Identification of the computed tomography dose index for tube voltage variations in a polyester-resin phantom.

The aim of this study is to measure the volumetric computed tomography dose index (CTDI) for different tube voltages for a polyester-resin (PESR) phantom, and to compare it to values for a standard polymethyl methacrylate (PMMA) phantom. Both phantoms are head phantoms with a diameter of 16 cm. The phantoms were scanned by a CT scanner (GE Revolution EVO 64/128 slice) with tube voltages of 80, 100, 120, and 140 kV. The other scan parameters were constant (i.e. tube current of 100 mA, rotation time of 1 s, and collimation width of 10 mm). The CTDI and CTDI were obtained by measuring the dose with an ionization chamber inserted into five holes within the phantoms. The CTDI was calculated based on the CTDI and CTDI values. The measurements were repeated three times for each hole. It was found that the CTDI values for the PESR phantom were dependent on tube voltage value, and were similar to the dependency in a PMMA phantom. The maximum CTDI difference between the PESR and PMMA phantoms was 7.5%. We conclude that the dose measured in the PESR phantom is similar to that in the PMMA phantom and that the PESR phantom can be used as an alternative if the PMMA phantom is not available.