Patent Description:
Each transducer array is configured as a set of capacitively coupled electrode elements (about <NUM> in diameter) that are interconnected via flex wires. Each electrode element includes a ceramic disk that is sandwiched between a layer of an electrically conductive medical gel and an adhesive tape. When placing the arrays on the patient, the medical gel adheres to the contours of the patient's skin and ensures good electric contact of the device with the body. The adhesive tape holds the entire array in place on the patient as the patient goes about their daily activities.

The amplitude of the alternating current that is delivered via the transducer arrays is controlled so that skin temperature (as measured on the skin below the transducer arrays) does not exceed a safety threshold of <NUM>° C. The temperature measurements on the patient's skin are obtained using thermistors placed beneath some of the disks of the transducer arrays. In the existing Optune® system, each array includes <NUM> thermistors, with one thermistor positioned beneath a respective disk in the array. (Note that most arrays include more than <NUM> disks, in which case the temperature measurements are only performed beneath a sub-set of the disks within the array).

The thermistors in each of the four arrays are connected via long wires to an electronic device called the "cable box" where the temperature from all <NUM> thermistors (<NUM> arrays <NUM> thermistors per array A, A, B, B) is measured and analog-to-digital converted into digital values for each thermistor. These measurements are then transmitted from the cable box to the AC voltage generator via an additional two wires that facilitate two-way digital serial communications between the cable box and the AC voltage generator. The controller in the AC voltage generator uses the temperature measurements to control the current to be delivered via each pair of arrays A, A, B, B in order to maintain temperatures below <NUM>° C on the patient's skin. The current itself is delivered to each array via an additional wire (i.e., one wire for each array) that runs from the AC voltage generator through the cable box to the array.

In the existing Optune® system there are four long <NUM>-wire cables (each of which runs between a respective array and the cable box) and one <NUM>-wire spiral cord that runs between the AC voltage generator and the cable box. Each of the <NUM>-wire cables has <NUM> wires for carrying signals from the <NUM> thermistors, <NUM> wire for the common of all <NUM> thermistors, plus <NUM> wire for providing the TTFields signal to the array. The <NUM>-wire spiral cord has <NUM> wire for power to the cable box (Vcc), <NUM> wire for ground to the cable box, <NUM> wires for data communication (to send the temperature readings to the AC voltage generator), plus <NUM> wires for the TTFields signals (i.e., one for each of the four arrays). <CIT> discloses a skin surface based apparatus for use together with an AC signal generator and temperature sensors for imposing electric fields through a target region in a subject's body.

One aspect of the invention is directed to an apparatus for delivering tumor treating fields according to claim <NUM>.

Various embodiments are described in detail below with reference to the accompanying drawings, wherein like reference numerals represent like elements, and wherein dotted lines represent implanted components.

Instead of using transducer arrays positioned on the patient's skin to deliver TTFields (as in the <FIG> embodiment described above), the embodiments described herein use transducer arrays that are implanted within a patient's body to deliver TTFields. Implanting the transducer arrays can provide a number of potential advantages. These potential advantages include (<NUM>) hiding of the arrays from people with whom the patient interacts; (<NUM>) improving patient comfort (by avoiding the skin irritation, sensations of heating, and/or limitations on motion that can result from arrays that are positioned on the patient's skin); (<NUM>) improving electrical contact between the transducer arrays and the patient's body; (<NUM>) eliminating the need for shaving regions on which the arrays are placed (as hair growth can interfere with the delivery of TTFields); (<NUM>) avoiding the risk that detachment of the transducer arrays will interrupt the delivery of TTFields; (<NUM>) significantly reducing the power required to deliver TTFields (e.g., by reducing the physical distance between the transducer arrays and the tumor and bypassing anatomical structures that have high resistivity, e.g., the skull); (<NUM>) significantly reducing the weight of the device that must be carried by the patient (e.g., by using smaller batteries to take advantage of the reduced power requirements); (<NUM>) avoiding the skin irritation that can occur when transducer arrays are positioned on the patient's skin; and (<NUM>) making it possible to deliver TTFields to anatomic structures that cannot be treated using transducer arrays positioned on the patient's skin (e.g., the spinal cord, which is surrounded by highly conductive cerebrospinal fluid that is in turn surrounded by the bony structure of the spine, both of which interfere with the penetration of TTFields into the spinal cord itself).

