Abstract:
Methods and apparatus are provided for brachytherapy treatment of prostate disease for use in conjunction with needles containing a plurality of radioactive seeds. The apparatus comprises a housing and plunger assembly operable by a single clinician. The plunger is coupled to the housing, so that when the apparatus is actuated the needle is retracted against the plunger and the plurality of radioactive seeds is ejected.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application is a continuation-in-part of U.S. patent application Ser. No. 09/522,282, filed Mar. 9, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to improved apparatus and methods for the treatment of prostate cancer. More particularly, the present invention provides improved methods and apparatus for administering brachytherapy.  
         BACKGROUND OF THE INVENTION  
         [0003]    Excluding non-melanoma skin cancers, prostate cancer is the most common cancer afflicting American men. The American Cancer Society estimates that over 180,00 new cases will be diagnosed in the U.S. in the year 2000 alone, and that nearly 32,000 people will die from the disease. Prostate cancer is second only to lung cancer as the leading cause of cancer death in men, accounting for roughly 11%.  
           [0004]    Prostate cancer is defined as malignant tumor growth within the prostate gland. Its cause is unknown, although high dietary fat intake and increased testosterone levels are believed to be contributory factors. A letter scale (“A” through “D”), which accounts for the location of the cancer, is commonly used to classify the stage of disease. In Stage A, the tumor is not palpable, but is detectable in microscopic biopsy. Stage B is characterized by a palpable tumor confined to the prostate. By Stage C, the tumor extends locally beyond the prostate with no distant metastasis. By Stage D, cancer has spread to the regional lymph nodes or has produced distant metastasis.  
           [0005]    In the early stages, prostate cancer is most commonly treated by prostate removal or by brachytherapy. More advanced cases are treated by hormonal manipulation or orchiectomy to reduce testosterone levels and curb spreading of the disease, by chemotherapy, or by external beam radiation therapy.  
           [0006]    With regard to treatment of early stage prostate cancer, the state of the art has several drawbacks. Radical prostatectomy is often recommended for treatment of localized stage A and B prostate cancers. Under general or spinal anesthesia, an incision is made through a patient&#39;s abdomen or perineal area, and the diseased prostate is removed. The procedure is lengthy, especially if a lymph node dissection is simultaneously performed, and requires a hospital stay of 2-5 days. Possible complications include impotence and urinary incontinence.  
           [0007]    Internal radiation therapy or brachytherapy has recently been modified and holds great promise for the treatment of early stage prostate cancer. Radioactive pellets or seeds of, for example, iodine-125, gold-198, palladium-103, ytterbium-169, or iridium-192, are deposited directly into the prostate through needle placement. Imaging tests, such as transrectal ultrasound, CT scans, or MRI, are used to accurately guide placement of the radioactive material. Advantageously, radiation is administered directly to the prostate with less damage to surrounding tissues, requiring a significantly smaller radiation dosage as compared to external beam radiation therapy. Furthermore, the procedure need only be performed once. Complications include a lower, yet still significant, incidence of impotence and urinary incontinence, compared to prostate removal procedures.  
           [0008]    The radioactive seeds are placed inside thin needles, which are inserted through the skin of the perineum (area between the scrotum and anus) into the prostate. U.S. Pat. No. 5,928,130 to Schmidt provides a slightly modified example of such a needle device. Each needle is slowly retracted with a spinning motion by a first practitioner while a plunger within the needle, and proximal of the radioactive seeds, is held stationary by a second practitioner. The plunger keeps the seeds in place during retraction of the needle, while rotation of the needle during retraction prevents jamming of the seeds while delivering the seeds in a line within the prostate.  
           [0009]    The seeds, which are permanently implanted, give off radiation for weeks or months. Their presence causes little discomfort, and they are left in the prostate after decay of the radioactivity. For about a week following needle insertion, patients may experience pain in the perineal area, and urine may have a red-brown discoloration.  
