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Characterization of a Prototype Rapid On-Board KV Imaging System Designed for a Ring Shape Radiation Therapy Unit

B Cai*, T Mazur , E Laugeman , J Park , G Hugo , S Mutic , H Li , Washington University in St. Louis, St Louis, MO


(Tuesday, 7/31/2018) 1:15 PM - 1:45 PM

Room: Exhibit Hall | Forum 6

Purpose: To characterize the performance of a prototype kV imaging system on-board the Halcyon linear accelerator (Varian Medical Systems) with rapid imaging capabilities and an advanced, iterative reconstruction algorithm (iCBCT).

Methods: Imaging quality and radiation dose were evaluated for 11 imaging protocols available for 3D kV CBCT acquisitions. It was characterized by measurements that assessed slice sensitivity profiles, low-contrast and spatial resolution, image uniformity and noise, as well as CT number and geometric accuracy. Image accuracy was further evaluated using an anthropomorphic pelvis phantom with added bolus layers to determine the robustness of 4 pelvis imaging protocols with increasing patient size from 38 cm to 53 cm diameters (5cm incremental). Imaging dose for all 11 protocols was measured using a CTDI phantom and pencil chamber. Additional imaging studies were performed with torso and pelvis phantoms to compare workflow efficiency with the similar imaging protocol executed on C-arm linacs (Truebeam/Trilogy, Varian Medical Systems).

Results: All major image quality indicators derived from the standard imaging phantoms on Halcyon and C-arm machines showed comparable values with the regular reconstruction algorithm. The iCBCT scans tend to reduce the noise therefore provide better contrast-to-noise (CNR) ratio. Scanning time of fast protocols ranges between 17-25 seconds while similar scans on C-arm machines require at least 60 seconds for a full rotation scan. The fast scans yield half of the dose compared to the regular scan on pelvis protocols, while about 10% lower for thorax fast protocol.

Conclusion: The rapid on-board kV imaging system provides additional benefits for facilitating and optimizing radiation delivery workflow. Quantitative task-based image quality metrics integrating real patient study should be further investigated to accommodate additional clinical applications. The clinical usage of rapid imaging and the advanced iCBCT reconstruction should take into account patient size, radiation dose, and ultimate radiation delivery task.

Funding Support, Disclosures, and Conflict of Interest: This project receives funding from Varian Medical System.


Not Applicable / None Entered.


IM/TH- RT X-ray Imaging: CBCT imaging/therapy implementation

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