WO1999001174A1 - Compact cartridge for afterloader and method - Google Patents

Abstract

A compact cartridge (20) for an afterloader (10) includes a housing (21) containing a radioactive source wire, and a dummy test wire each accommodated in a helical groove on the periphery of a wire storage drum (124). The wires are contained in the grooves (125) by low friction bearings such as rollers (140) so that advancement of the wire from the drum is under very low friction conditions. The cartridge is removably inserted in the head (16) of an afterloader apparatus that engages a primary drive system (38), and an emergency retract mechanism (40) mounted in the head. The cartridge also contains an electronics board (123) with software for updating the software in the control electronics for the afterloader.

Description

COMPACT CARTRIDGE FOR AFTERLOADF.R AND MFTHnn

Background of the Invention

The present invention relates to a method of and an apparatus for the handling and precise

positioning of radioactive sources used in radiation oncology and intravascular radiotherapy,

particularly to a device known as an afterloader, which advances a wire or cable having a

radioactive source at the tip along a catheter or other closed pathway to a position within the

body of a patient for a predetermined period of time and which thereafter withdraws the wire and

radioactive source from the patient.

It is known in the medical field to use afterloader devices in the treatment of cancerous

tumors using radioactive sources having intensity greater than that which can safely be handled.

Typically one or more catheters, needles, or other closed pathways (hereafter "catheters") to the

treatment site are positioned in the patient. The catheters are then attached to the afterloader

which advances the radioactive source at the end of the wire, sometimes called a sourcewire,

along the catheters according to a predetermined sequence calculated to deliver a therapeutic dose

of radiation to the tumor. Typical of the prior art apparatus are those disclosed in U.S. patent

Nos. 4,631,415; 4,881,937; and 5,030,194. Many of these prior art devices advance the

sourcewire by means of a friction drive belt trained about a wheel with the wire sandwiched

between the belt and wheel.

Less well known but rapidly gaining acceptance is the use of radiation to prevent or

inhibit restenosis following percutaneous transluminal coronary angioplasty (PTCA) or other

arterial lumen opening procedure. PTCA, also known as balloon angioplasty, is the predominant

treatment for coronary vessel stenosis. Approximately 300.000 procedures were performed in the United States (U.S.) in 1990 and an estimated 400,000 in 1992. The U.S. market constitutes

roughly half of the total market for this procedure. The increasing popularity of the PTCA

procedure is attributable to its relatively high success rate, and its minimal invasiveness

compared with coronary by-pass surgery. Patients treated by PTCA, however, suffer from a high

incidence of restenosis, with about 35% of all patients requiring repeat PTCA procedures or by¬

pass surgery, with attendant high cost and added patient risk. More recent attempts to prevent

restenosis by use of drugs, mechanical devices, and other experimental procedures have had

limited success.

Restenosis occurs as a result of injury to the arterial wall during the lumen opening

angioplasty procedure. In some patients, the injury initiates a repair response that is

characterized by hyperplastic growth of the vascular smooth muscle cells in the region

traumatized by the angioplasty. The hyperplasia of smooth muscle cells narrows the lumen that

was opened by the angioplasty, thereby necessitating a repeat PTCA or other procedure to

alleviate the restenosis.

Preliminary studies indicate that intravascular radiotherapy (IRT) has promise in the

prevention or long-term control of restenosis following angioplasty. It is also believed that IRT

may be used to prevent stenosis following cardiovascular graft procedures or other trauma to the

vessel wall. A proposed IRT method disclosed in copending application Serial No. 08/644,101

assigned to the assignee of this invention is first to advance a flexible catheter (radioguide

catheter) through the cardiovascular system of the patient until the distal tip is at or near the

region of the vessel that has been subjected to the angioplasty procedure. Subsequently, a

sourcewire is advanced, preferably by an afterloader, along the radioguide catheter until the

radiation source is disposed at the affected region. The radiation source is held at the affected region for a predetermined treatment period calculated to deliver an effective dose of radiation,

then is withdrawn.

It will be appreciated from the foregoing that highly accurate positioning of the source

within the patient is essential to maximize the effectiveness of the treatment while minimizing

the damage to adjacent healthy tissue. It will also be appreciated that the source must be

advanced to the treatment site as quickly as possible to minimize injury to healthy tissue along

the catheter leading from outside the body of the patient to the treatment site.

To minimize trauma to sensitive tissue, the catheters and sourcewires that are

used in sensitive areas are chosen to be as small as practicable, typically on the order of 0.5

millimeters. Use of these small diameter sourcewires presents special problems for the

afterloader, for the small diameter wire does not have sufficient column strength to be driven into

the catheter unless the afterloader design incorporates special precautions to prevent wire

buckling. These problems associated with the potential buckling of the sourcewire are

compounded by the need for rapid advancement of the sourcewire to avoid damaging healthy

tissue.

