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REVIEW ARTICLE
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Diagnostic reference levels for computed tomography examinations in pediatric population - A systematic review


1 Department of Medical Imaging Technology, Manipal College of Health Professions, Manipal Academy of Higher Education, Manipal, Karnataka, India
2 Department of Radiodiagnosis and Imaging, Kasturba Medical College and Hospital, Manipal Academy of Higher Education, Manipal, Karnataka, India

Date of Submission14-Jul-2020
Date of Decision29-Aug-2020
Date of Acceptance07-Oct-2020
Date of Web Publication22-Jan-2021

Correspondence Address:
Rajagopal Kadavigere,
Department of Radiodiagnosis and Imaging, Kasturba Medical College and Hospital, Manipal Academy of Higher Education, Manipal - 576 104, Karnataka
India
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jcrt.JCRT_945_20

 > Abstract 


Computed tomography (CT) has vital role in diagnosis of various pathologies using cross sectional images. Besides the advantages of CT in pediatric radiology, radiation dose has a significant adverse effect as children are more vulnerable than adults. Establishing Diagnostic Reference levels (DRLs) will determine unusual increase in radiation doses and therefore helps in optimizing the radiation dose by maintaining optimum diagnostic image quality. The objective of the review is to explore the literature on DRLs in pediatric CT examinations and techniques that have been used to establish them. Detailed search was done in PubMed-Medline, Scopus CINAHL, Web of Science, and the Cochrane Library databases to find studies that have established DRLs for pediatric CT examinations. The Preferred Reporting Items for Systematic Review and Meta-Analyses methodology was used to assess the relevant articles. The articles which assessed DRLs in pediatric CT examinations were included. A total of 501 articles were identified, of which 21 articles were included after a detailed screening process. Our review showed increased in pediatric patient dose surveys across the world and also increased in awareness for establishing DRLS among pediatric CT examinations. The review also demonstrated wide variation in DRLs and also deviation in the scanning techniques, protocols used and categorization methods used for establishing DRLs. As the pediatric population is more sensitive to radiation, the current review emphasizes the need for optimization of protocols and international standardization for establishing DRLs to facilitate a more feasible way of comparison of dose globally across CT sites.

Keywords: Computed tomography, diagnostic reference levels, dose length product, pediatric population, volumetric CT dose index



How to cite this URL:
Priyanka, Kadavigere R, Sukumar S, Pendem S. Diagnostic reference levels for computed tomography examinations in pediatric population - A systematic review. J Can Res Ther [Epub ahead of print] [cited 2021 Mar 4]. Available from: https://www.cancerjournal.net/preprintarticle.asp?id=307511




 > Introduction Top


Computed tomography (CT) is a crucial imaging modality used in radiology to diagnose various pathologies using cross sectional images. Over the past decade, pediatric CT imaging has been increased with the advancements in CT technology such as shorter acquisition times, reduced artifacts, improved contrast and temporal resolution, thereby increasing the diagnostic confidence. Despite its advantages in pediatric imaging, radiation poses significant adverse effects. Children are 2-3 times more vulnerable because of the effect of mitosis in developing organs and the long anticipated lifetime for developing cancer cells. The young girls are more prone to radiation risks such as radiation-induced solid cancer especially from CT abdomen and pelvis. There is high risk of leukemia from CT head in children <5 years of age.[1],[2],[3],[4],[5],[6],[7]

The International Commission on Radiation Protection (ICRP 103) proposed principles on radiation protection which includes justification, optimization and dose limitation to ensure that the risk of radiation dose to the patients do not offset the benefit gained from the CT imaging.[8] In order to optimize dose in CT, selecting suitable scanning protocols that corresponds to region of examination and patient age or size which will assure that the dose to individual patient is kept minimal. Diagnostic Reference levels (DRLs) was introduced in 1990 and its implementation was recommended in the ICRP 60 and 73.[9],[10]

DRL is specified at 75th percentile of CT patient or anthropomorphic phantom dose data from survey that will be carried across a broad user base using specific dose-measurement protocol. The dosimetric quantities recommended in the guidelines for the establishment of DRLs are volumetric CT Dose Index (CTDIv) for one slice and Dose Length Product (DLP) for whole coverage volume.[10],[11],[12] Due to wide range of sizes of pediatric, the establishment of age- and weight-specific DRLs were recommended by ICRP 135 and European guidelines on DRL for pediatric imaging.[13],[14] The objective of the review is to explore the literature on existing DRLs and techniques used for establishing them in pediatric CT examinations.


