MXPA98006488A - Stent with radioisotopes with greater intensity of radiation field at the extremes of the st - Google Patents

Abstract

The present invention relates to a stent with radioisotopes having increased radioactivity in the end regions of the stent compared to the central region of the stent. To minimize neointimal hyperplasia that may exist to a greater degree at the ends of a stent that is implanted in an artery of a human body, the amount of radioactivity placed at or near the ends of the stent should be increased compared to the amount of radioactivity on the rest of the stent. A further objective of this invention is to increase the radiation field at the end of a stent with radioisotopes by placing additional metal surfaces at the ends of the stent to have additional surfaces on which a radioisotope can be placed.

Description

STENT WITH RADIOISOTOPES WITH GREATER INTENSITY OF FIELD THE RADIATION AT THE EXTREMES OF THE STENT FIELD OF USE This invention is in the field of intravascular stent to maintain vascular opening.

BACKGROUND OF THE INVENTION Stent with radioisotopes have been shown to be effective in reducing neointimal hyperplasia within the arteries of laboratory animals, suggesting a treatment to reduce recurrent stenosis in humans. At the end of the 90s, these stent will be used to avoid the vascular closure of angioplasty with distension in human individuals. Stent with radioisotopes used in animals have had a urm distribution of a radioisotope that is inside the metal of the stent. A urm distribution of the radioisotope results in a field of decreased variation in the ends of the stent where a greater tendency to form proliferative cell growth may occur.

COMPENDIUM OF THE INVENTION In order to minimize the neointimal hyperplasia that may exist to a greater degree at the ends of a stent, the The concentration of surface radioactivity placed in c near the ends of the stent should be increased compared to the surface concentration of the radioactivity on the rest of the stent. Therefore, an objective of this invention is to increase the radiation field at the end of a stent with radioisotopes by placing a larger amount of the radioisotope at the ends of the stent. A further objective of this invention is to increase the radiation field at the end of a cc stent? Radioisotopes by placing additional metal surfaces at the ends of the stent to have additional surfaces This and other important objects and advantages of this invention will be apparent from the detailed description of the invention and the associated drawings that are provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of a cylindrical stent of the prior art having a radioisotope urmly positioned along the entire length of the stent, and also showing the intensity of the radiation field resulting from this urm distribution of the radioisotope.

Figure 2 is a side view of a stent that has a higher level of radioactivity near the ends of the stent and also shows the intensity of the radiation field resulting from this non-urm distribution of radioactivity compared to the stents of the stent. previous technique.

DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of a cylindrical stent one having a radial dimension R., rings' i r wn r? c? '' i ri l • »~ '' i H 'i x i' - ll p -c - * J • iJ1 a !. 1 t- i p n c n vi urm distribution of a radioisotope over its entire length. This urm distribution has been conventionally used in stents with radioisotopes of the prior art. This type of stent with radioisotopes is described in detail in U.S. Patent No. 5,059,166 which is included herein by reference. The solid line 2 in Figure 1 represents this urm distribution of the radioisotope along the length L of the stent 1 from its left end which is at a distance x = -L / 2 from the center of the stent 1 to its right end that is at a distance of x = + L / 2 from the center of the stent 1. The X axis in Figure 1 is parallel to the longitudinal axis of the stent. The long dotted line 4 in Figure 1 represents the intensity of the field or the intensity of the fields of radiation in human tissue along the surface of a cylinder having a radius of R + 2mm whose cylinder surrounds the stent 1. Line 4 indicates the intensity of the radiation field along the surrounding cylinder from x = -L / 2 up to x = + L / 2 and also along the surrounding cylindrical surface extending beyond the ends of the stent 1. A theoretical analysis indicates that the intensity of the radiation field in human tissue along the surface Cylindrical surrounding the stent 1 is a means to the size at x = -L / 2 to x = + L / 2 when X = 0 which is the longitudinal center of the cylindrical surface surrounding the stent 1. As one moves longitudinally towards outside on the surrounding cylindrical surface of radius R + 2mm beyond the stent ends 1, the radiation champion descend to an almost insignificant value at x = -A and x = + A. Figure 2 is a side view of a cylindrical stent 1C of the present invention having longitudinal rings 11, circumferential 13, 15 and 17 and also having an increasing concentration of radioisotope positioned near the ends of stent 10. This increased concentration of the Radio activity of the ends of the stent is indicated by the solid line 12 of Figure 2. The distribution of the resulting field along a cylindrical surface surrounding the stent 1 with a radius of R + 2mm is shown by dashed line 14 in Figure 2. By increasing the concentration of a radioisotope placed near the ends of the stent 10, the intensity of the radiation field at the ends of the stent can be made equal to the intensity of the field at the center of the stent 10. In addition, the intensity of the radiation field may extend to a greater distance in the x and -x directions beyond the ends of the stent 10. Specifically, Figure 2 shows as a comparison line 4 (of Figure 1) for a uniform concentration of the radioisotope in a stent compared to line 14 which is for the non-uniform distribution of the radioisotope shown by line 12 in Figure 2. As can be clearly seen in Figure 2, the intensity of the radiation field at the ends of the surface The cylindrical surrounding is greater than the field strength of a uniform concentration of the radioisotope as shown by line 4 in Figures 1 and 2. In fact, in x -B and x + B in the Fi Figure 2 shows that the intensity of the radiation field along the surface of the surrounding cylinder of radius R + 2mm extends a considerable distance beyond x = -A and x = + A. Thus, for the same concentration of the radioisotope per unit length in the stent center for the stent 1 and the stent 10, a higher level of radioisotope at the ends of the stent 10 will result in a more uniform radiation field strength on the stent. the length of the surrounding cylinder and also an effective radiation field extending a greater distance beyond the ends of the stent 10 and beyond the points x = -L / 2 and x = + L / 2 of the surrounding cylinder. Having an increased radiation field at the ends of a stent is useful for reducing the growth of proliferating cells after the stent is placed inside an artery. As seen in Figure 2, the stent 10 may have additional rings 15 placed in close proximity to the ends of the stent 10. The rings 15 provide additional surface area on which the radioisotope is collated. In addition, the end rings 17 may also be wider to provide additional surface on which the additional radioisotope material may be placed. These additional surfaces can be used to improve the intensity of the radiation field at the ends of the stent 10 even if the density of the radioisotope per itr of the surface area of the stent is uniform. It should be understood that the stent 10 can be made radioactive by implantation of the ion of a radioisotope on the surface of the metal stent. In addition, the beam of an ionized radioisotope can be directed to place more of the radioisotope near the ends of the stent compared to x = 0. Usually a radioisotope of beta particle like phosphorus 32 would be the ion implanted in the stent metal. Beta-gamma or gamma particles that emit isotopes can also be used with the stent. In addition, it may be advantageous to place an anti-thrombogenic coating on the surface of the stent before (or preferably) after the radioisotope been ion implanted in the stent. It should also be understood that the stent can be manufactured in a variety of shapes and sizes and can be self-expanding, as described in U.S. Pat. j-j? you. ^ i ~ TT C1 NT ^ A 1 ~ "-i, f, h R Hirihp???: £? j- £ -4r * - £ scpppc rri Dri ri nn H pc are included here as a reference. The radioisotope can be electroplated in the stent instead of using ion implantation It is also possible to place the radioisotope on the stent by vapor deposition It is also conceivable that the distribution of radioisotope at the ends of the stent may have a different shape than that of the stent. which is shown with line 12 in Figure 2. Specifically, some comparatively short distance at the end of the stent may have an increased amount of radioisotope per unit length compared to the central portion of the stent, but this larger amount of the radioisotope per Unitary length may be uniform near the end of the stent Other various modifications, adaptations and alternative designs are certainly possible in light of the previous teachings. Therefore, it should be understood at this time that within the scope of the appended claims the invention may be practiced in a manner different from that specifically described herein.

Claims (10)

1. A radioisotope stent comprising a thin-walled, generally cylindrical metal structure, the stent having an end region near each end of the stent and a central region generally located at the longitudinal center of the stent. The stent includes a radioactive material that is a radioisotope, the radioisotope being fixedly attached to the metal of the stent, having the ep ep " unit length of the stent in the stent's end regions compared to a smaller amount of radioisotope

L. U u u i i tt «* -? _- t. C 'and j. w I - w C li ^ ialv -C - ± - • The stent of claim 1, wherein the amount of radioisotope per unit length of the stent continuously increases towards the stent ends from the same point between the stent center and the end of the stent, the amount of radioisotope per unit length of the stent reaches a maximum amount of the radioisotope per unit length at the ends of the stent.

3. The stent of claim 1, wherein the radioisotope that is fixedly attached to the stent is a radioisotope emitter of beta particles.

4. The stent of claim 3, wherein the radioisotope is phosphorus 32.

5. The stent of claim 1, wherein the stent is coated with an anti thrombogenic coating.

6. The stent of claim 1, wherein the stent is adapted to be expanded by an inflatable balloon. The stent of claim 1, wherein the stent is adapted to be self-expanding. The stent of claim 1, wherein the stent metal has a surface and at least some of the radioisotope is plated onto the surface of the stent to form a surface coating. The stent of claim 1, wherein the stent metal has a surface and the stent has at least some of the radioisotope ion implanted in the metal of the stent to form a radioactive stent in which the radioisotope ions are introduced just downstream of the stent. the surface of the stent. The stent of claim 1, wherein the stent end region has more surface area per unit length of the stent compared to the surface area per unit length of the stent in the central region of the stent, the stent having an amount generally uniform radioisotope per unit surface area of the stent thus providing an increased amount of the radioisotope per unit length of the stent in the end regions of the stent.