BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a device which may be inserted into blood vessels, body cavities, etc. for radiating selectable areas in the vessels or cavities, for therapeutic or other purposes. More particularly, the present invention relates to an expandable catheter for placing in direct contact with a selected area in a blood vessel, body cavity or the like, which allows both radial and longitudinal control of radiation dosage. 
     2. State of the Art 
     Catheters have long been used for threading into blood vessels or other body orifices for such purposes as delivering emboli to target locations, delivering therapeutic drugs to such locations, sensing conditions in the vessel or cavity by sensors inserted into the catheter, etc. Typically, a guide wire is first threaded into the vessel or cavity until the distal end of the guide wire reaches a target location, and then the catheter which is placed about the guide wire is moved to the target location as guided by the guide wire. Then, depending upon the treatment, the guide wire may be withdrawn or left in place and the treatment commenced, such as by injecting drugs through the catheter to the target location. 
     There are some diseases, such as restenosis, which become sited in blood vessels or body cavities which cannot be effectively treated by drugs, but instead respond to appropriate doses of radiation from a radioactive source. Effective treatment of such diseases requires exposure of diseased tissues to levels of radiation within a therapeutic range. This presents a problem if the diseased areas are not readily accessible but can only be reached by a pathway which extends past healthy tissue to the diseased area. It would thus be desirable to have an apparatus for selectively exposing areas of blood vessels, body cavities and the like to radiation from a radioactive source which may be threaded into a patient&#39;s anatomy such as by means of a catheter. 
     However, it is desirable to provide the radiation dose to the diseased area without exposing surrounding healthy tissue to such radiation. Thus, it is desirable to place the radiation source in as close a proximity to the diseased area as possible in order to produce a desired benefit, while also keeping the radiation source as far away from healthy tissue as possible. It would thus be desirable to provide an apparatus and method for selectively exposing areas of blood vessels, body cavities and the like to radiation in which healthy tissue in such vessels and cavities are protected from such radiation during insertion of the device and treatment therewith. It would thus also be desirable to have an apparatus for selectively exposing areas of blood vessels, body cavities and the like to radiation from a radioactive source wherein the radiation dose may be both radially and longitudinally controlled relative to the patient&#39;s anatomy. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a method and apparatus for selectively exposing areas of blood vessels, body cavities and the like to radiation from a radioactive source inside. 
     It is another object of the invention to provide such an apparatus which allows sufficient flow of bodily fluids around or through the apparatus during insertion and treatment. 
     It is still another object of the invention to provide an apparatus for selectively exposing areas of blood vessels, body cavities and the like to radiation from a radioactive source wherein the radiation dose may be both radially and longitudinally controlled relative to the patient&#39;s anatomy. 
     It is also an object of the invention to provide such an apparatus and method in which healthy tissue in such vessels and cavities are protected from radiation during treatment. 
     It is yet another object of the invention to provide such an apparatus and method which allows for the safe handling and insertion of the radiation source into blood vessels, body cavities and the like. 
     It is a further object of the invention, in accordance with one aspect thereof, to provide such a method and apparatus which allows for selectively placing a radiation source in close proximity to a target area, but removed from adjacent areas. 
     The above and other objects of the invention are realized in a specific illustrative embodiment of apparatus for selectively irradiating blood vessels, body cavities and the like. Such apparatus includes a catheter having a distal end for threading into a blood vessel or body cavity, and having at least one lumen. Also included is a wire for threading into the lumen of the catheter, the wire having a proximal end and a distal end, and a radiation source disposed near the distal end for irradiating tissue adjacent to the radiation source. 
     In accordance with one aspect of the invention, the catheter includes a section which absorbs radiation from the radiation source so that when the radiation source is positioned within the section, radiation is substantially blocked or reduced from reaching adjacent tissue. 
     In accordance with another aspect of the invention, a portion of the catheter near the distal end is formed to spread apart when positioned in a blood vessel or cavity, and move into close proximity or contact with the vessel or cavity walls where a diseased area is located. Then, the radiation source on the wire may be moved in the catheter to a position adjacent the diseased area, for irradiating the diseased area. 