With respect to the IRT application, in order to reach the site where the PTCA has been

performed, the IRT sourcewire must often follow a tortuous pathway through the narrow twisted

openings of the coronary arteries. In order to avoid blocking blood flow in these narrow

openings, use of the smallest possible radioguide catheter and sourcewire is often required. If,

however, the tiny radioguide catheter becomes kinked or otherwise obstructed as it is implanted,

unless the obstruction is detected, the afterloader may drive the sourcewire through the wall of

the catheter and even through the wall of the patient's blood vessel, with dire consequences. This

problem is solved by the use of an active force feedback to enable the afterloader to drive a sourcewire through a catheter or other pathway at the highest possible speed without risk of

puncturing a catheter or buckling the sourcewire as disclosed in copending U.S. Patent

Application Serial No. 08/436,075, the disclosure of which is incorporated herein by reference.

Another problem with prior art afterloaders is that the sourcewires in the afterloaders

typically must be replaced by highly trained technicians. Such technicians must be periodically

called upon to load the replacement sourcewire into the afterloader and verify the proper

functioning of the afterloader system. In the case of short half-life sources, frequent replacement

of sourcewires by skilled technicians obviously represents a significant cost in the maintenance

of an afterloader. One solution to this problem is disclosed in the aforesaid copending U.S.

application Serial No. 08/436,075. That solution involves the use of a replaceable modular

"cassette" in which most of the components of the wire storage and wire drive systems are

mounted in a cartridge that can be readily detached from the afterloader housing and replaced

with a new cartridge. The sourcewire is loaded into the cartridge at the manufacturer and the

proper operation of all the drive mechanisms, monitoring devices and other key components is

verified by the manufacturer before the cartridge is delivered to the user. In this way, the

cartridge can be installed in the afterloader at the user's facility by relatively unskilled persons

with confidence that the afterloader system will function correctly.

It is important that such a replacement cartridge be relatively compact and lightweight

for ease of handling, and have a rugged, highly reliable design to permit afterloader installation

by unskilled persons and especially to minimize premature failures before sourcewire

replacement is required. Summary and Objects of the Invention

Accordingly, it is a principal object of the present invention to provide a replaceable

cartridge for an afterloader which includes a small, compact wire storage and drive system of

exceptional ruggedness and reliability which incorporates a sourcewire and other key

components of the afterloader that require service or replacement during the design life of the

system or that require assembly, testing or verification by highly skilled technicians.

Another principal object of the invention is to provide a containment system for the wire

stored on the wire storage drum of the wire storage and drive system which reliably and

effectively contains the wire on the drum and permits rapid advancement and retraction of the

wire with minimal friction.

Another important object of the present invention is to provide a compact afterloader

replacement cartridge which contains the afterloader system software so that software updates

are automatically provided for the afterloader and delivery system each time a sourcewire

cartridge is replaced.

Another significant object of the present invention is to provide a compact sourcewire

replacement cartridge for an afterloader which incorporates the mechanisms and performs the

functions necessary to store a sourcewire and deliver it to the lumen of a catheter during, e.g., an

IRT procedure, including active and inactive (dummy) wire storage/drive drums, a radiation safe,

an emergency retract system, system software, and all other necessary sensing and monitoring

components for the sourcewire.

A further important object of the present invention is to provide a wire storage and

delivery mechanism that is substantially fail-safe and permits withdrawal of the sourcewire from

a catheter in the patient being treated even in the event of failure of some or all of the wire storage drive components. This fail-safe capability is achieved by a unique arrangement of low friction bearing components for retaining the sourcewire in a helical groove of the sourcewire

storage drum.

According to the present invention, a compact, replaceable cartridge for an afterloader

is provided which contains an active sourcewire and radiation safe therefor, a combination

sourcewire storage and drive drum mechanism that is characterized by a rugged and reliable

design that requires no maintenance during the effective life of the radioactive source, and all

necessary monitoring and testing devices. The cartridge includes two substantially identical wire

storage and drive drums, one for the active sourcewire and one for an inactive or dummy test

wire. Each drum is provided with a groove in its periphery for storing and guiding the

advancement of the wire. Advantageously, the proximal end of each wire is anchored to its

respective drum so that it can be advanced by rotating the drum and circumferentially retaining

the wire in the groove of the drum with low friction elements, such as rollers or recirculating ball

bearings. Thus, the sourcewire is always under a compressive load from its anchored proximal

end to its distal end during the entire time it is advanced into the catheter.

