Patent Number: 048615200
Section: description

DETAILED DESCRIPTION OF THE INVENTION The known prior art source capsules can be best understood from FIG. 1, which shows a typical example thereof. The source capsule is composed of a tubular body 1 having a closed back end 2 and a cavity 3 for receiving and containing one or a plurality of radioactive sources 4, seven of which are shown in FIG. 1. The sources 4 are sealed in cavity 3 by plug 5 which, as shown in FIG. 5, is usually attached to tubular body 1 by a weld 6. Tubular body 1, in turn, is attached to a flexible cable 8 by means of a further weld 7. In such prior art devices, as shown in FIG. 1, the tubular body 1 has a typical length of 5.8 millimeters and the plug 5 has a typical length of 1.35 millimeters, the length of the plug being necessary to secure the plug in a holder during welding and performing the pull test, as explained above. Thus, the overall length of the capsule is 7.2 millimeters, apart from weld 7. Turning now to FIG. 2, which shows an embodiment of the present invention, the drivable radioactive source capsule of the present invention comprises a similar tubular body 1 having a similar cavity 3, but having a first end 10, which is preferably rounded as shown, formed thereon. By having such a rounded first end 10, as opposed to the plug 5 of the prior art (see FIG. 1), the first end of the capsule is much shorter than the front end of the prior art device containing the plug. This not only shortens the capsule, as noted above, but most desirably, locates the radioactive sources more near the front end of the capsule. This allows more accurate placement of the radioactive sources in the tissues being treated. Further, the entire metal walls and end of the capsule act as radiation shields. As shown in FIG. 1, the relatively massive plug 5 effects much greater shielding than the walls of the capsule. This results in a "dimple" in the isodose of radiation (the radiation dosage with respect to distance from the surfaces of the capsule). By eliminating the plug 5, the present rounded end does not effect a significant "dimple". Elimination of such "dimples" is especially important when using low energy-long wave length isotopes, such as Ir.sup.137, as opposed to higher energy sources such as cobalt 60. Tubular body 1 also has a second end 11 which is the terminus of the tubular body, as shown in Figure 2. As opposed to the prior art, the present invention provides a plug 12 having an elongated closure portion 13 with the diameter of the closure portion being substantially equal to the inside diameter (shown by arrows 14) of the tubular body 1. It will be appreciated in this regard that the term "substantially equal" means that the diameter of the elongated closure portion 13 is close to but slightly less than the inside diameter of tubular body 1, so that the closure portion 13 may be snugly fitted into tubular body 1. As can also be seen from FIG. 2, the closure portion 13 is of a sufficient length that it can be accurately placed in tubular body and will snugly contain the precise numbers of sources in the capsule such that the sources are not free to move within the capsule during use of the capsule. Of course, the radioactive sources will normally have a diameter essentially equal to (but slightly less than) the inside diameter of tubular body 1. Plug 12 also has a connection portion 15 disposed adjacent to the closure portion and forming a unitary plug. The diameter of the connection portion 15 is substantially equal to the outside diameter of the tubular body 1 and, also, preferably is substantially equal to the diameter of the drive cable 8. Thus, preferably the diameters of the drive cable 8, the plug 12 and the tubular body 1 are all substantially equal, so that the combination of the drive cable and capsule may be passed through a tubular guide for correctly disposing the capsule, with the radioactive sources therein, in the patient being treated. This is also preferred since if the diameter of the cable is substantially less than the diameter of the capsule, e.g. one-third less, (and, hence, also substantially less than the internal diameter of the tubular guide), the cable can bend or "snake" within the tubular guide during movement therethrough. This can result in not only binding of the cable, but also result in the cable actually moving the capsule a shorter distance through the tubular guide than would be indicated by the actual length of the cable having been driven from the head of the after loading apparatus. This could give a false indication as to the final position of the capsule in the patient being treated. Elongated flexible drive cable 8 is connected to the connection portion 15 of the plug 12 prior to assembly of the tubular body 1 to plug 12. By this arrangement, the radioactive sources 4 may be placed in the tubular body 1 through the opened second end 11, and the tubular body 1 is closed by disposing the closure portion 13 of plug 12 into the second end 11 of the tubular body 1 and attaching the closure portion 13 to the second end 11 of the tubular body 1. As noted above, the capsule is normally attached to the drive cable by welding. In the present invention, the drive cable 8 is welded to the connection portion 15 of plug 12 prior to closing tubular body 1 by plug 12. Thus, tongs or other similar holding devices can easily grip the combination of plug 12 