Dose optimisation in paediatric CT examination: Assessment on current scanning protocols associated with radiation dose

Journal Pre-proof Dose optimisation in paediatric CT examination: Assessment on current scanning protocols associated with radiation dose Muhammad Kabir Abdulkadir, Nur Atikah Yusra Mat Rahim, Nur Syazwani Mazlan, Norfataha Mohd Daud, Ibrahim Lutfi Shuaib, Noor Diyana Osman PII:

S0969-806X(19)30553-5

DOI:

https://doi.org/10.1016/j.radphyschem.2020.108740

Reference:

RPC 108740

To appear in:

Radiation Physics and Chemistry

Received Date: 29 May 2019 Revised Date:

25 November 2019

Accepted Date: 31 January 2020

Please cite this article as: Abdulkadir, M.K., Yusra Mat Rahim, N.A., Mazlan, N.S., Daud, N.M., Shuaib, I.L., Osman, N.D., Dose optimisation in paediatric CT examination: Assessment on current scanning protocols associated with radiation dose, Radiation Physics and Chemistry (2020), doi: https:// doi.org/10.1016/j.radphyschem.2020.108740. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Ltd.

Dear Editor,

Credit author statement

Noor Diyana Osman (corresponding author): Conceptualization, Methodology, Writing – review & Editing, Project administration, and Funding acquisition Muhammad Kabir Abdulkadir: Investigation, Data curation, Formal analysis, Visualisation, Writing- Original draft preparation. Nur Atikah Yusra Mat Rahim: Investigation, Formal analysis, Validation Nur Syazwani Mazlan: Investigation, Formal analysis, Validation Norfataha Mohd Daud: Supervision Ibrahim Lutfi Shuaib: Methodology, Writing – review & Editing, Supervision

Dose optimisation in paediatric CT examination: Assessment on current scanning protocols associated with radiation dose Muhammad Kabir Abdulkadira,b, Nur Atikah Yusra Mat Rahimc, Nur Syazwani Mazlanc, Norfataha Mohd Daudd, Ibrahim Lutfi Shuaiba, Noor Diyana Osmana,* a

Advanced Medical and Dental Institute, Universiti Sains Malaysia, Sains@Bertam, 13200 Bertam, Penang, Malaysia b Department of Medical Radiography, Faculty of Basic Medical Sciences, University of Ilorin, 240213 Ilorin, Nigeria c School of Health Sciences, Health Campus, Universiti Sains Malaysia, 11800 Kubang Kerian, Kelantan, Malaysia d Department of Radiology, Hospital Universiti Sains Malaysia, 11800 Kubang Kerian, Kelantan, Malaysia

ABSTRACT Request for paediatric CT imaging has been increasing recently, and thus assessment of current paediatric CT protocols is of crucial importance as to assess the associated potential risk and possibly identify the need to modify the current practice. The aim of this study was to optimise the current local practice through investigation on the radiation dose distribution and existing routine scanning protocols of paediatric head and abdomen CT examinations at Radiology Department, HUSM, Kelantan, Malaysia. A total of 250 paediatric (age between 0‒12 years) CT examinations (134 of head CT and 116 of abdomen CT scans) were retrospectively collected from PACS and further analysed. The dose metrics in volume CT dose index (CTDIvol) and dose length product (DLP) with combination of exposure parameters (kV, mAs, pitch, scan length and acquisition time) for paediatric CT imaging were evaluated. Third quartile values of local dose distribution were then compared with selected international DRLs. The third quartile values for CTDIvol (mGy) and DLP (mGy.cm) for head and abdomen CT scans with respect to the age groups were 0‒3 years (32/557 and 7/232), 4‒6 years (61/1105 and 9/251), 7‒9 years (117/1454 and 11/405), 10‒12years (117/2203 and 14/566) respectively. From the comparative study, the local dose received from paediatric head CT scans were higher than the recommended levels. This is mainly due to selection of scanning parameters which were higher than the optimised paediatric protocols. Tube voltage selection was ranged from 100‒120 kV for all age groups except the head CT scan in group 4 that used a constant 120 kV. Applied mAs varied in the ranges from 100‒410 mAs for head CT scan and 35‒100 mAs for abdominal CT scans and increases as the paediatric age increased. From the findings, review and optimisation on the current scanning protocols is required especially for head CT scan to complement the corresponding age groups and sizes while maintaining the diagnostic values. Keywords: Paediatric CT; Radiation dose; Dose optimization

