Abstract:
There is provided a device and a method for irradiating vascular tissues. The device generally includes a transfer device having a first chamber and a second chamber and a piston slidably disposed between the chambers. A ballon catheter is provided for positioning witin the vascular system and is connected to the transfer device such that an inflation lumen of the balloon catheter is in fluid communication with the second chamber. A proximal end of the balloon catheter is affixed to a mounting block which is configured to receive the transfer device. An inflation device is provided to force fluid into the first chamber such that the piston is driven to force a radioactive fluid contained in the second chamber into the balloon.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application Ser. No. 60/071,342 filed on Jan. 14, 1998, entitled “Device and Method for Radiation Therapy, ” the entire contents of which are incorporated herein by reference and also Ser. No. 60/077,294 filed Mar. 6, 1998, and a continuation of Ser. No. 09/073,932 filed May 6, 1998 now U.S. Pat. No. 5,961,439. 
    
    
     TECHNICAL FIELD 
     The technical field relates generally to the use of radiation therapy after an angioplasty procedure, to minimize the occurrence of restenosis and, more particularly, to a device and method for delivering a radio isotope to a stenotic region, e.g., in liquid or gaseous form, to inhibit restenosis. 
     DESCRIPTION OF THE RELATED ART 
     A common treatment for blockage or stenosis of the arteries is a procedure known as percutaneous transluminal angioplasty (PTA) and, when utilized within the coronary artery, is known as percutaneous transluminal coronary angioplasty (PTCA). During this procedure, the location of a stenotic constriction or blockage within the coronary artery is identified and a guide wire is advanced through the vascular system to a point distal to or beyond the blockage. Subsequently, an angioplasty catheter in one form having an inflatable angioplasty dilatation balloon at a distal end thereof or in a second form an atherectomy catheter, or a stent delivery catheter, is advanced along the guide wire until the balloon is located at the point of constriction. The balloon is then repeatedly inflated and deflated to open the constriction by compressing the plaque against the vessel walls. In this manner, a constriction within the vascular system may be opened to allow increased blood flow. Similarly, the plaque can be removed by atherectomy, or the plaque can be scaffolded by placing a stent. 
     The vascular tissue may respond to the trauma by proliferative growth of cells responsible for restenosis, e.g., smooth muscle tissue cells, deposition of extracellular matrix material. Upon increased growth of such cells, the formerly constricted area may become reconstricted or narrowed down, which is commonly referred to as “restenosis.” This can occur any time from within a few weeks to several years following the original angioplasty procedure, thus, often necessitating repeated angioplasty procedures to reopen the constriction. Other causes of restenosis have been reported including, but not limited to, elastic recoil of the vessel wall and focal shrinkage of the vessel wall, commonly referred to as “negative remodelling.” 
     It has been found that by exposing the vascular tissues to radiation subsequent to the balloon angioplasty procedure, the proliferative growth of the smooth muscle cells and/or vessel shrinkage responsible for restenosis is inhibited. However, difficulty in providing uniform radiation to the surrounding tissue may arise. Often, after expansion of a constricted area by a balloon angioplasty procedure, the resulting relatively unconstricted area has a generally asymmetrical cross-section. The asymmetrical cross-section may pose problems for those devices which are configured to position a radioactive source substantially at the center of the vascular structure. Thus, it would be desirable to have a device and method for delivering a radioactive dose in a substantially uniform manner to the site of a vascular constriction post-angioplasty. 
