). This can be attributed to the scan length and structures of the organs. The range of DLP (mGy.cm) was (54–1244), the upper value being more than 20 times that of the minimum value. This may be attributed to the fact that in some cases the technologists performed a simultaneous scan of the abdomen and pelvis based on the department protocol, seeking to avoid a request for the pelvis alone. In CT examination, with patients exposed to relatively high radiation dose, the use of ordinary dose values (CTDI or DLP) will provide less information regarding the radiation risks. An effective dose is the unit of choice in this situation (partial exposure) and, furthermore,
5. Conclusions The aim of this research for paediatric patients was to study the trend in CT dose from brain, chest and abdomen examinations at three hospitals in Saudi Arabia, also to investigate the causes of high radiation doses. The study has shown that patients are well protected and that the patient doses are below that of most previous studies. However, there is still a need to refer to criteria and for the continuous training of staff in radiation dose optimisation concepts, seeking to eliminate unnecessary CT procedures and dose. The absence of any standard protocol for CT procedure in all three hospitals was noted, resulting in wide variation of exposure parameters for the same age groups of patients. Local diagnostic reference levels have been proposed.
Fig. 1. Patient effective dose per procedure. 3
Radiation Physics and Chemistry xxx (xxxx) xxxx
M. Alkhorayef
Fig. 2. Patient doses compared with previous studies (mGy.cm).
Acknowledgements
951–957. Gao, Y., Quinn, B., Pandit-Taskar, P., et al., 2018. Patient-specific organ and effective dose estimates in pediatric oncology computed tomography. Phys. Med. 45, 146–155. Hwang, J., Do, K., Yang, D., Cho, Y., et al., 2015. A survey of pediatric CT protocols and radiation doses in south Korean hospitals to optimize the radiation dose for pediatric CT scanning. Medicine (Baltim.) 94 (50), e2146. Kritsaneepaiboon, S., Trinavarat, P., Visrutaratna, P., 2012. Survey of pediatric MDCT radiation dose from university hospitals in Thailand: a preliminary for national dose survey. Acta Radiol. 53, 820–826. McLean, D., Malitz, N., Lewis, S., 2003. Survey of effective dose levels from typical paediatric CT protocols. Australas. Radiol. 47, 135–142. MoH. Ministry of health, 2017. ANNUAL STATISTICAL BOOK. Available at: https:// www.moh.gov.sa/en/Ministry/Statistics/book/Documents/ANNUAL-STATISTICALBOOK-1438H.pdf , Accessed date: 2 December 2018. Rehani, M., 2015. Tracking of examination and dose: overview. Radiat. Prot Dosim 165 (1–4), 50–52. Sulieman, A., Vlychou, M., Tsougos, I., Theodorou, K., 2011. Radiation doses to paediatric patients and comforters undergoing chest X rays. Radiat. Protect. Dosim. 147 (1–2), 171–175. Sulieman, A., Mahmoud, M.Z., Serhan, O., Alonazi, B., Alkhorayef, M., Alzimami, K., Bradley, D., 2018. CT examination effective doses in Saudi Arabia. Appl. Radiat. Isot. 141, 261–265. Sulieman, A., 2015. Establishment of diagnostic reference levels in computed tomography for paediatric patients in Sudan: a pilot study. Radiat. Protect. Dosim. 165 (1–4), 91–94. Verdun, F.R., Gutierrez, D., Vader, J.P., Aroua, A., Alamo-Maestre, L.T., Bochud, F., Gudinchet, F., 2008. CT radiation dose in children: a survey to establish age-based diagnostic reference levels in Switzerland. Eur. Radiol. 18, 1980–1986.