           [0010]    Although, when performed correctly, radioactive seed implantation may provide several benefits, compared to prostate removal and other techniques, current surgical apparatus and methods for delivering the seeds to target locations within the prostate are somewhat crude and are subject to practitioner error. The procedure requires two practitioners working cooperatively to deliver the seeds. The depth to which the plunger is inserted into the needle, in the loaded and advanced states, is critical but crudely measured. The plunger and needle may accidentally move relative to one another during needle insertion or seed delivery, causing improper positioning of deposited seeds. The needle is somewhat flexible and should be inserted quickly to minimize bending at its distal tip, but this is often not done due to inexperience or technical ability of the practitioners, or to avoid potential relative movement between the plunger and the needle.  
           [0011]    Attempts have been made to address various aspects of these concerns. For example, U.S. Pat. No. 4,815,449 to Horowitz describes an absorbable member with seeds spaced within the member to facilitate proper spacing during delivery. U.S. Pat. No. 4,700,692 to Baumgartner describes apparatus for delivering all of the seeds simultaneously. PCT document WO 99/20337 to Rydell describes a gun-like apparatus for delivering seeds once the needle has been inserted into the prostate.  
           [0012]    While each of these devices may provide some benefit over the prior art, none satisfactorily addresses the shortcomings of current techniques. In view of the drawbacks associated with previously-known methods and apparatus for brachytherapy, it would be desirable to provide methods and apparatus that overcome such drawbacks.  
           [0013]    It further would be desirable to provide methods and apparatus that allow efficient preparation of the apparatus for therapeutic administration.  
           [0014]    It still further would be desirable to provide methods and apparatus for administering brachytherapy that require only one medical practitioner.  
           [0015]    It further would be desirable to provide methods and apparatus that yield easy measurement and maintenance of plunger depth within the needle.  
           [0016]    It would also be desirable to provide methods and apparatus for brachytherapy that allow rapid insertion of the needle while maintaining the distance between the needle and plunger.  
         SUMMARY OF THE INVENTION  
         [0017]    In view of the foregoing, it is an object of the present invention to provide methods and apparatus for brachytherapy that overcome drawbacks associated with previously-known methods and apparatus.  
           [0018]    It is also an object of the present invention to provide methods and apparatus that allow efficient preparation of the apparatus for therapeutic administration.  
           [0019]    It is another object to provide methods and apparatus for brachytherapy that require only one medical practitioner.  
           [0020]    It is yet another object to provide methods and apparatus that yield easy measurement and maintenance of plunger depth within the needle.  
           [0021]    It still further is an object of the present invention to provide methods and apparatus for brachytherapy that allow rapid insertion of the needle while maintaining the distance between the needle and plunger.  
           [0022]    These and other objects of the present invention are accomplished by providing methods and apparatus for brachytherapy treatment of prostate cancer comprising a specialized housing that maintains needle/plunger spacing, provides easy measurement of plunger depth within the needle, requires only one practitioner to operate, and enables rapid needle insertion. The plunger is either permanently or selectively fixed with respect to the housing, while the needle is removably coupled to the housing. Either the plunger or the housing wall is threaded to receive the needle. Measurement indicia on the apparatus simplify determination of plunger depth within the needle. Optionally, a locking mechanism may be used to maintain plunger depth during needle insertion. To deliver seeds, the needle is rotated while the housing is held stationary, causing the needle to retract along the screw thread.  
           [0023]    In a preferred embodiment, the needle is rotated manually, and includes a mechanism for first ejecting a seed-retaining plug disposed in a distal end of the needle. Alternatively, the needle may attach to a swivel that rotates the needle by pulling it proximally along the screw thread. In a still further embodiment, a pull tab may be used to rotate the needle.  
