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CT diagnostic reference levels based on clinical indications: results of a large-scale European survey



The objective of this study was to investigate the feasibility of defining diagnostic reference levels (DRLs) on a European basis for specific clinical indications (CIs), within the context of the European Clinical DRLs (EUCLID) European Commission project.


A prospective, multicenter, industry-independent European study was performed to provide data on 10 CIs (stroke, chronic sinusitis, cervical spine trauma, pulmonary embolism, coronary calcium scoring, coronary angiography, lung cancer, hepatocellular carcinoma, colic/abdominal pain, and appendicitis) via an online survey that included information on patient clinical, technical, and dosimetric parameters. Data from at least 20 patients per CI were requested from each hospital. To establish DRLs, a methodology in line with the International Commission on Radiological Protection (ICRP) Report 135 good practice recommendations was followed.


Data were collected from 19 hospitals in 14 European countries on 4299 adult patients and 10 CIs to determine DRLs. DRLs differ considerably between sites for the same CI. Differences were attributed mainly to technical protocol and variable number of phases/scan lengths. Stroke and hepatocellular carcinoma were the CIs with the highest DRLs. Coronary calcium scoring had the lowest DRL value. Comparison with published literature was limited, as there was scarce information on DRLs based on CI.


This is the first study reporting on feasibility of establishing CT DRLs based on CI using European data. Resulting values will serve as a baseline for comparison with local radiological practice, national authorities when DRLs are set/updated, or as a guideline for local DRL establishment.

Key Points

First study reporting on the feasibility of establishing CT diagnostic reference levels based on clinical indication using data collected across Europe.

Only one-fourth of the hospitals had CT machines less than 5 years old.

Large dose variations were observed among hospitals and CT protocols were quite different between hospitals.

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Fig. 1
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Automatic exposure control


Basic safety standards


Clinical indication


Computed tomography


Computed Tomography Dose Index


Average Volume Computed Tomography Dose Index for multiphase CT


Volumetric Computed Tomography Dose Index


Dose length product


Dose length product (DLP) per phase


Total DLP


Diagnostic reference levels


External Advisory Panel


European Study on Clinical Diagnostic Reference Levels for X-ray Medical Imaging


International Commission of Radiological Protection


Interactive Data Language


Research Electronic Data Capture


Statistical Analysis System


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The authors would like to acknowledge the contribution of hospital data managers without who establishment of EUCLID DRLs would not have been possible. Also the support of representatives of national authorities, professional societies, and European and International organizations is also acknowledged.


The EUCLID project was financially supported by the grant ENER/2017/NUCL/SI2.759174 of the European Commission.

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Corresponding author

Correspondence to Virginia Tsapaki.

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The scientific guarantor of this publication is Professor John Damilakis.

Conflict of interest

The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article.

Statistics and biometry

No complex statistical methods were necessary for this paper.

Informed consent

Written informed consent was waived by the Institutional Review Board.

Ethical approval

Institutional Review Board approval was obtained if necessary within the institution.


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Tsapaki, V., Damilakis, J., Paulo, G. et al. CT diagnostic reference levels based on clinical indications: results of a large-scale European survey. Eur Radiol 31, 4459–4469 (2021).

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  • Patient safety
  • Radiation exposure
  • Tomography scanners, X-ray computed