The use of a current sheet applicator array for superficial hyperthermia: incoherent versus coherent operation

There are a number of potential advantages to be gained by using an array of applicators in hyperthermia treatments compared with single applicator systems. These advantages include the possibility of greater spatial control of power deposition and conformability to nonplanar sites. Arrays of applicators can be driven either coherently or incoherently. In the case of coherent operation, an added advantage is the ability to steer power deposition by varying the phases of the antennas. In this study, we investigated the relative merits of the two modes of operation when a 2 x 2 planar array of current sheet applicators is used. The effective field size (EFS) of the array was calculated using a Gaussian beam representation of the applicators on a layered model in which the fat layer had its thickness varied. Good agreement was obtained between the square of the electric field distribution (E2) and quantitative experimental results. It is shown that when the planar array is used with a fat layer greater than about 2 mm present, it should be driven incoherently as this results in a significantly larger EFS than that obtained when the array is driven coherently.