The present invention relates to therapeutic radioactive devices and methods of use thereof, and more particularly, to devices and methods for providing a radiation source for temporary application in the treatment of stenosis and/or brachytherapy.
Various techniques have been developed to treat many different conduits in the body when these conduits have become reduced in size due to the existence of a stenosis or when these conduits have been completely occluded.
With respect to vascular conduits, angioplasty has been used to open an artery or blood vessel in the region where the stenosis or the occlusion has occurred. A typical angioplasty procedure includes making a small incision through the body and into, for example, a blood vessel, and then maneuvering a guide wire through the vascular system to a point beyond the stenosis or occlusion within the blood vessel. A catheter with a balloon near its distal end can subsequently be threaded over the guide wire and advanced to the point of stenosis or occlusion. The balloon may thereafter be inflated and deflated several times, if necessary, to widen the constricted area within the blood vessel, and may thereafter be withdrawn from the body. In certain cases, a stent may be deployed to the now widened area within the blood vessel to mechanically maintain a channel across the previously constricted area.
However, despite the initial observed reduction in the area of stenosis or occlusion as a result of angioplasty, many patients unfortunately exhibit a reoccurrence of the stenosis within a few months of the original procedure.
Although the original stenosis is thought to occur by means of the build up of plaque over a relatively long period of time, it is now believed that the recurrence of the stenosis after the original angioplasty procedure may be unrelated to the cause of the original stenosis. It is believed that the inflation of the balloon catheter used in the angioplasty procedure or the placement of a stent in the area of the stenosis may cause irritation to the blood vessel, which can subsequently cause hyperplasia (i.e., inducing the blood vessel cells to rapidly reproduce), resulting in restenosis.
It has been proposed that if the site of stenosis in the blood vessel were treated with a radiation dose, the mechanism that causes hyperplasia may be destroyed without harming the blood vessel itself. During this procedure, it should be noted that it is important to precisely control the amount of radiation that is directed to the blood vessel wall, since too little radiation could actually induce hyperplasia within the irritated vessel, while too much radiation could destroy a portion of the blood vessel.
U.S. Pat. No. 5,840,064 issued to Liprie, discloses a method and apparatus for introducing radiation to the site of a stenosis in a blood vessel to endeavor to prevent restenosis and claims a device for treating an occlusion or a constriction in a vessel or other conduit in the body wherein said radioactive source is cesium-137, cobalt-60, iodine-125, iodine-131, cobalt-57, iridium-192, gold-198, palladium-103, strontium-89, strontium-90, phosphorus-32, or yttrium-90.
U.S. Pat. No. 6,024,690 issued to Lee et al. discloses a radiation source with delivery wire for delivering a dose of radiation to a treatment site within a vessel. The radiation source comprises a radioactive segment that includes rhenium having a half-life of less than approximately one hundred (100) hours.
U.S. Pat. No. 6,071,227 issued to Popowski et al. discloses medical appliances for the treatment of blood vessels by means of ionizing radiation and claims a medical appliance wherein the radioactive radiation emitter is the beta radiation emitter Yttrium-90.
Various therapeutic techniques have also been developed for treatment of tumorous, pre-cancerous, or other diseased tissue. One technique, known as brachytherapy, places radioactive sources at or near the treatment site to provide site-specific delivery of radiation therapy, potentially reducing undesirable side effects associated with teletherapy, such as irradiation of healthy tissue. A common brachytherapy technique uses catheters to deliver radiation to the treatment site. In this technique, numerous catheters may be simultaneously inserted into the treatment site, sewn into place, loaded with solid isotopic pellets for a prescribed time, and then removed. The process of placing a number of catheters simultaneously within the appropriate region is cumbersome and time-intensive. Additionally, invasive insertion and external exposure of the catheters presents an increased risk of infection to the patient, and can result in significant discomfort for the patient during treatment. Finally, any subsequent treatment, for example, treatment following tumor recurrence, requires that the entire process be repeated from the beginning.
Another common brachytherapy technique employs radioactive implants to deliver radiation therapy. In this technique, numerous radioactive pellets or seeds are implanted directly into the treatment site. However, the radiation fields generated by the implants are typically highly non-uniform, resulting in highly non-uniform distributions of radiation dose across the treatment site.
Although somewhat useful, the radionuclides provided above, along with those generally used in brachytherapy and/or the treatment of stenosis, can have certain undesirable effects. For example, beta-emitting radionuclides, such as strontium-89, strontium-90, phosphorus-32, yttrium-90 and rhenium-188 suffer from rapid dose drop-off within the blood vessel to be treated. Moreover, the dose perturbation due to the presence of a calcified plaque or a metallic stent is significant for the beta source. The dose reduction in the region beyond a plaque or a stent could be more than 20%. This reduction can result in significant underdosing and affect the outcome of the treatment Low energy gamma-emitting radionuclides, on the other hand, such as iodine-125 and palladium-103, experience even more significant dose perturbation due to the presence of a calcified plaque or a metallic stent.
High energy gamma-emitting radionuclides, such as cesium-137, cobalt-60, iodine-131, cobalt-57, iridium-192 and gold-198 are characterized by a significant potential for excessive whole-body dose to the patient, the cardiologist and the staff. Radiation safety considerations require the use of heavy lead shields to reduce exposure rates within the catheterization laboratories. Adequate shielding of catheterization laboratories to provide radiation protection to clinicians, as well as personnel outside the laboratory is a significant and costly task.
Accordingly, it is desirable to provide a radiation source which can be implanted at a treatment site to provide a sufficient uniform dose distribution throughout the surrounding tissue, even in the presence of calcification and/or of a stent, with a sufficiently long half-life to adequately treat the patients.
In accordance with an embodiment of the present invention, a source for delivering radiation, for instance, X-ray radiation, to a treatment site is provided. The source includes at least one insert having tungsten enriched with tungsten-180 and a capsule within which the insert is placed. The tungsten, in one embodiment, may be enriched to include at least about 30 atomic percent of tungsten-180 and is capable of being activated, so as to transform a portion thereof to an amount of X-ray emitting tungsten-181 with a radiation dose rate sufficient for treatment within a period of one hour. The insert, in certain embodiments, may be provided with a central core around which the tungsten-180 may be placed. The X-ray radiation emitted preferably has a range of from about 50 keV to about 70 keV. The capsule, similarly, may be made from a material that permits X-ray radiation in the range of from about 50 keV to about 70 keV to pass therethrough. In addition, as the capsule may be irradiated to activate the insert therein, the capsule should include materials that contain minimally acceptable amounts of isotopes that can be transmuted into radioactive isotopes that emit undesirable radiations. Moreover, if transmutation does occur, the radioactive isotopes should have such short half-lives or very low dose rates that their activities have little effect on healthy tissue.
In accordance with another embodiment, the present invention provides a method for generating radiation for treatment of diseased tissues. The method includes providing at least one insert having tungsten enriched with tungsten-180 that is capable of being activated to transform a portion thereof to an amount of X-ray-emitting tungsten-181. Next, the insert may be encased within a capsule. Once encased, the capsule and the insert therein may be exposed to a neutron flux, so as to transform a portion of the tungsten-180 to an amount of X-ray-emitting tungsten-181 with a radiation dose rate sufficient for treatment within a period of one hour. In an alternate embodiment, the insert may be irradiated prior to encasing the insert within the capsule. The irradiated insert, along with the capsule, may thereafter be delivered to the diseased tissue site for treatment, and removed once treatment is completed.