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Overcoming Range Limitation of Carbon Ions for Relative Stopping Power Reconstruction by Using KV Projection Information

D Shrestha*, Y Zhang , S Niu , J Wang , UT Southwestern Medical Center, Dallas, TX


(Monday, 7/30/2018) 1:15 PM - 1:45 PM

Room: Exhibit Hall | Forum 6

Purpose: Carbon CT has been explored for direct reconstruction of the tissue relative stopping power (RSP). However, for sites of large thickness such as lateral pelvis, limited range of the carbon ions may limit the number of projection views available during carbon CT projection acquisition. Here, we developed a novel carbon-kV CT technique by using kilovoltage (kV) photon projections to make up the otherwise missing information for the RSP reconstruction using carbon ions

Methods: In the proposed carbon-kV CT scheme, 30 projections long anterior-posterior (AP) and PA directions will be scanned by carbon ions, while 30 lateral projections will be acquired with kV x-rays. These 60 projections were uniformly distributed over 360o at a regular interval of 6^o. The phantom used in the simulations had dimensions of 40cm x 28cm x 25cm. The Geant4 toolkit was used to simulate the carbon projections while the photon projections were created using ray tracing technique. An initial kVCT image was reconstructed from photon projections using the Algebraic Reconstruction Technique (ART) with Total Variation (TV) regularization. The resulting image was converted into an RSP image using a standard HU-RSP calibration curve. This RSP image was then used as a priori during the RSP reconstruction from the carbon projections. The resulting RSP image was in turn used as a priori for the kVCT reconstruction. The above processes were performed alternatively until a good quality carbon-kV CT was obtained

Results: Carbon-kV CT yielded high resolution RSP images with well distinguishable material inserts. The overall uncertainty of RSP, relative to the ground truth, was reduced to 4% in carbon-kV CT compared to 12.5% when using the carbon projections only

Conclusion: kV x-ray projections can help RSP reconstruction in carbon CT in the cases where the projection views are limited due to range limitations of the carbon ions


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