WO2011113875A1

WO2011113875A1 - A system with temperature control in a target area within a body

Info

Publication number: WO2011113875A1
Application number: PCT/EP2011/054002
Authority: WO
Inventors: Roman Iustin; Tomas Gustafsson
Original assignee: Micropos Medical Ab
Priority date: 2010-03-16
Filing date: 2011-03-16
Publication date: 2011-09-22

Abstract

The present invention relates to a system with temperature control in a target area within a body. The system comprises a device, such as an electrode or reflector, configured to be fixated to the target area within the body; a first antenna element; a control unit configured to generate a first RF- signal to be transmitted from the first antenna element; and a plurality of external antenna elements, each external antenna element being configured to receive a reception signal originating from said RF- signal. The control unit determines electrical properties of tissue within the body based on the reception signals; calculates and generates transmission signals based on the determined electrical properties of tissue; and transmits the transmission signals from the external antenna elements to transfer energy to a point within the target area to increase the temperature in the target area.

Description

A SYSTEM WITH TEMPERATURE CONTROL IN A TARGET AREA WITHIN A BODY

Technical field

The present invention relates to a system for temperature control in a target area within a body, for instance during radiotherapy using an implantable electrode provided with a transmitter and a temperature sensor.

Background

Research has shown that it may be beneficial to be able to control the temperature in a target area during radiotherapy to increase the efficiency of the treatment.

It is well known for a skilled person that microwave radiation will affect the temperature of tissue within a body, and that it is possible to focus the microwave energy it the tissue property is known in advance. This is normally not the case for a living body. This problem has been addressed by creating a computer model of a body and simulating transmissions from a target area within the body and simulating signals received from the simulated transmissions at a plurality of positions outside the body based on knowledge of the body anatomy at a certain point of time. Based on the simulated received signals, it is possible to calculate phase and amplitude of microwave signals to be transmitted from antennas at the plurality of positions in order to focus the microwave energy to the target area.

However, tissue property within a living body is not easy to establish since it varies over time when different organs within the body moves around. Thus, there is a need for further improvements.

A solution for localized heating has been proposed in US 4,679,561, in which electrodes are arranged close to the target area within a body. An internal antenna is connected to the electrodes and an external antenna transmits energy to the internal antenna which results in an increased temperature of the target area. However, this requires an undesired operation by a surgeon to arrange the electrodes at the correct position close to the target area. Summary of the invention

An object with the present invention is to provide a system with more accurate temperature control within a target area inside a human body compared to prior art technologies.

This object is achieved by arranging an antenna element close to a desired target area within a body. A control unit generates and forwards an RF- signal to the antenna element which is transmitted from the antenna element. The transmitted signal is received by a plurality of antenna elements, which are arranged outside the body. The received signals are forwarded to the control unit, which determine the electrical properties of tissue situated between the antenna element inside the body and the externally arranged antenna elements. Furthermore, the control unit is configured to calculate and generate transmission signals based on the determined electrical properties of tissue and thereafter transmit the transmission signals in order to affect the temperature in the target area by transferring energy to a point therein.

An advantage with the present invention is that a continuous adaptation of changes in electrical properties in the tissue is obtained.

Another advantage with the present invention is that the positioning of the required components close to the target area is less complicated compared to prior art techniques.

Further objects and advantages may be found by a skilled person in the art from the detailed description. Brief description of drawings

The invention will be described in connection with the following drawings that are provided as non-limited examples, in which:

Fig. 1 shows a first embodiment of an implantable electrode suitable for carrying out the invention.

Fig. 2 shows a second embodiment of an implantable electrode suitable for carrying out the invention.

Fig. 3 shows a third embodiment of an electrode suitable for carrying out the invention. Fig. 4 shows a first embodiment of a system for radiotherapy treatment with temperature control according to the invention.

Fig. 5 shows a second embodiment of a system suitable for hypothermia treatment with temperature control according to the invention.