The author extends his appreciation to the Deanship of Scientific Research at King Saud University, Saudi Arabia, for funding this work through research group No (RG-1438-072). Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.radphyschem.2019.04.011. References Alamo-Maestre, L.T., Bernier, M.O., Rehel, J.L., Brisse, H.J., Wu-Zhou, X., Caer-Lorho, S., Jacob, S., et al., 2012. Radiation exposure from CT in early childhood: a French largescale multicentre study. Br. J. Radiol. 85 (1009), 321–329. Alkhorayef, M., Hamza, Y., Sulieman, A., Salih, I., Babikir, E., Bradley, D.A., 2019. Effective dose and radiation risk estimation in certain paediatric renal imaging procedures. Radiat. Phys. Chem. 154, 64–68 2019. Berrington de González, A., Mahesh, M., Kim, K.P., Bhargavan, M., Lewis, R., Mettler, F., Land, C., 2009. Projected cancer risks from computed tomographic scans performed in the United States in 2007. Arch. Intern. Med. 14 (22), 2071–2077 169. Bochud, F., author Frush, D., Donnelly, L., Rosen, N., 2003. Computed tomography and radiation risks: what pediatric health care providers should know. Pediatrics 112 (4),
4
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Survey of paediatric imaging exposure from computed tomography examinations M. Alkhorayef Department of Radiological Sciences, College of Applied Medical Sciences, King Saud University, P.O Box 10219, Riyadh, 11433, Saudi Arabia
ARTICLE INFO
ABSTRACT
Keywords: Computed tomography Radiation exposure Patient doses Medical dosimetry Cancer risk
This study investigated the paediatric patient doses received in Saudi Arabia during CT examinations of the brain, abdomen and chest. The study includes data from a total of 59 patients from three hospitals, the mean age and age range of the paediatric cases being 5.10 (0.01–13) years, mean weight and weight range 20 (3–40) kg. The range of DLP (mGy.cm) per procedure was 113–995, 54–1244 and 30.0–190.0 for brain, abdomen and chest procedures, respectively. DRLs were proposed for all three procedures, the values being comparable with European Guidelines on Quality Criteria for Computed Tomography. The study has shown there to be a need in Saudi Arabia to refer to such criteria as well as a need for continuous training of staff in radiation dose optimisation concepts.
1. Introduction While computed tomography (CT) represents just 5% of all X-ray imaging procedures nevertheless use of the modality accounts for some 40%–67% of all medical radiation exposures. The dose from a single CT examination ranges from 1.0 mSv to 27.0 mSv (Bernier et al., 2012). Worldwide, CT contributes to in excess of 70% of the collective dose from diagnostic X-ray examinations. Thus, due to the introduction of complex procedures such as CT angiography and perfusion, patients are being exposed to higher radiation doses. Since in Saudi Arabia available patient dose data from use of diagnostic radiology is limited, further radiation dose measurements are required (Alkhorayef et al., 2019; Sulieman et al., 2018). Exposure of the general population to ionising radiation is of particular concern due to the risks associated with radiation. Protection of paediatric patients is of particular concern, the nature of the sensitive organs of the young being acknowledged, including the brains, thyroid gland and gonads, all susceptible when in the developmental stage. A specific concern is the greater risk of carcinogenesis than that for adults, the longer life expectancy of the paediatrics also meaning they have greater time for the cancer effect to manifest. In regard to diagnostic procedures, justified according to predefined criteria by qualified medical practitioners to diagnose a clinical problem and optimised, then the benefits from the clinical diagnosis are viewed to outweigh the expected radiation risk (Sulieman et al., 2011). It is especially important to make sure that CT scans in children are performed with exposure settings that are adjusted for an optimised
outcome. Such conditions imply that individually, as a result of CT radiation examination, there remains a small but nevertheless statistically significant increased risk of developing cancer (Frush et al., 2003). The International Commission on Radiological Protection (ICRP, 2007) estimated the cancer risk for the whole population per effective dose unit to be 5.5 × 10−2 Sv−1. Thus, a radiation dose of 50 mSv has a probability of three cancer incidents in 330 procedures. The probability of fatal and non-fatal cancer at doses > 100 mGy is proportionally increased with doses according to linear no threshold model. Berrington de González et al. reported that almost 29,000 of the expected cancers in the United States were possibly linked to radiation exposure from CT scans (Berrington de González et al., 2009). In another study, Sodickson et al. (2009) quantified that radiation exposure from CT procedures generated 0.7% of the total anticipated cancer incidents and 1% of total cancer mortality (Sodickson et al., 2009). Cancer risk apart, the well documented link between radiation tissue reactions due to lengthy medical exposures, skin injuries and other deterministic effects included, are a concern in regard to CT angiography and interventional radiology. Thus, while at medical imaging levels using CT tissue reaction effects do not occur in normal practice, limited cases have been reported of skin erythema and hair loss during poor CT machine settings per CT brain perfusions (ICRP, 2007). In Saudi Arabia in 2017, out of a total of 144 million visits to the hospitals and healthcare centres, 14.3 million patients were investigated with radiology in all health sectors (MoH, 2017), equating to 1 out of 10 patients. The Saudi population is estimated to be 33.4 million, thus the ratio of radiological investigations to the total
E-mail address: [email protected]. https://doi.org/10.1016/j.radphyschem.2019.04.011 Received 15 December 2018; Received in revised form 1 April 2019; Accepted 7 April 2019 Available online 26 April 2019 0969-806X/ © 2019 Elsevier Ltd. All rights reserved.
