Rationale and objectives: The purpose of this study was to demonstrate the use of a phantom to standardize low-dose chest computed tomographic (CT) protocols in children with cystic fibrosis.
Materials and methods: Spiral chest CT scans of a Plexiglas phantom simulating airway sizes (internal diameter, 1.1-16.4 mm; wall thickness, 0.4-4.6 mm) in children with cystic fibrosis were obtained using two multidetector CT (MDCT) scanners (GE VCT and Siemens Sensation 64). Quantitative airway measurements from both scanners were compared with micro-CT airway measurements over a range of doses (0.2-1.8 mSv) to evaluate bias and variance of measurements. The effective doses for CT protocols were estimated using the ImPACT CT Patient Dosimetry Calculator.
Results: Both MDCT scanners were able to accurately measure airway sizes down to 3 mm internal diameter and 1.3 mm airway wall thickness, with errors of <3.5%. ImPACT estimates of effective dose were different for the MDCT scanners for a given peak tube voltage and product of tube current and exposure time. Accuracy and precision were not found to be associated with dose parameters for either machine. Bias in all measurements was strongly associated with airway diameter (P values < .00001), but the magnitude of bias was small (mean, 0.07 mm; maximum, 0.21 mm). Differences between machines in error components were on the order of a few micrometers.
Conclusions: The use of a standard airway phantom confirms that different MDCT scanners have similar results within dose ranges planned for potential future clinical trials. Standardized protocols can be developed that adjust for differences in radiation exposure for different MDCT scanners.