Fast Output Sampling Controller for Hyperthermia Systems

A tumor layer surrounded by muscle layer is modeled by bio heat transfer equation. A state space model to the bio heat transfer problem is obtained by a finite difference method. This model is reduced to a lower order model. A fast output sampling feedback controller is designed for controlling the temperature profile in hyperthermia cancer treatments. The performance evaluation for the controller is done using simulations with a one dimensional layered models of the tumor, which is heated by a single scanned focused ultrasound transducer. The performance criterion in terms of time domain specifications for the controller has been framed and the performance analysis is carried out for varying blood perfusion rate. The Fast output sampling controller is capable of giving desired closed loop behavior and closed loop stability. Linear Matrix Inequality optimization is used to reduce the magnitude of the control effort needed to control the temperature in tissue.

I Introduction

HYPERTHERMIA, the heating of cancerous tumors, can improve complete response rates when added as an adjuvant to radiation therapy. [1] The microwave, the ultrasound and the laser are the popular sources used to deposit spatial heating for treating the tumor in the deep biological body. Temperature feedback control has the potential to enhance hyperthermia treatments by providing more uniform heating of the target volume and improving the response time to reach therapeutic temperatures.