WO2013076440A1

WO2013076440A1 - Radio frequency surgical probe

Info

Publication number: WO2013076440A1
Application number: PCT/GB2012/000845
Authority: WO
Inventors: Zhigang Wang
Original assignee: The University Of Dundee
Priority date: 2011-11-21
Filing date: 2012-11-20
Publication date: 2013-05-30
Also published as: GB201120023D0; GB2510309B8; GB201409118D0; GB2510309B; GB2510309A

Abstract

An apparatus for treating a solid tumour to destroy tumour. It has a radio frequency (RF) probe with a distal portion which has mechanically rigid electrodes which when deployed form an electrical bridge circuit with each electrode component being electrically insulated. The deployed electrodes define a region within which a return path for a radio frequency current can be created such that the current is transmittable with more uniform distribution between a pair of opposite and parallel electrodes via the return path. The electrodes are provided with a switch to turn the electrodes on and off in order to change the shape and position of the return path to provide a desired heating effect on the solid tumour when situated within the region.

Description

Radio Frequency Surgical Probe

Introduction The present invention relates to an apparatus and method for destruction and separating/removing solid tumours and in particular to the application of

radiofrequency (RF) electromagnetic energy this purpose.

Background

Cancer in solid organs (e.g. liver, kidney, breast) can be destroyed by heat created by an alternating current or a direct current to weaken or kill cells. This technique is generally known as thermal therapy and there are three commonly used techniques for destroying cells in this way.

Cell hyperthermia exposes the cancer cells to slightly higher temperatures of around 39 to 50°C to damage and kill cancer cells or to make cancer cells more sensitive to the effects of radiation and certain anti-cancer drugs. Hyperthermia is known to be useful for treatment of a small number of cancer types, is not in widespread use and is most effective when used alongside conventional therapies.

Electrosurgery is the application of a high-frequency electric current to biological tissue as a means to cut, coagulate or desiccate tissue. Its benefits include the ability to make precise cuts with limited blood loss. Electrosurgical devices are frequently used during surgical operations helping to prevent blood loss in hospital operating rooms or in outpatient procedures.

In electrosurgical procedures, the tissue is heated by an electric current to

around/above 100°C which causes rapid heating and destruction of cells at or near the "blade". Although electrical devices may be used for the cauterization of tissue in some applications, the term electrosurgery is usually used to refer to a quite different method than electrocautery. The latter uses heat conduction from a probe heated to a glowing temperature by a direct current (much in the manner of a soldering iron). Electrosurgery, by contrast, uses alternating current to directly heat the tissue itself.

Radio frequency ablation (RFA) is a technique in which dysfunctional tissue is ablated using the heat generated from a high frequency alternating current to treat a medical disorder. An important advantage of RF current (over previously used low frequency AC or pulses of DC) is that it does not directly stimulate nerves or heart muscle and can therefore often be used without the need for general anaesthetic. RFA is performed to treat tumours in lung, liver, kidney, bone and (rarely) in other body organs. Once a patient has been diagnosed as having a tumour is confirmed, the medical procedure involves the insertion of a needle-like RFA probe inside the tumour. The radiofrequency waves passing through the probe increase the temperature within tumour to above 50°C which results in the destruction of the tumour. Generally RFA is used to treat patients with small tumours that originated within the organ (primary tumours) or those tumours which have spread to the organ (metastasis).

One advantage of this approach is that it may allow the patient to avoid major surgery for the removal of the tumour. An RF signal may be applied percutaneously with image guidance by CT, MR) or external ultrasound, or laparoscopically with visual guidance accompanied by contact ultrasound.

One of the challenges in thermal therapy is delivering the appropriate amount of heat to the correct part of the patient's body. For this technique to be effective, the temperatures must be high enough, and the temperatures must be sustained long enough, to damage or kill the cancer cells. However, if the temperatures are too high, or if they are kept elevated for too long, then serious side effects, including death can result. The smaller the area to which the heat is applied and the shorter the treatment time the less are the side effects.