*Corresponding author at: Oncological and Radiological Sciences Cluster, Advanced Medical and Dental Institute, Universiti Sains Malaysia, Sains@Bertam, 13200 Bertam, Penang, Malaysia Email address: [email protected] (N. D. Osman)

1. Introduction Request for paediatric CT imaging by clinicians increase recently, accounting for 11% of total CT examinations (Bernier et al., 2018). The rise in patronage was attributed to advancement in CT technology especially multi-slice CT (MSCT) and helical CT capability, and this has greatly increased the diagnostic capability and CT benefits over other imaging modalities (Negal et al., 2007; Bernier et al., 2018). Stochastic risks are the primary concern in paediatric computed tomography (CT) imaging due to relatively smaller patient size, higher radiation dose associated with CT imaging, longer remaining life spans and greater sensitivity to ionizing radiation (ACR, 2014). Previous study has stated that the lifetime radiation-induced cancer mortality risk is higher in paediatric CT as compared to adult due to larger lifetime risks per unit dose (Brenner et al., 2001). Hence, an assessment on dose to this population undergoing CT examinations in our population is needed to assess the associated potential risk and possibly identify a need to optimize current practice. Since optimisation is an important step towards achieving patient safety and prevention of unnecessary doses in medical imaging procedures, it has become pertinent and highly advocated that consistent assessment on CT protocols and dose are performed (Huda and Mettler, 2011; ACR, 2014; Anupam, 2015). Establishment of diagnostic reference levels (DRLs) is recommended as an optimisation tool for medical exposures, because dose limits are not applicable to this exposure category (EC, 2015). The established DRLs is based on the recommended displayed CT dose metrics such as volume CT dose index (CTDIvol), weighted CT dose index (CTDIw) in mGy and dose length product (DLP) in mGy.cm (EC, 2015). These dose indicators are based on measurements in standard polymethyl acrylate (PMMA) phantoms of reference sizes (16 cm and 32 cm) (Huda W. and Mettler FA., 2011). CTDIvol and DLP are preferable because it is more sensitive to changes in scan parameters. Theoretically, CTDIvol and DLP values depend on the selected exposure factors, such as kV, mA, time, and collimation and pitch. However, proper selection and manipulation of the scanning factors have been described as an important tool in achieving dose optimisation in CT imaging (Huda W. and Mettler FA., 2011; Anupam et al., 2015; EC, 2015). Therefore, this study is intended to investigate local radiation dose during paediatric CT imaging and assess if current scanning protocols are adequately justified to ensure dose optimisation at our centre. Review on paediatric doses from CT examinations will help identify any unjustified exposure in our current practice by comparing local dose data with the recommended DRLs and established standards from other countries as recommended by the American Association of Physicists in Medicine (AAPM) (ACR, 2014; Almohiy, 2014). Besides, AAPM has also advocate the replacement of the current CTDIvol and DLP displays to a more accurate size specific dose estimate (SSDE) method as reported in AAPM Report 204. SSDE method takes account of individual patient size and described a better depiction of absorbed dose. To our knowledge, the national diagnostic reference levels (NDRLs) for paediatric CT imaging are not yet available and study on SSDE in paediatric CT are not broadly reported at national level. Thus, this study serves as a preliminary work to propose new optimised scanning protocols for paediatric CT and subsequently established a local DRLs for paediatric CT imaging in our future study. 2. Materials and methods 2.1. Study Population This study received human ethical approval for clinical data study from the ethical committee of Universiti Sains Malaysia (USM) (Study protocol code: USM/ JEPeM/17030180), and the need to obtain