Please cite this article as: M. Alkhorayef, Radiation Physics and Chemistry, https://doi.org/10.1016/j.radphyschem.2019.04.011
Radiation Physics and Chemistry xxx (xxxx) xxxx
M. Alkhorayef
population is 0.43. Thus, the Saudi population is exposed to high collective doses. Therefore, an accurate estimate of patient doses is recommended to avoid unnecessary exposure. The radiology departments are well equipped with advanced imaging modalities but the number of published studies is quite limited compared to the massive number of medical procedures, including CT. Of the data available for CT paediatric examinations, these include McLean et al. (2003), Verdun et al. (2008), Kritsaneepaiboon et al. (2012), Sulieman et al. (2015), Hwang et al. (2015) and Gao et al. (2018). Much more limited studies have been conducted in Saudi Arabia, including Sulieman et al. (2018), the authors noting that a CT dose optimisation protocol has yet to be implemented in many of the radiology departments. The present multicentre survey is needed in seeking to assess the level of patient exposure, with comparison made against international guidelines and diagnostic reference level (DRL). The particular objective of present study is to investigate paediatric patient doses received during certain CT examinations, also seeking to provide local DRLs for the brain, abdomen and chest.
Table 2 The mean values and standard deviation of the demographic data. Parameter
Age (Year)
Height (cm)
Weight (kg)
Average Max Min Median SD
5.10 13 0.01 3.9 4.8
79.2 140 25 8.5 40.1
20 40 3 7 18.5
Table 3 CT Patient dose values for paediatric CT brain. Parameter
Average ± sd
Minimum
Maximum
Tube voltage (kVp) Tube current-time product (mAs) Slice thickness Pitch
120 241.5 ± 45 1.8 ± 1.4 0.4
120 91 1 0.4
120 478 5 0.4
the field of view, with use being made of a tissue equivalent phantom, the yield being multiplied by exposure to absorbed dose conversion factor.
2. Materials and methods 2.1. Patient dose measurements
CTDI =
Radiation doses per CT brain, abdomen and chest procedure were assessed in three hospitals for a total of 59 paediatric patients, the clinical procedures having been justified by qualified physicians. The Ethics and Research Committee approved the study and consent was obtained for all patients prior to examination. The different CT systems used, with detectors ranging between 16 and 128, have been identified in Table 1. The clinical indications included trauma, pneumonia and abdominal disorders. The mean age and age range was 5.10 (0.01–13) years, with mean weight and weight range of 20 (3–40) kg. Significant variation was noticed between patient age and weight (Table 2). The image acquisition parameters that were used are presented in Table 3. The dose measurements for each whole procedure comprised volume CT dose index (CTDIvol (mGy) per single slice and the dose length product (DLP, mGy.cm). Accurate measurement of standard patient size has been important, allowing comparison with other studies. The study, originally designed for adults as well as paediatric patients, has been exclusively conducted herein for paediatric cases. The actual scan parameters used for a number of individual standard patients were recorded during routine examinations. Patient demographic data were collected, e.g., age (years), gender, weight (kg) and height (cm). Record was also made of image acquisition parameters: tube potential (kVp), tube current (mA), exposure time (s), slice thickness (mm). Organ equivalent and effective doses were assessed using normalised DLP values (mGy.cm) published by the ImPACT group (ImPACT, 2011).
CTDIw =
installation
Detected Type
A B C
Philips Siemens Siemens
Brilliance Light speed SOMATOM Definition
2004 2008 2014
16 64 20
1 CTDIcenter + CTDIperiphery 3
CTDIvol =
equation 2
CTDIw pitch
equation 3
To calculate the patient dose per whole procedure, CTDIvol is multiplied by the scan length to obtain the DLP, as illustrated in equation (4)
DLP (mGy . cm) = CTDIvol
scan length
equation 4
DLP (mGy.cm) was used to calculate the effective dose (H) using software provided by the National Radiological Protection Board, (NRPB-SR250, 1996), now part of Public Health England). The risk (RT) of cancer probability per CT procedure was calculated by multiplying the effective dose (E) by the risk factor (R) (ICRP, 2007). 3. Results While the same 120 kVp tube voltage has been used in all three hospitals, the tube current-time product (mAs) showed wide variation, of up to five times. This variation can increase the uncertainty of dose measurement and effective dose estimation since patient weight can be expected to increase with age. Patient doses in the three hospitals are presented in Table 4. In general, the variations in dose are due to differences that include the number of scans, tube current and repeated scans. Measured patient doses in terms of DLP (mGy.cm) for all patients are shown in Table 4. Patient effective doses per procedure are presented in Fig. 1. The estimated effective dose from the abdomen procedure is observed to be greater than that for the chest and brain procedure. In paediatric patients all organs are in close vicinity, thus a small field size, may expose large number of sensitive organs.