Fig. 6a shows a fourth embodiment of an implantable electrode suitable for carrying out the invention.

Fig. 6b shows a reflector adapted to replace an electrode provided with an internal antenna element for carrying out the invention.

Fig. 7 shows a flow chart of a method for obtaining temperature control.Detailed description Figure 1 describes a first embodiment of an electrode 10 suitable for use in a system according to the invention. The electrode 10 comprises a main unit 11 arranged at a first end of a cable 12 and a connector 13 arranged at a second end of the cable 12. The cable 12 comprises two wires 14 within a shield 15, preferably a shielded twisted pair, which interconnects the connector 13 with the main unit 1 1. A biocompatible cover is preferably arranged over the cable and the main unit to avoid any problems that could occur when the electrode 10 is partly positioned within a body as indicated by the dash-dotted line.

The main unit 1 1 comprises an antenna element 17 configured to transmit and receive an electromagnetic signal 18. The transmitted electromagnetic signal is adapted to be received in an external antenna unit (not shown) to track variations of a position of the electrode relative a radiation source (not shown). The antenna element 17 is connected over the wires 14. It is also possible to track variations of the position of the electrode by receiving multiple electromagnetic signals 18 in the antenna element 17 originating from a plurality of external antenna elements arranged in the external antenna unit (not shown) .

The antenna element 17 is further suitable to emit a microwave signal adapted to be received in a plurality of microwave antennas arranged outside the body, with the purpose of investigating, and monitoring, the electrical properties of tissue between the antenna element 17 and the microwave antennas.

The main unit 1 1 is fixable relative a target area 1 within the body and the radiation source emits radiation into the target area.

The connector 13 is adapted to be connected to an external control unit 16, which in turn is in communication with the radiation equipment, the external antenna elements in the external antenna unit and the microwave antennas (which may be an integral part of the external antenna unit) . It should be noted that the connector 13 is configured to be arranged outside the body when the main unit 11 is fixated in relation to the target area 1. If the antenna element 17 is configured to transmit the electromagnetic signal, the control unit generates and controls the electromagnetic signal 18 which is transmitted from the antenna element 17 and thereafter is received by a plurality of external antenna elements in the external antenna unit (not shown), as well as the microwave signal received by the microwave antennas. On the other hand, if the antenna element 17 in the electrode is configured to receive multiple electromagnetic signals 18, the control unit generates and controls the multiple electromagnetic signals transmitted from the external antenna unit. In a preferred embodiment, the antenna element 17 may also be used to detect changes in the ambient temperature, e.g. within the target area 1, as indicated by the dotted arrows in figure 1. The antenna element 17 has an internal resistance indicative of surrounding temperature in the target area 1, and the externally arranged control unit 16 may monitor the surrounding temperature of the target area 1 by measuring the internal resistance. The temperature dependency of the antenna element is calibrated by measuring the internal resistance at two specific temperatures, e.g. at 22 °C (room temperature) and at 37°C (in the target area 1 before radiotherapy

commences) . The internal resistance may be measured at the same time as the electromagnetic signal(s) is/ are transmitted, or received, in the antenna element 17. It could be beneficial to control the temperature of the target area 1 during radiotherapy and the system, as described in more detail below, is therefore provided with microwave antennas that may transmit signals in order to focus their energy on a selected target area 1 and increase the temperature based on the monitored tissue properties.

It should be noted that the electrode 10 is suitable to use when the operating frequency for tracking position and the frequency for microwave heating are essentially the same, as an example the operating frequency may be 3.0 GHz and the microwave heating frequency is 3.3 GHz, provided the antenna element is designed to have an operating frequency of 3-3.3 GHz.

