Peter Deuflhard

Clinical evaluation and verification of the hyperthermia treatment planning system hyperplan

PURPOSE A prototype of the hyperthermia treatment planning system (HTPS) HyperPlan for the SIGMA-60 applicator (BSD Medical Corp., Salt Lake City, Utah, USA) has been evaluated with respect to clinical practicability and correctness. MATERIALS AND METHODS HyperPlan modules extract tissue boundaries from computed tomography (CT) images to generate regular and tetrahedral grids as patient models, to calculate electric field (E-field) distributions, and to visualize three-dimensional data sets. The finite difference time-domain (FDTD) method is applied to calculate the specific absorption rate (SAR) inside the patient. Temperature distributions are calculated by a finite-element code and can be optimized. HyperPlan was tested on 6 patients with pelvic tumors. For verification, measured SAR values were compared with calculated SAR values. Furthermore, intracorporeal E-field scans were performed and compared with calculated profiles. RESULTS The HTPS can be applied under clinical conditions. Measured absolute SAR (in W/kg), as well as relative E-field scans, correlated well with calculated values (+/-20%) using the contour-based FDTD method. Values calculated by applying the FDTD method directly on the voxel (CT) grid, were less well correlated with measured data. CONCLUSION The HyperPlan system proved to be clinically feasible, and the results were quantitatively and qualitatively verified for the contour-based FDTD method.

Global Inexact Newton Multilevel FEM for Nonlinear Elliptic Problems

The paper deals with the multilevel solution of elliptic partial differential equations (PDEs) in a finite element setting: uniform ellipticity of the PDE then goes with strict monotonicity of the derivative of a nonlinear convex functional. A Newton multigrid method is advocated, wherein linear residuals are evaluated within the multigrid method for the computation of the Newton corrections. The globalization is performed by some damping of the ordinary Newton corrections. The convergence results and the algorithm may be regarded as an extension of those for local Newton methods presented recently by the authors. An affine conjugate global convergence theory is given, which covers both the exact Newton method (neglecting the occurrence of approximation errors) and inexact Newton-Galerkin methods addressing the crucial issue of accuracy matching between discretization and iteration errors. The obtained theoretical results are directly applied for the construction of adaptive algorithms. Finally, illustrative numerical experiments with a NEWTON-KASKADE code are documented.

Numerical algorithms and visualization in medical treatment planning

After a short summary on therapy planning and the underlying technologies we discuss quantitative medicine by giving a short overview on medical image data, summarizing some applications of computer based treatment planning, and outlining requirements on medical planning systems. Then we continue with a description of our medical planning system HyperPlan. It supports typical working steps in therapy planning, like data aquisition, segmentation, grid generation, numerical simulation and optimization, accompanying these with powerful visualization and interaction techniques.

Biomechanisches Modell zur Abschätzung der individuellen Gesichtsmimik

In dieser Arbeit prasentieren wir ein biomechanisches Modell des Weichgewebes inklusive der Gesichtsmuskulatur zur Abschatzung der individuellen Gesichtsmimik in der Gesichtschirurgie.

Validierung eines linear elastischen Modells für die Weichgewebesimulation in der Mund-Kiefer-Gesichtschirurgie

In dieser Arbeit untersuchen wir den Gultigkeitsrahmen eines linear elastischen Modells fur die Weichgewebesimulation in der Mund-Kiefer-Gesichtschirurgie. Insbesondere die Quantifizierung und die Uberwachung des auf die geometrische Nichtlinearitat zuruckzufuhrenden Linearisierungsfehlers bei groβen Deformationen werden diskutiert.