           [0024]    Methods of using the present invention are also provided. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    Additional objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims, in which:  
         [0026]    [0026]FIG. 1 is a schematic view of a prior art method of performing brachytherapy;  
         [0027]    FIGS.  2 A- 2 G are schematic views detailing the prior art method in greater detail;  
         [0028]    [0028]FIG. 3 is an isometric exploded view of a first embodiment of apparatus constructed in accordance with the present invention;  
         [0029]    [0029]FIG. 4 is a cross-sectional view of the apparatus of FIG. 3;  
         [0030]    [0030]FIG. 5 is a cross-sectional view of an alternative embodiment of apparatus of the present invention;  
         [0031]    [0031]FIG. 6 is an isometric exploded view of a further alternative embodiment of the present invention comprising a swivel;  
         [0032]    [0032]FIG. 7 is a cross-sectional view of the apparatus of FIG. 6;  
         [0033]    [0033]FIG. 8 is an isometric exploded view of a still further alternative embodiment with a syringe swivel;  
         [0034]    [0034]FIG. 9 is a cross-sectional view of the apparatus of FIG. 8;  
         [0035]    [0035]FIG. 10 is an isometric exploded view of yet another alternative embodiment of apparatus of the present invention comprising a pull tab;  
         [0036]    [0036]FIG. 11 is a cross-sectional view of the apparatus of FIG. 10;  
         [0037]    [0037]FIG. 12 is a detail view of the cross-section of FIG. 11;  
         [0038]    [0038]FIG. 13 is a plan view of a preferred embodiment of the apparatus of the present invention;  
         [0039]    [0039]FIGS. 14A and 14B are, respectively, side sectional and exploded perspective views of the internal structure of the apparatus of FIG. 13; and  
         [0040]    [0040]FIGS. 15A and 15B are, respectively, side sectional and exploded perspective views of another illustrative embodiment of the apparatus of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]    The present invention provides methods and apparatus for improved administration of brachytherapy. More particularly, the present invention provides a threaded housing with that maintains the position of the plunger with respect to the needle and provides controlled retraction of the needle.  
         [0042]    Referring now to FIGS. 1 and 2A- 2 G, the prior art method of performing brachytherapy is described. The method and apparatus are as taught by Peter Grimm, DO, in a pamphlet entitled, “Ultrasound Guided Implantation of the Prostate: A Practical Review Course.” As seen in FIG. 1, brachytherapy apparatus  50  comprises transrectal ultrasound probe  52 , guide block  54 , needle  56 , plunger  58 , and radioactive seeds  60 . Ultrasound probe  52  is advanced through a patient&#39;s rectum R to facilitate imaging of the patient&#39;s prostate P. Prostate P surrounds the urethra U and is just proximal of the bladder B. Needle  56 , loaded with seeds  60  and plunger  58 , is advanced through the patient&#39;s perineum Pe into prostate P, where needle  56  is retracted and seeds  60  are delivered to the patient.  
         [0043]    With reference to FIG. 2, a previously known seed delivery method is described in greater detail. Needle  56  has proximal end  62 , sharpened distal end  64 , and a lumen extending therebetween. Proximal end  62  comprises hub  66  for easy grasping of the needle. The opening at the distal tip of needle  56  is initially filled with a material that prevents seeds  60  from falling out of the-needle, and may comprise, for example, bone wax that melts when placed inside the body. The needle lumen typically is filled in an alternating pattern of seeds  60  and spacers  68 .  
         [0044]    Once a required number of seeds have been loaded, plunger  58  is inserted into proximal end  62  of needle  56  and is advanced distally until it abuts the proximal-most seed. Plunger  58  comprises grip  70  at its proximal end. The distance from the distal end of grip  70  to the distal end of the plunger is equal to the length of needle  56 . Thus, since seeds  60  and spacers  68  are of known length, measurement of D 1 , the distance plunger  58  extends proximally of needle  56  in the loaded configuration, provides verification of the number of seeds  60  located within the needle lumen, as seen in FIG. 2A.  
         [0045]    Ultrasound probe  52  provides signals that are converted by a previously known ultrasound system to display ultrasonic image  72  of base plane BP, which is located at a tangent to the distal surface of prostate P. All positions within the prostate are determined relative to base plane BP. With seeds  60  loaded into needle  56  and the distance D 1  verified; the needle, seeds, and plunger  58  are inserted through guide block  54  and into the patient until needle  56  appears as target T on ultrasonic image  72  and extends about a centimeter distal of base plane BP, as depicted in FIG. 2B. The apparatus is then retracted until target T disappears (FIG. 2C) and is once again advanced until target T just reappears (FIG. 2D). All the while, distance D 1  is maintained.  
         [0046]    Once needle  56  is aligned with base plane BP, a distance D 2  between the proximal face of guide block  54  and the proximal face of hub  66  is established, as shown in FIG. 2E. D 2  serves as the reference distance for determining insertion depth for all subsequent needle insertions. A first medical practitioner then holds needle  56  stationary while a second medical practitioner advances the first seed  60  to the distal tip of the needle with plunger  58 , as depicted in FIG. 2F. The advancement distance equals the length BW of the plug in the distal tip of the needle.  
