Phased array for microwave hyperthermia: a preliminary study in a computational muscle phantom

Microwave hyperthermia, in conjunction with radio- or chemotherapy, has shown be beneficial in cancer treatment. An elevated temperature within a tumor, typically between 40-44/spl deg/C, exhibits a beneficial effect in terms of local control and survival of cancerous cells. Due to naturally occurring higher vascularization around tumors, local heating of the tumor aids in the tumor-suppressing drug uptake. Further, due to high water content tumors represent good targets for high microwave absorption. The frequency of operation should be low enough to allow for a sufficient penetration depth without compromising spatial resolution. The main challenge of hyperthermia systems is to focus the radiated energy on the embedded tumor without harmful effects to the surrounding healthy tissues. In this work, 915-MHz and 2450-MHz half-wavelength (/spl lambda//2) circular dipole arrays are numerically compared with regards to the point-wise specific absorption rate (SAR) calculated within a cylindrical muscle phantom irradiated by the antenna array. Results suggest how strategically chosen phase differences between elements of the antenna array allow for shifting of the heating focus.

I. NUMERICAL METHOD AND SIMULATION PARAMETERS

An eight-element circular annular phased array (APA) [3], consisting of either a 915-MHz and 2450-MHz half-wavelength dipole elements, is placed 1mm from a cylindrical phantom. The phantom was assigned electrical parameters equal to those of the muscle tissue. Antennas are distributed around the phantom to ensure equal distance between adjacent elements. Each antenna is fed with a , 100-V voltage source. The simulation tool used for this study was SEMCAD [4] (3-D solver, based on finite-difference time-domain (FDTD) method [5]). FDTD grid resolved the geometry to 0.25mm.