title: Quasistatic zooming for regional hyperthermia treatment planning.
abstract: Due to current computer limitations, specific absorption rate (SAR) distributions in regional hyperthermia treatment planning (HTP) are limited to centimetre resolution. However, since patient anatomy is highly structured on a millimetre scale, millimetre-resolution SAR modelling is required. A method called quasistatic zooming has been developed to obtain a high-resolution SAR distribution within a volume of interest (VOI): using the low-resolution E-field distribution and the high-resolution patient anatomy, the high-resolution SAR distribution is computed within a small zoom volume Q (small compared with the wavelength in water (lambda(w))). Repeating this procedure yields the zoomed-resolution SAR distribution in an arbitrary VOI. To validate this method for a VOI that is not small compared with lambda(w), high-resolution finite-difference time-domain (FDTD) modelling is needed. Since this is impractical for a clinical applicator, a computer model of a small applicator has been created. A partial patient anatomy is inserted into the applicator and both high- and low-resolution SAR distributions are computed for this geometry. For the same geometry, zoomed-resolution SAR distributions are computed with different sizes of Q. To compare the low- and zoomed-resolution SAR distributions with the high-resolution one, the correlation and averaged absolute difference are computed. These numbers are improved considerably using zooming (correlation 58% to 92%; averaged absolute difference 43% to 20%). These results appear to be independent of the size of Q, up to 0.3 lambda(w). Quasistatic zooming is a valuable tool in high-resolution regional HTP.
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: A A
authors.initials: AA
authors.lastname: De Leeuw
authors.forename: H
authors.initials: H
authors.lastname: Kroeze
authors.forename: J J
authors.initials: JJ
authors.lastname: Lagendijk
mesh_terms: D003198:Computer Simulation; D005334:Fever / Q000628:therapy*; D006801:Humans; D015233:Models, Statistical; D019047:Phantoms, Imaging; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012984:Software