Purpose: The purpose of this work was to compare radiation dose distribution along the z-axis for dual-energy volume CT scans and conventional single-energy helical CT scan examinations.
Methods: An anthropomorphic phantom was used along with optically stimulated luminescence (OSL) dosimeters along the z-axis. The phantom was scanned with the chest protocol for dual-energy CT (DECT) and single-energy CT (SECT) on a 320-Slice Canon CT scanner. The DECT protocol used a volumetric acquisition and the SECT protocol used a helical acquisition. Tube current modulation was used for all scans. The standard deviation and slice thickness pertaining to the x-y modulation setting was matched for both DECT and SECT scans. The OSL dosimeters were placed on top of the phantom along the z-axis. The amount of OSL dosimeters used matched scan range with an additional twenty dosimeters to account for the periphery of the dose profile. Each OSL dosimeter was placed without space in between them. All OSL dosimeters were corrected for energy and scatter dependence by using calculated correction factors.
Results: For a scan range of 160 mm which is equivalent to one volume, DECT showed no beam overlap in the dose profile. However, in scan ranges over 160 mm a noticeable beam overlap was observed in the point doses measured which resulted in a 40%-45% dose increase at the beginning and ending of each volume. SECT showed a 35%-60% dose difference along the z-direction from the use of tube current modulation.
Conclusion: The radiation dose observed in volume DECT may lead to an increase in patient dose in certain areas along the z-axis due to beam overlapping. SECT does not show the same beam overlapping trend. However, SECT shows an increase in radiation dose as a result of the use of tube current modulation.