Journal List > Prog Med Phys > v.28(1) > 1098585

Kim, Park, Park, and Chang: Dosimetric Effects of Low Dose 4D CT Using a Commercial Iterative Reconstruction on Dose Calculation in Radiation Treatment Planning: A Phantom Study

Abstract

We investigated the effect of a commercial iterative reconstruction technique (iDose, Philips) on the image quality and the dose calculation for the treatment plan. Using the electron density phantom, the 3D CT images with five different protocols (50, 100, 200, 350 and 400 mAs) were obtained. Additionally, the acquired data was reconstructed using the iDose with level 5. A lung phantom was used to acquire the 4D CT with the default protocol as a reference and the low dose (one third of the default protocol) 4D CT using the iDose for the spine and lung plans. When applying the iDose at the same mAs, the mean HU value was changed up to 85 HU. Although the 1 SD was increased with reducing the CT dose, it was decreased up to 4 HU due to the use of iDose. When using the low dose 4D CT with iDose, the dose change relative to the reference was less than 0.5% for the target and OARs in the spine plan. It was also less than 1.1% in the lung plan. Therefore, our results suggests that this dose reduction technique is applicable to the 4D CT image acquisition for the radiation treatment planning.

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Fig. 1.
Mean change in HU depending on the CT scan parameter for different density materials relative to the default scan parameter.
pmp-28-27f1.tif
Fig. 2.
1 Standard deviation change in HU depending on the CT scan parameter for different density materials relative to the default scan parameter.
pmp-28-27f2.tif
Fig. 3.
4D CT images of the lung phantom acquired using the default scan parameter (600 mAs) without iDose (left) and the low dose scan parameter (200 mAs) with iDose (right).
pmp-28-27f3.tif
Fig. 4.
DVH comparison between the dose calculations on the CT images reconstructed with and without using iDose for the Spine 2D parallel-opposite (AP-PA) and VMAT plan.
pmp-28-27f4.tif
Fig. 5.
DVH comparison between the dose calculations on the CT images reconstructed with and without using iDose for the Lung 3D conformal and VMAT plan.
pmp-28-27f5.tif
Fig. 6.
Mean and 1 standard deviation changes in HU when using the x-ray energy of 90 kVp.
pmp-28-27f6.tif
Table 1.
Dose-volumetric parameters of target (PTV) and normal tissues (left and right lung, spinal cord) for spine and lung plan.
  Spine Lung
  2D (AP-PA) VMAT 3D CRT VMAT
  Default iDose Default iDose Default iDose Default iDose
PTV                
D95% (Gy) 30.1 30.0 29.9 29.8 60.3 60.0 60.2 59.6
D5% (Gy) 31.0 30.9 32.1 32.0 64.4 64.2 65.1 64.5
Minimum (Gy) 29.9 29.8 24.2 24.2 58.2 57.6 58.3 57.7
Maximum (Gy) 31.3 31.2 32.9 32.8 64.7 64.5 65.7 65.1
Mean (Gy) 30.5 30.4 31.3 31.2 62.6 62.3 63.2 62.6
Left lung                
V20Gy (%) 0.0 0.0 0.0 0.0 10.6 10.6 9.3 9.2
Mean (Gy) 0.3 0.3 0.9 0.9 6.5 6.5 6.0 6.0
Right lung                
V20Gy (%) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Mean (Gy) 0.3 0.3 0.9 0.9 0.9 0.9 1.3 1.3
Spinal cord                
V13.5Gy (%) 27.8 27.8 8.8 8.8 0.2 0.2 0.0 0.0
Maximum (Gy) 31.6 31.5 28.6 28.5 13.7 13.7 9.5 9.5
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