Note that in all of the embodiments described herein, it is important to include sensors for measuring temperature (such as thermistors) on or near the transducer arrays so that tissue temperature can be controlled and thermal damage to tissue avoided. In situations where a given transducer array is made up of a plurality of individual elements (e.g., ceramic discs) it is preferable to distribute a plurality of temperature sensors (e.g., thermistors) among the plurality of individual elements.

One approach (not shown) for using implantable electrodes has a block diagram that is similar to the prior art <FIG> embodiment described above, except that the transducer arrays A, A, B, B are all implanted in the patient's body (e.g., between the scalp and the skull, or adjacent to the dura). While this approach enjoys advantages <NUM>-<NUM> listed above, it also suffers from a number of disadvantages. More specifically, each of the transducer arrays is connected to the cable box/AC voltage generator via a relatively long and bulky <NUM>-conductor cable that extends outside of the body through a surgical incision or port (<NUM> conductor for applying the AC voltage to the respective transducer array, plus <NUM> conductors that are used to obtain temperature readings from <NUM> different locations on the respective transducer array). The use of <NUM> conductor cables could make the system cumbersome. In addition, including a component that passes through the person's skin into the person's head raises the risk of acquiring an infection, which can be particularly problematic in the context of the brain.

<FIG> depicts an improvement with respect to the approach described in the previous paragraph. In this approach, the number of conductors in each cable that must pass through the patient's skin is reduced from <NUM> to <NUM>, which will significantly reduce the bulk and size of those cables. This may be accomplished, for example, by implanting additional electronics E adjacent to each of the implanted transducer arrays A, B and using a hub-based architecture. When the hub-based architecture is used, each of the electronic blocks E includes a multiplexor that reduces the number of conductors required for obtaining temperature measurements from <NUM> to <NUM>, and a hub <NUM> is used to collect the temperature readings from each of the transducer arrays and forward those readings to the AC voltage generator <NUM>. The AC voltage generator <NUM> can then control the current that is applied to each of the transducer array pairs A/A, B/B in order to ensure that the transducer arrays do not overheat. Examples of circuitry that may be used to implement these electronic blocks E and the hub can be found in <CIT>, entitled Temperature Measurement in Arrays for Delivering TTFields. Note that while this embodiment does reduce the size and bulk of the wires that must pass through the person's skin, and provides advantages <NUM>-<NUM> listed above, it does not alleviate the risk of infection that is associated with a component that passes through the person's skin into the person's head.

<FIG> depicts a variation on the <FIG> approach. In the <FIG> embodiment, instead of positioning the hub outside the patient's body and running four cables through the patient's skin (as in <FIG>), the electronics E, the transducer arrays A, B, and the hub <NUM> are implanted in the patient's body. In this <FIG> embodiment, only a single cable (i.e., the cable that runs between the hub <NUM> and the AC voltage generator <NUM>) must pass through the patient's skin. Optionally, this cable is connectorized using the depicted port <NUM>. In the example depicted in <FIG>, the hub <NUM> is positioned somewhere in the patient's thorax, and four <NUM>-conductor cables run between the electronics E and the transducer arrays A, B in the patient's head and the hub <NUM> in the patient's thorax. This positioning is advantageous because there are no wires that pass directly from the outside world directly into the patient's head, thereby reducing the risk of a serious infection. But in variations of the <FIG> embodiment, the hub <NUM> may be positioned in the patient's head, in which case the port <NUM> that provides access would also be positioned in the patient's head.

In these <FIG> embodiments, the hub <NUM> collects temperature measurements from each of the transducer arrays A, B via the electronics E and forwards those temperature measurements to the AC voltage generator <NUM> via the port <NUM>. The AC voltage generator <NUM> can then control the current that is applied to each of the transducer array pairs A/A, B/B in order to ensure that the transducer arrays do not overheat. This embodiment also provides advantages <NUM>-<NUM> listed above.

<FIG> depicts another approach that uses implantable electrodes and also provides advantages <NUM>-<NUM> listed above. In this embodiment, the electrodes A, B, the hub <NUM>, and the AC voltage generator <NUM> are all implanted within the patient's body. Power for the hub <NUM> and the AC voltage generator <NUM> is provided via a port <NUM> that is positioned somewhere on the patient's skin (e.g. in the thorax). The power source (e.g. the battery) in this embodiment is external, and the battery provides power to the hub <NUM> and AC voltage generator <NUM> via the port. The port <NUM> is connected to the hub <NUM> and AC voltage generator <NUM> via appropriate wiring (e.g. a two conductor cable).

