Array for delivering tumor treatment fields (ttfields) with a set of electrode elements having individually adjustable active areas

Abstract

To provide an array for delivering a tumor treatment electric field with a set of electrode elements having individually adjustable active areas.SOLUTION: Tumor treatment fields (TTFields) can be delivered to a subject's body using electrode elements arranged in sets, each set including a respective first electrode element and a respective second electrode element arranged in thermal contact with one another. A separate first conductor provides a conductive path between each first electrode element and a respective pin of the connector. The second conductor provides a conductive path between all of the second electrode elements and another pin of the connector. A temperature sensor is disposed in thermal contact with each set of electrode elements. Because the electrode elements are arranged in sets, the current flowing through any given set can be reduced (relative to its maximum value) by turning off the first electrode element in the given set to prevent the region corresponding to the given set from overheating.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 150,425, filed February 17, 2021, which is incorporated herein by reference in its entirety. [Background technology]

[0002] TTFields therapy is a proven approach for treating tumors. Figure 1 shows a schematic diagram of a prior art Optune® system for delivering TTFields. TTFields are delivered to a patient via four transducer arrays 21-24 placed on the patient's skin in close proximity to the tumor (e.g., as shown in Figures 2A-2D for an individual with glioblastoma). The transducer arrays 21-24 are arranged in two pairs, with each transducer array connected to an AC signal generator 20 via a multi-wire cable. The AC signal generator (a) transmits an AC current through one pair of arrays 21, 22 during a first period, inducing an electric field with a first direction through the tumor, and then (b) transmits an AC current through the other pair of arrays 23, 24 during a second period, inducing an electric field with a second direction through the tumor, and then repeats steps (a) and (b) for the duration of the treatment.

[0003] Each transducer array 21-24 is configured as a set of capacitively coupled electrode elements E (e.g., a set of nine electrode elements, each approximately 2 cm in diameter) interconnected via a flex circuit. Each electrode element includes a conductive substrate with a dielectric layer (more specifically, a layer of ceramic material with a high dielectric constant) disposed thereon. Each electrode element is sandwiched between a layer of conductive medical gel and adhesive tape. When the array is placed on a patient, the medical gel conforms to the contours of the patient's skin, ensuring good electrical contact of the device with the body. The adhesive tape holds the entire array in place on the patient as they go about their normal daily activities.

[0004] The amplitude of the alternating current delivered through the transducer array is controlled so that the skin temperature (as measured on the skin beneath the transducer array) does not exceed a safety threshold of 41°C. Temperature measurements on the patient's skin are obtained using thermistors T placed under some of the disks of the transducer array. In existing Optune® systems, each array contains eight thermistors, one thermistor positioned under each disk of the array (note that most arrays contain nine or more disks, in which case temperature measurements are only taken under a subset of the disks in the array).

[0005] The AC signal generator 20 obtains temperature measurements from all 32 thermistors (4 arrays x 8 thermistors per array), and a controller within the AC signal generator uses the temperature measurements to control the current delivered through each pair of arrays to maintain a temperature below 41°C on the patient's skin. The current itself is delivered to each array via additional wires (i.e., one wire 28 for each array 21-24) that run from the AC signal generator 20 to each array. The additional wires (not shown) for each array 21-24 are used as common returns for all eight thermistors. Thus, each of the four cables terminating on arrays 21-24 in the existing Optune system have a total of 10 conductors. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2018 / 0050200 Summary of the Invention [Means for solving the problem]

[0007] One aspect of the present invention is directed to a first device for applying an alternating current electric field to a subject's body. The first device includes at least four sets of electrode elements, a connector, at least four first conductors, a second conductor, at least four temperature sensors, and a support configured to hold the set of electrode elements against the subject's body. Each set of electrode elements includes a respective first electrode element and a respective second electrode element disposed in thermal contact with the respective first electrode element. The connector has at least four first pins and a second pin. Each of the at least four first conductors provides a conductive path between (a) a respective one of the first pins and (b) a respective one of the first electrode elements. The second conductor provides a conductive path between all of the second pins and the second electrode elements, and each of the at least four temperature sensors is disposed in thermal contact with a respective one of the set of electrode elements.

[0008] In some embodiments of the first device, within each set of electrode elements, the area of ​​each second electrode element is at least twice the area of ​​each first electrode element.

[0009] In some embodiments of the first device, the device has at least nine sets of electrode elements, the connector has at least nine first pins, the device has at least nine first conductors, and the device has at least nine temperature sensors.

[0010] In some embodiments of the first device, each temperature sensor comprises a thermistor having a first terminal and a second terminal, the connector has a third pin, and each first conductor provides a conductive path between (a) a respective one of the first pins, (b) a respective one of the first electrode elements, and (c) the first terminal of the respective thermistor. In these embodiments, the device further comprises a third conductor providing a conductive path between the third pin and at least one second terminal of the thermistor. Optionally, in these embodiments, the second terminals of all of the thermistors are wired together.

[0011] In some embodiments of the first device, each temperature sensor comprises a thermistor having a first terminal and a second terminal, the connector has a third pin, and each first conductor provides a conductive path between (a) a respective one of the first pins, (b) a respective one of the first electrode elements, and (c) the first terminal of the respective thermistor. In these embodiments, the device further comprises a third conductor providing a conductive path between the third pin and at least one second terminal of the thermistor. In these embodiments, the thermistors are wired in series, starting with the first thermistor and ending with the last thermistor. The second terminal of each thermistor except the last thermistor is wired to the first terminal of each subsequent thermistor, and the third conductor provides a conductive path between the third pin of the connector and the second terminal of the last thermistor.

[0012] In some embodiments of the first device, each temperature sensor comprises a region of pyroelectric material.

[0013] In some embodiments of the first device, each first electrode element comprises a conductive plate with a dielectric layer disposed thereon, each second electrode element comprises a conductive plate with a dielectric layer disposed thereon, and the support is configured to hold the first electrode element and the second electrode element against the subject's body such that the dielectric layer of the first electrode element and the dielectric layer of the second electrode element face the subject's body.

[0014] Another aspect of the present invention is directed to a second device for applying an AC electric field to a subject's body using at least four sets of electrode elements, each set of electrode elements including a respective first electrode element and a respective second electrode element disposed in thermal contact with the respective first electrode element, and each set of electrode elements disposed in thermal contact with a respective temperature sensor. The second device includes an AC signal generator for generating an AC output signal. The second device also includes a connector including at least four first and second pins, each first pin corresponding to a respective one of the first electrode elements, and the AC output signal being applied to the second pin. The second device also includes at least four first switches, each configured to selectively apply or not apply the AC output signal to a respective one of the first pins depending on the state of at least one control signal. The second device also includes an amplifier configured to receive input from each temperature sensor and generate a corresponding output. The second device also includes a controller configured to set at least one control signal to a state that determines whether an AC output signal is applied or not applied to each first pin based on the output of the amplifier.

