Abstract:
In a system and method for x-ray brachytherapy, a probe is introduced into the body of a subject, the probe carrying an x-ray source that radiates x-rays into an exposure area outside of the probe within the body of the subject. A number of markers are located in or on the probe, that are detectable in an image generated by an imaging device. The markers are located in or on the probe in a known spatial relation to the exposure area, so that the position of the exposure area can be determined by identifying the markers in the displayed image.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention concerns a device for x-ray brachytherapy as well as a method for positioning of a probe inserted into the inside of a body for x-ray brachytherapy. 
         [0003]    2. Description of the Prior Art 
         [0004]    X-ray brachytherapy is a therapeutic treatment with x-rays in which the x-ray source is brought very close to the tissue to be treated (for example a tumor or a vessel wall) after the implementation of a endovascular dilatation. In order to able to insert the x-ray source with the aid of a catheter or a probe either without an invasive procedure or with an optimally minimally-invasive procedure inside a body, a miniaturized x-ray source, is required, as is known from U.S. Pat. No. 6,721,392, for example. This is arranged at the distal end of a probe that, for example, is intraoperatively positioned in a tumor or tumor bed (after its extraction), as is explained in detail in the PR information of Carl Zeiss AG, Medical Engineering Innovation by Carl Zeiss AG, “Intraoperative Strahlentherapie mit dem INTRABEAM System von der Carl Zeiss AG” state as of, September 2004, for example. 
         [0005]    A miniaturized x-ray source that is arranged in a catheter with which it can be inserted into the body cavities (lumen) in order to irradiate selected tissue zones from the immediate surroundings from there is known from United States Patent Application Publication 2003/0149327 A1. It contains a shielding rotatable around the axis of the catheter in order to radiate the x-rays in a targeted manner at least perpendicular to the axis in a selected solid angle. The surroundings of the catheter can be observed with an optical observation device arranged in a catheter. A light source that exposes only the part of the surface of the hollow space that is also irradiated is used for this purpose. 
         [0006]    Given endovascular brachytherapy with a beta or gamma radiator arranged in the tip of a catheter, it is also known from DE 10 2004 008 373 B3 (for example) to arrange an optical observation device in the catheter. For this a brachytherapy catheter is integrated into a unit with an OCT catheter operating on the basis of optical coherence tomography (OCT). 
         [0007]    For the therapeutic success it is essential that the x-rays radiating out of the catheter from the x-ray source in an exposure area for most part exclusively strike the tissue (for example the tumor) to be treated in order to ensure an optimally low exposure of the healthy tissue located near this. This requires a precise positioning of the exposure area, i.e. a precise positioning and alignment of the x-ray source or of the solid angle in which the x-rays exit. 
       SUMMARY OF THE INVENTION 
       [0008]    An object of the present invention is provide a device for x-ray brachytherapy with a probe that can be inserted inside a body, with which probe a precise positioning of the exposure area is possible. A further object of the invention is provide a method for positioning a probe inserted inside a body for x-ray brachytherapy. 
         [0009]    With regard to the device, the cited object is achieved by a device containing a probe that can be inserted into the inside of a body, the probe at its distal end having an x-ray source that radiates x-ray radiation into an exposure area outside of the probe. Multiple markers is provided that are detectable in an image generated by an imaging device and that are arranged in or at the probe in a known spatial relation to the exposure area. The position of the exposure area in this image can then be concluded from the position of these markers in the image. In other words: the markers at least indirectly mark the exposure area. This enables a precise positioning of the exposure area, i.e. a precise positioning of the x-ray source and of the solid angle region in which the x-rays generated by the x-ray source are radiated. 
         [0010]    As used herein the term “probe” is an instrument that can be introduced into the inside of a body. This can be both a catheter (in the narrower sense) that is inserted into body cavities (transluminal) and a needle-like instrument that can be placed within a tissue zone (percutaneous or interstitial). 
         [0011]    An imaging device in the sense of the invention is any device that can be used in medical diagnostics with which two-dimensional or three-dimensional images can be generated that render an area located inside a body. The invention is also not limited to the use of a single imaging device. Rather, imaging systems based on different principles can also be used, in particular imaging devices generating ultrasound images and x-ray images as well as tomographical imaging systems operating on the basis of magnetic resonance. In this case it is advantageous when the markers are detectable in all employed imaging devices. 
