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Evaluation of Accurate Iodine Content in the Context of Radiotherapy Application

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A Lapointe

A Lapointe1*, A Lalonde 1, H Bahig2 , J Carrier1,2,3 , S Bedwani1,2,3 , H Bouchard1,2,3 , (1) Universite de Montreal, Montreal, QC, (2) Centre Hospitalier de l'Universite de Montreal (CHUM), Montreal, QC, (3) Centre de Recherche du Centre Hospitalier de l'Universite de Montreal (CRCHUM), Montreal, QC,


WE-DE-605-7 (Wednesday, August 2, 2017) 10:15 AM - 12:15 PM Room: 605

Purpose: The use of contrast agents enhances tumour delineation during radiotherapy treatment planning, but usually requires an additional CT scan without contrast to achieve accurate dose calculation. The purpose of this work is to propose and validate two virtual non-contrast (VNC) methods from contrast-enhanced dual-energy CT (DECT) for use in radiotherapy applications.

Methods: Methods based on eigentissue decomposition (ETD) and two-material decomposition (2-MD) are proposed to extract VNC electron density on contrast-enhanced DECT images. The first method is developed for treatment planning and uses the contrast agent plus components of the ETD orthogonal material base. The second method is designed for specific organs and uses 2-MD with variable electron density and a priori knowledge of the elemental composition. The proposed methods are tested in a simulation environment and compared to the common three-material decomposition (3-MD) technique. Prior to comparing the methods with patient data, a new stoichiometric calibration is adapted to the presence of high atomic number materials.

Results: Simulation results show that ETD and 2-MD with a priori systematically outperform 3-MD respectively with and without a priori on the nature of the tissue. Theoretical findings are in agreement with real patient images, where the mean error on HU numbers for 5 different structures contoured by a radiation oncologist are 9, 13 and 24 for the 2-MD with a priori, the ETD method and the 3-MD method respectively. VNC electron density is also found in agreement with the scan without contrast agent (p>0.14).

Conclusion: Both simulations and patient data show that ETD and 2-MD with a priori methods are best able to produce accurate VNC HU and electron density values for radiotherapy applications. Producing accurate VNC images with DECT is expected to provide less imaging dose to the patient and reduce the scanning time.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by MITACS and Siemens Healthcare.

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