WO2000048664A2

WO2000048664A2 - Automatic ribbon delivery system for intravascular radiation therapy

Info

Publication number: WO2000048664A2
Application number: PCT/US2000/003927
Authority: WO
Inventors: Jeffrey L. Wilkinson; Steven K. Moore; William H. Taylor; Robert A. Till, Jr.
Original assignee: Cordis Corporation
Priority date: 1999-02-16
Filing date: 2000-02-15
Publication date: 2000-08-24
Also published as: WO2000048664A3

Abstract

A delivery device (10) provides for the attachment of a special intravascular radiation therapy catheter (not shown), through which a drive mechanism (48) extends, and retracts a ribbon (38). In the unlikely event this mechanism (48) fails during retrieval, stranding the radioactive elements (not shown) outside the containment area (44), A back-up method of retrieving the ribbon (38) is available.

Description

AUTOMATIC RIBBON DELIVERY SYSTEM FOR INTRAVASCULAR RADIATION THERAPY

FIELD OF THE INVENTION

The present invention relates to medical devices generally, and to delivering and positioning radioactive ribbons or wires into the body of a patient, which are commonly used in radiation oncology and intravascular radiotherapy. In particular, the present invention relates to devices, often referred to as "pigs" or "afterloaders," such devices advance a ribbon having a radioactive source at its distal end along a catheter previously positioned within the body of a patient for a predetermined period of time, and later withdraw the ribbon from the patient.

BACKGROUND AND SUMMARY OF THE INVENTION Restenosis after arterial intervention in general, and after percutaneous transluminal coronary angioplasty ("PTCA") in particular, is a concern of physicians practicing PTCA today. Conventional PTCA is performed using a standard balloon catheter such as the type described in U.S. Patent Number 5,304,197 entitled "Balloons For Medical Devices And Fabrication Thereof," issued to Pinchuk et al. on April 19, 1994, which is incorporated into this disclosure by reference. Balloon catheters are typically used with a guidewire which is inserted into the patient's artery until its distal end is advanced past the diseased or stenotic area of the vessel, where there is a buildup of material. Balloon catheters typically have a guidewire lumen so that the proximal end of the guidewire can be inserted into the distal end of the balloon catheter. Thereafter, the balloon catheter is advanced over the guidewire until the balloon is adjacent the buildup of material, and the balloon is then inflated to compress the buildup. Finally, the balloon is deflated and the catheter is pulled back through the guidewire and removed from the patient's vasculature.

Restenosis of the artery may occur after this procedure, in which the same area of the vessel may collapse or become clogged again. Recent technology has discovered that treating the diseased area of the vessel with local radiation after balloon angioplasty may help prevent restenosis.

Accordingly, the present invention provides for an improved source wire delivery system or afterloader, which is especially useful for intravascular radiation therapy ("IRT"). Such technology is described in U.S. Patent Number 5,199,939 entitled "Radioactive Catheter," issued to Dake et al. on April 6, 1993, which is incorporated into this disclosure by reference. Prior technology contemplates the delivery of unspecified doses of radiation via wires having radioactive distal tips. A catheter would be inserted into the vasculature and advanced to the site of the previous angioplasty. The radioactive source wire would then be advanced through a lumen in the catheter so that its radioactive tip is adjacent the diseased site and can deliver the requisite amount of radiation. Thereafter the catheter and wire were removed. Such a device is described in PCT Application PCT/US94/04857 entitled "Radioactive Source Wire, Apparatus And Treatment Methods," and published on November 10, 1994 as WO 94/25106. Because the intensity of the radiation delivered to the vessel wall varies in inverse proportion to the square of the distance between the radioactive source and the vessel wall, it is desirable to center the radioactive wire within the vessel. This is also true when exposing a vessel to a light source. Centering thus prevents areas of the vessel from being overexposed or underexposed to the radiation. One such way to center the radioactive wire would be to deliver the wire to the site via a central lumen of a spiral balloon catheter. An example of a spiral balloon catheter is given in U.S. Patent Number 4,762,130 issued to Fogarty et al. on August 9, 1988, entitled "Catheter With Cork-Screw Like Balloon," which is incorporated into this disclosure by reference.

It will be appreciated that several features are desirable: accurate positioning of the source wire or ribbon within the patient, storing the radioactive wire safely when not in use, and delivering it upon demand.