The low friction elements for retaining the wire in the groove overcomes the wire spillage

problems with the prior art devices which employ flexible friction belts to retain the wire on the

drum. In the preferred embodiment, a plurality of rollers are mounted about substantially the

entire periphery of the wire storage drum. The wire is thus positively prevented by the rollers

from disengaging or spilling from its groove even under conditions of maximum wire

advancement rate and maximum compressive force on the wire. The wire is urged radially

outwardly against the roller surfaces during advancement resulting in a slight increase in the

diameter of the wire loops in the groove of the drum. Any circumferential movement of the wire relative to the drum axis owing to that increase in diameter is substantially frictionless because the wire bears against the rollers.

A single primary drive mechanism is mounted in the afterloader apparatus housing and

is selectively coupled to one or the other of the storage/drive drums in the replaceable cartridge

for advancing a respective active or inactive wire into a catheter up to the treatment site.

Emergency battery-powered and manual sourcewire retract mechanisms are mounted in the

afterloader housing and are engageable with the active wire storage/drive drum for effecting

withdrawal of the active sourcewire from the catheter upon a main power failure or primary drive

failure.

Brief Description of the Drawings

The above and other objects, aspects, features and attendant advantages of the present

invention will become apparent from a consideration of the ensuing detailed description of

presently preferred embodiments and methods thereof, taken in conjunction with the

accompanying drawings, in which:

FIG. 1 is an exploded perspective view of an afterloader apparatus illustrating one

embodiment of a replaceable sourcewire cartridge for use in the afterloader;

FIG. 2 is a top plan view partly in cross-section of the replaceable cartridge of FIG. 1

illustrating the manner of engagement between the cartridge components and the components of

the afterloader apparatus;

FIG. 3 is a partial top plan view, partly in cross-section, of the afterloader apparatus

showing the primary drive system and emergency retract system engaged with the drive

components of the replaceable cartridge; FIG. 4 is a fragmentary side elevation view of the emergency retract system taken along line 4-4 of FIG. 3 showing the emergency retract system in its disengaged position;

FIG. 5 is a fragmentary side elevation view of the emergency retract system taken along

line 4-4 of FIG. 3 showing the emergency retract system in its engaged position;

FIG.6 is a fragmentary side elevation view of the primary drive system engaged with the

dummy wire drive;

FIG. 7 is a side view, partly in cross-section, of the dummy drive taken along line 7-7

of FIG. 2 showing the grooved dummy wire drum and the limit stop mechanism for the dummy

wire drum;

FIG. 8 is a perspective view of a washer of the limit stop mechanism of FIG. 7;

FIG. 9 is a cross-sectional detail view of the double slide wire guide mechanism for the

active drive taken along line 9-9 of FIG. 2;

FIG. 10 is a fragmentary cross-sectional view taken along line 10-10 of FIG. 9 showing

the details of the wire slide mechanism;

FIG. 11 is a fragmentary view shown as detail A-A in FIG. 7 illustrating the engagement

between the rollers and the wire in the groove of the dummy storage and drive drum; and

FIG. 12 is a fragmentary perspective view of one of the wire drums showing the manner

in which a wire is anchored to the drum.

Detailed Description of Preferred Embodiments and Methods of the Invention

Referring now in detail to the drawings, there is illustrated in FIG. 1 an embodiment of

an afterloader apparatus which is designated generally by reference numeral 10. Afterloader

apparatus 10 comprises a base 12 which is preferably wheeled, a pedestal 14 and a head 16 which is vertically adjustable with respect to the pedestal 14 by means of an adjustment mechanism (not

shown). An appropriate handle (not shown) may be mounted to the base or pedestal for use in

positioning the apparatus 10 in a desired location. The head 16 may support a video monitor

screen 18, such as an LCD touch screen display or the like. The front or forward end of the head

16 is provided with a receptacle opening 19 for removably receiving a replaceable cartridge or

cassette 20. The cartridge 20 comprises a housing 21 with a sourcewire opening 22 in the front

wall 24 thereof. As described in greater detail hereinafter, the cartridge 20 contains two elongate

wires, namely, an active sourcewire and a dummy test wire, each stored on a respective

storage/drive drum, a radiation shield or safe and necessary sensing, monitoring and software

components of the system.

Replaceable cartridges 20 are preferably provided, by the afterloader manufacturer or its

distributor with all components loaded and tested so that when a cartridge is inserted into the

receptacle opening 19 and mechanically and electrically engaged with the mating system

connections in the head 16, the afterloader apparatus is ready for use in a medical procedure.

Preferably, the cartridge 20 also contains the system software so that software updates are

automatically provided with each exchange of a cartridge. For that purpose, the afterloader

apparatus contains a rewritable non-volatile program memory which is updated by the cartridge

software. The replaceable cartridge of the invention permits the user to readily and safely

exchange sourcewires as required by decay of the radioactive source without the assistance of

highly skilled technicians.