RF probes and instruments come in various designs and configurations. For example, the 17-gauge needle electrode (Cool-tip RFA, Valleylab-Covidien, USA approved by the United States Food and Drug Administration (FDA)), can be configured as a cluster (3-needles) and may be used in treating non-resectable liver tumours, This is a mono-polar RFA system which requires a skin pad-electrode to provide an electrode for the current return path to the RF generator. Monopolar RFA systems such as that described in Zerfas et al, US patent 7458971 B2, Dec. 2008 can use a probe with an array of electrodes or expandable hooks.

Young & Zerfas, (US patent 7524318, Apr 2009) discloses a system with various configured electrodes exemplified by the Christmas tree-like RITA needle (RITA Medical System, Inc., USA) or LeVeen electrode (umbrella-shaped array) from Boston Scientific (www.bostonscientific.com). Tissue impedance and/or in-situ temperature measurement are used as feedback to a control system which provides the appropriate level of RF energy output. Bipolar RF probes can be created by closely arranging 2 electrodes at the tip of an RFA needle such as in CelonProSurge (www.celon.com) applicator [Anticancer Res 29:1309-1314 (2009)]. Bipolar and multipolar RFA electrode systems are shown in Lee, Jr. et al, US patent 7520877 B2, Apr 2009.

Where tumour cells have not been completely destroyed residual viable cancer cells will be present in the patient and will result in cancer recurrence after treatment. When using existing RFA devices, it is difficult to know where the RFA treatment margin is and it is difficult to deliver the RFA within the margin. It is also difficult to heat the tumour uniformly across the tumour to achieve RF ablation of the whole targeted tissues within the treatment margin. Current RFA technology provides an RFA electrode (or multiple electrodes) which when inserted into the target tumour, heats the tumour tissue around the

electrode(s). The heat then conducts to the outer regions achieving volumetric thermal ablation The use of point source heating creates a reduction in heat intensity at a distance from the electrode and a non-uniform heat distribution especially to the periphery of the tumour and an inability to accurately determine the physical extent to which treatment has been effective and therefore the treatment margin. This problem accounts for the inability of the current RFA technology to treat effectively tumours which are >3.5 cm. Tissue heterogeneity and local thermal losses (heating sink effect from blood vessels) also contribute to non-uniform heat distribution and to the potential for incomplete ablation which causes the presence of residua⁾ viable cancer cells and hence recurrence of the cancer after treatment.

Summary of the Invention

In accordance with a first aspect of the invention there is provided an apparatus for treating a solid tumour to destroy tumour cells therein, the apparatus comprising: a radio frequency (RF) probe having a distal portion for treating said tumour cells and a proximal portion,

wherein the distal portion comprises a plurality of substantially mechanically rigid electrodes which when deployed form an electrical bridge circuit with each electrode component being electrically insulated and which define a region within which a return path for a radio frequency current can be created such that the current is transmittable with more uniform distribution between a plurality of said electrodes via the return path and wherein the electrodes are provided with a switch to turn the electrodes on and off in order to determine the shape and position of the return path to provide a desired heating effect on the solid tumour when situated within the region.

Preferably, the current is transmittable between a pair of said opposite and parallel located electrodes

Preferably, the plurality of electrodes comprises a central elongate electrode having a longitudinal axis and a plurality of peripheral electrodes which are coupled to and radially extendable from a retracted position on the longitudinal axis of the elongate electrode to an extended position at a predetermined distance from the longitudinal electrode to define the region containing the return path.

Optionally, the plurality of electrodes comprises an array of electrodes. Optionally, the plurality of electrodes are spaced apart along a longitudinal member or probe.

Preferably, the peripheral electrode comprises at least two electrodes articulatably connected to move from the retracted position to the extended position. Preferably, the apparatus comprises first and second peripheral electrodes. Preferably, the first and second peripheral electrodes are arranged on opposing sides of the elongate electrode.

Optionally, the first and second peripheral electrodes are arranged adjacent to one another on the elongate electrode.

Preferably, the peripheral electrode comprises at least two rigid arms articulatably connected to move from the retracted position to the extended position.

Preferably, the articulatable connection comprises a hinge.

Optionally, the articulatable connection comprises a flexible mechanical structure or joint.

Preferably, the peripheral electrode is fixedly connected to the elongate electrode at the distal end of the apparatus end remote and is slidably connected to the elongate electrode at the proximal end of the apparatus.

Optionally, a third peripheral electrode can be arranged on the front side of the elongate electrode.

