- Radiation Protection is based on three principles: justification,
optimisation and limitation.
Diagnostic Reference Levels (DRLs) are an important tool of optimisation and do not represent a limitation (Fig.1).
Therefore,
the International Atomic Energy Agency (IAEA) and the World Health Organisation (WHO) have included the establishment,
the use of,
and the regular update of diagnostic reference levels for radiological procedures,
including interventional procedures,
in particular for children,
in their Bonn call for action (action 2).
By the new Basic Safety Standards Directive,
DRLs have become a part of the European legislation.
Similarly,
based on the Bonn call the European society of Radiology (ESR) has integrated the collection and use of DRLs into its own call for action.
- DRLs are used for radiological examinations using ionising radiation; they should primarily be established for frequent examinations and for those contributing significantly to the population dose and,
thus,
they should include interventions.
DRLs are usually defined by the 75th percentile (3rd quartile) of the dose distribution of a representative survey (Fig.
2).
- DRLs are derived from the patient population undergoing one specific examination,
and they are used to identify those centres / countries where an optimisation is required.
In other words,
they must not be applied to individual patients.
- DRLs are defined for standard-sized patients.
- DRLs are given in a radiation quantity that can easily and directly be measured; effective dose,
a calculated quantity that requires additional assumptions,
does not qualify for DRLs.
- Obviously,
staying within DRLs excludes top exposure but does not mean that optimisation is ideal; in many situations,
exposure can be reduced to values much lower than the DRL without compromising the image quality required for the specific question.
Although DRLs have been useful,
several limitations with their use exist:
1.
DRL definitions and the methodology used to establish DRLs are currently not uniform.
2.
Patients most often are not standard-sized
3.
DRLs have been used for examinations of one (or more than one) region using a specific modality.
However,
different clinical questions of the same area do not require the same image quality and,
thus,
not the same protocol.
E.g.,
it is not logical to use the same DRL for the diagnosis of kidney stones and of liver metastases.