The following applications are cross-referenced and incorporated herein by reference:
U.S. Provisional Patent Application No.  60/360,241 entitled xe2x80x9cDelivery System and Method for Interstitial Radiation Therapy Using Seed Strands Constructed With Preformed Strand Housing,xe2x80x9d by Terwilliger et al.,  filed Feb. 26, 2002. ( WORLD 01000US2)
U.S. Provisional Patent Application No.  60/360,272 entitled xe2x80x9cDelivery System and Method for Interstitial Radiation Therapy Using Strands Constructed With Extruded Strand Housing,xe2x80x9d by Terwilliger et al.,  filed Feb. 26, 2002. ( WORLD01000US4)
U.S. Provisional Patent Application No.  60/360,299 entitled xe2x80x9cDelivery System and Method for Interstitial Radiation Therapy Using Seed Elements With Ends Having One of Projections and Indentations,xe2x80x9d by Terwilliger et al.,  filed Feb. 26, 2002. ( WORLD-01003US0)
U.S. Provisional Patent Application No.  60/360,260 entitled xe2x80x9cDelivery System and Method for Interstitial Radiation Therapy,xe2x80x9d by Terwilliger et al.,  filed Feb. 26, 2002. ( WORLD-01004US0)
The present invention relates to systems and methods for delivering a plurality of radioactive sources to a treatment site. 
In interstitial radiation therapy, one method for treating tumors is to permanently place small, radioactive seeds into the tumor site.  This method is currently accomplished by one of the following two procedures: (a) loose seeds are implanted in the target tissue, and/or (b) seeds are contained within a woven or braided absorbable carrier such as braided suture material and implanted in the target tissue.  The loose seeds, however, are dependent on the tissue itself to hold each individual seed in place during treatment, and the woven or braided sutures do not assist in the placement of the seeds relative to the target tissue. 
There have been many developments in brachytherapy (i.e. therapy relating to treating malignant tumors with such radioactive seeds).  In one technique, hollow metal needles are inserted into the tumor and the seeds are thereafter inserted into the needles, while the needles are being retracted to deposit the seeds in the tumor at the desired locations.  Such devices are shown in U.S. Pat.  No.  4,402,308 which is incorporated herein by reference.  The most commonly used instruments are the Henschke and Mick devices.  The use of such devices has distinct disadvantages.  The overall length of such devices is over 20 cm and such devices have significant weight making them difficult to manipulate. 
Another disadvantage of the above technique is that the seeds are deposited in a track made by the needle.  When the needle is withdrawn, there is a tendency for the seeds to migrate in that track resulting in a poor distribution of the seeds.  Because the energy levels are low, distribution between centers of adjacent seeds should be on the order of about 1 cm for certain treatments.  Poor distribution of seeds can result in undesirable concentrations of seeds resulting in either an over-dosage or an under-dosage of radiation.  Additionally, over time, the seeds tend to migrate along the needle track, away from the tumor, and accordingly patients commonly must repeat the procedure within a couple months to have seeds re-implanted near the tumor. 
Further complicating the procedure is the fact that the seeds are small, because they need to fit in small bore needles to prevent excessive tissue damage.  Due to their small size and high seed surface dose, the seeds are difficult to handle and to label, and can easily be lost.  In addition, the technique of implantation of individual seeds is time consuming. 
One preferred method of introducing seeds into the tumor site is using a pre-manufactured elongated assembly or implant that contains seeds spaced between spacers at 1 cm increments.  This assembly is capable of being loaded into an introducer needle just prior to the procedure.  What is desired in using an elongated assembly of seeds and spacers is the ability to insert such an assembly into a tumor site to provide controlled and precise placement of the radioactive seeds. 
While assemblies with bio-absorbable materials and spaced radioactive seeds are known for use as interstitial implants, such assemblies are not entirely satisfactory.  In one instance, the elongated implant is made using a bio-absorbable material consisting of an Ethicon Vicryl. RTM.  This material is commonly known as PGA.  Radioactive seeds and teflon spacers are inserted into the material.  Needles loaded with the seeds in the carrier bio-absorbable material are sterilized or autoclaved causing contraction of the carrier material and resulting in a rigid column of seeds and spacers.  This technique was reported in xe2x80x9cUltrasonically Guided Transperineal Seed Implantation of the Prostate: Modification of the Technique and Qualitative Assessment of Inplantsxe2x80x9d by Van""t Riet, et al.,  International Journal of Radiation Oncology, Biology and Physics, Vol.  24, No.  3, pp.  555-558, 1992 which is incorporated herein by reference.  Such rigid implants have many drawbacks, including not having the ability to flex with the tissue over the time that the bio-absorbable material dissolves. 
As the tissue or glands being treated shrink back to pre-operative size, and thus as the tissue recedes, a rigid elongated implant does not move with the tissue, but remains stationary relative to the patient.  The final location relative to the tumor is thus not maintained and the dosage of the radioactive seeds does not meet the preoperative therapy plan. 