     In use, the wire would be threaded into the lumen of the catheter until the radiation source is positioned within the section which is absorbent of radiation, and then the catheter and wire would be threaded either directly into the blood vessel or cavity, or through another larger catheter to the target area in the vessel or cavity. All the time during the movement of the catheter to the target location, the radiation source would be maintained within the absorbent section of the catheter to reduce the chance of radiation damage to healthy tissue past which the radiation source is moved. 
     After the end portion of the catheter has moved to the target location, the wire is manipulated so that the radiation source is moved out of the absorbent section of the catheter into the portion of the catheter adjacent the diseased area to enable irradiating the diseased area. After completing the irradiation for the desired time, the radiation source may be moved back to within the absorbent section, or, more preferably, the wire is further retracted so that the radiation source becomes contained within another radiation absorbent section disposed proximally from the coiled distal end. The catheter and wire may then be withdrawn from the vessel or cavity. Alternatively, the entire catheter and wire may be drawn into a second, larger catheter, and withdrawn through or with the second catheter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and features of the present invention will be apparent to those skilled in the art, based on the following description, taken in combination with the accompanying drawings, wherein: 
     FIG. 1A shows a cross-sectional view of a blood vessel that is partially occluded by buildup on the inner surface thereof; 
     FIG. 1B shows a cross-sectional view of the blood vessel of FIG. 1A after balloon angioplasty, such that one side is substantially thicker than the other, and containing a prior art device for irradiating the inner surface thereof; 
     FIG. 2A shows a longitudinal cross-sectional view of a prior art radiation delivery device disposed within a blood vessel; 
     FIG. 2B shows a graph of the radiation dose provided by the radiation delivery device of FIG. 2A; 
     FIG. 3 shows a perspective, partially cut-away view of a radiation exposure device for vessels, body cavities and the like, made in accordance with the principles of the present invention; 
     FIG. 4 shows a cross-sectional view of a blood vessel containing a radiation exposure device for vessels, body cavities and the like, made in accordance with the principles of the present invention; 
     FIG. 5A shows a closeup cross-sectional view of a blood vessel containing the radiation exposure device of the present invention wherein the radiation source is located proximal to an exterior cut formed on the surface of the catheter; 
     FIG. 5B shows a closeup cross-sectional view of a blood vessel containing the radiation exposure device of the present invention wherein the radiation source is located proximal to an interior cut formed on the surface of the catheter; 
     FIG. 5C shows a closeup cross-sectional view of a blood vessel containing an embodiment the radiation exposure device of the present invention wherein cuts are formed only on the outside surface of the coil; and 
     FIG. 6 shows a variable speed power retracting motor and its control apparatus for selectively retracting the flexible wire and radiation source through the catheter. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made to the drawings in which the various elements of the present invention will be given numeral designations and in which the invention will be discussed so as to enable one skilled in the art to make and use the invention. It is to be understood that the following description is only exemplary of the principles of the present invention, and should not be viewed as narrowing the pending claims. 
     FIG. 1A shows a cross-sectional view of a blood vessel  10  that is partially occluded by buildup  12  on its inner surface  14 . Such buildup or blockages may be created by a variety causes, such as cholesterol, or excessive proliferation of smooth muscle cells on the inner wall  14  of the vessel  10 . It will be apparent that this condition results in a substantial reduction of the cross-sectional area of the vessel lumen  16  and hence of blood flow through this section, which in the case of coronary arteries, for example, will result in damage to the coronary muscle, and may precipitate a heart attack or other serious coronary event. To remedy vessel blockages of this sort, balloon angioplasty is frequently used to widen the vessel to a proper diameter. FIG. 1B shows a cross-sectional view of the blood vessel  10  of FIG. 1A after balloon angioplasty, where the increase in inner vessel diameter is apparent. 
     However, while widening the vessel as needed, balloon angioplasty does not actually remove the blockage. As a result, the vessel will frequently be left with an excessively thick wall  18  on one side or another. This wall thickening is shown by comparison of the normal wall  20  having thickness T 0 , with thickness T 1  of wall  18  as shown in FIG.  1 B. Moreover, angioplasty does not remedy the underlying cause of the blockage, and after the procedure the vessel wall may continue to increase inwardly, eventually producing another blockage. For example, a lesion on the side  14  of the blood vessel  10  may precipitate smooth muscle cell proliferation, which will produce buildup toward the center of the vessel again. 
