Surgery – Radioactive substance applied to body for therapy – Radioactive substance placed within body
Reexamination Certificate
1999-04-26
2001-11-20
Lacyk, John P. (Department: 3736)
Surgery
Radioactive substance applied to body for therapy
Radioactive substance placed within body
Reexamination Certificate
active
06319188
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns treatment of vascular walls to prevent restenosis after balloon angioplasty and/or stent implantation, and particularly the invention concerns a catheter with an X-ray tube at its distal end, for performing such treatment.
As a treatment for coronary artery disease, balloon angioplasty, or percutaneous transluminal angioplasty has been used on an increasing basis. In a great number of cases, often estimated at up to 50 percent, restenosis occurs at the site where the angioplasty was administered. Restenosis is the re-closing of arteries after balloon angioplasty and/or stenting. The re-closing is caused by a hyperproliferative cellular response to the balloon and stent injuries. The scarring of the vessel can be sufficiently severe to obstruct blood flow through the vessel. As one type of countermeasure, stents have recently come into wide use, the stent being a metal, tubular vascular prosthesis which is implanted after angioplasty to mechanically hold the vessel lumen open. However, even with a stent in place, in-stent restenosis still tends to occur in more than 25 percent of cases.
Drugs have been suggested and tried for the purpose of preventing or limiting restenosis. These include heparin, dexamethasone and integralin, as well as others. These drugs have generally comprised anticoagulants and arterial smooth muscle proliferation inhibitors as well as agents to prevent aggregation of platelets. Catheters have been suggested for helping assure that the drug is applied directly to the site in question. Effective local application of such drugs is difficult and generally unproven as to effectiveness.
Radiation is known to be effective in reducing restenosis after angioplasty. This has been done using a radioactive isotope mounted on the tip of a catheter, emitting gamma or beta radiation, inserted into the vessel until the emitter is at the lesion location. Problems with the use of radioactive isotopes may include the need for a shielded operating room, with special care and handling of the radioactive sources and the catheter and problems of disposal; the effect of the radiation throughout the length of the blood vessel through which it is inserted, when only one particular site is desired to be irradiated; and inadequate control of the depth of penetration of the radiation from the isotope sources.
See, for example, U.S. Pat. No. 5,199,939 disclosing a catheter with a radioactive source for irradiating an angioplasty site to prevent restenosis.
U.S. Pat. Nos. 4,143,275, 5,153,900, 5,428,658, 5,422,926, 5,442,678, 5,452,720, 5,621,780, RE34,421, and PCT Publication WO 97/7740 all disclose X-ray devices for delivering radiation to remote positions in the body, including narrow passageways as small as blood vessels. Thus, these latter patents and publications describe radiation emitters which can be switched on and off, not involving use or handling of radioactive isotopes. Several of these patents describe probes with fiber optic cables leading to X-ray tubes, the fiber optic designed to carry light which activates a photo cathode in the tube. To date none of these proposed X-ray delivery devices has been built and effectively used in the human vascular system. Problems of X-ray absorption, sufficient power, lengthy treatment times, and bonding and sealing of the X-ray tube to the catheter have not been adequately addressed in the prior art.
SUMMARY OF THE INVENTION
The present invention is a vascular catheter having an X-ray tube as a distal end, sufficiently small and flexible to be inserted through a vein or artery to reach an intended treatment site, such as in the coronary arteries of a patient. The X-ray catheter is capable of delivering X-ray radiation of sufficient power to treat the vascular walls to prevent restenosis, particularly following balloon angioplasty. In the X-ray tube itself, the walls are highly insulative and at the same time highly transmissive to X-ray radiation. The level of X-ray radiation is sufficient to achieve the needed radiation dosage within a short period of time, such as within ten minutes.
In a preferred embodiment of the invention, a vascular X-ray catheter comprises a flexible optical fiber having a bore through its length, a first electrical conductor extending through the bore of the fiber, a second conductor on the outer surface of the fiber, and an essentially cylindrical tube formed of insulative and X-ray transmissive material secured on the distal end of the optical fiber. The tube has a proximal end secured in sealed connection to the outer wall of the fiber, at a position slightly back from the end of the fiber, and the tube has a distal end, thus defining a vacuum chamber within the tube. A cathode is secured to the end of the optical fiber within the tube, the cathode being electrically connected to the first conductor in the bore of the fiber. The cathode is a thermionic cathode, excitable by heat to emit electrons. Within the tube and near its distal end, an anode is positioned, the anode comprising a target for emitting X-rays when bombarded by electrons. At the proximal end of the optical fiber is an optical radiation emitting device, such as a diode laser, for delivering optical radiation through the optical fiber of sufficient power to heat the cathode so as to emit electrons.
In a preferred embodiment the diameter of the tube, which is greater than that of the optical fiber, is no greater than about 1.5 mm.
The invention also encompasses a method of use of the vascular catheter, for preventing restenosis within the lumen of a vascular element of a patient, particularly following angioplasty. The method includes advancing the X-ray catheter through the patient's lumen to a desired location at a site of the lumen to be treated, then activating an X-ray tube at the tip of the catheter by directing optical radiation through the flexible catheter shaft, which comprises an optical fiber, while also establishing through conductors carried by the catheter an electrical potential between a cathode and an anode within the X-ray tube. The cathode is secured to the end of the optical fiber and comprises a thermionic cathode, emitting electrons when excited by heat resulting from the optical radiation impinging on the cathode. According to the method the X-ray tube is activated for a period of time effective to deliver an appropriate dose of X-ray radiation to the vessel wall to prevent or retard restenosis. The X-ray tube is then deactivated and the catheter is removed.
REFERENCES:
patent: 5090043 (1992-02-01), Parker et al.
patent: 5428658 (1995-06-01), Oettinger et al.
patent: 6108402 (2000-08-01), Chornenky
Cadugan Joseph A.
Freiburger Thomas M.
Lacyk John P.
Xoft microTube, Inc.
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