Surgery – Radioactive substance applied to body for therapy – Radioactive substance placed within body
Reexamination Certificate
1997-11-03
2001-07-24
Lacyk, John P. (Department: 3736)
Surgery
Radioactive substance applied to body for therapy
Radioactive substance placed within body
Reexamination Certificate
active
06264596
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to intra-vascular stents. More specifically, the present invention is related to a non-radioactive stent capable of being made radioactive in-situ, after placement within a blood vessel. The stent can be used to inhibit restenosis of blood vessels.
BACKGROUND OF THE INVENTION
Coronary arteries provide blood and nutrients to the heart muscle. The arteries are subject to atherosclerosis or hardening of the arteries. Vascular regions have plaques formed within, resulting in stenosed regions having reduced cross-sectional area. The reduced area causes a reduction in transport of blood, oxygen, and nutrients which can result in angina, myocardial infarction and death.
A commonly used method for treating atherosclerosis is Percutaneous Transluminal Coronary Angioplasty (PTCA). PTCA includes insertion of a balloon catheter through an incision in the femoral artery near the groin, advancement of the balloon over the aortic arch, further advancement within the selected coronary artery, continuing until the balloon portion is placed across the stenosed region. The balloon is inflated, widening the narrowed vessel region.
After catheter withdrawal, significant vessel reclosure may develop. The reclosure may occur within hours or days of dilation, an “abrupt reclosure.” When reclosure does occur, however, it more commonly occurs progressively, within six months of the angioplasty. The gradual reclosure is referred to as “restenosis”, and largely negates the dilatation treatment. More highly stenosed vessel regions have a greater chance of becoming restenosed.
One approach to dealing with restenosis utilizes stents which are short tubular sections having a lumen therethrough, placed across the recently dilated vessel region. Stents can be either self-expanding or balloon-expandable. Stents are normally left in place indefinitely.
Use of radiation to kill and inhibit growth of cancerous cells is well known. The use of radiation to inhibit restenosis has been proposed. Use of a catheter having a radioactive source on the distal end has been proposed in U.S. Pat. No. 5,199,939 (Dake et al.). The catheter must be held in place during the entire therapy, which is considerably shorter than the months long period over which restenosis is believed to occur. Any radiation delivered must be delivered within the short period the catheter tip is in place. U.S. Pat. No. 5,059,166 (Fischell et al.) proposes using a radioactive stent. As a stent can be left in place indefinitely, the radiation exposure period more closely matches the time period over which restenosis can occur.
Use of a radioactive stent can present drawbacks. A radioactive stent can require shielding both during storage and during placement within the patient. During stent placement, the stent is normally mounted within a delivery device and inserted into the vasculature of the patient. A common entry site is an incision in the femoral artery near the groin. The stent placement procedure is typically performed with several medical personnel present who require shielding if the radiation source is sufficiently strong.
Radioactive stents can have a shelf-life limitation, especially when the radioisotope has a half-life on the same order as the expected shelf life. For example, a stent made radioactive with an isotope having a half-life of about a month will lose half its radioactivity in a month on the shelf. This can present a variation in radiation strength dependent upon the time a stent resides in a warehouse or sits unused in a hospital. The half-life of a radioisotope, if sufficiently small, can preclude its use with stent technology if a significant portion of radioactivity is lost during stent manufacture, shipping and storage. Another limitation with current stent technology is that the stent radioactivity must be decided at the time of manufacture rather than treatment.
What remains to be provided is a method for delivering concentrated radiation at a dilated, stented site without requiring placement of a radioactive stent. What remains to be provided is a device allowing placement of a non-radioactive stent within the vasculature which can be made radioactive in-situ, after placement.
SUMMARY OF THE INVENTION
The present invention includes devices and methods for inhibiting restenosis of blood vessels using stents. The stents are non-radioactive when placed within the blood vessel and are made radioactive in-situ, after placement within the vessel. Stents according to the present invention are adapted to bind a radioactive substance which is preferably injected into the blood stream after stent placement. The stent preferably has a strong and selective affinity for binding the radioactive substance. A preferred stent attains the binding affinity by having a first substance immobilized on the stent surface, where the first substance is adapted to bind the later-to-be injected radioactive substance. The injected radioactive substance is bound to, and is collected at, the stent, thereby concentrating radiation over the stent.
A preferred stent is tubular in shape and has a stent body, with the first substance immobilized on the stent body. In one embodiment, the first substance is avidin and the second substance is radioactive or radio-labeled biotin. In another embodiment, the first substance is protamine and the second substance is radio-labeled heparin. Protamines are strongly basic proteins of relatively low molecular weight. Heparin is an acid mucopolysaccharide. Protamine and heparin also exhibit a highly selective affinity for each other. Other complementary pairs within the scope of the invention include proteins/antibodies, ligands/anti-ligands, and proteins/monoclonal antibodies.
In use, the stent, either self-expanding or expandable, can be put into place using well known devices such as pusher tubes or stent delivery balloon catheters. Stents are preferably put into position after a stenosis dilation procedure such as angioplasty or atherectomy. A preferred use of the stents is the inhibition of restenosis in coronary arteries after angioplasty. After the stent expands into position across a stenosed vessel region, the stent delivery equipment can be removed from the patient. If desired, the patient can be removed from the site of the dilation procedure.
The second, radioactive substance can then be provided, preferably in shielded form. In one method, a shielded hypodermic syringe is provided. In another method, the radioactive substance is injected into an I.V. bag. The radioactive substance can be injected into the blood stream of the patient using any suitable injection means and body site. The radiation exposure can thus be limited to a short time period and a small, easily shielded area. The number of people exposed to the radiation and possibly requiring shielding can be much more limited during an injection than during a stent placement procedure in an operating room. In particular, only radiation medicine personnel need be present during injection.
After injection, the radioactive substance circulates through the blood stream of the patient, with a portion passing through a stented site such as a coronary artery. With each pass through the stent, a substantial amount of the radioactive substance is bound to the stent. Over time, a substantial portion of the radioactive substance is selectively bound to the stent, thereby rendering the stent radioactive and providing radiation to the vessel and inhibiting restenosis. The remainder of the radioactive substance is processed by the liver and excreted in urine. The present invention can be provided as a stent suitable for later injection of a complementary radioactive substance, or as a kit having both stent and complementary radioactive substance.
In one method, radioactive substance is injected one time after stent implantation. The amount of radiation to be delivered can be decided at the time of injection. In another method, radioactive substance can be injected multiple times, over a longer time period.
Crompton Seager & Tufte, LLC.
Lacyk John P.
Meadox Medicals Inc.
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