[0015] In some embodiments of the second device, the controller is configured to (a) determine, based on the output of the amplifier, when at least one of the first electrode elements is hotter than the other first electrode elements, and (b) set at least one control signal to a state that controls the first switch such that no AC signal is applied to at least one respective first pin.

[0016] In some embodiments of the second device, the controller is configured to (a) determine, based on the output of the amplifier, when at least one of the first electrode elements is hotter than a threshold level, and (b) set at least one control signal to a state that controls the first switch such that no AC signal is applied to at least one respective first pin.

[0017] In some embodiments of the second device, the input from the temperature sensor arrives via the same first pin that corresponds to the first electrode element.

[0018] Another aspect of the invention is directed to a first method for applying an alternating current electric field to a body of a subject. The first method includes positioning at least four sets of electrode elements on or within the body of the subject, each set of electrode elements having an adjustable active area. The first method also includes exciting each of the sets of electrode elements using its entire active area, measuring the temperature of each of the sets of electrode elements, and reducing the active area of ​​at least one of the sets of electrode elements based on a corresponding one of the temperature measurements.

[0019] In some examples of the first method, the active area of ​​a given set of electrode elements is reduced if the electrode elements of the given set are hotter than the electrode elements of other sets. In some examples of the first method, the active area of ​​a given set of electrode elements is reduced if the electrode elements of the given set are hotter than a threshold level.

[0020] Another aspect of the present invention is directed to a second method for applying an alternating current electric field to a subject's body. The second method includes positioning at least four sets of electrode elements on or within the subject's body, each set of electrode elements having an adjustable active area. The second method also includes exciting each of the sets of electrode elements using its entire active area, measuring the temperature of each of the sets of electrode elements, and reducing the active area of ​​at least one of the sets of electrode elements based on a corresponding one of the temperature measurements. The positioning step includes positioning at least four first electrode elements on or within the subject's body and at least four second electrode elements on or within the subject's body. Each first electrode element is wired so that it can be excited independently of the other first electrode elements. Each second electrode element is positioned adjacent to and in thermal contact with a respective one of the first electrode elements. The second electrode elements are wired together such that either all of the second electrode elements must be collectively energized or may not be collectively energized. The energizing step includes energizing all of the first electrode elements and the second electrode elements. The active area reduction includes de-energizing selected ones of the first electrode elements based on the respective temperature measurements.

[0021] In some examples of the second method, de-energizing a given first electrode element occurs when the given first electrode element is hotter than other first electrode elements.

[0022] In some examples of the second method, de-energizing a given first electrode element occurs when the given first electrode element is hotter than a threshold level. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic diagram of a prior art Optune® system for delivering TTFields. [Figure 2A]FIG. 1 illustrates the positioning of a transducer array on a person's head to treat a brain tumor. [Figure 2B] FIG. 1 illustrates the positioning of a transducer array on a person's head to treat a brain tumor. [Figure 2C] FIG. 1 illustrates the positioning of a transducer array on a person's head to treat a brain tumor. [Figure 2D] FIG. 1 illustrates the positioning of a transducer array on a person's head to treat a brain tumor. [Figure 3] Schematic representation of the transducer array used to apply TTFields to a subject's body. [Figure 4A] 1A-1C illustrate different approaches for positioning a temperature sensor in thermal contact with an electrode element in a transducer array. [Figure 4B] 1A-1C illustrate different approaches for positioning a temperature sensor in thermal contact with an electrode element in a transducer array. [Figure 4C] 1A-1C illustrate different approaches for positioning a temperature sensor in thermal contact with an electrode element in a transducer array. [Figure 5] FIG. 1 illustrates a transducer array with individual control over the current passing through nine different regions of the transducer array. [Figure 6] FIG. 6 is a block diagram of a system using four copies of the transducer array of FIG. 5 to apply TTFields to a subject. [Figure 7] FIG. 10 illustrates another transducer array that provides individual control of the current passing through nine different regions of the transducer array. [Figure 8] FIG. 8 is a block diagram of a system using four copies of the transducer array of FIG. 7 to apply TTFields to a subject. [Figure 9] 9 is a schematic diagram of a circuit suitable for implementing each switch within banks 1L and 1R in the embodiments of FIGS. 6 and 8. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0024] Various embodiments are described in detail below with reference to the accompanying drawings, wherein like reference numerals refer to like elements, and wherein:

[0025] While the approach described above in Figure 1 is highly effective for delivering TTFields to tumors, the effectiveness of the treatment is reduced if good electrical contact is not maintained between each element in the four transducer arrays 21-24 and the human body. This may occur, for example, if the hydrogel underneath one or more elements of the transducer array dries out over time or due to hair growth underneath one or more of the elements.

[0026] For example, assume there are nine electrode elements E in each transducer array 21-24, and the hydrogel under a single electrode element E on the front transducer array 21 dries, and sufficient hydrogel is present under (a) all other electrode elements E on that transducer array 21 and (b) all electrode elements E on the other transducer arrays 22-24. In this situation, the resistance between the single electrode element E and the person's body is higher than the resistance between any of the other electrode elements and the person's body. This increase in resistance causes the temperature of the single electrode element E to rise more than the other electrode elements.

[0027] In this situation, because all of the electrode elements E in each transducer array 21-24 are wired in parallel, the AC signal generator 20 must limit the current applied across the anterior / posterior pair of transducer arrays 21, 22 to keep the temperature of a single electrode element E on the anterior array 21 below 41° C., even though the temperatures of all of the remaining electrode elements E on the anterior and posterior transducer arrays 21, 22 may be below 41° C. Such a reduction in current may cause a corresponding reduction in the strength of the electric field at the tumor, potentially reducing the efficacy of the treatment.

[0028] One possible approach to address this situation is to wire a separate conductor to each of the nine electrode elements (as opposed to the prior art approach of wiring all of the electrode elements together in parallel). If this approach is implemented, it would be possible to switch off the AC signal to any electrode element that is overheating without switching off the AC signal to other electrode elements on the same array. This approach is referred to herein as the "individually addressable electrode approach."

[0029] However, completely switching off electrode elements using the individually addressable electrode approach can increase the current passing through the remaining electrode elements, increasing their temperature. In addition, completely switching off electrode elements can have adverse effects on the distribution of the electric field within the subject's body. Furthermore, the inventors have determined that in most situations, a current reduction of less than 20% will prevent any given electrode element from overheating. As a result, completely switching off electrode elements using the individually addressable electrode approach may be considered overkill. The embodiments described below alleviate or minimize the problems identified in this paragraph by replacing each prior art electrode element with a set of electrode elements.

