Patent Application
20050101826
This invention relates to methods of fabricating brachytherapy implant seeds, to methods of fabricating brachytherapy implant seed cores, and to brachytherapy implant seeds independent of method of fabrication.
Radiation therapy (radiotherapy) refers to the treatment of diseases, primarily but not limited to the treatment of tumors such as cancer, with radiation. Radiotherapy is used to destroy malignant or unwanted tissue without causing excessive damage to the nearby healthy tissues.
Ionizing radiation can be used to selectively destroy cancerous cells contained within healthy tissue. Malignant cells are normally more radiosensitive than healthy cells. Therefore, by applying radiation of the correct amount over the ideal time period, it is possible to destroy all of the undesired cancer cells while saving or minimizing damage to the healthy tissue. For many decades, localized cancer has often been cured by the application of a carefully determined quantity of ionizing radiation during an appropriate period of time. Various methods have been developed for irradiating cancerous tissue while minimizing damage to the nearby healthy tissue. Such methods include the use of high-energy radiation beams from linear accelerators and other devices designed for use in external beam radiotherapy.
Another method of radiotherapy includes brachytherapy. Here, substances in the form of seeds, needles, wires or catheters are implanted permanently or temporarily directly into/near the cancerous tumor. Radioactive materials used include radon, radium and iridium-192. More recently, the radioactive isotopes cesium-131, iodine-125 and palladium-103 have been used. Examples are described in U.S. Pat. Nos. 3,351,049; 4,323,055; and 4,784,116, which are incorporated herein by reference.
During the last 30 years, over 100 papers (both scientific and lay publications) have been published on the use of iodine-125 and palladium-103 in treating slow growth prostate cancer. Despite the demonstrated success of iodine-125 and palladium-103, there are certain disadvantages and limitations in their use. While the total dose can be controlled by the quantity and spacing of the seeds, the dose rate is set by the half-life of the radioisotope (60 days for 1-125 and 17 days for Pd-103). For use in faster growing tumors, the radiation should be delivered to the
The use of sealed radioactive sources became so widespread that standards used for production were established for radiation protection. Leakage test methods for sealed radioactive sources continue to be refined (ISO 9978:1992(E) and ISO 2919:1999(E)). In order to meet these standards, the sealed seeds must be exposed to various environmental stresses while remaining completely sealed. The most difficult test to pass is the impact test, which requires that the metal seed body be placed on a steel anvil, and that a 2.54 cm diameter, 50 gram weight be dropped on the seed from a height of 1 meter. Even though the typical titanium cased seed can is then flattened, there must be no leakage from the metal seed body. To pass this stringent test, seed manufacturers (e.g., in constructions such as in prior art such as U.S. Pat. Nos. 4,702,228; 4,784,116; 4,891,165; 5,405,309, etc.) incorporate thick end welds, thick end caps and/or massive internal components in order to retain the original cylindrical shape. However, these characteristics can result in non-uniform dosimetric patterns around the seed due to the self-absorption of the radiation. This non-isotropic dose increases the probability that cancer cells residing in this shadowed low dose area will survive and give rise to a return of the cancer at a later date.
Several prior art seed designs (U.S. Pat. Nos. 3,351,049; 4,994,013; and 5,163,896) suggest the use of plastics, a multitude of ion exchange resin types (nylon, cellulose ester or acetate binders, or rubber) to capture and hold the radioactive material. With increasing concentrations of radioisotopes, unacceptable gas pressure (e.g., H2, CO, CO2, CH4, etc.) may be generated by the autoradiolysis of organic materials within the cavity of the seed. Release of radioactive material due to a breach in the seed can by over-pressurization is a risk.
While the invention was motivated in addressing at least some of the above issues, it is in no way so limited. The invention is only limited by the accompanying claims as literally worded, without interpretative or other limiting reference to the specification, and in accordance with the doctrine of equivalents.
The invention comprises methods of fabricating brachytherapy implant seeds, methods of fabricating brachytherapy implant seed cores, and brachytherapy implant seeds independent of method of fabrication. In one implementation, a brachytherapy implant seed includes a sealed inorganic metallic cylinder having a radioactive core received therein. The radioactive core includes an inorganic amorphous silicate glass tube having an exterior surface extending axially along the tube. An inorganic crystalline ceramic coating is received on at least a portion of the inorganic amorphous glass tube exterior surface. The coating includes a therapeutic dose of radioactive material. A radiographic marker is received within the sealed inorganic metallic cylinder.
