ESR News May 2016

Establishing European Diagnostic Reference Levels for paediatric imaging: an update on the PiDRL project

John Damilakis, Professor of Medical Physics


There is little information on Diagnostic Reference Levels (DRLs) for paediatric examinations and procedures. The main reasons for this is a) that the number of examinations carried out in children is lower compared to adults and b) data need to be categorised into age or weight subgroups. The ‘European DRLs for Paediatric Imaging’ project (abbreviation: PiDRL) is a European Commission project that aims to a) develop a methodology for establishing and using DRLs for paediatric medical imaging and b) update and extend the European DRLs. The professional organisations involved include the ESR as coordinator, as well as EFOMP, EFRS, and ESPR, covering the key European stakeholders and professional groups with relevance to radiation protection of paediatric patients. The PiDRL project has very recently drafted European Guidelines on how to establish and how to use paediatric DRLs.

The main recommendations of ‘PiDRL European Guidelines’ are summarised as follows:

  • All examinations resulting in high collective doses should have DRLs. This can include both the most common low dose examinations and the less common high dose examinations.
  • The application of DRLs should be the responsibility of all providers of x-ray imaging. This means that DRLs should also be applied to imaging performed outside the radiology department.
  • The physical quantity used to establish DRLs should be an easily measurable quantity, usually directly obtainable from the x-ray equipment console, obtained either by manual recording or preferably by automatic recording and analysis. Organ doses and effective dose are not considered feasible as a DRL quantity because these cannot be easily determined.
  • The values used for patient dose monitoring, at the display unit and in the DICOM header should be regularly calibrated or checked for all beam qualities used in clinical practice.
  • The parameters to group the patients should be patient weights for all body examinations and patient ages for all head examinations. For body examinations, in the transition period until data from weight-based patient dose surveys becomes available, age can be used as an additional grouping parameter and for the purpose of comparing proposed new weight-based DRLs with earlier age-based DRLs (trend analysis).
  • The DRLs can also be given as a DRL curve by expressing the DRL quantity as a continuous function of the grouping parameter (e.g. DLP as a function of patient weight) provided the collected data for setting of the DRLs indicates a clear relationship between patient doses and the grouping parameter.
  • The DRLs should be based on sufficient patient dose data determined or collected from the records of individual paediatric patients. Using data obtained only from typical protocol data or from measurements in phantoms is not recommended.
  • National DRLs (NDRLs) should be based on national patient dose surveys with a representative sample of all radiological institutions and all types of equipment and practices in the country when practical.
  • For NDRLs, by definition, the 3rd quartile or the 75th percentile value of the median (the 50th percentile) values of the distributions of patient doses obtained from a representative sample of radiology departments in the country should be determined, for a defined clinical imaging task (i.e., common indication based protocol) surveyed for standardised patient groupings.
  • For the setting of DRLs, statistically relevant numbers of patient dose data should be collected. From each hospital or radiology department a representative sample of at least 10 patients per procedure type and per patient group is recommended for non-complex examinations such as radiography and CT, and at least 20 patients per procedure type and per patient group for complex procedures such as fluoroscopy and fluoroscopically guided procedures.
  • In collecting the patient dose data for the DRLs, likewise in daily imaging practices, there should always be a system in place to judge whether image quality is adequate for the diagnosis according to the indication of the examination. This could be based,on image quality assessment of typical test cases by several radiologists, for example. The image quality requirement should be based on clinical grounds only.
  • Due to the generally large amount of data needed and the large number of potential errors when these data are to be collected during routine practice, automatic data collection is recommended wherever possible.
  • Besides the actual patient dose data according to the recommended patient grouping, other data from the examination characteristics (e.g. x-ray equipment type, exposure parameters, use of AEC) should be collected for evaluation and decision making when DRLs are to be established.
  • Patient dose surveys for the basis of setting the NDRLs, should be conducted by the authoritative body which sets the DRLs or by another competent institution, with the collaboration of national professional/scientific societies or at least having recognised clinical experts as consultants in the process.
  • The complete history of the patient dose surveys for the setting of DRLs, including all essential dosimetric and statistical information (e.g. quantities and their collected values, coverage of institutions and practices, sample sizes) should be documented and preferably reported.