Since effective delivery of TTFields requires delivery of power on the order of <NUM>-<NUM> W, care must be taken to minimize heat dissipation in all embodiments where the AC voltage generator <NUM> is implanted within a patient's body (including this <FIG> embodiment). This is because any inefficiencies will lead to heating of tissue surrounding the field generator, which could lead to thermal damage of tissue in the patient's body. To accomplish this, the AC voltage generator <NUM> must operate with very high efficiency. One example of a circuit that is suitable for implementing a high efficiency AC voltage generator is described in <CIT>, entitled High Voltage, High Efficiency Sine Wave Generator with Pre-Set Frequency and Adjustable Amplitude.

The AC voltage generator <NUM> in these embodiments may optionally operate by starting with a low-voltage AC signal and amplifying and filtering that signal using circuitry integrating a transformer and LC filter. In some embodiments, an independent circuit combining the transformer and LC filter could be connected to each transducer array (or even to each element of each transducer array). In these embodiments, the low-voltage signal generator could be connected to each array (or element) via a wire placed remotely from the arrays. In this configuration, heat generated through losses within the system would be spread over a larger volume thereby reducing the risk of thermal damage to tissue, while enabling delivery of higher field intensities. To further reduce losses, the circuit on each array (or element) could be designed with a switch that switches the low voltage signal coming from the signal generator, thereby potentially reducing the losses within the system associated with switching at the arrays.

Optionally, the power source in the <FIG> embodiment may comprise multiple small batteries that are woven into a piece of clothing. This type of design would enable delivery of high power for extended periods of time while minimizing patient discomfort.

<FIG> depicts a variation on the <FIG> embodiments that also provides advantages <NUM>-<NUM> listed above. In the <FIG> embodiments, instead of providing power to the hub <NUM> and AC voltage generator <NUM> directly via a wired connection that passes from the outside world into the patient's body via a port <NUM> that is installed on the person's skin (as in <FIG>), power in the <FIG> embodiment is provided to the hub <NUM> and the AC voltage generator <NUM> using a wireless connection. This may be accomplished, for example, by implanting a first circuit <NUM> inside the patient's body close to the patient's skin. The first circuit is configured to receive energy via inductive coupling. A second circuit <NUM> (which may optionally be powered by a battery and/or the AC main) is configured to transmit energy to the first circuit <NUM> via inductive coupling. The second circuit <NUM> is positioned outside the patient's body adjacent to the first circuit <NUM> during operation, so that energy can be inductively coupled from the second circuit <NUM> into the first circuit <NUM>. The construction of these circuits <NUM>, <NUM> for transmitting and receiving energy via inductive coupling are well known in the art and are commonly used, for example, for charging cell phones etc..

Optionally, the bulk and weight of the hardware that must be carried around by the patient can be advantageously reduced by providing multiple copies of the second circuit <NUM> at various locations that are frequented by the patient. For example, one copy of the second circuit <NUM> may be provided at the patient's office, a second copy of the second circuit <NUM> may be provided in the patient's car, a third copy of the second circuit <NUM> may be provided in the patient's living room, and a fourth copy of the second circuit <NUM> may be provided in or near the patient's bed. When multiple copies of the second circuit <NUM> are provided, the patient places the inductive coupling region of whichever second circuit <NUM> is nearby adjacent to the first circuit <NUM> implanted in their body so that the nearby second circuit <NUM> can power the implanted AC voltage generator <NUM> via inductive coupling. This arrangement can be particularly advantageous for people that move between various locations in a repeatable pattern (e.g., people who drive to work in the same car every day, work at the same desk every day, relax in the same living room every evening, and sleep in the same bed every night. Optionally, multiple copies of the second circuit <NUM> may be incorporated into a mattress so that the patient will not have to be hooked up to wires when they sleep, and can move around on the mattress.

<FIG> depicts yet another embodiment that uses implanted electrodes and also provides advantages <NUM>-<NUM> listed above. Notably, the battery <NUM> in the <FIG> embodiment is implanted in the patient's body, and the implanted battery <NUM> is charged via induction. One challenge with this design is that the implanted battery <NUM> has to store relatively large amounts of energy. Thus, charging the battery <NUM> via induction may require the creation of large magnetic fluxes over extended periods of times. One method for overcoming this problem is a system in which a mattress incorporating a coil is used. The patient sleeps on this mattress, and the battery <NUM> powering the TTFields device is charged as the patient sleeps. In other embodiments, the coil could surround the bed.