It is known in the medical field of oncology to use afterloader devices in the treatment of cancerous tumors using radioactive sources. Typically one or more catheters are positioned in the patient and are attached to the afterloader, which advances the radioactive source wire along the catheters according to a predetermined sequence calculated to deliver a therapeutic dose of radiation to the tumor. Examples of afterloaders can be found in U.S. Patents 5,865,720, February 2, 1999; 5,857,956, January 12, 1999; and 5,092,834, March 3, 1992 entitled "Apparatus And Method For The Remote Handling Of Highly Radioactive Sources In The Treatment Of Cancer," all of which are incorporated into this disclosure by reference. The functions of a delivery device according to the present invention include providing for the safe storage, deployment, and retrieval of a ribbon containing radioactive elements. A delivery device arranged generally according to the present invention provides for the attachment of a special intravascular radiation therapy catheter, through which a drive mechanism in the delivery device extends and retracts the ribbon. In the unlikely event this mechanism fails during retrieval, essentially stranding the radioactive elements outside the radioactive shielding containment area, a backup means of retrieving the ribbon is available. Additional features may include a mechanism to restrict unauthorized access, and a way to temporarily immobilize the ribbon during the treatment period. The delivery device can function as a stand-alone manual delivery device or in combination with an automated system (auto-ready). When connected to the automated system, several additional features of the delivery device can then be accessed, including internal data storage for configuration information, sensing catheter attachment, home position indication, and motor control of the extension / retraction mechanism.

These and various other objects, advantages and features of the invention will become apparent from the following description and claims, when considered in conjunction with the appended drawings.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other aspects of the present invention will best be appreciated with reference to the detailed description of the invention in conjunction with the accompanying drawings, wherein:

Figure 1 is a perspective view of a delivery device made in accordance with the principles of the present invention;

Figure 2 is an exploded view of the device shown in Figure 1 ; Figure 3 is a partial cross-sectional view of the device shown in Figure 1 ;

Figure 4 is an exploded view of the device shown in Figure 3; Figure 5 is a longitudinal cross-sectional view of the device shown in Figure 1 ;

Figure 6 is a simplified perspective view of an emergency pull tab and ribbon guide feature made in accordance with one embodiment of the present invention;

Figure 7 is an exploded view of the attachment mechanism for securing the device to the catheter and sensing such attachment, made in accordance with an alternative embodiment of the present invention;

Figure 8 is an exploded view of a ribbon drive mechanism made in accordance with the present invention;

Figure 9 is a simplified perspective view of the reel assembly shown in Figure 8; Figure 10 is a top view of the assembly shown in Figure 9.

Figure 11 is an exploded view of a pinch wheel assembly made in accordance with the present invention;

Figure 12 is a bottom view of the device shown in Figure 1;

Figure 13 is a cross-sectional view of Figure 1 taken so as to show the brake assembly made in accordance with one embodiment of the present invention;

Figure 14 is an exploded view of a crank made in accordance with one embodiment of the present invention;

Figure 15 is a perspective view of the device shown in Figure 1 and a cart for holding the device, made in accordance one embodiment with the present invention; Figure 16 is a side view of another embodiment of a device made in accordance with the present invention; and

Figure 17 is a schematic diagram of forces describing one aspect of the present invention.

DF.T Aπ F.D DESCRIPTION OF THE PREFERRED EMBODIMENT

The basic construction of a delivery device can best be explained by referring to the following description taken in conjunction with the attached drawings and claims. The functions of the delivery device according to the present invention include safely storing, accurately extending and retracting a spooled flexible ribbon having one or more radioactive source elements. As seen from the figures, the device may preferably provide for appearance, structural integrity, and portability. It may preferably consist of a rigid aluminum skeleton for strength, surrounded by plastic skins, jackets or coatings that provide external appearance aesthetics and protection to internal components.

Radiation Shielding: One of the safety functions of a delivery device according to the present invention, an embodiment of which is indicated generally at 10, is to provide shielding for radioactive elements in the ribbon. For shielding purposes, this delivery 10 device incorporates a shielding assembly 44 of a split lead casing 55 and 56 surrounding a tungsten core 64 (see Figures 3 and 4). The split lead design allows for placement of guide tubes 60 (hypo-tube), tungsten core 64, and a sensor assembly 62 within the containment area. The shield assembly 44 is held together with metal bands 58 and is jacketed by the aluminum skeleton (chassis) 40 made of matching chassis halves 42 using through bolts to clamp them together (see Figure 3).