informed consent was waived. This retrospective study evaluated data of 250 paediatric patients (130 males and 120 females) who were referred to the Radiology Department, Hospital Universiti Sains Malaysia (HUSM), Kelantan for CT examination. The data from May 2011 until March 2017 were retrieved from the picture archiving and communication system (PACS). All paediatric CT examinations were performed using single-energy 64 slices Siemens SOMATOM Definition AS+ CT scanner (Siemens Healthineer, Germany) at HUSM. Individual patient dose data, including the acquisition factors and patient demographic information were recorded and evaluated. The ages of recruited paediatric population were ranged from 0‒12 years. The paediatric population were classified into four age groups which were 0‒3 years (as Group 1), 4‒7 years (Group 2), 7‒9 years (Group 3), and 10‒12 years (Group 4). 2.2. Paediatric CT Protocols The CT scanner used in this study was equipped with automatic exposure control (AEC), known as CARE Dose4D software. Data were obtained using both single sequence (without contrast) and multiphase sequence (with contrast) protocols. 47% (63 of 134) of head CT scan and 99.2% of abdomen CT scan were performed by multi-phase protocol, involving contrast medium. There are five manufacturer’s default protocols available for paediatric head CT and were used in routine clinical practice namely head routine child, head routine > 6-month child, head routine < 3 years, head routine < 6 years child, and head routine adult. For abdominal CT scan protocols, they are categorized and selected based on patient weight namely abdomen routine child, < 20 kg child, < 35 kg child, < 50 kg child, and routine adult protocols. Each protocol has unique scanning parameters such as tube voltage (kVp), effective tube current (mAs), exposure time (s), pitch and scan length. 2.3. CT Dose Assessment All patient dose data including CTDIvol (in mGy) and DLP (in mGy.cm) values were retrieved from the PACS. The CTDIvol and DLP for head CT examination are reported based on reference phantom size of 16 cm while the abdomen CT examination values are estimated to 32 cm reference phantom. The weighted CT dose index (CTDIw) was calculated from the displayed CTDIvol value using the following equation; CTDIw = CTDIvol × pitch

(1)

Other factors that influence radiation dose were also retrieved from the dose report including number of scan (single or multiple sequence), kVp, mAs, scan length, pitch, and application of tube current modulation. The third quartile (or 75th percentile) values of the local dose distribution were determined, as recommended by the AAPM and European guidelines on DRLs for paediatric imaging (ACR, 2014; Almohiy H, 2014). The third quartile of local CTDIvol and DLP values for both paediatric head and abdomen CT studies were compared with the selected DRLs and current CT protocols were reviewed. 3. Results A total of 250 paediatric CT examinations including both head and abdomen CT (134 of head CT study and 116 of abdominal CT study) were retrospectively surveyed and further analysed. The population comprises of 130 males (52%) and 120 females (48%) paediatric patients (age between 0‒12 years). The patients were categorized into four age groups; group 1‒4. The demographic distributions of the entire population were 79 (31.6%), 52 (20.8%), 46 (17.2%), and 51 (20.4%) for group 1 to 4. The distributions of the paediatric patients underwent head CT scans for all groups are group 1 (38.8%), group 2 (21.6%),

group 3 (19.4%) and group 4 (20.1%). However, for abdominal CT scan, group 1 (35.3%) was the most predominant and followed by 22.4% and 18.9% for group 2 and 3, respectively. Fig. 1 shows the distribution of paediatric patients underwent head and abdomen CT examinations based on the number of scan phases. All scans were performed using the helical scan mode, all abdominal scans except one were performed with single or more than one scan sequence (for contrast medium application). For paediatric head CT examination, most of the paediatric patients (97%) underwent single or 2 scan phases protocol. While for abdomen CT examination, most of paediatric patient (88%) underwent more than single scan, with 10% of them received 3 and 4 scan phases, respectively. 1 phase

2 phases

3 phases

4 phases

100

No. of patients

80

60

40

20

0 Head CT

Abdomen CT

Fig. 1. Distribution of paediatric patients underwent head and abdomen CT scans based on number of scan phase.