     SUMMARY 
     There is provided a device and a method of irradiating vascular tissues which have been subjected to a balloon angioplasty procedure. The device generally includes a balloon catheter having an expandable balloon which can be positioned over a guide wire within the vascular tissue, a transfer device for transferring radioactive material, e.g., fluid, from the transfer device to the balloon and an inflation device for forcing the radioactive fluid out of the transfer device and into the balloon. The balloon catheter includes an inflation lumen extending from an interior of the balloon through the catheter to a proximal portion of the catheter. The balloon catheter also includes a guide wire lumen. The guide wire lumen may extend the entire length of the catheter from its distal to its proximal end or may extend from the distal end to a point just proximal of the balloon. The transfer device includes first and second chambers which are separated by a movable piston or membrane. The first chamber is configured to receive a fluid to move the piston within the transfer device while the second chamber is configured to receive, retain and shield or isolate the radioactive fluid prior to injection into the balloon catheter. The inflation device provides a fluid, preferably saline, to the first chamber to move the piston by creating a positive or negative gauge pressure in the first chamber. Preferably, The inflation device may include a pressure gauge as well as an overpressure relief valve. As used herein, the term “radioactive fluid” is intended to encompass liquids, gases, solids and/or combinations thereof. 
     A mounting block may also be provided to connect the second chamber of the transfer device to the inflation lumen of the balloon catheter. Specifically, the mounting block retains the proximal end of the balloon catheter with the inflation lumen in fluid communication with the second isotope containing chamber in the mounting block. The mounting block includes an injection port having a self-sealing septum which is in fluid communication with the second isotope containing chamber. 
     In one embodiment, the mounting block is interlocked to the proximal end of the balloon catheter by use of a bayonet style fitting. It is further contemplated that other interlocking optical, mechanical and/or electrical features and/or structures may be provided, and may include recognition features to ensure that only a catheter suitable for radiation therapy is coupled to the transfer device. Moreover, such recognition features and/or structures may provide information to an associated system to identify to the system characteristics of the catheter, e.g., catheter length and size, capacity, etc., which may be used in controlling the transfer device to assure transfer of an appropriate quantity of isotope containing material to the balloon catheter. The system may calculate, display and/or control treatment time and dose delivery and may monitor system integrity, e.g., using fluid pressure sensors in the catheter, second chamber or mounting block. 
     The transfer device includes an injection needle which extends from the second chamber and is provided to pierce self-sealing septum in order to draw and inject the radioactive fluid through the self-sealing septum. Preferably, the injection needle is provided with an elastomeric boot surrounding the needle which acts as a seal against the septum. The transfer device may also be provided with a needle shield extending from the second chamber and surrounding the injection needle. The transfer device may be connected to the mounting block by suitable means such as a bayonet style mounting fixture. 
     There may also be provided a separate source or container for the radioactive fluid which also has a self-sealing septum. The source will also include a bayonet style mounting fixture for affixing to the transfer device in order to load the transfer device with the radioactive fluid. Additionally, an aspiration syringe may be provided having a needle to pierce the septum of the mounting block in order to draw air out of the balloon and inflation lumen of the balloon catheter to create a vacuum therein. 
     There is also disclosed a method for irradiating vascular tissues which includes providing a transfer device having first and second chambers and a piston movably disposed within the chambers, an inflation device for moving the piston within the first and second chambers and a balloon catheter for carrying a radioactive fluid from the second chamber of the transfer device to a balloon on a distal end of the balloon catheter. The method includes loading radioactive fluid into the second chamber of the transfer device, positioning the balloon at a stenotic region within the vascular system, attaching the transfer device to a proximal portion of the balloon and attaching an inflation device to the transfer device such that the inflation device can force fluid into the first chamber of the transfer device. The method further includes forcing fluid from the inflation device into the transfer device to force the piston to force the radioactive fluid out of the second chamber of the transfer device and into the balloon to substantially fill the balloon thereby irradiating surrounding tissues with the radioactive fluid. The method may further include the step of removing air from the balloon catheter prior to the step of inserting the catheter in the vascular system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various embodiments are described herein with reference to the drawings wherein: 
