Patent Number: 061920959
Section: description

PREFERRED EMBODIMENT OF THE INVENTION .sup.133 Xe Radioactive Stent In a half-life of 5.25 days, xenon-133 undergoes .beta.-disintegration, whereupon it emits .beta.-rays at a maximum energy of 350 keV, as well as 81 keV of .gamma.-rays and internal conversion electrons due to .gamma.-decay. This means that not only .beta.-rays but also internal conversion electrons are expected to contribute to intravascular irradiation. In addition, due to their low energy, .beta.-rays are only applied to intimae and will not affect other parts of the blood vessels. As a further advantage, .sup.133 Xe which is gaseous is easy to handle and has a higher ionization efficiency than .sup.32 p to be ion injected more efficiently with an ion injector. Ion Injection with Ion Injector As shown in FIGS. 1 and 2, ion injection is performed in vacuo with a uniform irradiating unit 10 provided within an ion injector 8 and this is in order to achieve uniform ion injection into the surfaces of cylindrical stents 2 made of stainless steel, tantalum or its alloys. Since the created ion beam has a larger diameter and a shorter length than the stents, uniform irradiation of the entire surface of each stent has to be assured by using a uniform irradiating unit equipped with a rotating table 3 capable of not only rotation but also vertical movements. Connecting Nuclear Reactor to Ion Injector Xenon- 133 is a nuclear fission product which is constantly generated by nuclear fission in fuel rods in a nuclear reactor upon irradiation of 1.sup.235 U with neutrons. If the fuel rods are connected to an ion source 9 in the ion injector via piping, the gaseous .sup.133 Xe generated in the fuel rods can be transferred through the piping to the ion source in the ion injector. Radioactive stents can be mass produced by allowing the supplied .sup.133 Xe to be continuously ion injected into the surfaces of stents by means of the ion injector. Stated more specifically, if neutrons impinge on .sup.235 U in the fuel rods 5 in the nuclear reactor 4, the resulting nuclear fission of .sup.235 U gives rise to .sup.133 Xe in a gaseous form. The generated .sup.133 Xe gas passes through the piping 6 to enter a Xe purifier 7, where it is worked up to the pure form. The pure .sup.133 Xe gas moves on through the piping 6 to be supplied into the ion source 9 within the ion injector 8 . The supplied .sup.133 Xe gas is ionized to yield an ion beam, which is introduced into the irradiating unit 10 in the ion injector and directed to one of the stents positioned on the vertically movable rotating table 3 in the irradiating unit. Since the rotating table is capable of not only rotation on its shaft but also vertical movements, all stents erected on the table are uniformly irradiated with the ion beam, whereby .sup.133 Xe is uniformly injected into the surfaces of the stents. The following example is provided for the purpose of further illustrating the present invention. EXAMPLE Gaseous 1.sup.33 Xe (40 MBq) was transferred to a 3.8-L sample container via a vacuum line. The container was also charged with ca. 3 cm.sup.3 of concentrated .sup.129 Xe isotope as a mass indicator in mass spectrometry. The container was connected to a Nielsen-type ion source in an ion injector, from which 40 keV or 60 keV of .sup.133 Xe was ion injected into the surfaces of stents each having a length of 14 mm and an outside diameter of 1.4 mm. To assure uniform irradiation of the surface of each stent, the ion injector was equipped with a vertically movable rotating irradiator (see FIG. 1). While the .sup.133 Xe ion beam 1 was flying in a fixed path, the rotating table 3 not only moved vertically but also rotated, thereby permitting the .sup.133 Xe ion beam 1 to impinge uniformly on the surfaces of eight stainless steel stents 2 erected on the rotating table 3 . The radioactivities of the stents thus injected with .sup.133 Xe were measured with a Ge semiconductor detector and the results are shown in Table 1, from which one can see that stents having radioactivities of up to 98 kBq were produced by ion injection of .sup.133 Xe as a .beta.-emitter. TABLE 1 Stent NO. Radioactivity, kBq 1 74.5 2 36.9 3 40.7 4 24.9 5 93.4 6 97.9 The radioactive stents produced by the above-described method were kept in place for 4 weeks in the abdominal aortas of rabbits; they proved to retard the growth of vascular smooth muscles. FIG. 2 shows a general layout for connecting a nuclear reactor to the ion injector in such a way as to enable mass production of .sup.133 Xe radioactive stents. Xenon-133 produced in the fuel rods 5 in the nuclear reactor 4 passes through the piping 6 to enter the Xe purifier 7, where it is deprived of .sup.131 I and other impurities; the pure .sup.133 Xe also passes through the piping 6 to be transferred into the ion source 9 in the ion injector 8, where it is ionized and accelerated; the accelerated ion beam of .sup.133 Xe is injected into the surfaces of stents erected on the rotating table in the uniform irradiating unit 10 of the ion injector. The .sup.133 Xe radioactive stents produced in accordance with the present invention proved to be capable of retarding the growth of vascular smooth muscles of the abdominal aortas of rabbits. Therefore, if such .sup.133 Xe radioactive stents are applied to patients suffering from arteriosclerosis, it is expected that they can retard the growth of vascular smooth muscles, thereby preventing the restenosis of opened blood vessels. If a uniform irradiator is employed in an ion injector connected to a nuclear reactor, radioactive stents featuring uniform irradiation with .sup.133 Xe can be produced in high volume.