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Pulmonary Nodule Radiotherapy Follow-up using Dynamic Contrast Enhancement CT Host Publication: Finds and Results from the Swedish Cyprus Expedition: A Gender Perspective at the Medelhavsmuseet Authors: P. Clerinx, R. Deklerck, K. Nieboer, S. Bral, D. Verellen, J. De Mey and G. Storme Publication Date: Dec. 2007 Number of Pages: 4
Abstract: A feasibility study was conducted to develop a practical methodology for efficiently assessing the in vivo effects of radiotherapy on pulmonary nodules using dynamic contrast-enhanced volumetric computed tomography (DCE-CT) maps.
CT is widely accepted as the method of choice for lung tumor imaging, exhibiting the highest sensitivity of all imaging modalities for detection of pulmonary nodules, although specificity is limited. Functional imaging of lung tumors with DCE-CT in oncology has focused in the past on gaining additional information which can be used for the determination of tumor malignancy. For instance, a multi-center study demonstrated that peak enhancement of pulmonary nodules has a sensitivity of 98% and a specificity of 58% for determining malignancy. In DCE-CT, the amount of contrast enhancement is considered to be indicative for malignant angiogenesis, which influences both the transport by blood flow and the exchange by diffusion of the contrast agent between intravascular and extracellular compartments.
DCE-CT can be used to derive tissue perfusion related parameters. While CT dynamic perfusion studies have been reported as early as 1980 by Axel et al., similar developments in lung cancer imaging have only surfaced more recently, stimulated by the advent of faster spiral CT systems in the 1990's. Modern scanners allow measurement of enhancement over time at small time intervals. This permits detailed modeling of the distribution of contrast agent and quantification of tissue perfusion and permeability by examining the relationships between tissue and arterial enhancement, and in some cases also venal enhancement.
However, currently a gap remains between sufficient temporal sampling to perform haemodynamic modeling and obtaining an adequate spiral scan length to cover the complete area of interest. The combination of both requirements would necessitate 256 detector-row CT scanners for many applications, which will likely remain unavailable for most clinical environments for the near future. DCE-CT in oncology has therefore been limited to measurements on a single tumor level, up to a maximum coverage of 4 cm with 64 detector-row scanners, while mean cranial-caudal pulmonary movement amplitudes of 12 mm have been observed for unattached lower lobe tumors by real-time marker tracking during free breathing. Onishi et al. observed a mean maximum tumor displacement of 3.1 mm along the cranial-caudal axis in a deep inspiration breath-holding study. Performing repeated helical scans under breath-hold conditions offers the advantage of full tumor coverage. Combined with non-rigid registration techniques local variations in dynamic contrast-enhancement at the tumor level can easily be evaluated.
The aim of this study was to develop a practical method to perform whole tumor DCE-CT imaging of lung nodules of proven malignancy to assess local changes in morphology and dynamic enhancement after therapy. Automated non-rigid registration of images was performed to compensate for residual movement prior to calculating time-averaged enhancement overlay maps. The proposed methodology was tested by an experienced radiologist (KN) to evaluate the feasibility of this approach.
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