Patent Publication Number: US-7909821-B2

Title: Deflectable interstitial ablation device

Description:
This application is a continuation of U.S. patent application Ser. No. 10/004,759, filed on Dec. 4, 2001, now U.S. Pat. No. 6,482,203, which is a continuation of U.S. patent application Ser. No. 09/661,835, filed on Sep. 14, 2000, now U.S. Pat. No. 6,352,534, which is a continuation of U.S. patent application Ser. No. 08/940,519, filed on Sep. 30, 1997, now U.S. Pat. No. 6,238,389. The disclosures of each of the above applications are incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to an interstitial ablation device and method for performing tissue ablation, and in particular, to an improved interstitial ablation device providing enhanced electrode placement and control. 
     BACKGROUND 
     Ablation devices can be used to treat tumors in the body. In particular, ablation devices can be used to treat benign prostatic hypertrophy or hyperplasia (BPH), a condition resulting in an enlargement of the prostate gland. This is a common medical problem typically experienced by men over 50 years of age. Hyperplastic enlargement of the prostate gland often leads to compression of the urethra, which results in obstruction of the urinary tract. 
     An ablating needle can be used with a cystoscope to treat BPH by ablating a prostatic adenoma, which is a benign tumor inside the prostate. To perform the ablation procedure, a physician inserts a distal end of the cystoscope into the urethra of a patient while viewing the advance through an eye piece of the cystoscope. The needle electrode is also introduced into the urethra through a working channel of the cystoscope. The cystoscope and the needle electrode are typically introduced inside the urethra sequentially. The distal end of the needle electrode is positioned adjacent the prostate near the prostatic adenoma. The physician then causes the needle electrode to penetrate the urethral wall, such that it is positioned inside the prostatic adenoma. Radiofrequency (RF) energy is applied to the needle electrode to coagulate tissue surrounding the electrode. Coagulation causes necrosis of the prostatic adenoma, resulting in atrophy of the prostate and a reduction in the compressive forces that interfere with urine flow through the urethra. 
     During the ablation procedure, it is important that the needle electrode be positioned precisely, because inaccurate electrode placement can cause incontinence in the patient. Visualization is typically provided by inserting the needle electrode through a cystoscope. One disadvantage of the ablation device insertable through a cystoscope is that it is difficult to feed the device through a working channel of the cystoscope and requires a lot of juggling which can make accurate placement of the needle electrode difficult. Moreover, it is often difficult to observe the distal tip of the needle electrode as the electrode penetrates the urethral wall, because the distal end of the electrode is typically deflected in order to penetrate the urethral wall while the viewing device itself does not deflect along with the needle electrode. 
     Existing interstitial ablation systems are also uncomfortable for the patients and cumbersome for the physician performing the procedure. Most cystoscopes and ablation systems integrating imaging devices tend to be rigid and uncomfortable for patients when inserted through a body lumen such as the urethra. The systems also have numerous knobs and dials that the physician must adjust for controlling needle deployment, fluid introduction, and application of RF energy. 
     Thus, there remains a need for an interstitial ablation device that provides accurate electrode placement and better control of the electrode, reduces patient discomfort and simplifies the process of performing ablation. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention features a deflectable interstitial ablation device. In one embodiment, the device includes an elongated housing, an electrode mounted within the elongated housing, a driver coupled to the electrode, an imaging device integrally mounted within the elongated housing, and a deflection system disposed within the elongated housing. The elongated housing has a proximal end, a distal end, and a deflectable segment. The electrode is deployable from a first position within the elongated housing to a second position a predetermined distance beyond the distal end of the elongated housing, and has a flexible portion capable of deflecting with the deflectable segment of the elongated housing. The driver exerts a force sufficient to drive the electrode from the first position to the second position in a single motion. The imaging device has a flexible portion capable of deflecting with the deflectable segment of the elongated housing. The deflection system controllably deflects the deflectable segment of the elongated housing to a desired angle. The deflection system has a proximal end in communication with a steering mechanism. 