Alternatively, a transcutaneous energy transfer system (see, e.g., <NPL>) could be used to charge the implanted battery <NUM>. In this case, a coil connected to a circuit designed to charge the implanted battery would be implanted transcutaneously. Charging would be performed with a separate device <NUM>, which the patient would place close to the implanted coil <NUM>. The external device could be fixed to the patient's body using a garment designed to fit tightly to the body, or using a medical adhesive. The patient would only be required to use the external charger when charging the implanted battery. This could occur for instance at night, while the patient is sleeping, thereby minimizing the need for the patient to carry an external device.

Optionally, the implanted transducer array elements may be configured to permit dynamic alteration of the field distribution in order to optimize delivery of TTFields. Unlike the situation with external transducer arrays, once the transducer arrays have been implanted it will be impractical to adjust the position of the transducer arrays in order to optimize the field distribution within the patient's body. A different approach for controlling the field distribution within the patient's body is therefore desirable when implantable arrays are used. One suitable approach for this purpose would be to implant transducer arrays with a relatively large number of switchable elements. The field can then be shaped by choosing subsets of array elements that are switched on when the field is delivered. As the tumor changes over time (response or progression), the field distribution could be changed by changing the array elements through which the field is generated.

Optionally, in any of the embodiments described above, the transducer arrays may be positioned on the dura. The advantage of this configuration is that power required to deliver TTFields to the brain would be reduced, because the field would not have to pass through the highly resistive layer of the skull. At the same time, this placement would reduce the need for invasive placement of the arrays in the brain-reducing the risk of damage to brain tissue and possibly the risk of infections. This configuration would also enable delivery of TTFields to large portions of the brain, as opposed to only delivering the TTFields to the tumor. In some cases, treating large portions of the brain may be advantageous. For instance, when treating the brain for metastases. In some embodiments, when treating regions of the body other than the head, the arrays could be placed subcutaneously to enable treatment of large regions. In other embodiments, the arrays could be placed in close proximity to the tumor. Placement in close proximity to the tumor would enable localized delivery of TTFields and reduce the power needed to deliver the fields.

In all of the embodiments described above, any component that is described as being implanted must be configured for implantation before it is actually implanted in a person's body. This means that it must be dimensioned to fit within the location where it will be implanted, and that all surfaces that might come into contact with tissue in the person's body must be biocompatible.

Optionally, in any of the embodiments described above, when the transducer arrays are implanted in the immediate vicinity of a tumor, the arrays could be made from or coated with a cytotoxic agent (e.g., platinum). Electrolysis caused by electric fields is expected to lead to release of platinum into the region around the tumor. Platinum is known to exert a cytotoxic effect on cancer cells, and therefore, release of platinum into the tumor may advantageously increase the anti-cancer effect of the TTFields treatment.

Optionally, in any of the embodiments described above, the transducer arrays A, B and the electronics E that are implanted into the patient's head may be designed as described below in connection with <FIG>. The advantage of this configuration is that average field intensity can be maximized while minimizing the risk of heating by monitoring and adjusting the current to each electrode element in each transducer array independently, thereby improving the efficiency of TTFields delivery. These embodiments operate by alternately switching the current on and off for each individual electrode element that begins to overheat in order to reduce the average current for those electrode elements, without affecting the current that passes through the remaining electrode elements (which are not overheating).

Assume, for example, a situation in which <NUM> mA of current is passing through a transducer array that includes <NUM> electrode elements, and only a single one of those electrode elements begins to overheat. Assume further that a <NUM>% reduction of current through the single electrode element would be necessary to prevent that single electrode element from overheating. The embodiments described herein can cut the average current through the single electrode element by <NUM>% by switching the current through that single electrode element on and off with a <NUM>% duty cycle, while leaving the current on full-time for all the remaining electrode elements. Note that the switching rate must be sufficiently fast so that the instantaneous temperature at the single electrode element is never too hot, in view of the thermal inertia of the electrode elements. For example, a <NUM>% duty cycle could be achieved by switching the current on for <NUM> and switching the current off for <NUM>. In some preferred embodiments, the period of switching the current on and off is less than <NUM>.

When this approach is used, the current through the remaining <NUM> electrode elements can remain unchanged (i.e., <NUM> mA per electrode element), and only the current through the single electrode element is reduced to an average of <NUM> mA. The average net total current through the transducer array will then be <NUM> mA (i.e., <NUM>×<NUM> + <NUM>), which means that significantly more current can be coupled into the person's body without overheating at any of the electrode elements.