     FIG. 1 is a perspective view of a system for providing a fluid radiation therapy treatment; 
     FIG. 1A is a perspective view of a radiation fluid source container; 
     FIG. 1B is an enlarged perspective view of the distal end of a treatment catheter associated with the system of FIG. 1; 
     FIG. 1C is a perspective view, partially shown in section, of a transfer device associated with the system of FIG. 1; 
     FIG. 1D is an enlarged view of a booted needle of the transfer device of FIG. 1C; 
     FIG. 2 is a perspective view of the transfer device and radiation fluid source container; 
     FIG. 2A is a side elevational view, partially shown in section, illustrating the assembled inflation device, transfer device and radiation fluid source container of the system of FIG. 1; 
     FIG. 2B is an enlarged side view, shown in section, illustrating engagement of the transfer device with the fluid source container; 
     FIG. 2C is an enlarged view illustrating engagement of the inflation device with the transfer device as well as a pressure relief valve associated with the inflation device; 
     FIG. 3 is a side view, partially shown in section, of the balloon catheter, mounting block and aspiration syringe of FIG. 1; 
     FIG. 3A is an enlarged sectional view of the distal end of the balloon catheter of FIG. 3; 
     FIG. 3B is an enlarged view of the distal end of the mounting block associated with the catheter of FIG. 3; 
     FIG. 3C is an enlarged view of the proximal end of the mounting block associated with the catheter of FIG. 3; 
     FIG. 4 is a side view, shown in section, of the distal end of the balloon catheter of FIG. 1, inserted into a vascular system over a guide wire and positioned at a location of an expanded stenotic region; 
     FIG. 5 is a perspective view of the transfer device being moved into engagement with the mounting block; 
     FIG. 6 is an enlarged perspective view of the device for radiation therapy of FIG. 1 with the balloon catheter inserted into a patient; 
     FIG. 7 is a side elevational view, partially shown in section, of the assembled inflation device, transfer device and mounting block; 
     FIG. 7A is an enlarged view illustrating injection of radioactive fluid from the transfer device-to the mounting block; 
     FIG. 8 is a side view, shown in section, illustrating expansion of the balloon at the distal end of the catheter by the radioactive fluid and into contact with the surrounding tissue; 
     FIG. 9 is an enlarged view of the pressure relief valve associated with the inflation device in operation; 
     FIG. 10 is an elevational cross-section view of a rapid exchange style catheter for use with the system of FIG. 1; and 
     FIG. 10A is an enlarged view of the distal end of the balloon catheter of FIG.  10 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is disclosed a preferred embodiment of a system  10  for radiation therapy. System  10  is particularly configured to deliver a source of radioactive fluid to a treatment balloon which has been positioned within a vascular system at the site of a previous angioplasty procedure. System  10  generally includes a device for radiation therapy  12 , a container such as a vial or other source of radioactive fluid  14 , and an aspiration syringe  16 . Device for radiation therapy  12  includes a balloon catheter  18  which extends from a mounting block  20 . A transfer device  22  is removably engagable with mounting block  20 . There is also provided an inflation device  24  which is removably engagable with transfer device  22 . Inflation device  24  is provided to force radioactive fluid out of transfer device  22  and through mounting block  20  into balloon catheter  18 . Preferably, a pressure relief valve  26  may be positioned between inflation device  24  and transfer device  22  to prevent over expansion of balloon catheter  18 . 
     Inflation device  24  is of known type utilized in balloon angioplasty procedures and may include a pressure gage  28  to monitor the exact pressures. This is particularly preferable in the present radiation treatment procedure where it is not necessary to reach high pressures within the balloon catheter, but rather to merely expand the balloon to the point that it contacts surrounding tissue and plaque. 
     In order to connect transfer device  22  to inflation device  24 , transfer device  22  is provided with a flange  30  at a proximal end  32  thereof. Flange  30  is engagable with a threaded coupling  34  associated with inflation device  24 . Similarly, to connect transfer device  22  to mounting block  20 , transfer device  22  is provided with the male half of a “bayonet-type” or “luer” fitting  36  at a distal end  38  thereof. The male half of the bayonet or luer fitting  36  is engagable with a female half of a bayonet or luer fitting  40  positioned on mounting block  20 . As used herein, the term proximal refers to that portion of the device closer to the user while the term distal refers to that part of the device further from the user. In order to prevent leakage of radioactive fluid during transfer from transfer device  22 , mounting block  20  is preferably provided with a self-sealing elastic septum  42  which is in fluid communication with balloon catheter  18 . 
