Ionising radiation may produce deterministic and stochastic effects.

Deterministic effects only occur once a threshold of exposure (i.e. a specific dose) has been exceeded. The severity of deterministic effects increases with dose. Examples of deterministic damage are skin burns or hair loss; higher doses cause internal organ failure. There is no threshold level for stochastic effects. Stochastic effects are those which occur by chance, so the probability that radiation exposure will cause a stochastic effect depends on dose. The severity of stochastic damage, however, is unrelated to dose.

The aim of radiation protection is to reliably prevent the deterministic effects of radiation and to reduce the risk of stochastic effects to a reasonably achievable level. The dose limits are set so that deterministic effects are ruled out.

Legislation now distinguishes between three different exposure scenarios:

  • Planned exposure due to activities or work (including flying personnel)
  • Existing exposure due to construction products, radon in restrooms and at workplaces as well as exposure due to the effects of emergency exposure and
  • Emergency exposure due to accidents, deliberate exposures and the exposure of rescue workers in emergency situations.

In order to keep the risk of stochastic damage from ionising radiation as low as possible, three general principles for dealing with ionising radiation have been defined for radiation protection. These principles are based on recommendations from the International Commission on Radiological Protection (ICRP) and have been incorporated into radiation protection legislation:

  1. Justification
  2. Dose limitation
  3. Optimisation of protection

Justification

Each new application of ionising radiation or each new human use of radioactive materials must be justified. This requirement for justification also applies when, due to new activities, people are occupationally exposed to existing, mostly natural radiation at an increased level (e.g. cosmic radiation during flights or due to activities involving NORM – naturally occurring radioactive material). The requirement for justification means that any exposure to ionising radiation is only permitted when it is associated with a reasonable benefit to individuals or to society. In this case, "reasonable" means that the benefit outweighs any possible harm to health. This risk-benefit assessment may also be required in the case of important new findings concerning existing activities.

In medicine, where ionising radiation is used for diagnostic and therapeutic purposes, the requirement for justification takes a very specific form: with medical applications, a physician with expertise in the field of radiation protection has to declare the so-called "justifying indication". The justifying indication requires the statement that with this special application to a specific person, the health benefits of exposure to ionising radiation outweigh the risk.

Dose limitation

Radiation from planned exposures of human beings must not exceed certain dose limits (dose limitation). Different limit values apply to the general population and to persons occupationally exposed to radiation.

The limit values for the general 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 in which people can be exposed to ionising radiation:

  • by breathing (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 doses are strictly adhered to and that no single exposure pathway determines the entire exposure.

For occupational radiation exposure, there are different limit values for

  • the whole body and additionally for body organs,
  • different periods (month, year, working life),
  • 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, the justifying indication by the specialist physician and the requirement for optimisation apply. Using diagnostic reference values, a guide value is given which – with due consideration for the individual patient’s condition – should not be reached where possible or should be adhered to.

Optimisation

Even if an activity that is connected with radiation exposure is justified, the overriding requirement of optimisation requires that any unnecessary radiation exposure and contamination be avoided.

Optimisation aims to keep as low as is reasonably achievable

  • the likelihood of exposure,
  • the number of exposed persons and
  • the individual dose to which a person is exposed,

taking into account the latest technical knowledge and economic and social factors. In German radiation protection law, the minimisation principle applies: this means that unnecessary exposure to radiation must be avoided and unavoidable exposure must be kept as low as possible.

The requirement for optimisation also applies when effective limit values are adhered to. In this case, exposure must be kept as far below the relevant limit value as possible.