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. 2019 Aug 29;1(1):20190028.
doi: 10.1259/bjro.20190028. eCollection 2019.

Registration accuracy with the low dose kilovoltage cone-beam CT: A phantom study

Yoshiki Takei, Hajime Monzen  1 , Kenji Matsumoto  1 , Kohei Hanaoka  1 , Mikoto Tamura  1 , Yasumasa Nishimura  2
Affiliations

Registration accuracy with the low dose kilovoltage cone-beam CT: A phantom study

Yoshiki Takei et al. BJR Open. .

Abstract

Objective: The aim of this study was to investigate low-dose kilovoltage cone-beam CT (kV-CBCT) for image-guided radiotherapy, with a particular focus on the accuracy of image registration with low-dose protocols.

Methods: Imaging doses were measured with a NOMEX semiconductor detector positioned at the front of head, thorax, and pelvis human body phantoms while kV-CBCT scans were acquired at different tube currents. Aspects of image quality (spatial resolution, noise, uniformity, contrast, geometric distortion, and Hounsfield unit sensitivity) and image registration accuracy using bone and soft tissue were evaluated.

Results: With preset and the lowest tube currents, the imaging doses were 0.16 and 0.08 mGy, 5.29 and 2.80 mGy, and 18.23 and 2.69 mGy for head, thorax, and pelvis, respectively. Noise was the only quality aspect directly dependent on tube current, being increased by 1.5 times with a tube current half that of the preset in head and thorax, and by 2.2 times with a tube current 1/8 of the preset in the pelvis. Accurate auto-bone matching was performed within 1 mm at the lowest tube current. The auto-soft tissue matching could not be performed with the lowest tube current; however, manual-soft tissue matching could still be performed within 2 mm or less.

Conclusion: Noise was the only image quality aspect dependent on the imaging dose. Auto-bone and manual-soft tissue matching could still be performed at the lowest imaging dose.

Advances in knowledge: When optimizing kV-CBCT imaging dose, the impact on bone and soft tissue image registration accuracy should be evaluated.

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Figures

Figure 1.
Figure 1.
A schematic diagram of the measurement geometry for imaging dose with kilovoltage cone-beam CT.
Figure 2.
Figure 2.
Catphan uniformity module (CTP486). ROIs were generated at the center and each of the four peripheral locations to evaluate uniformity.
Figure 3.
Figure 3.
The relationship between and measurement dose by NOMEX and CTDI provided by manufacturer. The standard deviation (1SD) of the measurement by NOMEX was less than 1.0%.
Figure 4.
Figure 4.
Results of the image quality test; (a) spatial resolution, (b) noise, (c) uniformity, (d) contrast, (e) geometric distortion.
Figure 5.
Figure 5.
Phantom images (head, thorax, pelvis) from the planning CT (pCT), CBCT preset protocol (preset), and minimum dose condition (min).
Figure 6.
Figure 6.
Three-section images (transvers, sagittal, coronal) inside the pelvic cavity of the pelvic phantom from the planning CT (pCT), CBCT preset condition (680 mAs), half preset condition (340 mAs), and minimum dose condition (85 mAs).
Figure 7.
Figure 7.
Results of the soft tissue matching by manual-registration for the pelvic phantom. Error bars represent one standard deviation.
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