Patent Number: 051209730
Section: summary

TECHNICAL FIELD OF THE INVENTION The invention relates to a method and device for inserting radioactive radiation sources into applicators and for withdrawing the radiation sources, comprising at least one shielded loading and/or storage station for the radiation sources, and a flexible thrust wire guided in a channel and having a coupling adapted to release the radiation source in the radiation position. BACKGROUND OF THE INVENTION AND PRIOR ART A device of this kind is described in European published application No. 0 158 630. It consists of one or more identical modules each comprising a shielded loading and/or storage station for radiation sources, which may not be identical, and a push rod, and offers the possibility of separating the conveying device from a hollow needle in the radiation position by operating a coupling between the radiation source and the push rod that is releasable in the radiation position. The radiation source can be introduced into the hollow needle by the push rod under remote control, and is released and deposited therein. During the treatment the hollow needle can be separated from the push rod so as to give the patient a large measure of freedom of movement. At the end of the treatment the conveying device is again coupled with the hollow needle, so that after engagement of the coupling the individual radiation sources can again be withdrawn individually into the loading and/or storage station. This known device has the disadvantage that a module with a conveying device is required for each radiation source. A further and more serious disadvantage is that in order to leave a radiation source in an applicator the coupling has to be released within the applicator. However, since the space available in hollow radiation needles for interstitial use is very limited, it is difficult to arrange a reliable release mechanism for the coupling in the radiation needle. OBJECT OF THE INVENTION It is therefore an object of the invention to provide a device and a process by means of which it is possible to bring radiation sources from a loading and/or storage station into an applicator, separate them there from the conveying device, leave them there for the duration of the treatment of a patient, and withdraw them again at the end of the treatment by means of the conveying device without operating or controlling the coupling in the region of the applicator. The means for doing this should be of simple construction and easy to use. SUMMARY OF THE INVENTION To this end, the invention consists in providing, in a device of the kind mentioned above, two drives connected respectively to a thrust and a traction wire each guided in a channel, the channels being combined at a fork. In cooperation with a radiation source the traction wire has a releasable coupling effective in the direction of traction and the thrust wire has a releasable coupling effective only in the direction of thrust. A switch is located between the channels leading to the applicators and those leading to the loading and/or storage station on the one hand and the fork on the other hand, and a means for releasing the coupling effective in the direction of traction is located between the switch and the fork. The switch may have a plurality of entrances and exits. The entrances may be connected via channels to the loading and/or storage station and the exits via channels to a corresponding number of applicators. In order to extract a radiation source from a storage channel in the loading and/or storage station and introduce it into one of the applicators, the traction cable having a releasable coupling effective in the direction of traction is first of all advanced by means of one of the two drives via the fork and the appropriately set switch into a storage channel of the loading and/or storage station, is coupled with the radiation source, and withdraws it into the region of the release means for the coupling effective in the direction of traction, which is arranged between the fork and the switch. There, the radiation source and the traction wire are separated, the traction wire is again withdrawn to its end position, and the thrust wire is advanced through the fork until it reaches the radiation source: it then pushes the radiation source through the switch into the applicator. Since there is no connection effective in the direction of traction between this thrust wire and the radiation source, the thrust wire merely serves to move the radiation source forward by pushing and can be withdrawn to its starting position after bringing the radiation source into the applicator, leaving the radiation source in the applicator. It will thus be seen that with two drives, one of which moves the radiation source in the direction of traction and the other in the direction of thrust, and by the provision of a fork and a switch, a very large number of radiation sources can be brought from a loading and/or storage station to a corresponding number of applicators. The applicators can then be separated from the device and remain in the patient. The device does not have to be recoupled with the applicators until the treatment is finished, when the radiation sources are moved successively back to the loading and/or storage station in the manner described. The radiation sources can comprise needle-shaped holders that are filled with radioactive material and have at one end a sleeve with inwardly-facing spring elements which, together with a pin that is located on one end of the traction wire and can be introduced into the sleeve, forms the releasable coupling effective in the direction of traction. Once introduced into the sleeve the pin is held frictionally by the ends of the springs and can be separated in a simple manner by means of a stop cooperating with an end face of the sleeve. For this purpose the greatest diameter of the end of the traction wire with the pin may be less than the diameter of the sleeve, and the stop may consist of a wire duct having an internal diameter greater than the diameter of the end of the traction wire carrying the pin but less than the diameter of the sleeve. Alternatively the radiation sources may consist of needle-shaped holders that are filled with radioactive material and have at one end a sleeve with inwardly-facing resilient hooks which, together with a locking groove on a pin located at one end of the traction wire to engage with the hooks, forms the releasable coupling effective in the direction of traction. In this case a form-locking connection is formed between the hooks and the groove in the pin which cannot come apart as the radiation source is transported through the channels. In this case the means of releasing the coupling effective in the direction of traction may comprise wedge-shaped faces that engage under oblique faces on the hooks, with the greatest diameter of the end of the traction wire carrying the pin being less than the diameter of the sleeve and the internal diameter of a wire duct through the release means being greater than the diameter of the end of the traction wire carrying the pin but less than the diameter of the sleeve. As another possibility, the radiation sources may consist of needle-shaped holders that are filled with radioactive material and consist at one end of magnetic material which, together with an extension, also of magnetic material, at one end of the traction wire, forms the releasable coupling effective in the direction of traction. In this case the release means can also consist of a stop cooperating with an end face of the sleeve, as described above for the first embodiment.