An apparatus for treating a target region in a joint of an elbow of an arm or a knee of a leg of a subject's body with TTFields, the apparatus comprising: a first set of one or more capacitively-coupled electrodes (60; 60'); a first substrate (62; 62') configured to hold the first set of one or more electrodes (60; 60') against the subject's body so that the first set of one or more electrodes (60; 60') partially surrounds a first side of the arm or leg at a position that is proximal to the target region; a second set of one or more capacitively-coupled electrodes (60; 60'); a second substrate (62; 62') configured to hold the second set of one or more electrodes (60; 60') against the subject's body so that the second set of one or more electrodes (60; 60') partially surrounds a second side of the arm or leg at a position that is distal to the target region, wherein the second side of the arm or leg is opposite to the first side of the arm or leg; a third set of one or more capacitively-coupled electrodes (60; 60'); a third substrate (62; 62') configured to hold the third set of one or more electrodes (60; 60') against the subject's body so that the third set of one or more electrodes (60; 60') partially surrounds the second side of the arm or leg at a position that is proximal to the target region; a fourth set of one or more capacitively-coupled electrodes (60; 60'); a fourth substrate (62; 62') configured to hold the fourth set of one or more electrodes (60; 60') against the subject's body so that the fourth set of one or more electrodes (60; 60') partially surrounds the first side of the arm or leg at a position that is distal to the target region; and an AC voltage generator configured to generate, in a repeating and alternating sequence, a first AC voltage with a frequency of 100-500 kHz between the first set of one or more electrodes (60; 60') and the second set of one or more electrodes (60; 60'), and a second AC voltage with a frequency of 100-500 kHz between the third set of one or more electrodes (60; 60') and the fourth set of one or more electrodes (60; 60'); wherein the configuration of the first, second, third and fourth sets of one or more electrodes (60; 60') results in two electric fields that form an X-shape through the target region. a first set of one or more capacitively-coupled electrodes (60; 60'); a first substrate (62; 62') configured to hold the first set of one or more electrodes (60; 60') against the subject's body so that the first set of one or more electrodes (60; 60') partially surrounds a first side of the arm or leg at a position that is proximal to the target region; a second set of one or more capacitively-coupled electrodes (60; 60'); a second substrate (62; 62') configured to hold the second set of one or more electrodes (60; 60') against the subject's body so that the second set of one or more electrodes (60; 60') partially surrounds a second side of the arm or leg at a position that is distal to the target region, wherein the second side of the arm or leg is opposite to the first side of the arm or leg; a third set of one or more capacitively-coupled electrodes (60; 60'); a third substrate (62; 62') configured to hold the third set of one or more electrodes (60; 60') against the subject's body so that the third set of one or more electrodes (60; 60') partially surrounds the second side of the arm or leg at a position that is proximal to the target region; a fourth set of one or more capacitively-coupled electrodes (60; 60'); a fourth substrate (62; 62') configured to hold the fourth set of one or more electrodes (60; 60') against the subject's body so that the fourth set of one or more electrodes (60; 60') partially surrounds the first side of the arm or leg at a position that is distal to the target region; and an AC voltage generator configured to generate, in a repeating and alternating sequence, a first AC voltage with a frequency of 100-500 kHz between the first set of one or more electrodes (60; 60') and the second set of one or more electrodes (60; 60'), and a second AC voltage with a frequency of 100-500 kHz between the third set of one or more electrodes (60; 60') and the fourth set of one or more electrodes (60; 60'); wherein the configuration of the first, second, third and fourth sets of one or more electrodes (60; 60') results in two electric fields that form an X-shape through the target region.