Siemens SOMATOM Sensation Cardiac Version A60 Operations Instructions download pdf (Page 13)

General

Dose Information

The dose as described by CTDI

is displayed on the

user interface for the selected scan parameters. The

CTDI

is measured in the dedicated plastic phantoms –

16 cm diameter for head and 32 cm diameter for

body (as defined in IEC 60601-2-44). This dose number

gives a good estimate for the average dose applied

in the scanned volume as long as the patient size is

similar to the size of the respective dose phantoms.

Since the body size can be smaller or larger than 32 cm,

the CTDI value displayed can deviate from the dose in

the scanned volume.

The CTDI

value does not provide the entire information

of the radiation risk associated with CT examination.

For the purpose, the concept of the “Effective Dose“ was

introduced by ICRP (International Commission 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 com-

plicated 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.

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Siemens SOMATOM Sensation Cardiac Version A60 Operations Instructions Page 13