Patent Description:
The efficacy of TTFields treatment depends on the field intensity (or power density) of the electric field that is delivered to the tumor. Some experiments have shown, for example, that TTFields are more effective when the field intensity is at least <NUM> V/cm.

The traditional approach for estimating the field intensity (or power density) that is delivered to the tumor relies on numeric simulation techniques that (a) generate a model of the electrical characteristics of the relevant body part from an MRI, (b) position model electrodes on the model body part, and (c) calculate what the intensity of the electric field will be within the tumor when a given AC voltage is applied to the model electrodes. Although this technique can be very useful for determining where to position the arrays on the subject's body and what voltages must be applied in order to achieve the desired field intensity, the technique relies on assumptions about the electrical characteristics (e.g., conductivity) of the tissue between the electrodes.

For example, in the case of a brain tumor, an MRI of the brain is obtained; the MRI is segmented into different types of tissue (e.g., white matter, gray matter, cerebrospinal fluid, etc.); a conductivity value obtained from the scientific literature is assigned to each type of tissue; and the assigned conductivities are used to make a 3D model of the brain, skull, and scalp. Model electrodes are then positioned on the <NUM>-D model, and numeric simulation techniques are used to determine the field intensity within the tumor when a voltage is applied to the model electrodes. But because this technique uses conductivity values obtained from the literature for each type of tissue (instead of using the actual conductivity of each voxel for the specific subject who is about to receive treatment using TTFields), the technique can only provide an estimate of the field intensity or power density in the tumor.

<CIT> discloses a computer-implemented medical data processing method for determining a stimulated nerve fibre disposed in an anatomical body part of a patient's body.

<CIT> discloses an apparatus for determining a thermal property of tissue of a patient, which includes a base unit with one or more energy sources and at least two leads.

<CIT> discloses an apparatus for imposing an electric field in target tissue within an anatomic volume (e.g., to apply TTFields to treat a tumor), which optimizes the position of electrodes by obtaining electrical measurements in the anatomic volume and generating a 3D map of the conductivity directly from the obtained electrical measurements, without segmenting the anatomic volume into tissue types.

<CIT> discloses an illustrative insertion management system for identifying one or more attributes of a lead insertion procedure in which an electrode lead having a plurality of electrodes is inserted into a cochlea of a recipient of a cochlear implant.

<CIT> discloses a method which includes sequentially activating a plurality of respective electrode pairs of an implanted cochlear implant, thereby generating respective localized electric fields, concurrently with respectively measuring, for the plurality of activated respective electrode pairs, an electrical characteristic between the respective electrodes of the respective electrode pairs resulting from the respective localized electric fields, thereby obtaining a measurement set, and determining, from the measurement set, a distance between the electrode array and a wall of the cochlea.

An aspect of this application is directed to an apparatus for generating an output specifying locations for one or more electrode arrays for applying alternating electric fields to a target region in a subject's body according to claim <NUM>.

Embodiments of the invention are disclosed in the the dependent claims.

The embodiments described herein rely on actual measurements of electrical characteristics (e.g., impedances) obtained from the actual subject that is being treated (or will be treated) with TTFields. This approach can provide a significant improvement with respect to the prior art approach described above that uses conductivity values obtained from the scientific literature.

<FIG> depict four transducer arrays 50A/50P/<NUM>/50R (where A, P, L, and R stand for anterior, posterior, left, and right, respectively) that are placed on the subject's skin in close proximity to a tumor (e.g., on the head for a person with glioblastoma). The transducer arrays <NUM> are arranged in two pairs, and each transducer array is connected via a multi-wire cable to an AC signal generator.

<FIG> depicts one approach for implementing each of the arrays 50A, 50P, <NUM>, and 50R depicted in <FIG>. Unlike the prior art configuration, (in which all of the electrode elements within any given transducer array are wired in parallel), this <FIG> embodiment provides an individual conductor for each of the electrode elements <NUM> in each of the transducer arrays <NUM>, and this individual conductor terminates at a connector <NUM>. This makes it possible to independently switch the current on and off for any given individual electrode element <NUM> in any one of the arrays <NUM>. Note that while <FIG> depicts nine electrode elements <NUM> within any given transducer array <NUM>, the number of electrode elements may vary (e.g., between <NUM> and <NUM>).

