13. Types of exposure radiation.

External radiation exposure- The assessment of doses from exposure to radiation from external sources is usually performed either by individual monitoring using personal dosimeters worn on the body.

Internal radiation exposure- The system of dose assessment of intakes of radionuclides. The intake can be estimated either from direct measurements (e.g., external monitoring of the whole body) or indirect measurements (e.g., urine or faeces).

Public exposure- The basic principles of estimation of e?ective doses are the same for members of the public as for workers. The annual e?ective dose to members of the public is the sum of the e?ective dose obtained within one year from external exposure and the committed e?ective dose from radionuclides incorporated within this year.

Medical exposure of patients- The relevant quantity for planning the exposure of patients and risk-bene?t assessments is the equivalent dose or the absorbed dose to irradiated tissues.

14. Categories of exposure.

Occupational exposure

Occupational exposure is de?ned by the Commission as all radiation exposure of workers incurred as a result of their work.

Public exposure

Public exposure encompasses all exposures of the public other than occupational exposures and medical exposures of patients. The component of public exposure due to natural sources is by far the largest, but this provides no justi?cation for reducing the attention paid to smaller, but more readily controllable, exposures to man-madesources. Exposures of the embryo and fetus of pregnant workers are consideredand regulated as public exposures.

Medical exposure of patient

Radiation exposures of patients occur in diagnostic, interventional, and therapeutic procedures. The exposure is intentional and for the direct bene?t of the patient. Particularly in radiotherapy, the biological e?ects of high-dose radiation, e.g., cell killing, are used for the bene?t of the patient to treat cancer and other diseases.

15. Levels of radiological protection.

16. Principals of radiological protection.

The principle of justi?cation: Any decision that alters the radiation exposure situation should do more good than harm. This means that, by introducing a new radiation source, by reducing existing exposure, or by reducing the risk of potential exposure, one should achieve su?cient individual or societal bene?t to o?set the detriment it causes.

The principle of optimisation of protection: the likelihood of incurring exposures, the number of people exposed, and the magnitude of their individual doses should all be kept as low as reasonably achievable, taking into account economic and societal factors.

The principle of application of dose limits: The total dose to any individual from regulated sources in planned exposure situations other than medical exposure of patients should not exceed the appropriate limits recommended by the Commission.

17. Bystander effect (definition)

18. Non-targeted biological effects and targeted biological effects

The universality of the target theory of radiation-induced effects is challenged by observations on non-targeted effects such as bystander effects, genomic instability and adaptive response. Essential features of non-targeted effects are that they do not require direct nuclear exposure by radiation and they are particularly significant at low doses. This new evidence suggests a need for a new paradigm in radiation biology. The new paradigm should cover both the classical (targeted) and the non-targeted effects. New aspects include the role of cellular communication and tissue-level responses. A better understanding of non-targeted effects may have important consequences for health risk assessment and, consequently, on radiation protection. Non-targeted effects may contribute to the estimation of cancer risk from occupational, medical and environmental exposures. In particular, they may have implications for the applicability of the Linear-No-Threshold (LNT) model in extrapolating radiation risk data into the low-dose region. This also means that the adequacy of the concept of dose to estimate risk is challenged by these findings. Moreover, these effects may provide new mechanistic explanations for the development of non-cancer diseases. Further research is required to determine if these effects, typically measured in cell cultures, are applicable in tissue level, whole animals, and ultimately in humans.