Low attenuation guide wire for intravascular radiation delivery

Details Low attenuation guide wire for intravascular radiation delivery Low attenuation guide wire for intravascular radiation delivery

1999-10-07

2001-03-20

Gilbert, Samuel G. (Department: 3736)

Surgery

Radioactive substance applied to body for therapy

Radioactive substance placed within body

C600S585000

Reexamination Certificate

active

06203485

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to devices and methods for intravascular ionizing radiation therapy. More specifically, the present invention relates to improved guide wires for intravascular ionizing radiation therapy.
BACKGROUND OF THE INVENTION
Intravascular ionizing radiation therapy is being used increasingly to treat vascular disease, and has been proposed as both a primary and a secondary therapy for treating vascular restrictions. Clinical studies have shown that ionizing radiation may be effectively used to inhibit or prevent restenosis after percutaneous translumenal coronary angioplasty (PCTA). For example, U.S. Pat. No. 5,643,171 to Bradshaw et al disclose a method and apparatus for intravascular radiotherapy for prevention of restenosis following angioplasty or other procedures that cause smooth cell proliferation.
As best seen in
FIG. 1
of Bradshaw et al., a catheter
10
is illustrated having an elongate shaft
12
with a distal treatment section
14
and a distal tip
16
. Attached to the distal treatment section
14
is a centering balloon
40
. The elongate shaft
12
also includes a treatment channel
20
as best seen in FIG.
2
. The treatment channel
20
allows for the introduction of a source wire (not shown) having a distal radioactive section. With this design, the catheter
10
allegedly maintains the treatment channel
20
, and thus the source wire, in the center of the vessel, despite vessel curvature in the region the vessel being treated, for uniform delivery of radiation.
One disadvantage of this particular design is the arrangement of the catheter
10
relative to the guide wire
32
, which may block radiation from reaching the vessel wall
30
. In particular, the shaft
12
includes a distal Monorail®-type guide wire lumen
24
that allows the catheter to be advanced over the guide wire
32
until the treatment section
14
is disposed in the target area
34
of the blood vessel
30
. The distal Monorail®-type lumen
24
opens at the distal tip of the shaft and exits through the lateral surface of the shaft
12
distal of the balloon
40
. Thus, the guide wire
32
extends adjacent the catheter
10
and centering balloon
40
at the target area
34
of the blood vessel
30
.
Because guide wires are conventionally formed of metal alloys such as stainless steel, the guide wire
32
will tend to attenuate radiation emitted by the source wire disposed in the treatment channel
20
. Attenuation of the radiation causes a shadow to be cast on the vessel wall
30
in the target area
34
such that a portion of the target area
34
is not uniformly exposed to ionizing radiation. Failure to expose the entire target area
34
to ionizing radiation may give rise to restenosis at the unexposed or underexposed region. The recurrence of restenosis anywhere in the target area
34
is clearly disadvantageous since the primary objective of the therapy is to prevent or otherwise inhibit restenosis.
The initial response to solving this problem may be to move (e.g., retract or withdraw) the guide wire
32
to avoid blocking radiation. However, retraction of guide wire in the proximal direction such that the guide wire
32
does not extend across the target area
34
, is not a particularly viable option because vascular access across the target area
34
would be lost and access to the guide wire lumen
24
at the distal tip of the shaft
12
would also be lost. In many instances, it is undesirable to lose vascular access across the target area
34
since the restriction may recoil rendering it difficult if not impossible to renavigate the guide wire
32
across the target site
34
. Without the guide wire
32
disposed across the target area
34
, it would be difficult to redilate or otherwise treat the vascular restriction. In addition, losing access to the guide wire lumen
24
makes it difficult, if not impossible, to steer or guide the catheter
10
through the vascular channel. Thus, it is extremely undesirable to retract the guide wire
32
in the proximal direction. Because it is undesirable to retract the guide wire
32
in the proximal direction, the guide wire
32
must be left in place where it will inevitably attenuate radiation emitted from the source wire .
SUMMARY OF THE INVENTION
The present invention overcomes these disadvantages by providing a low attenuation guide wire for use in combination with a radiation device (e.g., source wire) having a distal portion emitting ionizing radiation. The guide wire includes a proximal region and a distal region, wherein the distal region is less attenuating to ionizing radiation than the proximal region. The distal region of the guide wire may remain disposed adjacent the distal ionizing radiation emitting portion of the radiation device without significantly compromising the emission or absorption of radiation. Thus, the guide wire does not need to be removed or retracted in order to effectively deliver ionizing radiation to the vascular target site. This is particularly beneficial when it is desirable to maintain vascular access across the target site and when it is desirable to use rapid exchange type catheters (e.g., Monorail® catheters).
The distal region may be less attenuating to low energy gamma, high energy gamma, and/or beta radiation, depending on the material(s) selected and the attenuation characteristics desired. The material(s) selected may have a lower atomic number, a lower atomic weight, and/or a lower density than the proximal region, also depending the attenuation characteristics desired for different types of ionizing radiation. The region less attenuating to ionizing radiation may comprise one or more polymers, metals, or composites thereof. Preferably, the distal end of the distal region is relatively more radiopaque to facilitate radiographic visualization and fluoroscopic navigation.


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