         [0047]    Finally, the second medical practitioner holds plunger  58  stationary while the first practitioner rotates and proximally retracts needle  56  to sew the seeds in a line within prostate P, as shown in FIG. 2G. The needle and plunger are then removed from the patient, and the procedure is repeated at other locations as necessary.  
         [0048]    With reference now to FIGS. 3 and 4, a first embodiment of apparatus constructed in accordance with the present invention is described. Apparatus  100  comprises housing  102 , plunger  104 , needle  106 , and optional lock  108 . Lock  108  is configured to be received in slot  110  of needle  106 . Needle  106  further comprises lumen  107 , an actuator comprising male screw thread  112 , and measurement indicia  113 . Housing  102  comprises lumen  114 , in which plunger  104  is rigidly fixed, threaded bore  116  with female screw thread  118 , and standard bore  120 . When assembled, male thread  112  of needle  106  engages female thread  118  of housing  102 , and plunger  104  extends into lumen  107  of needle  106 .  
         [0049]    A method of using apparatus  100  in accordance with the principles of the present invention is now described. Needle  106 , loaded with seeds  60  and spacers.  68  in lumen  107 , is inserted through bore  120  until male thread  112  of needle  106  just mates with female thread  118  of bore  116 .  
         [0050]    At this point, plunger  104  extends partially within lumen  107  of needle  106 , so that plunger  104  just contacts the proximal-most seed  60 . Also, slot  110  of needle  106  is just distal of the opening to bore  120 . Lock  108  is removably received within slot  110  and ensures that plunger  104  is not advanced distally with respect to needle  106  until the needle is inserted within a patient&#39;s prostate. Lock  108  ensures that distance D 1  between the proximal end of needle  106  and proximal base  122  of bore  116  (which is roughly equal to the length of bore  116 ) is maintained during insertion. Since D 1  is positively maintained during insertion, the apparatus of the present invention should advantageously cause medical practitioners to be less reticent about rapid insertion of the needle into a patient.  
         [0051]    Measurement indicia  113  of needle  106  permit easy determination of distance D 1 , and, thus, verification of the number of seeds  60  contained within lumen  107  of needle  106 . As an illustrative example, D 1  is such that the proximal-most indicator mark  113  extends beyond the distal end of housing  102 . If this marking is ‘0’, the proximal end of needle  106  is in contact with proximal base  122  of bore  116 . If it is ‘1’, there is one centimeter of separation, etc.  
         [0052]    After insertion of the needle into the patient, lock  108  is removed, thereby allowing relative movement between plunger  104  and needle  106 . Initially, needle  106  is held stationary while housing  102  is rotated to advance the distal-most seed  60  to the tip of needle  106 . Then, housing  102  is held stationary while needle  106  is rotated. This causes needle  106  to retract proximally along thread  118  while plunger  104  remains stationary, thereby controllably sewing seeds  60  in a row in the prostate. Since the sewing motion is simplified, compared to prior art apparatus  50 , only one practitioner is required to perform the procedure.  
         [0053]    The distance D 1  may be altered as needed by altering the length of bore  116  and, thus, the length of housing  102 . Alternatively, bore  116  may be of a standard length in excess of that required for D 1 . Needle  106  then may comprise multiple slots  110  along its length to receive lock  108 . The distance D 1  then may be fixed at a variety of lengths.  
         [0054]    Referring now to FIG. 5, an alternative embodiment of the present invention is disclosed. Apparatus  130  comprises housing  132 , plunger  134 , needle  136 , and lock  138 . Lock  138  is configured to be received in slot  140  of needle  136 . Needle  136  further comprises lumen  137 , female screw thread  142  along the walls of the proximal portion of its lumen, and measurement indicia (not shown). Plunger  134  comprises male screw thread  144  along its proximal end. Housing  132  comprises lumen  146 , in which plunger  134  is rigidly fixed, and bore  148 .  
         [0055]    Needle  136 , loaded with seeds  60  and spacers  68 , is inserted through bore  148  until female thread  142  of needle  136  just mates with male thread  144  of plunger  134 . Thus, apparatus  130  is similar to apparatus  100 , except that needle  136  threadingly engages plunger  134 , rather than the housing.  
