  X-ray CT dose measurement has mainly been performed using an ionization
chamber dosimeter. Therefore, the dose distribution has not been sufficiently
studied. We investigated the importance of evaluating the two or
three-dimensional dose distributions for X-ray computed tomography (CT). To
confirm this purpose, we investigated the effects of phantom size and exposure
parameters on the phantom diameter. We performed 12 scans using XR-QA2 film and
cylindrical acrylic phantoms of two lengths. The tube current and slice
thicknesses were varied as exposure parameters. The dose distribution of the
primary and scattered radiation was visu-alised using ImageJ. The results were
evaluated using the profile curves, three-dimensional surface plots, and
subtrac-tion dose images. We observed changes in the dose distributions for
scans with and without phantoms. However, no significant differ-ence in the
dose distribution was observed with changes in the lengths of the phantom. To
visualise the dose distribution, three-dimensional surface plots and
subtraction images were found helpful. We must confirm that the dose
distribution does not change for phantoms with multiple diameters in future
studies. For using a clinical application, accurate quantitative assessment of
dose distribution requires improved accuracy of the calibration curve.