Optionally, a fourth peripheral electrode can be arranged on the back side of the elongate electrode.

Optionally, the peripheral electrode comprises a shape memory alloy.

Preferably, the shape memory alloy can be changed in-situ to its previously heat- treated shape to optimally conform to any specific requirements of the volume where the tumour is to be destroyed. Preferably, the end of the elongate electrode which is remote from the handle comprises a cutting tip for easy insertion into a tumour.

Preferably, the peripheral electrodes are further configured by external electrical connection in series to function as a single bipolar or monopolar electrode.

Preferably, the bipolar electrode has an RF return path provided by a central elongate electrode. Preferably, the monopolar electrode has an RF return path provided by a skin mountable electrode.

Preferably, the cutting tip is heated. Preferably, the cutting tip is heated electrically.

Preferably, the proximal end of the apparatus comprises a handle.

Preferably, the apparatus further comprises a temperature sensor for measuring temperature in the region.

Preferably, the temperature sensor measures differences in temperature across the region. Optionally, the temperature sensor is located on the longitudinal electrode.

Optionally, the temperature sensor comprises a plurality of sensors positioned on one or more of the electrodes. In accordance with a second aspect of the invention there is provided a method for treating a solid tumour to destroy tumour cells therein, the method comprising the steps of: positioning a plurality of electrodes to define a region around a target such that a current is transmittable between at least two of said electrodes via an electrical return path in the region;

determining a desired current distribution within the region that is required to heat the target

switching the electrodes to turn the electrodes on and off in order to obtain the desired shape and position of the return path to provide the current distribution and heating effect. Preferably, the method further comprises the step of changing the desired current distribution and switching the electrodes to turn the electrodes on and off in order to obtain the desired shape and position of the return path in response to the change to the desired current distribution. Preferably, the step of changing the desired current distribution further comprises determining the temperature within the region to find areas which are too hot or too cold and switching the electrodes to change the position and shape of the return path to adjust the temperature across the region. Preferably, the plurality of electrodes comprises a central elongate electrode having a longitudinal axis and a plurality of peripheral electrodes which are coupled to and radially extendable from a retracted position on the longitudinal axis of the elongate electrode to an extended position at a predetermined distance from the longitudinal electrode to define the region containing the return path.

Optionally, the plurality of electrodes comprises an array of electrodes.

Optionally, the plurality of electrodes are spaced apart along a longitudinal member or probe.

Preferably, the peripheral electrode comprises at least two electrodes articulatably connected to move from the retracted position to the extended position.

Preferably, the peripheral electrodes are substantially rigid. Preferably, the first and second peripheral electrodes are arranged on opposing sides of the elongate electrode. Optionally, the first and second peripheral electrodes are arranged adjacent to one another on the elongate electrode.

Preferably, the articulatable connection comprises a hinge.

Preferably, the peripheral electrode is fixedly connected to the elongate electrode at the distal end of the apparatus end remote and is slidably connected to the elongate electrode at the proximal end of the apparatus. Optionally, a third peripheral electrode can be arranged on the front side of the elongate electrode.

Optionally, the peripheral electrode comprises a shape memory alloy.

Preferably, the shape memory alloy can be changed in-situ to its previously heat- treated shape to optimally conform to any specific requirements of the volume where the tumour is to be destroyed.

Preferably, the end of the elongate electrode which is remote from the handle comprises a cutting tip for easy insertion into a tumour. Preferably, the cutting tip is heated.

Preferably, the cutting tip is heated electrically. Preferably, the proximal end of the apparatus comprises a handle.

Preferably, the apparatus further comprises a temperature sensor for measuring temperature in the region. Preferably, the temperature sensor measures differences in temperature across the region.

Optionally, the temperature sensor is located on the longitudinal electrode. Optionally, the temperature sensor comprises a plurality of sensors positioned on one or more of the electrodes.

In accordance with a third aspect of the invention there is provided a computer program having program instructions for implementing the method in accordance with the second aspect of the present invention.

