An apparatus for inducing an alternating electric field in a target region in a subject's body, the apparatus comprising: a pulse generator configured to generate a series of pulses of alternating current between a first output terminal and a second output terminal, with an amplitude that depends on a state of at least one control input; and a controller configured to send signals to the at least one control input that cause the pulse generator to output pulses having a first amplitude between the first output terminal and the second output terminal during each of a plurality of first time intervals, wherein the controller is further configured to, during each of a plurality of second time intervals, each of which immediately follows a respective one of the plurality of first time intervals, either (i) send signals to the at least one control input that cause the pulse generator not to output pulses during each of the plurality of second time intervals or (ii) send signals to the at least one control input that cause the pulse generator to output pulses having a second amplitude between the first output terminal and the second output terminal during each of a plurality of second time intervals, wherein the second amplitude is less than half the first amplitude, wherein the controller is further configured to accept at least one first input signal from at least one first temperature sensor and to accept at least one second input signal from at least one second temperature sensor, wherein the plurality of first time intervals includes at least 10 first time intervals, wherein the plurality of second time intervals includes at least 10 second time intervals, wherein each of the plurality of first time intervals is at least one minute long, wherein each of the plurality of second time intervals is at least one minute long, and wherein each series of pulses includes at least 10 pulses. a pulse generator configured to generate a series of pulses of alternating current between a first output terminal and a second output terminal, with an amplitude that depends on a state of at least one control input; and a controller configured to send signals to the at least one control input that cause the pulse generator to output pulses having a first amplitude between the first output terminal and the second output terminal during each of a plurality of first time intervals, wherein the controller is further configured to, during each of a plurality of second time intervals, each of which immediately follows a respective one of the plurality of first time intervals, either (i) send signals to the at least one control input that cause the pulse generator not to output pulses during each of the plurality of second time intervals or (ii) send signals to the at least one control input that cause the pulse generator to output pulses having a second amplitude between the first output terminal and the second output terminal during each of a plurality of second time intervals, wherein the second amplitude is less than half the first amplitude, wherein the controller is further configured to accept at least one first input signal from at least one first temperature sensor and to accept at least one second input signal from at least one second temperature sensor, wherein the plurality of first time intervals includes at least 10 first time intervals, wherein the plurality of second time intervals includes at least 10 second time intervals, wherein each of the plurality of first time intervals is at least one minute long, wherein each of the plurality of second time intervals is at least one minute long, and wherein each series of pulses includes at least 10 pulses.