Dr. Masoud Hashemi Profile

Dr. Masoud Hashemi

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Proceedings Article | 1 March 2019 Paper

Investigation of calibration-based projection domain dual energy decomposition CBCT technique for brain radiotherapy applications

Shailaja Sajja, Masoud Hashemi, Christopher Huynh, James Mainprize, Markus Eriksson, Young Lee, Hakan Nordstrom, Anula Nico, Fang-Fang Yin, Arjun Sahgal, Mark Ruschin

Proceedings Volume 10948, 109483A (2019) https://doi.org/10.1117/12.2510430

KEYWORDS: Aluminum, Calibration, Radiotherapy, Dual energy imaging, Calcium, Head, Signal attenuation, Brain, Visualization, X-ray computed tomography

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The purpose of the present study was to develop and evaluate a practical dual-energy imaging approach for enhancing on-board cone-beam CT (CBCT) image quality for brain radiotherapy applications. The proposed primary technique involves a projection domain calibration procedure. In-house fabricated aluminum and acrylic step wedges were stacked and oriented orthogonally to each other to produce 72 unique combinations of two-material path lengths, i.e. 8 acrylic steps × 9 aluminum steps. High (120 kV) and low (70 kV) energy projections were acquired of the step wedges and a 3rd order polynomial fit was used to map the log-normalized projection intensities to the known acrylic and aluminum thicknesses. The subsequent model was tested on two phantoms: 1) in-house DE phantom with PMMA background and calcium inserts of different concentrations (5 mg/mL, 200 mg/mL and 400 mg/mL) and 2) a RANDO head phantom. The decomposed projections were reconstructed separately as aluminum-only and acrylic-only reconstructions. In addition, virtual monochromatic projections (VMPs) obtained by combining the aluminum-only and acrylic-only projections were reconstructed at different keVs. A quantitative improvement was observed in the SDNR (signal difference to noise ratios) of the calcium inserts using Aluminum-reconstructions and synthesized VMPs (40 to 100 keV) compared to the single energy reconstructions. A reduction in beam hardening was observed as well. In addition, a qualitative improvement in soft-tissue visualization was observed with the RANDO phantom reconstructions. The findings indicate the potential of dual energy CBCT images: material specific images as well as VMPs for improved CBCT-based image guidance. The present approach can readily be applied on existing commercial systems and a feasibility study on patients is a worthwhile investigation.

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