     To solve this problem, it has been found that exposing the inner vessel wall in the location where undesirable proliferation of smooth muscle cells is taking place to doses of radiation is effective to stop such undesirable cell proliferation. Also shown in FIG. 1B is a prior art device placed approximately in the center of the vessel for irradiating the inner surface thereof. This prior art device comprises a rod  24  or other elongate member which is impregnated with radioactive material  26  near its distal end, and is extended into a blood vessel or body cavity, approximately in the center thereof as shown. Radiation, symbolized by arrows  28 , is emitted from the material  26  to irradiate the diseased portion  18  of the vessel  10 . However, it will be apparent that with devices of this configuration, the entire wall of the vessel  10  will be exposed to approximately the same dose of radiation, including both diseased portions  18  and healthy portions  20 . This raises several problems. First, the healthy tissue  20  is more likely to be damaged by the radiation exposure. Second, because the diseased tissue  18  is thicker and radiation decreases in intensity in proportion to the distance from the source, some of the tissue that most needs the exposure will receive less than some healthy tissues that need none. As a result, for the treatment to be effective, the total exposure intensity must be increased, resulting in more damaging exposure to healthy tissues. 
     There are additional concerns with such prior art radiation exposure devices. FIG. 2A shows a longitudinal cross-sectional view of the prior art radiation delivery device  22  disposed within a blood vessel  10  having a plurality of stents  30  placed therein, such as from a previous procedure. The distal end  26  of the elongate rod is impregnated with radioactive material, and is frequently sheathed in a radiation absorbing tube during insertion into the patient, such as by a shielded portion  34  of the distal end of a delivery catheter  32 . Upon reaching the target location  36  the radiation absorbing end  34  of the delivery catheter  32  is retracted, and the anatomy is exposed to radiation from the rod  26  for some predetermined length of time before the rod  26  is retracted back into the shielding end  34  of the catheter  32 . 
     This prior art apparatus and method, however, presents several problems. First, radiation from the ends of the rod, symbolized by arrows  28   a , will naturally irradiate portions of the vessel or cavity wall, designated generally at locations  38 , beyond the target area  36 , albeit with radiation levels which generally fall below the intended therapeutic level as one moves away from the radiation source. This radiation is sometimes called “edge effect” radiation. FIG. 2B shows a graph of the radiation dose provided by the prior art radiation delivery device of FIG. 2A as a function of the location along the length of the vessel wall, showing the radiation provided to the target area  36 , and the edge effect radiation areas  38  at the extreme ends of the graph. To be effective against the diseased tissue, the radiation dose must be within a therapeutic dose window, designated T.D. in FIG.  2 B. Radiation in excess of this therapeutic dose will cause excessive damage to body tissues; radiation below the minimum therapeutic dose, outside the T.D. window, will not be effective to achieve the desired therapeutic results. 
     However, below the therapeutic dose window is an irritation dose window, designated I.D. in FIG.  2 B. Irradiation of tissues with radiation doses below the I.D. window will have no effect. However, irradiation of tissues with radiation doses within the irritation dose range is responsible for many of the undesirable and dangerous side effects associated with radiation therapy. Such irritation radiation may cause lesions  40  in otherwise healthy tissue within the edge effect areas  38 , thus prompting the growth of smooth muscle cells. Consequently, the edge effect radiation  28   a  may cause further disease in the very attempt to remedy it. 
     To solve these and other problems, the inventors have developed a novel radiation delivery device  50 , shown in FIG. 3, for exposing blood vessels, body cavities, and the like to more controllable radiation doses. This device, in various embodiments allows a radiation dose to be provided at a target location within a patient&#39;s anatomy, wherein the radiation dose may be both radially and longitudinally controlled. As shown in FIG. 3, the radiation delivery device  50  is shown inserted into a blood vessel  10 , and generally comprises a catheter  52  having a single lumen  54 . An end section  52   a  of the catheter  52  includes a plurality of cuts or grooves  56  positioned to provide flexibility. These cuts  56  may be formed only on the exterior of the coil only, or may be formed substantially on the exterior and interior of the coil, and are preferably staggered in their location on opposing sides of the catheter  52 . The cuts  56  may extend either partially or completely through the thickness of the wall of the catheter  52 , depending on the degree of radiation damping desired, and the desired degree of modification of the catheter flexibility and torsional stiffness, as will be explained below. In one embodiment, the cuts preferably have a depth approximately equal to 80% of the tube diameter. 
