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. 2017 Jul-Sep;42(3):171-180.
doi: 10.4103/jmp.JMP_24_17.

Study of Variation in Dose Calculation Accuracy Between kV Cone-Beam Computed Tomography and kV fan-Beam Computed Tomography

Venkatesan Kaliyaperumal  1 , C Jomon Raphael  1 , K Mathew Varghese  1 , Paul Gopu  1 , S Sivakumar  1 , Minu Boban  1 , N Arunai Nambi Raj  2 , K Senthilnathan  3 , P Ramesh Babu  3
Affiliations

Study of Variation in Dose Calculation Accuracy Between kV Cone-Beam Computed Tomography and kV fan-Beam Computed Tomography

Venkatesan Kaliyaperumal et al. J Med Phys. 2017 Jul-Sep.

Abstract

Cone-beam computed tomography (CBCT) images are presently used for geometric verification for daily patient positioning. In this work, we have compared the images of CBCT with the images of conventional fan beam CT (FBCT) in terms of image quality and Hounsfield units (HUs). We also compared the dose calculated using CBCT with that of FBCT. Homogenous RW3 plates and Catphan phantom were scanned by FBCT and CBCT. In RW3 and Catphan phantom, percentage depth dose (PDD), profiles, isodose distributions (for intensity modulated radiotherapy plans), and calculated dose volume histograms were compared. The HU difference was within ± 20 HU (central region) and ± 30 HU (peripheral region) for homogeneous RW3 plates. In the Catphan phantom, the difference in HU was ± 20 HU in the central area and peripheral areas. The HU differences were within ± 30 HU for all HU ranges starting from -1000 to 990 in phantom and patient images. In treatment plans done with simple symmetric and asymmetric fields, dose difference (DD) between CBCT plan and FBCT plan was within 1.2% for both phantoms. In intensity modulated radiotherapy (IMRT) treatment plans, for different target volumes, the difference was <2%. This feasibility study investigated HU variation and dose calculation accuracy between FBCT and CBCT based planning and has validated inverse planning algorithms with CBCT. In our study, we observed a larger deviation of HU values in the peripheral region compared to the central region. This is due to the ring artifact and scatter contribution which may prevent the use of CBCT as the primary imaging modality for radiotherapy treatment planning. The reconstruction algorithm needs to be modified further for improving the image quality and accuracy in HU values. However, our study with TG-119 and intensity modulated radiotherapy test targets shows that CBCT can be used for adaptive replanning as the recalculation of dose with the anisotropic analytical algorithm is in full accord with conventional planning CT except in the build-up regions. Patient images with CBCT have to be carefully analyzed for any artifacts before using them for such dose calculations.

Keywords: Cone-beam computed tomography; dose calculation; fan-beam computed tomography; quality assurance.

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Conflict of interest statement

There are no conflicts of interest.

Figures

Figure 1
Figure 1
C-shaped, cylindrical, ring-shaped target, and target in buildup region in Catphan
Figure 2
Figure 2
(a) High-contrast resolution, low-contrast resolution, spatial linearity of fan beam-computed tomography and cone-beam computed tomography images. (b) Hounsfield unit comparison of fan beam-computed tomography and cone-beam computed tomography images
Figure 3
Figure 3
(a) Hounsfield unit value in X and Z axis fan beam-computed tomography versus cone-beam computed tomography RW Plates. (b) Hounsfield unit value in X and Z axis fan beam-computed tomography versus cone-beam computed tomography - Catphan phantom
Figure 4
Figure 4
(a) Comparison of dose distribution between fan beam computed tomography and cone-beam computed tomography plans for C-shaped target. (b) Comparison of dose distribution between fan beam-computed tomography and cone-beam computed tomography plans for ring shaped target. (c) Comparison of dose volume histograms between fan beam-computed tomography and cone-beam computed tomography plans for C-shaped target and ring-shaped target
Figure 5
Figure 5
(a) Comparison of fan beam-computed tomography and cone-beam computed tomography plans –Buildup region target. (b) Comparison of fan beam-computed tomography and cone-beam computed tomography plans -simple cylindrical target and 4 sides OAR (c) Comparison of dose volume histograms for fan-beam computed tomography and cone-beam computed tomography plans – Buildup region target and simple cylindrical target and 4 sides OAR
Figure 6
Figure 6
HU mapping in the ROI of 12 mm x 12 mm for head and neck case - FBCT and CBCT
Figure 7
Figure 7
Dose comparison in the left buccal mucosa case- fan beam-computed tomography and cone-beam computed tomography - 6 MV
Figure 8
Figure 8
Dose comparison in the sacrum case- fan beam-computed tomography and cone-beam computed tomography - 15 MV
See this image and copyright information in PMC

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