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Abstract
Purpose: A reentrant-cavity-based applicator can produce a concentrated electric field between reentrant electrodes for localized heating. However, this field is inadequate for treating early small tumors localized in the head and neck. In order to safely heat such well-localized lesions, the electric field distribution should be more localized.
Materials and methods: In order to achieve localized heating, four parameters of the reentrant cavity (applicator height, outer diameter, reentrant diameter, and reentrant gap size), which influence the distribution of the electric field produced in the reentrant gap, are optimized using the Taguchi method. The variation in the heating characteristics affected by the size of the heating object is estimated using the signal-to-noise ratio (SNR) index. In this study, the electromagnetic field distributions in a cylindrical phantom and an oblate sphere phantom are analyzed by the three-dimensional finite element method, and the full width at half height (FWHH) of the specific absorption rate (SAR) distribution in the reentrant gap is evaluated.
Results: It is shown that the optimized applicator yields both the maximum SNR and minimum mean FWHH, and the sizes of the heating region in the phantom expressed using the averaged FWHH values of the SAR distribution are 60 and 80 mm along the radial and long-axis directions of the applicator, respectively.
Conclusions: A heating region can be robustly and optimally localized by using the Taguchi method and considering the variation in the size of the heating object.