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Methodological accuracy of image-based electron density assessment using dual-energy computed tomography.
Christian Möhler1,2, Patrick Wohlfahrt3,4, Christian Richter3,4,5,6
1German Cancer Research Center (DKFZ), Division of Medical Physics in Radiation Oncology, Heidelberg, Germany.
Medical Physics
|April 12, 2017
Summary
Dual-energy computed tomography (DECT) offers accurate electron density determination for radiotherapy. A simple alpha-blending method with empirical calibration achieves low uncertainty, making further algorithm refinement unnecessary.
Area of Science:
- Medical Physics
- Radiotherapy Physics
- Medical Imaging
Background:
- Electron density is critical for accurate dose calculations in radiotherapy.
- Dual-energy computed tomography (DECT) provides a method to determine electron density by utilizing photon attenuation at two energy spectra.
- Existing DECT algorithms often rely on reconstructed CT numbers, introducing potential inaccuracies.
Purpose of the Study:
- To quantify the methodological and calibration uncertainty of a simple alpha-blending approach for electron density determination using DECT.
- To assess the accuracy of DECT-based electron density estimation for radiotherapy applications.
Main Methods:
- Electron density was calculated using a one-parametric linear superposition (alpha blending) of two DECT images.
- Empirical calibration of the blending parameter was performed using the affine relation between photon attenuation cross sections.
- Methodological uncertainty was isolated from CT-specific effects like noise and beam hardening.
Main Results:
- The alpha-blending approach demonstrated universal applicability to human tissue mixtures with a methodological uncertainty of 0.2% (excluding high-Z elements).
- The proposed calibration procedure is bias-free, straightforward, and yields consistent results across different experimental setups.
- A general calibration per scanner type and voltage combination is feasible.
Conclusions:
- The alpha-blending DECT approach offers high suitability for clinical electron density assessment in radiotherapy.
- The minimal methodological uncertainty associated with this method suggests that further refinement of existing image-based DECT algorithms is not recommended.