Abstract:
Transurethral catheter ( 10 ) for the heat treatment of body tissue surrounding the catheter, including an elongated light carrier ( 11 ). A light receiving and light distributing elongated light probe ( 12 ) is operatively connected to said light carrier ( 11 ), and the light probe ( 12 ) comprises light reflecting surfaces ( 13 ) for preventing received light from escaping from the probe ( 12 ). At least one light emitting section ( 14 ) is formed in the probe ( 12 ) for emitting light into said body tissue.

Description:
TECHNICAL FIELD 
     Laser treatment of benign prostatic hyperplasia (BPH) is a developing, minimally invasive method. The method relies on the conversion of light absorbed by the tissue into heat, inducing irreversible tissue alterations. 
     PRIOR ART 
     Various treatment strategies exist. One of the most frequently employed technique is visual laser ablation of the prostate (VLAP), using the Nd:YAG laser and side-firing fibres for transurethral irradiation. A common procedure is to irradiate at 60 W for 60 s in four quadrants, producing rapid and selective coagulation of the hyperplastic tissue. Current side-firing fibres placed in the urethra irradiates a spot approximately 2 mm in diameter, resulting in limited lateral extension of the coagulated volume. 
     A drawback in this procedure is that repeated irradiation steps are required for producing coalescing lesions. The efficient heating from a concentrated beam will require an effective monitoring of the temperature development in the tissue, so as to avoid unwanted damages of other parts of the surrounding tissues. It is difficult to achieve this type of monitoring and the patient would be exposed to a higher risk than if another type of heating is used. Due to the fact that very high energies are absorbed in a small local spot, the patient needs in most cases general or spinal anesthesia. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to avoid the above specified drawback. A further object is to provide a device which at a low risk for the patient facilitates an effective treatment. These objects are achieved by a device as claimed in the independent claim. 
     The device according to the invention will make it possible to treat the entire length of the prostatic urethra after positioning a light probe in one single location. In a preferred embodiment this could be achieved by using a laser probe with an illumination field in the shape of a rectangular bar instead of a circular spot. 
     In a preferred embodiment the device is formed as a side-firing laser catheter. It will fulfill the following requirements: lateral irradiation in order to heat the lateral prostatic lobes selectively, extended length of laser emission in order to treat a large portion of the prostatic urethra in a single session, and minimized loss of laser light for good light economy. Other right sources may also be used. 
     Further objects and advantages of the invention are shown in the description below and in the accompanying drawings and dependent claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be understood from the following description of embodiments thereof given by way of example only with reference to the accompanying drawings in which: 
     FIG. 1 is a schematic perspective view of one embodiment of a device according to the invention, 
     FIG. 2 is a side elevation view of the device in FIG. 1, 
     FIG. 3 is a longitudinal sectional view of the device in FIG. 1, 
     FIG. 4 is a cross sectional view of the device in FIG. 1, 
     FIG. 5 is a side elevation view of an alternative embodiment of a device according to the invention, 
     FIG. 6 is a schematic side view partly in section of the device in FIG. 5 at a location of treatment in the human body, and 
     FIG. 7 is a cross sectional view of the device in FIG.  6 . 
    
    
     DETAILED DESCRIPTION 
     In the embodiment shown In FIG. 1 a transurethral catheter  10  is partly cut to show an elongated light carrier  11  and laser probe  12 . The light carrier  11  preferably is an optical fibre. The laser probe is fabricated from a 6 mm diameter and 35 mm long cylinder of a highly diffuse reflective, plastic material, (SPECTRALON, LABSPHERE, NORTH SUTTON, N.H.). A 1 mm wide and 28 mm long slit  15  has been cut in the probe. A small hole is drilled in one end-face of the cylinder to permit the insertion of a 600 μm core diameter optical fibre. The fibre extends a few mm into the slit with an end part  11 ′. The cylinder is flattened parallel to the slit  15  to allow circulation of cooling water around the probe in two semicircular spaces,  16  formed between the probe  12  and the catheter  10 . The width of the catheter wall in this embodiment is approximately 1 mm. Light entering the slit from the fibre will scatter on surfaces surrounding the slit and finally exit through the slit opening. 
     Preferably the laser probe  12  is flexible, so as to be readily inserted within the prostate tissue through the urethra. In the location of treatment the probe may be bent and preferably the probe operates with the same effect in such a position. In an embodiment where the probe is formed with a slit  15  it may be necessary or at least appropriate to provide distance elements  17  which will maintain the slit dimensions even when the probe is bent. Preferably, the distance elements  17  are made of translucent material, so as not to deteriorate the light emitting properties of the probe. In the embodiment shown the distance elements extend transverse to the longitudinal direction of the probe, but it may be appropriate to provide a distance element extending in the longitudinal direction of the probe. It is also possible to provide a distance element  17  completely filling up the slit  15 . 
     In the catheter shown there is also provided a first tubular carrier  18  for a set of temperature transducers  19  (see also FIG.  6 ). The temperature transducers  19  are supported on a wire  20  which can be extended from an opening in the catheter  10 . A second tubular means  21  can be used for draining the bladder (see FIG. 6) and a third tubular means  22  can be used to inflate a balloon (see FIG. 6) which is used to maintain the catheter in a desired position. The probe will transmit up to 95% of the power emitted by the plane-cut optical fibre. By painting the outer aspect of the probe with opaque, reflective paint, the emission through the slit will be up to 80%. 
