Metal treatment – Process of modifying or maintaining internal physical... – Processes of coating utilizing a reactive composition which...
Reexamination Certificate
2000-05-24
2003-07-22
King, Roy (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Processes of coating utilizing a reactive composition which...
C148S253000, C148S243000, C148S264000
Reexamination Certificate
active
06596097
ABSTRACT:
BACKGROUND OF INVENTION
Brachytherapy is a general term covering medical treatment which involves placement of a radioactive source near a diseased tissue and may involve the temporary or permanent implantation or insertion of a radioactive source into the body of a patient. The radioactive source is thereby located in proximity to the area of the body which is being treated. This has the advantage that a high dose of radiation may be delivered to the treatment site with relatively low dosages of radiation to surrounding or intervening healthy tissue.
Brachytherapy has been proposed for use in the treatment of a variety of conditions, including arthritis and cancer, for example breast, brain, liver and ovarian cancer and especially prostate cancer in men (see for example J. C. Blasko et al.,
The Urological Clinics of North America
, 23, 633-650 (1996), and H. Ragde et al.,
Cancer
, 80, 442-453 (1997)). Prostate cancer is the most common form of malignancy in men in the USA, with more than 44,000 deaths in 1995 alone. Treatment may involve the temporary implantation of a radioactive source for a calculated period, followed by its removal. Alternatively, the radioactive source may be permanently implanted in the patient and left to decay to an inert state over a predictable time. The use of temporary or permanent implantation depends on the isotope selected and the duration and intensity of treatment required.
Permanent implants for prostate treatment comprise radioisotopes with relatively short half-lives and lower energies relative to temporary sources. Examples of permanently implantable sources include iodine-125 or palladium-103 as the radioisotope. The radioisotope is generally encapsulated in a titanium casing to form a “seed” which is then implanted. Temporary implants for the treatment of prostate cancer may involve iridium-192 as the radioisotope.
Recently, brachytherapy has also been proposed for the treatment of restenosis (for reviews see R. Waksman,
Vascular Radiotherapy Monitor
, 1998, 1, 10-18, and
MedPro Month
, January 1998, pages 26-32). Restenosis is a re-narrowing of the blood vessels after initial treatment of coronary artery disease.
Coronary artery disease is a condition resulting from the narrowing or blockage of the coronary arteries, known as stenosis, which can be due to many factors including the formation of atherosclerotic plaques within the arteries. Such blockages or narrowing may be treated by mechanical removal of the plaque or by insertion of stents to hold the artery open. One of the most common forms of treatment is percutaneous transluminal coronary angioplasty (PTCA)—also known as balloon angioplasty. At present, over half a million PTCA procedures are performed annually in the USA alone. In PTCA, a catheter having an inflatable balloon at its distal end is inserted into the coronary artery and positioned at the site of the blockage or narrowing. The balloon is then inflated which leads to flattening of the plaque against the artery wall and stretching of the artery wall, resulting in enlargement of the intraluminal passage way and hence increased blood flow.
PTCA has a high initial success rate but 30-50% of patients present themselves with stenotic recurrence of the disease, i.e. restenosis, within 6 months. One treatment for restenosis which has been proposed is the use of intraluminal radiation therapy. Various isotopes including iridium-192, strontium-90, yttrium-90, phosphorus-32, rhenium-186 and rhenium-188 have been proposed for use in treating restenosis.
Conventional radioactive sources for use in brachytherapy include so-called seeds, which are sealed containers, for example of titanium or stainless steel, containing a radioisotope within a sealed chamber but permitting radiation to exit through the container/chamber walls (U.S. Pat. Nos. 4,323,055 and 3,351,049). Such seeds are only suitable for use with radioisotopes which emit radiation which can penetrate the chamber/container walls. Therefore, such seeds are generally used with radioisotopes which emit &ggr;-radiation or low-energy X-rays, rather than with &bgr;-emitting radioisotopes.
Brachytherapy seeds comprising a coating of radioactive silver iodide on a silver wire encapsulated inside a titanium container are known in the art (U.S. Pat. No. 4,323,055). Such seeds are formed by first chloriding or bromiding the silver to form a layer of silver chloride or bromide, and then replacing the chloride or bromide ions with radioactive iodide ions (I-125) by ion exchange. Such seeds are available commercially from Medi-Physics, Inc., under the Trade Name I-125 Seed® Model No. 6711 or OncoSeed™ Iodine-125 seeds (Nycomed Amersham).
Other conventional brachytherapy seeds comprise titanium containers encapsulating ion exchange resin beads onto which a radioactive ion, for example I-125, has been absorbed (U.S. Pat. No. 3,351,049). The immobilisation of a radioactive powder within a polymeric matrix has also been proposed (WO97/19706).
The processes disclosed in U.S. Pat. No. 4,323,055 for the production of I-125 containing seeds involve a number of separate steps. We believe a more efficient and rapid method for the production of radioactive sources comprising insoluble salts, especially silver salts, is desirable from a manufacturing viewpoint.
SUMMARY OF INVENTION
According to one aspect of the invention there is therefore provided a method for the immobilisation of one or more radioisotopes on the surface of a metal substrate, said method comprising treating the substrate with an oxidising agent to produce metal cations, in the presence of a source of a radioactive anion containing one or more radioisotopes, which anion forms an insoluble salt with said metal cations. Preferably, the radioactive anion will be present in solution or in a dispersion. Preferably, a binding agent will also be present. The products of the method of the invention are radioactive substrates.
Any metal which can form an insoluble salt with a radioactive anion on oxidation may be used as the metal substrate in the method of the invention. Suitable metals include silver, copper, lead, zinc, palladium, thallium, cadmium, lanthanum and gold. Preferably, the metal substrate is silver. The substrate may be made of solid metal or a suitable material plated with a layer of metal, for example silver, zinc, palladium or thallium. Suitable materials for plating include other metals, for example gold, copper or iron, and plastics, for example polypropylene, polystyrene, nylon, delrin, Kevlar™, and any other plastic or composite which can form a solid rod for plating with the metal of interest. Suitable plating methods are known in the art and include chemical deposition, sputtering and ion plating techniques.
The substrate should be of a suitable size and dimensions for incorporation into a source, for example a seed, for use in brachytherapy. Conventional seeds for use in the treatment of prostate cancer, for example, are typically substantially cylindrical in shape and approximately 4.5 mm long with a diameter of approximately 0.8 mm, such that they may be delivered to the treatment site using a hypodermic needle. For use in the treatment of restenosis, a source should be of suitable dimensions to be inserted inside a coronary artery, for example with a length of about 10 mm and a diameter of about 1 mm, preferably a length of about 5 mm and a diameter of about 0.8 mm, and most preferably with a length of about 3 mm and a diameter of about 0.6 mm. Sources for use in the treatment of restenosis are typically delivered to the treatment site using conventional catheter methodology.
Preferably, the substrate is of a suitable size and dimensions to fit inside a conventional seed container, such as those disclosed in U.S. Pat. No. 4,323,055 which is hereby incorporated by reference. Preferred seed containers are those made of titanium, titanium alloy or stainless steel. Preferably, the substrate will be substantially cylindrical in shape, for example in the form of a rod or wire. Suitable dimensions are about 3 m
Bacon Edward
Gustow Evan
McIntire Gregory
Snow Robert
Amersham PLC
King Roy
Wilkins, III Harry D.
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