Patent Publication Number: US-2009234224-A1

Title: Positioning Device and a System for Detecting the Position of Such a Device

Description:
TECHNICAL FIELD 
     The present invention relates to a positioning device configured to be arranged to a target area inside a body. The invention also relates to a system for detecting a position of such a device. 
     BACKGROUND TO THE INVENTION 
     In the published Swedish patent SE 511 291 is a method disclosed for administrating treatment radiation towards a target area, such as a tumour, within a patient. The administration direction is determined by providing a reference object which is inserted into the body of the patient close to the target area. The reference object has reference markings that may be detected using computed tomography (CT) or X-ray. 
     A drawback with the prior art is that an amount of radiation has to be used to detect the position of the reference object. The patient is submitted to an unnecessary exposure of radiation before the actual treatment may commence. 
     A solution to this drawback is directed to the use of magnetically activated sensors, or markers. These may be wirelessly implanted into a body and the markers could be tracked using an induced magnetic field. The sensors are normally permanently inserted into the body, and may migrate over time. 
     A drawback with this solution is that Magnetic Resonance Imaging (MRI) may not be used unless the sensors are removed. 
     Another solution is to provide a marker with an electromagnetic transmitter at the tip of the device that is inserted into the body and a receiver unit is placed outside the body to track the movement of the tip during the inserting procedure. 
     This solution has a drawback in that it experience a limited resolution, which leads to that x-ray normally still needs to be used to verify the position of the sensor/marker. 
     SUMMARY OF THE INVENTION 
     An object with the invention is to provide a device which may be used in a system to detect the position of the device which overcomes the above mentioned drawbacks. 
     The object is achieved in a device configured to be arranged in relation to a target area within a body. The device comprises at least one transmitter configured to emit an electromagnetic signal, which signal is received in at least three positions by a receiver arranged outside the body. The electromagnetic signal is generated in an externally arranged control unit and the device is configured to be connected to the control unit through transmission lines. The frequency of the emitted electromagnetic signal must be selected in such a way that a distance from each transmitter to each of the receiver&#39;s positions is within the same integer number of wavelengths of the electromagnetic signal. 
     The object is also achieved by a system using a device as described above. 
     An advantage with the present invention is that x-ray is not needed to be used to verify the position of the device. 
     Another advantage is that the present invention can be used to locate the device at all times after the device has been inserted into a body, which makes it possible to verify its position inside the body during e.g. treatment or feeding. 
     Still another advantage with the present invention is that there is a possibility for automation, i.e. radiation treatment can be administered automatically. 
     Still another advantage with the present invention is that the need for picture estimation by a doctor is eliminated, due to auto-positioning of the device. 
     An advantage with a preferred embodiment is that MRI may be used on the body since the positioning device easily may be removed from the body without the need for a surgical procedure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a first embodiment of a positioning device according to the invention. 
         FIG. 2  shows a second embodiment of a positioning device according to the invention. 
         FIG. 3  shows a third embodiment of a positioning device according to the invention. 
         FIG. 4  shows a fourth embodiment of a positioning device according to the invention. 
         FIG. 5  shows a plot illustrating the near field effect of electromagnetic signals. 
         FIG. 6  shows a fifth embodiment of a positioning device according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a first embodiment of a positioning device, which in this embodiment is a removable catheter  10 , according to the invention. The catheter  10  comprises a transmitter  11  arranged close to the tip  12  of the catheter. An expandable portion  13  of the catheter  10  is provided between the transmitter  11  and the tip  12  of the catheter  10 . A transmission line  14  connects the transmitter  11  with an externally arranged control unit  15 . 
     This type of positioning device is preferably used during cancer treatment, such as prostate cancer, breast cancer uterus cancer, and a very accurate position of the prostate  17  (target area) is required to optimise the treatment procedure. The catheter is in this example inserted through a natural opening, as illustrated in  FIG. 1 , and the expandable portion  13  is inserted into the bladder  16  where it is expanded to fixate the transmitter  11  relative to the prostate  17  before the treatment begins. 
     An electromagnetic signal is generated in the control unit  15  and is thereafter transmitted from the transmitter  11 . The electromagnetic signal is adapted to propagate with a wavelength in the body and, in a first example, a phase difference of the electromagnetic signal is detected in at least three positions  18 , preferably four or more positions, by a receiver  19  arranged outside the body. The wavelength is selected so that a distance from the transmitter  11  to each of said at least three positions  18  is within the same integer number of wavelengths of the electromagnetic signal. The distance between each transmitter and the positions  18  of the receiver  19  is preferably selected so that they operate in a near field region. A prior art detector system is described in an international patent application PCT/SE05/000646, assigned to the same applicant, wherein a transmitter arranged in relation to a target area inside a body transmits a signal having a frequency within the range of 5-350 MHz and a phase difference from the transmitted signal is detected by a receiver at three, or more, positions to track variations in position of the transmitter. 
     The prior art system described defines a transmitter and a multiple of receiving antennas that operates in a near field region. The behaviour of an electromagnetic signal in the near field region is known for a skilled person and is described in a publication with the title “Near field Phase Behavior”, by Hans Gregory Schantz, IEEE APS Conference July 2005. In this publication the author presents a reprint of a plot published in “Electric waves”, by Heinrich Hertz, London, Macmillian &amp; Co. 1893, page 152 and a plot, shown in  FIG. 5 , was published by Q-track in 2004. 