Another system for providing an elongated implant having radioactive seeds disposed therein is disclosed in U.S. Pat.  No.  4,697,575 which is incorporated herein by reference.  In this reference, a plurality of encapsulated radioactive seeds are positioned in a predetermined array.  The seeds are encapsulated in individual capsules, with each capsule having a projection on one capsule end and a complementary recess on the remaining capsule end.  A projection in one capsule is engageable with a recess in an adjacent capsule such that the desired number of seeds can be plugged together to form a column of rigid, bio-absorbable and elongated material.  This implant is not entirely satisfactory inasmuch as it is time consuming and inefficient to carry out the manipulative steps of assembling such a strand of elongated material.  Further the implant is quite rigid as it is inserted into a patient without the use of an introduction needle, as the implant itself acts as a rigid needle that is undesirably left in place. 
In another embodiment disclosed in the above patent, a rigid needle implant containing radioactive segments, with break points, is inserted into the tumor.  The needle implant is made of a bio-absorbable polymer that is rigid enough to be driven into the tumor without deflection and without the use of a separate hollow needle.  When the proper depth is reached with the rigid polymer needle, the remaining, uninserted portion of the needle is broken off.  This embodiment has the disadvantage of the above embodiment.  As the implant is too rigid, the implant does not follow the tumor as it shrinks back to its normal size. 
In U.S. Pat.  No.  6,163,947, Coniglione, issued Dec. 26, 2000, and incorporated herein by reference, a string of hollow seeds described in U.S. Pat.  No.  5,713,828, issued Feb. 3, 1998, also incorporated herein by reference, are strung onto a thin strand of suture material to form an array of seeds.  This string of seeds is delivered into the tumor site placed within a hollow needle.  Since the hollow lumen of the seeds are substantially smaller in diameter in relation to the outside diameter of the seed body, the string of suture material must be substantially smaller in diameter than the seeds themselves.  The resulting diameter of the suture makes the suture axially weak and the suture can fold up between the seeds within the needle lumen as pressure is applied on the proximal end of the strand within the needle.  Thus the difference in diameter between the seed and the thin suture material makes the assembly susceptible to collapse from axial force applied on the proximal end, resulting in jamming of the assembly within the needle lumen and/or the assembly not maintaining the proper desired spacing between radioactive seeds as the assembly is expelled into the treatment site. 
One relevant reference discloses modification of the needle structure to include a reloadable cartridge.  In such reference the needle is inserted and as a cartridge of seeds is emptied, the plunger of the device is withdrawn and a new cartridge containing radioactive seeds is loaded into the syringe (Moore, U.S. Pat.  No.  4,086,914, issued May 2, 1978).  Another reference offers a device for implanting individual seeds in a planar dispensing device with multiple needles to ensure accurate placement of the seeds relative to one another and the treatment site (Kirsch, U.S. Pat.  No.  4,167,179 issued September 1979).  Another reference disclosed a shielding devices for bead strands which prevents radiation exposure for health care personnel performing treatment with the radioactive seeds (Windarski, U.S. Pat.  No.  4,509,506 issued April 1985).  All of the above references are incorporated herein by reference. 
In another technique for treating tumors disclosed in U.S. Pat.  No.  5,460,592 and incorporated herein by reference, seeds are held in a woven or braided bio-absorbable carrier such as a braided suture.  The carrier with the seeds laced therein is then secured in place to form a suitable implant.  This braided assembly exhibits many drawbacks, as and when the braided assembly is placed into the tumor.  The needle that carries the braided assembly must be blocked at the distal end to prevent body fluids from entering the lumen.  If body fluid reaches the braided assembly while the assembly is still in the lumen of the needle, the braided assembly can swell and jam in the lumen.  Because the assembly is made of a braided tubular material, it is difficult to push the assembly out of the needle.  As the needle is withdrawn from the tumor, pressure on the proximal end of the braided assembly causes the braid to expand and jam inside the lumen of the needle.  Finally, if the braided strand is successfully expelled from the needle, the relative spacing of the seeds may not be maintained, if the braided material has collapsed. 
Another apparatus for automated production of brachytherapy devices is the Mentor Isoloader(trademark).  The Isoloader(trademark) consists of an interface to commercial treatment planning systems, a shielded seed cartridge, a shielded needle cartridge, a shielded needle holder and a radiation detector for seed assay.  The Isoloader(trademark) picks the radioactive seeds, tests each one for radiation and then automatically loads the seed into a needle.  The apparatus provides for automated loading and verification of radioactive seeds into needles.  With the Isoloader(trademark) system, the clinician plans the treatment for a specific patient using standard software, and orders brachytherapy seeds of a suitable quantity and activity level for that patient.  The seeds are shipped to the clinician in a pre-sterilized cartridge with a memory chip containing the individual data and seed specifications.  The cartridge is inserted into the Isoloader(trademark), and the seeds are automatically loaded into the surgical needles according to the treatment plan.  The Isoloader(trademark) produces a rigid needle system that does not move with the tissue, as the tumor shrinks during treatment. 
Other references that address such implants and materials include the following, all of which are incorporated herein by reference. 
