A method of controlling electric fields created by a plurality of electrodes. The method includes repetitively applying multiple sets of voltages to at least some of a plurality of electrodes over a treatment period to achieve and maintain a target temperature, the at least some of the electrodes being treatment electrodes. The sets of voltages may be in patterns such that a unique current pattern between electrodes is created for each set of voltages, resulting in temperature averaging. The voltage at each electrode may be determined based on a temperature of an adjacent electrode. The voltage at each electrode may also or alternatively be determined based on an estimated voltage at the electrode.
