CAPSULE FOR RADIOACTIVE SOURCE

Abstract: A drivable radioactive source capsule is provided which comprises a tubular body (1) containing therein a plurality of radioactive sources (4). The said tubular body (1) has a first end and a second end which is a terminus of the tubular body. A plug (5; 12) has an elongated closure portion with the diameter of the closure portion being substantially equal to the inside diameter of said tubular body (1). The closure portion is disposed within the tubular body through the second end thereof and is attached to the second end of the tubular body. The plug (5; 12) has a connection portion adjacent the closure portion with the diameter of the connecting portion being substantially equal to the outside diameter of the tubular body. An elongated flexible drive cable (8) is connected to the connection portion of the plug (5; 12). By this arrangement, radioactive sources (4) may be placed in the tubular body (1) and the body is closed by disposing the closure portion of the plug into the second end of the tubular body and attaching the closure portion to the second end of the tubular body.

Description: The invention relates to a method for producing a drivable, radioactive source capsule. While apparatus of the above nature has been used for some time, a particular problem in connection therewith has been the ability of the capsule containing the radioactive source to be driven through the apparatus, especiaiiy the tubular guise, when that tubular guide is disposed in a tortuous path. The capsule, for safety reasons, must ensure that the radioactive source or sources contained therein are not dislodged from the capsule either while in the after loading apparatus or while passing through the tubular guide or while in the patient. To this end, the capsules are made of metal, and the radioactive source or sources are sealed in the metal capsule, usually by welding, to ensure that no dislodging of the radioactive sources will take place. Since the capsule is made of metal, the capsule is rigid, and when the capsule encounters a tortuous turn in the tubular guide, or other parts of the apparatus or in the patient, the capsule may not be able to traverse that tortuous turn and becomes lodged. As can be appreciated from the foregoing, it is therefore important that the length of the rigid capsule be as short as possible. Typically, the internal diameter of the tubular guide will only be about 1.5 millimeters or less and, consequently, the diameter of the capsule must be about 1.5 millimeters or less, usually about 1.1 millimeters. The capsules most often contain one or a plurality of radioactive sources, e.g. 4, 5, 6, 7, 8 or even 10 or more, and the length of the capsule is correspondingly increased with the number of sources. A typical capsule, containing seven radioactive sources, will have an overall length of approximately 7.2 millimeters. When a capsule of that length encounters a tortuous turn, e.g. in the tubular guide, the chances of the capsule binding in that turn significantly increases. As can be appreciated from the foregoing, even small deviations in the length of the capsule significantly affect the ability of the capsule to traverse such tortuous turns. In usual and known method of manufacturing source capsules,a flexible transport cable is attached to the back end of a capsule. The front end of the capsule is open so that the required radioactive source or numbers of sources may be placed into the capsule. Thereafter, the front end of the capsule is sealed by inserting a rounded plug into the front end of the capsule, and that plug is then attached to the capsule, usually by welding. However, in such a welding operation, the plug must be held in position for welding by a holder having a pair of tongs or grippers with the result that the plug must have a certain minimum length in order to be securely held by such holder during the welding operation. In addition, the attachment, e.g. weld, is tested by a strong axial pull on the plug and the apparatus for gripping the plug for such pull test requires a plug of substantial relative length, e.g. about a minimum of 1.35 millimeters. As can be appreciated, this pull test is necessary in order to insure that the plug is well attached to the capsule, since if the plug dislodged from the capsule and allowed the source or sources to be lost in the apparatus, or much worse in the patient, disastrous results would ensue. Consequently, the overall length of the capsule, with the plug attached, is increased beyond that necessary for the capsule containing the radioactive sources, and this increased length increases the chances of the capsule binding in the tubular guide or other parts of the apparatus during an attempted traverse of a tortuous turn. For the sake of completeness US-A-2,816,341 is mentioned from which a radioactive source capsule is known, which capsule is rounded at the front and can be closed with a plug at the rear end. The plug is, however, fastened by screwing, and in turn must be attached to a next auxiliary member forming part of a drive cable. The capsule thus formed is of considerably overall inflexible length. As can, therefore, be appreciated, it would be a substantial advantage to the art to provide a capsule which can contain the same number of radioactive sources as known capsules, but which capsule is of a significantly shorter length than the known capsules. Therefore the invention provides a method according to claim 1. The invention can be more fully understood from the following detailed description. Figure 1 is a partial cross-section of known prior art source capsules having a flexible drive cable attached thereto. Figure 2 is a partial cross-section of the source capsule according to the present invention having a flexible drive cable attached thereto. Figure 3 is similar to Figure 2, but shows the source capsule of the present invention attached to a flexible drive cable, with additional sources in the source capsule. Figure 4 is a detail of Figure 2; and Figure 5 is a detail of Figure 1. The known prior art source capsules can be best understood from Figure 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 Figure 1. The sources 4 are sealed in cavity 3 by plug 5 which, as shown in Figure 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 Figure 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, as explained above. Thus, the overall length of the capsule is 7.2 millimeters, apart from weld 7. Turning now to Figure 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 rounded first end 10, 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. 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 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 Figure 2, the closure portion 13 is of a sufficient length that it can be accurately placed in tubular body 1 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, substantially is equal to the diameter of the drive cable 8. Thus, 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. 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 the drive cable 8. 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 and welding plug 12 thereto. 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. 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 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. Also, drive cable 8 is attached to connecting portion 15 of plug 12 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 die casting techniques. The plug 12, again made of metal such as steel, can either be machined or 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 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 1 through the second end 11. Thereafter, the closure portion 13 is attached to the second end 11 welding as described above. Preferably, the wires of cable 8 are first welded together to form a solid end and a thread is formed on the solid end. The connection portion 15 is also threaded (not shown in the drawings) and the threaded solid end of cable 8 is threaded into connection portion 15 and then welded, as described above. As shown in Figure 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 Figure 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. Figure 3 shows an embodiment similar to Figure 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.

Claims: 1. Method for producing a drivable, radioactive source capsule, wherein a tubular body (1) having a closed anal and open end is produced, a flexible drive cable (8) is welded to the connecting portion of a plug (12) provided also with a closure postion, the connecting portion having a diameter substantially equal to the outside diameter of the tubular body (1) and the closure portion having a diameter substantially equal to the inside diameter of the tubular body, a plurality of radioactive sources is placed in said tubular body through the open end thereof, the closure portion of the plug is disposed within the tubular body through the open end thereof and the closure portion is welded (6) to the open end of the tubular body. 2. Method according to claim 1 wherein said welding of the drive cable to the connecting portion of the plug is by laser welding. 3. Method according to calim 1 wherein the weld of the closure portion of the plug to the tubular body is an electron-beam weld. 4. Method according to claim 2 wherein the end ot the flexible drive cable (8) is welded into a solid end, a thread is formed on the solid end and the threaded solid end is welded onto the connecting portion of said plug.

Inventors: VAN 'T HOOFT, ERIC, VAN ZWOL, LIBBE
Applicants: VAN 'T HOOFT, ERIC
Application year: 1989
Main classification: G21G4
IPC codes: A61N5, G21G4, A61M36