[0030] FIG. 3 is a schematic diagram of a transducer array 50 including nine sets of electrode elements 52 / 53 used to apply TTFields to a subject's body. Each set includes a first electrode element 52 and a second electrode element 53 arranged in thermal contact with each other. The entire array 50 includes at least four sets of first and second electrode elements 52 / 53 (e.g., nine sets 52 / 53 in the embodiment illustrated in FIG. 3, or another number between 4 and 50). A separate first conductor is wired to each first electrode element 52, allowing the AC signal to any given one of the first electrode elements 52 to be switched on or off independently. However, all of the second electrode elements 53 are wired in parallel to the second conductor, meaning that as soon as an AC signal is applied to the second conductor, the AC signal reaches all of the second electrode elements 53.

[0031] In some preferred embodiments, the second electrode elements 53 in any given set are at least twice the area of ​​their respective first electrode elements 51. For purposes of discussion, assume that within any given set of electrode elements 52 / 53, 70% of the total area is occupied by the second electrode elements 53 and 30% of the total area is occupied by the first electrode elements 52. When delivering TTFields, the current passing through the electrode elements 52 / 53 of any given set is related to the active area of ​​that set. As a result, when a given AC voltage is applied to both the first electrode element 52 and the second electrode element 53, a full measure of current (i.e., 100%) passes through the set 52 / 53. However, if the same AC voltage is applied only to the second electrode element 53 and not to the first electrode element 52, the current passing through the entire set 52 / 53 drops from 100% to a lower level (e.g., 80%).

[0032] Assume that an AC voltage is applied to the second electrode element 53 via the second conductor during a time interval (e.g., a 1 second time interval). Further assume that during this same time interval, the same AC voltage is applied (via the corresponding first conductor) to a first electrode element 52 in the set of electrode elements 52 / 53 labeled X, but no AC voltage is applied to a first electrode element 52 in the set of electrode elements 52 / 53 labeled Z. In this situation, because current is related to the active area, a full measure of current (i.e., 100%) passes through the set 52 / 53 labeled X, while a lower current passes through the second set 52 / 53 labeled Z.

[0033] The first and second electrode elements 52 and 53 in any given set 52 / 53 are shaped and positioned to be in thermal contact with one another (i.e., so that heating the first electrode element 52 causes heating of the second electrode element 53, and vice versa). Note that the thermal contact between the first and second electrode elements 52 and 53 may be indirect thermal contact with intervening components disposed between the first and second electrode elements 52 and 53. One preferred approach to achieving thermal contact between the first and second electrode elements 52, 53 in any given set is to shape these electrode elements 52, 53 as alternating spirals (not shown) or as alternating square spirals (as shown in FIG. 3). In alternative embodiments, different alternating patterns (e.g., alternating stripes or alternating comb patterns) may be used. In this regard, interleaving the first and second electrode elements 52, 53 improves the thermal contact between the first and second electrode elements 52, 53, minimizing temperature variations between these elements.

[0034] A temperature sensor is disposed in thermal contact with each set of electrode elements 52 / 53 (here again, the thermal contact may be indirect). The number of temperature sensors preferably matches the number of sets of electrode elements. For example, if four sets of electrode elements 52 / 53 are used, there will be four temperature sensors. In some embodiments, thermistors are used as temperature sensors.

[0035] FIG. 4A illustrates a first approach for positioning a temperature sensor (e.g., a thermistor 54) in thermal contact with the first and second electrode elements 52, 53. In this approach, the thermistor 54 is positioned in the open space between the first and second electrode elements 52, 53 in each set 52 / 53 such that the thermistor 54 is disposed in thermal contact with both the first and second electrode elements 52, 53. FIG. 4B illustrates a second approach for positioning the temperature sensor. In this approach, the first and second electrode elements 52, 53 occupy substantially the entire area of ​​the set 52 / 53, and the thermistor 54 is positioned on the back side of the set 52 / 53 such that the thermistor 54 is disposed in thermal contact with both the first and second electrode elements 52, 53. This approach is particularly well suited when the first and second electrode elements 52, 53 are implemented using respective wiring of a flex circuit. Two approaches for using a set of thermistors as temperature sensors are described below with respect to FIGS.

[0036] 4C shows a third approach for positioning the temperature sensor. In this approach, the first and second electrode elements 52, 53 occupy substantially the entire area of ​​the set 52 / 53, and temperature sensing is performed by positioning an area of ​​pyroelectric material (not shown) in thermal contact behind both the first and second electrode elements 52, 53. This approach is also particularly well suited when the first and second electrode elements 52, 53 are implemented using respective traces of a flex circuit. A description of how the area of ​​pyroelectric material is used to sense temperature is provided below.

[0037] The embodiments described herein advantageously provide the ability to reduce the current flowing through a given region of the transducer array 50 without completely blocking the current flowing through that region.

[0038] One approach to controlling the current passing through each region of the transducer array is to (1) start with the prior art configuration shown in FIG. 1, (2) reconfigure each electrode element E to resemble the shape of the second electrode element 53 shown in FIG. 3, (3) add nine additional electrode elements shaped like the first electrode element 52 shown in FIG. 3 and alternating with the original electrode element E, and (4) add additional conductors running to each new electrode element so that the new electrode elements can be excited individually. While this approach is feasible, it requires nearly doubling the number of conductors in each cable running to the transducer array. For example, a transducer array with nine controllable regions would require a total of 20 wires in each cable (i.e., one to provide common access to all of the original electrode elements, nine to provide individual access to each of the nine new electrode elements, an additional nine for the signal from the thermistor, plus one additional wire to serve as a common return for all nine thermistors). Such a significant increase in the number of wires in each cable tends to make the cables inflexible and more cumbersome, making the system more difficult to use and potentially reducing patient compliance.

[0039] The embodiments described below advantageously provide the ability to control the current sent through individual regions of the transducer array 50 without unduly increasing the number of conductors in the cables that terminate on the transducer array. These embodiments can be used to implement systems that distribute the functions of outputting current (to generate TTFields) and taking temperature readings into mutually exclusive time slots or stages. In these systems, because the temperature readings are not taken at exactly the same instant while the transducer array is outputting current, the same set of conductors can be used to output current and input temperature readings. This advantageously reduces the total number of conductors that must be included in each cable.

[0040] One suitable approach for distributing the functions of outputting current and obtaining temperature readings into mutually exclusive time slots or phases is to (i) output current for a time interval (e.g., 1 second), then turn off the current, then (ii) spend a short period (e.g., 10 milliseconds) obtaining a temperature reading, and then repeat these two steps (i) and (ii) in a recurring alternating order (e.g., 12-18 hours daily). The operation of the system during each of these phases (i.e., the power output phase and the temperature reading phase) is described below for various embodiments.