Figure 2 describes a second embodiment of an electrode 20, preferably an implantable electrode, suitable for medical applications. The electrode 20 comprises a main unit 21 arranged at a first end of a multi wire cable 22 and a connector 23 arranged at a second end of the multi wire cable 22. The multi wire cable 22 comprises in this embodiment of two pairs of electrical connections (such as twisted pair wires) 24' and 24" within a shield 25, which interconnects the connector 23 with the main unit 21. An explant line 7, e.g. an aramid fibre (aromatic polyamide), having a tensile strength over 100 Newton (> 100N) is preferably arranged beside the cable 22 and connected between the main unit 21 and the connector 23 to facilitate the removal of the main unit 21 from a target area 1. A biocompatible cover 9 is preferably arranged over the explant line 7, the cable 22 and the main unit 21 to avoid any problems that could occur when the electrode 20 is partly positioned within a body as indicated by the dash-dotted line. The main unit 21 comprises an antenna element 17, e.g. implemented as a coil on a ferrite rod, configured to transmit an electromagnetic signal 18 adapted to be received in a receiving unit (not shown) to track variations of a position of the electrode relative a radiation source (not shown) . The antenna element 17 is connected over one pair of electrical connections, i.e. the wires of a first of the twisted pair wire, 24'. It is also possible to track variations of the position of the electrode by receiving multiple electromagnetic signals 18 in the antenna element 17 originating from a plurality of external antenna elements in the external antenna unit (not shown) . The explant line 7 is preferably attached to the ferrite rod of the antenna element 17. The main unit 21 is fixable relative the target area 1 within a body and the radiation source emits radiation into the target area 1. In order to monitor the administered dose in the target area from the radiation source, the main unit 21 is also equipped with a dose measuring unit 28, which in this embodiment is connected over another pair of electrical connections, i.e. the wires of a second twisted pair wire, 24" and an identification unit 29 positioned at the connector 23. The shield 25 of the multi wire cable 22 is only used for shielding in this embodiment.

The connector 23 is configured to be connected to an external control unit 26, which in turn is in communication with the radiation equipment and the external antenna unit. It should be noted that the connector 23 is configured to be arranged outside the body when the main unit 21 is fixated in relation to the target area 1.

The control unit is, in this embodiment, configured to verify the identification of the implant (and thereby the patient since the implant is fixated to the patient during the complete radiotherapy treatment process) and thereafter measure administered dose from a radiation source. The dose measuring and identification unit is described in more detail below. If the antenna element 17 is configured to transmit the electromagnetic signal, the control unit also generates and controls the electromagnetic signal 18 which is transmitted from the antenna element 17 and thereafter is received by a plurality of receiving elements in the external antenna unit (not shown) . On the other hand, if the antenna element 17 in the electrode is configured to receive multiple electromagnetic signals 18, the control unit generates and controls the multiple electromagnetic signals transmitted from the external antenna unit.

As mentioned above, the antenna element 17 has an internal resistance indicative of surrounding temperature in the target area 1 , and the

externally arranged control unit 26 may monitor the surrounding

temperature of the target area 1 by measuring the internal resistance. The dose measuring unit 28 and the identification unit 29 will operate in two modes, a first mode in which the radiation from the radiation source will create a DC current measured by the control unit 16, and a second mode in which the control unit verifies the identity from the identification unit 29.

The dose measuring unit 28 and the identification unit 29 are connected in parallel over the second twisted pair wire 24". The dose measuring unit comprises a dose measuring diode and the identification unit 29 comprises a switch in series with an electronic identification tag. The switch makes it possible to switch between the two modes of operation, as mentioned above. The first mode, i.e. dose measuring mode, is achieved when zero volt DC is applied between the wires 24", and the second mode, i.e. the identification mode, is achieved when a DC voltage is applied over the measuring diode to arrange the diode in reverse, e.g. by applying five volts reverse DC over the wires 24".