Each transducer array <NUM> includes at least four electrode elements <NUM>, which are labeled E1-E9 in the <FIG> example. In some embodiments, each of these electrode elements <NUM> is implemented using an electrically conductive substrate (e.g., a round metal substrate) with a dielectric layer disposed thereon. In some preferred embodiments, each of these electrode elements <NUM> is a disc-shaped capacitively coupled electrode element (e.g., with a <NUM> diameter) that is similar to the prior art electrode elements used in the Optune® system, and the dielectric layer comprises a thin layer of ceramic material with a very high dielectric constant (e.g., > <NUM>). In other preferred embodiments, each of the electrode elements is implemented using a conductive pad on a flex circuit, and the dielectric layer comprises a thin layer of a polymer with a high dielectric constant (e.g., > <NUM>). In some preferred embodiments, the electrical connection to each of the electrode elements <NUM> comprises one or more traces on a flex circuit and/or one or more conductive wires.

In some preferred embodiments, each electrode element <NUM> is sandwiched between a layer of an electrically conductive medical gel (on the side that faces the subject) and a support structure <NUM>. The support structure <NUM> holds the entire array <NUM> in place on the subject (e.g., using an adhesive) against the subject's body so that the dielectric layer of the electrode elements <NUM> faces the subject's body and can be positioned in contact with the subject's body. Optionally, this support structure <NUM> may comprise a flexible backing (e.g., a layer of foam material). Preferably, a layer of hydrogel is disposed between the dielectric layer of the electrode elements <NUM> and the subject's body when the transducer array <NUM> is placed against the subject's body. Construction of the support structure <NUM> may be implemented using any of a variety of conventional approaches that will be apparent to persons skilled in the relevant arts, including but not limited to self-adhesive fabric, foam, or plastic sheeting.

The connector <NUM> has at least four pins. In the illustrated embodiment, the number of pins is the same as the number of electrode elements <NUM>, and each of the first pins corresponds to a respective one of those electrode elements <NUM>. Note that as used herein, the term "pin" can refer to either a male or female pin of the connector <NUM>. Each transducer array <NUM> also has a plurality of conductors, and the number of these first conductors will depend on the number of electrode elements <NUM>. Each of these conductors provides an electrically conductive path between the conductive substrate of one of the electrode elements <NUM> and a respective one of the pins in the connector <NUM>. Each of these conductors may be implemented, for example, using a plurality of segments of wire and/or a plurality of traces on a flex circuit.

Because the connector <NUM> has an individual pin that corresponds to each of the individual electrode elements <NUM>, the system that mates with the connector <NUM> can selectively energize or not energize each of the electrode elements <NUM> individually by either applying or not applying a signal to the respective pin on the connector <NUM>.

<FIG> is a block diagram of a system that uses four copies of the transducer array <NUM> (described above in connection with <FIG>) to apply TTFields to a subject. These four copies 50A/50P/<NUM>/50R are positioned on the subject's body (e.g., placed on the subject's skin) anterior, posterior, to the left, and to the right of a tumor, respectively.

The system includes an AC voltage generator <NUM> that generates an AC voltage between its two output terminals. One phase of the AC voltage generator's output is provided to banks of switches 25A and 25R; and the other phase of the AC voltage generator's output is provided to banks of switches 25P and <NUM>. In the illustrated embodiment, each bank of switches includes nine individual switches, each of which corresponds to a respective element on one of the transducer arrays 50A/50P/<NUM>/50R. The number of switches in each bank corresponds to the number of electrode elements in each array. So, for example, in embodiments that have four electrode elements in each array, each bank will include four switches.

The switches in banks 25R and 25A are arranged to, depending on the state of each individual switch, pass or block the first phase of the AC voltage generator's output to a corresponding element on the transducer arrays 50R and 50A. And the switches in banks 25P and <NUM> are arranged to, depending on the state of each individual switch, pass or block the other phase of the AC voltage generator's output to a corresponding element on the transducer arrays 50P and <NUM>.

The controller <NUM> controls the state of each switch within each of the banks 25A/25P/<NUM>/25R by issuing appropriate control signals to the banks of switches. For example, the controller <NUM> could output <NUM> control bits, with one bit corresponding to each of the switches, such that when the control bit for any given switch is a <NUM>, the switch will close, and when the control bit for any given switch is a <NUM>, the switch will open.

