Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-06-26
2001-08-14
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S467000
Reexamination Certificate
active
06273858
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to systems and methods devices for providing radiation therapy and, more particularly, to systems and methods for providing radiation therapy for the prevention of restenosis. According to another aspect, the invention generally relates to catheter guides for enabling clinicians to determine location or orientation of catheters.
BACKGROUND OF THE INVENTION
A leading cause of death in the western world is atherosclerosis. More than thirteen million people in the United States have been diagnosed with this disease with a large number of patients having arteries or veins that have become narrowed and need to be enlarged. Angioplasty, a common technique to enlarge an artery or vein, is an interventional radiologic technique in which a narrowed artery or vein is enlarged with the use of a balloon angioplasty catheter.
To perform an angioplasty, an angiogram is used to obtain a precise image of the narrowed artery or vein. A catheter is inserted into a blood vessel and is guided to the site of the narrowing with an X-ray monitor. A contrast medium is injected through the catheter and a series of X-ray images are obtained to outline the blood vessel. The images obtained from the X-ray are used to identify and measure the abnormal narrowing of the blood vessel. The initial catheter used for diagnostic purposes is then removed and a catheter having an inflatable balloon around its shaft is inserted. The balloon is inflated in the narrowed portion of the vessel to widen the artery or vein. In some cases, a metallic stent is placed within the blood vessel in order to widen the blood vessel.
Although the initial success rate is high, the long-term success rate of angioplasty is unfortunately rather low and a subsequent procedure is often necessary. It has been estimated that nearly 25-45% of the 450,000 coronary angioplasties done in the United States each year fail within the first few months of the operation. Restenosis is defined to be the reclosing of the artery or vein to less than 50% of its original size. Because of restenosis, an additional angioplasty or another procedure, such as bypass surgery, is necessary to reopen the blood vessel. The need for subsequent procedures has a traumatic effect on the patient and on those concerned about the patient's health and additionally greatly increases medical costs. In fact, the cost to the health care system in the United States for subsequent procedures has been estimated to be 2 billion dollars annually.
The problems associated with restenosis are not limited only with an angioplasty procedure but also occur with other coronary revascularization procedures. Restenosis, for instance, is also associated with rotoblator, atherectomy catheters, hot and cold laser catheters, transluminal extraction catheters, and ultrasonic ablation. The magnitude of the problem caused by restenosis is therefore quite extensive.
Restenosis is difficult to prevent since its cause is not completely understood. Restenosis, however, is believed to be primarily caused by intimal hyperplasia and negative remodeling, and, to a lesser extent, elastic recoil. Angioplasty, as well as other revascularization techniques, expose the medial smooth muscle of the blood vessel to circulating mitogenic factors when the artery is dilated. As a result of platelet degranulation, growth factors are released which induce mitogenesis and promote proliferation of cells. Vascular smooth muscle cells consequently migrate into the intima, where they synthesize collagen and elastin, which comprise the bulk of the restenotic lesion.
One approach to combating restenosis is through drug therapy. Some agents tested in restenosis trials include antiplatelet agents, anticoagulants, thromboxane antagonists, prostanoids, calcium channel blockers, ACE inhibitors, antiproliferative growth factor inhibitors, lipid lowering agents, vitamins and antioxidants, and corticosteroids and non-steriodial A. Another agent that has been used to prevent restenosis is hyaluaronic acid. The use of hyaluaronic acid is shown and described in U.S. Pat. No. 5,614,506 to Falk et al., the disclosure of which is incorporated herein. The use of agents to block restenosis has generally been met with failure or at most limited success. The drug trials involving these agents have been fraught with problems such as incomplete angiographic follow-up, variable definitions of restenosis, small sample sizes, and varying drug dosage.
Another approach used to combat is the use of a stent. A polymer stent, for instance, is placed within the treated blood vessel and delivers medicine to the damaged blood vessel. The polymer stent need not be removed since it naturally dissolves after the blood vessel has been repaired. Stents have produced promising results in that they appear to significantly reduce the rate of restenosis by approximately 10%. Studies of stent usage, however, have revealed undesirable side effects, such as an increased incidence of bleeding complications associated with stent implantation. Stents unfortunately are unable to completely eliminate restenosis and a need exists for a treatment method that even further reduces the rate of restenosis.
An emerging and promising treatment for coronary restenosis is intracoronary radiation therapy (ICRT). In general, intracoronary radiation therapy delivers radiation to a damaged area of the blood vessel to prevent restenosis. A delivery catheter allows a radiation source to be delivered to the angioplasty site where it remains for a number of minutes before being withdrawn. The radiation source may be a line or “train” of several miniature cylindrical sealed sources containing a radioactive material, such as Sr-90, Ir-192, I-125, or Re-186. Rather than a train of radiation sources, other irradiation delivery techniques include radioactive seeds or pellets, radioactive wires, intravascular x-ray sources, and liquid-filled balloons emitting particulate or electromagnetic radiation. A radiation source never comes in contact with the patient's tissue or blood and a transfer device shields the radiation from health care workers during its handling. One advantage of intracoronary radiation therapy is that it typically adds less than ten minutes to the total procedure time and is easily incorporated within the cath lab. An example of an intracoronary radiation therapy is shown and described in U.S. Pat. No. 5,683,345 to Waksman et al., the disclosure of which is incorporated herein.
Trials of intracoronary radiation therapy have produced promising results. In one trial, for instance, one-half of a group of patients received gamma radiation and the other half received placebo treatment while all of the patients in this trial had a coronary stent. The preliminary results of the study showed that the treated group had a restenosis rate of 17%, compared with a restenosis rate of 54% in the non-treated group. Intracoronary radiation therapy has also shown to be preferable over the use of a stent. For instance, coronary stents typically produce a late loss index of 25 to 30%, meaning that on average 70 to 75% of the initial improvement in lumen diameter achieved by angioplasty was still present six months later. In contrast, a study involving intracoronary radiation therapy reduced the late loss index to only 5%, meaning that on average 95% of the initial improvement in lumen diameter was still present six months later. When only those patients receiving a higher dosage of radiation were evaluated, the late loss index dropped to zero. This study therefore suggests that with proper dosing level, additional devices or therapies should not be necessary.
The success of the intracoronary radiation therapy trials also point to shortcomings of the therapy. As discussed above, the success of intracoronary radiation therapy depends upon the proper dosage level with dosimetry measured in the sub-millimeter range being essential to optimally prescribing and delivering the radiation to the lesion. Proper dosing is difficult
Crocker Ian R.
Fox Timothy H.
Emory University
Imam Ali M.
Kilpatrick & Stockton LLP
Lateef Marvin M.
Pratt John S.
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