For most of the examinations, the same scanning parameters were used for both non-contrast study and CT study with contrast. Selection of these study protocol and scanning parameters were determined based on individual patient age for head CT scan and patient weight for abdominal CT scan. Table 1 summarises the acquisition parameters used in this study for head and abdominal CT imaging. From the table, both head and abdomen CT scans use helical scan mode. The automatic exposure control (AEC) known as Siemens CARE Dose4D was utilised for both paediatric abdomen and head CT scans. Most of the CT scans used low pitch value (pitch <1) except for abdomen CT study for age group 1 to 3. Table 1 Summary of acquisition parameters during paediatric CT examination Age (year)

Number of patients (M, F)

Acquisition parameter Scan mode

Tube voltage (kVp)

Effective current (mAs)

Pitch

Scan time Scan length (s) (cm)

Tube current modulation

Head 0‒3 4‒6 7‒9 10‒12

52 (25, 27) 29 (15, 14) 26 (11, 15) 27 (14, 13)

Abdomen 0‒3 4‒6 7‒9 10‒12

41 (24, 17) 26 (12, 14) 22 (13, 9) 27 (16, 11)

Helical

Helical

100‒120 100‒120 100‒120 120

100‒410 160‒410 215‒410 410

0.8 0.55 0.55 0.55

3‒7 3‒7 4‒8 5‒8

12.0‒21.0 12.2‒24.5 15.3‒22.7 16.8‒20.9

80‒120 120 100‒120 120

35‒86 40‒179 47‒127 58‒110

1.2 0.6‒1.2 0.6‒1.2 0.6

2‒5 3‒9 4‒11 4‒12

12.1‒39.9 21.0‒40.2 23.9‒47.1 30.4‒49.0

Yes

Yes

In Table 2, the routine local acquisition parameters were compared with the optimized protocols for Siemens CT scanner (Nievelstein et al., 2010). As shown in Table 2, most of the routine acquisition parameters applied in this study were higher than the recommended optimized protocols. The use of higher mA and kV values were observed especially in the age group 3 and 4 for head CT scans as compared to the optimized protocol. Besides, the scan length used in this study were longer than the optimised protocols especially for head CT scan. These therefore one of the main causes for higher dose values of local paediatric head CT scan as compared to the established DRLs as shown in Figs. 3 and 4. However, applied parameters for abdominal scans were within the recommended limits of the optimised standards. Table 2 Comparison of study acquisition parameters with the optimised protocols for Siemens CT (Nievelstein et al., 2010). Acquisition parameters

Head CT

Abdomen CT

This study

Optimised

This study

Optimised

12.0‒21.0

5.0‒12.0

12.0‒49.0

22.0‒40.0

Tube Rotation Time (s)

0.3‒5.0

1.0

0.2‒0.5

0.5

Scan Method

Helical

Sequential

Helical

Helical

0.55‒0.8

‒

0.6‒1.2

0.5‒0.95

Slice thickness (mm)

0.6

2.5‒4

0.6‒1.2

0.75‒1.0

kVp (effective mAs) 0‒3 4‒6 7‒9 10‒12

100 (100‒410) 100‒120 (160‒410) 100‒120 (215‒410) 120 (410)

100 (170‒270) 100 (270‒345) 120 (240) 120 (240)

80‒100 (35‒86) 120 (40‒179) 100 (47‒127) 120 (58‒110)

100 (105‒145) 100 (185‒200) 100 (200) 120 (140)

Scan length (cm)