[0041] 5 is a schematic diagram of a first embodiment of a transducer array 50 that provides individual control over the current passing through nine different regions of the transducer array 50 during the current output stage. As described below in connection with FIG. 6, four copies of the transducer array 50 are preferably used to administer TTFields therapy to a person's head (or other body part).

[0042] Each transducer array 50 includes at least four sets of electrode elements 52 / 53. Each set 52 / 53 includes a respective first electrode element 52 and a respective second electrode element 53 arranged in thermal contact with one another. For ease of reference to the embodiment of FIG. 5, the first electrode elements 52 are labeled E1-E9, and the second electrode elements 53 are labeled A1-A9. The shape and positioning of the first and second electrode elements 52, 53 relative to one another are as described above in connection with FIGS. 3-4 (note that the shape and positioning are not shown in FIG. 5 to facilitate viewing the electrical interactions between the various components). The electrode elements 52 / 53 of each set are positioned in different regions of the transducer array 50, and the first and second electrode elements 52, 53 within any given set are positioned in thermal contact with one another.

[0043] The first and second electrode elements 52, 53 each have a conductive substrate with a dielectric layer disposed thereon. The conductive substrate may be implemented using a thin layer of metal. The dielectric layer may be implemented using a layer of a ceramic material or polymer with a high dielectric constant (e.g., at least 20).

[0044] In the embodiment shown in FIG. 5 , all of the first and second electrode elements 52, 53 are held in place by a support structure 59. The support structure is configured to hold the electrode elements against the subject's body so that the dielectric layers of the first and second electrode elements 52, 53 face the subject's body and can be positioned in contact with the body. Optionally, the support structure may include a flexible backing 59 (e.g., a layer of foam material). A layer of hydrogel is preferably disposed between the dielectric layers of the first and second electrode elements 52, 53 and the subject's body when the transducer array 50 is placed against the subject's body. Construction of the support structure 59 may be implemented using any of a variety of conventional approaches, including, but not limited to, a self-adhesive fabric, foam, or plastic sheeting, as will be apparent to those skilled in the art.

[0045] Each transducer array 50 also has a connector 57 used to transmit electrical signals into and out of the transducer array 50. The connector 57 has at least four first pins and second pins. In the illustrated embodiment, the number of first pins is the same as the number of first electrode elements 52, and each first pin corresponds to a respective one of these first electrode elements 52. In the illustrated embodiment, there is only a single second pin, labeled A. It should be noted that, as used herein, the term "pin" can refer to either a male or female pin of the connector 57.

[0046] Each first electrode element 52 (labeled E1-E9) is wired to a respective first pin of connector 57 via a respective individual first conductor. More specifically, each first conductor provides a conductive path between (a) a respective one of the first pins in connector 57 and (b) the conductive substrate of a respective one of first electrode elements 52 (E1-E9). These first conductors are numbered 1-9 immediately above "wire routing" block 55 (which routes the individual conductors together in a single cable 56). In some preferred embodiments, the electrical connection to each first electrode element 52 comprises one or more traces on the flex circuit and / or one or more conductive wires.

[0047] Because connector 57 has a respective first pin corresponding to each respective first electrode element 52, and a conductive path exists between each first pin and a respective one of the first electrode elements 52, a system mated with connector 57 can selectively excite or not excite each first electrode element 52 individually by applying or not applying an AC signal to the respective first pin on connector 57. In contrast, all of the second electrode elements 53 (labeled A1 through A9) are connected via conductive paths (e.g., wired together in series or parallel) to the node labeled "A," which in turn terminates on the second pin of connector 57. As a result, a system mated with connector 57 must selectively excite or not excite all of the second electrode elements 53 by applying or not applying an AC signal to the second pin on connector 57.

[0048] Thus, when a system mating with connector 57 applies an AC signal to the second pin on connector 57, any given individual region of transducer array 50 will either (a) pass a full level of current (i.e., when each first electrode element 52 is energized), or (b) pass a lower level of current (i.e., when each first electrode element 52 is not energized). This advantageously provides the ability to reduce the current flowing through a given region of transducer array 50 without completely blocking the current flowing through that region.

[0049] Operation of the embodiment of FIG. 5 during the temperature reading phase will now be discussed. Each transducer array 50 also includes at least four temperature sensors, each positioned in thermal contact with a respective one of the electrode elements 52 / 53 of the set. In the embodiment illustrated in FIG. 5, the temperature sensors are implemented using thermistors 54, one thermistor positioned for each set 52 / 53 so that the thermistor 54 can sense the temperature of the first and second electrode elements 52, 53 in that set. This may be achieved, for example, using any of the approaches described above with respect to FIGS. 4A-4B. Each thermistor 54 has a first terminal (i.e., the lower terminal of the thermistor in FIG. 5) and a second terminal (i.e., the upper terminal of the thermistor in FIG. 5).

[0050] In this embodiment, each first conductor provides a conductive path between (a) a respective one of the first pins in connector 57, (b) a conductive substrate of a respective one of first electrode elements 52 (E1-E9), and (c) a first terminal of a corresponding thermistor 54.

[0051] In the thermistor-based embodiment of FIG. 5 , each transducer array 50 has a third conductor that provides a conductive path between a third pin of connector 57 (labeled C in FIG. 5 ) and at least one second terminal (i.e., the upper terminal in FIG. 5 ) of the thermistor 54. In the embodiment shown in FIG. 5 , all of the second terminals of the thermistors are wired together. In this embodiment, the third conductor provides a conductive path between the third pin of connector 57 and all of the second terminals of the thermistors 54. The third conductor may optionally be implemented using multiple segments of wire and / or multiple traces on a flex circuit.

[0052] Because connector 57 has a respective first pin corresponding to the first terminal of each thermistor 54, and a conductive path exists between each first pin and a respective one of the thermistors 54, a system mated with connector 57 has access to the first terminal of each thermistor 54. In addition, because the second terminals of all the thermistors 54 are all wired together and connected to a third pin (labeled C), a system mated with connector 57 also has access to the second terminal of each thermistor 54. As a result, a system mated with connector 57 can measure the resistance of any of the thermistors 54 during a temperature reading phase. This may be accomplished, for example, by sending a known power through each thermistor 54 and measuring the voltage that appears across each thermistor.

[0053] In particular, since any given first pin on connector 57 corresponds to a respective one of the individual first electrode elements 52 (during the current output phase) and also corresponds to a respective one of the individual thermistors 54 (during the temperature reading phase), each first pin on connector 57 serves two functions. This reduces the number of wires that must be included in each cable 56, which in turn advantageously makes the cables more flexible and less cumbersome.