 > Methods Top


Design

This review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines.[15]

Literature search strategy

An extensive literature search for relevant original research studies was performed using PubMed-Medline, Scopus, CINAHL, Web of Science, and the Cochrane Library to find studies that have established DRLs for pediatric CT examinations. The study retrieval method from each database are shown in [Table 1]. The search was limited to specific criteria of population (pediatric, human), age (<19 years), publication language (English), and publication year (2000–2020). The search term for the identification of articles is shown in [Table 2]. The protocol for this systematic review study was registered at PROSPERO with the registration number-CRD42019134446.
Table 1: Study retrieval methods from each database

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Table 2: The terms used to identify the relevant articles

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Selection criteria

Articles were selected considering the inclusion and exclusion criteria based on Participants Intervention Comparison and Outcome methodology [Table 3]. Articles with case studies, case reports, posters, and narrative literature reviews were excluded as they did not fulfill the criteria. All the articles (titles and abstracts) were initially independently screened by two reviewers and articles that discussed DRLs in pediatric CT examination were included in the full content review. The exclusion criteria were articles that proposed DRLs for adult CT examinations and phantom studies.
Table 3: Participants intervention comparison and outcome methodology for determining study eligibility

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Data extraction

The data from each included article were obtained by two authors and any discrepancies were resolved following discussion.

Quality assessment

Data from articles were assessed for quality of methods and outcomes. The reviewers assessed the quality of articles based on the assessment tool for quantitative studies developed by the Effective Public Health Practice Project. The articles were finally rated as high (1), moderate (2). Two authors independently rated the articles. Among 21 articles, 16 articles were rated as high and five articles were rated as moderate.


 > Results Top


Five hundred and one articles were identified through the combined literature search. Four hundred and ten duplicate articles were removed. The title and abstract of 65 studies were assessed and excluded as they did not meet the inclusion criteria. The full text of additional five studies were reviewed and excluded as they were found not meeting the review criteria (studies done from 2000 to 2020, pediatric patients undergoing CT, pediatric CT DRLs). Finally, 21 articles were included in the systematic review [Figure 1].
Figure 1: Flow diagram of included and excluded studies for the systematic review

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Characteristics of selected studies

Pediatric CT examinations have increased recently with the advancement in CT technology. The studies included cover different region in the world, with two each from Australia, Finland, Iran, the USA, Switzerland, one each from Germany, India, Italy, Japan, Kenya, Nigeria, Portugal, South Africa, Turkey, the UK, and one international study including sites from Asia, Europe, Africa, and Latin America. Pediatric patient doses were collected from the five manufactures: General Electric (GE), Siemens, Philips, Toshiba, and Hitachi which included both single and Multi-Slice CT. A total sample size of 66465 was recruited from the included studies. Twelve studies used prospective data collection,[16],[17],[18],[19],[20],[21],[22],[23],[24],[25],[26],[27] seven studies used retrospective data collection[28],[29],[30],[31],[32],[33] and two articles used both prospective and retrospective data collection.[34],[35] The main characteristics of the studies are summarized in [Table 4].
Table 4: Summary of characteristics of selected studies

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 > Discussion Top


Over the past two decades, there has been tremendous increase in the use of CT for pediatrics which is leading to higher risk of radiation induced cancers especially in CT examinations of abdomen and pelvis. Various CT Vendors, Hospital, and Imaging centers have initiated methods to optimize radiation dose to pediatrics. The technical advances to reduce radiation dose include iterative reconstruction techniques, tube voltage, and current modulation, Bow tie filters. The protocol optimization was done by setting age-, weight-based, and indications-based protocols for better dose reduction.[1],[37],[38],[39]

ICRP publication 60 has recommended the establishment of DRLs for imaging modalities and also insisted on conducting surveys on patient dose to establish DRL's globally.[8] ICRP publication 135 and European PiDRL project has recommended age and weight bands for establishing DRLs.[13],[14] Fourteen studies have used age-based grouping,[16],[17],[19],[21],[22],[23],[26],[27],[28],[29],[31],[33],[34],[36] six articles have used age- and weight-based grouping for establishing DRLs for pediatric CT examination[18],[20],[25],[32],[34],[35] and three study has used protocol based on the body width for establishing DRLs for abdomen pediatric CT examinations.[25],[30],[31] To the bet of our knowledge, this is the first extensive review done to include DRLs established for Pediatric CT examinations across the globe.

