an embodiment of the device disclosed herein that has a radiographically detectable band provides means whereby the device can be located after implantation . thus , embodiments of the present invention may be formed with a band of a radiographically - detectable material such as gold , platinum or another appropriate high - atomic - number element deposited near the center on the external surface of the hollow - tube - shaped seed - substrates . this band allows the visualization of the implanted device by standard radiographic procedures and allows the location and orientation to be accurately determined during treatment or in advance of surgery . the radiographically detectable band may be applied to entirely encircle the external surface of the hollow - tube - shaped seed - substrate at right - angles to the longitudinal axis of the seed . the band may be 1 . 2 mm wide and be centrally positioned to allow accurate determination of the position of the seed by standard radiographic , fluoroscopic or computer - tomography visualization . the band of radio - detectable material such as gold , platinum or another appropriate high - atomic - number element may be deposited by means similar to those described below for deposition of the radioactive source material . in manufacturing one embodiment of the invention disclosed herein , a therapeutic radioisotope is deposited on the outward - facing surface of the hollow - tube - shaped seed - substrate in such a manner as to produce an essentially uniform cylindrical radiation field in close proximity to the device . the radioactive layer is then covered by a sealing layer , the purpose of which is to prevent the escape of a significant amount of the radioactive material into the surrounding living body . the disposition of the radioactive source layer on the external surface of the hollow - tube - shaped seed - substrate may be varied to achieve different ends . as example , the radioactive source layer may extend over the entire external surface of the hollow - tube - shaped seed - substrate and extend over a previously - applied radiographically detectable band . in an alternative embodiment the radioactive source layer may be excluded from a region at each end of the external surface of the hollow - tube - shaped seed - substrate in order to provide a narrow non - radioactive ring at each end of the seed . in a further embodiment , the radioactive source layer may extend over the entire external surface of the hollow - tube - shaped seed - substrate with the exception of the region that bears the radiographically detectable band . an embodiment of the invention disclosed herein may have the central hollow - tube - shaped seed - substrate formed from a material essentially transparent to the radiation emitted by the therapeutic isotope . such materials may be elements such as titanium , carbon , tantalum , hafnium or zirconium or an alloy such as stainless - steel . alternatively , organic polymers may be used for fabrication of the hollow - tube - shaped seed - substrate and may be any of a number of materials such as polypropylene , polyethylene terephthalate , nylon , polyurethane , polyphenylene oxide blends , polyphenylsulfone , polysulfone , polyether sulfone , polyphenylene sulfide , phenyletheretherketone , polyetherimide or liquid crystal polymers . such polymers and their sources are disclosed in table 1 . table 1______________________________________acceptable nonabsorbable polymers withtheir trade names and commercial sourcesmaterial trade names sources______________________________________polyurethane texin , desmopan , bayer corp ., estane b f goodrichpolypropylene surgilene , prolene ethicon , american cyanamidpolyethylene impet , petra , rynite , allied , hoechst , terephthalate ( pet ) estar celanese , dupont , eastmanpolyphenylene oxide noryl , prevex general electricblends ( ppo ) polyphenylsulfone radel r amoco ( ppsu ) polysulfone ( psu ) udel , ultrason s amoco , basfpolyether sulfone ( pes ) radel a , ultrason e amoco , basfpolyphenylene sulfide fortron , ryton , supec hoechst , celanese ,( pps ) phillips , gephenyletheretherketone kadel , victrex amoco , victrex ( peek ) polyetherimide ( pei ) ultem genylon nylon dupontliquid crystal polymer vectra hoechst , celanese ( lcp ) ______________________________________ a further feature of embodiments of the invention is that the radioactive layer is covered by a sealing layer , the purpose of which is to prevent contact with the radioactive isotope and to prevent the escape of radioactive material into the surrounding living body . the sealing layer may be a material essentially transparent to the radiation emitted by the therapeutic isotope , such as pyrolytic carbon deposited from a chemical vapor . an alternative sealing layer such as titanium may be deposited from an atomic vapor . a further embodiment of the sealing layer may comprise an organic coating , as for example a coating formed from a heat shrinkable plastic , a coating produced by solvent evaporation , a coating produced by a polymerization reaction or by molding plastic around the exterior of the device . an optional feature of the invention disclosed herein is to provide a radiographically detectable band , desirably applied near the median point of the long axis of the device with sufficient width and opacity to make the device visible and its orientation apparent on a radiograph taken of a patient following implantation of the device . the lumen of the hollow - tube - shaped seed - substrate comprises a substantial proportion of the total diameter of the device . in a preferred embodiment , the total wall thickness of the seed including the inner tube substrate , radioisotope source material layer , radiographically - detectable band if present and sealing layer is approximately 0 . 