Brief Description of the Drawings

The present invention will now be described by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a schematic diagram of a first embodiment of the present invention in the extended position; Figure 2 shows a schematic diagram of a second embodiment of the present invention in the extended position;

Figures 3a and 3b show an embodiment of the present invention similar to that shown in figure 1 where the RF current is selectively switched on at a first combination of electrodes, figure 3c shows a calculated temperature iso-surface (>50°C) distribution within the region at 5 minutes;

Figure 4 shows an embodiment of the present invention similar to that shown in figure 1 where the RF current is selectively switched on at a second combination of electrodes;

Figure 5 shows an example of combined heating effect of the present invention after sequentially activated in figure 3b and figure 4; and

Figures 6a and 6b show an embodiment of the present invention similar to that shown in figure 1 where the RF current is selectively switched on at a third

combination of electrodes. Detailed Description of the Drawings

Figure 1 is a schematic drawing of a first embodiment of an RF probe 1 in

accordance with the present invention. The probe 1 comprises a handle or proximal portion 3 and a distal portion 5 which comprises a plurality of electrodes. A central electrode 15 extends from the top of the handle to the distal end of the device where it is connected to a joint 21. The left hand side of the distal end 5 of the probe 1 comprises electrodes 9 and 13. Electrode 9 is connected to electrode 13 by means of a joint 7 and to the proximal end of the probe by a joint 19. The joints allow the angle between the electrodes 9 and 13 and the angle between electrode 9 and the central electrode to be varied. Electrode 13 is connected to the distal end of the probe by joint 21 which allows the angle between the electrode 13 and the central shaft-electrode 15 to be varied.

The right hand side of the distal end 5 of the probe 1 comprises electrodes 7 and 11. Electrode 7 is connected to electrode 11 by means of a joint 23 and to the proximal end of the probe by a joint 19. The joints allow the angle between the electrodes 11 and 7 and the angle between electrode 11 and the central electrode to be varied. Electrode 7 is connected to the distal end of the probe by joint 21 which allows the angle between the electrode 7 and central shaft-electrode 15 to be varied.

In use, the probe may be inserted into a patient with the electrodes in a retracted position whereby all of the electrodes are substantially coaxial with the central electrode 5 thereby minimising the cross sectional area of the probe during insertion.

Figure 2 is a schematic drawing of a second embodiment of an RF probe 31 in accordance with the present invention. The probe 31 comprises a handle or proximal portion 33 and a distal portion 35 which comprises a plurality of electrodes. A central electrode 45 extends from the top of the handle to the distal end of the device where it is connected to a mounting 51 The left hand side of the distal end 35 of the probe 31 comprises electrodes 39 and 43. Electrode 39 is connected to electrode 43 by means of a joint 47 and to the proximal end of the probe by a joint 49. The joints allow the angle between the electrodes 39 and 43 and the angle between electrode 39 and the central electrode to be varied. Electrode 43 is connected to the distal end of the probe by joint 51 which allows the angle between the electrode 43 and the distal end of the probe 31 to be varied.

Use of an embodiment of the present invention similar to that shown in figure 1 will now be described with reference to figures 3 to 6. In figures 3 to 6, the same reference numerals have been used as in figure 1 where identical features of the apparatus are described. The present invention provides a plurality of electrodes which are switchable on and off in order to change the position and shape of the electrical return path which is situated within a region, typically inside a patient undergoing treatment for the removal and/or destruction of a solid tumour. One feature of the present invention is the ability to use changes in current distribution to produce controllable heat gradients within the region and to control temperature to a suitable level for cell necrosis. This is typically temperatures around or above 50° C:

Figures 3a, 3b and 3c show the use of the present invention to provide sequential heating with two parallel electrodes (7 and 9) which have been activated whilst the other electrodes remain switched off. In those circumstances, uniform RF current flows in the parallel electrode pair and the return path is concentrated in the region between electrodes 7 and 9.

As shown in Figure 3a the electrode 7 is connected to electrode 11 at the right hand side of the device. Electrode 9 is connected to array electrode 13 at the left hand side of the device. The central shaft can be configured as array electrode 15.

A sliding actuator 30 (or other displacement mechanism) is reciprocally mounted on the handle and is coupled to electrodes 9 and 11. Movement of the sliding actuator 30 up the handle bends towards the distal end causes the joints 17, 21 located between respective electrodes to bend and to extend the electrodes 7, 9, 11 and 13 into a range of positions which extend radially outwards from the central electrode 15 thereby allowing different deployed shapes. A locking mechanism is also provided to maintain the electrodes in their chosen position.

