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Image Quality of 4D-CBCT with Varying Gantry Rotation Speeds for Liver SBRT with Fiducial Markers

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Y Shimohigashi

Y Shimohigashi1,2*, R Toya3 , F Araki4 , K Yonemura1 , M Maruyama1 , Y Nakaguchi1 , Y Kai1 , (1) Department of Radiological Technology, Kumamoto University Hospital, (2) Department of Graduate School of Health Sciences, Kumamoto University, (3) Department of Radiation Oncology, Kumamoto University Hospital, (4) Department of Health Sciences, kumamoto University


SU-I-GPD-J-24 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: This study aimed to quantitatively evaluate the image quality of 4D-CBCT images with varying gantry rotation speeds (GRSs) for the appropriate image guidance of liver SBRT with fiducial markers.

Methods: We obtained 4D-CBCT (Elekta Symmetry™) projection data with a GRS of 50° min⁻¹ from six patients who received liver SBRT with gold fiducial markers (diameter: 2 mm). By varying the number of the original projection data, we generated 4D-CBCT images with a resolution of 10 phases for different GRSs of 50, 85, 100, and 200° min⁻¹. The image quality was evaluated by using signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and edge-response width (ERW; defined as the spatial width between 25% and 75% of the linear intensity profiles across the lung and liver boundary). The tumor positions were measured based on the coordinates of the central positions of the fiducial markers for all 10 phases in the 4D-CBCT images. The tumor positions with different GRSs were compared with a reference position with a GRS of 50° min⁻¹. Root mean square errors (RMSEs) of the tumor positions were calculated relative to the reference positions.

Results: The median values of the SNR and CNR decreased from 48.8 to 12.5 and from 22.5 to 5.8, respectively, as the GRS increased from 50 to 200° min⁻¹. The median values of the ERW increased from 9.75 to 16.1 mm as the GRS increased from 50 to 200° min⁻¹. The mean RMSEs were 2.0, 2.1, and 3.6 mm for GRSs of 85, 100, and 200° min⁻¹, respectively.

Conclusion: GRS is an important factor that affects the image quality in 4D-CBCT image acquisition. We report that the quality of image generated using a GRS of 200° min⁻¹ is unacceptable for image guidance of liver SBRT with fiducial markers.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by JSPS KAKENHI Grant Number 26861004.

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