         [0056]    With reference to FIGS. 6 and 7, a further alternative embodiment of the present invention is detailed. Apparatus  150  comprises housing  152 , plunger  154 , needle  156 , and lock  158 . Lock  158  is configured to be received in slot  160  of needle  156 . Needle  156  further comprises lumen  157 , male screw thread  162 , measurement indicia  163 , and swivel  164  including cord  166 . Housing  152  comprises lumen  168 , in which plunger  134  is rigidly fixed; threaded bore  170  with female screw thread  172 ; and a standard bore (not shown) similar to bore  120  of apparatus  100 . Housing  152  further comprises cord bore  174  through which cord  166  passes out of housing  152 .  
         [0057]    In use, cord  166  is threaded through cord bore  174  and the male and female screw threads are engaged as described hereinabove with reference to apparatus  100 . Needle  156  then may be retracted proximally with respect to housing  152  by holding the housing stationary and pulling cord  166  proximally. The needle rotates and retracts within the screw thread, while swivel  164  moves proximally in bore  168 , but does not rotate.  
         [0058]    Referring now to FIGS. 8 and 9, a still further alternative embodiment of the present invention is described. Apparatus  180  comprises housing  182 , plunger  184 , needle  186 , syringe swivel  188 , and lock  190 . Lock  190  is configured to be removably received in slot  192  of needle  186 . Housing  182  comprises lumen  194 , in which plunger  184  is rigidly fixed; threaded bore  196  with female screw thread  198 ; and a standard bore (not shown) similar to bore  120  of apparatus  100 . Housing  182  is formed in two halves  200  and  202  joined at hinge  204 . Hinge  204  preferably is a ‘living hinge’ as may be constructed using polymers, such as polypropylene, and previously known manufacturing techniques. Needle  186  further comprises lumen  187 , male screw thread  206 , measurement indicia  207 , and swivel attachment  208 . Syringe swivel  188  comprises swivel attachment  210 , bore  212 , and enlarged proximal end  214 , and is formed in two halves  216  and  218  joined at hinge  220 . As with hinge  204 , hinge  220  preferably comprises a living hinge.  
         [0059]    Housing  182  and syringe swivel  188  are opened at hinges  204  and  220 , respectively, so that swivel attachments  208  and  210 , and the male and female screw threads, engage each other. The housing and syringe swivel are then closed. After insertion into a patient, needle  186  may be retracted proximally with respect to housing  182  by holding the housing stationary and retracting enlarged end  214  of syringe swivel  188  proximally. Needle  186  rotates and retracts within the screw thread while syringe swivel  188  moves proximally but does not rotate.  
         [0060]    With reference to FIGS.  10 - 12 , yet another alternative embodiment of the present invention is described. Apparatus  230  comprises housing  232 , plunger  234 , needle  236 , pull tab  238 , and lock  240 . Lock  240  is configured to be received in slot  242  of needle  236 . Needle  236  further comprises lumen  237 , male screw thread  244 , and measurement indicia  245 . Housing  232  comprises lumen  246 , in which plunger  234  is rigidly fixed, threaded bore  248  with female screw thread  250 , standard bore  252 , and slot lumen  254  configured to receive pull tab  238 . Slot lumen  254  is preferably located just off center of the radial axis of housing  232  and communicates with bore  252 . Pull tab  238  comprises grip  256  and female threads  258 .  
         [0061]    Needle  236 , loaded with seeds  60  and spacers  68 , is inserted through bore  252  into threaded bore  248  until male thread  244  of needle  236  mates with both female screw thread  250  of housing  232  and female threads  258  of pull tab  238 . As most clearly illustrated in FIG. 11, needle  236  then may move relative to housing  232  simply by holding housing  232  stationary and pulling or pushing pull tab  238 . Pulling tab  238  causes needle  236  to rotate and proximally retract in a controlled fashion along screw thread  250  of housing  232 , and along threads  258  of pull tab  238 , thereby sewing the seeds along the needle track.  
         [0062]    Whereas the preceding embodiments contemplate that the needle include a thread that acts as an actuator in conjunction with a thread in the housing to retract the needle, if would be preferable to provide embodiments adapted to accept commercially available brachytherapy needles. Two such embodiments, which work in accordance with the principles of the present invention set forth hereinabove, are now described.  