     The plot describes the phase behaviour of the magnetic field (H-field) and the electrostatic filed (E-field) below one wavelength of an electromagnetic signal. In this near field region of an antenna, the magnetic field and electrostatic field phases radically diverge, and in a far field region, many wavelengths away from a transmit antenna, the magnetic and electrostatic field move with perfect synchronized phase.  FIG. 5  illustrates the effect of the near field region, and the phase delta between the magnetic field and electrostatic field at zero λ is 90 degrees, which decreases to a phase difference of 0 degrees at one λ. 
     The separation of the magnetic field and the electrostatic field in the near field region opens up a number of possibilities to construct improved measurement systems. The shape of the wave front of the electromagnetic signal may be used to determine the distance between the transmitter and the receiver. It is also advantageous to increase the sensitivity of the measurement system by introducing electrostatically shielded antennas, which is possible since the magnetic field and electrostatic field are separated in the near field region, whereby the magnetic field is used to determine the variations of the position of the transmitter. 
     A more detailed description of the detector system may be found in the international patent application with the application number PCT/SE05/000646, which is hereby incorporated by reference. 
     In a second example, amplitude difference of the electromagnetic signal is detected instead of the phase difference as described above. A transmitter arranged in relation to a target area inside a body transmits a signal having a frequency within the range of 1 kHz-350 MHz and an amplitude difference from the transmitted signal is detected by a receiver at three, or more, positions to track variations in position of the transmitter. The amplitude of the magnetic field is preferably measured when operating in near field, for instance by measuring absolute value or mean value of the magnetic field. 
     It is of course possible to combine the above described examples and use both phase and amplitude difference to determine variations of the position of the transmitter. 
     The receiver  19 , comprising a multiple of antennas at separate positions  18  (in this example four positions), is positioned on the outside of the body and is also connected to the control unit  15 , and a very accurate tracking of the transmitter  11 , and thus the prostate  17 , may be performed. When radiotherapy treatment is completed, the removable catheter  10  is removed by deflating the expandable portion  13  and withdrawing the catheter  10 . 
       FIG. 2  shows a second embodiment of a positioning device, which in this embodiment is a plaster  20 , which easily may be attached to the skin of a patient in an appropriate position. The plaster  20  comprises in this embodiment two transmitters  21  and  22  in a central part of the plaster  20  and two adhesive portions  23  to securely attach the plaster to the skin. The transmitter  21 ,  22  are connectable to a Control Unit, similar to the one described in connection with  FIG. 1 , through transmission lines  24 . 
     The plaster could, for instance, be used when a patient having breast cancer is exposed to radiotherapy treatment. The plaster  20  is then attached to the breast in such a way that a relative distance between a target area in the breast and each transmitter  21  and  22  is established. The breathing of the patient, and thus the movement of the breast due to breathing, can be tracked, and the radiotherapy treatment can now be controlled more accurately by adapting the exposure dose to the position of the target area. It is of course possible to have only one transmitter, or even have more than two transmitters, without deviating from the scope of the invention as defined in the claims. 
       FIG. 3  shows a third embodiment of a positioning device, in which in this embodiment is a feeding tube  30  having a first end  38  being arranged to be inserted into the stomach through the nose of a patient, and a second end  39  being arranged to be connected to a feeding arrangement (not shown). It is essential that the feeding tube  30  is not misdirected during the inserting procedure and by mistake entered into one of the lungs. The feeding tube  30  is therefore provided with a removable insert  31  having a transmitter  32  arranged in the end of the insert  31  that is intended to be aligned with the first end  38  of the feeding tube  30  during the inserting procedure. The transmitter  32  is provided with a transmission line  33 , which is connectable to a control unit (not shown) of the same type as described in connection with  FIG. 1 . 
     When the feeding tube has been placed in the right position, the insert  31  is withdrawn from the feeding tube  30  as illustrated by the arrow  34  in  FIG. 3 . The feeding through the feeding tube  30  may thereafter commence. 
     In an alternative embodiment, the transmitter  32  and the transmission line  33  are integrated into a wall  37  of the feeding tube  30 , which has the advantage that a removable insert is not necessary. The position of a hollow position secured device, such as a feeding tube, can continuously be monitored to track the position of the feeding tube  30  during feeding. 
       FIG. 4  shows a fourth embodiment of a positioning device, which in this embodiment is a catheter  40 , according to the present invention. The catheter  40  is kept in place at least during the radiotherapy treatment and could thereafter be removed or left in place. The catheter  40  is in this embodiment provided with three transmitters  41  having transmission lines  42  that are connectable to a control unit (not shown). The catheter is further provided with fastening means  43  in the shape of hooks, or other forms, e.g. spiral, that securely attaches the catheter  40  with the transmitters  41  to the prostate  17 . 
     A wire-based implant covered with biocompatible material, i.e. without the need of a protective catheter, is also conceivable. 
       FIG. 6  shows a fifth embodiment of a positioning device  50 , similar to the positioning device described in connection with  FIG. 4 . No catheter is provided and one or more transmitters  51  are arranged in a biocompatible capsule, and transmission lines connecting the transmitters  51  with an external control unit (not shown) are contained within a biocompatible lead  52 . In this embodiment, the fastening means are implemented as a multiple of tine elements  53 , in this example four elements, arranged on the outside of the lead  52 . Further examples of tine elements may be found in the published US application US 2006/0129218, assigned to Medtronic, Inc.