     In FIG.  2  and FIG. 3 the probe  12  and the distance elements according to one embodiments are shown in more detail. It can also be seen that the light carrier  11  extends into the slit  15 . 
     The cross sectional view in FIG. 4 shows the laser probe  12  centrally located within the catheter  10 . The second and third tubular means  21  and  22  are located in the semicircular spaces  16  on either side of the laser probe  12 . The water that is circulated through the semicircular spaces  16  is used to cool the probe  12 , so as to avoid heating of the anterior and posterior parts of the prostate. Water at a temperature of 5-20° C. can be flushed through the catheter. An appropriate rate is approximately 100-1000 ml/min Using a 10-60 W Nd YAG laser the treatment will be performed for a few minutes up to an hour. It is also possible to use other types of laser, e.g. diode laser, or a non-coherent light source. 
     A second embodiment of a laser probe according to the invention is shown in FIG.  5 . In this embodiment the complete probe  12  is made from a translucent flexible material, such as clear silicon, polycarbonate (with an appropriate plasticizer) and polyethylene. Besides two light emitting sections  14  on opposite sides of the probe  12  the complete exterior of the probe  12  is covered by a fight reflecting layer. Preferably the reflecting layer is formed by a highly reflective material, such as aluminum. The light carrier  11  extends into the probe and light will propagate within the probe to be repeatedly reflected by the reflecting layer. A major part of the light will firmly be emitted though the light emitting section  14 . In a simple embodiment the two light emitting sections  14  on opposite sides of the probe  12  extends over the complete side sections of the probe  12 . The dimensions of the side sections will correspond to the dimensions of the slits  15  in the embodiment according to FIGS. 1-4. 
     In FIG. 6 the catheter  10  has been inserted through the urethra to a position where a tip  23  of the catheter is located in the bladder  24 . A balloon  25 , also located inside the bladder, has been inflated. In this position and condition the balloon will maintain the catheter in position and ensure that the catheter cannot be withdrawn unintentionally. The balloon  25  is inflated through one of the tubular means. Another tubular means opens into the bladder and will permit a drain of the bladder during and optionally after the treatment. 
     In position the laser probe  12  is located centrally in the prostate  26  or as shown in FIG. 6 closer to the bladder neck. The wire  20  carrying the temperature transducers has been extended through the catheter at an appropriate angle in relation to the longitudinal direction of the catheter. 
     FIG. 7 shows schematically the temperature distribution in the prostate tissue. Light is emitted in four lobes. No light is emitted in the anterior or the posterior direction. The irradiated area will have the same rectangular shape as the slit by keeping the distance between the probe and the tissue surface short. Near the catheter wall, high temperatures are found in the laser-irradiated areas. Further out, the temperature distribution is more elliptical due to heat conduction. 
     In transverse cross-section, the temperature distribution close to the catheter wall is butterfly-shaped as shown at  27 . This is valid also at some distance from the catheter as shown at  26 . Further out, the distribution become elliptical, as shown at  29 . 
     The side-firing laser catheter according to the invention has been developed with the intention to permit selective coagulation by selective laser irradiation of the hyperplastic prostate over the entire length of the prostatic urethra after placement of the catheter in one single position. The present probe relies on diffuse reflectance, while conventional side-firing fibres are equipped with gold-plated mirrors or utilise the principle of internal reflection. 
     The laser probe is inserted into a catheter with integrated water cooling, which is intended to be positioned within the prostatic urethra under, transrectal ultrasound guidance. Light is emitted in many directions through the slit but local tissue irradiation is achieved by ensuring that there is only a short distance between the slit opening and the urethral wall. 
     The area of the irradiated tissue surface is close to the area of the slit. Water circulation is employed to cool the laser prove and to permit deep thermal coagulation. The cooling will result in that the maximum temperature is forced a few millimeters into the tissue, which makes it possible to coagulate larger volumes without inducing carbonisation. 
     Without cooling, the catheter surface would reach the highest temperatures. The temperature of the cooling fluid should be chosen so as to force the temperature rise deep into the tissue without causing carbonisation of the urethra. The cooling water temperature typically will be 5-20° C. 
     Longitudinally, in the plane of fight emission, a tissue area extending more than 30 millimeters can be treated, which in vivo would enable rapid coagulation. The longitudinal extension of the temperature distribution depends on the length of the laser probe. Longer probes can be used for treatment of longer prostates. 
     The transverse cross-sectional temperature distribution will be elliptical a few millimeters from the catheter wall. Due to heat conduction, the temperature distribution becomes more and more circular when irradiating for longer times (result not shown). The shorter the duration of the treatment, the greater the difference in temperature between the laser irradiated areas and the areas shielded from direct laser irradiation. However, too short a treatment limits the tissue volume raised to therapeutic temperatures. 
     The laser power should thus be chosen as high as possible without inducing carbonisation, which may lead to catheter destruction. With this setting, coagulation of the urethra will occur, as is the case in VLAP.