Surgery – Radioactive substance applied to body for therapy – Radioactive substance placed within body
Reexamination Certificate
2001-12-31
2004-01-20
Winakur, Eric F. (Department: 3736)
Surgery
Radioactive substance applied to body for therapy
Radioactive substance placed within body
Reexamination Certificate
active
06679824
ABSTRACT:
This invention relates to radiotherapy. More particularly, it relates to radioactive sources for use in brachytherapy and to methods for the preparation of such sources.
Brachytherapy is a general term covering medical treatment which involves the 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 casing such as titanium to form a “seed” which is then implanted. Temporary implants for the treatment of prostate cancer may involve iridium-192 as the radioisotope.
Conventional radioactive sources for use in brachytherapy include so-called seeds, which are sealed containers, for example of titanium, containing the 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.
U.S. Pat. No. 4,815,449 discloses a substantially non-deflecting, linear, elongated member for insertion in tumours and made of a bioabsorbable material in the form of a needle or thin pointed cylinder with a plurality of radioactive seeds disposed therein in a predetermined array.
U.S. Pat. No. 5,460,592 discloses a method and apparatus for transporting a radioactive device. The device comprises a flexible, elongated woven or braided bio-absorbable carrier material having spaced radioactive seeds disposed therein. On heating, the carrier material holding the seeds becomes semi-rigid. A length of the semi-rigid carrier material with radioactive seeds disposed therein may then be loaded into a conventional, hollow metal dispensing needle or applicator cartridge which is used to implant the radioactive seeds into or contiguous to the treatment site, for example a tumour.
A commercial product consisting of iodine-125 seeds regularly spaced at between 0.6 and 1.2 cm centre to centre inside a braided, semi-rigid bioabsorbable suture material is available from Medi-Physics Inc. under the trade name I-125 RAPID Strand™. This product may be used to treat conditions such as head and neck cancers, including those of the mouth, lips and tongue, brain tumours, lung tumours, cervical tumours, vaginal tumours and prostate cancer.
One advantage of this type of semi-rigid carrier is that the radioactive seeds are implanted or inserted into a patient with a pre-determined spacing, depending on their spacing in the carrier material. The bioabsorbable material is then slowly absorbed into the patient's body to leave the spaced seeds in position. This predetermined spacing and the semi-rigid nature of the carrier aids a physician in calculating both the total radiation dose and the dose profile which will be delivered by the seeds inside a patient's body, and also aids in accurate placement of the seeds. In addition, more than one seed is implanted at once, so lessening the time taken for implantation over that required for the placement of individual loose seeds. The risk of seed migration away from the site of implantation is also reduced (Tapen et al.,
Int. J. Radiation Oncology Biol. Phys.,
vol. 42(5), pages 1063-1067, 1998).
However, radioactive sources according to U.S. Pat. Nos. 4,815,449 and 5,460,592 have a number of disadvantages. The manufacturing process requires a heating step to stiffen the carrier material holding the radioactive seeds. Excessive heat may damage the carrier material, and strict control of the heating and cooling process is critical so as to change the crystalline structure of the carrier material sufficiently to cause stiffening but without causing burning. Even when stiffness is maximised within the possibilities existing within U.S. Pat. No. 5,460,592, the carrier material is not sufficiently stiff to fully guard against jamming of the carrier within the dispensing needle or applicator when in the surgeon's hands. Jamming of the carrier within a needle is generally irreversible, so that the needle then has to be disposed of, taking into account the fact that it is now “hot” due to the presence of radioactive seeds. In addition, if the needles are not well plugged, blood and other body fluids may enter the needle and cause the bioabsorbable material to swell, again causing jamming of the carrier in the dispensing needle (Butler et al.,
Radiation Oncology Investigations
4:48-49, 1996).
The manufacturing process disclosed in U.S. Pat. No. 5,460,592 is also very labour intensive and does not lend itself easily to automation. In addition, each carrier must be visually examined after the stiffening step to ensure that the seeds are securely retained in the braided bioabsorbable material.
There is therefore a need for an improved radioactive source which does not suffer from all the disadvantages of the known sources, and which can preferably be produced using an automated manufacturing process.
In one aspect of the invention there is therefore provided a radioactive member for use in brachytherapy comprising an essentially stiff elongate, single stranded bioabsorbable carrier material with spaced radioactive sources disposed therein. The sources are preferably retained therein by deformation of the carrier material around the sources on heating, followed by subsequent cooling.
In a further aspect of the invention, there is provided a radioactive member for use in brachytherapy comprising an elongate bioabsorbable carrier material with one or more slots therein in which one or more radioactive sources are disposed in a spaced relationship. Preferably, the carrier material is essentially stiff. The slots may comprise a continuous groove or a series of discrete openings longitudinally spaced along the carrier material. Preferably, the sources are securely retained in the carrier material by heat sealing.
As a further feature of the invention there is provided a method for the production of a radioactive member for use in brachytherapy comprising an elongate, bioabsorbable carrier material with spaced radioactive sources disposed therein, said method comprising the steps of:
a) providing an elongate preferably essentially stiff and preferably single stranded bioabsorbable carrier material,
b) providing a plurality of radioactive sources,
c) heating the radioactive sources to a temperature above the melting or softening temperature of the carrier material,
d) placing the heat
Helle Kevin
Rapach Mike
Reed Jay
Shanks Charles E.
Cai Li
Medi--Physics, Inc.
Veniaminov Nikita R
Winakur Eric F.
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