FIGS. 2 and 3 are top views of the head 16 and the cartridge 20 illustrating the manner

in which the cartridge is inserted into the receptacle opening 19 of the head in the direction of

the arrow B (FIG. 2). The head 16 has a space or cavity 26 formed in part by side walls 28, 30 and end wall 32. A pair of tapered engagement pins 34 are mounted to the end wall 32 for

mechanically engaging in a corresponding pair of holes 36 in the rear wall 25 of the cartridge and

locating the cartridge in position as shown in FIG. 3. An electrical connection (not shown)

between the cartridge electrical components and the electrical components of the afterloader

control system (not shown) in the head is also made when the cartridge is fully inserted into the

space 26. If desired, a sensor and indicator (not shown) may be provided for sensing when the

cartridge 20 is fully engaged both mechanically and electrically into the head.

Mounted in the head 16 are the primary drive system 38 and the emergency retract system

40 which are engageable with cooperative components of the cartridge as explained in more

detail hereinafter. The primary drive system 38 comprises a primary drive motor 42 with a

vertically oriented output shaft 44 and spur gear 46 for driving a main drive gear 48 through an

idle gear 50. Drive gear 48 is rotatably mounted at one end of an engagement arm 52 which is

pivotable about the axis of the output shaft 44 of the drive motor 42 at a point intermediate the

ends of the arm 52.

The rear wall 32 of the head has a central opening 33 for receiving the drive gear 48 and

arm 52 when the cartridge 20 is placed fully inserted into the head 16 as shown in FIG. 3. When

the cartridge 20 is fully inserted, the drive gear is located in a neutral position between the

dummy drive unit 54 and the active drive unit 56 in the cartridge, but is not drivingly engaged

with either unit upon insertion. Spring-biased plungers 53, 55 maintain the arm 52 in the neutral

position.

The other end 58 of the engagement arm 52 is connected to a pair of solenoids 60, 62 by

an actuating rod 57. The solenoids comprise a dummy drive solenoid 60 and an active drive

solenoid 62 which pull the end 58 of arm 52 via rod 57 in opposite first and second directions, respectively, to pivot arm 52 about shaft 44 and thereby engage the drive gear 48 with either the

dummy drive unit 54 or the active drive unit 56 as shown and described hereinafter in connection

with FIG. 6. A power supply board 64 (FIG. 2) for the primary drive system 38 is mounted in

the housing above the active drive solenoid 62. A brake 65 is provided on the dummy drive unit

54 to hold the dummy wire in the park or retracted position except during a treatment.

The emergency retract system 40 is used to retract the active sourcewire from a catheter

either by means of battery power or manually in the event of a power failure or primary drive

failure. Emergency retraction is necessary to avoid a radioactive overdose of the patient and

operating personnel. System 40 comprises a battery-powered retract motor 66 with a vertically

oriented shaft 68 upon which a spur gear 70 is mounted for driving a main gear 72. Main gear

72, in turn, meshes with retract gear assembly 74 mounted in the cartridge 20 when the cartridge

is inserted into the head. An opening 35 (FIG. 3) in rear wall 32 of the cartridge accommodates

main gear 72 and permits it to engage with retract gear assembly 74.

The retract motor 66 and main gear 72 are mounted on a plate 76 which is pivotable about

the axis of a rotatable shaft 78. Plate 76 is forced by a spring 80 to rotate clockwise about shaft

78 so that gear 72 is biased into meshing engagement with retract gear assembly 74. A further

gear 82 is mounted to shaft 78 and meshes with main gear 72. Shaft 78 extends through the top

of housing 16 and is provided at its upper free end with a hand wheel (not shown) for manually

retracting the sourcewire in the event of failure of both the primary drive system 38 and the

emergency retract system 40.

A retract solenoid 84 operates a disengagement lever 86 to disengage the emergency

retract system 40 from the active drive unit 56 only during a treatment of a patient. At all other

times, including when there is a power failure or a drive failure, solenoid 84 is deenergized so that the emergency drive system is engaged with the active drive unit 56. Operation of the emergency retract system 40 is described in more detail hereinafter in connection with FIGS. 4

and 5.

In addition to the dummy drive unit 54 and active drive unit 56, the cartridge 20 also

houses take-off mechanisms 88, 90 for the dummy wire (not shown) and the active sourcewire

(not shown), respectively. As each wire is taken off the storage drive of its respective drive unit,

it passes through a respective take-off tube 92, 94. Each take-off tube 92, 94 engages in a

respective pivot block 96, 98 from which the wires are guided into separate, parallel passages in

a radiation safe or source shield 100 by tubes 102, 104. A shutter mechanism 106 is provided

on the outward end of shield 100 and includes a shutter 108 with a passage (not shown) and a

shutter actuator 110 for positioning the shutter passage to connect either the active sourcewire

or the dummy wire to the catheter path. A tube 112 connects the shutter passage to a home

sensor unit 114 which precisely locates the distal tip of the dummy wire or active sourcewire.