Ribbon Home Position Sensor (Auto-Ready Feature):

The design of the delivery device 10 may include a sensor assembly 62 and associated circuitry to detect the passage of the ribbon tip past a fixed point within the radiation shield 44 of the delivery device 10 (see Figure 4). This sensor 62 is used to indicate that the ribbon is properly stowed in the dwell area of the radiation shield 44. Low-cost acrylic optical fibers may be used, along with an LED and detector to form a photo-interrupter within the radiation shield 44. The detector has a fixed detection threshold. The LED is driven by an adjustable direct current source. The magnitude of the current is set using a non-volatile programmable device that simulates a potentiometer. Adjustment to this device can be made non-intrusively using a simple electrical connection to the delivery device 10.

Due to the possible adverse effects of gamma radiation on acrylic optical fibers, there may be some increased attenuation over time of the optical transmittal of the optical fibers. Periodic resetting of the appropriate LED current (and consequently LED light output) during routine maintenance of the delivery device compensates for transmittance changes of the optical fibers due to gamma radiation exposure. Emergency Ribbon Retraction:

In the delivery device 10, an alternative means of retrieving the ribbon may be accomplished by providing access to the proximal end of the ribbon, allowing it to be hand- drawn back into the shielded area 44. Within the delivery device 10, the ribbon is wound onto a reel assembly 46, and fed through an enclosed pathway 68 (see Figure 5). The emergency ribbon access pull tab 54, shown in Figure 6 is located in the path of the ribbon between the drive mechanism 46 and the containment area 44. The ribbon passes through a hole in the pull tab 54. During normal operation, the ribbon would be deployed and retrieved sliding through this hole. In the unlikely event the drive mechanism becomes disabled, access to the ribbon is possible by removing the access cover 28, grasping the pull tab 54 by the ring, and pulling it free from the ribbon guide. The ribbon, running through the pull tab 54, will come with it (see Figure 6). From this point, the ribbon can be pulled by hand until the radioactive portion is back within the shielding 44.

This method for providing access to the ribbon is simple, cost effective, reliable, and easy to use.

Catheter Attachment and Sensing (Auto-Ready Feature):

Luer type connectors are a medical industry standard. However, sensing the proper attachment of the connecting device using this technique is another novel feature of the present invention. The design of this catheter attachment / sensor allows for easy migration to possible future connector-specific luer designs.

An interventional radiation catheter can be attached to the delivery device 10 to provide a guide within the patient for the ribbon containing the radioactive elements. The attachment mechanism 16 (see Figures 5, and 7) on the delivery device 10 secures the catheter to the delivery device 10 and indicates such securement through an electrical interface. The mechanism accepts a standard 6 degree female locking luer on the hub of the catheter. The luer-lock mechanism 16 may include a base 82, spring 78, male luer fitting 74, lock nut 76, and an end cap 80. The male luer portion 74 of the mechanism mates to the catheter hub, guiding it as the hub is drawn into the lock nut. This allows the attachment to be made without spinning the catheter. Unlike standard luer connectors, the male luer 74 in this mechanism is free to translate or retract into the assembly as the catheter hub is drawn in. This translation actuates a micro switch that can signal to an automatic delivery device computer, whether the catheter has been attached properly.