European guidelines on DRL for pediatric imaging (PiDRL project) has recommended the guidelines for establishing pediatric DRLs and also reviewed the DRLs across the Europe.[14] In contrary to the prior literature, our systematic review found increased pediatric patient dose surveys for recent years. Apart from European countries, other regions in the world have also started realizing the importance of conducting pediatric regional dose surveys and establishing local, national DRLs. However, there was only one study which established regional DRLs in India. Hence, there is need for more studies in establishing pediatric CT DRLs compared to other countries.[24]

Age- and weight-based protocol for establishing diagnostic reference level

In establishing DRLs using age-based protocol, few studies have followed grouping range such as <1 year, 1–5 years, 6–10 years, and 11–15 year, whereas other studies have used grouping such as <5 years, 5–10 years, and more than 10 years [Table 5]. In establishing DRL using weight-based protocols, uniformity in ranging the weight group was not followed [Table 6]. The current review noticed that there is lack of standardization of age- and weight-based protocol for pediatric CT examination for comparison of DRLs. IRCP 135 and European guidelines (PiDRL project) have recommended weight bands of < 5 kg, 5–<15 kg, 15–<30 kg, 30–<50 kg, and 50–<80 kg. Age bands recommended are < 1 month, 1 month–<4 years, 4–<10 years, 10–<14 years, 14–<18 years.[14] Few recent articles have used age and weight bands recommended by the ICRP 135.[19],[22],[26],[27],[35] Future studies need to establish DRLs in pediatric based on the age and weight bands recommended by IRCP 135 and European guidelines (PiDRL project).
Table 5: Computed tomography diagnostic reference levels (volumetric computed tomography dose index/weighted computed tomography dose index, and dose length product) based on the patient age for head, chest, abdomen

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Table 6: Computed tomography diagnostic reference levels (volumetric computed tomography dose index and dose length product) based on the patient weight for head, chest, and abdomen

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Dose indices used for establishing diagnostic reference levels

The review found that CTDIv and DLP were commonly used dose descriptors for establishing DRLS. In addition to that few studies, used weighted CT Dose Index (wCTDI) and weighted DLP to establish DRLs.[19],[20],[21] The DRLs have been established using 50th, 75th, and 90th percentile values. However, 75th percentile was widely followed among all the studies for establishing the DRLs.

Comparison of diagnostic reference levels among various studies

Our study found the DRLs in terms of CTDIv was ranging from 18 to 72 mGy for CT head, 2.4-23 mGy for CT chest, and 5-17 mGy for CT abdomen. The DRL in terms of DLP was ranging from 230 to 1824 mGy/cm for CT head, 45–800 mGy/cm for CT chest, and 104–750 mGy for CT abdomen which could be used for comparison while establishing the DRLs in respective centers. The literature review noticed wide variation in DRLs in terms of CTDIv and DLP for pediatric CT examination between the CT centers and also noticed no uniform maintenance of protocol. Galanski et al. found that for pediatric brain examination CTDIv and DLP was lower when compared to the UK survey for all the age groups except for the age group up to 1 year. For chest and abdomen examinations, the CTDIv and DLP was significantly lower for all the age groups.[17] The studies done by Verdun et al., Ataç et al. and Saravanakumar et al. found that the DRLs for all age categories was similar to or lower than international DRLs for CT head. However, for chest and abdomen CT examination, the DRLs was higher than European DRL and other studies.[14],[18],[22],[24] The study done by Santos et al. proposed age categorized national pediatric CT DRLs and found that DRLs for CT head was higher than those of the European values whereas for CT chest examination DRLs was similar to the European values for all age categories.[29] Wagner et al. proposed DRLs for CT brain, facial bone, and petrous bone and found that DRLs was lower than studies in Switzerland and European countries.[33] Similarly, Brady et al. established local DRL in terms of CTDIv and DLP values using age based protocol for brain, chest, and abdomen/pelvis examination and found that DRL was similar to or lower than international DRLs.[28] The Japanese survey showed that the DRL in terms of CTDIv, DLP was higher for CT head, chest, and abdomen examination compared to other published surveys.[23]

