A 433 MHZ LUCITE CONE WAVE-GUIDE APPLICATOR FOR SUPERFICIAL HYPERTHERMIA

The effective held size (EFS, SAR > 50% of the maximum SAR at 1 cm dep th) of a conventional 433 MHz water filled waveguide applicator (32 cm (2), aperture area 100 cm(2)) has been increased by: (1) replacement o f the two diverging brass side walls which are parallel to the directi on of the electric field by Lucite walls; and (2) Placement of a heter ogeneous permittivity in the centre of the aperture. SAR distributions were measured at several depths in layered fat-muscle phantoms. With Lucite side walls the SAR distribution becomes wider in the H-plane of the aperture, resulting in a circular SAR distribution. In this situa tion the EFS is 67 cm(2). Additional insertion of a PVC cone with a to p angle of 15 degrees at the centre of the aperture increases the EFS to 91 +/- 6 cm(2) for a waterbolus of 18 x 18 x 1 cm(3). The experimen ts also demonstrated that the resulting EFS is affected by the waterbo lus size and shape. Calorimetric measurements showed that the efficien cy of the improved applicator is comparable to the efficiency of the c onventional water filled waveguide applicator, 50 and 56% respectively . The modifications reported provide a simple and inexpensive means to increase the EFS and can be easily implemented in water filled wavegu ide applicators.