Ionising radiation can trigger both deterministic and stochastic effects. Deterministic effects occur only above the dose threshold. There is no threshold value for stochastic effects.
The aim of radiation protection is to prevent the deterministic effects of radiation reliably and to reduce the risk of stochastic effects to a reasonably achievable level. The dose limit values are set so that deterministic effects are ruled out.
To keep the risk of stochastic damage from ionising radiation as low as possible, three general principles have been set out in radiation protection. These principles are based on recommendations from the International Commission on Radiological Protection (ICRP). The German Radiation Protection Act and the European Directive 2013/59/Euratom make these principles legally binding:
Justification
Dose limitation
OptimisationLegal requirement for justification
Every new application of ionising radiation or each new use of radioactive materials by man must be justified in advance. This legal requirement for justification also applies when, due to new activities, people are occupationally exposed to existing radiation at increased levels (for example, cosmic radiation during flights or radon in mines or waterworks).
The legal requirement for justification means that new activities are permitted only when they are associated with a reasonable benefit for the individual and for society. In this case, “reasonable” means that the benefit outweighs any health detriment that may result from the activity. The legal requirement for justification also means that existing activities are reviewed in case of significant new findings.
In medicine, where ionising radiation is used for diagnostic and therapeutic purposes, we speak of the justifying indication.
The benefit and potential damage cannot be objectively determined in each case. Therefore, it may not be easy sometimes to justify new activities.
Legal requirement for dose limitation
Doses of radiation that people are subjected to during justified activities must not exceed certain limit values (dose limitation). Different limit values apply for the general population and for persons occupationally exposed to radiation.
Limit values for the population
The limit values for the population determine the maximum total radiation an individual may receive from justified activities (for example, from the operation of nuclear power plants). These limit values are often underpinned by additional limit values for specific exposure pathways. Here, an exposure pathway describes the ways that people can be exposed to ionising radiation:
by inhalation
by intake through food (ingestion) or
externally through ambient radiation.Limit values for certain exposure pathways ensure that the limit values for the effective dose and organ equivalent doses are strictly adhered to, and that no single exposure pathway determines the entire exposure.
Limit values for persons occupationally exposed to radiation
For occupational radiation exposure there are different limit values for
the whole body and additionally for body organs,
different periods (month, year, career),
different groups of people (adolescents, adults, women of child-bearing age, pregnant women).However, there are no limit values for medical radiation exposure, i.e. for diagnostics or therapy. Here, justifying indication by the specialist doctor and the legal requirement for optimisation apply. Using diagnostic reference values, a guide value is given which – considering the individual patient’s condition – should not be reached or be adhered to as closely as possible.
Legal requirement for optimisation
If an activity involving radiation exposure and contamination is justified, the aforementioned principle of optimisation requires that any unnecessary exposure and contamination be avoided.
Optimisation requires that
the likelihood of exposure,
the number of exposed persons and
the individual dose affecting a personare kept as low as reasonably achievable (so-called “ALARA principle”: As Low As Reasonably Achievable). The current technical state of knowledge, as well as economic and social factors, are to be considered.
The legal requirement for optimisation also applies when currently effective limit values are adhered to. In this case, according to the ALARA principle, exposure must be kept as far below the respective limit value as possible.