and drive cable 8 for accurately placing plug 12 into tubular body 1, welding plug 12 thereto and performing the required pull test. By this arrangement, as opposed to the prior art, there is no need for an elongated plug, which elongated plug substantially increases the overall length of the capsule and adversely effected the isodose line, as explained above. Further, the radioactive sources are contained within the tubular body 1 between the first end 10 and the closure portion 13 of plug 12 so that the radioactive sources are very snugly held within the capsule. After such assembly, the closure portion 13 of plug 12 is attached to the second end 11 of tubular body 1 in any manner desired, but most often this attachment will be by a weld, as in the prior art. However, as noted above, that weld can be easily achieved without the necessity of the extended plug, which was required in the prior art. It has been found in this latter regard, that the weld of the closure portion 13 to the second end 11 is most advantageously carried out when the weld is an electron-beam weld. While electron-beam welding is well known in the art and the details thereof need not be set forth herein for sake of conciseness, with electron-beam welding, weld 6 (see FIG. 4) can very accurately and precisely attach closure portion 13 to second end 11 of tubular body 1. As can be appreciated, the welding of plug 12 to tubular body 1 must be a very accurate weld in order to ensure that plug 12 is fully seated in tubular body 1 and that the attachment of plug 12 to tubular body 1 is quite secure in order to avoid radiation source leakage or dislodgment of the plug, for the reasons explained above. Also, drive cable 8 can be attached to connecting portion 15 of plug 12 in any desired manner, but it is far preferable that that attachment be by means of a weld. However, in this case, it is preferred that the weld is a laser weld. Again, laser welding is well known in the art and need not be described herein for conciseness purposes, but laser welding has been found to be most effective in attaching the flexible drive cable (usually made of steel) to the connecting portion 15 of plug 12. It has been found that laser welding ensures a good connection of cable 8 to plug 12 so that no separation thereof occurs even when the cable and capsule are passed through tortuous turns in the tubular guide. In regard to the method of producing the capsule of the present invention, it is only necessary to provide the tubular body 1 having the rounded end 10. Means of producing such tubular bodies are well known in the art and need not be described herein. The tubular bodies are normally made of steel or like rigid metal material and can be formed by conventional machining techniques. The plug 12 preferably is machined, but it can be formed by a die casting technique, both of which processes are well known in the art. The flexible drive cable is then attached to the connection portion 15 of plug 12, preferably by welding as described above. A plurality of radioactive sources are then placed in tubular body 1 through second end 11. The closure portion 13 of plug 12 is then disposed within the tubular body through the second end 11. Thereafter, the closure portion 13 is attached to the second end 11, preferably by welding as described above. Preferably, the wires of cable 8 are first welded together to form a solid end and then simply butt welded to connection portion 15. However, if desired, a thread may be formed on the solid welded end of cable 8. The connection portion 15 may also be internally threaded (not shown in the drawings) and the threaded solid end of cable 8 is threaded into the internal threads of connection portion 15 and then welded, as described above. As shown in FIG. 2, with the present arrangement, the same number of sources, i.e. 7 sources, can be contained in a capsule with an overall length of 5 millimeters, as opposed to the overall length of 5.85 millimeters in the prior art capsules. Further, since the present plug 12 being previously attached to cable 8 can be much shorter than the prior art plug 5, the overall length of the capsule and plug of the present invention, as shown in FIG. 2, can be 5.5 millimeters, as opposed to the overall length of 7.2 millimeters with plugs of the prior art. This results in a shortening of the overall length of the capsule by 1.7 millimeters. While this shortening may seem quite small, that amount of shortening provides considerable advantages in passing the rigid capsule through a tortuous turn of, for example, a tubular guide and is a decided advantage in the art. In addition, the present rounded end provides a much more desirable isodose line, as explained above. FIG. 3 shows an embodiment similar to FIG. 2, but where the capsule contains eight radioactive sources. Again, it will be seen that the overall length is 6 millimeters, as opposed to the prior art capsule containing only seven sources and having an overall length of 7.2 millimeters. Thus, with the present invention, an additional source can be added to the capsule, while at the same time, substantially shortening the capsule, as opposed to prior art capsules. It will be apparent to those skilled in the art that modifications of the above-described invention can be easily appreciated, and it is intended that those modifications being included- .within the spirit and scope of the annexed claims.