     To facilitate loading of the radioactive fluid into transfer device  22 ,  20  source  14  also includes a female half of a bayonet or luer fitting  44  which is engagable with the male half of the bayonet or luer fitting  36  on transfer device  22 . Additionally, source  14  also includes a self-sealing elastic septum  46  to prevent inadvertent leakage of radioactive fluid. 
     Referring now to FIG. 1A, it can be seen that the bayonet style fitting  44  on source  14  is of known variety including a plurality of L-shaped slots  48  formed within a circumferential flange  50 . It is contemplated that other locking structures such as, e.g., luer locks, may be substituted for the bayonet-style fitting  44 . Self-sealing septum  46  projects a predetermined distance above flange  50 . Referring for the moment to FIG. 1B, it can be seen that a distal end  52  of balloon catheter  18  generally includes an elastomeric sleeve or balloon  54  mounted on a catheter shaft  56 . Balloon catheter  18  may be configured as either an over the wire (OTW) type catheter or a rapid exchange “RE” catheter. When an OTW style catheter is used with device  12  for radiation therapy, a guide wire lumen  58  extends generally throughout the length thereof for receipt of a guide wire  126  as described hereinbelow. 
     Referring now to FIG. 1C, it can be seen that transfer device  22  includes an enlarged saline housing  60  and a radioactive fluid housing  62  extending from extended large saline housing  60 . A needle shield  64  extends distally from radioactive fluid housing  62  and is provided with a plurality of projections  66  which form the male half of the bayonet fitting  36  on distal end  38  of transfer device  22 . As noted above, flange  30  is provided at proximal end  32  of transfer device  22  for engagement with inflation device  24 . In order to transfer radioactive fluid between transfer device  22  and self-sealing septum  42  of mounting block  20  or self-sealing septum  46  of source  14 , transfer device  22  is provided with a booted needle  68  provided within needle shield  64 . Booted needle  68  extends distally from radioactive fluid housing  62 . Referring for the moment to FIG. 1D, booted needle  68  generally includes an inner needle  70  having a sharply pointed tip  72  which is configured to pierce elastomeric self-sealing septums  42  and  46 . Needle  70  may be formed of any suitable material, for example, stainless steel. Booted needle  68  further includes an elastomeric sleeve or boot  74  which surrounds needle  70 . Boot  74  is provided to further shield pointed tip  72  of needle  70  and to serve as a further seal against a septum to prevent inadvertent release of radioactive fluid when fluid is being drawn into or forced out of needle  70  or when the system is disconnected. 
     Referring to FIG. 2, in order to load the radioactive fluid from source  14  into transfer device  22 , transfer device  22  is positioned such that male bayonet  36  at the distal end  38  thereof is brought into engagement with the female bayonet fitting  44  on source  14 . As transfer device  22  is brought into engagement with source  14 , booted needle  70  (FIG. 1D) is brought into engagement with and pierces self-sealing septum  46 . 
     Referring now to FIG. 2B, the construction of transfer device  22  will now be described. Enlarged saline housing  60  defines an internal saline chamber  76  for receipt of saline fluid S from inflation device  24 . Similarly, radioactive fluid housing  62  defines an interior isotope chamber  78  for receipt of the radioactive fluid or isotope I from source  14 . The isotope I is stored in isotope chamber  78  until it is forced out into balloon catheter  18  during use. In order to move the isotope fluid I out of or into isotope chamber  78 , there is provided a piston  80  movably positioned within chambers  76  and  78 . Piston  80  includes an enlarged piston head  82  positioned within saline chamber  76  and a smaller piston head  84  which is movably positioned within isotope chamber  78 . A piston shaft  86  connects piston heads  82  and  84 . It should be noted that the particular dimensions of piston head  82  and piston head  84  may be varied in order to produce desired magnification or reduction of relative fluid pressure between saline fluids in saline chamber  76  and isotope fluid I in isotope chamber  78 . Also it should be noted that if saline chamber  76  and isotone chamber  78  are of the same diameter then piston heads  82  and  84  can be replaced with a single piston. 