Figure 3 shows a third embodiment of an electrode 30 comprising a main unit 31 arranged at a first end of a cable 32 and a connector 33 arranged at a second end of the cable 32. The cable 33 comprises four wires 34 within a shield 35, preferably a first and a second twisted pair cables, which interconnects the connector 33 with the main unit 31. A biocompatible cover 9 is preferably arranged over the cable and the main unit to avoid any problems that could occur when the electrode 30 is partly positioned within a body as indicated by the dash-dotted line.

The main unit 31 comprises a first antenna element 37 configured to transmit and receive an electromagnetic signal 39. In this embodiment the antenna element is configured to receive transmitted electromagnetic signals originating from a plurality of external antenna elements arranged in the external antenna unit (not shown) to track variations of a position of the electrode relative a radiation source (not shown) . The antenna element 37 is connected over two of the wires 34, e.g. a first twisted pair cable.

The main unit further comprises a second antenna element 27 adapted to emit a microwave signal 38 to be received in a plurality of microwave antennas arranged outside the body, with the purpose of investigating, and monitoring, the electrical properties of tissue between the second antenna element 27 and the microwave antennas. The second antenna element is preferably a dielectric resonant element connected over two separate wires 34, e.g. a second twisted pair cable.

It should be noted that the third embodiment of the electrode 30 is suitable to use when the operating frequency for tracking the position and the frequency used for microwave heating are different, as an example the operating frequency for tracking may be 300 MHz and the microwave heating frequency may be 1 1 times higher, i.e. 3.3 GHz. The main unit 31 is fixable relative a target area 1 within the body and the radiation source emits radiation into the target area. In order to monitor the administered dose in the target area from the radiation source, a dose measuring unit 28, as described in connection with figure 2 may be added. The connector 33 is adapted to be connected to an external control unit 36, which in turn is in communication with the radiation equipment, the external antenna elements in the external antenna unit and the microwave antennas (which may be an integral part of the external antenna unit). It should be noted that the connector 33 is configured to be arranged outside the body when the main unit 31 is fixated in relation to the target area 1.

externally arranged control unit 36 may monitor the surrounding

temperature of the target area 1 by measuring the internal resistance. Figure 4 shows a first embodiment of a system 40 according to the invention for performing radiotherapy using radiation equipment 41 with a radiation source, a control unit 42, an external antenna unit 43 and an electrode 44 as described in connection with figure 1 and 2. The control unit 42 is connected to the radiation equipment 41 , the external antenna unit 43 and also communicates with the electrode by wires, or alternatively through a wireless connection.

The electrode 44 comprises a main unit 45 where the antenna element for transmitting an electromagnetic signal and the optional dose measuring unit are situated, and the main unit is fixated in relation to a target area 46 within a body 47. The external antenna unit 43 comprises a plurality of external antenna elements 48a, which are used to track the antenna element in the electrode 44. The control unit 42 is also configured to keep track of the distance between the external antenna elements 48a in the external antenna unit 43 and the radiation source in the radiation equipment 41 in order to control the radiation beam 49. The system further comprises a plurality of microwave antennas 48b, preferably arranged in the external antenna unit, configured to receive microwave signals transmitted from the antenna element in a monitor mode and configured to transmit microwave signal in order to focus microwave energy to the target area in a heat mode. The antenna element in the electrode 44 will act as a microwave transmitter during the monitor mode and may be used for positioning during the heat mode since the antenna element is only needed to monitor tissue properties. In the heat mode, the transmissions from the microwave antennas 48b are also controlled by the control unit 42 to focus microwave energy to a position within the target area 46. Therefore, it is essential that the control unit 42 performs the different tasks in a sequential manner to avoid any undesired interferences between the different modes of operations.

If the system only also is configured to measure temperature in the target area, it could be used to control the signals transmitted from the microwave antennas 48b in order to monitor the temperature in the target area 46.

It should be noted that the microwave frequency of the transmitted RF signal used for determining the electrical properties of tissue preferably is the same for the generated and transmitted transmission signals from the microwave antenna elements in the external antenna unit.