Ribbon Drive Mechanism: The ribbon may be formed as a nylon covered, braided steel cable with radioactive elements at one end. The ribbon 38 preferably has an outer diameter between 0.0285" and 0.0305". A drive mechanism 48 may be provided to propel the ribbon out of the delivery device 10, inside the catheter until it reaches the distal end. To accomplish this, the device 10 uses a reel 96 that contains a spiral-wound groove 106 on its circumference. The ribbon is loaded onto the reel 96 by guiding it into the groove 106 and pressing it in with a pinch wheel 52 (see Figures 3, 8, 9, 10, and 11). The groove geometry is such that when the ribbon is pressed into the groove 106, the sides of the groove 106 grip it. This allows the reel 96 to apply force on the ribbon during extension. The ribbon is closely guided through the device to prevent it from buckling. The reel groove 106 must maintain alignment with the guide path during extension and retraction (reloading) of the ribbon. To do this, the reel 96 translates along its axis during rotation by means of a screw thread arrangement between it and the spindle 110 it rides on. The thread pitch of the spindle 110 matches that of the spiral ribbon groove 106. The driving force for extension and retraction of the ribbon is applied by manually rotating a crank assembly 20. The crank assembly 20 is attached to a slip clutch 94, which in turn is attached through an axle 50 to a drive gear assembly 86. The drive gear assembly 86 applies a rotational force on the reel 46 through two pins on the drive gear 86, which slide in slots on the reel 46. The drive gear 86 is accessible from the bottom of the device through a slot in the foot 36 (see Figure 12). When loaded on an automatic delivery device, a friction wheel will pass up through the slot and engage the drive gear 86. The friction wheel is part of a motor assembly that allows computer control of the extend and retract operation.

Slip Clutch: The slip clutch 94 contained in the drive mechanism provides a safety function for this device. The technique for locating the radioactive elements in the ribbon at the proper treatment site in the patient requires first that the catheter be positioned as needed at the site. The ribbon is then extended into the catheter until it reaches the distal end. The slip clutch 94 prevents the ribbon from imparting a force large enough to puncture the catheter when it reaches the distal end or at any point along the catheter that might be kinked. In addition, by limiting the force, the slip clutch 94 reduces the chances of jamming the drive mechanism 48. The slip clutch 94 functions by limiting the torque that can be transmitted from the crank assembly 20 to the drive gear. It is specified with different slip torques for extension (CW rotation) and retraction (CCW rotation). The extension slip torque is set to prevent the damage as described above. The retraction torque is set to a value significantly higher than the extension torque. This is an added safety measure to ensure that once the ribbon is extended into the catheter, it can be retract back into the device.

Ribbon Loading / Home Position Stop:

The device 10 is designed to make it very easy to load 'hot' ribbons with minimal exposure to the technicians performing the work. There is a load position stop that locates the reel 96 in the proper position for loading the proximal end of the ribbon onto the reel 96. The pinch wheel bracket 114 swings up out of the way to provide easy access to the locking screw 108 that locks the end of the ribbon onto the reel 96. The home position stop is then pre-set for the minimum size ribbon length. The loading of the ribbon can be handled under computer by engaging the drive gear 86 with a friction wheel similar to the automatic delivery device function described above. When the distal ('hot') end of the ribbon is properly located within the shield assembly, the technician would lock down the slide 102 on the home position stop and replace the cover 28. This provides for a minimum of exposure time to the technician (see Figures 8-10). The device is designed to accommodate ribbons of different lengths and numbers of radioactive elements. To properly shield the radioactive elements, they must be positioned within a certain area (home position) in the shield assembly 44. During the loading procedure, the ribbon is wound onto the reel 96 until the distal end of the ribbon, with the radioactive elements, is located at this home position as indicated by the sensor assembly 62 (see Figure 4). The reel / home position stop (see Figure 13 and 14) is designed so that, at ribbon loading, as the ribbon nears the home position the slide 102 contacts a set screw 100 in the right chassis 42 and begins to slide along the toothed bar 104. Once the ribbon is at the home position, a set screw 98 on the slide 102 is tightened to lock the slide 102 in place on the bar 104. During subsequent retractions, the crank 20 is turned until the slide 102 contacts the set screw 100 in the chassis 42 thus positioning the ribbon in its proper home position.

Position Indicator:

The device 10 may provide an approximate indication of the ribbon position during extension and retraction. An indicator 24, visible through a window in the upper housing 32, tracks a spiral groove cut in the drive gear 86 (see Figures 1, 8, and 13). Since the drive gear 86 is linked directly to the reel 96, the indicator's 24 movement reflects proportionally the reel rotation, and thus the ribbon linear travel.

Lock Mechanism: A security locking mechanism 30 may be is provided to prevent unauthorized use of the device 10. The mechanism 30 consists of a standard tubular lock, a cam 122, link 124, and spring bolt 120. The spring bolt 120 is anchored to chassis 40. It passes through a slot in the wall of the chassis 40 and slips between the teeth on the drive gear 86 (see Figures 1, 8, and 13). This prevents the drive gear 86 from rotating, which in turn prevents the reel 96 from moving. To unlock the device the lock / cam assembly rotates, pulls on the link 124, which then deflects the spring bolt 120 away from the teeth on the drive gear 86 and freeing up the drive mechanism 48.

