Abstract:
An assembler which limits the amount of torque that may be applied to a brachytherapy cartridge magazine when its cap is threaded onto same. The assembler is constructed so that the brachytherapy cartridge will rotate within the assembler before a destructive torque is applied while the cap and cartridge magazine are screwed together.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of brachytherapy equipment. More specifically, the present invention is directed to an assembler for preventing a destructive torque being applied to a brachytherapy cartridge. 
     BACKGROUND OF THE INVENTION 
     Brachytherapy seed cartridges are provided with a number of radioactive brachytherapy seeds, e.g. I-125 or Pd-103 seeds, and used as a supply source of those seeds to be loaded into a seed applicator. The seed applicator is used to implant the seeds within a patient. FIGS.  1  and  2 A-C depict a typical seed cartridge  10  manufactured and sold by Mick Radio-Nuclear Instruments, Inc. of Mount Vernon, N.Y., U.S.A. Cartridge  10  includes a magazine  12  and a cap  14 . Magazine  12  includes an elongate seed channel  16  for receiving transversely-aligned brachytherapy seeds  18  and dispense aperture  20  from which the seeds are dispensed into the applicator. Cap  14  supports an elongate plunger  22  which is spring-biased to extend into channel  16  and urge the seeds  18  towards dispense aperture  20 . Magazine  12  further includes an external helical thread  24  for mating with an internal helical thread, not shown, within cap  14 . Cap  14  includes an external thread  26  to secure the assembled cartridge  10  in a V-block for steam sterilization. 
     To form a disposable, or single-use, cartridge  10 , magazine  12  and cap  14  are typically made of a suitable plastic material capable of withstanding steam sterilization. Alteniatively, cap  14  may be formed from stainless steel or brass in order to provide additional shielding. This later feature recognizes that a technician holding a cartridge component in each hand while threading the two components together, due to the proximity of the radioactive seeds to the technician&#39;s hands and fingers, presents exposure risks which should be minimized further. 
     Moreover, the art has seen instances of magazine  12  deforming and/or breaking when a technician applies a tightening torque to cap  14  which exceeds the torsional limit of the plastic magazine  12 . Typically, the magazine body is deformed so as to pinch on channel  16  and cause a functionality failure where the seeds will not descend properly under the spring tension of the plunger. The deformed or broken magazine  12  can also lose containment of the radioactive seeds, resulting in a loss of the loaded seeds and a potential hazard to personnel handling the cartridge. 
     SUMMARY OF THE INVENTION 
     In view of the needs of the prior art, the present invention provides an assembler which limits the amount of torque that may be applied to a brachytherapy cartridge during assembly when its cap is threaded on. The assembler is constructed so that the brachytherapy cartridge will rotate within the assembler before a destructive torque is applied by the cap to the magazine while the cap and magazine are screwed together. The assembler may be operated, and the cartridge thus assembled, using only one hand. The assembler includes a cartridge-receiving block having an elongate block body defining a cartridge aperture and an elongate cartridge receptacle extending about the longitudinal axis of the body. The longitudinal axis of the body is desirably closely aligned with the longitudinal axis of rotation of both the body and the cartridge. The cartridge receptacle extends in fluid communication with the cartridge aperture. The cartridge aperture and cartridge receptacle are sized and shaped to receive a portion of the cartridge magazine therein so as to allow the threaded assembly of a the cartridge cap assembly to the magazine. The block may rotate about the longitudinal axis. As the cap is threaded to complete the cartridge, the block body and the cartridge will begin to rotate about the axis before a damaging torque is applied from the cap to the cartridge. The assembler may include a planar base on which the block is rotationally mounted. Additionally or alternatively, the assembler may include a housing within which the block may rotate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a brachytherapy seed cartridge to be assembled using the present invention. 
         FIG. 2A  depicts the brachytherapy seed cartridge of  FIG. 1  showing the magazine filled with brachytherapy seeds. 
         FIG. 2B  depicts the brachytherapy seed cartridge of  FIG. 1  showing the magazine empty of brachytherapy seeds. 
         FIG. 2C  depicts the brachytherapy seed cartridge of  FIG. 1  with the cap separated from the magazine. 
         FIG. 3  depicts a brachytherapy seed cartridge assembler of the present invention. 
         FIG. 4  is a top elevational view of the assembler of  FIG. 3 . 
         FIG. 5  is a cross-sectional view of the assembler of  FIG. 3  taken through the line  5 - 5  of  FIG. 4 . 
         FIGS. 6 and 7  depict the base of the assembler of  FIG. 3 . 
         FIGS. 8 and 9  depict the housing of the assembler of  FIG. 3 . 
         FIG. 10  is an exploded view of the cartridge-receiving block of the assembler of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIGS. 3-5  depicts a seed cartridge assembler  100  of the present invention. The components of assembler  100  are desirably formed from stainless steel although other suitable materials may alternatively be used. Assembler  100  includes a cartridge-receiving block  102 , shown in phantom lines in  FIG. 3 , having an elongate block body  104  defining a cartridge aperture  106  and an elongate cartridge receptacle  108  extending about the longitudinal axis x of body  104 . Cartridge receptacle  108  extends in fluid communication with cartridge aperture  106 . Furthermore, cartridge aperture  106  and cartridge receptacle  108  are sized and shaped to receive at least a portion of a magazine  12  therein so as to expose the tread  24  of magazine  12  and to thereby allow the threaded assembly of cartridge cap  14  to magazine  12 . The depth of cartridge receptacle  108  may be selected according to the number of seeds which are typically to be loaded into magazine  12 , so as to expose the uppermost seed and provide a visual cue that the correct number of seeds are loaded into the magazine prior to threading cap  14  thereon. 
