Surgery – Radioactive substance applied to body for therapy
Reexamination Certificate
1999-09-08
2001-07-10
Gilbert, Samuel G. (Department: 3736)
Surgery
Radioactive substance applied to body for therapy
C600S003000, C606S194000
Reexamination Certificate
active
06258019
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to prepared catheters for intraluminal treatment of a vessel section with ionizing radiation. In particular, the invention relates to prepared balloon catheters for such use.
BACKGROUND OF THE INVENTION
Catheters for intraluminal treatment of a vessel section with ionizing radiation are used, for example, during or after percutaneous transluminal angioplasty, such as balloon dilatation or atherectomy of a stenosed blood vessel section, in order to prevent restenosis of this section. This is based on the theory that application of a defined dose of ionizing radiation can inhibit excessive cell proliferation triggered by the angioplasty and that by this means, restenosis of the treated vessel section can be avoided. A catheter of the generic type, however, can also be used for radiation treatment of other body cavities such as the esophagus or trachea or for treatment of the prostate.
A balloon catheter of the type mentioned in the introduction is known from EP 633,041 A1, in which a guide wire is arranged to be longitudinally displaceable in a central guide wire lumen of a two-lumen balloon catheter. An emitter of radioactive radiation in the form of a filament is incorporated into the tip of the guide wire. The second lumen serves as an inflation lumen for the balloon. Inflation of the balloon serves to radially center the radiation emitter positioned in the guide wire lumen in the vessel section that is to be treated. In this way, a radiation dose distribution is obtained uniformly about the circumference of the vessel wall. For applying the pressure to the balloon, a conventional liquid solution is used. The radiation source preferably used is yttrium-90, an easily screenable beta emitter with a half-life of 2.7 days, a mean electron energy of 0.942 MeV and a maximum electron energy of 2.28 MeV.
Over the greater part of its course from the emitter positioned in the balloon to the vessel wall to be treated, the radioactive radiation has to pass through inflation medium, in which process—as in any matter—radiation energy is absorbed. Thus, the energy dose available at the surface of the vessel wall, and the depth of penetration of the radiation into the vascular tissue at the wall, depend on the initial activity of the source, on the coefficient of absorption of the inflation medium, and on the length of travel of the radiation through the inflation medium.
The conventional liquid solution used to inflate the balloon includes saline and radiopaque contrast media which have a significant coefficient of absorption. Thus, known catheters of the type mentioned in the introduction suffer the drawback of long irradiation times, and consequently, long treatment times. Because of the necessary centering of the emitter in an inflated balloon, the flow of blood in the treated vessel has to be interrupted during this long treatment, which is undesirable.
The increasing importance of minimally invasive surgery and the treatment of ever narrower blood vessels demand guide catheters, and consequently balloon catheters, of ever smaller profile. Flexibility as well as longitudinal force and torsion transmission of the guide wire, balloon catheter and guide catheter must be guaranteed, as well as low friction between guide wire and balloon catheter. An adequately short deflation time for the balloon and a sufficiently large annular lumen for the flow of contrast medium are also necessary. If the inflation lumen is too narrow, the inflation medium can no longer flow quickly enough out of the balloon. A catheter with slow emptying of the balloon blocks the bloodstream for longer and thus, for example, also precludes the possibility of responding quickly to an ischemic reaction on the part of the patient during treatment.
SUMMARY OF THE INVENTION
The invention is therefore based on the object of providing a balloon catheter, in which as small a proportion as possible of the ionizing radiation is absorbed on its travel from the source through the inflated balloon to the vessel section that is to be treated. It is also based on the object of providing a balloon catheter which has short deflation times and has a small overall profile.
According to a first embodiment of the invention, the object is achieved by means of a balloon catheter inflated with a gas, as opposed to a conventional liquid. When the inflation medium is a gas, the radiation passes through a medium with a comparatively low coefficient of absorption, since the latter is generally higher for liquids than it is for gases. Therefore, the radiation attenuates only slightly as it passes through the inflation medium, so that a sufficient radiation dose can be delivered to the vessel section within a short time. In addition, the radiation intensity is less dependent on the source distance, as a result of which inaccuracies in the centering of the source have only slight effects on the uniformity of the dose distribution.
Furthermore, gas-filled balloons have up to about three times shorter deflation times compared to balloons which have been inflated with liquid, a fact which is attributable to the lower viscosity of gases compared to liquids. The advantage of this is, for example, that when providing treatment using a balloon which interrupts the flow of blood, it is possible to respond quickly to an ischaemic reaction on the part of the patient by deflating the balloon.
Further yet, when the inflation medium used is a gas (i.e., a lower viscosity than the conventional inflation liquid media), it is possible, while having essentially the same deflation time, for the inflation lumen to be made smaller in cross-section along the greater part of its length running within the patient during treatment, with greater advantages for all other properties of the catheter. For example, as a result of the smaller overall profile, the flow of contrast medium is improved, while at the same time, however, the flexibility and the kink resistance are also improved, since with smaller shaft diameters the wall thickness can be reduced. The reduction in cross-section which can be achieved by means of the invention can either be specified in absolute values, as specified in the claims, or, as specified in other claims, as a function of the maximum use volume of the balloon which has to be deflated.
In a preferred embodiment of the invention, the inflation medium is carbon dioxide. In the treatment of blood vessels, it is possible, in the event of a leaking or defective balloon, for the blood to absorb a certain amount of carbon dioxide without harming the patient. Since carbon dioxide is transported anyway in the blood, its biological tolerability in humans is not in question.
In a further advantageous embodiment of the invention, the inflation lumen has, along the greater part of its length lying within the patient's body during treatment, a cross-sectional area of at most 0.300 mm
2
, or at most 0.200 mm
2
. The cross-sectional area of the inflation lumen can also be defined as a function of the balloon volume, for example when expressed in mm
2
, not greater than a maximum use volume of the balloon in mm
3
divided by 1200 or 1600. By reducing the cross-sectional area of the inflation lumen, the overall profile of the catheter can be made smaller, as a result of which a catheter according to the invention is suitable for minimally invasive percutaneous transluminal treatments via small puncture openings and guide catheters. In addition, the catheter can also be used in correspondingly narrower vessels, in which case the time for the balloon to empty still remains small compared to known catheters with liquid inflation media.
In sum the present invention relates to a catheter for intraluminal treatment of a vessel section, which catheter has an elongate shaft with a proximal end and a distal end, a balloon which is arranged at the distal end of the shaft and can be inflated to a maximum use volume, and an inflation lumen which runs through the shaft and opens into the balloon, and which catheter is filled w
Ghielmetti Cirillo
Popowski Youri
Schwager Michael
Verin Vitali
Crompton Seager & Tufte, LLC.
Gilbert Samuel G.
Sci-Med Life Systems, Inc.
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