Brake: When the ribbon has been positioned properly within the catheter, the brake 26 is set to prevent unintentional movement. The brake mechanism is essentially a friction brake consisting of a brake shoe 118 with rubber contact pad, a brake lever 26, and a spring (see Figure 17). The brake lever / spring uses an over-center design to hold the brake in either the activated or released positions.

Crank Handle: The handle 22 for the crank assembly 20 has an active and a stowed position. The pivot axis for the handle 22 is spring loaded to the crank body 20. As the handle is rotated, the spring is stretched forcing the handle 22 into one of two stable positions, lying flat in the groove on the crank body (stowed) or 90 degrees out in the active position. In the active position, the base or swivel part of the handle 22 is held firm in the crank body 20 while the handle grip is free to rotate about its own shaft during crank rotation (see Figure 14).

Cart Mounting: The device 10 may be designed to locate and lock in place on carts defined for this system. This includes the current manual cart 126 and a future automatic delivery device.

A recessed well 132 on the cart's top surface positions the delivery device 10 and provides lateral constraints (see Figure 15). A release handle 128 operates a set of spring loaded locking pawls 130 deflect as the delivery device is set in place and then snap over mating features on the chassis of the delivery device 10. This secures the delivery device 10 in place for transport. It also maintains the contact force between the drive gear and friction wheel in the automatic delivery device version.

Radiation Shielding / Home Position Sensor: The split design of the lead shielding 44 components allows for the placement of the home position sensor 62 within the shield area. This affords greater confidence that the radioactive elements are in their proper location within the shield 44.

The optical sensing of the location of the ribbon with correction for radiation damage provides an inexpensive and non-intrusive way of determining position of the ribbon within the shield area.

Ribbon Drive Mechanism:

The drive mechanism of the present invention effectively accomplishes the proverbial push on a rope. By confining the ribbon within a pathway and gripping it with the reel, the mechanism forces the ribbon out through the pathway into the catheter. The design challenge is to guarantee a solid grip on the ribbon in the groove given, the manufacturing variations in producing ribbons. The groove geometry and pinch force generated is desirable, and the drive mechanism also incorporates an ability to be driven via a friction drive with no change of hardware. The mechanism provides ease of manual cranking at high extend and retract rates, keeping ribbon transit times to a minimum.

Ribbon Loading / Home Position Stop:

The device minimizes the radiation exposure to personnel during ribbon loading. The home position stop assembly can adjust for various lengths of ribbons. However, the home position stop requires very little adjustment by the loading technician. In a possible alternative embodiment of the present invention, the catheter attachment assembly could be modified to work with fluid systems, of course still provide for securing the catheter and indicating that it is present. One example would be attaching tubing or a fitting to the end of the plunger opposite the male luer end. When a catheter or any other luer mating component is inserted over the male luer fitting, it would be secured by the lock nut pulling the connector tight enough to acquire a low pressure fluid seal. At that point, the plunger would activate the microswitch indicating that proper attachment has occurred.

The device of the present invention, as shown in Figure 15, incorporates an automated control system within the basic cart functions. Part of this automated system is a motor drive / control unit that drives the extend / retract mechanism of the delivery device. The motor drive mechanism designed for this function involves a drive wheel that engages the drive gear component of the delivery device ribbon extend / retract mechanism via an opening in the bottom side of the device. The drive wheel is an elastomeric ring molded over a metal hub. The hub assembles to a slip clutch, which is connected through a gear set to the drive motor. An encoder is added to the system to provide rotational feedback to the controller. The drive gear in the delivery device is made of aluminum with a diamond knurl finish on the contact surface to enhance the tractive drive effort. The drive wheel and portions of the motor / gear / clutch assembly are mounted on a spring- loaded arm that is attached to the cart by a hinge or pivot. As the delivery device is mounted to the cart, the drive gear on the device makes contact with the drive wheel on the cart. The arm deflects, resisted by the spring force, until the device is seated in the well on the cart. The spring provides for a consistent force within a defined range.