Figure 5 shows a second embodiment of a system 50 according to the invention for hypothermia treatment using an element 51 arranged close to a target area 1 inside a body 52. Examples of elements that could be used in this embodiment are an implantable electrode as described in connection with figures 1 and 6a, or a reflector as described in connection with figure 6b. Further, the system comprises a control unit 54 connected to a circular shaped external antenna unit 53 with a plurality of external microwave antennas 57.

The external antenna unit 53 communicates with the control unit 54 by wires as indicated by 55, and optionally communicates with the element 51 as indicated by 56 either by wire, using the electrode 10 in figure 1, or alternatively through a wireless connection, using a wireless electrode as disclosed in figure 6a. If a reflector, as disclosed in figure 6b is used, no communication is available between the control unit 54 and the reflector. Fig. 6a shows a fourth embodiment of an implantable electrode 60 suitable for carrying out the invention. The electrode 60 comprises a main unit 61 arranged at a first end of a cable 12 and an internal control unit 62 arranged at a second end of the cable 12. The cable 12 comprises two wires 14 within a shield 15, preferably a shielded twisted pair, which interconnects the internal control unit 62 with the main unit 61. A biocompatible cover is preferably arranged over the cable and the main unit to avoid any problems that could occur when the electrode 60 is completely positioned inside a body.

The main unit 61 comprises an antenna element 59 configured to transmit and receive a microwave signal 58. The transmitted microwave signal is adapted to be received in a plurality of microwave antennas, such as the microwave antennas 57 shown in figure 5, arranged outside the body, with the purpose of investigating, and monitoring, the electrical properties of tissue between the antenna element 59 and the microwave antennas. The antenna element 59 is connected to the external control unit over the wires 14 and the wireless interface between the internal control unit 62 and the external control unit 64. It is also possible to receive microwave signals in the microwave antenna 59 originating from the plurality of microwave antennas arranged in the external antenna unit (not shown) . The main unit 61 is fixable relative a target area 1 within the body in which the temperature is controlled by emitting microwave signals from the external microwave antennas. The internal control unit 62 further comprises transceiver circuitry (not shown) connected to a first antenna 62b that communicates wirelessly via a second antenna 64b with the external control 64 which in turn is connected to external microwave antennas. The implantable electrode 60 is powered by an energy source 63 preferably arranged within the internal control unit 62. The energy source 63 may be implemented as a battery or a capacitor that is charged wirelessly by the external control unit 64. It should be noted that the implantable electrode 60 is configured to be arranged completely inside the body when the main unit 61 is fixated in relation to the target area 1.

In a preferred embodiment, the antenna element 59 may also be used to detect changes in the ambient temperature, e.g. within the target area 1, as previously described in connection with figure 1.

Fig. 6b shows a system 65 including a reflector 66 that in combination with external antennas 67 and 68 may be used for carrying out the invention. The reflector 66 is positioned in the vicinity of, preferably within, a target area 1, which is intended to be subject to hypothermia treatment, and a microwave signal is transmitted from an external transmitting antenna 67, reflected against the reflector 66 and received at multiple microwave antennas 68. The control unit 69 estimates the electrical properties of the tissue between the reflector and the microwave antennas 68. It is also possible for the

transmitting antenna 67 to receive a reflected signal and thereby determine the properties of the reflected signal at the reflector. This information is used to estimate the electrical properties of the tissue.

This information may be used to generate suitable microwave signals to be transmitted from each microwave antenna 68 (and also from the

transmitting antenna 67) to focus at a point close to the reflector to increase the temperature.

Figure 7 shows a flow chart describing the process for controlling the temperature in a target area, e.g. during radiotherapy treatment or during hypothermia treatment. The process starts at step 70 and continues to step 71 in which a microwave signal generated in an external control unit is transmitted from an antenna element fixated to a target area within a body, or transmitted from an external antenna and reflected in a reflector element as disclosed in fig. 6b. A signal originating from the microwave signal is received in a plurality of externally arranged antenna elements and the difference in amplitude and phase compared to the transmitted microwave signal is measured in the control unit, step 72.

