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Respiratory Motion Guided Four Dimensional Cone Beam Computed Tomography: Image Quality Analysis

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R O'Brien

R O'Brien*, B Cooper, J Kipritidis, C Shieh, P Keall, Sydney Medical School, The University of Sydney, Camperdown, NSW 2006, Australia

WE-G-134-7 Wednesday 4:30PM - 6:00PM Room: 134

Purpose: he aim of Respiratory Motion Guided-4DCBCT (RMG-4DCBCT) is to improve image quality and reduce radiation dose in 4DCBCT imaging. In current generation 4DCBCT, the gantry rotation speed and imaging frequency are constant and independent of the patient's breathing which leads to projection clustering. We have developed a software system which regulates the gantry velocity and projection time interval, in response to the patient's real time respiratory signal, so that a full set of near-evenly spaced projections can be acquired for each respiratory phase. We present our results analysing the quality of images produced with RMG-4DCBCT using the Catphan phantom.

Methods: The RMG-4DCBCT software: (1) optimizes the gantry trajectory and projection pulse rate schedule based on the patients predicted breathing trace, (2) adjusts the gantry velocity and projection pulse rate according to the patients real time breathing signal and (3) sends commands to the gantry and kilovoltage imager. Acquisition of 60, RMG-4DCBCT(60), and 120, RMG-4DCBCT(120), half fan projections in each of 10 respiratory phases was simulated in real-time using 111 breathing traces from 24 lung cancer patients. A dataset containing 608 half fan projections of the Catphan phantom was sampled to reconstruct 4DCBCT images using both conventional 4DCBCT and RMG-4DCBCT. From the reconstructed images a streak ratio (SR) was calculated to quantify image quality.

Results: The average SR was reduced from 5.16 with conventional 4DCBCT to 1.5 with RMG-4DCBCT(120) and 2.9 with RMG-4DCBCT(60). The average time required to acquire the dataset was 240 seconds with conventional 4DCBCT, 599 seconds for RMG-4DCBCT(120) and 260 seconds for RMG-4DCBCT(60). If we force RMG-4DCBCT to acquire 120 projections in exactly 240 seconds the SR is 4.2.

Conclusion: There are less streak artifacts with RMG-4DCBCT than conventional 4DCBCT. The imaging time for RMG-4DCBCT depends on the patients breathing rate and number of projections acquired.

Funding Support, Disclosures, and Conflict of Interest: This project is supported by an NHMRC Australia Fellowship and NHMRC project grant 1034060.

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