Radiation delivery system and method

Surgery – Radioactive substance applied to body for therapy – Radioactive substance placed within body

Reexamination Certificate

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C424S001110, C424S001530

Reexamination Certificate

active

06500108

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to radiation delivery systems and more particularly, to a radiation delivery system and method for using the same for brachytherapy of benign, such as neointimal hyperplasia in coronary arteries (restenosis), or malignant proliferative disease.
BACKGROUND OF THE INVENTION
Restenosis is the recurrence of blood flow obstruction in blood vessels previously treated by percutaneous transluminal coronary angioplasty (PTCA), a medical procedure that improves vascularization of occluded blood vessels using a number of techniques that include catheter-based balloon expansion, stent placement, rotational artherectomy, laser ablation, etc. Although the exact mechanism that results in the production of restenosis is unclear, it is believed to involve neointimal or adventitia hyperplasia (i.e., cell proliferation), vascular recoil, inflammatory processes, or some combination thereof initiated by PTCA. Restenosis is reported to occur in 30 to 50 percent of all PTCA procedures, and follow-up treatment results in increased patient risks, complications, and health care costs (see Tilkian, A. G., and Daily, E. K. Cardiovascular Procedures. Diagnostic Techniques and Therapeutic Procedures. C. V. Mosby Company, St. Louis, Mo. 1986, ISBN 0-8016-4965-X, hereby incorporated by reference).
Intravascular brachytherapy (IVB), a medical procedure involving the delivery of a therapeutic dose of radiation to a tissue portion subsequent to PTCA treatment, shows great promise in reducing the rate of subsequent restenosis.
Typically, a radiation delivery system (RDS) is used for IVB that includes a PTCA catheter-based device such as a stent, balloon catheter, ribbon, wire, etc. that has been modified to include an attached radioactive material. (see Alice K. Jacobs in “Selection of Guiding Catheters, Practical Angioplasty, David Faxon ed., Raven Press, New York, 1993, hereby incorporated by reference).
FIG. 1
shows a process flow chart describing the IVB process. Briefly, the RDS is used it irradiate a lesion following an angioplasty procedure. The RDS is inserted into the guiding catheter and into the body, and passes through the same blood vessels as during the angioplasty procedure. The RDS is positioned near the lesion and allowed to remain there until the radioactive element can provide a therapeutic radiation dose across the lesion.
Results from clinical trials indicate that IVB treatment of blood vessels with a radiation dose of about 15-30 Gray (Gy; 1 Gy=100 rads) significantly reduces the rate of restenosis after PTCA. Table 1 describes several radiation delivery systems that can be used for IVB.
TABLE 1
Radiation Delivery Systems for Intravascular Brachytherapy
Radionuclide
and method of
RDS
production
Advantages
Disadvantages
Gamma
192
Ir
Uniform dose distribution
Offsite production
wire
neutron
Small RDS diameters can
of
192
Ir
activation
pass through narrow
Long Treatment
vessels
times
Re-usable
Radiation hazard
to staff (
192
Ir is a
high energy &ggr;
source)
Beta
90
Y
Minimal radiation hazard to
Offsite production
wire
neutron
staff (90Y is a high energy
of
90
Y
activation
beta-emitter
Long treatment
Re-usable
times
Weekly delivery
Beta
90
Sr/
90
Y
Minimal radiation hazard to
Offsite production
source
fission
staff since
90
Y is a beta-
Large RDS
train
product
emitter
diameters limit
Re-usable
use with small
vessels
Coated
32
P
stent can be left in place
Offsite production
stent
fission
Minimal radiation hazard to
&bgr; energy may be
and/or
product
staff
too low
balloon
Frequent source
exchanges
Liquid-
186
Re or
188
Re
High Energy &bgr;-emitter
Contamination
filled
neutron
188
Re is available readily
hazard
balloon
activation
from a tungsten generator
Radiation hazard
188