         [0063]    Referring now to FIGS. 13 and 14, a preferred embodiment of the present invention suitable for commercial manufacture is described. Apparatus  260  includes housing  261  having spiral groove  262  on its interior surface, knob  263  rigidly coupled to actuator  264 , needle coupling  265  and stop mechanism  266  coupled to plunger  267 . Plunger  267  is disposed within the lumen of seed-laden needle  275  when needle  275  is coupled to needle coupling  265 . In this embodiment, plunger  267  is selectively set to a predetermined seed length using stop mechanism  266 , before needle  275  is attached to needle coupling  265 .  
         [0064]    Needle coupling  265  is disposed for sliding translation and rotation in central bore  268  of actuator  264 , and includes pin  269  that extends through elongated slot  270  of actuator  264  and extends into spiral groove  262 . Actuator  264  is rotatably disposed in housing  261 . Rotation of knob  263  causes rotation of actuator  264 , thereby driving pin  269  along spiral groove  262  and elongated slot  270 . This is turn causes needle coupling to be rotated and advanced or retracted through central bore  268  of actuator  264 . When a seed-laden needle is coupled to needle coupling  265 , rotation of knob  263  causes the needle to be rotated and retracted into housing  261 . Plunger  267 , which remains stationary during needle retraction, causes the seeds to be ejected from the distal tip of the needle.  
         [0065]    Stop mechanism  266  permits the number of seeds to be varied from needle to needle during a particular procedure, and includes a coarse adjustment for the number of seeds used in a given needle, and a fine adjustment feature that permits the plug at the distal end of the needle to be ejected without changing the position of the distal tip of the needle. Stop mechanism includes stop body  271  having ratchet  272  slidably disposed in lumen  273 , wherein the travel is limited by pin  274  that extends into elongated slot  276  (this subassembly is shown in exploded view in the upper right hand portion of FIG. 14B). Stop body  271  includes a series of partial circumference through-wall slits  277  arranged along its length at predetermined distances (e.g., 1 cm apart), and includes fiducial markings F on the upper surface of the stop body (see FIG. 13) aligned with slits  277 .  
         [0066]    Distal end  278  of stop body  271  extends through rear cover  279  of housing  261  and window  280  of lock  281 , and is affixed to collar  282 . Rear cover  279  includes notch  283  that accepts tab  284  of lock  281  and spring  285 . Tab  284  includes button  286  and is biased upward by spring  285 . Button  286  permits lock  281  to be depressed to permit stop body  271  to be advanced distally through window  280 . Spring  285  causes the lower edge of window  280  to engage one of slits  277  and a corresponding one of teeth  287  of ratchet  272  when button  286  is released.  
         [0067]    Stop body knob  288  is affixed to proximal end  289  of stop body  271 . Distal end  290  of ratchet  272  extends through spring  291  and is rigidly coupled to ratchet knob  292 . Spring  291  biases ratchet knob  292  in a proximal direction. Teeth  287  of ratchet  272  include sloped proximal edges  293 . The sloped proximal edges of teeth  287  permit ratchet  272  to be advanced through window  280  of lock  281  in the distal direction by urging ratchet knob  292  in the distal direction, while simultaneously maintaining engagement between a selected slit  278  in stop body  271  and lock  281 . This in turn permits plunger  267  to be advanced one unit in the distal direction, e.g., to eject the needle plug, while maintaining the position of the distal tip of stationary.  
         [0068]    Operation of apparatus  260  is now described. To use apparatus  260 , the clinician rotates knob  263  to advance needle coupling  265  to its distal-most position, and depresses button  286  to ensure that lock  281  is disengaged from ratchet  272  and ratchet knob  292  is biased in the proximal direction by spring  291 . The clinician then sets the seed length by depressing button  286  and advancing or retracting stop body  271  using stop body knob  288  until the desired fiducial mark F is aligned with the endface of rear cover  279 . Button  286  then is released to capture the corresponding slit in stop body  271 .  