The system may even be configured to increase the current through the remaining nine electrode elements in order to compensate for the reduction in current through the single electrode element. For example, the current through the remaining nine electrode elements could be increased to <NUM> mA per electrode element (e.g., by sending a request to the AC voltage generator to increase the voltage by <NUM>%). If this solution is implemented, the average net total current through the entire transducer array would be (<NUM> electrodes × <NUM> mA + <NUM> electrode × <NUM> mA × <NUM> duty cycle) = <NUM> mA, which is extremely close to the original <NUM> mA of current.

If, at some subsequent time (or even at the same time), the temperature at a second electrode element begins to overheat, a similar technique (i.e. a reduction in the duty cycle from <NUM>% to something less than <NUM>%) may be used to prevent the second electrode element from overheating.

In some embodiments, this technique may be used to individually customize the duty cycle at each of the electrode elements in order to maximize the current that flows through each of those electrode elements without overheating. Optionally, instead of taking remedial action to reduce the duty cycle only when a given electrode element begins to overheat, the system may be configured to proactively set the duty cycle at each of the electrode elements in a given transducer array individually so as to equalize the temperature across all of the electrode elements in the array. For example, the system could be configured to individually set the duty cycle at each electrode element so as to maintain a temperature that hovers around a set temperature at each of the electrode elements. Optionally, the system may be configured to send a request to the AC voltage generator to increase or decrease the voltage as required in order to achieve this result.

This approach can be used to ensure that each and every electrode element will carry the maximum average current possible (without overheating), which will provide an increased field strength in the tumor and a corresponding improvement in the treatment.

<FIG> depicts an embodiment that periodically switches the current on and off for each individual electrode element that begins to overheat. The hub/AC voltage generator <NUM> has two outputs (OUT1 and OUT2), each of which has two terminals. The hub/AC voltage generator <NUM> generates an AC signal (e.g. a <NUM> sine wave) between the two terminals of each of those outputs in an alternating sequence (e.g., activating OUT1 for <NUM> sec. , then activating OUT2 for <NUM> sec. , in an alternating sequence). A pair of conductors <NUM> are connected to the two terminals of OUT1, and each of those conductors <NUM> goes to a respective one of the left and right transducer assemblies <NUM>, <NUM>. Each of these transducer assemblies includes a plurality of electrode elements <NUM> (which collectively correspond to the transducer arrays A, B in <FIG>) and electronic components <NUM>, <NUM> (which correspond to the electronics E in <FIG>). A second pair of conductors <NUM> are connected to the two terminals of OUT2 and each of those conductors <NUM> goes to a respective one of the front and back transducer assemblies (not shown). The construction and operation of the front and back transducer assemblies is similar to the construction of the left and right transducer assemblies <NUM>, <NUM> depicted in <FIG>.

Each of the transducer assemblies <NUM>, <NUM> includes a plurality of electrode elements <NUM>. In some preferred embodiments, each of these electrode elements <NUM> is a capacitively coupled electrode element. However, in this <FIG> embodiment, instead of wiring all of the electrode elements <NUM> in parallel, an electrically controlled switch (S) <NUM> is wired in series with each electrode element (E) <NUM>, and all of these S+E combinations <NUM>+<NUM> are wired in parallel. Each of the switches <NUM> is configured to switch on or off independently of other switches based on a state of a respective control input that arrives from the digital output of the respective controller <NUM>. When a given one of the switches <NUM> is on (in response to a first state of the respective control input), current can flow between the electrical conductor <NUM> and the respective electrode element <NUM>. Conversely, when a given one of the switches <NUM> is off (in response to a second state of the respective control input), current cannot flow between the electrical conductor <NUM> and the respective electrode element <NUM>.

In some preferred embodiments, each of the capacitively coupled electrode elements <NUM> is disc-shaped and has a dielectric layer on one side.

In some preferred embodiments, each of the capacitively coupled electrode elements <NUM> comprises a conductive plate with a flat face, and the dielectric layer is disposed on the flat face of the conductive plate. In some preferred embodiments, all of the capacitively coupled electrode elements are held in place by a support structure. In some preferred embodiments, the electrical connection to each of the electrode elements <NUM> comprises a trace on a flex circuit.

Each of the transducer assemblies <NUM>, <NUM> also includes a temperature sensor <NUM> (e.g., a thermistor) positioned at each of the electrode elements <NUM> so that each temperature sensor <NUM> can sense the temperature of a respective electrode element <NUM>. Each of the temperature sensors <NUM> generates a signal indicative of the temperature at (e.g., beneath) the respective electrode element <NUM>. The signals from the temperature sensors <NUM> are provided to the analog front and of the respective controller <NUM>.