15 mm , and the lumen diameter is approximately 0 . 51 mm , large enough to admit the passage through it of suturing needles and sutures . in other embodiments of the instant invention , the wall of the hollow - tube - shaped seed - substrate may be pierced transversely by one or more perforations . in embodiments that have perforations through the wall of the tube , the perforations may be shaped and oriented in any direction in order to best serve the purposes disclosed below . in embodiments of the device that are provided with perforations , the perforations provide access for body fluids to the lumen of the tube . perforations in the wall of the tube may also provide anchor points as tissue grows into the holes . perforations may desirably be in the range of 0 . 031 to 0 . 31 mm wide . the hollow - tube - shaped seed - substrate of the instant invention may be made of titanium or other biocompatible metal or may be made of synthetic material such as plastic . where titanium or other biocompatible metal is used , the tubes may be formed by a standard cold - drawing processes to form metal tubes . for example , hollow - tube - shaped seed - substrates of the instant invention may be made from astm b265 - 78 grade 2 titanium by forming tubular sections 4 . 5 mm in length , 0 . 57 mm in outside diameter and 0 . 5 mm inside diameter . such titanium tubes are available commercially in the u . s . a . from the uniform tube company , collegeville , pa . 19426 . where the hollow - tube - shaped seed - substrate of the instant invention is made of plastic or synthetic material , the seed - substrate may be formed by extruding or molding the tube from the mass material in a manner suitable to the material being formed . a number of engineering plastics represent acceptable materials including polypropylene , polyetherimide , polyethylene terephthalate , nylon , polyurethane , polyphenylene oxide blends , polyphenylsulfone , polysulfone , polyether sulfone , polyphenylene sulfide , phenyletheretherketone , polyetherimide or liquid crystal polymers . these materials are available from suppliers listed in table 1 . other polymeric and plastic materials that are suitable for use in the present invention will be obvious to those skilled in art . the radioactive source material of the instant invention is disposed as a layer on the external surface of the hollow - tube - shaped seed - substrate . the instant invention differs in this respect from prior art brachytherapy devices . in the prior art , brachytherapy devices are generally disclosed in which the radioactive source material is present in association with a pellet or rod contained within an encapsulating chamber . the structure of the instant invention is advantageous in that all components of the source , including the disposition of the radioactive source material and a radiographically detectable band , if present , are deposited onto the external surface of the structural member of the seed , the hollow - tube - shaped seed - substrate . the central lumen of the seed - substrate is unobstructed , thus making the hollow design possible with all the subsequent advantages imparted by that design . designers of prior art brachytherapy devices made use of internal components such as pellets or rods to provide a support for the radioactive source material of the seed . in some prior art designs , radiographically - detectable markers were also encapsulated together with the radioactive source material . the use of such internal components in prior art designs requires an encapsulating chamber and precludes a hollow - tube - shaped seed design . the radioactive source layer is applied to the hollow - tube - shaped seed - substrate by any of a variety of conventional process such as sputtering , laser ablation , cathodic arc plasma deposition , curvilinear cathodic arc plasma deposition , vapor deposition , or electroplating . such known processes are further set forth in u . s . pat . no . 