The electrical properties of tissue arranged between the transmitting antenna element and each externally arranged antenna element is

determined in the control unit, step 73, and the control unit thereafter calculates and generates suitable microwave signals for transmission from the externally arranged antenna elements, step 74. It should be noted that "suitable" microwave signals generally implies that the microwave signals will generate microwave energy focussed to a specific point within the target area, as is obvious for a skilled person in the art.

In step 75, the suitable microwave signals are transmitted from the externally arranged antenna elements create energy focussed to the specific point, and if the electrical properties of the tissue should be continuously monitored, step 76, the flow is feed back to step 71. If not, the flow ends, step 77.

In an alternative embodiment, the flow is fed back to step 71 via an

intermediate step 78, in which the temperature in the target area is measured and information is provided to step 74 to properly generate suitable microwave signals for transmission when maintaining a desired temperature within the target area. However, the alternative embodiment requires that an antenna element is arranged in the vicinity of, preferably within, the target area to be able to measure the temperature as described above.

It should be noted that the target area normally defines a volume.

Claims

1. A system with temperature control in a target area within a body, said system comprises:

a device configured to be fixated to said target area within the body, - a first antenna element,

a control unit connected to the first antenna element, said control system is configured to generate a first RF-signal to be transmitted from said first antenna element, and

a first set of external antenna elements, each external antenna element being configured to receive a reception signal originating from said first RF-signal,

c h a r a c t e r i z e d i n that said control unit further is configured to determine electrical properties of tissue within the body based on the reception signals; to calculate and generate transmission signals based on the determined electrical properties of tissue; and to transmit said

transmission signals from said first set of external antenna elements to transfer energy to a point within said target area to increase the temperature in the target area.

2. The system according to claim 1, wherein said device is an

implantable electrode provided with said first antenna element.

3. The system according to any of claims 1-2, wherein said device further is provided with a temperature sensor connected to said control unit, said control unit further is configured to detect temperature changes in the target area as a result of the transferred energy.

4. The system according to claim 3, wherein the temperature sensor is implemented in the antenna element, whereby an internal resistance in the antenna element is indicative of surrounding temperature in the target area.

5. The system according to claim 3 or 4, wherein the transmission signals generated in said control unit are based on the detected temperature changes.

6. The system according to claim 1, wherein the first antenna element is an external antenna element and said device is a reflector configured to reflect the first RF- signal generated by said first antenna element.

7. The system according to any of claims 1-6, wherein the first RF- signal is a microwave signal and said transmission signals creates focused microwave energy to said point.

8. The system according to any of claims 1 -7, wherein the system further comprises a second set of external antenna elements configured to be arranged outside said body, and said control unit further is configured to generate a second RF-signal to be transmitted from a second antenna element and to be received by said second set of external antenna elements for tracking variations of a position of the electrode relative to said second set of external antenna elements.

9. The system according to any of claims 1 -7, wherein the system further comprises a second set of external antenna elements configured to be arranged outside said body, and said control unit further is configured to generate a second RF-signal to be transmitted from said second set of external antenna elements and to be received by a second antenna element for tracking variations of a position of the electrode relative to said second set of external antenna elements.

10. The system according to any of claims 8 or 9, wherein said first antenna element and second antenna element are separately connected to said control unit.

1 1. The system according to any of claims 8 or 9, wherein said first antenna element and second antenna element form a common antenna element connected to said control unit.

12. The system according to any of claims 1- 1 1 , wherein the system further comprises radiation equipment connected to said control unit, said radiation equipment comprises a radiation source for radiotherapy treatment, and said electrode further comprises a dose measuring unit connected to said control unit, wherein said control unit is configured to detect administered dose in the target area from the radiation source.