X-ray or gamma ray systems or devices – Source
Reexamination Certificate
2000-02-28
2001-11-20
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Source
C378S121000, C378S064000, C378S065000, C378S207000
Reexamination Certificate
active
06320935
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and method for providing x-ray brachytherapy treatment in humans. More specifically, the present invention relates a dosimetry system used in conjunction with a miniature x-ray emitting transducer, which measures a radiation dosage, displays an instantaneous and cumulative radiation dose, and adjusts the operating parameters of the x-ray emitting transducer during treatment via a control feedback loop.
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 pain and suffering of these patients, recurrent stenosis imposes a serious economic burden on society, with estimated restenosis 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 proved 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 developing after a few months following balloon angioplasty. Stents can be inserted into an occluded artery to hold it open. Stents may 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, a proliferation of smooth muscle cells from the lesion into the lumen, 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 cells in the irradiated region. 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, that penetrates the artery wall at a two mm depth over the lesion length.
Because of the promise that radiation holds for avoiding recurrent restenosis, many methods have been proposed to provide ionizing radiation treatment. These treatment methods may be grouped into three categories: conventional external x-ray irradiation; gamma and beta brachytherapy; and x-ray brachytherapy
External x-ray irradiation cannot treat restenosis safely and effectively. The clinically required doses needed to successfully treat arterial lesions may damage the heart muscle and other organs, due to the non-localized nature of external x-rays. Conventional x-ray radiation for radiotherapy is produced by the following process. High energy electrons are generated and accelerated in a vacuum to impact on a metal target. The sudden deceleration of the high speed electrons into a solid target produces x-rays. Characteristic x-ray radiation results due to a process wherein the bombarding electron ionizes the atom it strikes by removing an electron from one of the atomic orbital shells, leaving a vacancy. An electron from a more remote atomic orbital shell fills this vacancy by jumping to the vacant atomic orbital shell. The consequent release of energy appears as an x-ray photon. Bremsstraalung x-ray radiation is the result of an interaction between a high speed electron and a nucleus. As the electron passes in the vicinity of a nucleus, it suffers a sudden deflection and acceleration. As a result, a part or all of its energy is dissociated from it and propagates in space as an x-ray photon. Conventional x-ray production tubes operate at high voltages, in the range of from 200 kV to 500 kV. However, appreciable x-rays may be produced in x-ray tubes having acceleration voltages as low as 20 kV. The x-ray emission 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.
In gamma and beta brachytherapy, a radioactive source is introduced to the treatment site using a special radiation catheter, and the source is placed at this treatment site for a predetermined time, as to deliver the proper radiation dose. Presently, 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
SV or gamma emitting
192
Ir, are at various stages of development and clinical evaluation. Radioactive stents are also used as alternative delivering means, composed of the above radioactive isotopes.
The gamma and beta radioactive sources used by radiation catheters and radioactive stents have several drawbacks. Their ability to provide selective control of treatment time, radiation dosage, or radiation intensity is limited; and the handling of radioactive materials presents logistical, regulatory, and procedural difficulties. In addition, these 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 involves a regulatory burden due to the need to comply with nuclear regulatory requirements.
X-ray brachytherapy offers an alternative approach to providing ionizing radiation treatment. In x-ray brachytherapy an internal x-ray emitting miniature energy transducer generates x-rays in-situ. This system offers certain advantages with respect to intra vascular gamma and beta sources. These advantages are, but 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 that raises from the need to comply with nuclear regulatory requirements.
Another method for the production of x-rays that can possibly contribute to x-ray brachytherapy is direct conversion of light into x-ray radiation. 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
2
. With the development of the femtosecond laser, such power densities are achievable with moderate size lasers (See C. Tillman et al, NIMS in Phys. Res. A
394
(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 these power density levels.
A variety of medical applications of the direct laser light conversion method of x-ray 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 radiotherapy.
Based on the above, an in-situ radiation treatment apparat
Bukshpan Shmuel
Shinar Guy
Ho Allen C.
Kim Robert H.
Rossi & Associates
X-Technologies, Ltd.
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