Motor Drive Mechanism: The friction created by the contact between the elastomeric drive wheel and knurled aluminum drive gear can provide sufficient torque transfer to eliminate the need for a meshed gear driven system. A friction drive system has the advantages of low noise, easy mate-up, and minimal backlash. Noise and backlash may be associated with gear driven systems. Since the delivery device is designed to be loaded and unloaded from the cart on a routine basis, it is important to ensure that the driving and driven members align and mate properly. The friction drive system does not require accurate alignment or tight tolerances. The spring-loaded arm and compliant drive wheel adjust for misalignments and dimensional variations between the delivery device and the cart motor drive

Hardware:

A series of tests were run to evaluate the magnitude of torque that could be transmitted through the friction drive given various materials, finishes, and normal force in the presence of fluid contamination. It was found that the direction the drive wheel was rotated had an impact on the amount of torque generated between the two wheels. The difference was attributed to the fact that the radial force was changing as a result of the difference in rotational direction (refer to Figures 16 and 17). The motor drive mechanism was designed to have the tangent line 140 of contact between the drive wheel 134 and drive gear 138 in the delivery device pass through the pivot point 136 of the arm. This would ensure that the radial force would not be affected by direction of rotation of the drive wheel. This allows a minimum radial force to be defined that would accommodate the same torque in both rotational directions. Minimizing the radial force in turn minimizes the stresses and deflection in the axle supporting the drive gear. It would also reduce the amount of wear on the elastomeric drive wheel.

One modification to this embodiment is to have the tangent line of the contact between the elastomeric drive wheel and the aluminum knurled drive gear is purposely non-colinear (as in Figure 17). This would create different radial forces (and therefore torques) between the drive wheel rotating one direction and the drive wheel rotating the opposite direction. This was considered in this application because of the preference to have a limit of 120 ounce-inches of torque when retracting the ribbon and only 64 ounce- inches of torque when extending the ribbon. There are some advantages of creating different torques based on the tangent line location relative to the arm pivot. If placed properly, it would create a situation that would minimize the radial force (and therefore wear of drive components) for one direction and maximize the radial force for the other, higher torque, direction. This would reduce the load requirements on the spring, and therefore make the assembly of the spring easier. Using this relationship between dN and dF would provide the desired clockwise and counter-clockwise torque values for the properly calculated spring torque (spring torque would add or subtract from W-dW depending on the actual arrangement of the arm).

The device design allows easy migration to different ribbon diameters for different treatment protocols. Although particular embodiments of the present invention have been shown and described, modification may be made to the device and/or method without departing from the spirit and scope of the present invention. The terms used in describing the invention are used in their descriptive sense and not as terms or limitations.

It should be understood that an unlimited number of configurations for the present invention could be realized. The foregoing discussion describes merely exemplary embodiments illustrating the principles of the present invention, the scope of which is recited in the following claims. Those skilled in the art will readily recognizer from the description, claims, and drawings that numerous changes and modifications can be made without departing from the spirit and scope of the invention.

Claims

CLAIMS What is claimed is:

1. An automatic system for delivering a flexible ribbon with radioactive source elements to a desired site for medical treatment of a patient, comprising: a main housing; a containment vessel removably affixed to the main housing and having a shielding bottle of radioactive shielding material; a hypotube within the containment vessel defining a narrow passage for a ribbon extending from a proximal end to a distal end of the containment vessel; a luer-lock fitting affixed to and communicating with a distal end of the hypotube, for removably attaching a catheter defining a ribbon lumen to the luer-lock fitting; a quick release mechanism removably affixing the containment vessel to the main housing; a drive mechanism within the main housing for extending and retracting a ribbon out through the hypotube and luer-lock fitting, including a rotatable reel having a spiral groove for receiving the ribbon; and a flexible ribbon with radioactive source elements at a distal end of the ribbon, mounted about the reel and received in the spiral groove and extending through the hypotube; such that in the unlikely event the drive mechanism renders the ribbon unretrievable, the quick release mechanism may be actuated to remove the containment vessel from the main housing and exposing the proximal portion of the ribbon, thus allowing the ribbon to be manually retracted until the radioactive source elements are within the containment vessel shielding bottle.