[0054] FIG. 6 is a block diagram of a system that uses four copies of transducer array 50 (described above in connection with FIG. 5) to apply TTFields to a subject. In FIG. 6, these four copies are labeled 50A, 50P, 50L, and 50R, where A, P, L, and R refer to front, rear, left, and right, respectively. The lower portion of FIG. 6 shows AC voltage generator 35 and "CAD box" 30 as separate blocks, the latter containing temperature measurement block 32, controller 34, and a group of switches 1L, 2L, 3L, 1R, 2R, and 3R. In some embodiments, the components in the two blocks 35, 30 may be physically separated into two separate housings. However, in alternative embodiments, the components in these two blocks 35, 30 are combined into a single housing.

[0055] For simplicity, only the left and right channels are shown in FIG. 6. However, the remaining channels (i.e., the front and rear channels) operate in the same manner as the left and right channels, respectively. In addition, each transducer array 50 in FIG. 6 is shown with only four first electrode elements 52 and four thermistors 54 for simplicity. However, an actual system is expected to have a larger number of first electrode elements and thermistors (e.g., between 9 and 30), as well as a larger number of certain other components (e.g., switches, conductors, etc.), depending on the number of first electrode elements 52 actually used in each transducer array 50.

[0056] The system of FIG. 6 can measure the temperature of the thermistor 54 in the left channel 50L during a temperature reading phase by subsequently controlling electronically controlled switches in group 2L (which may be implemented using bidirectional analog switches) to select each thermistor. For example, switches C and 1 should be closed to select thermistor T1, switches C and 2 should be closed to select thermistor T2, and so on. After a given one of the thermistors T1-T4 in the transducer array 50L is selected, the temperature measurement block (TMB) 32 can determine the thermistor's temperature by measuring the thermistor's resistance. This may be accomplished, for example, by using a current source generating a known current (e.g., 150 μA) positioned within the TMB 32 so that a known current is sent through whichever thermistor is selected by the group of switches 2L at any given moment. The known current induces a voltage across the selected thermistor (T1-T4), and the temperature of the selected thermistor can be determined by measuring this voltage. Controller 34 then executes a program that selects each thermistor T1-T4 and then measures the voltage developed across each thermistor (which indicates the temperature at the selected thermistor). Examples of suitable hardware and procedures that may be used to obtain temperature readings from each thermistor are described in U.S. Patent Application Publication No. 2007 / 0122999, which is incorporated herein by reference in its entirety.

[0057] Measuring the temperature of the thermistor 54 in the right channel 50R is accomplished using the same approach as described above for the left channel 50L, except that group 2R of switches is used instead of group 2L. Corresponding groups of switches (not shown) are also provided for the other channels 50A, 50P, and a similar approach is used for those channels as well.

[0058] Assume that during a given time interval (e.g., 1 second) during the current output phase, the AC voltage generator 35 applies an AC signal between the L and R terminals. This AC signal is applied to the A terminals of the left and right transducer arrays 50L and 50R, meaning that the output of the AC voltage generator is applied to all of the second electrode elements 53 (A1-A4). Based on temperature readings obtained from the thermistors 54 (T1-T4) during the temperature reading phase, the controller 34 controls the switches in group 1L to either turn on or off current (generated within the AC voltage generator 35) to each corresponding first electrode element 52 (E1-E4) during the next current output phase. For example, to leave full current in all four of the sets 52 / 53, all four of the switches in group 1L should be closed. To reduce the current passing through the E1 / A1 set 52 / 53 of electrode elements (see FIG. 5), switch 1 in group 1L should be opened, to reduce the current passing through the E2 / A2 set 52 / 53 of electrode elements, switch 2 in group 1L should be opened, etc.

[0059] Controlling the current sent through an individual first electrode element during the current output phase can therefore be used to reduce the current passing through a given region when that region begins to heat up, which can advantageously prevent overheating without completely shutting off the current passing through the given region.

[0060] In some embodiments, the controller 34 may be programmed to maintain temperatures in all of the regions below a safety threshold (e.g., below 41°C) as follows: Begin by closing all of switches 1-4 in group 1L so that a full measurement of current (i.e., 100%) passes through each set of electrode elements 52 / 53 during the current output phase. Then, during the temperature reading phase, based on the signal arriving via the TMB 32, the controller 34 determines whether the temperature in each region exceeds an upper threshold (e.g., 40°C) below the safety threshold. If the controller 34 detects this condition, the controller 34 reduces the current passing through the warmer regions by turning off the signal to the first electrode element 32 in those regions during the next current output phase. Notably, this procedure only reduces the current passing through specific regions of the transducer array 50, but does not reduce the current passing through the remaining regions on the transducer array 50.

[0061] Optionally, the decision by the controller 34 to turn off a given first electrode element 52 may be based on the rate at which the corresponding thermistor 54 heats (as measured via the temperature sensor 54 and the TMB 32 during two or more time-spaced temperature reading phases). More specifically, if the controller 34 recognizes that a given thermistor 54 heats up faster than expected, the controller 34 may proactively open the switch supplying the corresponding first electrode element 52 during a subsequent current output phase.

[0062] Optionally, the controller 34 can control the current passing through any given region on the transducer array 50 based on real-time temperature measurements. For example, when the temperature at a given region reaches 40°C, the controller 34 can open the switch supplying the corresponding first electrode element 52, reducing the current passing through the corresponding region during the current output phase. The controller 34 then waits until the temperature measured using the temperature sensor 54 drops below a second temperature threshold (e.g., below 38°C). When the temperature drops below this second temperature threshold, the controller 34 can close the switch supplying the corresponding first electrode element 52, restoring the current passing through the corresponding region during the current output phase to its original value.

[0063] Individually switching the current to each first electrode element 52 in the right channel 50R is achieved using the same approach as described above for the left channel 50L, except that a group of switches 1R is used instead of group 1L. Corresponding groups of switches (not shown) are also provided in the other channels 50A, 50P, and a similar approach is used for those channels as well.

[0064] In some preferred embodiments, the AC signal generator 35 (a) sends an AC current through the anterior / posterior arrays 50A / 50P for a first period (e.g., 1 second) that induces an electric field with a first direction through a tumor in the subject's body, and then (b) sends an AC current through the left / right arrays 50L / 50R for a second period (e.g., 1 second) that induces an electric field with a second direction through the tumor, and then repeats steps (a) and (b) for the duration of the treatment. In these embodiments, the controller 34 may determine whether to switch each first electrode element 52 on or off just prior to each 1-second time interval.

[0065] Optionally, an additional group of switches 3L may be provided, each switch in the group wired in parallel with a corresponding one of the thermistors T1-T4 such that when a given one of switches 1-4 is closed, a respective one of the thermistors T1-T4 is shorted out.

