title: Quasistatic zooming of FDTD E-field computations: the impact of down-scaling techniques.
abstract: Due to current computer limitations, regional hyperthermia treatment planning (HTP) is practically limited to a resolution of 1 cm, whereas a millimetre resolution is desired. Using the centimetre resolution E-field distribution, computed with, for example, the finite-difference time-domain (FDTD) method and the millimetre resolution patient anatomy it is possible to obtain a millimetre resolution SAR distribution in a volume of interest (VOI) by means of quasistatic zooming. To compute the required low-resolution E-field distribution, a low-resolution dielectric geometry is needed which is constructed by down-scaling the millimetre resolution dielectric geometry. In this study we have investigated which down-scaling technique results in a dielectric geometry that yields the best low-resolution E-field distribution as input for quasistatic zooming. A segmented 2 mm resolution CT data set of a patient has been down-scaled to 1 cm resolution using three different techniques: 'winner-takes-all', 'volumetric averaging' and 'anisotropic volumetric averaging'. The E-field distributions computed for those low-resolution dielectric geometries have been used as input for quasistatic zooming. The resulting zoomed-resolution SAR distributions were compared with a reference: the 2 mm resolution SAR distribution computed with the FDTD method. The E-field distribution for both a simple phantom and the complex partial patient geometry down-scaled using 'anisotropic volumetric averaging' resulted in zoomed-resolution SAR distributions that best approximate the corresponding high-resolution SAR distribution (correlation 97, 96% and absolute averaged difference 6, 14% respectively).
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
authors.forename: J B
authors.initials: JB
authors.lastname: Van de Kamer
authors.forename: H
authors.initials: H
authors.lastname: Kroeze
authors.forename: A A
authors.initials: AA
authors.lastname: De Leeuw
authors.forename: J J
authors.initials: JJ
authors.lastname: Lagendijk
mesh_terms: D016880:Anisotropy; D003198:Computer Simulation; D006801:Humans; D006979:Hyperthermia, Induced; D007091:Image Processing, Computer-Assisted; D019047:Phantoms, Imaging; D055672:Static Electricity; D013813:Therapy, Computer-Assisted