Evaluation of microwave interstitial antennas in the phantom with varying cross-section.

Dipole-regular microwave interstitial antennas are characterized with a "dead" space located along the tip segment of the antenna. The length of the "dead" space is on the order of 2 cm or larger, depending on the antenna's insertion depth. If the insertion depth is smaller than 4 cm, then coupling of the antennas to tissue becomes a problem. Catheters that facilitate the placement of antennas into tumor frequently protrude beyond the tissue. This provides the opportunity of exposing part of the antenna tips (with low radiation output) beyond the tissue. Decoupling of this part of the antennas from the tissue reduced the dead space and improved microwave power transfer to the tissue. This concept was investigated using a muscle equivalent phantom consisting of five segments with thicknesses varying from 3 cm to 8 cm. The transfer of microwave power to the phantom and SAR distributions along the central axis of a rectangular array of four antennas were evaluated by measuring rates of temperature rise. The protrusion lengths that improved the array performance were found for each segment of the phantom.