         [0069]    A seed-laden needle is then slid proximal-end first over plunger  267  and the luer of the needle affixed to needle coupling  265 , for example, using luer threads (not shown) disposed in distal end of needle coupling  265 . The needle and apparatus of the present invention then is inserted into the patient&#39;s prostrate using a needle guide and an rapid insertion technique. Once the needle position is confirmed, e.g., using ultrasound, the clinician urges ratchet knob  292  in the distal direction to eject the plug from the distal tip of the needle. In particular, when ratchet knob  292  is advanced, window  280  of lock  281  rides along the sloped edge of tooth  288  and locks into the next proximal-most tooth  288  of ratchet  272 , while stop-body  271  remains engaged with lock  281 . This step is similar to that illustrated in FIG. 2F.  
         [0070]    Once the plug is ejected from the distal end of the needle, housing  261  is held stationary by the clinician in one hand while knob  263  is rotated by the other. Rotation of knob  263  causes actuator  264  to rotate within housing  261 , thereby causing pin  269  to be retracted along spiral groove  262  in housing  261 . This in turn causes needle coupling  265  to be retracted into central bore  268  of actuator  264 , thereby also rotating the needle attached to needle coupling. Because plunger  267  remains fixed at the depth selected on stop body relative to the housing, rotation and retraction of the needle causes the seeds to be ejected into the prostrate. Accordingly, a single clinician can implant seeds faster and more accurately than the conventional method using two clinicians.  
         [0071]    When all the seeds in the needle have been implanted, the needle is removed from the patient and knob  263  is rotated in the reverse direction to fully expose needle coupling  265 . The spent needle is removed from needle coupling  265 , and then the process described above is repeated for subsequent needles, until the procedure is completed. Apparatus  260  preferable can be manufactured from low-cost plastic components with few machined or stamped metal components, and is therefore disposable after use for a single patient.  
         [0072]    Referring now to FIGS. 15A and 15B, an alternative embodiment of the apparatus suitable for commercial manufacture is described. Apparatus  300  is less preferred than the embodiment of FIGS. 13 and 14, and employs several machined components. Accordingly, the embodiment of FIG. 15 may be more suitable for manufacture from metallic alloys, and therefore autoclavable for repeated use.  
         [0073]    Apparatus  300  comprises many of the components employed in the embodiment of FIGS. 13 and 14, including housing  301  having spiral groove  302  on its interior surface, knob  303  rigidly coupled to actuator  304 , needle coupling  305  and stop mechanism  306  coupled to plunger  307 . Plunger  307  is disposed within the lumen of a seed-laden needle when such a needle is coupled to needle coupling  305 . As in the previous embodiment, plunger  307  is selectively set to a predetermined seed length using stop mechanism  306 , before the needle is attached to needle coupling  305 .  
         [0074]    Needle coupling  305  is disposed for sliding translation and rotation in central bore  308  of actuator  304 , and includes pin  309  that extends through elongated slot  310  of actuator  304  and extends into spiral groove  302 . Actuator  304  is rotatably disposed in housing  301 , so that rotation of knob  303  causes rotation of actuator  304 , thereby driving pin  309  along spiral groove  302  and elongated slot  310 . This is turn causes needle coupling to be rotated and advanced or retracted through central bore  308  of actuator  304 . When a seed-laden needle is coupled to needle coupling  305 , rotation of knob  303  causes the needle to be rotated and retracted into housing  301 . Plunger  307 , which remains stationary during needle retraction, causes the seeds to be ejected from the distal tip of the needle.  
         [0075]    Stop mechanism  306  performs the same function as stop mechanism of  266  of the embodiment of FIGS. 13 and 14 by permitting the number of seeds to be varied from needle to needle during a particular procedure. This embodiment also includes a coarse adjustment for the number of seeds used in a given needle, and a fine adjustment feature that permits the plug at the distal end of the needle to be ejected without changing the position of the distal tip of the needle.  
         [0076]    Stop mechanism  306  includes stop body  311  having threaded rod  312  extending therethrough. Stop body  311  includes a series of partial circumference through-wall slits  313  arranged along its length at predetermined distances (e.g., 1 cm apart), and includes fiducial markings F on the upper surface of the stop body aligned with slits  313 . Stop body also includes a longitudinally-oriented slot that permits threaded pawl  314  to engage the threads of threaded rod  312 .  