Pitch

In Fig. 2, estimated dose quartiles distribution for both CTDIvol and DLP values based on paediatric age groups for this study is presented. As shown in the box plot, the dose distributions (interquartile range and median values) were increased as paediatric age increased. However, for head CT scan, the interquartile range and median values of the CTDIvol were almost comparable for age group 3 and 4. The dose distribution of CTDIvol and DLP were higher for paediatric head CT scan as compared to abdomen CT scan. From our findings, most of the third quartile value of CTDIvol and DLP for head CT scan were higher for female patient than the male except in age group 3. Whereas, in the abdominal CT scan, most of the dose values for female patients were higher than male patients for all the age group except for age group 1.

Figs. 3 and 4, shows comparison of CT dose in CTDIvol and DLP (represented as third quartile or 75th percentile) for each age group and CT examination for this study with previous established DRLs and the European guidelines on DRLs for paediatric CT imaging (EC, 2015). The selected established DRLs were based on the dose survey conducted in Britain, Japan, Switzerland (Brady et al., 2012; Yonekura, 2015; Wagner et al., 2018). For head CT examination, data from this study were compared with 4 different international DRLs (Fig. 3) whilst for abdomen CT examination, data were only compared with 3 different DRLs (Fig. 4). (a)

(b)

(c)

(d)

Fig. 2. Box-plot showing the estimated paediatric dose for each age group represented as (a) CTDIvol and (b) DLP for head CT scan and (c) CTDIvol and (d) DLP for abdomen CT scan. Data are defined as median (horizontal line inside boxes), interquartile range (boxes), and highest and lowest values (ends of whiskers).

The comparative study reveals that the third quartile values for this study were higher (1% to 70%) than the lowest values of the established DRLs for the head CT scan except for the age group of 0-3 years whose values were below some of the selected DRLs. However, in paediatric abdominal CT scan, most of the third quartile values of CTDIvol are higher than the selected DRLs for most of the age groups. Conversely, the third quartile values of DLP reported from this study were predominantly lower than the selected DRLs. In general, the most significant difference in terms of CTDIvol and DLP between age groups was observed between group 0-3y and 10-12y and the least significant difference was observed between age group 4-6y and 7-9y.

4. Discussion This study presented the distribution of local radiation dose (CTDIvol and DLP) associated with routine scanning protocols for both paediatric head and abdomen CT imaging at HUSM, Kelantan, Malaysia. The third quartile values of the local dose metrics were compared with the established DRLs of Japanese, British, Swiss and European. These international DRLs were among the most recently published data and were selected to ensure the comparative study was accurate as the CT technological advancement of all the comparing standards are exactly at the same level. Although this study was conducted based on the data from only one centre, but this centre is considered as one of the tertiary or referral hospital for EastCoast region of Malaysia with very high number of patient throughput underwent CT imaging procedure. In routine local clinical practice, the selection of exposure setting is based on the dedicated scanning protocols for various paediatric age groups as set by the CT scanner. The choice of image acquisition protocol in this study was influenced by patient’s age and weight for head and abdominal CT scans, respectively. As depicted in Table 1, the paediatric protocol for each group has varying combinations of scanning parameters in terms of tube kV, mA, exposure time and pitch value. These scanning parameters tend to increase or decrease with the changes in paediatric patient’s age and weight. Previous studies have proved that varying kV and effective mAs have direct effect on radiation dose, CTDIvol (Negal et al., 2007; Almohiy, 2014; Anupam et al., 2015). Other scanning factors such as scan length and pitch are more significantly affected the entire CT scan and therefore influence DLP value. From the survey, scanning parameters for routine adult protocol were used for paediatric CT scans for older age group (10‒12 years old) which contributes to higher local dose to paediatric population. However, the adult protocols will lead to underestimation of dose received by paediatric patients as it is based on larger phantom size (32 cm) as compared to real paediatric size. (a)

This Study

Swiss 2018

Japan 2015

EC 2015

British 2012

(b)

140

This Study

Swiss 2018

Japan 2015

EC 2015

British 2012

2500

DLP (mGy.cm)

CTDIvol (mGy)

120 100 80 60

2000

1500

1000

40 500

20 0

0 0-3y

4-6y

7-8y

10-12y

0-3y

4-6y

7-8y

10-12y

Fig. 3. Comparison of 3rd quartile dose values received from paediatric head CT scan; (a) CTDIvol (mGy) and (b) DLP (mGy.cm) of this study with other established DRLs.