The home sensor unit 114 may include an optical, mechanical, inductive, capacitive or magnetic

sensor which produces an output to the afterloader control system when the distal tip passes the

home sensor unit either upon extension or retraction. Upon extension, the amount of wire

extended can be measured and upon retraction, it can be determined that the entire wire has been

retracted and that no wire breaks have occurred.

A radiation detector 115, such as a solid state radiation detector, is embedded in the

radiation safe 100. When a new source calibration is entered into the control electronics, the

detector 115 provides a coarse validation of the source activity. When the active sourcewire is

advanced from the drive unit 56, the detector operation can be checked by observing a drop in

the output of the detector. At the conclusion of a treatment, the detector 115 provides an indication that the entire source has been retracted to its proper position in the safe 100 and has not, for example, broken off in the catheter. The detector may also be used to verify source decay calculations made by the control electronics.

A catheter receiver assembly 116 is mounted to the inside front wall 24 of the housing

21. Assembly 116 receives and locks the catheter in place and provides a signal to the afterloader

control system indicating that the catheter is attached to the cartridge. The catheter receiver

assembly 116 also contains a scanner and electronics for decoding machine readable information

on the catheter so that such information can be inputted into the afterloader control system as

described in the aforesaid copending U.S. Patent Application Serial No. 08/436,075. The

catheter receiver assembly 116 may be connected to a force sensor 118 for sensing the force

applied to the catheter by the wire during insertion of the wire. This sensed force may be used

to control the insertion and insertion rate of the wire as described in the aforesaid copending U.S.

Patent Application Serial No. 08/436,075.

Referring to FIGS. 4 and 5, there are illustrated the disengaged and engaged positions,

respectively, of the emergency retract system 40. Retract gear assembly 74 is mounted in a

unidirectional bearing 75 so as to permit rotation in only one direction, namely, the direction for

withdrawing or retracting the active sourcewire from the catheter. The retract gear assembly 74

includes first and second retract gears 77, 79 with gear 79 splined to gear 77 so as to be axially

(vertically) movable with respect thereto. In the position shown in FIG. 4, gear 79 is at its

uppermost axial position disengaged from the retract reel gear 81 of the active drive unit 56. In

the position shown in FIG. 5, gear 79 is at its lowermost axial position engaged with the retract

reel gear 81. The gear 79 is fixedly mounted to a shaft 83 which may be spring-biased

downwardly so as to urge the gear 79 toward its engaged position with retract reel gear 81. As seen in FIG. 4, the retract solenoid 84 is energized since power is applied to the afterloader and a treatment is being performed. In this condition, the plunger 85 of the solenoid

84 pushes downwardly on the disengagement lever 86 which rotates counterclockwise about

pivot pin 87 as viewed in FIG. 4, and forces drive pin 89 upwardly into engagement with shaft

83 thereby disengaging gear 79 from gear 81. So long as power is applied to the afterloader

during a treatment, the emergency retract system 40 will remain in the position shown in FIG.

4 disengaged from the active drive unit 56. Should power be lost to the afterloader, or when no

treatment is being performed, the solenoid 84 will be deenergized thus permitting the plunger 85

to retract to the position shown in FIG. 5. When that occurs, the disengagement lever 86 rotates

clockwise about pivot pin 87 lowering drive pin 89 and permitting shaft 83 to move axially

downwardly (optionally under the force of a spring) so that gear 79 of the retract gear assembly

74 engages with gear 81. Preferably, immediately upon loss of power to the afterloader, the

battery (not shown) which supplies power to emergency retract motor 66 is automatically

connected to the motor 66 by a solenoid switch or the like to cause the motor to rotate gear train

70, 72, 77, 79, 81 and retract the sourcewire from the catheter in the body of the patient. Should

the battery or motor 66 be inoperative or defective, the afterloader operator may use the manual

handwheel attached to shaft 78 to rotate gear train 82, 72, 77, 79, 81 and manually retract the

sourcewire from the catheter. The unidirectional bearing 75 locks the drive in the fully retracted

position at all times except during a treatment and also prevents manual operation of the

emergency retract system in a direction to advance the sourcewire further into the catheter.

FIGS. 3 and 6 illustrate the manner in which the primary drive system 38 is connected

to the dummy drive unit 54 which is substantially identical to the drive system connection to the

active drive unit so that only one such connection need be described. With the cartridge 20 fully inserted into the head 16, the drive gear 48 is disposed in a neutral position between the primary reel gears 120 of the drive units 54, 56. When it is desired to drive the dummy drive unit 54, for

example, solenoid 60 is energized which urges the end 58 of arm 52 upwardly as viewed in FIG.

3 and the gear 48 downwardly into engagement with gear 120.