In the case of figure 3 a to c, and 4 to 6 when the electrodes 7, 9, 11 and 13 are deployed inside a patient to the site of a tumour or target. The positioning of the electrodes which form the probe at the margin or periphery of the tumour is dependent upon the size of margin that the surgeon wishes to have and other considerations such as whether other treatment of the tumour has been undertaken and the quality of the electrode/tissue interface required to obtain the appropriate level of impedance in the region.

Figures 3a and 3b show a treatment sequence in accordance with the present invention in which array electrodes 7 and 9 are activated while other array electrodes are effectively switched off by being suspended in high impedance (high Z). This will result in RF current flow uniformly from electrodes 7 to 9 through the return path as illustrated by the lines 53 in figure 3b. The parallel arrangement of the electrodes 7 and 9 produces a substantially even current distribution due to the parallel arrangement of the two activated electrodes which will generate a heated volume with a substantially even heat distribution. Figure 3c shows a FE (finite element method) simulated RF ablated volume with a temperature iso-surface >50°C at 5 minutes treatment time. A second example of a treatment sequence in accordance with the present invention is shown in figure 4. In this example, electrodes 11 and 13 are activated while the other electrodes are suspended in high impedance (high Z). This will result in RF current flowing uniformly from electrodes 11 to 13 through the return path as illustrated by the lines 55 figure 4. The parallel arrangement of the electrodes 1 and 13 produces a substantially even current distribution due to the parallel arrangement of the two activated electrodes which will generate a heated volume with a substantially even heat distribution. This will generate similar heated volume as shown in Figure 3c.

In the next embodiment of the present invention, the switching sequences as described with respect to figures 3b and 4 are used in together but sequentially. This combined treatment changes the shape and position of the return path and has a consequent effect upon the heat distribution within the region. One example of the resultant combined treated volume (region) has temperature iso-surfaces which are illustrated in Figure 5. This treatment sequences can be repeated many times automatically via computer control algorithm to obtain optimal RF ablation of tissue using lower RF dose (current/power) in each particular sequence.

There will also be an integrated miniature temperature sensor at electrode 5 to determine whether the heated volume extends sufficiently through the central area. In the case of a large target, there might be a central area of the region which remains unheated to the specified temperature where the above sequence is used. This is illustrated in Figure 5 which shows the apparatus of the invention 1 and the heated areas 63, 65, 67 and 69 as a white small area (hole) 61 which is not heated to a sufficiently high temperature for cell necrosis.

One of the advantages of the present invention is that where part of the region is not heated to a sufficient temperature, The electrodes may be switched and a different RF heating sequence can be used which concentrates the return path (and therefore heating effect) upon the area which has been insufficiently heated. In this example, all of the electrodes, 7, 9, 11, 13 and 15 are activated with the longitudinal electrode 15 as the positive electrode and electrodes, 7, 9, 11 and 13 as negative or ground electrodes, as shown in figure 6a. The above sequence causes there to be a return path from each of the electrode 7, 9, 11 and 13 to the

longitudinal electrode 15. Figure 6b shows an embodiment of the apparatus of the present invention 1 with lines showing F current flow 71 and shading 73 which depicts the region where high RF current density is to be found around electrode 15 and where a heated temperature iso-surface/volume will arise. In use, it is possible to combine all of the RF current switching sequences as described above to produce a treatment effect which results in the complete RF ablation of the whole targeted volume. Rotating the probe by 180 degrees may be needed to locate the array electrodes in a perpendicular plane and to RF ablate a spherical/cylindrical tumour volume. In this example of a probe with 4 limbs located in two perpendicular planes (right/left, and front/back), there would be no need for the rotation of the probe because the treatment sequences in two limbs could be repeated.

