Risk organ

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A risk organ ( English organ at risk ) is in the radiation therapy of malignant tumors ( cancer ) a healthy tissue or organ with a certain sensitivity to radiation, which is located in the vicinity of a tumor is located or in the irradiated volume. It is therefore subject to a certain radiation exposure . For radiation planning , it is therefore necessary to know the tolerance doses of the organs at risk and to adapt the prescribed therapy dose in terms of spatial location and duration of application. The aim is to protect the healthy tissue as much as possible, while destroying the malignant tumor as much as possible.

An example of an organ at risk is the spinal cord (myelon) in the treatment of a lung tumor.


In therapeutic practice it is important whether the irradiation of an organ at risk could result in a complete or only partial loss of function. Therefore, the International Commission on Radiation Units and Measurements ( ICRU , in Reports 50 and 62) divides them into "serial", "parallel" or at the same time "serial" and "parallel" organs:

Damage to part of a “serial” organ means that the organ can no longer fulfill its function. Example: Radiation damage to the spinal cord structure can interrupt nerve conduction.

If a “parallel” organ suffers partial radiation damage, its function is limited, but not completely failed. For example, if a part of the lung is affected, the exchange area is reduced, but gas exchange can still take place in the undamaged part of the lung .

Many organs are so complex that they consist of both serial and parallel components. A nephron, for example, is part of the kidneys and consists of a very complex sequence of both possible units.


  • Hanno Krieger: Radiation sources for technology and medicine. (Teubner Verlag, 2005) ISBN 3-8351-0019-X