     In one embodiment, the imaging device includes a plurality of illumination optical fibers and a plurality of viewing optical fibers extending from the proximal end to the distal end of the elongated housing. The viewing optical fibers can comprise a fused bundle of viewing optical fibers surrounded by illumination optical fibers, wherein the viewing optical fibers are in communication with a lens disposed at the distal end of the elongated housing. In another embodiment, the electrode is a hollow needle electrode and an insulation sheath surrounds the needle electrode. The needle electrode and the insulation sheath are individually and slidably mounted inside the elongated housing, such that the insulation sheath is capable of covering a proximal portion of the needle electrode which extends beyond the distal end of the elongated housing. In still another embodiment, the driver coupled to the electrode can exert a force within the range of ¼ lb to 1 lb to drive the electrode from the first position to the second position in a single motion. 
     In another embodiment, the device includes an elongated housing, an electrode mounted within the elongated housing, an imaging device integrally mounted with the elongated housing, a deflection system disposed within the elongated housing, and a foot pedal for deploying the electrode. 
     In another aspect, the invention features a method for treating tissue. A deflectable interstitial ablation device is inserted into a body lumen which provides access to the tissue to be treated. The deflectable interstitial ablation device includes an elongated housing having a deflectable segment, a deployable electrode mounted within the elongated housing, a driver coupled to the electrode for exerting a force to drive the electrode, an imaging device integrally mounted with the elongated housing, and a deflection system disposed within the elongated housing. The distal end of the elongated housing is positioned near the tissue. The deflectable segment of the elongated housing is deflected toward the tissue, thereby deflecting the electrode and the imaging device toward the tissue along with the deflectable segment. The electrode is deployed to penetrate a wall of the lumen and to position a distal end of the electrode adjacent the tissue. Radio frequency energy is applied to the electrode in an amount and for a duration sufficient to ablate the tissue. 
     In one embodiment, an insulation sheath is deployed to cover a proximal portion of the deployed electrode to protect the wall of the lumen from directly contacting the needle electrode during the treatment. In another embodiment, a balloon disposed on a body of the elongated housing of the deflectable interstitial ablation device is inflated to secure the position of the elongated housing inside the lumen. In yet another embodiment, a basket disposed on a body of the elongated housing of the deflectable interstitial ablation device is expanded to secure a position. In still another embodiment, the distal end of the elongated housing is connected to an actuator in communication with a foot pedal and the foot pedal is depressed to deploy the electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is described with particularity in the appended claims. The above and further advantages of this invention may be better understood by referring to the following description taken in conjunction with the accompanying drawings. 
         FIG. 1A  shows a side view of a deflectable interstitial ablation device according to one embodiment of the invention. 
         FIG. 1B  shows a portion of the deflectable insterstital ablation device having a basket for maintaining the placement of the device in a body lumen, according to one embodiment of the invention. 
         FIG. 2  illustrates a deflecting segment of the deflectable interstitial ablation device of  FIG. 1A . 
         FIG. 3  shows a cross sectional view of the deflectable interstitial ablation device of  FIG. 1A  cut through lines  3 ′- 3 ″. 
         FIG. 4  shows a cross sectional view of a distal end of the deflectable interstitial ablation device of  FIG. 1A  cut through lines  4 ′- 4 ″. 
         FIG. 5A  is a side view of a kinetically deployable needle electrode according to one embodiment of the invention. 
         FIG. 5B  is a cross sectional view of the kinetically deployable needle electrode of  FIG. 5A  prior to deployment. 
         FIG. 5C  is a cross sectional view of the kinetically deployable needle electrode of  FIG. 5A  in a loaded position. 
         FIG. 5D  is a cross sectional view of the kinetically deployable needle electrode of  FIG. 5A  with the needle electrode deployed. 
         FIG. 5E  is a cross sectional view of the kinetically deployable needle electrode of  FIG. 5A  with the needle electrode and the insulation sheath deployed. 
         FIG. 6  shows a transurethral interstitial ablation system employing a foot pedal according to one embodiment of the invention. 
         FIG. 7  shows an actuator for deploying a needle electrode according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1A and 4 , a deflectable interstitial ablation device  10  includes an elongated housing  12 , an electrode  14  extending within the elongated housing  12 , an imaging device  16  integrally mounted with the elongated housing  12  and a deflection system  18  disposed within the elongated housing  12 . The electrode  14  can comprise a needle electrode having a sharpened tip, or an electrode having a blunt tip. The elongated housing  12  has a proximal end, a distal end and a deflectable segment  22  further as further shown in  FIG. 2 . The elongated housing  12  can be constructed to be flexible so that the housing  12  may be inserted into the urethra without much discomfort. In one embodiment, the housing  12 , can be, for example, a flexible multi-lumen catheter. In another embodiment, the housing  12 , can be, for example, a substantially rigid, single lumen catheter having a deflectable segment  22 . In one detailed embodiment, the housing  12  can have a diameter from about 15 to 16 French. It is to appreciated that the diameter of the housing  12  can vary depending on the intended use of the ablation device  10 . 
