[Determination of the effective dose for CT examinations and influence of the setup parameters]

CT examinations are considered to be high dose applications in radiation diagnostics. Consequently, radiation exposure and its potential reduction are an important issue. The aim of this paper is to determine effective doses for CT examinations under clinical conditions. The effective doses were determined from organ dose measurements with an optimal amount of effort.

The measured point doses in the various organs in an anthropomorphic phantom were weighted with respect to morphology and location in the radiation field and were averaged to obtain the organ doses. These doses together with the individual radiation sensitivities were able to be used to calculate the effective dose. The following examinations were taken into consideration: thorax, abdomen and skull. Only one parameter was changed for each measurement (the high voltage of the X-ray tube, the pitch, the collimation, or the automatic adjustment of the tube current to correct the individual absorption in the phantom).

The effective doses for the thorax examinations were between 5 and 7 mSv, and for the abdomen between 8 and 15 mSv depending on the technique and parameters. In some of the organs the organ doses can be in excess of 25 mSv. Our results were compared to the corresponding results of two commercial computer programs for dose calculations. The calculated effective doses generally showed lower values.

It is possible to determine the effective dose from 24-point dose measurements by optimizing the choice of measuring location in the phantom. The individual adaptation of parameters such as tube voltage, exposure, pitch, collimated slice thickness, and investigation volume must be taken into consideration from case to case.