The Calculation of displacement vector fields (DVFs) allows a propagation of the CTV contours from planning image to daily control images.

<p>Left: The arrows (green) represent an exemplary DVF of the transformation between a planning CT image and a control CT image. The CTV contour (blue) was propagated to fCTV of the fraction (red). Right: the fCTV of patient #19 propagated to all control CT images are displayed on the planning CT image.</p

Margin evaluation measurements.

<p>The CTV (red) is propagated to the fraction control CT image (fCTV, orange) to calculate CTV volume missed by the treatment <b><i>V</i>_{fCTV \ ITV}</b> and the volume of healthy tissue being hit .</p

Man values and standard deviations of margin metrics for all three different margin generation approaches.

<p>Man values and standard deviations of margin metrics for all three different margin generation approaches.</p

Mean distance between ITV and transformed spinal cord d_SC(z) of different margin approaches for all patients.

<p>Mean distance between ITV and transformed spinal cord d_SC(z) of different margin approaches for all patients.</p

Margin sizes for all three different margin generation methods.

<p>Margin sizes for all three different margin generation methods.</p

Distance between ITV and OARs per CT slice.

<p>The slice wise distance between ITV and spinal cord <b><i>d</i></b>_<b>SC</b><b>(</b><i><b>z</b></i><b>)</b> is used to estimate the risk to the spinal cord.</p

ITV margins (green) of an exemplary patient (#19).

<p>Left: Approach 1 with a 3 mm constant margin; center: Approach 2 with a variable margin based on distances; right: Approach 3 with a variable margin approach using biomechanical modeling.</p

The finite element model of the patient is deformed.

<p>Left: the finite element mesh model of the patient’s skin in the planning configuration (grey) and the selected anatomical landmarks (green) as well as their position in the fraction control CT image (red). The patient model is deformed by a force based boundary condition between the landmarks. Right: Landmarks were pulled towards their position in the fraction CT, the mesh is deformed resulting in rising of the right shoulder.</p

Clinical Target Volume (CTV) of a head and neck cancer patient.

<p>Left: Volume rendering of the planning CT image for an exemplary head and neck cancer patient receiving an IMRT treatment under daily image guidance. The clinical target volume (CTV) is displayed in red, brainstem in green. The stereotactic external frame is used as positioning device. Center: A transversal CT slice of the same patient of the mandibular region is displayed. The clinical target volume (CTV, red) and the spinal cord (green) as organ at risk are shown as planning contours. Right: CTV contours of different treatment days are plotted on the same planning CT slice to visualize daily variations.</p

Schematic representation of the competing margin generation concepts to cope with residual deformations after a simulated IGRT correction.

<p>Approach 1: The constant margin is applied by increasing the CTV (red) contours by 3 mm resulting in the internal target volume (green). Approach 2: The variable margin is applied locally by increasing the CTV (red) by a value calculated using measured landmark displacements of adjacent landmarks. Approach 3: The variable finite-element-model-based margin is created by statistical sampling of the propagated target volumes based on DVFs generated from landmark displacements by the patient-specific biomechanical model.</p