With this arrangement, when the controller <NUM> issues control signals to close all nine switches in bank 25R and to close all nine switches in bank <NUM>, one phase of the AC voltage generator's <NUM> output will be routed to all of the electrode elements R1-R9 in the first transducer array 50R, and the other phase of the AC voltage generator's output will be routed to all of the electrode elements L1-L9 in the second transducer array <NUM>. Because the arrays <NUM> and 50R are positioned on the subject's skin to the left and to the right of the tumor, respectively, the AC voltage on those transducer arrays <NUM> and 50R will induce an electric field through the subject's body, and the field lines of this electric field will run generally from right to left and left to right, as depicted schematically by the dashed lines in <FIG>. Note that in reality, the electric field lines will not be straight. But straight dashed lines are nevertheless used in <FIG> to represent the general direction of the field lines.

Similarly, when the controller <NUM> issues control signals to close all nine switches in bank 25A and to close all nine switches in bank 25P, one phase of the AC voltage generator's <NUM> output will be routed to all of the electrode elements A1-A9 in the third transducer array 50A, and the other phase of the AC voltage generator's output will be routed to all of the electrode elements P1-P9 in the fourth transducer array 50P. Because the arrays 50A and 50P are positioned on the subject's skin anterior and posterior with respect to the tumor, respectively, the AC voltage on those transducer arrays 50A and 50P will induce an electric field through the subject's body, and the field lines of this electric field will run generally from front to back and back to front, as depicted schematically by the dashed lines in <FIG>.

By periodically switching (e.g., every <NUM> second) back and forth between the two states described in the preceding paragraphs (i.e., one state in which all switches in banks 25R and <NUM> are closed, and another state in which all switches in banks 25A and 25P are closed), the controller causes the system to induce an electric field through the tumor that switches direction every <NUM> second. And the electric fields resulting from this control sequence will be equivalent to the electric fields that are induced in a subject's body using the prior art Optune® system (in which all of the electrode elements in any given transducer array are wired together in parallel), and can therefore be used to treat a tumor in the target volume.

Notably, in addition to replicating the sequence of electric fields that is provided by the prior art Optune® system, the <FIG> embodiment provides an important additional capability. This is because the very same hardware that induces the TTFields in the subject's body (as described above) can also be used to perform impedance tomography of the portion of the subject's body that lies between the transducer arrays 50A/50P/<NUM>/50R. In alternative embodiments, separate sets of electrode elements are used for applying the TTFields and for performing the impedance tomography. When separate sets of electrode elements are used for these two functions, those separate sets of electrode elements match each other in some embodiments. Optionally, the set of electrode elements that is used for making impedance tomography measurements may be integrated into a snug-fitting cap, vest, or other garment.

More specifically, if the controller <NUM> closes a single switch selected from bank 25R and also closes a single switch selected from bank <NUM>, the output of the AC voltage generator <NUM> will be imposed between a single electrode element <NUM> from the first array 50R and a single electrode element <NUM> from the second array <NUM>. By measuring the voltage and current of the AC voltage generator <NUM>, the impedance of the path that includes the two selected electrode elements can be determined. Referring now to <FIG>, if the controller <NUM> closes switch #<NUM> in the first bank 50R and also closes switch #<NUM> in the second bank <NUM>, and measures the voltage and current of the AC voltage generator <NUM>, the impedance of the path that includes elements R1 and L1 (represented schematically by the dashed line between those two elements) can be determined. Similarly, if the controller <NUM> closes switch #<NUM> in the first bank 50R and also closes switch #<NUM> in the second bank <NUM>, and measures the voltage and current of the AC voltage generator <NUM>, the impedance of the path that includes those elements R1 and L2 (represented schematically by the dashed line between those two elements) can be determined. Note that <FIG> only depicts four paths (using dashed lines) for clarity. But when the left array and the right array each include <NUM> elements, a total of <NUM>×<NUM>=<NUM> paths/combinations exist. Preferably, the controller <NUM> sequentially closes a single switch in the first bank 50R and a single switch in the second bank <NUM> corresponding to each of those <NUM> combinations, measures the voltage and current of the AC voltage generator <NUM> for each combination, and determines the impedance of the circuit that includes each of those <NUM> paths based on the voltage and current measurements.

