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Synthetic Gated CBCT Imaging for Lung SBRT

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X Li

X Li1*, P Zhang2 , R Gewanter1 , M Chan3 , X Tang4 , M Hunt2 , (1) Memorial Sloan Kettering Cancer Center, Rockville Centre, NY, (2) Memorial Sloan Kettering Cancer Center, New York, NY, (3) Memorial Sloan-Kettering Cancer Center, Basking Ridge, NJ, (4) Memorial Sloan-Kettering Cancer Center, Harrison, NY


SU-E-J-152 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Due to slow scanning speed, when free breathing CBCT (FBCBCT) is used to localize target in lung SBRT treatment, respiratory motion induced image artifacts may degrade the image quality and compromise the target positioning accuracy. The purpose of this study is to investigate the feasibility of synthetic gated CBCT (SGCBCT) imaging for lung SBRT treatment.

Methods: Two Lung SBRT patients were selected for this study. The amplitudes of tumor respiratory motion were 1.2cm and 3.0cm (Superior-Inferior).Each Lung SBRT patient underwent FBCBCT scan, and then the acquired projection images were exported to an in-house program for off-line analysis. Firstly a semi-automatic algorithm was used to trace the diaphragm movement from those projection images in order to correlate respiratory phases with each projection image. Secondly, a Feldkamp-Davis-Kress (FDK) algorithm was utilized to reconstruct the gated CBCT (GCBCT) images based on the projection images within the gating windows (35~65% for exhale; 85~15% for inhale). Thirdly, the bony structures were automatically segmented from FBCBCT images using Fuzzy C-mean segmentation method. Finally, the SGCBCT was generated by replacing the HU value of the GCBCT image with the value of FBCBCT image for the voxels that belong to the bony structure based on the above segmentation results.

Results: Due to the respiratory motion effect, the targets determined by FBCBCT have reduced image contrast and blurred boundary between tumor and surrounding normal lung tissues. Compared to FBCBCT, the SGCBCT images at exhale and inhale not only delineate the target with enhanced image contrast and much clearer boundary with less motion artifacts, but also determine the amplitudes of tumor respiratory motion.

Conclusion: SGCBCT provides better representation of the moving lung tumor with less motion artifacts, and has a potential to improve the positioning accuracy in lung SBRT treatment.

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