5 , 342 , 238 to good , the disclosure of which is hereby incorporated by reference . for example , but not by way of limitation , the radioactive layer on the hollow - tube - shaped seed - substrate may be electroplated onto the external surface of the hollow - tube - shaped seed - substrate . the exact method for application of the layer depends upon the material to be deposited and the material of which the tube is constructed . if the tube is constructed from a material which does not conduct electricity , such as a plastic , the outer surface must first be metallized to make it conducting . this may be achieved by any one of several standard techniques commonly used in the plastics industry . if the tube is constructed from a material difficult to electroplate , such as titanium , a surface pretreatment is required to obtain reliably - adherent electrodeposition of plating layers . for example , a surface pretreatment procedure for titanium has been disclosed by pratt whitney aviation that includes an abrasive blast , a hot alkaline cleansing in 30 % potassium hydroxide , a hydrochloric acid pickle , a &# 34 ; bright dip &# 34 ; ( achieved by dipping in an aqueous solution of 12 % by volume acetic acid , 70 % hydrofluoric acid and 1 % nitric acid ), an &# 34 ; anodic etch &# 34 ; for 6 minutes at 162 amperes per square meter ( achieved in 13 % by volume hydrofluoric acid , 83 % acetic acid and 4 % water ), a &# 34 ; sulfate nickel strike &# 34 ; to an approximate thickness of 25 microinches followed by drying in air for 2 hours at 48 degrees c . this process achieves deposition of a thin nickel layer onto the surface of the titanium , thus providing a more advantageous surface layer for electroplating . if desired , a radiographically detectable band , for example a band of gold approximately 0 . 01 mm thick by 1 . 2 mm wide , deposited from a commercial electroplating solution ( for example aurotechp1 from at & amp ; t electroplating chemicals and services ) can be deposited directly onto a previously - applied thin nickel layer applied as described above . embodiments of the instant invention may incorporate different therapeutic isotopes in order to achieve different therapeutic purposes and to achieve different activities . for example , beta - particle emitting isotopes such as yttrium - 90 and phosphorus - 32 may be prepared with total activities of from 0 . 1 to 100 millicuries . beta - emitting devices are anticipated to be used for therapy where relatively little penetration of the radioactivity is desired . in other embodiments isotopes that emit electromagnetic radiation are used . such embodiments may have activities as high as 10 curies and are used in applications such as short - term applications of only a few minutes to prevent or inhibit the restenosis of blood vessels after angioplasty . if the therapeutic radioisotope is palladium - 103 , the radioactive source material layer may be deposited onto the hollow - tube - shaped seed - substrate by the method disclosed in u . s . pat . no . 5 , 405 , 309 to carden , the disclosure of which is hereby incorporated by reference . this electroplating technology can provide apparent activities of from 0 . 1 to 300 millicuries per seed . if the therapeutic radioisotope to be used is iodine - 125 , a uniform layer of silver is first deposited onto the outer surface of the hollow - tube - shaped seed - substrate . any of the techniques cited above can be used for this purpose provided a uniform and adherent layer of approximately 0 . 025 mm thickness results . the iodine - 125 is then chemisorbed onto the silver layer by the method disclosed in u . s . pat . no . 4 , 323 , 055 to kubiatowicz , the disclosure of which is hereby incorporated by reference . this procedure can provide apparent seed activities of from 0 . 1 to 100 millicuries per seed . the radioactive material layer may be deposited in a radioactive form such as the application of palladium - 103 , iodine - 125 or yttrium - 90 . alternatively , a precursor isotope such as gold - 197 , yttrium - 89 or palladium - 102 may be deposited and then transmuted in situ , for example , by bombardment with neutrons , into the desired therapeutic isotope . for example , yttrium - 89 may be deposited on the outer surface of the hollow - tube - shaped seed - substrate by electroplating or otherwise depositing the yttrium - 89 , and yttrium - 90 may be produced by bombardment with neutrons to transmute the non - radioactive isotope . gold - 198 ( generally referred to by this designation , though containing gold - 199 isotope as well ), yttrium - 90 and palladium - 103 may be produced by analogous processes . the application of brachytherapy sources for the medical therapeutic application of radiation requires that the radioactive source be entirely sealed to prevent escape of the radioisotope . this is essential to preclude the systemic distribution of the isotope within the patient and contamination of medical personnel , medical facilities and the general environment . in the preferred embodiments of the instant invention , the entire radioisotope source layer is provided with a biologically - compatible , radiation - permeable , surface - sealing layer that entirely seals the external surface of the hollow - tube - shaped seed - substrate with the radioactive and radiographically detectable layers applied thereon . the sealing layer seals to the ends of the hollow - tube - shaped seed - substrate ensuring a hermetic seal . the sealing layer prevents radioactive materials from escaping and provides a radioactive device which meets the normal definition of a &# 34 ; sealed source .