Table 6-1 Characteristics of ¹³³Xe implanted stent

Fig. 6-15 Radioactive stent implantation therapy for preventing restenosis of coronary arteries (1) insert catheter with guide wire into the point of stenosis (2) pull out the catheter (protection sheath) (3) expand the balloon to extend the stent (4) shrink and pull out the balloon to leave the stent

Fig. 6-16 133Xe ion implantation Radioactive 133Xe gas is transferred to the ion source from the bomb, ionized and accelerated by the accelerator. The 133Xe ion beam is selected by the mass-analyzing magnet and implanted into the stents mounted on the holder, which rotates and moves up and down.

As a therapeutic method for myocardial infarction caused by arteriosclerosis in coronary arteries, a balloon is introduced into the blood vessel to expand it, or a mesh cylinder called a stent is implanted in the vessel to prevent its narrowing or stenosis (Fig. 6-15). However, restenosis occurs in about 30% of patients if only such angioplastic methods are applied. This might be caused by quick proliferation of intimal cells. In order to avoid this, it is thought that endovascular irradiation would be effective in suppressing the proliferation of the cells, by inserting a radioactive micro-source in the blood vessel. Techniques are under development using radioisotopes such as 90Sr, 90Y, 32P, 186Re and 192Ir emitting beta-ray or low energy gamma-ray, which are temporarily inserted, or using permanently implanted radioactive stents. In JAERI, a novel technique was developed to produce radioactive stents by the implantation of xenon-133 (133Xe) ions using an on-line isotope separator (ISOL) (Fig. 6-16). It was reported that 32P (half-life 14.3 day, maximum energy 1.71 MeV) was used as a beta-ray source on the surface of stent. The 133Xe gives shorter endovascular irradiation time corresponding to its short half-life of 5.25 day, avoiding a disturbance in the recovery of the intima. Further, due to the maximum beta-ray energy of as low as 0.346 MeV, the risk to surrounding nontarget tissues can be reduced (Table 6-1). In order to realize the homogenious implantation of 133Xe ion beam on the surface of cylindrical stents, an up-down driven rotary target holder was designed for irradiation. Using this apparatus, up to 8 stents with radioactivity of a maximum of 98 kBq can be simultaneously processed. Through animal experiments the inhibitive effects on restenosis have been shown.

Reference S. Watanabe et al., Production of Radioactive Endovascular Stents by Implantation of 133Xe Ions, Appl. Radiat. Isot. 51 (2), 197 (1999).

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