University of Southern California The USC Andrew and Erna Viterbi School of Engineering Microwave Systems, Sensors and Imaging Lab

Synergistic microwave and ultrasound cancer treatment systems.

Thermal therapies - particularly the use of thermal ablation (including microwave, RF, cryoablation, and high-intensity-focused ultrasound), hyperthermia, and heat activated drug delivery in the treatment of cancer have been the focus of increasing laboratory and clinical research. In the various ablation methods, either significantly elevated temperatures (typically above 50 ◦ C) generated by electromagnetic waves or ultrasound, or freezing temperatures generated by cryogens are used to cause very rapid and localized tissue destruction. In the case of hyperthermia, moderately elevated temperatures (typically between 40 ◦ C and 45 ◦ C) have been shown to achieve cytotoxic effects that render cancer cells more vulnerable to radiotherapy and chemotherapy, as well as inducing both apoptotic and necrotic cell death given a sufficient thermal dose. Motivated by this knowledge, researchers have developed microwave systems capable of inducing localized hyperthermia as an adjuvant cancer treatment modality.

With these potential applications in mind, a pre-clinical prototype of a non invasive thermal therapy system has been developed by researchers within MiXIL for the targeted treatment of breast cancer cells using focused microwaves. In the system, an array of antennas operating at 915 MHz is used to focus continuous-wave microwave energy transcutaneously into the pendent breast suspended in a coupling medium (shown in Fig. 1). Prior imaging studies are used to ascertain the material properties of the breast tissue, and these data are incorporated into a multiphysics model. Time-reversal techniques are then employed to find a solution (relative amplitudes and phase) for focusing at a given location, resulting in maximal thermal dose at the tumor location. Using this system, focal spot sizes in the array plane of approximately 1.5 cm in diameter have been achieved and significant differential heating in the target region has been observed in focused heating tests within tissue-mimicking gelatin phantoms.

Based on these results, the system has the potential to offer improved targeting and delivery of focused heating over current microwave thermal therapy systems, without the need for invasive probes.

Two-dimensional microwave thermal therapy system prototype

Two-dimensional microwave thermal therapy system prototype. (a) Signal generator, (b) 12-channel electronic phase control, (c) 10-W per channel amplifiers (120 W total), and (d) 12-element therapy array.