Gear 120 is secured to the end of the drive shaft 122 for the dummy wire drive drum 124

which is shown and described in greater detail in connection with FIG. 6. When primary drive

motor 42 is rotated in one direction, gear train 46, 50, 48, 120 rotates the dummy wire drum 124

to advance the dummy wire contained in the groove on the periphery of the drum 124 through

tube 92 and into the catheter. When the motor 42 is rotated in the opposite direction, gear train

46, 50, 48, 120 rotates the drum 124 in the opposite direction to retract the dummy wire into the

groove.

An electro-mechanical limit stop mechanism 126 is provided for limiting the number of

revolutions of the drive drum 124 and therefore the maximum length of wire advanced into the

catheter. The operation of the limit stop mechanism 126 is described in more detail hereinafter

in connection with the description of FIGS. 7 and 8.

The drive shaft 122 is coupled to an encoder 128 which detects the incremental length

of wire advanced from or retracted to the drum 124. A motor current sensor 130 may also be

provided for sensing the current applied to the drive motor 42. Such sensor may be used to

control the force applied to the sourcewire or dummy wire during advancement thereof in the

manner described in copending U.S. Patent Application Serial No. 08/436,075.

The cartridge 20 also includes an internal electronics board 123 which contains software

from which the afterloader control system boots and which updates the control system software,

e.g., a rewritable, non-volatile program memory, contained in the afterloader head 16. FIGS. 7-12 illustrate the dummy drive unit 54 in greater detail. It should be understood that the dummy drive unit 54 and the active unit 56 are substantially identical in construction and

operation and any significant differences will be specifically described herein.

Drive unit 54 comprises drive drum 124 having a diameter of about 3 inches and a helical

groove or thread 125 machined in the periphery thereof for storing a flexible wire W having a

diameter of about .020 inch. The drum 124 is fixedly mounted on drive shaft 122 which is

rotatably mounted in a pair of double or redundant bearings 132, 134 for rotation about the

vertical axis of shaft 122. Double bearings 132, 134 are supported in a pair of plates 136, 138

which are mounted in the cartridge 20 in fixed, spaced relationship to one another by a plurality

of posts (not shown). Double bearings are preferably used for each bearing 132, 134 so that if

one of the bearings of a double bearing should fail, the drive will continue to function normally.

The wire W is contained in the helical groove 125 by a plurality of low friction elements

such as rollers 140 (FIG. 11) which surround the drum 124 over substantially its entire

circumference. The rollers 140 provide a low friction containment of the wire W in groove 125

such that, as the drum rotates in a direction to advance the wire into the catheter (i.e., unwinds

the wire from the drum), the wire expands outwardly against the rollers 140. The proximal end

141 of the wire W is anchored to the drum along one face 142 thereof (FIG. 12) and enters the

helical groove 125 from an arcuate groove 144 in face 142.

Because the wire is contained in the groove by the low friction rollers 140, the driving

force of the drum 124 on the wire W acts from the proximal end 141 thereof and thus places the

wire in compression along its entire length when the wire is driven into the catheter (i.e.,

unwound from the drum). Advantageously, the rollers 140 completely contain the wire W in the

groove 125 with little or no slack in the wire along its path. Such tight containment of the wire positively prevents spillage of the wire from the drum which was possible in prior art belt drives.

With reference to FIGS. 3, 9 and 10, the wire take-off mechanism 90 for the active

sourcewire drive unit 56 will be described. Mechanism 90 comprises a slider block 148 made

of a low friction material, such as UHMW plastic, which replaces several of the rollers 140. A

hole 150 having a diameter slightly larger than the diameter of the wire W is drilled through the

slider 148 along an axis tangential to the periphery of the drum 124. The slider 148 is mounted

in a linear bearing 146 which permits the slider 148 to be moved by the wire W so that the slider

148 follows the helical groove 125 transversely across the drum periphery. One suitable linear

bearing is made by the PIC Company of Middlebury, CT. In the case of the take-off mechanism

90 for the active sourcewire drive unit 56, the slider 148 is supported in a pair of linear bearings

146, 152 (FIG. 2) so that if one of the bearings should seize or otherwise fail, the other bearing

will still permit the slider to move under the force of the wire being payed off the drum. As

shown in FIG. 2, the dummy drive unit 54 has only a single linear bearing 146 although two

such bearings could be provided if desired.

Take-off pivot tube 94 (FIG. 10) engages in a tapered bore 156 of the slider 148 so that

as the slider moves across the drum periphery, the take-off tube 94 pivots in the bore 156 as the

slider 148 follows the helical groove 125 in the drum. The take-off tube 94 also pivots with

respect to a tapered bore (not shown) in pivot block 98 from which the wire W passes through

tube 104, shield 100 and tube 112 into the catheter receiver 116. The wire take-off mechanism

88 for the dummy drive unit 54 operates in the same way as take-off mechanism 90 for the active

drive unit 56.