In embodiments where thermistors are used as the temperature sensors <NUM>, temperature readings may be obtained by routing a known current through each thermistor and measuring the voltage that appears across each thermistor. In some embodiments, thermistor-based temperature measurements may be implemented using a bidirectional analog multiplexer to select each of the thermistors in turn, with a current source that generates a known current (e.g., <NUM>µA) positioned behind the multiplexer, so that the known current will be routed into whichever thermistor is selected by the analog multiplexer at any given instant. The known current will cause a voltage to appear across the selected thermistor, and the temperature of the selected thermistor can be determined by measuring this voltage. The controller <NUM> runs a program that selects each of the thermistors in turn and measures the voltage that appears across each of the thermistors (which is indicative of the temperature at the selected thermistor) in turn. An example of suitable hardware and procedures that may be used to obtain temperature readings from each of the thermistors is described in <CIT>.

In some preferred embodiments, the controller <NUM> may be implemented using a single-chip microcontroller or Programmable System on Chip (PSoC) with a built in analog front end and multiplexer. Suitable part numbers for this purpose include the CY8C4124LQI-<NUM>. In alternative embodiments, other microcontrollers may be used with either built-in or discrete analog front ends and multiplexers, as will be apparent to persons skilled in the relevant arts.

In alternative embodiments, not shown, an alternative approach (e.g., the conventional voltage divider approach) for interfacing with the thermistors may be used in place of the constant current approach described above. In other alternative embodiments, a different type of temperature sensor may be used in place of the thermistors described above. Examples include thermocouples, RTDs, and integrated circuit temperature sensors such as the Analog Devices AD590 and the Texas Instruments LM135. Of course, when any of these alternative temperature sensors is used, appropriate modifications to the circuit (which will be apparent to persons skilled in the relevant arts) will be required.

In some embodiments, the controller <NUM> is programmed to keep the temperature at all of the electrode elements below a safety threshold using intelligence that is built into each transducer assembly <NUM>. This may be accomplished, for example, by programming the controller <NUM> to start out by setting its digital output so that each of the switches <NUM> is continuously on (i.e., with a <NUM>% duty cycle). Then, based on signals arriving via the controller <NUM> analog front end, the controller <NUM> determines whether the temperature at each of the electrode elements exceeds an upper threshold that is below the safety threshold. When the controller <NUM> detects this condition, the controller <NUM> reduces the duty cycle for the corresponding switch <NUM> by toggling the corresponding digital output at the desired duty cycle. This will interrupt the current to the corresponding electrode element <NUM> at the same duty cycle, thereby reducing the average current at the specific electrode elements <NUM> whose temperature exceeds that upper threshold. The level of reduction in current is determined by the duty cycle. For example, using a <NUM>% duty cycle will cut the current by half; and using a <NUM>% duty cycle will cut the current by <NUM>%.

Notably, this procedure only interrupts the current to specific ones of the electrode elements <NUM> on the transducer assembly <NUM>, and does not interrupt the current to the remaining electrode elements <NUM> on that transducer assembly <NUM>. This eliminates or reduces the need to cut the current that is being routed through the electrode elements when only a small number of those electrode elements are getting hot.

A numeric example will be useful to illustrate this point. Assume, in the <FIG> embodiment, that the left and right transducer assemblies <NUM>, <NUM> are implanted on the left and right sides of a subject's head, respectively; that all of the switches <NUM> in the transducer assemblies <NUM>, <NUM> are in the ON state with a <NUM>% duty cycle; and that the hub/AC voltage generator <NUM> is initially outputting <NUM> mA of current into the conductors <NUM>. An AC voltage will appear between the electrode elements <NUM> of the left transducer assembly <NUM> and the electrode elements <NUM> of the right transducer assembly <NUM>, and the <NUM> mA AC current will be capacitively coupled through the electrode elements <NUM> through the subject's head. The controller <NUM> in each of the transducer assemblies <NUM>, <NUM> monitors the temperature at each of the electrode elements <NUM> in that transducer assembly by inputting signals from each of the temperature sensors <NUM> via the analog front end of the controller <NUM>. Now assume that a given one of the electrode elements <NUM> in the transducer assembly <NUM> begins to overheat. This condition will be reported to the controller <NUM> in the transducer assembly <NUM> via a signal from the corresponding temperature sensor <NUM>. When the controller <NUM> recognizes that the given electrode element <NUM> is overheating, the controller <NUM> will toggle the control signal that goes to the corresponding switch <NUM> at the desired duty cycle in order to periodically interrupt the current to the given electrode element <NUM> and maintain a lower average current.