[0066] The reason for including the additional group of switches 3L is that (a) current from the AC voltage generator 35 flows through the first electrode element 52 of the left channel 50L, the subject's body, and the first electrode element 52 of the right channel 50R during the current output phase, and (b) if power to any of the first electrode elements 52 of the left channel 50L is turned off by a corresponding one of the switches in group 1L, current can sneak out through the thermistor 54 in the left channel 50L. For example, assume that only switch #2 in group 1L is turned off (i.e., open). Because switches #1, #3, and #4 are turned on (i.e., closed), the AC voltage generator 35 applies voltage to electrode elements E1, E3, and E4. Thermistors T1 and T2 provide a path for current to flow from E1 to E2, thermistors T3 and T2 provide a path for current to flow from E3 to E2, and thermistors T4 and T2 provide a path for current to flow from E4 to E2. This is equivalent to a parallel combination of E1, E3, and E4 wired in series with E2. Because the number of thermistors in this parallel combination increases linearly with the number of first electrode elements 52, the current in a single thermistor E2 (wired in series with the parallel combination) can become significant. The inclusion of any additional group of switches 3L provides the system with the ability to prevent power loss in that single thermistor E2 by closing the corresponding switch #2 in group 3L.

[0067] To accomplish this (in those embodiments including the additional group of switches 3L), the controller 34 may be programmed so that whenever a given one of the switches in group 1L is opened, the corresponding switch in group 3L is closed. This prevents the thermistor 54 associated with the switched-off first electrode element 52 from dissipating too much power, as described in the previous paragraph.

[0068] In those embodiments including an additional group of switches 3L, individual bypassing of each thermistor 54 in the right channel 50R is achieved using the same approach as described above in connection with the left channel 50L, except that a group of switches 3R is used in place of group 3L. Corresponding groups of switches (not shown) are also provided in the other channels 50A, 50P, and a similar approach is used for those channels as well.

[0069] Figure 7 shows a second embodiment of a transducer array 150 that provides individual control over the current passing through nine different regions of the transducer array 150 during the current output phase. As described below in connection with Figure 8, four copies of the transducer array 150 are preferably used to administer TTFields therapy to a person's head (or other body part).

[0070] Each transducer array 150 includes at least four sets of electrode elements 152 / 153. Each set 152 / 153 includes a respective first electrode element 152 and a respective second electrode element 153 that are disposed in thermal contact with one another. For ease of reference, the first electrode elements 152 are labeled E1-E9, and the second electrode elements 153 are labeled A1-A9. The first and second electrode elements 152, 153 are similar to the first and second electrode elements 52, 53, respectively, of the embodiment of FIGS. 5-6 described above. The electrode elements 152, 153 of each set are positioned in different regions of the transducer array 150, and the first and second electrode elements 152, 153 in any given set are positioned in thermal contact with one another.

[0071] The first and second electrode elements 152, 153 are held in place by a support structure 159, which is similar to the support structure 59 in the embodiment of FIG.

[0072] Each transducer array 150 also has a connector 157 that is used to transmit electrical signals into and out of the transducer array 150. The connector 157 has at least four first pins and second pins. In the illustrated embodiment, the number of first pins is the same as the number of first electrode elements 152, and each first pin corresponds to a respective one of these first electrode elements 152. In the illustrated embodiment, there is only a single second pin, labeled A. It should be noted that, as used herein, the term "pin" can refer to either a male or female pin of the connector 157.

[0073] Each transducer array 150 also has at least four first conductors, the number of which depends on the number of first electrode elements 152. For example, in the embodiment shown in FIG. 7 , which includes nine first electrode elements 152, there are nine first conductors. Each of these first conductors provides a conductive path between (a) a respective one of the first pins in the connector 157 and (b) the conductive substrate of a respective one of the first electrode elements 152 (E1-E9). These first conductors are labeled 1-9 immediately above the “wire routing” block 155 (which routes the individual conductors together in a single cable 156). As with the embodiment of FIG. 5 , each of these first conductors may optionally be implemented using multiple segments of wire and / or multiple traces on a flex circuit.

[0074] 5-6, the system mating with connector 157 can selectively excite or not excite each first electrode element 152 individually by applying or not applying an AC signal to the respective first pin on connector 157 during the current output phase. However, because all of the second electrode elements 153 are wired together, all of the second electrode elements 153 must or may not be selectively excited together by applying or not applying an AC signal to the second pin on connector 157. Thus, any given individual region of transducer array 150 either (a) passes a full level of current (i.e., when each first electrode element 152 is excited) or (b) passes a lower level of current (i.e., when each first electrode element 152 is not excited).

[0075] Operation of the embodiment of FIG. 7 during the temperature reading phase will now be discussed. Each transducer array 150 also includes at least four temperature sensors, each disposed in thermal contact with a respective one of the electrode elements 152, 153 of the set. As with the embodiments of FIGS. 5-6, the temperature sensors may be implemented using thermistors 154. Each thermistor 154 has a first terminal (i.e., the lower terminal of the thermistor in FIG. 7) and a second terminal (i.e., the upper terminal of the thermistor in FIG. 7). In these embodiments, each first conductor provides a conductive path between (a) a respective one of the first pins in the connector 157, (b) the conductive substrate of a respective one of the first electrode elements 152 (E1-E9), and (c) the first terminal of the corresponding thermistor 154.

[0076] In particular, the multiple thermistors 154 in this embodiment of Figure 7 are arranged in series, starting with the first thermistor (i.e., the top left in Figure 7) and ending with the last thermistor (i.e., the bottom right in Figure 7), with the second terminal of each thermistor except the last being wired to the first terminal of each subsequent thermistor.

[0077] Each transducer array 150 has a third conductor that provides a conductive path between the third pin of the connector 157 and the second terminal of the last thermistor 154 (i.e., the upper terminal of the bottom right thermistor in FIG. 7 ). The third conductor may optionally be implemented using multiple segments of wire and / or multiple traces on a flex circuit.

[0078] Because connector 157 has a respective first pin corresponding to each respective first electrode element 152, and a conductive path exists between each first pin and a respective one of first electrode elements 152, a system mated with connector 157 can selectively excite or de-excite each first electrode element 152 individually by applying or not applying a signal to the respective first pin on connector 157 during a current output phase. Because the two terminals of any given one of the thermistors 154 are wired to different pins on connector 157, a system mated with connector 157 has access to both terminals of each thermistor 154. As a result, a system mated with connector 157 can measure the resistance of either of the thermistors 154 during a temperature reading phase.

