By a proper design, leaky-wave applicators allow a simple ap- proximation of the field in the medium under treatment by means of a single inhomogeneous plane-wave. The aim of this Communication is to investi- gate the effectiveness of such an approximation when it is used for the eval- uation of the thermal pattern inside the medium under treatment. In par- ticular, the thermal pattern acquired by a thermocamera is compared with numerical simulations of the thermal distribution inside a muscle phantom tissue radiated by a channel guide leaky-wave applicator. The results con- firm that the single pole-wave approximation gives a correct prediction of the temperature distribution inside the medium under treatment.