Effects of External Temperature on Therapeutic Heating with Interstitial Instrumentation

Use of interstitial instrumentation for therapeutic heating is often compromised by uncontrollable thermal washout caused by stochastically distributed heat sinks. The heat sinks effects may be mitigated by, among others, control of the external temperature during the heating. For these procedures temporal characterization becomes crucial. We propose transient FEA simulations as a reliable method of modeling the temporal behavior at different external temperatures. Heating curves obtained in measurements of ultrasonic heating in a brain phantom are modeled using the simulations. On achieving good agreement between the simulation and experimental results, we proceeded with the simulation of heating in a complex head model. Heating efficacy is described in terms of extent and volume of thermal dose. The extent and the volume increased by 40 to 100% for the temperatures of 18 to 470C. We found that there is monotonic but nonlinear dependence between the extent and the volume of the thermal dose on external temperature