     In order to provide accurate placement of the electrode  14  inside the urethra, the present invention further provides means for stabilizing the position of the device  10  before deploying the electrode  14 . In one embodiment, the elongated housing  12  of the invention includes a balloon  24  for securing the position of the device  10  while the electrode  14  is deployed at the ablation site. The elongated housing  12  includes a fluid port with a luer fitting  26  for introducing a fluid such as, for example, air or water for inflating the balloon  24 . The fluid enters the balloon  24  through an inflation sleeve further shown in  FIG. 2  to inflate the balloon  24 . Another advantage provided by the balloon  24  is that the balloon  24  can block the blood vessels on the urethral wall and slow down heat conduction provided by the blood vessels. In one embodiment, the balloon  24  is compliant enough to fit inside the urethra. In one detailed embodiment, the balloon is constructed of latex or silicone. The diameter of the inflated balloon, in one embodiment, can be about 30 French. 
     In another embodiment, as shown in  FIG. 1B , the elongated housing  12  can include a basket  25  to stabilize the device  10  position during deployment of the electrode  14 . The basket  25  can comprise a wire mesh attached to an outer surface of the housing  12  surrounding the electrode  14 , the imaging device  16  and the deflection system  18 . The housing  12  can further be surrounded by an elongated sheath or catheter  27  such that the wire mesh comprising the basket  25  remains retracted during placement of the device and expands into the basket  25  shown in  FIG. 1B  to secure the position and placement of the electrode  14  after the electrode  14  has been exposed. 
     As shown, the proximal end of the elongated body  12  is in communication with a detachable eye piece coupler  28 . A detachable eye piece  30  is coupled to the eye piece coupler  28 , and the physician observes insertion of the device  10  into the urethra and the electrode  14  deployment by looking into the eye piece  30 . 
     The proximal end of the elongated body  12  is also in communication with a handle  32 . The handle  32  includes a slide member  34  for controlling deployment of the electrode  14 . In one embodiment, the handle  32  can include two slide members (not shown), one for controlling the movement of the electrode  14  and the other for controlling the movement of the insulation sheath  40 . In another embodiment, the slide member  34  can control the movement of the electrode  14  and the insulation sheath  40  secured to the electrode  14 , to expose a predetermined amount of the electrode  14 . As shown, the handle  32  also includes an electrical connector  38  for coupling the proximal end of the electrode  14  to a power source (not shown). In a preferred embodiment, the power source is an RF generator, however it is to be appreciated that other energy sources can be used, such as a microwave generator. The handle  32  further includes a luer port  36  for injecting fluid and an irrigation port  31  for removing fluid. In one embodiment, the fluid can be a conductive fluid for improving ablation procedures. Conductive fluids, can include, for example, saline and lydocaine. The use of a conducting fluid prevents desiccation of tissue and prevents an increase in the impedance during the ablation procedure. 
     Referring to  FIG. 2 , the electrode  14  can be deployable from a first position within the elongated housing  12  to a second position beyond the distal end of the elongated housing  12  as shown. In one embodiment, the electrode  14  deploys to a predetermined distance beyond the distal end of the elongated housing  12 . It is to be appreciated that the distance the electrode  14  deploys can vary depending on the intended application. As shown, the electrode  14  also has a flexible portion  40   a  which deflects along with the deflectable segment  22  of the elongated housing  12 . In one detailed embodiment, the deflectable segment  22  is located at the distal end of the elongated housing  12  and has a dimension of from about 2.5 cm to about 4.5 cm measured from the distal end of the housing  12 . It is to be appreciated that the length of the deflectable segment  22  can fall outside of the above range, depending on the intended application of the device  10 . In one embodiment, the dimension and position of the flexible portion  40   a  of the electrode  14  corresponds to that of the deflectable segment  22  of the elongated housing  12 . Referring to  FIG. 2 , illustrated in phantom in a deflected position, is the deflectable segment  22  and electrode&#39;s flexible portion  40   a  at the distal tip of the elongated housing  12 . 
