Effective thermal conductivity: will it permit quantitative hyperthermia treatment planning?

A program to quantify the effective thermal conductivity prior to hyperthermia treatment in order to estimate the required local distribution of specific absorption ratio (SAR) is described. A rational database is sought to relate the measured local SAR of specific applications to thermal dissipation, tumor depth, and tumor volume. Such data are fit to a quantitative model for treatment temperature as a function of SAR and effective thermal conductivity. Effective conductivity probes are placed using a hollow 18 gauge blunt-tipped needle system under X-ray guidance. Multiple sensors and/or pullback techniques measure the spatial variation in effective thermal conductivity. Initial experiments with a perfused dog kidney model show that a distinctive relationship exists between SAR, tissue effective thermal conductivity, and the resulting steady-state tissue temperature rise. These measurements, when combined with the SAR capabilities of the available heating devices, allow the proper choice of heating modality and applicator and indicate the likelihood of achieving therapeutic levels without unacceptable heating of adjacent tissue