X-ray or gamma ray systems or devices – Source – Electron tube
Reexamination Certificate
2000-10-20
2002-08-20
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Source
Electron tube
C378S119000, C378S122000, C600S425000
Reexamination Certificate
active
06438206
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and method for providing x-ray therapy in humans. More specifically, the present invention relates to an apparatus and method for providing in-situ radiation treatment that utilizes a miniature energy transducer to produce x-rays, wherein the energy transducer defines a cavity that communicates with an evacuation opening and is continuously evacuated through a flexible tube by a dynamic pumping mechanism in order to maintain a desired vacuum level.
BACKGROUND OF THE INVENTION
Restenosis is a heart condition that afflicts 35%-50% of all people who undergo balloon angioplasty to improve blood flow in narrowed sclerotic arteries. The condition consists of a significant re-closing of the treated artery segment hours to several months after the procedure. As a result, the arterial lumen size is decreased and the blood flow downstream from the lesion site is impaired. Consequently, patients afflicted with restenosis must undergo an additional balloon angioplasty, and in some cases a coronary bypass surgery must be performed. Aside from the pain and suffering of these patients, recurrent stenosis is also a serious economic burden on society, with estimated expenses as high as 3.0 billion dollars per year in the United States economy alone.
Attempts to treat restenosis have been concentrated in both the pharmacological and medical device areas. While pharmacological solutions have been proven effective in treating only acute restenosis, a condition developing immediately after balloon angioplasty, some progress has been made with medical devices in the treatment of long term restenosis, a condition that develops up to a few months following balloon angioplasty. An example for such medical device is the stent. Stents can be inserted into an occluded artery to hold it open. Stents have been shown to prevent two of the three mechanisms that cause recurrent stenosis, namely, elastic recoil of the artery and negative remodeling of the arterial structure. The third mechanism, neointimal growth, consists of hyper-proliferation of smooth muscle cells from the lesion into the lumen and is not prevented by stents.
Ionizing radiation holds great promise for treating restenosis. Ionizing radiation serves to damage undesirable hyper-proliferating tissue and ultimately to prevent the hyper-proliferation of smooth muscle cells in the irradiated region. Research has shown that gamma and beta radiation delivered at the location of stenotic lesions effectively stop both animal and human intimal proliferation. The effective, yet non-hazardous, required dose to treat human restenosis is between seven and forty Gray (mjoule/gram), preferably a dosage greater than fifteen Gray measured two mm from the center of the radiation source that penetrates the artery wall at a two mm depth over the lesion length.
In view of the above, various methods have been proposed to provide ionizing radiation treatment. For example, radiation catheters, based on the use of radioactive sources such as beta-emitting
32
P,
90
Sr/
90
Y,
188
W/
188
Re, beta+emitting
48
V or gamma emitting
192
Ir, are at various stages of development and clinical evaluation. The radioactive sources, in a variety of configurations, are introduced to the treatment sites using special radiation catheters and the radioactive source is placed at the treatment site for a predetermined time period as to deliver the proper radiation dose. Radioactive stents are also used as alternative delivery means, incorporating some of the above radioactive isotopes.
The gamma and beta radioactive sources used by the present radiation catheters and radioactive stents, however, have several drawbacks including a limited ability to provide selective control over the dose distribution or overall radiation intensity, and the logistical, regulatory, and procedural difficulties involved in dealing with radioactive materials. In addition, gamma-emitting devices jeopardize patients by exposing healthy organs to dangerous radiation during the introduction of the radiation source. Hospital personnel that handle radioactive materials are also at risk due to exposure. In addition to the risks these devices impose on patients, hospital staff, and the environment, use of these devices invokes a regulatory burden due to the need to comply with nuclear regulatory requirements.
An additional approach to providing ionizing radiation treatment is through the use of an x-ray emitting energy transducer that is not radioactive. Conventional x-ray radiation for radiotherapy is produced by high-energy electrons generated and accelerated in a vacuum to impact a metal target. The emitted x-ray power is directly proportional to the electron beam current. However, the efficiency of x-ray generation is independent of electron current, but rather depends on the atomic number of the target material and on the acceleration voltage. Yet, another method for the production of x-rays is by direct conversion of light into x-ray radiation. It is known that the interaction of light with a target can produce highly energetic x-rays when the power densities achieved are in the range of 10
16
-10
17
watt/cm . With the development of femtosecond laser, such power densities are achievable with moderate size lasers (See C. Tillman et al, NIMS in Phys. Res. A394 (1997), 387-396 and U.S. Pat. No. 5,606,588 issued to Umstadter et al., the contents of each of which are incorporated herein by reference). A 100 femtosecond, one mJ laser pulse focused down to a 3 micron spot, for example, will reach this power density level.
A variety of medical applications of the direct laser light conversion method of xray generation are currently in the development stage. The direct laser light conversion method, for example, has been considered for medical imaging (See, Herrlin K et al. Radiology (USA), vol. 189, no. 1, pp. 65-8, October 1993). Another medical application of femtosecond lasers is in improved non-thermal ablation of neural or eye tissue for surgical purposes (See, F. H. Loesel et al. Appl.Phys.B 66,121-128 (1998)). The development of compact table top models of femtosecond lasers makes laser generated x-rays an attractive alternative for radioactive material based radiotherapy.
Based on the above, an x-ray radiation treatment apparatus and method has been developed. In x-ray treatment an internal x-ray emitting miniature energy transducer generates x-rays in-situ. Co-pending and commonly assigned U.S. patent application Ser. No. 09/325,703 filed Jun. 3, 1999, and U.S. patent application Ser. No. 09/434,958 filed Nov. 5, 1999, describe miniaturized energy transducers that are coupled to flexible insertion devices to permit x-ray radiation treatment within the human body. Use of the miniaturized x-ray emitting energy transducer offers certain advantages with respect to intra vascular gamma and beta sources. These advantages are, but are not limited to, localization of radiation to the treatment site so that the treatment site may be irradiated with minimal damage to surrounding healthy tissue; reduction of hospital personnel risk due to exposure to radioactive materials; and minimization of the regulatory burden and additional costs that arise from the need to comply with nuclear regulatory requirements.
A variety of different types of cathode and anode structures have been proposed for the energy transducer. One proposal is to utilize a hollow cathode, which includes a cathode shell that defines a cavity. A light pulse is introduced into the cavity in order to heat an outer surface of the cathode shell, thereby causing thermionic emission of electrons from the outer surface. Another proposal for a hollow cathode incorporates the use of an electron escape nozzle, wherein an ion and electron plasma is generated in the cavity either by applying a light signal to an inner surface of the cathode shell or by providing a spark gap in the cavity of the conducting cathode shell. The electrons exit the cathode shell via the escape nozzle and are a
Goldschmidt Aharon
Shinar Guy
Barber Therese
Porta David P.
Rossi & Associates
X-Technologies, Ltd.
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