CHAIR OF MEDICAL

SYSTEMS TECHNOLOGY

Dose measurements and calculations for tube current modulation and filtering in CT

The ALARA ("As Low As Reasonably Achievable") principle in the field of medical radiation protection requires that any unnecessary radiation exposure of the patient must be avoided. This comes from the background that some studies suggest that even low doses of radiation could increase the risk of cancer to a non-unconsiderable degree. It is therefore essential to precisely define, calculate and measure the radiation doses in the CT.

Tube current modulation is a method of reducing the radiation dose by automatically adapting the radiation intensity to the absorption capacity of the irradiated area. The aim of our research is to calculate the influence of tube current modulation and filtering on the incidental radiation dose and to measure it in various clinically used systems. Methods are developed to determine the so-called dose conversion factors more precisely. These methods are based on measurements on test objects (CTDI phantom) as well as on Monte Carlo simulations of the generation of the dose, as well as calculations of the filter settings of the CT systems being examined.

Topics:

• Development of a method for the exact calculation of the "bowtie" filter.
• Measurement of the tube current modulation on the CTDI phantom.
• Development of a new phantom for more precise measurement of the tube current modulation.
• Determination of the accuracy of the calculated dose conversion factors for the tube current modulation.