Konversionsfaktoren zur Ermittlung der effektiven Dosis für Patienten aus dem Dosisflächenprodukt bei Röntgendurchleuchtungsuntersuchungen

Abstract

The effective dose, which is related to the stochastic radiation risk, cannot be measured directly. Therefore, conversion coefficients for estimating the effective dose for patients were calculated for fluoroscopy X-ray examinations from the dose area product which can be easily measured. Conversion coefficients were calculated using the PC-based Monte Carlo program PCXMC in software version 1.5.1. Conversion coefficients were determined for tube voltages between 60 kV and 110 kV, for additional cupper filtration up to 0.9 mm, for different projections (a. p., p. a. and lateral) and X-ray field size (between 20 cm x 20 cm and 40 cm x 40 cm in image plane) and field position (from head to leg). Tube voltage, filtration and field position have a significant effect on conversion coefficients. Conversion coefficients increase as the tube voltage and filtration increase. Depending on the radiation spectrum used, the conversion coefficients may differ up to a factor of 4 for the same X-ray examination. The highest conversion coefficients were found for irradiation of the body region followed by the head and leg region. The effect of the field size and projection is moderate. Conversion coefficients for a. p. projection are higher than those for p. a. and lateral projections. Effective dose can be easily estimated by multiplying relevant conversion coefficients by the dose area product. Using conversion coefficients from the literature that do not take additional cupper filtration into consideration can underestimate the effective dose by a factor or up to 2 or more depending on the filtration used.