         [0077]    Distal end  315  of stop body  311  extends through rear cover  319  of housing  301  and window  320  of lock  321 , and is affixed to collar  322 . Rear cover  319  includes notch  323  that accepts upper and lower tabs  324  and  325  of lock  321 , spring  326 , and pawl  314 . Upper tab  324  serves as a button and is biased upward by spring  326 . Upper tab  324  permits lock  321  to be depressed to permit stop body  311  to be advanced distally through window  320 . Spring  326  causes the lower edge of window  320  to engage one of slits  313 , and for pawl  314  to engage threaded rod  312 , when the upper tab is released.  
         [0078]    Distal end  328  of threaded rod  312  is affixed to sleeve  329 . Sleeve  329  is coupled to cap  330 , which is disposed in bore  331  in stop knob  332 . Cap  330  is keyed to the shape of bore  331 , so that rotation of stop knob  332  causes rotation of cap  330 , sleeve  329  and threaded rod  312 . Collar  334  is affixed to proximal end  335  of stop body  311 , and includes circumferential groove  336 . Stop knob  332  includes pin  337  that extends into groove  336 , thereby permitting rotation of stop knob  332 , but not translation. Spring  338  is captured on sleeve  329  between collar  334  and cap  330 , and biases cap  330  in a proximal direction.  
         [0079]    Rotation of stop knob  332  causes rotation of cap  332 , sleeve  329  and threaded rod  312 . Because threaded rod  312  is threadedly engaged with pawl  314  by the biasing action of spring  326 , rotation of stop knob  332  causes threaded rod  312  to advance distally, thereby causing plunger  307  to advance in the distal direction. Accordingly, after the needle has been inserted into the patient, stop knob  332  may be rotated to eject the plug at the distal end, while maintaining the position of the distal tip of stationary.  
         [0080]    Operation of apparatus  300  is similar to that of the embodiment of FIGS. 13 and 14, and is now described. To use apparatus  300 , the clinician rotates knob  303  to advance needle coupling  305  to its distal-most position, and depresses upper tab  324  to ensure that lock  321  is disengaged from slit  313  and pawl  314  is disengaged from threaded rod  312 , whereby cap  330  is biased in the proximal direction by spring  338 . The clinician then sets the seed length by depressing upper tab  324  of lock  321  and advancing or retracting stop body  311  using stop knob  332  until the desired fiducial mark F is aligned with the endface of rear cover  319 . Upper tab  324  then is released to capture the corresponding slit in stop body  311 , and so that pawl  314  engages threaded rod  312 .  
         [0081]    A seed-laden needle is then slid proximal-end first over plunger  307  and the luer of the needle affixed to needle coupling  305 , for example, using luer threads (not shown) disposed in distal end of needle coupling  305 . The needle and apparatus of the present invention then is inserted into the patient&#39;s prostrate using a needle guide and an rapid insertion technique. Once the needle position is confirmed, e.g., using ultrasound, the clinician rotated stop knob  332  to advance threaded rod  312  and plunger  307  to eject the plug from the distal tip of the needle.  
         [0082]    Once the plug is ejected from the distal end of the needle, housing  301  is held stationary by the clinician in one hand while knob  303  is rotated by the other. Rotation of knob  303  causes actuator  304  to rotate within housing  301 , thereby causing pin  309  to be retracted along spiral groove  302  in housing  301 . This in turn causes needle coupling  305  to be retracted into central bore  308  of actuator  304 , thereby also rotating the needle attached to needle coupling. Because plunger  307  remains fixed at the depth selected on stop body relative to the housing, rotation and retraction of the needle causes the seeds to be ejected into the prostrate.  
         [0083]    When all the seeds in the needle have been implanted, the needle is removed from the patient and knob  303  is rotated in the reverse direction to fully expose needle coupling  305 . The spent needle is removed from needle coupling  305 , and then the process described above is repeated for subsequent needles, until the procedure is completed.  
         [0084]    Although particular embodiments of the present invention have been described above in detail, it will be understood that this description is merely for purposes of illustration. Specific features of the invention are shown in some drawings and not in others; this is for convenience only, and any feature may be combined with another in accordance with the invention. Further variations will be apparent to one skilled in the art in light of this disclosure and are intended to fall within the scope of the appended claims.