[The characterization of semirigid coaxial antennae for interstitial and endocavitary microwave hyperthermia].

PURPOSE

The increased dissemination of interstitial hyperthermia techniques requires suitable action in quality assurance for the used applicators. This work presents physical-technical methods for complete characterisation of interstitial and endocavitary coaxial antennas used for microwave hyperthermia.

METHODS

After a short introduction about the antennas' physical principle 2 fundamental experiments for acquisition of specific absorption rate (SAR) are described: There are the thermometric method, especially the power pulse technique, using a static solid state phantom and the direct measurement of the amplitude square of emitted electric field using miniaturized E-field probes in a fluid phantom. Principal problems occurring during E-field measurements in the near field zone of insulated antennas in media (phantom fluid) are discussed in detail.

RESULTS

Characteristic relative SAR profiles were found for each tested applicator design. The profiles were described using the following parameters: depths of SAR maximum, effective heating lengths and lengths of the dead end of the antennas relative to the 50%-iso-SAR-surface. Antenna designs for endocavitary and interstitial purposes were measured at variable insertion depths. The changing SAR-patterns were discussed regarding the found measurement data. Additionally measurements of parallel and inclined antenna arrays consisting of 4 interstitial applicators are described.

CONCLUSION

The final discussion give future perspectives to forthcoming developments for interstitial and endocavitary microwave hyperthermia.