In one implementation, a method of fabricating a brachytherapy implant seed comprises providing an inorganic amorphous silicate glass tube having an exterior surface extending axially along the tube. At least a portion of the tube exterior surface is coated with ceramic precursors. After the coating, the ceramic precursors are exposed to a temperature effective to form a continuous inorganic crystalline ceramic coating from the precursors over the tube exterior surface portion. After the exposing, a therapeutic dose of radioactive material is sorbed onto the ceramic coating. At least a portion of the ceramic coated glass tube with therapeutic dose of radioactive material is provided within an inorganic metallic cylinder. An inorganic metallic cap is welded onto an end of the inorganic metallic cylinder having the portion of the ceramic coated glass tube with therapeutic dose of radioactive material therein.
In one implementation, a method of fabricating a brachytherapy implant seed core comprises providing a tube having an exterior surface extending axially along the tube. A vessel is provided which comprises a die passageway sized to slideably receive the tube therethrough to form a coating onto the tube exterior surface. A mixture of ceramic precursors is provided within the vessel. The tube is moved into the ceramic precursor mixture within the vessel and through the die passageway to out of the vessel effective to form a coating of the ceramic precursors onto the tube exterior surface. The ceramic precursor coating is exposed to a temperature effective to form an inorganic crystalline ceramic coating over the tube exterior surface portion. After such exposing, a therapeutic dose of radioactive material is sorbed onto the ceramic coating.
In one implementation, a method of fabricating a brachytherapy implant seed core comprises providing a tube having an exterior surface extending axially along the tube. A mold is provided which comprises a mold cavity sized to receive the tube and form a coating thereover. A mixture of ceramic precursors is inserted to within the mold cavity. The tube is inserted to within the mold cavity. An adherent coating of the ceramic precursors is formed onto the tube exterior surface within the mold cavity. After such forming, the mold is destructively melted. After the melting, the ceramic precursor coating is exposed to a temperature effective to form an inorganic crystalline ceramic coating over the tube exterior surface. After such exposing, a therapeutic dose of radioactive material is sorbed onto the ceramic coating.
In one implementation, a method of fabricating a brachytherapy implant seed comprises providing an inorganic metallic cylinder. An inorganic metallic cap is welded onto an end of the inorganic metallic cylinder. The welding comprises firing a series of laser pulses towards the cap and cylinder while rotating the cap and cylinder effective to form, a series of overlapping welds. In one implementation, adjacent welds overlap one another by no more than 50% calculated as weld diameter overlap divided by weld diameter. In one implementation, the laser pulses are fired towards the cap and cylinder at a firing angle from perpendicular to an outer surface of the metallic cylinder. A radioactive core is provided within the inorganic metallic cylinder. The radioactive core comprises a therapeutic dose of radioactive material.
Other aspects and implementations are contemplated.
Preferred embodiments of the invention are described below with reference to the following accompanying drawings.
This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8).
In accordance with preferred aspects of the invention, a preferred embodiment brachytherapy implant seed is initially described with reference to
One preferred embodiment cylinder 12 comprises a cylindrical section 16 and a pair of opposing end caps 18 and 20. Components 16, 18 and 20 are preferably comprised of the same material, with caps 18 and 20 being welded to cylindrical section 16. Exemplary preferred methods of fabrication are described subsequently. An exemplary preferred length for cylindrical section 16 is from 1.0 mm to 10.0 mm. An exemplary preferred thickness for the wall of section 16 is from 0.05 mm to 0.1 mm. An exemplary preferred outside diameter, or maximum cross-dimension, of cylinder 12 is from 0.1 mm to 2.0 mm. A preferred thickness range for caps 18 and 20 is also from 0.05 mm to 0.1 mm, with the caps preferably having a diameter or maximum cross-dimension which is slightly larger than that of cylindrical section 16. Caps 18 and 20 are preferably adhered to cylindrical section 16 by welding in a preferred manner to be described subsequently. Preferably, a uniform wall thickness of components 18, 16 and 20 is utilized for cylinder construction 12.