     Assembler  12  also includes planar base  110  on which block  102  may rotate about longitudinal axis x. With additional reference to  FIGS. 6 and 7 , planar base  110  includes opposed major surfaces  112  and  114  and a stepped passageway  116  extending therebetween. Passageway accommodates a pivot pin  118  having opposed free end  120  and head  122  and an elongate pin body  124  extending therebetween. Block body  106  defines a pin aperture  126  and an elongate pin receptacle  128  extending about longitudinal axis x. Pin receptacle  128  extends in fluid communication with pin aperture  126  and is positioned in overlying registry with passageway  116  of base  110 . Pivot pin head  122  seats against step  130  in base  110  and pin free end  120  is received within pin receptacle  128 . 
     Assembler  110  further includes a housing  132  affixed to base  110 . Housing  132  is desirably formed from stainless steel or another suitable radiation shielding material. With further reference to  FIGS. 8 and 9 , housing  132  includes a transversely-extending planar cover surface  134  supporting perimetrically-descending elongate planar walls  136   a - d . Walls  136   a  and  136   d  further include flanges  138  and  140  for secure fastening of housing  132  to base  110  so that walls  136   a - d  are upstanding from base  110 . Cover  134  of housing  132  defines a housing aperture  142  in fluid communication with cartridge aperture  106  and cartridge receptacle  108 . Block  102  and cover  132  are desirably coplanar across housing aperture  142 . Housing  132  further defines a block cavity  144  within which cartridge block  102  may rotate about axis x. 
     As particularly shown in  FIGS. 3 ,  5  and  10 , block body  102  includes cylindrical projection  150  defining cartridge aperture  106  that is coextensive with housing aperture  142  so as to prevent a loose brachytherapy seed from passing between housing cover  134  and block body  102 . 
     With particular reference to  FIG. 10 , block body  102  includes an elongate rectangular body  200  and a corner cap  202  forming an upper quadrant thereof. Desirably, block body  102  is first machined to provide cylindrical projection  150  on a top surface  204 . Projection  150  desirably being formed with dimensions which allow it to extend flush with cover surface  134  of housing  132  and in sliding abutment with housing  132  at aperture  142 . Corner cap  202  is then cut away from body  200  to allow cartridge aperture  106  and cartridge receptacle  108  to be machined into an exposed face  206 . Cartridge receptacle  108  is further defined by a transversely-extending planar step surface  208  and planar surfaces  210 ,  212 ,  214  adjacent thereto and descending away from cartridge aperture  106 . Cartridge aperture  106  and cartridge receptacle  108  are fully defined by providing planar surface  216  of corner cap  202  against faces  206  and  218  of body  200 . Cartridge receptacle  108  desirably conforms to the portion of magazine  12  of a cartridge  10  inserted therein. A bolt  220  is shown to extend through a bolt passageway defined by corner cap  202  and into an internally-threaded bolt receptacle  222  opening on face  206  to hold cap  202  to body  210 . While corner cap  202  is shown bolted to body  200 , it will be appreciated that any known fastening means may be used to reassemble the two components of block body  102 . 
     Thus the present invention further contemplates that block  102  may take any shape. Additionally, the present invention further contemplates that a block of the present invention may be provided unconstrained, that is without a mounting plate or housing. Desirably, axis x of body  104  is closely aligned with one of the rotational axes of block  102  and the cartridge inserted therein so that when rotation of block  102  is caused by screwing the cap  14  to the magazine  12 , any shear or non-axial loads on the cartridge components are minimized. For example, by way of illustration and not of limitation, the present invention further contemplates that the assembler includes an open cylindrical wall mounted on the planar base. The cylindrical wall would extend about block  102  so as to allow block  102  to rotate about axis x. It is further contemplated that a cylindrical wall could receive a cylindrical block defining the cartridge receptacle. Additionally, the cylindrical wall and the block are contemplated as being shaped so that the cylindrical wall positively holds the block against the base, so as to obviate the need for a pivot pin. And while cartridge receptacle  108  has been shown to closely conform to the portion of the cartridge  10  inserted therein, it is further contemplated that receptacle  108  may have any shape which ensures that block  102  will begin to rotate before the tightening of cap  14  onto magazine  12  causes damage to the magazine. These and other modifications will be apparent to one of ordinary skill in the art as being within the scope of the present invention. 
     According to a method of using the present invention, a magazine  12  loaded with brachytherapy seeds  18  is inserted into cartridge receptacle  108 . A cap  14  can then be assembled to magazine  12  by inserting the plunger  22  into channel  16  and threading cap  14  onto thread  24 . As cap  14  is tightened onto magazine  12 , block  102  will begin to rotate prior to the torque applied to cartridge  10  exceeding the structural limits of the body of magazine  12 . Testing on Mick cartridges has determined that the torque applied between magazine  12  and cap  14  should be less than about 1 inch-pound. However, it is contemplated that the rotational inertia of the present invention may be selected to accommodate any brachytherapy seed cartridge having two components to be threadably mated. 
     Additionally, to lessen the exposure risk to the radioactive seeds in the magazine, the present invention allows a technician to assemble the cartridge components using only one hand. The loaded cartridge may be positioned within the assembler and the cap then brought upon the cartridge thread and screwed down into place. If the weight and inertia, or friction force between the base and the surface upon which it rests, are sufficient, the technician may perform this assembly using only one hand. The technician may also use their free hand to hold the assembler by the base while threading the cap onto the magazine. Alternatively still, the technician may use their free hand to grasp the assembler by the housing while threading the cap onto the magazine. 
     While the particular embodiment of the present invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the teachings of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. The actual scope of the invention is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.