         [0012]    Moreover, both the navigation and the identification of the spatial position of the exposure area are made easier if the probe and the position of the x-ray source itself are detectable in the image. 
         [0013]    If a shielding that can be moved relative to the x-ray source is arranged in the probe to adjust the exposure area, the exposure area can be adjusted more flexibly even given a stationary probe. In this case the markers are advantageously spatially coupled to the shielding. As an alternative to this, in this case the markers can also be arranged stationary on or in the probe when the position of the shielding (i.e. the position of a window or an aperture from which the x-rays exit) is detected relative to the markers with the aid of a sensor or is already known in advance by controlling the movement of the shielding. 
         [0014]    In a preferred embodiment of the invention, the device is an imaging device that can be positioned independent of the probe to generate an image rendering at least one part of the exposure area as well as a display device to show the image and to indicate the exposure area in the image. This enables a particularly simple and graphic positioning of the exposure area. 
         [0015]    Moreover, if lines of equal dose rating are mixed into the exposure area rendered in the image, the dose rating required at different locations of the exposure area can be adjusted in a targeted manner. 
         [0016]    It is particularly advantageous when an optical image of an environment of the probe containing at least one part of the exposure area is generated with the aid of an operation observation device arranged in or on the probe. The correct navigation of the probe is additionally made easier when the exposure area is indicated in the optical image. 
         [0017]    In an embodiment of the invention, the imaging device is an ultrasound applicator, in particular an ultrasound probe that can be inserted into a cavity of the body, which ultrasound probe advantageously exhibits an ultrasound transducer arrangement to generate ultrasound images in two slice planes perpendicular to one another. 
         [0018]    A device according to the invention is in particular suitable for insertion into a urethra or a ureter and for therapeutic treatment of a prostate, bladder or kidney tumor. 
         [0019]    The above object also is achieved in accordance with the present invention by a method for positioning an x-ray brachytherapy probe in the interior of the body of a living subject, including the steps of inserting an x-ray brachytherapy probe into a living subject, the probe having a distal end at which an x-ray source is located, radiating x-rays from the x-ray source into an exposure area in the body of the subject outside of the probe, providing a number of markers in or on the probe in a known special relation to the exposure area, and obtaining an image of the probe and at least a portion of the exposure area with the markers being visible in the image, and using the markers that are visible in the image to position the probe and thus to also position the exposure area. 
         [0020]    The above-discussed advantages that are achieved by the device in accordance with the present invention are also achieved by the method in accordance with the present invention. 
         [0021]    In an embodiment of the method, an optical image of a subject region containing at least one part of the exposure area is generated in which optical image the exposure area is indicated, in particular in that a luminophore is applied that preferably accumulates in a tumor. The exposure area can then be correctly positioned in a particularly simple and graphic manner in that the exposure area is brought into congruence with the area marked by the luminophore. 
         [0022]    In a further preferred embodiment of the invention, an ultrasound marker is applied which is a substance that preferably accumulates in a tumor and is accompanied by gas bubbles or generates these. These gas bubbles are particularly clearly shown in an ultrasound image. 
         [0023]    A method according to the invention is in particular suitable to assist the treatment of a prostate, bladder or kidney tumor in which the probe is inserted into a urethra or a ureter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  schematically illustrates an embodiment of an x-ray brachytherapy system constructed and operating in accordance with the present invention. 
           [0025]      FIGS. 2 and 3  respectively show ultrasound images obtained in planes that are perpendicular to each other and intersect each other, with the exposure area being mixed into the respective images of the intersection planes. 
           [0026]      FIG. 4  schematically illustrates an optical image obtained in the environment of the probe of the brachytherapy system in accordance with the present invention, wherein pathological tissue in the environment has been made visible by a luminophore carried by the probe. 
           [0027]      FIG. 5  schematically illustrates a further embodiment of the x-ray brachytherapy system in accordance with the present invention, using an extracorporeal ultrasound applicator as the imaging device. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    According to  FIG. 1 , a probe  6  (a catheter in the example) in which an x-ray source  8  is arranged at its distal end is inserted into a cavity (lumen)  2  of a body  4  (which is, for example, a urethra). A shielding  10  is associated with the x-ray source  8 , which shielding  10  in the exemplary embodiment contains a cylindrical part  10   a  that is provided in its circumference with a diaphragm or aperture  12  through which x-rays  14  can exit perpendicular to the longitudinal axis  16  of the probe  6 , i.e. radially in a (for example conical) exposure area  18  defined by the shape of the aperture  12  and its distance from the anode of the x-ray source  8 , which exposure area  18  is emphasized by hatching in  FIG. 1  and is indicated by boundary lines  19 . 