     Referring to  FIGS. 2 and 3 , the electrode  14  can be a needle electrode surrounded by an insulation sheath  40 . The needle electrode  14  and the insulation sheath  40  are placed inside an electrode guide tube  41  disposed inside the elongated housing  12 . The insulation sheath  40 , for example, may be constructed from an insulating polymer material such as polyimide. In another embodiment, the needle electrode  14  can be coated with an insulator, such as Teflon or ceramic. The needle electrode  14  and the insulation sheath  40  can be individually and slidably mounted inside the elongated housing  12 , such that the insulation sheath  40  is capable of covering a proximal portion of the needle electrode  14  extending beyond the distal end of the elongated housing  12 . By adjustably covering a proximal portion of the electrode  14  with the insulation sheath  40 , the physician can control the amount of electrode  14  that is exposed, and thus control the conductive region and consequently, the size of the ablation area. This feature is important in transurethral interstitial ablation of prostate tissue, because urethral walls can be protected from being ablated during the procedure. Alternatively, the insulation sheath  40  can be fixed to a proximal portion of the needle electrode  14  and the needle electrode  14  can be slidably mounted inside the elongated housing  12 . In another embodiment, as shown in  FIG. 3 , the electrode  14  can comprise a hollow electrode  14  including a passageway  43 . In one embodiment, the hollow electrode  14  has an inner diameter of approximately 0.011 inches and an outer diameter of approximately 0.02 inches. The insulation sheath  40  has an outer diameter of approximately 0.03 inches and an inner diameter of about 0.025 inches. The electrode guide tube  41  has an inner diameter of about 0.039 inches. It is to be appreciated that the above dimensions are illustrative, and are not intended to be restrictive, as other dimensions can be used depending in whole or in part, on the intended application of the device. 
     Referring to  FIGS. 3 and 4 , the imaging device  16  disposed inside the elongated housing  12  includes a illumination region  44  and a viewing region  42 . Both regions  42  and  44  can include a plurality of optical fibers  46  extending from the proximal end to the distal end of the elongated housing  12 . In the embodiment of  FIGS. 3 and 4 , the illumination region  44  includes a plurality of optical fibers  46  in communication with a light source (not shown) at a proximal end. The plurality of optical fibers  46  surrounds the viewing region  42 . The viewing region  42  can include a fused bundle of optical fibers  48  in communication with an objective lens  50  at the distal end for focusing an image. An example of the objective lens  50  is a gradient index (GRIN-self) objective lens having a diameter of about 0.039 inches. The illumination region  44  and the viewing region  42  may be arranged in other ways and may comprise optical components other than or in addition to those described above. In other embodiments, other imaging devices can be used for viewing the area of tissue in question. In one embodiment, the imaging device  16  is surrounded by an outer sheath comprising a polymeric material  47 . In another embodiment, the imaging device  16  is disposed inside the elongated housing  12  without an outer sheath. In one detailed embodiment, the imaging device  16  has a viewing angle  13  of about 70 degrees, as shown in  FIGS. 1 and 2 . It is to be appreciated that the viewing angle  13  can be greater or less than 70 degrees depending in whole or in part, on the intended application of the device. 
     Referring to  FIGS. 1 and 4 , the deflection system  18  controllably deflects the deflectable segment  22  by an angle of up to 180 degrees in one direction and 180 degrees in the opposite direction with respect to the longitudinal axis of the elongated housing  12 . In one embodiment, the deflection system  18  includes a flexible wire  54  extending from the proximal end to the distal end of the elongated housing  12  and a flat spring  56  in communication with the flexible wire  54  disposed at the distal end of the elongated housing  12 . The proximal end of the flexible wire  54  is in communication with a steering mechanism  52 , shown in  FIG. 1A  as mounted on the handle  32 . The steering mechanism  52  can pull the flexible wire  54  and cause the flat spring  56  to gradually deflect toward a direction to which the wire  54  is pulled. Details of the steering mechanism are described in U.S. Pat. No. 5,273,535, which is incorporated herein by reference. In one detailed embodiment, the deflection system  18  has an outer diameter of approximately 0.02 inches. It is to be appreciated that the diameter of the deflection system  18  can vary depending in whole or in part, on the intended application of the device. 
