Comparison of six microwave antennas for hyperthermia treatment of cancer: SAR results for single antennas and arrays

Abstract

Interstitial techniques of inserting catheters into tumors for the purpose of applying therapeutic irradiation and hyperthermia are in widespread use. Several miniature microwave antenna designs are currently used for these treatments. These include multisection, hot-tip, 2- and 3-node, dipole and helical antennas, all of which are commercially available. The antenna designs are diverse enough to have a dramatic effect on the power deposition patterns either as single antennas or when used in arrays. Aside from the dipole antenna, most of the antennas have never been evaluated experimentally or theoretically in arrays, although the array configuration is used in the vast majority of all clinical treatments. Power deposition or SAR (specific absorption rate) tests were run in muscle equivalent phantom. Single antennas were evaluated at 400 points in a plane and isoSAR contours drawn, normalized to maximum SAR. Single antennas were also compared in large and small diameter catheters to evaluate catheter dependent antenna performance. The dipole, multisection, hot-tip and helical antennas were evaluated in arrays of four antennas located at the corners of a square, spaced 2.0 cm apart. Arrays of antennas were evaluated at 441 points in three planes orthogonal to the antenna axes. Results in the single antenna studies showed that the dipole was less affected by snugness of catheter fit than the multisection, hot-tip or helical antennas. In large catheters, the latter three antennas showed more extreme tip heating performance. The 2- and 3-node antennas deposited only 20% SAR in the distal 30 mm of antenna length. In arrays, the multisection, hot-tip, and dipole antennas all yielded 80–90% SAR centrally in the central measurement plane. Comparing the three antennas, the dipole array deposited 20% more power centrally in a plane near the insertion point, and the multisection and hot-tip antenna designs deposited 10% more central power in a plane near the antenna tips. The helical antenna array deposited only 30% SAR centrally in the plane near the antenna tips and in the central plane. Only 10% SAR was measured centrally near the insertion point, as expected for tip-heating antennas. Finally, the clinical significance of the results is discussed as applied to human tumors undergoing hyperthermia treatments.