The limit stop mechanism 126 (FIG. 7) comprises a stack of washers 160 each having

an overhanging tang or tab 162 and a central bore 164 (FIG. 8). A bearing sleeve (not shown) is provided on the shaft 122 for receiving the bores 164 of the washers so that undesired lockup between the washers will not seize the drive shaft 122. The washers 160 are stacked on a switch

lever 166 which is rotatably mounted on the bearing sleeve of shaft 122. Lever 166 has a lever

arm 168 which engages the tang 162a of the lower most washer 160a. An upper stop cap 170

is fixed to the upper end of the shaft 122 by means of set screws 172 and is provided with an

overhanging tang (not shown) which engages the tang 162b of the uppermost washer 160b.

As the shaft rotates in one direction or the other, the tangs 162 engage one another

seriatim from tang 162b to tang 162a. Tang 162a engages the lever arm 168 of switch lever 166

to rotate against spring force until one of a pair of microswitches 174 is operated. Each

microswitch 174 transmits a signal to the afterloader control system electronics to indicate that

the wire W has reached the limit of its travel in that direction or to control the primary drive

system 38. It will be appreciated by those skilled in the art that the stop positions for advancing

and retracting the wire W can be adjusted for any given or desired wire length by varying the

number of washers 160 on the shaft and by adjusting the angular position of the overhanging tang

on the upper stop cap 170.

Although certain presently preferred embodiments of the present invention have been

specifically described herein, it will be apparent to those skilled in the art to which the

invention pertains that variations and modifications of the various embodiments shown and

described herein may be made without departing from the spirit and scope of the invention.

Accordingly, it is intended that the invention be limited only to the extent required by the

appended claims and the applicable rules of law.

Claims

What is claimed is:

1. An apparatus for advancing an elongate wire into and out of a catheter implanted

in a patient comprising: a housing adapted to receive a proximal end of the catheter;

a drive mechanism mounted to said housing for advancing the wire into the

catheter, said drive mechanism including a first wire storage drum having a rotational axis and

a periphery with a groove formed therein for receiving the elongate wire, a plurality of low

friction elements mounted about the periphery of the drum adjacent the groove for retaining the

wire in the groove during advancement of the wire into the catheter; and

means for rotating said drum to advance the wire from and retract the wire into

the groove.

2. The apparatus of claim 1, wherein said elements comprise rollers having an axis

of rotation, the axes of rotation of the rollers being arranged parallel to the rotational axis of the

drum.

3. The apparatus of claim 1, wherein said wire has proximal and distal ends, the

proximal end of said wire being affixed to said drum such that the force applied to said wire

when the drum is rotated to advance the wire is a compressive force from end to end of the wire.

4. The apparatus of claim 1, including a second drive mechanism mounted to said

housing for advancing a dummy wire into said catheter, said second drive mechanism including a second wire storage drum having a rotational axis and a periphery with a groove formed therein for receiving the dummy wire, a plurality of low friction elements mounted about the periphery

of said second drum adjacent the groove thereof for retaining the dummy wire in the groove

during advancement thereof into the catheter, and means for selectively connecting the drum

rotating means to one of said first and second wire storage drums.

5. The apparatus of claim 4, wherein said elements comprise rollers.

6. The apparatus of claim 4, including a head for receiving the housing, said

selective connection means and said rotating means being mounted in said head and extending

through said housing for selective engagement with said first and second wire storage drums.

7. The apparatus of claim 6, wherein said housing comprises a cartridge adapted to

be removably inserted into said head.

8. The apparatus of claim 1 , including a head for receiving the housing, said housing

comprising a cartridge adapted to be removably inserted into said head.

9. The apparatus of claim 8, wherein said head includes control system software and

including an electronics board mounted in said housing, said electronics board containing means

for updating the control system software.

10. The apparatus of claim 1 , including an emergency retract mechanism engageable with said wire storage drum for rotating said drum so as to retract the wire from the catheter in response to a loss of electrical power to said apparatus

11. The apparatus of claim 10, including means for automatically connecting the

emergency retract mechanism to the wire storage drum and means for energizing the emergency

retract mechanism in response to loss of electrical power to said apparatus or failure of the drum

rotating means.

12. The apparatus of claim 11 , wherein the automatic connection means includes a

solenoid which, when actuated, disengages the emergency retract mechanism from the wire

storage drum.

13. The apparatus of claim 10, including a head for receiving the housing, the

emergency retract mechanism being mounted in said head and extending through said housing

for engagement with said wire storage drum.

14. The apparatus of claim 11, wherein said energizing means comprises a battery

powered motor.

15. The apparatus of claim 4, wherein the grooves in said drums are helical grooves

and including a slider for taking off the wire from the groove of a respective drum, each slider

being mounted in at least one linear bearing for movement transversely across the periphery of

its respective drum, the wire in each groove passing through a hole in the slider associated therewith so that such slider takes the wire off its associated drum as such drum is rotated.