This Study

(a)

Japan 2015

EC 2015

This Study

British 2012

16

EC 2015

British 2012

(b) 700

14

600 DLP (mGy.cm)

12 CTDIvol (mGy)

Japan 2015

800

10 8 6

500 400 300

4

200

2

100 0

0 0-3 y

4-6 y

7-8 y

10-12 y

0-3 y

4-6 y

7-8 y

10-12 y

Fig. 4. Comparison of 3rd quartile dose values received from paediatric abdomen CT scan (a) CTDIvol (mGy) and (b) DLP (mGy.cm) of this study with other established DRLs.

For assessment on the current local scanning protocols, all the collected scanning parameters were compared with the optimised protocols recommended by previous study (Nievelstein et al., 2010), as shown in Table 2. From observation, the acquisition parameters such as kVp, and mAs were higher than the optimised protocols. This is one of the reasons that lead to higher local patient dose as compared to other published DRLs. The indicated scan length in paediatric head CT examination also longer than the scan length for optimised protocols. However, this is because the scan length of this study is indicated for both brain and head CT scans, while the optimised protocols is specifically for brain CT imaging. The optimised protocols also suggested thicker slice thickness for head CT scan as compared to the selected slice thickness used in this study. As suggested by AAPM, the paediatric routine protocols should always apply the automatic exposure control (AEC) setting during the acquisition such as CARE Dose4D and CARE kV for Siemens SOMATOM Definition AS+ CT scanner (AAPM, 2017). AAPM Working Group, the Alliance for Quality Computed Tomography (AQCT) has releases a new Routine Paediatrics Abdomen and CT protocols as a guidance. Based on the AAPM guidance, the recommended paediatric protocols for Siemens SOMATOM Definition AS+ CT scanner are 100 kV, 208 mAs, pitch of 1.4 and slice thickness of 5.0 mm (AAPM, 2017). From the findings, higher dose values were observed in female patient for most of the age groups and body region, as compared to male. In recent recommendation, multiphase CT examinations are discouraged in paediatric CT imaging. However, CT examinations involving more than one scan sequence (contrast and non-contrast phase) were still used in this centre (Fig. 1), which lead to higher cumulative dose values. A recent study done on paediatric samples reported a significant increase in effective dose to due to delay scan in CT abdomen/pelvis examinations (Mohd Tap et al., 2018). In general, the results in Fig. 2 were in line with findings reported in the previous literatures which have indicated an increased radiation dose with increasing patient age and weight when the optimal technique and protocols were used for image acquisition (Huda and Mettler, 2011; Ae-Yeon et al., 2015; Anupam et al., 2015; Kalpana et al., 2015; Khalid et al., 2015; Abdulkadir et al., 2016). This relationship was also observed in this study, as patient dose values were increased from younger age group (0‒3 years) to older age group (10‒12 years) for all body regions. EC and AAPM recommended the importance of periodic assessment on patients’ dose through the establishment of DRLs. In this study, the local dose distributions were compared with other established DRLs to assess the current CT protocols used in this centre. The comparative study revealed higher local dose values for head CT scan (Fig. 3) and hence indicating a requisite for review or optimization of head CT protocols. A time frame of 3 years to maximum of 5 years was recommended for revision of local DRLs as a major process of dose optimization (Brady et al., 2012). ACR has stated the DRLs for paediatric abdomen in CTDIvol is 15 mGy (for reference phantom of 16 cm) and 7.5 mGy (for reference