Figures 1 and 3 to 6 show embodiments of the present invention each of which have two limbs each comprising two electrodes and being arranged around a central shaft which also comprises an electrode. Figure 2 shows a one limb structure which has one limb comprising two electrodes and being arranged around a central shaft which also comprises an electrode. It will be appreciated a device in accordance with the present invention can be provided with additional limbs, for example, two limbs could be added in the plane perpendicular to the plane in which the first two limbs are located and have a similar structure to that described above with the electrodes joint connected and a sliding/locking mechanism for conformal deployment. In addition, it will be appreciated that alternative electrode geometries may be used to provide configurable heating of a region where the region forms the return path for the RF current. For example one or more linear probes could have a plurality of switchable electrodes thereby forming an array of switchable elements. This would also allow the shape and position of the return path to be tailored to the shape and position of a tumour. The rigid electrode may be made of shape memory alloy (SMA) materials such as Nickel Titanium (NiTi or Nitinol) with any suitable pre-treated shapes. For example, a straight rigid SMA wire or strip in Figs. 1-5 can be changed in-situ to its previously heat-treated shape such as a curved wire or strip when it is heated (by RF current) above its transformation temperature. The transformation temperature of Nitinol material can be adjusted and may be set to that from body temperature up to 100 degree C, for example at 50 degree C. The selection of pre-treated shapes for the rigid electrode is to optimally conform to any specific or irregular cancer geometry of individual patient, thus this will cause less damage to the surrounding healthy tissue beyond its margin clearance (e.g. 5mm):

Improvements and modifications may be incorporated herein without deviating from the scope of the invention.

Claims

1. An apparatus for treating a solid tumour to destroy tumour cells therein, the apparatus comprising:

a radio frequency (RF) probe having a distal portion for treating said tumour cells and a proximal portion,

2. An apparatus as claimed in claim 1 wherein, the current is transmittable between a pair of said opposite and parallel located electrodes

3. An apparatus as claimed in claim 1 or claim 2 wherein, the plurality of electrodes comprises a central elongate electrode having a longitudinal axis and a plurality of peripheral electrodes which are coupled to and radially extendable from a retracted position on the longitudinal axis of the elongate electrode to an extended position at a predetermined distance from the longitudinal electrode to define the region containing the return path.

4. An apparatus as claimed in claim 1 or claim 2 wherein, the plurality of electrodes comprises an array of electrodes.

5. An apparatus as claimed in claim 1 or claim 2 wherein, the plurality of electrodes are spaced apart along a longitudinal member or probe.

6. An apparatus as claimed in claim 3 wherein, the peripheral electrode comprises at least two electrodes articulatably connected to move from the retracted position to the extended position.

7. An apparatus as claimed in claims 3, 5 or 6 wherein, the apparatus comprises first and second peripheral electrodes.

8. An apparatus as claimed in any of claims 3, and 5 to 7 wherein, the first and second peripheral electrodes are arranged on opposing sides of the elongate electrode.

9. An apparatus as claimed in any of claims 3, and 5 to 8 wherein, the first and second peripheral electrodes are arranged adjacent to one another on the elongate electrode.

10. An apparatus as claimed in any of claims 3, and 5 to 9 wherein, the

peripheral electrode comprises at least two rigid arms articulatably connected to move from the retracted position to the extended position.

11. An apparatus as claimed in claim 0 wherein, the articulatable connection comprises a hinge or flexible mechanical structure.

12. An apparatus as claimed in any of claims 3, and 5 to 1 wherein, the peripheral electrode is fixedly connected to the elongate electrode at the distal end of the apparatus end remote and is slidably connected to the elongate electrode at the proximal end of the apparatus.

13. An apparatus as claimed in claim 3, further comprising, a third peripheral electrode arranged on the front side of the elongate electrode.

14. An apparatus as claimed in claims 3 or claim 13 further comprising a fourth peripheral electrode arranged on the back side of the elongate electrode.

15. An apparatus as claimed in any preceding claim wherein, the peripheral electrode comprises a shape memory alloy.

16. An apparatus as claimed in claim 15 wherein, the shape memory alloy is changeable in-situ to its previously heat-treated shape to optimally conform to any specific requirements of the volume where the tumour is to be destroyed.

17. An apparatus as claimed in claim 3 wherein, the end of the elongate electrode which is remote from the handle comprises a cutting tip for easy insertion into a tumour.

18. An apparatus as claimed in claim 2 wherein, the peripheral electrodes are further configured by external electrical connection in series to function as a single bipolar or monopolar electrode.

19. An apparatus as claimed in claim 18 wherein the bipolar electrode has an RF return path provided by a central elongate electrode.

20. An apparatus as claimed in claim 18 wherein the monopolar electrode has an RF return path provided by a skin mountable electrode.