         [0029]    The cylindrical part  10   a  of the shielding  10  is arranged within the probe  6  such that it can be rotated around its longitudinal axis  16  so that the exposure area  18  can likewise be pivoted on this longitudinal axis  16 . The outer wall of the probe  6  advantageously is formed of a polymer material, such that it is at least semi-permeable to ultrasound. 
         [0030]    The shielding  10  possesses on its front side a front plate  10   b  that is provided with a closable diaphragm (not shown in detail in the Figure) with which it is possible to selectively radiate x-rays  14  in the direction of the longitudinal axis  16 . In this case either a movable lock is provided with which the aperture  12  can be closed or an additional shielding is provided that is arranged in the probe  6  such that the aperture  12  can be positioned in the region of this shielding. 
         [0031]    An ultrasound probe  24  generating an ultrasound image is inserted as an imaging device into an additional cavity  22  of the body  4  located in proximity to the cavity  2  (for example the rectum), in which ultrasound probe  24  is arranged at its distal end an ultrasound transducer arrangement  30  that generates an ultrasound image from a flat subject area  34  (illustrated by boundary lines  32 ) that overlays at least a portion of the exposure area  18 . The ultrasound transducer arrangement  30  is a linear transducer array or two linear transducer arrays that generate ultrasound images in slice planes perpendicular to one another (in the example parallel and perpendicular to the plane of the drawing). Probes of this type are known in ultrasound diagnostics as biplanar rectal probes. 
         [0032]    Moreover, in  FIG. 1  the ultrasound probe  24  is shown in a position (marked by dashes) in which it generates an ultrasound image in a subject plane perpendicular to the plane of the drawing which intersects the plane of the drawing in an intersection line  38  marked by dashes. 
         [0033]    Moreover, the probe  6  contains a schematically indicated optical observation device  40  with which a subject region can be observed that renders at least a portion of the exposure area  18 . 
         [0034]    A number of markers  36  (of which only three are shown in  FIG. 1 ) are arranged in the probe  6 . These markers  36  (for example spheres or gas-filled (air) cavities with approximately 1 mm diameter) are detectable in the ultrasound image generated by the ultrasound transducer arrangement  30  and enable a reconstruction of the intersection surface of the exposure area  18  with the subject plane detected by the ultrasound transducer arrangement  30 . In the example the markers  36  are rigidly coupled on the rotatable cylindrical part  10   a  of the shielding and are located in a stationary relation to the exposure area  18 . For example, the markers simultaneously have an increasing angle position and an increasing distance relative to a presentable geometric point (for example the proximal edge of the cylindrical part  10   a ). The angle position can then be concluded from the distance of a marker  36  from the edge. All markers  36  are located at a point of the probe  6  that can be shown in an ultrasound image or that is transparent to ultrasound. In the example illustrated in the Figure, markers  36  are shown that are located in a plane that contains the center axis of the bundle of x-rays  14 . If these three markers  36  are detected in an ultrasound image, this is an indication that the imaged subject plane likewise contains this center axis. The position of the exposure area  18  can now be concluded from the position of the three markers  36  in the ultrasound image. 
         [0035]    In an embodiment the markers  36  can also be depicted in an x-ray image, such that position and angle position of the probe  6  can also be monitored with an x-ray apparatus. 
         [0036]    The probe  6  and the ultrasound probe  24  are connected to a control and evaluation device  42  with which the x-ray source  8 , the ultrasound transducer arrangement  30  and the observation device  40  are controlled and the signals transmitted from the ultrasound transducer arrangement  30  and from the observation device  40  are evaluated so that they can be presented as an ultrasound image or as an optical image on a display device  44  (for example a monitor). With the aid of the control and evaluation device  42 , the markers  36  can also be identified and the exposure area  18  can be reconstructed with accurate position and identified in the ultrasound image. 
         [0037]    In the example of  FIG. 1  a tissue zone  52  to be therapeutically treated (in the example a prostate tumor that should be irradiated with x-rays  14 ) is located in the region of the wall  50  of the cavity  2 . The tissue zone  52  to be treated can also be a different tumor accessible via a body opening, for example a bladder tumor or a kidney tumor. 