Similarly, referring now to <FIG>, if the controller <NUM> closes switch #<NUM> in the third bank 50A and also closes switch #<NUM> in the fourth bank 50P, and measures the voltage and current of the AC voltage generator <NUM>, the impedance of the path that includes elements A1 and P1 (represented schematically by the dashed line between those two elements) can be determined. Although only four paths are depicted (using dashed lines), when the anterior and posterior arrays each include <NUM> elements, a total of <NUM>×<NUM>=<NUM> paths/combinations exist. Preferably, the controller <NUM> sequentially closes a single switch in the third bank 50A and a single switch in the fourth bank 50P corresponding to each of those <NUM> combinations, and determine the impedance of the circuit that includes each of those <NUM> paths as described above in connection with <FIG>.

These <NUM>+<NUM>=<NUM> measurements are then fed into a conventional back propagation algorithm to determine the impedance at each voxel within a set of voxels that is positioned in the subject's body between the transducer arrays 50A/50P/<NUM>/50R. (When the number of electrode elements in each array is greater than nine, the number of measurements will be larger; and when the number of electrode elements in each array is less than nine, the number of measurements will be smaller. ) Notably, the resolution of these voxels need not be high, and relatively large voxels (e.g., voxels on the order of <NUM><NUM>) are suitable for the purposes described herein. In one example, a volume that measures <NUM> × <NUM> × <NUM> could be divided into a <NUM> × <NUM> × <NUM> array of voxels, which would mean that there are <NUM> voxels. Similarly, a volume that measures <NUM> × <NUM> × <NUM> could be divided into a <NUM> × <NUM> x <NUM> array of voxels, which would mean that there are <NUM> voxels.

Optionally, additional impedance measurements of the volume between the transducer arrays may be obtained and used to refine the calculation of the impedance at each voxel within the target volume. More specifically, referring now to <FIG>, if the controller <NUM> closes switch #<NUM> in the second bank <NUM> and also closes switch #<NUM> in the third bank 50A, and measures the voltage and current of the AC voltage generator <NUM>, the impedance of the path that includes elements L1 and A1 (represented schematically by the dashed line between those two elements) can be determined. Although only four paths are depicted (using dashed lines), a total of <NUM>×<NUM>=<NUM> paths/combinations exist. So the controller <NUM> can sequentially close a single switch in the second bank <NUM> and a single switch in the third bank 50A corresponding to each of those <NUM> combinations, and determine the impedance of the circuit that includes each of those <NUM> paths as described above. Similarly, referring now to <FIG>, if the controller <NUM> closes switch #<NUM> in the first bank 50R and also closes switch #<NUM> in the fourth bank 50P, and measures the voltage and current of the AC voltage generator <NUM>, the impedance of the path that includes elements R1 and P1 (represented schematically by the dashed line between those two elements) can be determined. Although only four paths are depicted (using dashed lines), a total of <NUM>×<NUM>=<NUM> paths/combinations exist. So the controller <NUM> can sequentially close a single switch in the first bank 50R and a single switch in the fourth bank 50P corresponding to each of those <NUM> combinations, and determine the impedance of the circuit that includes each of those <NUM> paths as described above in connection with <FIG>.

When the optional additional impedance measurements described in the previous paragraph are obtained, those impedance measurements are fed into the back propagation algorithm that determines the impedance at each voxel within the target volume to improve the accuracy of the resulting impedance tomography image.

When the impedance of each of the voxels in the region that lies between the transducer arrays is known, those impedances are used to make a model of the body part (e.g., the head). The electric field intensity (or power density) that is delivered to the tumor can then be calculated by applying model voltages to model electrodes that are positioned on the model of the body part, and calculating what the field intensity (or power density) will be within the tumor when a given AC voltage is applied to the model electrodes. And this information can be used to generate a plan for treating the target region with TTFields.

Notably, unlike the prior art techniques described in the background section, when the impedance at each voxel is generated using impedance tomography as described above, the result does not rely on assumptions about the electrical characteristics (e.g., conductivity) of the tissue between the electrodes. More specifically, because this technique uses impedance values for each voxel that are obtained by making measurements of the specific subject who is about to receive treatment using TTFields, this technique can provide improved accuracy with respect to the prior art techniques. Moreover, the techniques described herein that rely on actual impedance measurements advantageously eliminate cumbersome and computation-intensive finite element simulations.

<FIG> depicts a method that uses a set of electrodes positioned on a subject's body to generate a plan for treating a target region in the subject's body using TTFields. Viewing <FIG> together with <FIG>, in step S20 a first set 50R of N electrode elements is positioned on the subject's body on a first side (e.g., the right side) of the target region, and a second set <NUM> of M electrode elements is positioned on the subject's body on a second side (e.g., the left side) of the target region that is opposite to the first side. Both N and M are at least <NUM>, and in the illustrated embodiment N=<NUM> and M=<NUM>.