[0079] In particular, since any given first pin on connector 157 corresponds to a respective one of the individual first electrode elements 152 (during the current output phase) and also corresponds to a respective one or two of the individual thermistors 154 (during the temperature reading phase), each first pin on connector 157 serves two functions. This reduces the number of wires that must be included in each cable 156, which in turn advantageously makes the cables more flexible and less cumbersome.

[0080] FIG. 8 is a block diagram of a system that uses four copies of the transducer array 150 (described above in connection with FIG. 7) to apply TTFields to a subject. In FIG. 8, these four copies are labeled 150A, 150P, 150L, ​​and 150R, where A, P, L, and R refer to front, rear, left, and right, respectively. The lower portion of FIG. 8 shows the AC voltage generator 35 and the "CAD box" 130 as separate blocks, the latter containing a temperature measurement block 132, a controller 134, and a group of switches 1L, 2L, 3L, 1R, 2R, and 3R. In some embodiments, the components in these two blocks 35, 130 may be physically separated into two separate housings. However, in alternative embodiments, the components in these two blocks 35, 130 are combined into a single housing.

[0081] For simplicity, only the left and right channels are shown in FIG. 8. However, the remaining channels (i.e., the front and rear channels) operate in the same manner as the left and right channels, respectively. Additionally, each transducer array 150 in FIG. 8 is shown with only four first electrode elements 152 and four thermistors 154 for simplicity. However, an actual system is expected to have a larger number of first electrode elements and thermistors (e.g., between 9 and 30), as well as a larger number of certain other components (e.g., switches, conductors, etc.), depending on the number of first electrode elements 152 actually used in each transducer array 150.

[0082] The system of Figure 8 can then measure the temperature of thermistor 154 in left channel 150L during the temperature reading phase by controlling electronically controlled switches in groups 2L and 3L (which may be implemented using bidirectional analog switches) to select each thermistor. For example, switches 1 and 2 should be closed to select thermistor T1, switches 2 and 3 should be closed to select thermistor T2, switches 3 and 4 should be closed to select thermistor T3, and switches 4 and N should be closed to select the last thermistor (i.e., T4 in Figure 8). After a given one of thermistors T1-T4 in transducer array 150L is selected, temperature measurement block 132 can determine the temperature of that thermistor by measuring the resistance of the thermistor, as described above in connection with Figure 6.

[0083] Measuring the temperature of the thermistor 154 in the right channel 150R is accomplished using the same approach as described above for the left channel 150L, ​​except that groups of switches 2R and 3R are used instead of groups 2L and 3L. Corresponding groups of switches (not shown) are also provided for the other channels 150A, 150P, and a similar approach is used for those channels as well.

[0084] Assume that during a given time interval (e.g., 1 second) during the current output phase, the AC voltage generator 35 applies an AC signal between the L and R terminals. This AC signal is applied to the A terminals of the left and right transducer arrays 150L and 150R, meaning that the output of the AC voltage generator is applied to all of the second electrode elements 153 (A1-A4). Based on temperature readings obtained from thermistors 154 (T1-T4) during the temperature reading phase, the controller 134 controls the switches in groups 1L and 1R (and corresponding switches in the front and rear channels, not shown) to either turn on or off current (generated within the AC voltage generator 35) to each of the corresponding first electrode elements 152 (E1-E4) during the next current output phase, as described above in connection with FIG. 6 . For example, to leave full current in all four of sets 152 / 153, all four of the switches in group 1L should be closed. To reduce the current passing through the E1 / A1 set 152 / 153 of electrode elements (see FIG. 7), switch 1 in group 1L should be opened, to reduce the current passing through the E2 / A2 set 152 / 153 of electrode elements, switch 2 in group 1L should be opened, and so on.

[0085] Similar to the embodiment of Figures 5-6, controlling the current sent through individual first electrode elements during the current output phase can be used to reduce the current passing through a given region when that region begins to heat up, which can advantageously prevent overheating without completely shutting off the current passing through the given region.

[0086] In alternative embodiments, instead of implementing a temperature sensor using a thermistor (as described above in connection with FIGS. 5-8), temperature sensing may be implemented using multiple regions of pyroelectric material. Examples of suitable pyroelectric materials include PVDF homopolymer, PVDF organic derivatives such as P(VDF-TrFE), and PVDF ceramic composites, where PVDF is poly(vinylidene fluoride) and TrFE is trifluoroethylene. In some embodiments, the pyroelectric material is Piezotech® RT-FC, a P(VDF-TrFE) copolymer. In some embodiments, the regions of pyroelectric material may be polymer layers such as poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) and / or poly(vinylidene fluoride-trifluoroethylene-1-chlorofluoroethylene).

[0087] The first and second electrode elements each have a front surface and a rear surface. Each region of pyroelectric material has a front surface and a rear surface, and the front surface of each region of pyroelectric material is disposed in electrical and thermal contact with the rear surface of the first / second electrode element of its respective set. The additional electrode region contacts the rear surface of the region of pyroelectric material.

[0088] Electrical and thermal contact between the front surface of each region of pyroelectric material and the rear surface of the first / second electrode element of each set may be achieved by placing these two surfaces in direct contact with each other (e.g., by depositing or spraying the first and second electrode elements onto the region of pyroelectric material during fabrication). Alternatively, another layer of material that does not obstruct electrical and thermal contact may be placed between these two surfaces.

[0089] Because the first and second electrode elements are each positioned in thermal contact with a respective one of the regions of the pyroelectric material, a temperature change in any given set of first / second electrode elements produces a corresponding temperature change in the respective region of the pyroelectric material. This temperature change produces a pyroelectric voltage across the opposing surface of each region of the pyroelectric material. The instantaneous value of this pyroelectric voltage can be measured via the first electrode element and the additional electrode region. Due to the thermal contact between the first and second electrode elements and the respective regions of the pyroelectric material, the measured electrical signal not only indicates a change in temperature in each region of the pyroelectric material, but also indicates a change in temperature of the first / second electrode elements of each respective set.

[0090] The regions of dielectric material may be distinct portions of flexible polymer separated by gaps. Alternatively, the regions of dielectric material may be regions within a single continuous sheet of flexible polymer material.

[0091] Pyroelectric material does not generate power based on its absolute temperature. Instead, it generates an electrical output that is a function of changes in temperature. Each of the first and second electrode elements is positioned in thermal contact with a respective region of pyroelectric material with similar characteristics. Thus, if the electrode elements of a given set are hotter than the electrode elements of another set, the temperature fluctuations in the given set will be greater than the temperature fluctuations in the other set. This causes the region of pyroelectric material positioned in contact with the given set to generate a greater electrical output than the region of pyroelectric material positioned in contact with the other set.