U.S. Patent Documents:
1,578,945 issued January 1923 to Withers
2,067,589 issued January 1937 to Antrim
3,351,049 issued November 1967 to Lawrence
Medi-Physics brochure entitled xe2x80x9cI-125 Seeds. RTM.  In Carrierxe2x80x9d, Model No.  6720. 
Medi-Physics brochure entitled xe2x80x9cI-125 Seed. RTM.  Source Model 6711xe2x80x9d. 
Martinez et al.,  Int.  J. Radiation Oncology Biol.  Phys.,  vol.  5, No.  3, March 1979, pp.  411-413. 
Accordingly, the present invention cures and addresses the disadvantages exhibited in the prior art devices and implants.  What is desired is to provide a bio-absorbable carrier material having seeds disposed within the material, with the seeds being accurately spaced a predetermined distance from one another, with the seeds repeatably maintaining that spacing, even after being introduced into the body. 
It is further desired that an elongated member with seeds be sufficiently rigid axially to allow expulsion of the member while maintaining the spacing between seeds, and that the member be flexible and pliable enough to move with the tissue as the tissue shrinks back to pre-operative size. 
Accordingly, some of the objectives of the present invention include providing an elongated member with seeds dispersed throughout, which obviates the aforementioned disadvantages and allows placement of the seeds in accurate positions to provide the desired interstitial radiation dose to the location derived from a preoperative dosimeter plan. 
A further object of the present invention is to provide a delivery system for interstitial radiation therapy, which is faster and easier to use than prior art systems. 
Another object of the present invention is a delivery system that causes a minimum of trauma to tissue. 
Yet another object of the present invention is a delivery system that allows for control of the radiation dosage given the tissue.  Still further objects of the present invention is a delivery system that can be used and placed with precision, and that maintains the position of the implant after the implantation, until the bio-compatible material dissolves and the seeds have become inert.  In another aspect the bio-compatible material is selected to absorb about when the half-life of the radioactive seeds is reached. 
A further aspect is to have the implant be echogenic. 
In accordance with an embodiment of the invention, the delivery system comprises a substantially axially stiff and longitudinally flexible elongated member that is bio-absorbable in living tissue.  The member has a length that greatly exceeds its width or diameter.  The elongated member has a plurality of radioactive seeds dispersed therein in a predetermined array. 
In another embodiment, the substantially axially stiff and radially flexible elongated member comprises a single continuous monofilament element of bio-compatible material that has a plurality of seed sources molded therein.  The bio-compatible material can be preferably a bio-absorbable polymer or copolymer material that encapsulates the plurality of radioactive seeds. 
A further embodiment of the invention is characterized as a substantially constant diameter elongated member of a bio-absorbable polymer with seeds positioned therein at predetermined spacing along its length, whose diameter is a close fit to the needle lumen, thus preventing collapse as axial force is applied on the proximal end of the elongated member.  The space between the seed sources is maintained throughout the insertion and expulsion of the elongated member.  The diameter of the polymer between the seeds maybe slightly reduced in relation to the overall diameter of the elongated member, but is of sufficient diameter so as to not allow collapse of the member within the needle lumen. 
The present embodiment of the invention further allows for variation in any spacing between seeds, as the semi-rigid, deflecting elongate member can be produced under a doctor""s prescription for each patient, with optimal seed distribution for a particular patient""s treatment program. 
Thus an object of the invention is to provide an implant that can be custom made as specified by a prescription for an individual patient. 
It is also desired that the present invention provide for elongate members shaped like half-shells.  Radioactive or other seed elements and/or spacers can then be placed within one half-shell.  The empty half-shell is then mated to the half-shell containing the seed elements or spacers, with the two half-shells now forming a tube structure that contains the seed elements and spacers.  Then the half-shells are heated, causing them to fuse into a single therapeutic element and fixing the seeds and spacers within the therapeutic element.  The resulting therapeutic element is axially rigid and radially flexible.  Two half-shells can also be assembled as described above containing the seed elements and spacers and liquid material flowed into the assembled half-shell.  The liquid material then solidifies, fusing the half-shells and fixing the seed elements and spacers inside.  The solidified material is axially rigid and radially flexible and may be a bio-absorbable polymer. 
In another embodiment, liquid polymer is flowed into a half-shell into which has previously been placed seeds.  The polymer can solidify at the other half-shell is placed in contrast with the first half-shell.  The assembly can be heated so the assembly fuses together. 
Another object of the present invention is to provide a bedside apparatus that produces interstitial radiation therapy seed strands made of a material having seeds disposed within the material with the seeds being accurately spaced a predetermined distance from one another. 
The present invention cures and addresses the disadvantages exhibited in the prior art devices, implants and manufacturing devices and methods.  It is also desired to provide a device and method that extrudes a bio-absorbable carrier material into an elongate hollow member and loads seeds within the bore of the extruded material, during or after extrusion, with the seeds being accurately spaced a predetermined distance from one another, and the seeds repeatably maintaining that spacing, even after being introduced into the body. 
Further aspects, objects, advantage and embodiment of the invention can be understood from the specification, the figures and the claims.