UNEXPECTED PHYSICAL PHENOMENA INDICATED BY FDTD MODELING OF THE SIGMA-60 DEEP HYPERTHERMIA APPLICATOR

We investigate the numerical convergence properties of two-dimensional (2-D) and three-dimensional (3-D) finite-difference time-domain (FDTD ) models of the BSD-2000 Sigma-60 annular phased array used for deep h yperthermia. The FDTD modeling data indicate unexpected physical pheno mena for the case of Sigma-60 excitation of an elliptical tissue phant om embedded in a circular water bolus, These phenomena include: 1) hig h-Q energy storage; 2) electromagnetic (EM) mode flipping within the w ater bolus/phantom; and 3) whispering-gallery transmission of energy t o the opposite side of the phantom relative to the exciting dipole pai r, We conclude that these phenomena substantially impact the FDTD nume rical modeling of this system, and further conclude that the whisperin g-gallery effect can impact clinical applications of the Sigma-60.