Surgery – Radioactive substance applied to body for therapy – Radioactive substance placed within body
Reexamination Certificate
2000-02-28
2001-11-27
Lacyk, John P. (Department: 3736)
Surgery
Radioactive substance applied to body for therapy
Radioactive substance placed within body
Reexamination Certificate
active
06322490
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the production of radioactive stent structures and, more particularly to positioning devices that allow stents to be selectively axially collapsible or reducible to facilitate either mass production or “point-of-use” production of radionuclides by irradiation with intense radiation beams so as to form radioactive stents suitable for therapeutic and/or diagnostic medical purposes.
2. Description of the Related Art
Radioactive materials have been used extensively for many years for therapeutic and/or diagnostic medical purposes. In this regard, radioisotopes are used to kill large volumes of cancer cells directly using large quantities of radioactive material. Alternatively, small amounts of radioisotopes are injected into the body or bloodstream and their position in the body is determined by observing the gamma rays emitted when they decay. Radioisotopes may also be bound to some chemical which is selected for its ability to localize at a problem area in the body thereby aiding in the diagnosis of disease.
Relatively newer therapies propose the use of small amounts of radioactivity to treat small tissue volumes, namely intravascular walls. For example, U.S. Pat. No. 5,059,166 to Fischell et al., the entire content of which is incorporated hereinto by reference, discloses embedding a radioactive isotope material into an existing stent structure, the radioactive material having a half-life of less than 100 days, which stent structure may be embedded into plaque tissue within a patient's arterial wall. The radioactive stent releases radiation so as to decrease the rate of proliferative cell growth of the traumatized arterial wall, i.e., to decrease intimal hyperplasia. As a result of such radiation therapy, restenosis after stent implantation is expected to be significantly reduced.
Another example is the use of esophageal stents to alleviate dysphagia in patients with esophageal cancer. Suppression of tumor regrowth through the stent mesh is a major quality of life concern for these patients. If an easy way of making such stents radioactive can be found, radioactive stents would be utilized.
A further example is the potential use of radioactive stents for the treatment of benign prostatic hyperplasia. Here stents are used to maintain urethral opening. If the stent could simultaneously provide radiation to reduce the affliction causing the stricture this would be advantageous.
Thus, there are many examples where out of control proliferative response (either benign or oncologic) compromises the ability of passageways in the human body to be maintained open. Stents themselves (meaning a rigid mesh structure to provide bracing for the walls) solve the physical-mechanical problem. Radiation from the stent can solve the cellular response that could otherwise grow through the stent and compromise the lumen.
While radiating tissue for medical diagnostic and/or therapeutic purposes is advantageous, there are several real and nontrivial problems associated with such “nuclear medicine”, primarily in the availability and/or accessibility of the physician to a source of suitable radioactive devices and materials.
SUMMARY OF THE INVENTION
With the current invention, a cost-effective, reliable technique is being proposed which would enable virtually any facility in need of radioactive stents (for whatever passageway in the body) the ability to produce the same “onsite.” Alternatively, it facilitates mass production at a central facility.
In preferred embodiments thereof, the target material is translated relative to the radiation beam along at least two (2) axes. In one example, a target cartridge is provided which includes a tubular shell formed of a material which is minimally, if at all, activated by the radiation beam or, if activated, has radioactivity that is very short lived in terms of minutes or less, e.g., aluminum, tungsten, tantalum. The tubular shell defines an interior hollow space which houses the target material to be irradiated, e.g., an intraluminal stent. The interior space may optionally be filled with a heat transfer fluid, e.g., water, air, an oxygen-less gas or an inert gas. End caps close each end of the tubular shell and are preferably one-piece solid structures formed of the same material as that of the tubular shell. The end caps therefore most preferably serve the purposes of allowing the target cartridge to be mechanically coupled to a translator assembly and provide a path of heat transfer to a heat-transfer fluid, e.g., liquid and/or gas, in contact therewith.
The translator assembly most preferably holds the target cartridge longitudinally so that it is positioned substantially transversely relative to the path of the radiation beam. By suitable adjustment shafts and linear rail assemblies, therefore, the entire target cartridge may be linearly translated simultaneously or periodically, sequentially parallel and perpendicular to the radiation beam path. At the same time, the target cartridge may be rotated about its axis. In such a manner, the target cartridge exposes the target material therewithin uniformly to the radiation beam.
In any irradiating system, depending upon the dimensions of the target material, it may take as long as several hours for the entirety of the target material to be uniformly exposed to the radiation beam. Where the target material is a stent intended for intravascular placement, the time required to irradiate the stent may become a critical factor in respect to the effective use of radioactive stents. Indeed, it is envisioned that a patient would be fully prepared for stent placement in advance of the irradiating procedure. It would be desirable, for the fully prepared patient to wait as little as possible for the stent irradiation process. Therefore, efficient production of radioactive stents would preferentially involve a design and packaging strategy which facilitates the radiation process.
Thus, it is an object of the invention to reduce the time required to irradiate the stent for the purpose of mass production or for “point of care” irradiation at the local clinical facility.
In this regard, Fischell, as noted above, relates to embedding the radioactive isotope material into an existing stent structure, the radioactive material having a half-life of less than 100 days. The present invention, in contrast, relates to the transmutation of inert stent material itself into a radioactive stent and the design of stent structure to optimize the transmutation process. Generation of a stent with short and long half-lives (greater than 100 days) are desirable and their optimum production are disclosed hereinbelow.
The foregoing object is achieved in accordance with the present invention by providing methods for irradiating stent structures that are selectively collapsible or reducible along their longitudinal axis to reduce the total length thereof. Providing a collapsible stent structure reduces the effective surface area which must be exposed to the radiation beam, thereby reducing the time required for the irradiation process. In addition, positioning devices to accomplish the above process are described.
In accordance with one embodiment of the invention, the collapsible stent structure is biased to a longitudinally extended form and is held in its collapsed state during the irradiation process. This enables the radioactive stent to automatically return to its extended disposition, ready for delivery to the patient, thereby minimizing post irradiation manipulation of the stent by medical practitioners and avoiding unnecessary exposure to the radioactive stent.
In the alternative, plunger structures that are selectively detachably coupled to opposite longitudinal ends of the stent may be provided so as to effect the collapse of the stent on urging the plungers towards one another and, likewise, to effect the re-elongation of the stent upon movement of the respective plungers apart. A clamping mechanism or like mechanical attachment to
Stack Richard S.
Weeks Kenneth J.
Duke University
Lacyk John P.
Nixon & Vanderhye PC
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