In step S30, the system sequentially measures, during a first window of time, a respective impedance between each of the N electrode elements in the first set 50R and each of the M electrode elements in the second set <NUM>. This may be accomplished, for example, by sequentially closing combinations of switches in the first bank 25R and the second bank <NUM> (as described above) so that an AC voltage is sequentially imposed between combinations of the electrode elements R1-R9 and L1-L9. While the AC voltage is imposed for each pair, the current and voltage is measured, and the impedance is calculated from those measurements. The first window of time should be long enough to obtain all necessary impedance measurements and will typically be less than <NUM> minutes (e.g., less than one minute).

Next, in step S40, the impedance at each of the voxels (e.g., at least <NUM> voxels or at least <NUM> voxels that correspond to the target region) within an impedance tomographic image is calculated (e.g., using a back propagation algorithm as described above). In step S60, a plan for treating the target region with TTFields is generated based on the calculated impedances of the voxels. The plan could include, for example, a recommendation of where to position the electrode elements (which are used to apply the TTFields) on the subject's body.

Although it is possible to implement the system that only positions electrode elements on first and second sides of the target region, improved results are obtained in embodiments that use optional additional sets of electrodes positioned on the subject's body. More specifically, as explained in connection with <FIG>, a third set 50A of X electrode elements is positioned on the subject's body on a third side (e.g., anterior) of the target region, and a fourth set 50P of Y electrode elements is positioned on the subject's body on a fourth side (e.g., posterior) of the target region that is opposite to the third side. Both X and Y are at least <NUM>, and in the illustrated embodiment X=<NUM> and Y=<NUM>. The system sequentially measures, during the first window of time, a respective impedance between each of the X electrode elements in the third set 50A and each of the Y electrode elements in the fourth set 50P. The calculating of the impedance at each of the voxels in step S40 is also based on the measured impedances between the electrode elements in the third set and the electrode elements in the fourth set (in addition to the measured impedances between the electrode elements in the first set and the electrode elements in the second set).

Optionally, after the plan for treating the target region with alternating electric field is generated, an alternating voltage is applied between a majority (e.g., all) of the electrode elements R1-R9 in the first set 50R and a majority (e.g., all) of the electrode elements L1-L9 in the second set <NUM> in step S70 in order to induce an electric field in one direction in the target region, and an alternating voltage is applied between a majority (e.g., all) of the electrode elements A1-A9 in the third set 50A and a majority (e.g., all) of the electrode elements P1-P9 in the fourth set 50P in order to induce an electric field in another direction in the target region.

The plan for treating the target region with alternating electric fields may comprise generating a recommendation to move at least one set 50A/50P/<NUM>/50R of electrode elements to a different position on the subject's body.

<FIG> depicts a method that uses both an MRI and a set of electrodes positioned on a subject's body to generate a plan for treating a target region in the subject's body using TTFields. First, in step S110, an MRI is obtained. Then, in steps S120-S140, an impedance tomographic image is obtained as described above in connection with S20-S40 in <FIG>. The impedance tomographic image should be obtained within <NUM> days of the MRI, and more preferably within <NUM> days or within <NUM> day of the MRI, to facilitate registration of those two images. In step S150, the impedance tomography voxels are registered to the MRI (e.g., using a conventional image registration algorithm), and the registration is stored in memory. In this embodiment, the plan for treating the target region using TTFields may be generated in step S160 based on both the MRI and the impedance tomography image. The plan could include, for example, a recommendation of where to position the electrode elements (which are used to apply the TTFields) on the subject's body. Finally, treatment of the target region using TTFields occurs in step S170. The MRI obtained in step S110 and the impedance voxels obtained in step S140 serve as baselines for future comparisons.

Subsequent to the registration that occurs in step S150, changes in the tumor can be tracked using only impedance tomography images (e.g., obtained by repeating steps S20-S40 in <FIG>) because if the tumor grows or shrinks, the impedance of voxels in the impedance tomography image will change. Thus, in some embodiments, the plan for treating the target region with alternating electric fields takes into account a comparison between the most recent impedances and the baseline impedances. For example, because tumors typically have different impedance than the tissue around it, a tumor can be detected by impedance tomography and changes in the tumor size can be tracked by impedance changes in the region of the tumor. For example, if the tumor impedance is higher that the tissue around it, an increase in the impedance of a voxel at the periphery of a tumor that was previously identified in the baseline MRI may be an indication that the portion of the tumor within that voxel has grown.

