Principles of radiation protection

Ionising radiation can trigger both deterministic and stochastic effects. Deterministic effects occur only above the threshold value of a dose. There is no threshold value for stochastic effects.

The aim of radiation protection is to prevent reliably the deterministic effects of radiation 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.

In order to keep the risk of stochastic damage from ionising radiation as low as possible, three general principles have been set out in radiation protection for dealing with ionising radiation. 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:

1. Justification
2. Dose limitation
3. Optimisation

Legal 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, mostly natural radiation at an increased level (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 possibly caused by 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 the possible damage cannot be determined objectively 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 person may receive from justified activities (for example due to the operation of nuclear power plants). These limit values are frequently underpinned by further limit values for certain 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 for the organ equivalent doses are strictly adhered to and that one exposure pathway does not determine 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 that is connected with radiation exposure and contamination is justified, the aforementioned principle of optimisation requires that any unnecessary radiation exposure and contamination be avoided.

Optimisation requires that

• the likelihood of exposure,
• the number of exposed persons and
• the individual dose affecting a person

are 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.