Absorbed power distributions from two tilted waveguide applicators.

One major problem in microwave-induced clinical hyperthermia treatment of superficial tumours is to obtain therapeutic temperatures at the tumour periphery and adequate deep heating when using a single applicator. The use of multiple applicators has therefore been investigated in order to improve the power distribution. Anatomical surface topography often permits the application of two tilted applicators, e.g. in the head and neck area, on extremities and on large protruding tumours. Theoretical calculations of the absorbed power distribution from such an applicator configuration were performed in a homogeneous muscle equivalent medium. The power distribution from two conventional radiative apertures (TE10) was studied at different frequencies, aperture sizes, tilting angles and non-coherent or coherent fields in phase, both theoretically and with phantom experiments using a thermographic camera. With controlled phase relations between two tilted applicators excited at the lower microwave or upper radiofrequency band, the absorbed power distribution can be varied in a wide range. The theoretical calculations and thermographic phantom experiments in simple geometries give valuable information on absorbed power distributions and guidance for the location of temperature probes in clinical hyperthermia.