     The end section  52   a  of the catheter  52  is heat treated to produce a coil shape when unconstrained as shown, but is formed of a material which is flexible enough to be drawn into a second catheter  64  and straightened, and conversely, may be extended therefrom upon introduction into the patient&#39;s anatomy, to resume its coiled shape. Consistent with these requirements, the catheter  52  may be made of nitinol, stainless steel, or other suitable materials, including polymer materials. In the coiled shape, the coils of the end section  52   a  press against the walls of the vessel  10  at the target location as generally shown in FIG. 3, providing a central hollow  16   a  through which bodily fluids may freely flow. The cuts or grooves  56   a  and  56   b  are preferably made by saw cutting or grinding, such as with an abrasive cutting blade, but may also be made by chemical etching, EDM, or other mechanical or chemical process. See U.S. patent application Ser. No. 08/714,555, filed Sept. 16, 1996, which as now issued as U.S. Pat. No. 6,014,919. 
     Disposed on the distal end of the catheter  52  is a tubular section  58  which is generally absorbent of radioactive emissions. That is, tubular section  58  substantially blocks the escape of radioactive emissions from radiation sources located within it. The purpose of this will be discussed momentarily. To serve this purpose, the tubular end section  58  is preferably made of tungsten, platinum, or other material which is capable of blocking or absorbing radiation emissions, such as Beta or Gamma rays. 
     Shown disposed in the lumen  54  of the catheter  52  is a wire  60 , at the distal end of which is located a radiation source  62 . Radiation source  62  could be formed in a wide variety of shapes. In FIG. 3 it is shown as a ball, but it could also be formed as an elongate piece of any desired length, and may be housed in a plastic sheath or other container disposed on the distal and of the wire  60 . In FIG. 3, the source  62  is shown disposed in a portion of the catheter  52  located adjacent one area of the side wall of the blood vessel  10 . In this location, the radiation source  62  would be emitting radioactive emissions, with the largest dose affecting the area of the wall in closest proximity to the source. Advantageously, the radiation source  62  could be iridium 192, phosphorus 32, strontium 90, or other radiation source depending upon the treatment to be administered and the nature of the diseased area of the vessel  10 . As is known to those skilled in the art, some of these radiation sources are beta emitters, and some are gamma emitters. 
     In use, the wire  60  would be threaded into the lumen  54  of the catheter  52  (under radio-protective conditions) until the radiation source  62  were positioned within the radiation absorbent section  58 . There are then several alternative methods by which the catheter  52  may be extended to the target location. First, the catheter  52 , with the wire disposed therein, could be threaded into the blood vessel  10  until the coil section  52  were disposed at the target location. 
     Alternatively, to facilitate ease of threading the catheter  52  into the patient, the coil section  52   a  could be uncoiled and threaded lengthwise into a slightly larger second catheter  64  which would prevent the coil section  52   a  from coiling. The second catheter  64  may be a typical venous catheter having a 0.014″ lumen, or it may comprise some other size and shape configuration as desired. Consequently, the preferred outside diameter of the catheter  52  is 0.014″, so as to coincide with the interior diameter of typical venous catheters. With this size of catheter  52 , the cuts will preferably be from 0.004″ to 0.012 inches deep, and be longitudinally spaced from 0.004″ to 0.015″ apart. The second catheter  64 , with catheter  52  threaded therein, is then inserted into the desired blood vessel or body cavity until the target location is reached. The second catheter  64  will also shield some radiation from reaching tissues that are passed as the device is inserted into the patient, and may also be advantageously provided with a radiation absorptive section  66  at its distal end, which will shield even more radiation during insertion. As yet another alternative, the catheter  52  may be straightened and inserted into another catheter, similar to catheter  64 , which is already in place, for example, if angioplasty has just been performed. The catheter  52  would be extended to the target location, and the previously placed catheter would be removed or retracted at least from the coil section  52   a  to allow the coil section to assume its coiled shape, expanded against the vessel  10  or body cavity walls. 
