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Monte Carlo Study On a Cone-Beam Computed Tomography Using a Cross-Type Carbon Fiber Antiscatter Grid

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K Usui

K Usui*, T Inoue , C Kurokawa , S Sugimoto , K Sasai , Juntendo University, Department of Radiation Oncology, Tokyo, Japan, K Ogawa*, Hosei University, Faculty of Science and Engineering, Tokyo, Japan


SU-F-J-70 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

If a cone-beam computed tomography (CBCT) image can be used for adaptive radiotherapy (ART), an irradiated actual dose distribution can be verified on every treatment day. However, a CBCT image is commonly degraded by scattered photons and thus cannot be directly used for dose calculation. The purpose of the present study is to evaluate whether a cross-type carbon fiber antiscatter grid improves CBCT image quality using a Monte Carlo (MC) method for achieving CBCT-based ART.

We designed a new carbon fiber (C₆H₁₀O₅) interspaced grid, which allows the grid ratio to be increased while maintaining the transmission of primary photons. The grid ratio was 20:1, and the grid frequency was 20 lp/cm, with lead strips oriented along the cone beam projections. The MC method was used to simulate a projection data acquisition system of a material phantom (water, lung, bone, cartilage, and adipose) with a bow-tie filter. The parameters used to evaluate the image quality were uniformity, contrast, and contrast-to-noise ratio (CNR). Moreover, to evaluate the accuracy of the CT number, we compared CT numbers between images reconstructed by only primary photons and those obtained using grids.

The proposed grid had a beneficial impact on the image quality and accuracy of the CT number. The uniformity was improved by approximately 70% compared to the case without the grid. The average contrast and CNR improved by 14.2% and 22.6%, respectively, when using the proposed grid. CT numbers using the proposed grid were most consistent with nominal CT numbers obtained with only primary photons.

The proposed cross-type carbon fiber grid improves CBCT image quality and achieves an accurate CT number, without increasing the imaging doses. Therefore, the cross-type carbon fiber antiscatter grid should be considered to achieve CBCT-based ART.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by Japan Society for the Promotion of Science KAKENHI. Grant Number 15K19211.

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