An apparatus for applying an alternating electric field to a subject's body, the apparatus comprising: a plurality of sets of at least two electrode elements (52, 52'); a support configured to hold the sets of electrode elements (52, 52') so that the electrode elements (52, 52') can be positioned in contact with the subject's body; a plurality of temperature sensors, wherein each of the sets of electrode elements (52, 52') has a single temperature sensor positioned to sense a temperature at the respective one of the sets of electrode elements (52, 52') and generate a respective signal indicative of the sensed temperature; an electrical conductor; a plurality of electrically-controlled switches (56, 56'), wherein each of the switches (56, 56') is configured, depending on a state of a respective control input, either to allow current to flow between the electrical conductor and respective ones of the electrode elements (52, 52') in each of the sets of electrode elements (52, 52') or prevent current from flowing between the electrical conductor and the respective ones of the electrode elements (52, 52') in each of the sets of electrode elements (52, 52'); and a controller configured to control the state of the control input of each of the switches (56, 56') in each of the sets of electrode elements (52, 52') based on the signal indicative of the sensed temperature generated by the respective temperature sensor in the respective set of electrode elements (52, 52'); wherein the electrode elements (52, 52') within each of the sets of electrode elements (52, 52') are arranged (i) concentrically, with the respective temperature sensor at the inner electrode element, or (ii) radially next to each other in the form of slices of a pie, with the respective temperature sensor at the center of the electrode elements (52, 52'). a plurality of sets of at least two electrode elements (52, 52'); a support configured to hold the sets of electrode elements (52, 52') so that the electrode elements (52, 52') can be positioned in contact with the subject's body; a plurality of temperature sensors, wherein each of the sets of electrode elements (52, 52') has a single temperature sensor positioned to sense a temperature at the respective one of the sets of electrode elements (52, 52') and generate a respective signal indicative of the sensed temperature; an electrical conductor; a plurality of electrically-controlled switches (56, 56'), wherein each of the switches (56, 56') is configured, depending on a state of a respective control input, either to allow current to flow between the electrical conductor and respective ones of the electrode elements (52, 52') in each of the sets of electrode elements (52, 52') or prevent current from flowing between the electrical conductor and the respective ones of the electrode elements (52, 52') in each of the sets of electrode elements (52, 52'); and a controller configured to control the state of the control input of each of the switches (56, 56') in each of the sets of electrode elements (52, 52') based on the signal indicative of the sensed temperature generated by the respective temperature sensor in the respective set of electrode elements (52, 52'); wherein the electrode elements (52, 52') within each of the sets of electrode elements (52, 52') are arranged (i) concentrically, with the respective temperature sensor at the inner electrode element, or (ii) radially next to each other in the form of slices of a pie, with the respective temperature sensor at the center of the electrode elements (52, 52').