Patent Publication Number: US-2007118009-A1

Title: Method for controlling the application of ionizing radiation to a body

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims priority of German application No. 10 2005 029 893.1 filed Jun. 27, 2005, which is incorporated by reference herein in its entirety.  
     FIELD OF THE INVENTION  
      The invention relates to a method for controlling the application of ionizing radiation to a body. It thus pertains to the field of brachytherapy. With brachytherapy, radioactive emitters are incorporated into the body to be treated so as to deliver a localized high radiation dosage and thus destroy malignant tissue. This can be effected by implanting seeds, i.e. radioactive emitter which remain in the body. Alternatively, a so-called afterloading can be carried out, in other words, a radiation source can be inserted and removed again. In both cases, it is necessary to position the radiation source as near as possible to the tumor.  
     BACKGROUND OF THE INVENTION  
      The contour of the tumor is usually determined on the basis of a three-dimensional image, for instance a computed tomography image or an image generated by means of magnetic resonance. The emitter and/or applicator (instrument with the emitter) is inserted using fluoroscopic control or with the aid of ultrasound imaging. In the prior art it is difficult to position the radiation source accurately relative to the position of a tumor previously located on the basis of the three-dimensional representation.  
     SUMMARY OF THE INVENTION  
      The object is thus to provide a method for controlling the application of ionizing radiation to a body, which, compared with the prior art, particularly allows better location of a therapeutic radiation source.  
      To achieve the object, the invention provides a method and an instrument according to the claims.  
      The method according to the invention thus comprises the steps: 
          creating a three-dimensional representation of the body,     providing an instrument, which can apply therapeutic radiation sources to a body, with a part of a locating system for locating the position of the therapeutic radiation sources on the instrument in the body,     inserting the instrument with therapeutic radiation sources into the body while simultaneously locating the position of the therapeutic radiation sources with the (complete) locating system,     assigning the located position of the therapeutic radiation sources to the three-dimensional representation of the body,     applying the therapeutic radiation source, when the located position corresponds to a position previously determined in the three-dimensional representation of the body.        