The illustrated preferred cylinder 12 is in the form of a hermetically sealed right cylinder having substantially flat ends. Flat ends. are preferred in providing an advantage of being able to stabilize the seed after being placed in position in the tumor or other tissue, as compared to implant seeds having rounded ends. Further, rounded ends have been known to jam in the needles during loading. Regardless, seeds having other than flat ends are also, of course, contemplated. One preferred embodiment example for cylinder construction 12 is a titanium right cylinder tube having a length of 4.3 mm, an inner diameter of 0.7 mm and an outer diameter of 0.8 mm, with end caps welded thereto having a thickness of 0.1 mm.
Radioactive core 14 comprises an inorganic amorphous silicate glass tube 22. Such tube can be considered as having longitudinally opposing ends 27 which, in the
An inorganic crystalline ceramic coating 30 is received on at least a portion of inorganic amorphous glass tube exterior surface 24. In the exemplary depicted
Exemplary preferred materials for inorganic crystalline ceramic coating 30 include metal silicates, for example aluminosilicates such as sodium aluminosilicate. In addition therewith or in substitution therefor, exemplary additional materials include silicates and oxides of aluminum, sodium, magnesium, potassium, calcium and lithium. Additionally, the preferred ceramic material 30 preferably is inherently chemically adsorptive or absorptive of one or more specific radionuclides or contains inorganic ion exchange material to be described subsequently.
Regardless, coating 30 comprises a therapeutic dose of radioactive material. In the particular exemplary
Brachytherapy implant seed 10 further comprises a radiographic marker that is received within the sealed inorganic metallic cylinder. By way of example only, such might comprise a metal vapor deposit, a metal paste, a metal ball, a metal wire, etc. Most preferably, the radiographic marker is received within the inorganic amorphous glass tube. In the depicted
The exemplary
By way of example only,
The above describes exemplary preferred brachytherapy implant seed embodiments independent of the method of manufacture. Described below are exemplary preferred methods of fabricating the above and other brachytherapy implant seeds in accordance with aspects of the invention, including methods of fabricating a brachytherapy implant seed core in accordance with aspects of the invention.
In one implementation, a method of fabricating a brachytherapy implant seed core is described with reference to
A mixture 51 of ceramic precursors is provided within vessel body 50. Exemplary ceramic precursors include any capable of providing the exemplary ceramic coatings provided above, for example a mixture of sodium silicate containing from about 10 weight percent to 40 weight percent aluminum oxide. In one exemplary embodiment, the mixture of ceramic precursors comprises an inorganic ion exchange material having an affinity for the radioactive material to be used subsequently. Exemplary preferred inorganic ion exchange materials include zeolites, and for example silicotitanate.
Referring to
Thereafter, the ceramic precursor coating on the tube is exposed to a temperature effective to form an inorganic crystalline ceramic coating (for example coating 30 of the first described embodiment) over the tube exterior surface. In reduction-to-practice examples, the coated tubing is air dried and subsequently placed in a furnace. Such was then heated to 170° C. for approximately 60 minutes to convert the precursor coating to an inorganic crystalline ceramic coating which comprised sodium aluminosilicate. By way of example only, an exemplary temperature range to form the ceramic material is from 100° C. to 500° C. In reduction-to-practice examples, the coated glass tube was then measured for uniform thickness and cut into 4.0 mm to 4.25 mm lengths. Preferred attributes are otherwise as described above with respect to coated glass tube 22.
Thereafter, a therapeutic dose of radioactive material is sorbed onto the ceramic coating. One preferred manner of doing so is contacting the ceramic coated exterior surface with a solution comprising radioisotope ions having an affinity for the ceramic material and/or ion exchange material within the ceramic material. For example, and by way of example only, a highly purified and accurately known amount of radioactivity in solution (mCi/ml) can be transferred to the ceramic coated cores by adsorption and/or absorption to the outer surfaces thereof by immersing the cores individually in 0.1 ml to 0.4 ml of solution for exemplary time periods of from 1 minute to 24 hours. Again, an exemplary preferred radiochemical is cesium-131. The solution and core are preferably gently agitated during the treatment time. A specific example solution comprised 0.25 ml of water containing 96.4 millicurries of cesium-131 per ml for treating a single core, with the treatment time being 14.5 hours, and with the solution being at ambient room temperature and pressure conditions. Greater than 88% of the radioactivity was transferred to the core. The solution can be acid, base, aqueous or non-aqueous largely dependent upon the isotope and the ceramic material (including any ion exchange material, if any) that are utilized. The radioactive loaded cores are then removed from the solution, and preferably air-dried for one hour with the aid of a heat lamp.