16. The apparatus of claim 4, wherein the wire on the first wire storage drum has a

radioactive source located adjacent the distal end thereof.

17. The apparatus of claim 16, including a radiation safe mounted in said housing,

means for guiding the wire from the first wire storage drum to the radiation safe and a radiation

detector in the radiation safe for detecting the presence of the radioactive source in the radiation

safe.

18. The apparatus of claim 17, including means for guiding the wire from the second

wire storage drum to said radiation safe.

19. The apparatus of claim 18 , wherein the means for guiding the wires from the wire

storage drums to the radiation safe comprise guide tubes extending between the drums and the

safe.

20. The apparatus of claim 7, including an emergency retract mechanism mounted in

said head and adapted to extend into said housing into engagement with said first wire storage

drum for retracting the wire from the catheter in response to loss of electrical power to said

apparatus or failure of the drum rotating means, and guide means cooperating between said head

and said housing for guiding said housing into position in said head for making engagement with

the drum rotating means and the emergency retract mechanism mounted in the head.

21. The apparatus of claim 10, wherein said emergency retract mechanism includes

means for preventing rotation of said drum in a direction to advance the wire into the catheter.

22. The apparatus of claim 21 , wherein said rotation prevention means comprises a

unidirectional bearing, and means connected to said emergency retract mechanism for manually

operating the emergency retract mechanism to retract the wire from the catheter.

23. The apparatus of claim 4, including limit stop means associated with each wire

storage drum for limiting the number of revolutions of each drum.

24. The apparatus of claim 23, wherein said limit stop means comprises a stack of

washers mounted concentrically to the rotational axis of each drum, each washer having an

overhanging tang engageable with the tang of an adjacent washer, at least one of said washers

being operative to actuate a first switch in a first direction of rotation of said drum and a second

switch in a second direction of rotation of said drum, the switches being operative to indicate or

control the number of revolutions of the drum in each direction.

25. The apparatus of claim 4, wherein said drum rotating means comprises a drive

motor with a rotational axis, said selectively connecting means comprising a drive gear rotatably

mounted adjacent one end of an engagement arm pivotable about an axis coincident with the

rotational axis of the drive motor, means connected to the other end of the engagement arm for

pivoting said arm and thereby urge said drive gear into operative driving engagement with one

or the other of said first or second wire storage drums.

26. A method of advancing an elongate wire into an out of a catheter implanted in a

patient, said wire having proximal and distal ends, comprising the steps of:

providing a wire storage drum having a periphery with a groove accommodating

the elongate wire, the proximal end of the wire being fastened to the drum;

rotating said drum in a direction to advance the wire out of the groove;

guiding said wire into said catheter; and

retaining said wire in said groove such that said wire is advanced from the drum

under compression in a low friction manner.

27. The method of claim 26, including the steps of providing an emergency retract

mechanism for retracting the wire from the catheter in an emergency, engaging the emergency

retract mechanism to the drum except during powered advancement of the wire into the catheter.

28. The method of claim 26, including the steps of providing a further wire storage

drum having a periphery with a groove accommodating a further elongate wire with proximal

and distal ends, the proximal end of the wire being fastened to the further drum, providing only

one drum rotating means, and selectively rotating one or the other of said drums with the drum

rotating means to advance or retract the wire accommodated in the groove of such drum.

29. A method of advancing an elongate wire into and out of a catheter implanted in

a patient comprising the steps of:

providing a housing containing first and second wire storage drums, each drum

having a periphery with a groove for accommodating a wire, the housing including means for -25- receiving one end of the catheter; providing a head containing a primary drive means for rotating the drums; inserting the housing into the head;

engaging the primary drive means with said first drum; and

rotating said first drum with the primary drive means in a direction to advance the

wire on said first drum into a catheter received in said catheter receiving means.

30. The method of claim 29, including the steps of rotating said first drum with the

primary drive means in a direction to retract the wire on said first drum from the catheter,

engaging the primary drive means with the second drum and rotating said second drum with the

primary drive means to advance the wire on said second drum into the catheter.

31. The method of claim 29, including the step of providing a radioactive source at

the distal end of the wire on said second drum.

32. Apparatus for advancing an elongate sourcewire into and out of a catheter

implanted in a patient, said sourcewire having a radioactive source at a distal end thereof,

comprising:

a cartridge comprising a housing and means for receiving one end of the catheter;

first and second wire storage drums mounted in said housing, said elongate

sourcewire being wrapped about said first drum, a dummy wire being wrapped about said second

drum;

a head member having means for receiving the cartridge; means in said head for rotating said first or second drums; means in said head for selectively engaging said rotating means with one or the other of said first and second drums when said cartridge is inserted into the receiving means in

said head.