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Application of Intra-Fractional Imaging for Pretreatment CBCT of Breath-Hold Lung SBRT

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D Cao

D Cao*, M Jermoumi, V Mehta, D Shepard, Swedish Cancer Institute, Seattle, WA


SU-F-J-30 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose:Clinical implementation of gated lung SBRT requires tools to verify the accuracy of the target positioning on a daily basis. This is a particular challenge on Elekta linacs where the XVI imaging system does not interface directly to any commercial gating solution. In this study, we used the Elekta’s intra-fractional imaging functionality to perform the pre-treatment CBCT verifications and evaluated both the image quality and gating accuracy.

Methods:To use intrafraction imaging tools for pre-treatment verifications, we planned a 360-degree arc with 1mmx5mm MLC opening. This beam was designed to drive the gantry during the gated CBCT data collection. A Catphan phantom was used to evaluate the image quality for the intra-fractional CBCT. A CIRS lung phantom with a 3cm sphere-insert and a moving chest plate were programmed with a simulated breath-hold breathing pattern was used to check the gating accuracy. A C-Rad CatalystHD surface mapping system was used to provide the gating signal.

Results:The total delivery time of the arc was 90 seconds. The uniformity and low contrast resolution for the intra-fractional CBCT was 1.5% and 3.6%, respectively. The values for the regular CBCT were 1.7% and 2.5%, respectively. The spatial resolution was 7 line-pairs/cm and the 3D spatial integrity was less than 1mm for the intra-fractional CBCT. The gated CBCT clearly demonstrated the accuracy of the gating image acquisition.

Conclusion:The intra-fraction CBCT capabilities on an Elekta linac can be used to acquire pre-treatment gated images to verify the accuracy patient positioning. This imaging capability should provide for accurate patient alignments for the delivery of lung SBRT.

Funding Support, Disclosures, and Conflict of Interest: This research was partially supported by Elekta

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