The above provides but one exemplary described embodiment of a method of fabricating a brachytherapy implant seed core in accordance with exemplary methodical aspects-of the invention. An additional method of fabricating a brachytherapy implant seed core comprises providing a tube having an exterior surface extending axially along the tube. Again preferably, the tube comprises an inorganic amorphous silicate glass material, for example tube 22 as described in the first embodiment. A mold is provided that comprises a mold cavity sized to receive the tube and form a coating thereover. By way of example only,
A mixture of ceramic precursors is inserted within the mold cavity, and the tube is inserted within the mold cavity. Preferably, the ceramic precursor mixture is provided within the mold cavity first, followed by the tube, although the reverse order of insertion is also contemplated. An adherent coating of the ceramic precursors is formed onto the tube surface within the mold cavity, for example merely by allowing the ceramic precursors to cure onto the outer tube surface for some acceptable period of time, for example from one hour to twenty-four hours.
Thereafter, the mold is destructively melted, preferably melting the mold away from the ceramic precursor-coated tube, and even more preferably melting and vaporizing the mold material. An exemplary preferred heating temperature range for the melting is from 100° C. to 170° C. where the mold material at least has a melting temperature which is at or below 170° C. Any residual mold material can be dissolved in any suitable solvent, for example hexane for wax. After the melting, the ceramic precursor coating is exposed to a temperature effective to form an inorganic crystalline coating over the tube exterior surface, for example ceramic coating 30 in the above-described first embodiment. An exemplary preferred temperature range is as described in the preceding embodiment above, with a specific example being 170° C. and which will also tend to burn off any remaining wax or other molding material. After the exposing, a therapeutic dose of radioactive material is sorbed onto the ceramic coating, for example using any of the above-described or other methods. Note that with any of the above-described embodiments, the ceramic coating might be formed onto end surfaces and/or onto interior surfaces of the tube. Further, the tube longitudinally-opposing ends might be opened or sealed as inserted into the mold cavity. Further, an inorganic metallic marker might be provided within the tube. By way of example only and in accordance with this aspect of the invention, exemplary preferred tubes are from 0.69 mm to 0.70 mm in diameter. A preferred average thickness of the coating is 0.15 mm. At least where a radiographic marker in the form of a wire or rod is used, and in accordance with this particular embodiment, a preferred length is approximately 3.8 mm.
Aspects of the invention also contemplate methods of fabricating a brachytherapy implant seed. In one implementation, such comprises providing an inorganic amorphous silicate glass tube having an exterior surface extending axially along the tube. Preferred tubes are those described above in the first embodiment. At least a portion of the tube exterior surface is coated with ceramic precursors. Exemplary preferred manners are those described above, for example including the methods described in connection with
After the coating action, the ceramic precursors are exposed to a temperature effective to form a continuous inorganic crystalline ceramic coating from the precursors over the tube exterior surface portion. Exemplary preferred manners and temperatures for the exposing are as described above. Thereafter, a therapeutic dose of radioactive material is sorbed onto the ceramic coating. Preferred and exemplary manners of doing so are as described above.
At least a portion of the ceramic-coated glass tube with a therapeutic dose of radioactive material is provided within an inorganic metallic cylinder. An exemplary cylinder is cylinder 12 of the first described embodiment. Preferably, an exemplary such right cylinder has one of its ends open and the other end closed, for example by welding one of caps 18 and 20 onto cylinder portion 16. If an inorganic metallic radioactive marker in the form of a rod or wire is to be used or received within the ceramic-coated glass tube, such might be provided therein before or after insertion of the radioactive glass tube within the inorganic metallic cylinder. Such a radiographic marker might be crimped or otherwise cemented, or even just loosely received within the glass core.
Regardless, an inorganic metallic cap is ultimately welded onto an end of the inorganic metallic cylinder having the portion of the ceramic coated tube with therapeutic dose of radioactive material received therein. Preferred manners of welding are described below.
Specifically, a form of precision laser welding is preferably used as the sealing method for end caps 18, 20 such that a minimum amount of the preferred titanium metal is melted. Preferably, the welding techniques also produce a seed with a uniform thick wall about the seed towards minimizing attenuation of the radiation field and in achieving a substantially uniform distribution of the radiation. In a preferred method, a 0.10 mm thick end cap of approximately 0.81 mm diameter is stamped out of titanium sheet stock, and may produce edges that are “bottle cap” in appearance. Such can facilitate the end cap being seated on the cylindrical body immediately prior to welding. A preferred technique holds the end cap in place over/onto the cylindrical section with a carbide tip. The end cap is then tack welded at two locations approximately from 120° to 180° apart. The carbide tip is removed after the initial tack welding.