     Regardless of which method is followed, during the threading of the catheter  52  into the blood vessel or body cavity, the radiation source  62  is advantageously positioned in the radiation absorbent section  58  so that tissue past which the radiation source  62  moves is essentially protected from radiactivity. Additionally, the diameter of the catheter  52 , and the second catheter  64  if provided, are chosen such that sufficient flow of bodily fluids is maintained through the vessel lumen  16  and the coil hollow  16   a  throughout the procedure. Progress of the catheter  52  or  64  into the anatomy may be tracked and monitored by any one of many methods well known in the art, such as x-ray fluoroscopy. Upon reaching the target location and expanding into its coiled shape, the wire  60  is partially withdrawn to move the radiation source  62  rearwardly in the catheter lumen  54  to the desired position against a side wall area to be irradiated. Such an area could be a diseased area infected with diseases such as smooth muscle cell proliferation or benign prostatic hyperplasia. 
     The configuration of the catheter  52  of this invention advantageously allows a user to control both the longitudinal and radial dose which is applied to the tissue. The longitudinal dose is controlled partly by the catheter  52  itself, which provides cuts  56   a  and  56   b  only on the outer and inner surfaces thereof relative to the coil lumen  16   a . Thus, unlike the prior art device  22  shown in FIG. 2A, because no cuts are provided which face in the longitudinal directions, the material of the catheter itself significantly reduces the radiation dose which radiates in a forward or backward direction. Additionally, the longitudinal dose is controlled by the pitch of the coils  52   a  and the speed with which the radioactive portion  62  is drawn through the lumen  54 . It will be apparent that these factors control the rate at which the radiation source  62  moves from the distal end of the coil to the proximal end thereof. 
     FIG. 4 shows a cross-sectional view of the blood vessel  10  containing the radiation exposure device  50  of the present invention, taken along section A—A. In this view the central hollow  16   a  of the coil and the direct contact of the coil  52   a  with the vessel wall  10  are clearly shown. As the wire  60  is partially withdrawn from the catheter  52 , it will negotiate a helical path as it passes through the catheter lumen  54 , which in the cross-sectional view of FIG. 4 causes a generally circular path of motion for the radiation source, around the perimeter of the vessel as shown by arrow  68 . It is this circular path that yields some of the great advantages of the present invention, as described in more detail below. 
     FIG. 5A shows a closeup cross-sectional view of part of the blood vessel  10  of FIG. 4, containing the radiation exposure device  50  of the present invention. In this view the radiation source  62  is located proximal to an exterior cut  56   a  formed on the surface of the coiled end  52   a  of the catheter 52 . The radial dose of radiation is advantageously controlled by these cuts, and also by the rate at which the radiation source  62  is drawn past a specific location of the coil. In the preferred embodiment, the cuts  56  are formed to be in the range of 0.001″ to 0.002″ wide, but other widths may be used. It will be apparent that the depth and longitudinal spacing of the cuts will depend on the desired flexure and radiation resistance characteristics of the device, among other considerations. 
     When the coil is curved and disposed in the vessel as shown, it will be apparent that by virtue of this curvature, the cuts  56   a  disposed on the outer surface of the coil  52   a  will be stressed in an open configuration, thus providing a “window” for radiation, designated by arrows  28 , to escape outwardly from the coil at each cut location. These cuts  56   a  may attain a width of 0.003″ to 0.004″ due to the bending of the catheter. However, because the cuts  56  are locationally staggered on opposite sides of the catheter, the inner surface of the catheter will provide no window at the location of an outer cut  56   a , and will provide a reduced window at the location of the cuts  56   b  formed on the inner surface of the coil. This configuration will partially block radiation from passing through to the central hollow  16   a  of the coil, and thence into the opposing wall of the vessel or body cavity. The material of the catheter  52   a  on the opposing side of the coil will also serve to further shield the opposing vessel wall from this transverse radiation. The great advantage of this configuration is that it creates a more uniform “view factor” for the surface of the body cavity, which thereby provides a more uniform dose of radiation to the areas where it is needed, and a reduced dose to areas that do not need it. 
     FIG. 5B shows a closeup cross-sectional view similar to that of FIG. 5A, except that the radiation source  62  is located proximal to an interior cut  56   b  formed on the surface of the catheter. As noted above, the curved configuration of the coil  52   a  causes these interior cuts to be mostly closed. Thus, while inner cuts  56   b  may be provided to increase the flexibility of the catheter, they will provide only a limited window for transverse radiation, shown by arrow  28 , and the material of the catheter on the opposing side of the coil will serve to further block this transverse radiation. Thus when the radiation source  62  is located adjacent to a cut  56   b  formed on the inner surface of the coil  52   a , the radial dispersion of radiation is still largely controlled. 