      The invention is thus essentially based on the use of a locating system which is linked to the applicator instrument. The three-dimensional position of the applicator can thus be determined during the insertion of the applicator into the body, and the treating doctor is no longer restricted to a control by means of ultrasound or fluoroscopic imaging. Ultrasound and fluoroscopic imaging can however also be used in addition.  
      The three dimensional representation is preferably created with the aid of computed tomography, C-arm computed tomography, magnetic resonance tomography or three-dimensional sonography.  
      The instrument can be constructed like conventional applicators in the prior art of brachytherapy and must only have space for the part of the locating system. Reference is made here to a “part of a locating system”, because the locating system comprises a part of the instrument and a part located outside the body of the patient, with the signals being emitted in at least one direction. For example, an electromagnetic locating system can feature a device outside the patient body, which serves as a source for electromagnetic radiation and an evaluation unit which detects the electromagnetic radiation received by a coil on the instrument (further details are not discussed here in terms of the lines connecting the coil to the outside world). The instrument used to apply therapeutic radiation sources to a body can comprise a rigid needle, in which the therapeutic radiation source is located, with this needle then being connected to the part of the locating system. It can also feature a flexible tube, in which the therapeutic radiation source is located, with this flexible tube then being connected to the part of the locating system.  
      To relate the signals received by the locating system to the position of the instrument, it may be necessary for the locating system to know the position of the body in the patient space. To this end, marker elements can be fixed to the body, which are to be identified in the three-dimensional representation of the body. If the locating system is then designed to determine the position of the marker objects, the mapped marker elements can be made to correspond to the located marker elements on the images, so that it is possible to assign the located position of the instrument to the three-dimensional representation of the body.  
      The assignment of the located position of the therapeutic radiation sources to the three-dimensional representation of the body can also include the therapeutic radiation sources or even the part of the instrument with which they are applied (instrument tip) being displayed in the three dimensional representation. A corresponding arrow can be marked on the three-dimensional image for instance, so that the treating doctor can detect where the therapeutic radiation sources are located at present on the basis of the three-dimensional representation serving to determine the tumor contours.  
      The instrument according to the invention is an instrument which can be inserted into the body of a patient in order to transport therapeutic radiation sources, as used conventionally with brachytherapy, and comprises in accordance with the invention a part of a locating system such that the position of the tip of the instrument can be determined with the complete locating system. It is thus implicitly assumed here that the therapeutic radiation sources are applied with the tip of the instrument, i.e. that it is important to determine the position of the tip, so as to establish where the therapeutic radiation sources reach, if they are emitted by the instrument into the body of the patient with the instrument in its current position.  
      The instrument can be a catheter, the tip of which is connected to an electromagnetic receiving coil, which is part of an electromagnetic locating system. It can also be a rigid instrument, whereby with such rigid instruments a part of the rigid instrument conventionally protrudes out of the body of the patient. Optical markers are then attached to this part as part of an optical locating system. The complete locating system then comprises an emitter, which emits light and a receiver, which receives a signal from the optical markers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A preferred embodiment of the invention is now described with reference to the drawing, in which;  
       FIG. 1  shows a patient examination with the instrument according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIG. 1  shows a schematic cross-sectional representation of patient  10 . The patient  10  has an organ  12  in which a tumor  14  is located. The tumor  14  was previously identified and pinpointed with the aid of a three-dimensional representation of the body of the patient  10 . The image data from the three-dimensional representation is stored on a computer system (not shown) and the tumor  14  is displayed on a screen  16 .  
      The tumor  14  is now treated brachytherapeutically, i.e. the tumor tissue is to be destroyed by means of radioactive radiation. To this end a radioactive emitter, i.e. a therapeutic radiation source, must be brought close to the tumor  14 . A catheter  18  is used for this purpose. The catheter  18  takes the form of a typical instrument (applicator) used for applying therapeutic radiation sources, as known from the prior art. In addition, in accordance with the invention, an electromagnetic receiving coil  20  is attached to the catheter  18 , said receiving coil being part of a locating system. A further part of the locating system is a generator  22  of electromagnetic radiation  24  only shown schematically in  FIG. 1 . The electromagnetic radiation  24  then induces a voltage in the receiving coil  20 , said voltage being supplied to an evaluation unit  26 . If the form of the electromagnetic radiation is suitable, it is known from the prior art that the three-dimensional position of the coil  20  can be located. If the position of the patient table is known, on the basis of the marker elements for instance, the tip of the catheter  18  can be schematically displayed in the three-dimensional representation on the screen  16  by an arrow  28 . The treating doctor thus tracks the position of the tip of the catheter  18  on the basis of the arrow  28  on the screen  16 , so as to obtain information about how close the catheter  18  is to the tumor  14 . If the catheter  18  is arranged sufficiently close to the tumor  14 , the therapeutic radiation source is emitted from the catheter  18  to the body  10 .  
      As already mentioned, the catheter  18  is a conventional application catheter for therapeutic radiation sources. The electromagnetic locating system comprising the generator  22  and the receiving coil  20  with the evaluation unit  26  is known as such in the prior art (c.f. for instance the article by P. G. Seiler et al., “A novel tracking technique for the continuous precise measurement of tumor positions in conformal radiotherapy”, Phys. Med. Biol., Volume 45 (2000), pages N103-N110). The invention firstly provides the link between such a locating system and an application catheter  18 , whereby it is possible to locate the tip of the catheter  18  and assign it to the three-dimensional representation displayed on the screen  16 . This enhances the usefulness of the three-dimensional representation. It is not only used beforehand to diagnose the tumors, but also during the operation. Fluoroscopic images or ultrasound images generated during the operation as well can also be displayed on the screen  16 , with the necessity for generating these images essentially diminishing due to the good support for the treating doctor on the basis of the representation of the arrow  28  on the screen  16 .