In one preferred implementation, the cap and cylinder are next rotated while firing a series of laser pulses towards the cap and cylinder effective to form a series of overlapping welds. Adjacent welds overlap one another by no more than 50% calculated as weld diameter overlap divided by weld diameter. More preferably, adjacent welds overlap one another by from 20% to 40%, and even more preferably from 20% to 30%, calculated as weld diameter overlap divided by weld diameter. A preferred effect, by way of example only and not by way of limitation, is to provide adequate weld overlap to obtain a good fluid tight seal while maintaining a mechanically strong seal capable of withstanding mechanical strength testing, for example tests ISO 9978:1992(E) and ISO 2919:1999(E).
Further preferably, the laser pulses are fired towards the cap and cylinder at a firing angle from perpendicular to an outer surface-of-the metallic cylinder. For example,
Further preferably, the laser pulses are fired towards the cap and cylinder, for example along line 76, such that the firing angle (as depicted) is in a direction towards a majority of length L. Also contemplated, but considerably less preferred, would be directing laser pulses along a firing line 77 at a firing angle B which is in a direction away from the majority of length L of metallic cylinder 16. Further preferably, the inorganic metallic cap can be considered as having an outermost edge away from the inorganic metallic cylinder. Preferably, the welding comprises aiming respective centers of the laser pulses at locations which are more proximate to such outermost edge than to an interface of the cap and cylinder. In one preferred embodiment, the centers of the laser pulses are aimed at such outermost edge. For example, cap 18 can be considered as having such an outermost edge 75 extending about the upper periphery of cap 18 in the
Regardless, the welding preferably produces a series of circumferential welds about the metallic cylinder and cap, sealing the two together. By way of example only, an exemplary rotation speed for the metallic cylinder and cap is from 3 to 4 seconds for a complete rotation, with pulse energy and pulse intervals preferably selected to produce a weld spot every 0.17 mm to 0.25 mm about the circumference of the cylinder. The welding zone is preferably continuously purged with an inert gas, for example argon, for example at a flow rate of from 2 to 3 standard cubic feet per hour. Exemplary preferred weld parameters are selected to produce a tweld zone of approximately 0.20 mm to 0.35 mm diameter per pulse. An exemplary preferred pulse energy is 218 volts, with laser hits occurring at lengths of 3 milliseconds to 6 milliseconds, with the time between laser hits being approximately 300 milliseconds. Such exemplary preferred conditions utilizing a pulse overlap of 25%, firing angles at 18% to 22% from perpendicular as described, with the center of the pulse aimed at the upper edge of the end cap, resulted in and enabled the produced seeds to withstand an impact test wherein a steel hammer with a diameter of 1 inch and weighing 50 grams was dropped onto the seed from a height of 1 meter. After the impact, the seed was tested for leak tightness by immersion in hot water at a temperature of between 90° C. and 95° C. for 1 minute, with no air bubbles having been formed on the outside of the seed.
The above describes but preferred techniques of welding in accordance with certain aspects of the invention. Yet, aspects of the invention further encompass methods of fabricating a brachytherapy implant seed utilizing one or a combination of the variously above-stated preferred exemplary welding attributes. In accordance with one implementation, a method of fabricating a brachytherapy implant seed comprises providing an inorganic metallic cylinder. An inorganic metallic cap is welded onto an end of the inorganic metallic cylinder. The welding comprises firing a series of laser pulses towards the cap and cylinder while rotating the cap and cylinder effective to form a series of overlapping welds. In one implementation, adjacent welds overlap one another by no more than 50% calculated as weld diameter overlap divided by weld diameter. In one implementation, the laser pulses are fired towards the cap and cylinder at a firing angle from perpendicular to an outer surface of the metallic cylinder. A radioactive core is provided within the inorganic metallic cylinder, with such core comprising a therapeutic dose of radioactive material. The radioactive core might be provided within the inorganic metallic cylinder before or after the welding, as well as the welding occurring with respect to both caps to opposing ends of the inorganic metallic cylinder. Radioactive core fabrication and other attributes with respect to the design and manufacture are preferably as described in the above embodiments, although in no way being required in accordance with these latter aspects of the invention as just so literally stated.
In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.
