Professor Guy Frija from Hôpital Européen Georges Pompidou, France, is one of the two project leaders of the EUCLID project. Prof Frija is also Chair of the EuroSafe Imaging Steering Committee.

This article was originally written for publication during ECR 2020 in March 2020 on the occasion of a planned EuroSafe Imaging session, ‘European study on clinical diagnostic reference levels (DRLs) (EUCLID) project: final results’ and updated in June 2020.

The EUCLID project’s study to establish clinical DRLs for Europe reaches its conclusions

Professor John Damilakis from the University of Crete, Greece, is one of the two project leaders of the EUCLID project.

It is well known that different image quality is needed for different clinical indications of the same anatomical area. For this reason, diagnostic reference levels (DRLs) should be established for a given clinical indication rather than anatomical area. The European Commission (EC) launched the ‘European study on clinical diagnostic reference levels for x-ray medical imaging’ (EUCLID) project in August 2017 to provide up-to-date clinical DRLs. This project is now concluding with the Final Report to be submitted next month. The main objectives of the project were: to conduct a European survey to collect data needed for the establishment of DRLs for the most important x-ray imaging tasks in Europe (from the radiation protection perspective), and to specify up-to-date DRLs for these examinations. A workshop was organised in Luxembourg in December 2019 to disseminate and discuss the results of the project. The draft final report was submitted to the European Commission in May 2020 and it is expected that a version of this will be published as part of their Radiation Protection Series in the coming months.

During the first months of EUCLID, a comprehensive review was carried out to identify the status of existing clinical DRLs for CT, interventional radiology (IR) and radiography in Europe and beyond. This was done by analysing recent studies, standards and publications. Information about existing clinical DRLs was collected from national competent authorities and other organisations involved in the project. The findings were taken into consideration during the finalisation of the list of clinical indications for which EUCLID was to establish DRLs (Tables 1 and 2).

Table 1: List of CT clinical indications
Clinical taskAnatomical locationProcedure
Detection or exclusion of a haemorrhage
HeadAll Phases
Chronic sinusitis
Detection or exclusion of polyps
NeckAll Phases
Cervical spine trauma
Detection or exclusion of a lesion
SpineAll Phases
Pulmonary embolism
Detection or exclusion
ThoraxAll Phases
Coronary calcium scoring
Risk stratification
Coronary ArteriesAll Phases
Coronary angiography
Vessels assessment
Coronary ArteriesAll Phases
Lung cancer
Oncological staging
First and F-up
All Phases
Hepatocellular carcinoma
Oncological staging
LiverAll Phases
Colic /abdominal pain
Exclusion or detection of a stone
AbdomenAll Phases
Detection or exclusion
AbdomenAll Phases
Table 2: List of Interventional radiology procedures
Clinical taskAnatomical locationProcedure
Arterial occlusive disease of iliac arteries
Angiographic diagnosis and endovascular treatment of arterial stenosis or occlusion causing intermittent claudication or ischaemia
PelvisRecanalisation & Stenting
Localisation and treatment of hepatocellular carcinoma
TACE: transarterial chemoembolisation
LiverTransarterial (chemo)embolisation of tumour vasculature and feeding hepatic arteries
Arterial occlusive disease of femoropopliteal arteries
Angiographic diagnosis and endovascular treatment of arterial stenosis or occlusion causing intermittent claudication or ischaemia
Lower extremityRecanalisation and angioplasty +-stenting
Biliary drainage
Localisation of biliary obstruction and percutaneous treatment of biliary obstruction
AbdomenPercutaneous transhepatic cholangiography and biliary drainage

EUCLID developed and implemented an EU-wide survey to collect data from 20 participating hospitals from 14 different European countries (Figure 1). The data was collected using a secure online web application for building and managing online surveys and databases. All data was continuously reviewed until the end of the data collection period (May 2019) in an attempt to avoid inaccurate records. A Scientific Board was set up for the verification of data collected for the establishment of clinical DRLs. Board members were representatives of national regulatory authorities and national scientific/professional societies from the countries in which data was collected. Twenty-fifth percentiles, medians, and 75th percentiles for dose quantities and dose indices were calculated for each of the clinical indications and procedures. CT DRLs were defined in terms of CTDIvol and DLP (Dose length Product). IR DRLs were defined in terms of KAP (Kerma Area Product), cumulative air kerma at the patient entrance reference point, fluoroscopy time, and total number of images.

Figure 1: EUCLID collected data from 14 European countries

Various scientific publications related to the EUCLID project’s results and aspects of its findings are planned by the end of 2020.

Further project information is available at