21. An apparatus as claimed in claim 17 wherein, the cutting tip is heated.

22. An apparatus as claimed in any preceding claim wherein, the apparatus further comprises a temperature sensor for measuring temperature in the region.

23. An apparatus as claimed in claim 22 wherein, the temperature sensor measures differences in temperature across the region.

24. An apparatus as claimed in claim 22 or claim 23 wherein, the temperature sensor is located on the longitudinal electrode. .

25. An apparatus as claimed in claim 22 or claim 23 wherein, the temperature sensor comprises a plurality of sensors positioned on one or more of the electrodes.

26. A method for treating a solid tumour to destroy tumour cells therein, the method comprising the steps of:

positioning a plurality of electrodes to define a region around a target such that a current is transmittable between at least two of said electrodes via an electrical return path in the region;

determining a desired current distribution within the region that is required to heat the target switching the electrodes to turn the electrodes on and off in order to obtain the desired shape and position of the return path to provide the current distribution and heating effect.

27. A method as claimed in claim 26 wherein, the method further comprises the step of changing the desired current distribution and switching the electrodes to turn the electrodes on and off in order to obtain the desired shape and position of the return path in response to the change to the desired current distribution.

28. A method as claimed in claim 26 or claim 27 wherein, the step of changing the desired current distribution further comprises determining the temperature within the region to find areas which are too hot or too cold and switching the electrodes to change the position and shape of the return path to adjust the temperature across the region.

29. A method as claimed in claims 26 to 28 wherein, the plurality of electrodes comprises a central elongate electrode having a longitudinal axis and a plurality of peripheral electrodes which are coupled to and radially extendable from a retracted position on the longitudinal axis of the elongate electrode to an extended position at a predetermined distance from the longitudinal electrode to define the region containing the return path.

30. A method as claimed in claim 26 wherein the plurality of electrodes form an array of electrodes.

31. A method as claimed in claim 26 wherein, the plurality of electrodes are spaced apart along a longitudinal member or probe.

32. A method as claimed in claim 29 wherein, the peripheral electrode comprises at least two electrodes articulatably connected to move from the retracted position to the extended position.

33. A method as claimed in claim 29 or claim 32 wherein, the peripheral electrodes are substantially rigid.

34. A method as claimed in any of claims 29, 32 or 33 wherein, the first and second peripheral electrodes are arranged on opposing sides of the elongate electrode.

35. A method as claimed in any of claims 29, 32 or 33, the first and second peripheral electrodes are arranged adjacent to one another on the elongate electrode.

36. A method as claimed in any of claims 29, 32 to 35 wherein, the peripheral electrode comprises at least two rigid arms articulatably connected to move from the retracted position to the extended position.

37. A method as claimed in claim 36 wherein, the articulatable connection comprises a hinge.

38. A method as claimed in any of claims 29 and 32 to 37 wherein, the peripheral electrode is fixedly connected to the elongate electrode at the distal end of the apparatus end remote and is slidably connected to the elongate electrode at the proximal end of the apparatus.

39. A method as claimed in any of claims 29 and 32 to 38 wherein, a third peripheral electrode can be arranged on the front side of the elongate electrode.

40. A method as claimed in any of claims 29 and 32 to 39 wherein, a fourth peripheral electrode can be arranged on the back side of the elongate electrode.

41. A method as claimed in any of claims 29 and 32 to 40wherein, the end of the elongate electrode which is remote from the handle comprises a cutting tip for easy insertion into a tumour.

42. A method as claimed in claim 41 wherein, the cutting tip is heated.

43. A method as claimed in any of claims 26 to 42 wherein the temperature of the region is measured.

44. A method as claimed in claim 43 wherein, the differences in temperature across the region is measured.

45. A method as claimed in claims 26 to 44 wherein the switching of the electrodes is adjusted in response to changes in temperature.

46. A method as claimed in claims 26 to 44 wherein, the peripheral electrode comprises a shape memory alloy.

47. A method as claimed in claim 46 wherein, the shape memory alloy is changeable in-situ to its previously heat-treated shape to optimally conform to any specific requirements of the volume where the tumour is to be destroyed.

48. A computer program comprising program instructions for implementing the method in accordance with claims 26 to 47.