[0092] The controller compares the temperature fluctuations of all electrode sets by sampling the signals generated by the areas of pyroelectric material positioned in thermal contact with these electrode sets. By analyzing how the electrical characteristics change over time, the controller can determine whether the temperature fluctuations of a given set are greater than the temperature fluctuations of another set. The controller can then use this information to normalize the temperatures of all electrode elements by turning off the first electrode elements in the hotter set to reduce the current flowing through the electrode elements of the hotter set.

[0093] Because pyroelectric materials respond to changes in temperature (as opposed to absolute temperature), a pyroelectric material cycled between 37°C and 37.2°C will produce the same output as the same pyroelectric material cycled between 40°C and 40.2°C. With this in mind, simply equalizing the temperatures of all electrode elements in any given transducer array, as described above, is not sufficient. Conversely, because the temperature of the transducer array should be maintained below a given threshold (e.g., 40°C), one additional piece of information is needed to ensure that the transducer array is not overheating. This additional information is the absolute temperature of at least one set of first and second electrode elements. If the absolute temperature of a single set of first and second electrode elements is known, and all of the electrode element temperatures are equalized, then no electrode element is hotter than the threshold temperature.

[0094] With this in mind, at least one absolute temperature sensor (e.g., a thermistor) is positioned in thermal contact with at least one set of first / second electrode elements, and the system includes circuitry to enable the controller to determine the temperature of the thermistor (and thereby determine the temperature of the electrode element in thermal contact with the thermistor).

[0095] FIG. 9 is a schematic diagram of a circuit suitable for implementing groups 1L and 1R in the embodiments of FIGS. 6 and 8 described above, and each switch within the corresponding group for the front and rear channels (not shown). The circuit includes two field-effect transistors (FETs) 66, 67 wired in series, configured to pass current in either direction. One example of a suitable FET for this circuit is the BSC320N20NSE (Infineon Technologies AG, Neubiberg, Germany). (Note that the diodes shown in FIG. 9 are inherently contained within the FETs 66, 67 themselves.) The series combination of the two FETs 66, 67 either conducts or blocks electrical flow depending on the state of a control input arriving from one of the digital outputs of the controller 34 described above. When the series combination is conducting, current can flow between the shared conductor and the respective first electrode element 52. On the other hand, when the series combination of FETs 66, 67 is not conducting, current does not flow between the shared conductor and the respective first electrode element 52.

[0096] In the embodiments described above with reference to Figures 5 and 7, all of the electrode elements 52, 53 are capacitively coupled, and the support structure 59 is configured to hold the electrode elements 52, 53 against the subject's body so that the dielectric layers of the electrode elements 52, 53 face the subject's body and can be positioned in contact with the subject's body. However, in alternative embodiments, electrode elements that are not capacitively coupled may be used. In this case, the dielectric layer of each electrode element is omitted, and the support structure 59 holds the electrode elements 52, 53 against the subject's body so that the conductive surfaces of the electrode elements 52, 53 face the subject's body and can be positioned in contact with the subject's body. Optionally, in these embodiments, a layer of hydrogel may be disposed between the conductive surfaces of the electrode elements 52, 53 and the subject's body when the transducer array 50 is placed against the subject's body.

[0097] While the present invention has been disclosed with reference to particular embodiments, many changes, modifications, and variations to the described embodiments are possible without departing from the sphere and scope of the invention as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but rather have the full scope defined by the language of the following claims and equivalents thereof. [Explanation of symbols]

[0098] 20 AC signal generator 21 Transducer Array 22 Transducer Array 23 Transducer Array 24 transducer array 30 CAD box 32 Temperature measurement block 34 Controller 35 AC voltage generator 50 Transducer Array 52 Electrode element 53 Electrode element 54 Thermistor 56 Cable 57 Connector 59 Support structure 66 Field-effect transistor 67 Field-effect transistor 132 Temperature measurement block 134 Controller 150 Transducer Array 152 Electrode element 153 Electrode element 154 Thermistor 156 Cable 157 Connector 159 Support structure E electrode element

Claims

1. 1. An apparatus for applying an alternating current electric field to a body of a subject using at least four sets of electrode elements, each of the sets of electrode elements including a respective first electrode element and a respective second electrode element disposed in thermal contact with the respective first electrode element, and each of the sets of electrode elements disposed in thermal contact with a respective temperature sensor, an AC signal generator for generating an AC output signal; a connector including at least four first pins and a second pin, each of the first pins corresponding to a respective one of the first electrode elements, and the AC output signal being applied to the second pins; at least four first switches each configured to selectively apply or not apply the AC output signal to a respective one of the first pins depending on the state of at least one control signal; an amplifier configured to receive an input from each said temperature sensor and to generate a corresponding output; a controller configured to set the at least one control signal to a state that determines whether the AC output signal is applied to each of the first pins based on the output of the amplifier.

2. 2. The apparatus of claim 1, wherein the controller is configured to: (a) determine, based on the output of the amplifier, when at least one of the first electrode elements is hotter than other first electrode elements; and (b) set the at least one control signal to a state that controls the first switch such that the AC signal is not applied to at least one respective first pin.

3. 2. The apparatus of claim 1, wherein the controller is configured to: (a) determine, based on the output of the amplifier, when at least one of the first electrode elements is hotter than a threshold level; and (b) set the at least one control signal to a state that controls the first switch such that the AC signal is not applied to at least one respective first pin.

4. 2. The apparatus of claim 1, wherein the input from the temperature sensor arrives through the same first pin that corresponds to the first electrode element.

5. The device of claim 1 further comprising at least four sets of electrode elements and respective temperature sensors.

6. The apparatus of claim 5 , wherein each of the temperature sensors comprises a thermistor.

7. each said first electrode element comprises a conductive plate with a dielectric layer disposed thereon; each said second electrode element comprises a conductive plate with a dielectric layer disposed thereon; 2. The device of claim 1, wherein a support is configured to hold the first electrode element and the second electrode element against the subject's body such that the dielectric layer of the first electrode element and the dielectric layer of the second electrode element face the subject's body.

8. each said temperature sensor comprising a thermistor having a first terminal and a second terminal; at least four first conductors, each providing a conductive path between (a) each of the first pins, (b) each of the first electrode elements, and (c) the first terminal of each thermistor; a second conductor providing a conductive path between the second pin and all of the second electrode elements; Furthermore, the connector has a third pin; 6. The apparatus of claim 5, further comprising a third conductor providing a conductive path between the third pin and the second terminal of at least one of the thermistors.

9. 9. The apparatus of claim 8, wherein the thermistors are wired in series, starting with a first one of the thermistors and ending with a last one of the thermistors, the second terminal of each thermistor except the last one being wired to the first terminal of each subsequent thermistor, and the third conductor provides a conductive path between the third pin of the connector and the second terminal of the last thermistor.

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