Diagnostic reference levels established using weighted computed tomography dose index, volumetric computed tomography dose index, dose length product and size-specific dose estimates

Few studies have used dose indices such as wCTDI, CTDIv, and DLP to establish pediatric DRLS. CTDI vol and DLP will not estimate the dose based on the physique and age of the patient. Hence, to resolve the problem, the American Association of Physicists in Medicine introduced size-specific dose estimates. Three articles stressed on establishing Diagnostic reference range (size-specific dose estimate) based on body width in CT pediatric examinations of thorax and abdomen which would help in reducing radiation dose.[25],[30],[31] Shrimpton et al. performed dose assessment to establish DRL in terms of CTDIw, CTDIv, and DLP for pediatric CT head and chest examination. They found that DRL in terms of CTDIw and DLP were 10%–40% lower than other studies. However, DRL in terms of CTDIv was similar to the other studies.[16] Goske et al. conducted a study to established DRLs in terms of CTDIw based on the body size of pediatric patients undergoing abdominal or abdominal and pelvic CT examination and found that DRL for abdomen was lower compared to other studies.[30] Similarly, Khosravi et al. and Afzalipour et al. performed dose assessment in terms of CTDIw and DLP to establish DRLs for head, sinus, chest, abdomen, and pelvis CT examinations using age categorized protocol. They found that there are variations in third quartile values of CTDIw and DLP between the CT centers indicating the need for dose optimization.[19],[26]

Indication, patient weight- and age-based protocol for establishing diagnostic reference level

Some articles reported establishing DRLs based on indications, one study by Jarvinen et al. reported indication-based dose indices for chest and abdomen and found no discrimination in dose indices between both. However, the dose level with indication ventricular size was considerably lower for the CT brain compared to routine. Another study done by Jarvinen et al. established DRLs for CT head and chest in terms of CTDIv and DLPw based on the indications. The DLPw for chest CT for indication cancer follow-up was lower than the value published in the UK and other study. The DLPw value for head CT for indication epilepsy was similar to the UK survey.[20],[34]

International diagnostic reference levels

One study by Vassileva et al. conducted study to establish international DRLs for CT Head, chest and abdomen examinations. The study included 32 countries and they reported that CTDIv was similar to the reference value for CT head, with few differences for chest and abdomen examinations compared to other studies in all the centers.[35]

Recommendations

The review recommends that there is need for consensus across worldwide with respect to age or weight categorization and implement using the age and weight bands suggested by ICRP 135 and European guidelines which helps in providing smooth comparison of DRLs across the state/nation and international levels. We recommend further studies to be based on establishing pediatric DRLs using automatic tube current and voltage, iterative reconstruction techniques which helps in maintaining the diagnostic image quality at lower radiation dose.

Limitations of our study are first, we did not include phantom studies. Second, studies with pediatric CT examination of angiography and extremities were not included. Third, we did not perform the meta-analysis which might be help in quantitative estimation of dose recorded for pediatric CT examination.


 > Conclusion Top


The literature concludes that over the past few years, pediatric patient dose surveys have increased considerably and awareness of establishment of pediatric DRLs across all the countries. However, the review found significant variation in DRL values between CT centers due to variation in scanning protocols. The review also concludes that sampling methods, procedure of collecting data and methods for measuring DRL vary among the studies. As few studies have shown higher radiation doses in pediatrics, efforts are still required in future for optimizing radiation dose in pediatric patients undergoing CT examination. A globally approved standard protocol that includes scanning techniques, dose measurement method, and DRL percentile needs to be established in order to make useful and accurate comparison with international DRLs. Future studies should focus on using age and weight bands recommended by ICRP 135 and European guidelines.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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