&# 34 ; in one embodiment the sealing layer may be made of a plastic material or any other biocompatible organic material , provided the material is adequately transparent to the therapeutic radiation and has sufficient durability to protect and retain the radioisotope . such a sealing layer will cover the entire external surface and the layers applied thereon of the hollow - tube - shaped seed - substrate . such a sealing layer may be made from a heat shrinkable plastic , or from a coating formed by solvent evaporation or polymerization reaction , or by molding plastic around the exterior of the device . the adjacent ends of the outer sealing layer and the hollow - tube seed - substrate are joined by the process of applying the sealing layer . in another embodiment the sealing layer may be made of a plastic material or any other biocompatible organic material , provided the material is adequately transparent to the therapeutic radiation and has sufficient durability to protect and retain the radioisotope . such a sealing layer will have the form of an outer tube that covers the entire external surface and the layers applied thereon of the hollow - tube - shaped seed - substrate . such a sealing layer may be made from any of a number of plastics shown in table 1 . the adjacent ends of the outer sealing tube and the hollow - tube seed - substrate may be joined by one of several processes . for example they may be joined by gluing , heat sealing , ultrasonic welding or solvent welding . manufactured devices are tested for physical integrity and leakage , following the appropriate standard as for example , ansi - 44 . 2 1973 , ansi - 542 1977 and / or iso - 2919 . these test standards ensure that devices comply with the requirements to be defined as sealed sources by testing for physical integrity and leakage . in another embodiment the sealing layer can be made of titanium , hafnium or zirconium metal or other suitable biocompatible metal that is adequately transparent to the therapeutic radiation . such a sealing layer will seal to the ends of the hollow - tube - shaped seed - substrate and cover the entire external surface and the layers applied thereon of the hollow - tube - shaped seed - substrate . this sealing layer may be applied as a hollow tube which is swaged and bonded on each end of the hollow tube seed substrate . in an alternative embodiment , the sealing layer may be applied as a layer of metal deposited by any of the means cited above to form the radioactive layer . in yet another embodiment the sealing layer can be made of a layer of titanium carbide , titanium nitride , titanium carbonitride , hafnium nitride , or zirconium nitride as disclosed by good , or be made of another suitable biocompatible metal or metal compound that is adequately transparent to the therapeutic radiation . such a sealing layer will cover the entire external surface and the layers applied thereon and seal to the ends of the hollow - tube - shaped seed - substrate or the internal surface of the hollow - tube - shaped seed - substrate in a manner that suffices to meet the objectives of the instant invention . a detailed description of a particular embodiment of the instant invention is made by reference to fig1 a and 1b . the embodiment of the instant invention disclosed in fig1 a comprises a novel brachytherapy seed - substrate that has the form of a hollow tube open on both ends and having an internal surface 102 and external surface 103 . the hollow - tube - shaped seed - substrate 101 of the device 100 may be made of titanium or other biocompatible metal or may be made of synthetic material such as plastic . the radioactive source material 104 is disposed as a uniform layer on the external surface 103 of the device . the radioactive layer 104 thus has the form of a cylinder disposed upon the external surface 103 of the hollow - tube - shaped seed - substrate 101 . a radiographically detectable layer 105 is shown layered on a portion of the external surface 103 of the hollow - tube - shaped seed - substrate . the radiographically detectable layer 105 is thus similarly in the form of a cylinder on the external surface 103 of the hollow - tube - shaped seed - substrate 101 disposed at right - angles to the long axis of the seed - substrate . the entire device 100 is provided with a biologically - compatible , radiation - permeable , surface - sealing layer 106 that entirely covers and seals the radioactive layer 104 , the radiographically detectable layer 105 and the ends of the hollow - tube - shaped seed device . the biologically - compatible , radiation - permeable , surface - sealing layer 106 is applied by a process such as shrink - wrapping and forms a seal 107 to the hollow - tube - shaped seed - substrate 101 . the lumen of the device 108 is shown . fig1 b shows the details of the hollow - tube - shaped seed - substrate 101 open at an end and having an internal surface 102 and an external surface 103 . the radioactive layer 104 is shown as a uniform layer on the external surface 103 of the device 100 . the device 100 is provided with a biologically - compatible , radiation - permeable , surface - sealing layer 106 that entirely covers and seals the radioactive layer 104 and the end of the device 100 . the biologically - compatible , radiation - permeable , surface - sealing layer 106 is applied by a process such as shrink - wrapping and forms a seal 107 to the tube - shaped seed - substrate 101 . the lumen of the device 108 is shown . fig2 a and 2b show a diagrammatic representation of a cross - section of an embodiment of the instant invention that is formed with a perforation 209 through the wall of the device 200 and is sealed with an electroplated sealing layer 206 . the cross - section shows a portion of the hollow - tube - shaped seed - substrate 201 and its internal surface 202 and its external surface 203 . the diagram shows the location of the radioactive layer 204 upon the external surface 203 of the hollow - tube - shaped seed - substrate 210 and the radiographically detectable layer 205 also disposed upon the external surface 203 of the hollow - tube - shaped seed - substrate 201 . the radioactive layer 204 is excluded from the terminal portion 207 of the external surface 203 of the hollow - tube - shaped seed - substrate 201 . the diagram shows the sealing - layer 206 covering the radioactive layer 204 , the radiographically detectable layer 205 and the external surface 203 of the hollow - tube - shaped seed - substrate 201 . the seal 207 between the electroplated sealing layer 206 and the end 210 of the hollow - tube - shaped seed - substrate 201 is shown . fig2 b shows a diagrammatic representation of the detail of a cross - section of an end of a device 200 of the instant invention that is formed with a electroplated sealing layer 206 . the cross - section shows a portion of the hollow - tube - shaped seed - substrate 201 and its internal surface 202 and its external surface 203 . the diagram shows the location of the radioactive layer 204 upon the external surface 203 of the hollow - tube - shaped seed - substrate 201 . the diagram shows the sealing - layer 206 covering the radioactive layer 204 . the end 207 of the hollow - tube - shaped seed - substrate 201 from which the radioactive layer 204 is excluded is shown , together with the seal 210 between the sealing layer 206 and the end 207 of the hollow - tube - shaped seed - substrate 201 . a novel feature of an embodiment of the brachytherapy device disclosed herein is the external tube that is swaged and laser welded to the hollow - tube - shaped seed - substrate shown in fig3 a and 3b . in fig3 a a diagrammatic cross section of a complete hollow - tube device 300 with an external sealing tube 311 is shown . the cross - section shows the hollow - tube - shaped seed - substrate 301 , its internal surface 302 and its external surface 303 . the diagram shows the location of the radioactive layer 304 upon the external surface 303 , the location of the hollow - tube - shaped seed - substrate 301 and that of the radiographically detectable layer 305 also disposed upon the external surface 303 of the hollow - tube device 300 . the diagram shows the outer sealing - layer 311 enclosing the radioactive layer 304 and the radiographically detectable layer 305 . the end of the hollow - tube device 300 showing the swaged region 312 and laser - welded region 313 is shown . fig3 b is a diagrammatic representation of a cross - section of the swaged and laser welded end of double - walled tube device shown in fig3 a . the cross - section shows the end of the tube - shaped seed - substrate 301 and its internal surface 302 and its external surface 303 . the diagram also shows the location of the radioactive layer 304 upon the external surface 303 of the hollow - tube - shaped seed - substrate 301 . the outer sealing - layer 311 is shown enclosing the radioactive layer 304 . the swaged region 312 and the laser - welded region 312 at the end of the sealed device is shown . a particular utility of the hollow - tube - shaped brachytherapy device disclosed herein is its ability to be surgically sewn into position by sutures or rigid elements passed through the lumen of the device . fig4 shows a perspective representation of a device 401 and a portion of a second device 402 of this invention disposed on a suture 403 . fig5 shows a view of a device of this invention 504 shown disposed on a rigid surgical support 505 as the device would be used in practice .
a novel brachytherapy device is formed from a hollow - tube - shaped seed - substrate , allowing the easy association of the device with suture material . this shape minimizes the chance of migration of implanted seeds due to better attachment to tissue . the distribution of the radioactive material on the exterior surface of the tubular device provides a relatively uniform radiation field around the hollow - tube - shaped brachytherapy seed source . brachytherapy devices are described that are inherently radioactive . also disclosed are devices that can be rendered radioactive by the transmuting effects of neutron irradiation . brachytherapy devices are discussed that facilitate medical application and improve safety for patients and medical personnel .