W generator
to staff
Frequent source
exchanges
Gas-
133
Xe
133
Xe is a commonly used
&bgr; energy of
133
Xe
filled
fission product
radionuclide
may be too low
balloon
Special ventil-
ation required for
radioactive gas
Examples of the coated stent and/or balloon, and the liquid filled balloon, are described in U.S. Pat. No. 5,730,698 to R. E. Fischell entitled “Balloon Expandable Temporary Radioisotope Stent System”, which issued Mar. 24, 1998. The '698 patent describes an over-the-wire balloon angioplasty catheter having a balloon surrounded by a reversibly deployable stent system. The balloon can be filled with a radioactive liquid, or the balloon and/or stent can be embedded or implanted with a radioactive material, such as
32
p.
Some delivery systems, like the one described in the '698 patent, involve the insertion and removal of the RDS, while others include a detachable portion, such as a detachable stent, which remains in the body and continues to irradiate tissue after the rest of the device has been removed.
Radiation delivery systems are generally not manufactured at the treatment center, i.e. the hospital, clinic, or the like. This is unfortunate since the most desirable radionuclides cannot be used because they have relatively short half lives (hours) and would decay significantly during shipping. Radiation delivery systems are, therefore, limited to radionuclides with intermediate to long half-lives of days, weeks, or even longer.
Longer lived radionuclides have lower specific activities (SA), and present additional problems with RDS storage, handling and waste disposal. Some beta emitting and gamma emitting radionuclides and their specific activities are listed in Table 2.
TABLE 2
Specific Activities of Radionuclides
Beta Emitter
SA (Ci/g)
Gamma Emitter
SA (Ci/g)
32
P
2.88 × 10
5
57
Co
8.54 × 10
3
89
Sr
2.81 × 10
4
67
Ga
6.04 × 10
5
90
Sr
1.45 × 10
2
99m
Tc
5.33 × 10
6
90
Y
5.50 × 10
5
103
Pd
6.74 × 10
4
91
Y
2.47 × 10
4
109
Cd
2.62 × 10
3
131
I
1.25 × 10
5
111
In
4.24 × 10
5
133
Xe
1.89 × 10
5
123
I
1.93 × 10
6
170
Tm
5.79 × 10
3
125
I
1.75 × 10
4
186
Re
1.92 × 10
5
131
Cs
1.04 × 10
5
188
Re
9.97 × 10
6
145
Sm
2.68 × 10
3
204
Tl
 4.6 × 10
2
153
Gd
3.56 × 10
3
210
Bi
1.25 × 10
5
169
Yb
2.46 × 10
4
192
Ir
9.29 × 10
3
197
Hg
2.51 × 10
5
201
Tl
2.16 × 10
5
There are clear advantages to a RDS that could be produced at or near the treatment center with short lived, high SA radionuclides. Short-lived radionuclides would allow administering the therapeutic dose over a short period of time, minimizing hazards to the patient, hospital workers, and anyone else handling the RDS. In addition, the clinician could select the treatment configuration of the RDS (balloon catheter, stent, guidewire, etc.) and the type of radiation (beta and or gamma radiation) at the treatment center and prepare the RDS immediately prior to use. The RDS geometry could then be based on actual patient parameters, such as the exact length of the lesion and vessel diameter, rather than the manufacturer predetermined parameters necessitated by offsite production.
Therefore, an object of the invention is a radiation delivery system that can deliver an effective dose of radiation to a tissue.
Another object of the invention is a radiation delivery system that can pass through narrow blood vessels.
Another object of the invention is a radiation delivery system that can be uniquely prescribed for a given patient and then manufactured and used at the treatment center.
Another object of the invention is a radiation delivery system that employs short-lived radionuclides with a high specific activity.
Yet another object of the invention is a radiation delivery system that remains intact after delivering a radiation dose to a tissue.
Still another object of the invention is a radiation delivery system that can be used for benign, such as neointimal hyperplasia in coronary arteries (restenosis), and malignant proliferative disease.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in

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