phantom of 32 cm) (ACR, 2017). However, the third quartile of CTDIvol in this study is higher (range between 32‒117 mGy for all age groups) than the recommended DRLs. The reported higher dose values may be attributed to the use of helical scan mode instead of axial scan mode, multiphase scanning, longer scan length and higher kV and effective mAs. Similar findings were also reported in the previous literatures (Negal et al., 2007; Khalid, 2014; Yonekura, 2015). This study focused on evaluation of local paediatric CT practice based on two criterions; the comparison with established DRLs and with optimised CT protocols. In this study, paediatric patients and reported dose were categorized based on age groups with respect to varying size of children with age due to limitation in available information such as paediatric weight and effective size. From the findings, few recommendations were suggested in order to optimize the current practice such as a modification on current scanning protocols to tailor with the individual patient size rather than utilisation of the pre-set factors or default setting by manufacturer. The development of indication-based protocols may also reduce radiation dose received by paediatric by limiting the number of scan phase during CT examination. 5. Conclusion Diagnostic reference levels are recommended as an optimisation tool for radiation doses assessment in medical imaging procedures involving the use of ionizing radiation. DRLs allow local practices to be compared and identify the unjustified practice delivering higher dose that exceeded the established DRLs under normal circumstances. The justification of current local practice and dose optimisation in paediatric CT can be achieved by performing review on the scanning parameters such as the applied tube kV, effective tube current (mAs) and scan length to suite the corresponding age groups while still retaining the diagnostic image quality. The scan phases should be limited by reducing contrast study and the risk of repeated examinations among paediatric patients. Establishment of local paediatric DRLs with adoption of recommended SSDE method offers more accurate method of calculating and reporting individual paediatric doses which tailored the specific individual size for better depiction of individual patient absorbed dose undergoing CT imaging. It is important to reduce the radiation dose received by paediatric patients and also the health risk to paediatric population. Future work should focus on establishment of local DRLs with adoption to SSDE technique for paediatric CT imaging. Acknowledgements This work was funded by Ministry of Education (MOE), Malaysia through Fundamental Research Grant Scheme (FRGS) (Project code: FRGS/1/2019/STG02/USM/02/6). The authors would also like to thank all the radiographers and staff at Radiology Department, HUSM Kelantan and School of Health Sciences, USM for their contribution and assistance during data collection and support throughout this work. References Abdulkadir, M.K., Schandorf, C., Hasford, S., 2016. Determination of computed tomography diagnostic reference levels in north-central Nigeria. Pacific journal of science and technology. 17(2), 341‒249. Ae-Yeon, H., Kyung-Hyun, J., Dong, H., 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 94, 50. Almohiy, H., 2014. Paediatric computed tomography radiation dose: A review of the global dilemma. World Journal of Radiology 28, 6(1), 1‒6. American Association of Physicist in Medicine, 2011. AAPM TG 204 Report: Size-specific dose estimates (SSDE) in paediatric and adult body CT examinations. American College of Radiology, 2014. ACR–AAPM practice guideline for diagnostic reference levels and achievable doses in medical x-ray imaging. 2013. American College of Radiology, 2017. ACR-SPR practice parameter for the performance of computed tomography (CT) of the abdomen and computed tomography (CT) of the pelvis. 2016.

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Highlights:

• Paediatrics are more prone to radiation risks • CT acquisition protocols should fit individual paediatric size • Accurate estimated CT dose for specific reference phantom size • Review on current CT protocols helps to identify the need for protocol modification • Established paediatric DRLs are the important tool for dose optimisation

Declaration of interests

√ The authors declare that they have no known competing financial interests or personal

relationships that could have appeared to influence the work reported in this paper.

The authors declare the financial interests/personal relationships which may be considered as potential competing interests:

Not applicable