Note that if the duty cycle at only one of the remaining electrode elements <NUM> is being reduced, it may be possible to maintain the original <NUM> mA current (and enjoy the advantages that arise from using the full current). However, if the duty cycle at a large enough number of the electrode elements <NUM> is being reduced, the original <NUM> mA current may have to be dropped. To accomplish this, the controller <NUM> can send a request to the hub/AC voltage generator <NUM> via the UART in the controller <NUM>. When the hub/AC voltage generator <NUM> receives this request, the hub/AC voltage generator <NUM> will reduce the output current at its corresponding output OUT1.

Optionally, the duty cycle that is selected by the controller <NUM> may be controlled based on the speed at which the given electrode element <NUM> heats up after current is applied to the given electrode element <NUM> (as measured via the temperature sensors <NUM> and the analog front end of the controller <NUM>). More specifically, if the controller <NUM> recognizes that a given electrode element <NUM> is heating up twice as fast as expected, the controller <NUM> can select a duty cycle of <NUM>% for that electrode element. Similarly, if the controller <NUM> recognizes that a given electrode element <NUM> is heating up <NUM>% faster than expected, the controller <NUM> can select a duty cycle of <NUM>% for that electrode element.

In other embodiments, instead of deterministically cutting the average current by reducing the duty cycle, the controller <NUM> can reduce the average current at a given electrode element <NUM> based on real-time temperature measurements by turning off the current to the given electrode element <NUM> and waiting until temperature measured using the temperature sensors <NUM> drops below a second temperature threshold. Once the temperature drops below this second temperature threshold, the controller <NUM> can restore the current to the given electrode element <NUM>. This may be accomplished, for example, by controlling the state of the control input to the switch <NUM> that was previously turned off so that the switch <NUM> reverts to the ON state, which will allow current to flow between the electrical conductor and the respective electrode element <NUM>. In these embodiments, the current to a given electrode element <NUM> may be repeatedly switched off and on based on real-time temperature measurements in order to keep the temperature at the given electrode element <NUM> below the safety threshold.

In the <FIG> embodiment, each of the transducer assemblies <NUM>, <NUM> is connected to the hub/AC voltage generator <NUM> via a respective cable. Notably only <NUM> conductors are required in each of the cables that run between the transducer assembly and the hub/AC voltage generator <NUM> (i.e., Vcc, data, and ground for implementing serial data communication, plus one additional conductor <NUM> for the AC current TTFields signal).

Note that in <FIG>, each transducer assembly <NUM>, <NUM> includes nine electrode elements <NUM>, nine switches <NUM>, and nine temperature sensors <NUM>. But in alternative embodiments, each transducer assembly <NUM>, <NUM> can include a different number (e.g., between <NUM> and <NUM>) of electrode elements <NUM> and a corresponding number of switches and temperature sensors.

In these embodiments, the decision to adjust the duty cycle or turn off one or more of the switches <NUM> in a given transducer assembly <NUM>, <NUM> in order to reduce the average current to one or more of the electrode elements <NUM> is made locally in each transducer assembly <NUM>, <NUM> by the controller <NUM> within that transducer assembly <NUM>, <NUM>. But in alternative embodiments, the decision to adjust the duty cycle or turn off one or more of the switches <NUM> may be made by the hub/AC voltage generator <NUM> (or another remote device). In these embodiments, the controller <NUM> in each of the transducer assemblies <NUM>, <NUM> obtains the temperature readings from each of the temperature sensors <NUM> in the respective transducer assembly and transmits those temperature readings to the hub/AC voltage generator <NUM> via the UART of the controller <NUM>. The hub/AC voltage generator <NUM> decides which, if any, of the switches require a duty cycle adjustment or should be turned off based on the temperature readings that it received, and transmits a corresponding command to the corresponding controller <NUM> in the corresponding transducer assembly <NUM>, <NUM>. When the controller <NUM> receives this command from the hub/AC voltage generator <NUM>, the controller <NUM> responds by setting its digital output to a state that will switch off the corresponding switch <NUM> at the appropriate times, in order to carry out the command that was issued by the hub/AC voltage generator <NUM>. In these embodiments, the hub/AC voltage generator <NUM> can also be programmed to reduce its output current if a reduction in current is necessary to keep the temperature at each of the electrode elements <NUM> below the safety threshold.