Table 1 CT machines. model
equation 1
CTDIvol is calculated using the following equation (3)
In CT procedures, the X-ray tube rotates around the patient, the dose being distributed homogeneously. To calculate the CTDIvol (mGy), DLP (mGy.cm) and Effective Dose (mSv) use has been made of equation (1). CTDI is the overall radiation deposited energy absorbed per slice (collimation). CTDI(mGy) is extrapolated from the CTDI100 (C/kg) measurement using an ionisation chamber of length 100 mm at the centre of
manufacture
D (Z ) dz
whereD(Z) = Profile of radiation exposure along z axis.N = slices number.T = slice thickness (mm) or the width of the tomographic volume. Because X-rays are absorbed linearly inside the body across the radiation field, the peripheral tissues receive greater doses than the tissues and organs in the centre during 360° X-ray tube rotation around the patient. Thus the appropriate weighting is taken into account using equation (2).
2.2. CT dose descriptors and measurement
Hospital
1 NT
2
Radiation Physics and Chemistry xxx (xxxx) xxxx
M. Alkhorayef
Table 4 Paediatric radiation doses (mGy.cm) during brain, chest, abdomen. CT Procedures
Hospital
Min
Median
Mean
3rd quartile
Max
Brain
A B C A B C A B C
113.0 115.0 118.0 72.0 54.0 60.0 33.6 30.0 42.6
280.0 290.0 310.0 310.0 92.8 280.5 49.2 36.0 55.7
300 ± 117 328.8 ± 225 350 ± 117 340.8 ± 200 94.5 ± 31 295.1 ± 230 62.5 ± 71 73.1 ± 78 80.4 ± 80
397.5 323.0 419.5 330.0 122.7 350.5 69.3 76.1 86.5
492.0 995.0 502.0 1014.0 138.0 1244.0 140.1 190.5 160.6
Abdomen Chest
4. Discussion
comparisons between different procedures are possible with different imaging modalities. In this study, the mean effective dose also showed wide variation (Fig. 2). Because the conversion factors and software used are the same, the difference is mainly due to a difference in DLP. Fig. 1 shows the radiation dose to patients in the three hospitals, no consistent trend in patient doses being found. Fig. 2 shows a comparison with previous studies, the dose being lower compared to previous published results. DRLs can be used to verify the practices for typical examinations for a group of standardised patients. This is done in order to ensure that the dose will not be exceeded in normal practice without adequate justification (ICRP, 2000). For paediatric CT procedures, and to the best of our knowledge, no previous proposal for DRLs has been made, either at the national or international level, Thus, based on ICRP recommendations, a third quartile value of the median value can be used as the DRL. Thus the proposal, one a local basis, is for the adoption of 380, 270 and 80 mGy cm for CT brain, abdomen and chest respectively.
CT scanning is recognised to be a high radiation dose modality when compared to other diagnostic X-ray techniques. Since its launch into clinical practice more than 30 years ago, CT scanner technology has developed and its use has become more widespread, with commensurate concerns over patient radiation doses. The introduction of multislice scanners has focused further attention on this issue and it is generally believed that it will lead to higher patient doses. Incidents resulting in tissue reactions have been reported by Rehani (2015). In this study a total of 59 paediatric patients undergoing different CT modalities have been studied, the patient doses resulting from different CT technologies, ranging from 16 to 64 slices. The results of this study show wide variations in patient dose among different hospitals in terms of DLP and CTDIvol. The patients were scanned with routine protocols adopted by the operator, use being made of 120 kVp and mAs in the range 91–478, as shown in Table 3, and with the pitch (0.4) or less than unity. These parameters produced the radiation values represented in Table 4, showing values of DLP ranging between 113 mGy cm to 995 mGy cm for brain procedures. The abdomen doses were found to be greater compared to the brain and chest CT examinations (Table 4). This can be attributed to the scan length and structures of the organs. The range of DLP (mGy.cm) was (54–1244), the upper value being more than 20 times that of the minimum value. This may be attributed to the fact that in some cases the technologists performed a simultaneous scan of the abdomen and pelvis based on the department protocol, seeking to avoid a request for the pelvis alone. In CT examination, with patients exposed to relatively high radiation dose, the use of ordinary dose values (CTDI or DLP) will provide less information regarding the radiation risks. An effective dose is the unit of choice in this situation (partial exposure) and, furthermore,
5. Conclusions The aim of this research for paediatric patients was to study the trend in CT dose from brain, chest and abdomen examinations at three hospitals in Saudi Arabia, also to investigate the causes of high radiation doses. The study has shown that patients are well protected and that the patient doses are below that of most previous studies. However, there is still a need to refer to criteria and for the continuous training of staff in radiation dose optimisation concepts, seeking to eliminate unnecessary CT procedures and dose. The absence of any standard protocol for CT procedure in all three hospitals was noted, resulting in wide variation of exposure parameters for the same age groups of patients. Local diagnostic reference levels have been proposed.