     For further control of radiation exposure, another alternative embodiment shown in FIG. 5C may be formed having cuts  56   a  only on the outside surface of the coil  52   a . In this embodiment, the cuts  56   a  on the outside surface preferably extend to a depth approximately equal to 80% of the diameter of the catheter  52 . This configuration significantly increases the flexibility of the distal end  52   a  of the catheter, and also provides a relative large, uniform window for radiation exposure. It also provides greater shielding on the inside of the coil, thus providing greater control of the exposure by blocking transverse radiation. 
     With the catheter  52  being coiled and having cuts as described, the radiation dosage may be very accurately controlled by adjusting the rate at which the radiation source  62  is retracted through the lumen  54 . For example, the vessel  10  of FIG. 4 is shown with a thickened side wall  18 . To prevent smooth muscle cell proliferation on the inner surface of the thickened portion  18  of the vessel wall, a therapeutic dose of radiation is required. However, because the opposing wall  20  is healthy, it is desirable not to expose that wall to even an irritation level of radiation. (See FIGS. 2A,  2 B) This is easily accomplished with the present invention. Once the coil  52   a  is in place, the wire  60  may be retracted according to a predetermined speed profile so as to match the dose to the area in contact with the apparatus. For example, the speed of retraction may be varied such that in its circular path of motion about the helical coil, the radiation source  62  passes by healthy tissues  20  at a relatively high speed, such that the radiation dose thereto is minimal. However, the speed of retraction may be advantageously reduced when the radiation source  62  is adjacent the diseased wall portion  18 , such that a larger dose is given thereto. The relative density of arrows  28  is intended to represent the variation in dosage at various locations around the perimeter of the vessel wall. 
     It will be apparent that retraction of the wire  60  through the tightly coiled catheter  52  will be resisted to some degree by friction between the wire and the inside wall of the catheter. This function will naturally limit the maximum length of the catheter coil  52   a  and the relative diameters of the wire  60  and the lumen of the catheter  52 . However, friction may be advantageously reduced through the use of biocompatible lubricious coatings and lubricants well known in the art which will allow more easy movement of the wire  60  within the catheter  52 . It will also be apparent that as with the catheter itself, the location of the radiation source  62  may be tracked by means of real-time x-ray imaging, x-ray fluoroscopy, angiography, or any other suitable tracking means known in the art. Such tracking may be perfomed relative to multiple axes, to provide very precise locational data. 
     To assist in the variable speed retraction of the radiation source  62  through the catheter  52 , the flexible wire  60  may be advantageously provided with a variable speed power retracting motor  70  and its control apparatus  80  or  82  as shown schematically in FIG.  6 . FIG. 6 depicts the catheter  52  contained within a second catheter  64  extending from a small incision  74  in the patient, which is provided to introduce the apparatus. The catheters  64  and  52  are connected to the end of a rigid catheter insertion device  76  via a releasable connector  79 . Such catheter insertion devices are well known in the art, and are routinely used in connection with angioplasty and other catheter-related or endoscopic procedures. In the embodiment as shown, the variable speed motor  70  is releasably connected via connector  81  to the proximal end of a branch  77  of the catheter insertion device  76 . It will be apparent that devices of other configurations, such as without branches or with multiple branches, may be used without affecting the operation of the present invention. 
     The catheter  52  extends to the connection of the motor  70 , and the wire  60  extends through the motor in such a manner as to allow retraction thereof The motor  70  comprises means  72  for gripping the proximal end of the wire  60  and pulling it out of the catheter  52 . This means for gripping may comprise opposing wheels as shown, or other means such as a rotatable spool for winding the wire. The motor  70  is connected to a controller which controls its speed. In one relatively simple embodiment, the motor  70  is connected to a hand-held controller  80  which has a speed control knob  84 , power switch  88 , and control readout  86 . In this embodiment, the user may manually control the speed of retraction of the radiation source, and monitor the retraction such as on an angiograph screen (not shown). 
