SAR PATTERNS FROM AN INTERSTITIAL MICROWAVE ANTENNA ARRAY HYPERTHERMIA SYSTEM.
Effective treatment of cancer using interstitial hyperthermia demands that the entire tumor volume be heated to temperatures in the 43 degree -55 degree C range while surrounding normal tissue is held near 43 degree C. A number of factors which affect the specific absorption rate (SAR, W/kg) patterns seen when using an interstitial microwave system in the clinic are discussed. Double-stub tuners, for example, can be used in the system to minimize reflected power from each antenna but may also introduce undesirable phase differences between the radiated electromagnetic waves. Similarly, power attenuators can be used to equalize the maximum SAR from each antenna, but the time and effort needed to adjust the attenuators may not be justified by the slight improvement in the SAR patterns. Experimental results corresponding to the use of double-stub tuners and power attenuators are compared with theoretical calculations and experimental results without tuners or attenuators. Comparisons are based on the size of the 50% iso-SAR volume. This volume has length defined in a direction parallel to the antenna axes and diameter measured in the junction plane.