     Referring further to FIG. 2B, it can be seen that source  14  defines an internal isotope chamber  78  which contains a quantity of radio active isotope I. Radio active isotope I is a beta or gamma emitting radio isotope and is preferably 50-100 millicuries of RE  188  which may be easily generated at hospitals and is readily available. A preferred radio active isotope is thus provided in liquid form and generally has a relatively short half life. However, safety precautions need be maintained to prevent contamination of the interventional cardiology laboratory. As shown, when needle shield  64  is engaged with source  14 , needle  70  is forced through self-sealing septums of boot  74  and septum  46 . Self-sealing septum  46  provides a fluid tight seal about needle  70 . Additionally, elastomeric boot  74  is compressed against elastomeric septum  46  and provides a further seal therebetween. Referring for the moment to FIG. 2B, in order to fill transfer device  22  with isotope I, inflation device  24  is engaged with transfer device  22  in a manner described hereinabove and is further illustrated in FIG.  2 C. Saline chamber  76  is initially completely filled with saline fluid S. Thereafter, transfer device is engaged with source  14  in a manner described hereinabove such that needle  70  punctures the elastomeric septum  46  and is in contact with isotope  1 . At this point, negative pressure is provided by inflation device  24  to draw saline out of saline chamber  76 . Upon drawing saline fluid S out of saline chamber  76 , piston  80  is drawn proximally within transfer device  22  thereby forming a vacuum in isotope chamber  78 . The vacuum created in isotope chamber  78  draws the isotope I from chamber  82  and source  14  into chamber  78  in transfer device  22 . Once a predetermined quantity of isotope I has been received within chamber  78  of transfer device  22 , transfer device  22  and source  14  may be rotated to disengage their bayonet fittings. Pulling source  14  away from transfer device  22  draws needle  70  through self-sealing septum  46  which thereafter seals about itself preventing any further release of radioactive isotope I from source  14 . In this manner, transfer device  22  is loaded with a predetermined amount of isotope I. Preferably, this procedure takes place inside a radiation laboratory. Once transfer device has been loaded with isotope I, it may be retained within a shielded container or safe for transport to the interventional cardiology laboratory prior to use. 
     Referring for the moment to FIG. 2C, and as noted above, inflation device  24  is provided with a pressure relief valve  26 . Pressure relief valve  26  is of known variety and generally includes a seal  88  having a shaft  90  extending therefrom. A spring  92  is provided about shaft  90  and biases seal  88  into engagement with fluid opening  95  in inflation device  24 . Spring  92  is of a predetermined resistance such that when the fluid pressure within inflation device  24  exceeds a predetermined amount, seal  88  allows fluid to flow from inflation device  24  and out through a drain tube  94  thereby relieving any excess pressure within device for radiation therapy  12 . 
     Referring now to FIG. 3, the details of the mounting block  20  and balloon catheter  18  will now be described. As shown, balloon catheter  18  extends distally from mounting block  20 . 
     Referring to FIG. 3A, the illustrated balloon catheter  18  is of the over the wire variety including a catheter shaft  56  defining a guide wire lumen  58  extending completely therethrough. As noted above, a balloon  54  is affixed to a distal end  52  of balloon catheter  18  and is mounted on catheter shaft  56 . It should be noted that balloon  54  may be formed from an elastic or inelastic material. The balloon  54  may act solely as a means to deliver the radiation therapy or it may provide a dilatation function within a vascular system. In either case, it as a chamber for radioactive fluid to provide uniform irradiation of the surrounding vascular tissue. Balloon catheter  18  includes a balloon inflation lumen  96  formed within catheter shaft  56 . Preferably, inflation lumen  96  is concentric with guide wire lumen  58 . A plurality of inflation ports  98  provide fluid communication between the inflation lumen  96  and an interior surface of balloon  54 . Inflation lumen  96  extends from inflation ports  98  approximately to a mid-portion  100  (FIG. 3) of mounting block  20 . 
