Surgery – Radioactive substance applied to body for therapy – Radioactive substance placed within body
Reexamination Certificate
1999-08-02
2001-07-24
Lacyk, John P. (Department: 3736)
Surgery
Radioactive substance applied to body for therapy
Radioactive substance placed within body
C600S008000
Reexamination Certificate
active
06264598
ABSTRACT:
BACKGROUND OF THE INVENTION
Radioactive seeds are routinely implanted to treat cancers, such as prostate cancer. The radioactive elements iodine-125, which has a 60-day half-life and emits a 31 keV x-ray, and palladium-103, which has a 17-day half-life and emits a 21 keV x-ray, both emit only soft x-rays from electron capture decay and are widely used in seeds for this type of radiotherapy.
Co-pending U.S. patent application Ser. No. 09/047,728 teaches a method of ion-implanting the precursor isotope Xe-124 into an aluminum pellet and subsequently activating the Xe-124 in a nuclear reactor to produce I-125 embedded beneath the surface of the aluminum pellet. Using this method for a palladium seed, however, would be extremely expensive because palladium which has been extensively enriched for Pd-102, which is the preferred activatable isotope, is costly. For example, 78% enriched Pd-102 (e.g., having 78% Pd-102) is available from Oak Ridge National Laboratory at a cost of approximately $867,000 per gram. Pd-104 and Pd-105 provide the balance of the palladium in this material, and it is substantially free of Pd-106, Pd-108, and Pd-110. The presence of Pd-108 and Pd-110 in particular is undesirable because, upon activation, these isotopes tend to form long-lived gamma-emitting isotopes.
U.S. Pat. No. 4,702,228 to Russell teaches using a substantially enriched separated isotope (i.e., enriched to a minimum of 50% Pd-102) to fabricate radioactive interstitial implants emitting radiation from Pd-103. The disadvantage of using this highly enriched, separated Pd-102 is that it is extremely expensive and is difficult to obtain in sufficient quantities. Russell teaches that this highly enriched isotope is necessary because natural palladium contains only about 1% Pd-102 and the remainder of the palladium absorbs much of the x-ray intensity generated by the radioactive Pd-103. However, the Russell design uses two spherical pellets approximately 0.6 mm in diameter in which the enriched palladium is distributed uniformly throughout the volume of the pellet. This design contributes to self-absorption because radiation from palladium atoms located away from the surface of the pellets must travel to the surface of the pellet without being absorbed along the way.
SUMMARY OF THE INVENTION
The present invention comprises an implantable article having disposed on all or a portion of the surface thereof a coating or layer of palladium which either contains a therapeutic amount of radioactive Pd-103, or contains an amount of non-radioactive precursor isotope Pd-102 sufficient to provide a therapeutic amount of Pd-103 upon thermal neutron activation. Because the palladium-coated article of the present invention has the palladium layer disposed on the exterior surface of the article rather than distributed throughout its volume, the distance radiation emitted from Pd-103 must travel to reach the surface is minimized. Thus, Pd-103 emissions are utilized more efficiently, and the palladium used in the coating or layer may contain a lower concentration of Pd-102 than is necessary in designs wherein the palladium is distributed throughout the volume of a device.
In one aspect, the invention comprises medical devices comprising a body having disposed thereon a coating or layer of palladium which is moderately enriched in Pd-102 and preferably substantially depleted in Pd-108 and Pd-110. The device may additionally comprise a coating, shell or container of a biocompatible material disposed on or surrounding the palladium-coated device. In certain embodiments, an adhesion layer may be deposited between the palladium layer and the body, or between the palladium and the biocompatible coating.
The device comprises a layer of palladium enriched in Pd-102 disposed on all or a portion of an exterior surface of the body. Pd-102 is a non-radioactive precursor isotope which can be activated in a nuclear reactor to form the radioactive isotope Pd-103. In preferred embodiments, the palladium layer is substantially depleted in Pd-110 and Pd-108. Upon exposure to thermal neutrons, some or all of the Pd-102 in the palladium layer may be converted to Pd-103. The amount of palladium disposed on the body is preferably sufficient to provide, upon activation of Pd-102 to Pd-103, a therapeutic dose of radiation. Preferably, the palladium layer is enriched to contain up to about 10% Pd-102, and more preferably, from about 2% to about 8% Pd. A layer of Pd having a thickness of from about 2 microns to about 10 microns is sufficient for this purpose. In a currently preferred embodiment, the palladium layer is from our 3 microns to about 8 microns thick.
In another aspect, the invention comprises an implantable radioactive device wherein the palladium layer includes Pd-103. In such embodiments, the palladium layer disposed on the body is enriched in Pd-102 and Pd-103, for example, up to about 10% Pd-102 and Pd-103 together, and preferably is substantially depleted in Pd-110 and Pd-108. In certain embodiments, the palladium layer comprises an amount of Pd-103 sufficient to provide a therapeutic dose of radiation. In a currently preferred embodiment, the radioactive device has an activity of between about 0.1 and about 10 millicuries. A layer of Pd having a thickness of from about 2 microns to about 10 microns is sufficient for this purpose.
A body useful in the medical device of the present invention comprises any structure, device or article having characteristics such as stability, resiliency, structure, and shape suitable for use as an implantable radioactive medical device. The body may comprise, for example, a stent, seeds, a wire, a wire segment, or other article suitable for implantation in a patient to deliver a localized dose of radiation. In a currently preferred embodiment, the body comprises a wire segment. The body may comprise any material suitable for use in an implantable medical device. The body material preferably comprises a metal, metal alloy, or ceramic. For example, a titanium alloy, titanium-vanadium-aluminum alloy, rhodium, vanadium, aluminum or combinations of these materials may be used. Ceramics useful in the present invention may comprise, for example, quartz (silicon dioxide), alumina (aluminum oxide) and titania (titanium dioxide).
The device may additionally include an adhesion layer disposed between the palladium layer and the body. The adhesion layer comprises a material, preferably a metal, which improves adhesion of the palladium to the body. The adhesion layer preferably comprises at least one material selected from the group consisting of aluminum, silicon, titanium, vanadium, and rhodium. The currently preferred material is titanium. The adhesion layer may be of any thickness sufficient to improve the adhesion of the palladium layer to the body, and preferably is as thin as possible to avoid altering the physical properties of the device. For example, the adhesion layer preferably is less than about 2000 Å thick, more preferably less than about 500 Å thick.
The device may further comprise a coating, layer, shell or capsule of biocompatible material disposed on and substantially surrounding (e.g., encapsulating) the palladium layer. Suitable biocompatible materials include titanium, stainless steel and combinations thereof. The biocompatible coating may be of any thickness that provides the desired encapsulation. A biocompatible coating used for encapsulation preferably is as thin as possible so as not to impede radiation emitted from Pd-103. For example, the biocompatible coating preferably is less than about 50,000 Å thick, more preferably less than about 10,000 Å thick, depending on the composition of the materials used and the radiation dosage desired for the targeted tissue. Alternatively, the biocompatible shell or sealed capsule of titanium between about 0.0025 and about 0.0125 cm thick. An adhesion coating, such as described above, may be included between the palladium layer and the biocompatible layer.
In one embodiment, the device may comprise a canister having
Foley Hoag & Eliot LLP
Implant Sciences Corporation
Lacyk John P.
LandOfFree
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