Dosimetric Investigations in Computed Tomography

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Abstract
Dose measurements free-in-air and in phantoms on computed tomography systems have been performed. For single slices the axial dose profile free-in-air and the corresponding computed tomography dose index (CTDI) are determined by TL dosemeters at the axis of rotation. For multiple slices the multiple scan average dose (MSAD) is determined with a pencil shaped ionisation chamber on the surface of the phantom. Measurements for the most commonly used sets of scanning parameters have been compared for the two methods for 25 CT units. Especially for narrow slices, measured profiles are significantly wider than the nominal slice width. Radial dose profile measurements in a phantom clearly divide the units into different groups depending on pre-patient filtration. The beam quality of the individual CT system doses are measured with an ionisation chamber free-in-air and covered with different materials for filtration. A beam quality corrected calibration of the TL chips has been investigated.

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