     As shown in FIG. 3B, catheter  18  is preferably secured to mounting block  20  by means of a threaded cap  102  at mid portion  100  which engages threads  104  formed in a distal end  106  of mounting block  20 . The particular balloon catheter  18  illustrated is of a variety specifically configured to engage mounting block  20 . However, it is also contemplated that standard configuration balloon catheters may be utilized with the present system requiring only minor modifications, as will be readily apparent to those skilled in the art, to the utilized catheter and mounting block  20 . A circular seal or “O” ring  108  is provided between threaded cap  102  and mounting block  20  to provide a fluid tight seal between catheter  18  and mounting block  20 . As shown, the inflation lumen  96  continues through mounting block  20  into an interior chamber  110  formed in mounting block  20 . 
     Referring to FIG. 3, as shown, chamber  110  is in fluid communication with an injection port  112 . Self sealing septum  42  is preferably mounted onto injection port  112 . Thus, any air to be aspirated out of catheter  18  or any isotope to be injected into catheter  18  will be drawn through inflation lumen  96 , chamber  110  and injection port  112  by means of a needle penetrating self sealing septum  42 . 
     Referring now to FIG. 3C, a proximal end  114  of catheter  18  extends out a proximal end  116  of mounting block  20 . Thus, mounting block  20  additionally serves as a “handle” for manipulation of balloon catheter  18  along a guide wire. As shown, a plurality of “O” rings  118  are provided between proximal end  114  of catheter shaft  56  and an inner surface of proximal end  116  of mounting block  20  to provide a fluid tight seal. 
     Referring back to FIG. 3, aspiration syringe  16  is of known variety and generally includes a syringe body  120  having a plunger  122  slidably mounted therein. A syringe needle  124  extends from syringe body  120 . In utilizing balloon catheter  18  to deliver an isotope fluid to a selected site, it is necessary to avoid problems with irregular dosimetry by providing a vacuum within balloon catheter  18 . Thus, in order to prepare balloon catheter  18  for use, aspiration syringe  16  is advanced toward mounting block  20  such that syringe needle  124  pierces self sealing septum  42  and enters chamber  110  of mounting block  20 . Plunger  122  is drawn to provide approximately a 60 cc vacuum on catheter  18  for about 10 seconds. Upon removal of aspiration syringe  16  from mounting block  20 , self sealing septum  42  seals about itself thereby retaining the vacuum within the assembled balloon catheter  18  and mounting block  20 . 
     Referring to FIG. 4, after an angioplasty procedure has been performed, the angioplasty dilatation balloon is removed from a patient leaving a guide wire  126  in place and extending down to the now expanded stenotic region of a vessel V having compressed plaque P. A proximal end of guide wire  126  may be inserted into guide wire lumen  58  at distal end  52  of balloon catheter  18  and balloon catheter  18  maneuvered to the constricted site along guide wire  126 . Once balloon catheter  18  has been positioned within a patient (FIG.  6 .), fluid transfer device  22  containing isotope I may be engaged with mounting block  20  in a manner described hereinabove (FIG.  5 ). 
     Referring to FIGS. 7 and 7A, upon engagement of fluid transfer device  22  with mounting block  20 , booted needle  68  of fluid transfer device  22  engages self sealing septum  42  of mounting block  20 . As shown, needle  70  pierces self sealing septum  42  while elastomeric boot  72  expands to provide an additional seal against self sealing septum  42 . Inflation device  24  may then be affixed to transfer device  22  in a manner described hereinabove and activated to a known predetermined pressure to drive saline into saline chamber  76  thereby forcing piston  80  to compress isotope I contained in isotope chamber  78  and force isotope I through needle  70  into chamber  110 . Isotope I forced through chamber  110  is unimpeded by air due to the vacuum created within the inflation chamber  110  and isotope I is forced into inflation lumen  96 . 
