AbstractID: 6557 Title: Comparison of Techniques for Microwave Heating of Primary Tumors of the Breast
There is growing interest in microwave heating as an adjuvant treatment for breast
tumors, as shown in phase III trials [C. C. Vernon et al, Int. J. Rad. Oncol. Biol. Phys. 35:731
(1996)]. This study was made to determine how to select the appropriate techniques for heating a
tumor with a specific shape, size, and location.
The methods used in this study included measurements in phantom models, and
numerical modeling. The heating techniques that were evaluated include the use of two 915
MHz waveguide applicators compressing the breast, a 915 MHz cylindrical phased array of
dipole antennas with a water bolus surrounding the breast, and a lower frequency (100-200
MHz) circularly-polarized spiral applicator.
There is a common misconception that a breast tumor would always heat more than the
surrounding fat tissue because of its higher water content. The results show that the polarization
has a significant effect when heating non-spherical tumors. The relative SAR in the tumor is
greatest when the electric field is parallel to the long-axis of the tumor. When the electric field is
normal to the long axis, the tumor SAR is decreased and the SAR of adjacent mammary tissue is
increased. Circular polarization with the spiral applicator overcomes some of the polarizationdependent effects, and the lower frequency causes improved penetration. Two-dimensional
phase-steering with a cylindrical phased array provides greater control of the heating than onedimensional steering with two opposing waveguide applicators.
This work was supported by the BSD Medical Corporation.