Fig. 1. Patient effective dose per procedure. 3
Radiation Physics and Chemistry xxx (xxxx) xxxx
M. Alkhorayef
Fig. 2. Patient doses compared with previous studies (mGy.cm).
Acknowledgements
951–957. Gao, Y., Quinn, B., Pandit-Taskar, P., et al., 2018. Patient-specific organ and effective dose estimates in pediatric oncology computed tomography. Phys. Med. 45, 146–155. Hwang, J., Do, K., Yang, D., Cho, Y., et al., 2015. A survey of pediatric CT protocols and radiation doses in south Korean hospitals to optimize the radiation dose for pediatric CT scanning. Medicine (Baltim.) 94 (50), e2146. Kritsaneepaiboon, S., Trinavarat, P., Visrutaratna, P., 2012. Survey of pediatric MDCT radiation dose from university hospitals in Thailand: a preliminary for national dose survey. Acta Radiol. 53, 820–826. McLean, D., Malitz, N., Lewis, S., 2003. Survey of effective dose levels from typical paediatric CT protocols. Australas. Radiol. 47, 135–142. MoH. Ministry of health, 2017. ANNUAL STATISTICAL BOOK. Available at: https:// www.moh.gov.sa/en/Ministry/Statistics/book/Documents/ANNUAL-STATISTICALBOOK-1438H.pdf , Accessed date: 2 December 2018. Rehani, M., 2015. Tracking of examination and dose: overview. Radiat. Prot Dosim 165 (1–4), 50–52. Sulieman, A., Vlychou, M., Tsougos, I., Theodorou, K., 2011. Radiation doses to paediatric patients and comforters undergoing chest X rays. Radiat. Protect. Dosim. 147 (1–2), 171–175. Sulieman, A., Mahmoud, M.Z., Serhan, O., Alonazi, B., Alkhorayef, M., Alzimami, K., Bradley, D., 2018. CT examination effective doses in Saudi Arabia. Appl. Radiat. Isot. 141, 261–265. Sulieman, A., 2015. Establishment of diagnostic reference levels in computed tomography for paediatric patients in Sudan: a pilot study. Radiat. Protect. Dosim. 165 (1–4), 91–94. Verdun, F.R., Gutierrez, D., Vader, J.P., Aroua, A., Alamo-Maestre, L.T., Bochud, F., Gudinchet, F., 2008. CT radiation dose in children: a survey to establish age-based diagnostic reference levels in Switzerland. Eur. Radiol. 18, 1980–1986.
The author extends his appreciation to the Deanship of Scientific Research at King Saud University, Saudi Arabia, for funding this work through research group No (RG-1438-072). Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.radphyschem.2019.04.011. References Alamo-Maestre, L.T., Bernier, M.O., Rehel, J.L., Brisse, H.J., Wu-Zhou, X., Caer-Lorho, S., Jacob, S., et al., 2012. Radiation exposure from CT in early childhood: a French largescale multicentre study. Br. J. Radiol. 85 (1009), 321–329. Alkhorayef, M., Hamza, Y., Sulieman, A., Salih, I., Babikir, E., Bradley, D.A., 2019. Effective dose and radiation risk estimation in certain paediatric renal imaging procedures. Radiat. Phys. Chem. 154, 64–68 2019. Berrington de González, A., Mahesh, M., Kim, K.P., Bhargavan, M., Lewis, R., Mettler, F., Land, C., 2009. Projected cancer risks from computed tomographic scans performed in the United States in 2007. Arch. Intern. Med. 14 (22), 2071–2077 169. Bochud, F., author Frush, D., Donnelly, L., Rosen, N., 2003. Computed tomography and radiation risks: what pediatric health care providers should know. Pediatrics 112 (4),
4