     Referring now to FIG. 8, as isotope I is forced through inflation lumen  96 , it passes through inflation ports  98  into an interior of balloon  54  thereby expanding balloon  54  into contact with the compressed plaque P and any other exposed vascular tissue V within the vascular system at the operative site. As noted above, balloon  54  may be formed as an elastic or inelastic balloon. In either event, pressures are maintained at sufficiently low levels such that balloon  54  does not perform any further dilatation within the previously expanded region of the vascular system. The balloon  54  is maintained in an inflated condition with isotope I for an appropriate treatment time. Depending on the treatment time, it may be desirable to undertake repeated inflations and deflations of balloon  54  with isotope I to allow a sufficient level of perfusion to occur in between balloon inflations. Alternatively, it is also contemplated that a balloon configuration utilized with the present system may have varying provisions for perfusion of blood flow past balloon  54 . This may be accomplished by separate perfusion chambers extending through balloon  54  or altering the surface of balloon  54  slightly to provide irregularities or minimal perfusion channels extending along the length thereof to the extent that it would not compromise uniform dosimetry of the surrounding tissue. 
     Referring now to FIG. 9, as noted above, pressure in inflation device  24  is maintained at a predetermined level such that the pressure of the isotope fluid within balloon  54  does not exceed another known and predetermined level. However, there is provided pressure relief valve  26  which, when the pressure of saline exceeds a predetermined level, will allow seal  88  to compress spring  92  thereby allowing saline S to pass through pressure relief valve  26  and be siphoned off through drain tube  94 . In this manner, over pressurization of balloon  54  may be avoided. 
     When the procedure is completed, device for radiation therapy  12  may be removed to a shielded container or safe for safe deactivation, disassembly and disposal. 
     Referring now to FIGS. 10 and 10A, an alternative balloon catheter  130  is provided for use with the above-described system. Balloon catheter  130  is of “rapid exchange” style. Balloon catheter  130  generally includes a catheter shaft  132  having a balloon  134  mounted on a distal end  136  of catheter shaft  132 . A guide wire lumen  138  extends from a distal port  140  formed in a distalmost end  142  of catheter shaft  134  and extends proximally beyond the length of the balloon to a proximal port  144  formed proximally of balloon  134 . It is also contemplated that the entire guide wire lumen including distal and proximal guide wire ports be located entirely distal of balloon  134 . 
     In order to form the relatively short guide wire lumen  138  extending along the length of balloon  134 , a plug  146  is provided within guide wire lumen  138 . Plug  146  defines a second lumen  148  which extends from plug  146  proximally to a proximalmost end  150  of catheter shaft  132 . By continuing a lumen from plug  146  to the proximalmost end  152  of catheter shaft  132 , lumen  148  is configured to receive a separate stiffening mandrel which may be inserted into lumen  148  to facilitate insertion of balloon catheter  18  along guide wire  126  as it is maneuvered through a patients vascular system. 
     Balloon catheter  130  is generally affixed to mounting block  20  in the same manner as that of balloon catheter  18  described hereinabove. Specifically, a threaded cap  152  is configured to engage threads  104  formed in a distal end  106  of mounting block  20 . 
     It will be understood that various modifications may be made to the disclosed embodiments. For example, various balloon configurations to provide uniform irradiation of tissue may be provided. Alternatively, multiple balloons may be used. Further, mounting block  20  and transfer device  22  may be modified to allow use thereof with standard known balloon angioplasty catheters thereby allowing the balloon angioplasty catheter to remain in place as air is aspirated out of the catheter and isotope is subsequently injected into the balloon thereby reexpanding the balloon into contact with surrounding tissue to provide uniform irradiation of the tissue. Additionally, alternative isotopes may be utilized depending upon the particular dosage required and half life of the isotope. Thus, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.