The dielectric parameters of excised EMT-6 tumours and their change during hyperthermia

The electrical impedance from 100 Hz to 40 MHz of freshly excised EMT-6 tumours was measured periodically while the tumours were exposed to typical hyperthermia heating regimens. During hyperthermia, the EMT-6 tumour displays a characteristic response sequence which includes cellular swelling, progressive membrane damage, cellular shrinking and subsequent progressive histolysis. It was found that the changes in the tumour tissue dielectric properties reflected these hyperthermia-induced histological changes. In particular the parameters delta epsilon, sigma s and fc progressed to, reached, and retreated from extrema as the cells swelled to a maximum and then contracted. These parameters continued retreating beyond their original values as the beta-dispersion progressively collapsed during the period of progressive histolysis. The Cole-Cole parameter alpha increased during most of these histological changes, indicating a broadening of the dispersion, which suggests differential cell response during this period. Differences in the time-course between dielectric components may reflect the combined effects of cellular swelling and concurrent progressive membrane changes. Changes in rate and shape of the dielectric response with hyperthermia temperature are discussed in terms of possible cellular responses during hyperthermia.