Quasistatic zooming for regional hyperthermia treatment planning

• Published in: Physics in medicine & biology Vol. 46; no. 4; pp. 1017 - 1030
• Main Authors: Kamer, J B Van de, Leeuw, A A C De, Kroeze, H, Lagendijk, J J W
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.04.2001; Institute of Physics
• Subjects: Biological and medical sciences; Computer Simulation; Fever - therapy; Humans; Medical sciences; Models, Statistical; Phantoms, Imaging; Radiotherapy Planning, Computer-Assisted - methods; Radiotherapy. Instrumental treatment. Physiotherapy. Reeducation. Rehabilitation, orthophony, crenotherapy. Diet therapy and various other treatments (general aspects); Software; Technology. Biomaterials. Equipments. Material. Instrumentation; Quasistatic problem; High resolution; Time domain method; Simulation; Absorptance; Magnetic field; Hyperthermia; Modeling; Treatment planning; Comparative study; Finite difference method; Test object
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/0031-9155/46/4/308

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.