In these embodiments, the controller <NUM> may be programmed to operate as a slave to a master controller located in the hub/AC voltage generator <NUM>. In these embodiments, the controller <NUM> starts out in a quiescent state, where all it does is monitor incoming commands from the master controller that arrive via the UART. Examples of commands that can arrive from the master controller include a "collect temperature data" command, a "send temperature data" command, and a "set switches" command. When the controller <NUM> recognizes that a "collect temperature data" command has arrived, the controller <NUM> will obtain temperature readings from each of the temperature sensors <NUM> and store the result in a buffer. When the controller <NUM> recognizes that a "send temperature data" command has arrived, the controller <NUM> will execute a procedure that transmits the previously collected temperature readings from the buffer to the hub/AC voltage generator <NUM> via the UART <NUM>. And when the controller <NUM> recognizes that a "set switches" command has arrived, the controller <NUM> will execute a procedure to output appropriate voltages on its digital output in order to set each of the switches <NUM> to a desired state (i.e., either ON, OFF, or switching between on and off at a commanded duty cycle) based on data that arrives from the hub/AC voltage generator <NUM>.

In the embodiments described above, a single controller <NUM> is used in each of the transducer assemblies <NUM>, <NUM> to control the switches <NUM> in that assembly and also to obtain temperature measurements from each of the temperature sensors <NUM> in that assembly. In alternative embodiments, instead of using a single controller <NUM> to control the switches <NUM> and to obtain the temperature measurements, those two tasks may be divided between two controllers, one of which is only used to control the switches <NUM>, and the other of which is used to obtain the temperature measurements from each of the temperature sensors <NUM> (e.g., using any of the approaches described above). In these embodiments, these two controllers may communicate directly with each other, and/or the hub/AC voltage generator <NUM>.

In other alternative embodiments (not shown), temperature measurement does not rely on a local controller that is positioned in the vicinity of the electrode elements <NUM>. Instead, wires run from each of the temperature sensors <NUM> back to the hub/AC voltage generator <NUM>, and the hub/AC voltage generator uses signals that arrive via these wires to determine the temperature at each of the temperature sensors <NUM>.

<FIG> is a schematic diagram of a circuit that is suitable for implementing the switches <NUM>, <NUM>' in the <FIG> embodiment described above. The circuit includes two field effect transistors <NUM>, <NUM> wired in series, which is a configuration that can pass current in either direction. One example of a suitable FET for this circuit is the BSC320N20NSE. (Note that the diodes depicted in <FIG> are inherently included within the FETs <NUM>, <NUM> themselves. ) The series combination of the two FETs <NUM>, <NUM> will either conduct or block the flow of electricity, depending on the state of the control input that arrives from one of the digital outputs of the controller <NUM> described above. When the series combination is conducting, current can flow between the shared conductor <NUM> and the respective electrode element <NUM>, <NUM>'. On the other hand, when the series combination of FETs <NUM>, <NUM> is not conducting, current will not flow between the shared conductor <NUM> and the respective electrode element <NUM>, <NUM>'.

Optionally, a current sensing circuit <NUM> may be positioned in series with the switch <NUM>, <NUM>'. The current sensing circuit <NUM> may be implemented using any of a variety of conventional approaches that will be apparent to persons skilled in the relevant arts. When the current sensing circuit <NUM> is included, it generates an output that is representative of the current, and this output is reported back to the controller <NUM> (shown in <FIG>). The controller <NUM> can then use this information to determine whether the measured current is as expected and take appropriate action if necessary. For example, if an overcurrent condition is detected, the controller <NUM> can turn off the corresponding switch. Of course, in those embodiments where the current sensing circuit <NUM> is omitted, it should be replaced with the wire (or other conductor) so that the current can flow between the shared conductor <NUM> and the top leg of the upper FET <NUM>.

Claim 1:
An apparatus for delivering tumor treating fields, the apparatus comprising:
a plurality of sets of electrode elements (A, B; <NUM>), wherein each of the sets of electrode elements (A, B; <NUM>) is configured for implantation within a person's body;
a plurality of temperature sensors (<NUM>) configured for implantation within the person's body and positioned to measure a temperature at each of the sets of electrode elements (A, B; <NUM>); and
a circuit (E; <NUM>) configured for implantation within the person's body and
collecting temperature measurements from the plurality of temperature sensors (<NUM>);
wherein all components for implantation are dimensioned to fit within locations for implantation and all surfaces for contact with tissue in the person's body are biocompatible.