     Referring to  FIGS. 5A-5E , in another embodiment, the deflectable interstitial ablation device  10  further includes a driver  75  located in the handle  32  and coupled to the electrode  14  for kinetically deploying the electrode  14 . In this embodiment, the electrode  14  can be a needle electrode having a sharpened tip. The driver  75  exerts a force sufficient to deploy the electrode  14  from inside the elongated housing  12  to a position beyond the distal end of the elongated housing  12  in a single motion. In one embodiment, the force of deployment can range from about ¼ lb to about 1 lb. A force in this range is sufficient to cause the electrode  14  to penetrate the urethral wall in a single motion. Kinetic deployment which permits sudden and high speed deployment facilitates electrode penetration through the urethral wall, reducing patient discomfort and improving the accuracy and control of needle deployment. In the present embodiment, such kinetic deployment is achieved by employing a driver  75  comprising a spring-operated actuating mechanism. 
     Referring to  FIG. 5A , the handle  32 ′ includes slots  60  and  61  having levers  62  and  63 , respectively, and a recess  64  having an actuator  66  on an outer surface of the handle  32 ′. Referring to  FIGS. 5B to 5E , contained within the housing  32 ′ are slide members  68  and  69 . The slide member  68  is connected to the insulation sheath  40 , and the slide member  69  is connected to the electrode  14 . The lever  62  is connected to the slide member  68  and the lever  63  is connected to the slide member  69 . Reduced proximal sections  70  and  71  of the slide members  68  and  69  are received within spring coils  72  and  73 , respectively. The actuator  66  is operatively coupled to the slide member  69 . In this embodiment, the electrode  14  and the insulation sheath  40  are sequentially propelled. 
     Referring to  FIG. 5C , prior to inserting the elongated sheath  12  inside the body, the device  10  is loaded by pulling the levers  62  and  63  in the proximal direction. As the lever  62  is pulled in the proximal direction, a projection  74  on the slide member  68  slides over and catches the distal surface of a catch or stop  76 , and as the lever  63  is pulled, a projection  78  of the slide member  69  catches on a stop  80 . Once the elongated sheath  12  is properly placed inside the body and the deflectable segment  22  is deflected by a desired angle, the needle electrode  14  and the insulation sheath  40  are deployed by pulling the actuator  66  proximally and then down. 
     Referring to  FIG. 5D , as the actuator  66  is pushed down, the stop  76  moves allowing the slide member  69  to move distally until the projection  78  is restrained by a stop  82 . The needle electrode  14  is propelled forward as the sliding member  69  is moved by the force from the coiled spring  73 . Referring to  FIG. 5E , as the slide member  69  moves forward, and just before the end of its distal movement as the projection  78  reaches the stop  82 , a trigger member  86  on the slide member  69  contacts a release member  88 . Movement of the release member  88  causes the projection  74  to disengage from the stop  76 , such that the slide member  68  is propelled forward by the force of the coiled spring  73 . As the slide member  68  propels forward, the insulation sheath  40  propels beyond the distal end of the elongated housing  12  covering a pre-determined portion of the needle electrode  14 . 
     Referring to  FIG. 5D , in one embodiment, only the needle electrode  14  is propelled with a spring operated actuating mechanism, while the insulation sheath  40  is glided over the needle electrode  14 . Once the needle electrode  14  has penetrated the urethral wall, gliding the insulation sheath  40  over the needle electrode  14  can be easily achieved without causing much discomfort to the patient. 
     In one embodiment, depth of needle electrode  14  penetration is controllable, such that different locations within the prostate can be reached by the needle electrode  14 . In one detailed embodiment, the steering mechanism  52  described above can provide depth control. For deeper penetration, the electrode  14  tip can be deflected closer to 90 degrees, whereas for shallow penetration, the needle electrode  14  tip can be deflected by a smaller angle, such as, for example, 45 degrees. In another detailed embodiment, depth of electrode  14  penetration is adjustable using a slide member on the handle  32 , which controls movement of the needle electrode  14  relative to the elongated housing  12 . In this embodiment, maximum penetration depth may be fixed by placing a stop inside the handle  32 . 