     In the preferred embodiment, the controller comprises a computer  82 , which is configured to cause the motor to retract the radiation source according to a preprogrammed exposure profile. The programmed exposure profile is designed to provide a uniform view factor to the affected tissue, and will allow for precise variation of the retraction speed, such that the portions of the anatomy most needing exposure receive a uniform therapeutic dose, but healthy portions receive much less—preferably less than an irritation dose. For example, the computer program may request information regarding the size and orientation of the target location, and the variation in the severity of the disease. Given these factors and the known diameter of the coil, the computer  82  calculates the speed variation required for optimal treatment, and automatically varies the speed of the motor  70  to cause the retraction speed to vary, such that the radiation source  62  will give precisely the proper exposure to each area of the vessel wall along its circular path—more exposure for more diseased locations, less exposure less diseased portions, and as little as possible for healthy tissue. 
     For embodiments of the invention having many turns of coil  52   a , or having a small diameter coil, it may be desirable to provide means to more easily retract the wire  60  through the coil. There are several methods which could accomplish this. The wire  60 , whether metal or polymer, could be lubricated with a suitably biocompatible lubricant. Additionally, the wire  60  could be vibrated as it is retracted to promote lubricity between the wire  60  and the lumen of the coil  52   a . These vibrations could fall within the audible or ultrasonic ranges. Yet another method to promote lubricity could be to rotate or spin the wire  60  and radiation source  62  as it is retracted. 
     Upon completion of the desired dosage time, there are several alternative methods for removing and preparing to remove the device. To prepare for removal, it is generally desirable to again shield the radiation source  62 . As one alternative, the radioactive source  62  could be moved forwardly in the catheter  52  (or the catheter  52  would be pulled rearwardly) until it were again positioned within the radiation absorbent section  58  at the distal tip. However, forward extension of the very thin wire  60  is very difficult. Alternatively, and more preferably, a second radioabsorbent section  59  could be provided at the proximal end of coil section  52   a , (See FIGS.  3  &amp;  6 ), and following irradiation of the tissue the wire  60  is further retracted until the radiation source  62  is positioned within radioabsorbent section  59 . As a third alternative, the entire catheter  52  with the wire  60  and radiation source  62  contained therein could be retracted into the distal end of the second catheter  64 . (See FIG.  3 ). To facilitate this method, the second catheter  64  is advantageously provided with a radiation absorbent section  66  on its distal end, as discussed above. It will be apparent that this radiation absorbent section  66  will need to have a length and location sufficient to ensure that the radiation source  62  will be shielded when the coil  52   a  is straightened and pulled into the second catheter  64 . The catheter  52  may then be removed from the patient. 
     Following any of these preparatory methods, the second catheter  64  having the catheter  52  and wire  60  contained therein could be entirely removed from the patient. This may be accomplished by disconnecting the motor  70  from the wire  60 , then disconnecting the catheter insertion device  76  from the second catheter  64  by means of connector  79 , and removing the entire catheter assembly through the incision  74 . Alternatively, if it is desired to leave the second catheter  64  in place for some other procedure, catheter  52  could be removed by disconnecting motor  70 , and removing the radiation delivery catheter  52  with the wire  60  contained therein through the opening in connector  81 . 
     This invention as described herein thus provides an accurate device and method for irradiating diseased tissues within the body, and allows control of both the longitudinal and radial exposure. It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention, and the appended claims are intended to cover such modifications and arrangements.
A device and method for irradiating with a desired radioactive emission the interior walls of blood vessels, body cavities and the like. The device includes a catheter for placement in the blood vessel, body cavity or the like, adapted for disposition adjacent the walls thereof. The distal end of the catheter is preferably configured to expand into a helical coil shape when unconstrained, but may be straightened when constrained within a second catheter. The catheter includes a section which is opaque to the radioactive emissions in question, and a wire slidably disposed therein for threading selectable distances into the catheter. A radioactive source is positioned at the distal end of the wire, and when positioned within the radio-opaque section of the catheter, radioactive emissions arc blocked from reaching adjacent tissue, allowing the radiation source to be safely guided to a target location. Upon reaching the target location, the radioactive source is moved out of the opaque section, and radioactive emissions are allowed to reach adjacent tissue for treatment. The radiation source is preferably retracted through the catheter at a variable rate, so as to vary the radiation exposure level of adjacent tissues.