         [0038]    This tissue zone  52  as well as the wall  50  are schematically depicted in the ultrasound image of  FIG. 2 . In this ultrasound image the intersection surface of the exposure area  18  with the subject plane detected by the ultrasound transducer arrangement is, for example, identified by rendering its lateral boundary lines  19 . The exposure area  18  mixed into the ultrasound image in this manner enables a correct positioning of the probe or, respectively, of the x-ray source. 
         [0039]    Three markers  36  with which a reconstruction of the position of the exposure area  18  is possible are apparent in the ultrasound image. In the example all three markers  36  are located in the image plane. In this case the center axis of the x-ray bundle lies in the subject plane (intersection plane) rendered in the ultrasound image and the cavity  2  and the probe  6  are shown in the idealized arrangement (shown in  FIG. 1 ) in the form of a longitudinal section. 
         [0040]    Moreover, lines  54  of equal dose rating that indicate the current local dose rating to the therapist are mixed into the ultrasound image, for instance. These lines  54  are located, for example, among one another at an interval that corresponds to the decrease of the dose rating to 1/e, respectively. These are approximately 1.2 cm given an x-ray radiator with an average energy of 20 keV in the tissue. The therapist can then adjust the required dose rating by changing the operating parameters of the x-ray source (anode current, acceleration voltage). These lines  54  of the same dose rating then shift in the ultrasound image corresponding to the dose rating changing with the variation of the operating parameters. 
         [0041]    The use of an ultrasound marker is also possible. A substance that preferably accumulates in the tumor and is simultaneously accompanied by, for example, small gas bubbles or that generates small gas bubbles is administered to the patient. These gas bubbles are particularly clearly shown in the ultrasound image. 
         [0042]    As explained in the preceding, in the shown example the center axis of the x-ray beam lies in the subject plane (intersection plane) rendered in the ultrasound image, such that the lines  54  have a circular arc-shaped form. 
         [0043]    In the example of  FIG. 3  an ultrasound image is shown as it can arise when the ultrasound probe  24  is located in a position marked by dashes in  FIG. 1  and the subject plane runs perpendicular to the plane of the drawing of  FIG. 1  and at an angle relative to the center axis of the probe  6 , as this is illustrated using the intersection line  38  (marked by dashes in  FIG. 1 ) between subject plane and plane of the drawing. In this case the cavity  2  and the probe  6  are visible in the form of a cross-section running at an angle. Like the lines  54  of equal dose rating, the boundary line  19  of the x-ray then has an approximately elliptical shape. If the intersection plane is oriented perpendicular to the center axis of the x-rays, the boundary lines  19  and the line  54  exhibit a circular shape. 
         [0044]    According to  FIG. 4 , an optical image, in which the wall  50  of the cavity is visible given corresponding illumination, is generated from the surroundings of the probe. A luminophore can be additionally applied (for example directly with the aid of the probe) preferentially accumulates in the tissue zone  52  if this is a tumor and that, for example, is excited by the light source used for illumination and emits fluorescence light in the visible range, so the tumor  52  can also be made visible in the optical image at least in its surface region with which it borders the cavity. If the envelope of the x-ray beam striking the surface of the wall  50  is additionally mixed in as a circular line  56  and its center axis is mixed in as a point  58 , the exact positioning can also be effected with the aid of the optical image in addition to the positioning with the ultrasound image since in this case image information exists from a different plane, for example a plane perpendicular to the image plane of the ultrasound image. 
         [0045]    In the exemplary embodiment according to  FIG. 5 , instead of an ultrasound probe that can be inserted into the inside of the body  5  an ultrasound head  60  is provided as an ultrasound applicator, which ultrasound head  60  is attached on the outer surface  62  of the body  4  and detects the probe  6  and the tissue zone  52  starting from this surface  62  of the cavity  2 . 
         [0046]    The invention is presented using a catheter inserted into the cavity of a body. In principle the invention is also suitable for probes that are directly inserted into the tissue, as this is the case in the invasive post-treatment (explained above) of a tumor bed of a previously removed tumor. The tissue zone to be treated can also be a vessel wall that should be irradiated after the implementation of a dilatation to reduce the restenosis rate. 
         [0047]    Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted heron all changes and modifications as reasonably and properly come within the scope of their contribution to the art.