2. The automatic system set forth in Claim 1, further comprising one or more markers on the ribbon, placed a predetermined distance proximal from the radioactive source elements, to remotely indicate when the radioactive source elements are located within the containment vessel shielding bottle.

3. The automatic system set forth in Claim 1, further comprising one or more protective structural elements affixed to or defined by the distal end of the containment vessel and extending distally beyond the luer-lock fitting, to protect the luer-lock fitting from damage.

4. The automatic system set forth in Claim 1, further comprising one or more first mechanical stops operatively coupled with the reel, and one or more corresponding second mechanical stops coupled to the main housing, arranged such that the first and second stops contact each other after the ribbon is extended a predetermined length by rotating the reel a number of revolutions.

5. The automatic system set forth in Claim 4, wherein one or more of the mechanical stops are adjustable, to account for differing lengths of catheters.

6. The automatic system set forth in Claim 1, further comprising one or more first mechanical stops operatively coupled with the reel, and one or more corresponding second mechanical stops coupled to the spool spindle, arranged such that the first and second stops contact each other after the ribbon is retracted a predetermined length by rotating the reel a number of revolutions, such that the radioactive source elements are retracted to a normal resting position within but not past the radioactive shielding material.

7. The automatic system set forth in Claim 1, further comprising a slip clutch for limiting the maximum torque transmitted from a drive input mechanism to the reel, for additional safety to avoid damage to a catheter affixed to the luer-lock fitting or possible injury to the patient.

8. The automatic system set forth in Claim 1, further comprising a security lock mechanism for preventing unauthorized use of the delivery system by selectively locking and preventing rotation of the drive mechanism.

9. The automatic system set forth in Claim 1, further comprising a position indicator operatively coupled with the drive mechanism and providing an approximate indication of the extension distance of the ribbon.

10. The automatic system set forth in Claim 1, further comprising a brake for selectively locking and preventing movement of the drive mechanism during dwell time of a medical procedure when the ribbon is extended and the radioactive source elements are disposed at the treatment site, to avoid dislodging the radioactive source elements from the treatment site.

11. The automatic system set forth in Claim 1, wherein the ribbon further comprises a nylon jacket surrounding a braided metal cable having one or more radioactive source elements at its distal end.

12. The automatic system set forth in Claim 1, further comprising a pinch wheel arranged in close proximity to the groove defined by the reel, the pinch wheel being rotatable about an axis parallel to an axis of rotation of the reel, an outer surface of the pinch wheel being spaced a certain distance from the outer surface of the reel, such that the pinch wheel presses the ribbon into the groove and the groove grips the ribbon so as to drive the ribbon in a direction tangent to the groove when the reel is rotated.

13. The automatic system set forth in Claim 1, wherein the ribbon exits the groove on the reel at a drive point, the drive point tending to remain at a constant angular position with respect to the main housing, and the drive point tending to shift in a lateral direction parallel to the rotational axis of the reel as the reel rotates and extends or retracts the ribbon, the system further comprising a mechanism for compensating for such shifting of the drive point.

14. The automatic system set forth in Claim 13, wherein the compensating mechanism further comprises a screw thread having a pitch equal to that of the groove defined by the reel, the reel being mounted about the screw thread such that the reel shifts laterally an equal and opposite distance as the drive point shifts during rotation of the reel.

15. A containment vessel for use with an automatic system delivering a flexible ribbon with radioactive source elements to a desired site for medical treatment of a patient, comprising: a shielding bottle of radioactive shielding material; a hypotube within the shielding bottle extending from a proximal end to a distal end of the shielding bottle, the hypotube defining a narrow passage for a ribbon extending from a proximal end to a distal end of the containment vessel, the hypotube defining a longitudinal axis; a luer-lock fitting affixed to and communicating with a distal end of the hypotube, for removably attaching a catheter defining a ribbon lumen to the luer-lock fitting; wherein the shielding bottle is arranged to provide radioactive shielding material in all radial directions around the longitudinal axis for a majority of the length of the hypotube; and the hypotube having at least two slight bends to shift a central portion of the hypotube to a path parallel to the longitudinal axis; such that radioactive shielding material is present in both a distal and proximal direction along the longitudinal axis of the hypotube, whereby radioactive shielding material surrounds a normal resting position of radioactive source elements on a ribbon in all spherical directions.