Siemens Software version syngo CT 2005C manual 2 3 mSv per year in Germany

Dose Information

The CTDIvol value does not provide the entire informa- tion of the radiation risk associated with CT examina- tion. For the purpose, the concept of the “Effective Dose“ was introduced by ICRP (International Commis- sion on Radiation Protection). The effective dose is expressed as a weighted sum of the dose applied not only to the organs in the scanned range, but also to the rest of the body. It could be measured in whole body phantoms (Alderson phantom) or simulated with Monte Carlo techniques.

The calculation of the effective dose is rather compli- cated and has to be done by sophisticated programs. These have to take into account the scan parameters, the system design of individual scanner, such as x-ray filtration and gantry geometry, the scan range, the organs involved in the scanned range and the organs affected by scattered radiation. For each organ, the respective dose delivered during the CT scanning has to be calculated and then multiplied by its radiation risk factor. Finally, the weighted organ dose numbers are added up to get the effective dose.

The concept of effective dose allows the comparison of radiation risk associated with different CT or x-ray exams, i.e. different exams associated with the same effective dose would have the same radiation risk for the patient. It also allows comparing the applied x-ray exposure to the natural background radiation,

e.g., 2 – 3 mSv per year in Germany.

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