Surgery – Radioactive substance applied to body for therapy – Radioactive substance placed within body
Reexamination Certificate
2000-11-17
2003-06-10
Jones, Melvin (Department: 3744)
Surgery
Radioactive substance applied to body for therapy
Radioactive substance placed within body
Reexamination Certificate
active
06575887
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a surgical implant for the localized application of radiation therapy, more particularly to a surgical implant intended for the prophylactic treatment or the mitigation of partial or total blockages in vessels, body ducts or other tubular body structures.
DESCRIPTION OF THE RELATED ART
A number of medical problems are the result of overexuberant cellular proliferation in tubular body structures. A large proportion of end-stage renal disease (ESRD) patients use an implanted synthetic vascular graft to provide vascular access for dialysis treatment. Palder S R, Kirkman R L, Whittemore A D, et al., Vascular Access for Hemodialysis. Patency Rates and Results of Revision., Ann. Surg., 1995; 202: 235-239, discussed that these grafts typically fail in 14-19 months with a reported primary occlusion rate of 15-50% at one year. Bethard G A, Mechanical Versus Pharmacomechanical Thrombolysis for the Treatment of Thrombosis of Dialysis Access Grafts, Kidney Int., 1994; 45: 1401-1406, demonstrated clinically that, most graft failures result from thrombosis (80-90%); and in turn, the thrombosis is typically caused by a low flow condition, most frequently (>90%) stenosis at the graft/vein anastomosis. The stenosis is the result of an overexuberant cellular proliferation that has been observed following other vascular interventions including angioplasty and synthetic graft placement. It is this failure rate, and the attendant need to repair or replace the vascular access that generate the high costs and hospitalization rates associated with the management of the ESRD patient.
A similar intimal hyperplasia phenomenon has prevented the adoption of small diameter synthetic vascular grafts for use in coronary artery bypass surgery. Other conditions requiring treatment include the growth or regrowth of tumor tissues on or adjacent to body vessels, ducts and passageways.
To date, approaches to removing narrowings and blockages from body passageways have been both mechanical and pharmacological. Although many of these treatments are successful in the immediate goal of restoring flow through the duct or vessel, they do not always treat the underlying cause of the stenosis; and reclosure may occur after a short period. Treatments that involve various medical devices include balloon angioplasty, embolectomy, surgical excision or by-pass, clot aspiration and intravascular stent implantation. In contradistinction to the present invention, most of these interventions are typically undertaken to treat an existing stenosis and not as prophylactic or preventative treatments. As such, they present the risks of a secondary surgical procedure in addition to the risks and potential adverse reactions associated with the primary procedure.
Pharmocologic therapy includes the use of various “blood-thinners” or anti-thrombotic agents. These powerful drugs are not suitable for all patients and are associated with a high risk of complication related to uncontrollable bleeding. While these drugs can often dissolve newly formed clots, they are less effective in removing established thrombus and have no impact on the overexuberant cellular proliferation (intimal hyperplasia) which may be the root cause of the stenosis.
With the acknowledged inadequacy of current stenosis and restenosis prevention techniques, the medical community has initiated experimental studies with a variety of local radiation delivery devices. It has been well established that radiation therapy is of value in mitigating exuberant cellular proliferation as in the case of cancer radiotherapy. More recent investigations have demonstrated the potential usefulness of various intravascular radiation delivery devices; however, no devices or treatments have thus far been developed specifically for the purpose of localized delivery of radiotherapy to tubular body structures by means of a circumferential wrap.
Some relevant proposed treatment means define devices that can be prepared in the form of sheets or films that are intended for use in essentially planar form. U.S. Pat. No. 4,946,435, describes a film sealed in an envelope. The device is flexible and can be conformed to provide radiation treatment to irregular contours. This patent discloses a polymeric radiation carrier film enclosed in a polymeric envelope. The patent describes a laminated structure but does not disclose use of a radiation attenuation element adjacent to the radioactive surface. Liprie describes a continuous radioactive sheet in U.S. Pat. No. 5,322,499. This device is defined to have an iridium/platinum core that is more rigid than an outer sealing coating. This soft outer cover is designed to allow the radioactive sheet to be cut into smaller sealed segments, thus creating sizes and essentially planar shapes suited for a particular application. This patent does not disclose the use of either an integral shield to protect non-targeted tissues or a radiation attenuation element to provide for a more even radiation dose gradient. In U.S. Pat. No. 5,342,283. Good describes radioactive microspheres that can be used to coat flexible substrates for use in the treatment of disease. This patent also does not disclose the use of either an integral shield to protect non-targeted tissues or a radiation attenuation element to provide for a more even radiation dose gradient. Park et al. describe a radioactive patch/film in U.S. Pat. No. 5,871,708. This device is designed to treat various kinds of cancers and dermal disease and consists of a laminated structure in which the radiation layer is not integral to the carrier film. This patent does not describe either a shield or a radiation attenuation element. None of the above mentioned patents contemplate treatment of obstructions in tubular body structures.
Some of the proposed radioactive devices were designed to provide radiation treatment as adjunctive therapy to coronary angioplasty procedures. A majority of coronary angioplasty procedures have been augmented with the placement of intravascular stents. One such device is described in U.S. Pat. No. 4,733,655 et seq. by Palmaz. These devices have improved six-month restenosis rates from nearly 40% to approximately 25%. Stents have also been placed across the graft/vein junction of failed dialysis access grafts as part of the effort to reopen the stenosed or occluded access grafts. Probably because the stent is placed across the return flow of blood at the juncture of the graft and the natural vein, success has been limited; and 50% of the stented grafts reclose within six months. Radioactive stents are currently being clinically studied as a potential improvement to non-radioactive stent placement following coronary angioplasty. The application of radioactive stents is described in U.S. Pat. No. 5,059,166. Early results seem to support use of the radioactive stents in conjunction with angioplasty, and six-month restenosis rates of less than 15% are being reported. However, radioactive stents will also physically obstruct flow in dialysis grafts.
Alternate treatment approaches for coronary artery restenosis involve the use of radioactive catheters or wires as part of the angioplasty procedure. These devices also require the use of a vascular puncture for access; but unlike the stent, do not involve permanent implantation of a device. The catheter type devices position an array of radioactive seeds or pellets at the site of the angioplasty for several minutes following the balloon angioplasty procedure. One example of a catheter type device has been described in U.S. Pat. No. 5,540,659. These devices deliver a single exposure dose; and thus present a much higher radioactivity dose rate than a stent implant that delivers radiation over a much longer time. This factor has raised radiation safety issues. Because the normal healing process following graft placement is quite different from the healing process following angioplasty it is unlikely that a one-time treatment with a catheter or wire device would be effective for use in treating graft related
Epsilon Medical, Inc.
Jones Melvin
Nissim Stuart H.
Woodbridge Richard C.
Woodbridge & Associates P.C.
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