Based on any detected growth, shrinkage, or movement of the tumor, it may be desirable to reposition the electrode elements (which are used to apply the TTFields) to locations that provide increased field strength at the new location of the tumor. Determining the new location for the electrode elements may be implemented using conventional software for that purpose (e.g., Novotal™). Comparing the impedance tomography images to previous impedance tomography images may reduce the need for repeat MRIs or at least extend the interval of time between repeat MRIs.

Optionally, a new impedance tomography image may be generated at periodic intervals (e.g., by repeating steps S20-S40 in <FIG>, e.g., once a day) or every time a new set of transducer arrays is positioned on the subject's body, and each new impedance tomography image is compared to one or more previous impedance tomography images (and optionally to the baseline MRI that was previously registered to the original impedance tomography image). Optionally, the conditions under which all of the impedance tomography images are obtained may be normalized to the extent possible (e.g., using new transducer arrays positioned on freshly shaved skin, normalizing the temperature and humidity at the time the impedance tomography images are captured, and/or normalizing the resting heart rate of the subject).

Optionally, whenever a new transducer array is positioned for the first time on the subject's body, an impedance tomography image is captured, and that impedance tomography image is compared to a previous impedance tomography image. This comparison can determine whether the new transducer array has been positioned in the same location on the subject's skin, or whether the new transducer array has been positioned at an offset location. In the latter situation, the system could output instructions that ask the subject (or a practitioner) to move one of the new transducer arrays to a new location (e.g., "move the right transducer array up <NUM>").

Note that while the embodiments above describe obtaining impedance measurements, similar results can be reached by replacing impedance measurements with conductance measurements. The nature of the changes required to switch from impedances to conductances will be apparent to persons skilled in the relevant arts.

Note also that while the embodiments above describe obtaining impedance measurements using transducer arrays positioned on the subject's body, the impedance measurements could also be obtained using transducer arrays positioned in the subject's body (e.g., by implanting the transducer arrays beneath the subject's skin).

Referring now to <FIG> taken alone, temperature sensors (e.g., thermistors, not shown) may optionally be incorporated into the array <NUM> to measure the temperature of the electrode elements; and hardware for sensing the temperature at each electrode element may be incorporated into the system.

Embodiments illustrated under any heading or in any portion of the disclosure may be combined with embodiments illustrated under the same or any other heading or other portion of the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

Claim 1:
An apparatus for generating an output specifying locations for electrode arrays (50A, 50P, <NUM>, 50R) providing sets of electrode elements (<NUM>; E1-<NUM>; A1-<NUM>, P1-<NUM>, L1-<NUM>, R1-<NUM>) for applying alternating electric fields to a target volume in a subject's body, characterized by the apparatus comprising a processor programmed to:
sequentially measure, during a first window of time and using a first set of at least four electrode elements (<NUM>; E1-<NUM>; A1-<NUM>, P1-<NUM>, L1-<NUM>, R1-<NUM>) positioned on or in the subject's body on a first side of the target volume and a second set of at least four electrode elements (<NUM>; E1-<NUM>; A1-<NUM>, P1-<NUM>, L1-<NUM>, R1-<NUM>) positioned on or in the subject's body on a second side of the target volume that is opposite to the first side, an impedance or conductance of each of respective paths between each of the electrode elements (<NUM>; E1-<NUM>; A1-<NUM>, P1-<NUM>, L1-<NUM>, R1-<NUM>) in the first set and each of the electrode elements (<NUM>; E1-<NUM>; A1-<NUM>, P1-<NUM>, L1-<NUM>, R1-<NUM>) in the second set;
calculate, based on the measured impedances or conductances of each of the respective paths between each of the electrode elements (<NUM>; E1-<NUM>; A1-<NUM>, P1-<NUM>, L1-<NUM>, R1-<NUM>) in the first set and each of the electrode elements (<NUM>; E1-<NUM>; A1-<NUM>, P1-<NUM>, L1-<NUM>, R1-<NUM>) in the second set, a first impedance or conductance at each of at least <NUM> voxels that correspond to the target volume; and
generate a first output specifying locations for one or more of the electrode arrays (50A, 50P, <NUM>, 50R), based on the first impedances or conductances of the voxels, for applying alternating electric fields to a first target in the target volume.