     Referring to  FIG. 6 , in another embodiment, the electrode  14  can be kinetically deployed using a foot pedal. As shown, the interstitial ablation system  89  includes a foot pedal  90 , a control and power source module  92 , an actuator, a light source  98 , the deflectable interstitial ablation device  10 , and a return electrode  91 . The light source  98  supplies light to the illumination region  44  of the imaging device  16 , described above in  FIGS. 3 and 4 . As shown in this embodiment, the return electrode  91  is placed on the patient  110 . The foot pedal  90  is coupled to the control and power source module via a cable  94 , and the control and power source module  92  is coupled to the actuator  96  via a cable  99 . In operation, a physician performing an ablation procedure properly places the ablation device  10  inside the patient&#39;s body, then steps on the foot pedal  90  to deploy electrode  14 , leaving his or her hands free to perform other functions. Additional features such as application of fluid to a treatment site, application of energy to the electrode  14 , and the triggering temperature measurement means at the distal end of the electrode  14  may also be activated using the pedal  90 . In one embodiment, the interstitial ablation system  89  can include several foot pedal actuators for performing each of these functions. In another embodiment, the interstitial ablation system  89  can include only one foot pedal used to activate multiple functions. In this embodiment, the control module  92  may be programmed to control the order of the performance of each function. 
     Referring to  FIG. 7 , shown is the actuator  96  which controls electrode deployment. In the present embodiment, the actuator  96  can comprise a solenoid  100 . As shown, the solenoid  100  is coupled to the control and power module  92  at a proximal end via a cable  105 , and coupled to the proximal end of the electrode  14  at a distal end via a luer fitting  104 . The actuator  100  is held within an actuator housing  102 , which is coupled to the luer fitting  104 . The luer fitting  104  is sized and shaped to attach to the proximal end of the elongated housing  12  of the deflectable interstitial ablation device  10 . Alternatively, the luer fitting  104  may be sized and shaped to attach to a working channel of a flexible cystoscope for those applications in which cystoscopes are used. When the foot pedal  90  is depressed, current from the power source  92  is applied to the solenoid  100 , which forces the electrode  14  to deploy beyond the distal end of the elongated housing  12 . Other types of actuators such as a rotary motors and linear motors, as well as other electromechanical devices can be used to perform these functions as well. It is to be appreciated that, a number of foot pedals and actuators for activating a mechanical event can be interchangeably used to actuate the electrode  14 , or provide fluid delivery and temperature sensing at the treatment site. 
     The deflectable interstitial ablation device  10  of the invention provides many other features typically performed in ablation procedures. As briefly described above, the deflectable interstitial ablation device  10  can be coupled to a fluid source to permits delivery of fluid to the housing  12  or to an internal bore (not shown) formed in the electrode  14  such that fluid is dispensed near the treatment site for providing cooling or for enhancing ablation. In such an embodiment, the fluid, can be for example, an electrolytic fluid which increases the ablation area, or a fluid that provides therapeutic effects. In another embodiment, the elongated housing  12  can include a separate passageway suitable for fluid delivery. In both embodiments, fluid can be introduced through the luer port  36  ( FIG. 1A ). In another embodiment, the solenoid can be coupled to a syringe for introducing fluid inside the elongated housing  12 . Application of current to the solenoid in this case would cause the syringe to discharge the fluid held within a fluid source into the elongated housing  12 . 
     In another embodiment, the deflectable interstitial ablation device  10  can include a temperature sensing system for measuring tissue temperature during the ablation procedure. In one detailed embodiment, the temperature sensing system can include a thermocouple disposed near the distal end of the electrode  14 , such as by being fixed at the distal end of the insulation sheath  40  that is fixed to the electrode  14 . In still another embodiment, the device  10  can include an impedance monitoring system in communication with the proximal end of the electrode  14 . The impedance monitoring system can measure impedance near the distal end of the electrode  14 . The interstitial ablation device can further employ a feedback system that uses the temperature and or the impedance data to control the delivery of RF energy to the electrode  14 . The control module  92  can, for example, include means for automatically adjusting the magnitude and duration of the ablation energy delivered to the electrode in response to one or both of these parameters. The interstitial ablation system can also include a safety feature which cuts off the delivery of energy when the temperature or the impedance value exceeds a threshold value. 
     The deflectable interstitial ablation device  10  of the present invention does not require the use of an endoscope and therefore can be entirely disposable. The disposable device can attach to reusable eye piece and other equipment such as a light source, and a control and power source module. In an alternative embodiment, the imaging system  16  can be removed from the device  10  for subsequent reuse. 
     As shown and described, the present invention features an improved transurethral interstitial ablation apparatus and method for performing transurethral ablation. While the invention has been particularly shown and described with reference to specific preferred embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.