X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
1999-05-13
2001-02-27
Church, Craig E. (Department: 2876)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S136000
Reexamination Certificate
active
06195411
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a highly miniaturized, low power, programmable radiation source for use in delivering predefined doses of radiation to a predefined region and more particularly to a miniaturized radiation source mounted in a flexible probe.
In the field of medicine, radiation is used for diagnostic, therapeutic and palliative treatment of patients. The conventional medical radiation sources used for these treatments include large fixed position machines as well as small, transportable radiation generating probes. The current state of the art treatment systems utilize computers to generate complex treatment plans.
These systems apply doses of radiation that are known to inhibit the growth of new tissue because the radiation affects dividing cells more than the mature cells found in non-growing tissue. Thus, the tissue in the site of an excised tumor can be treated to prevent the regrowth of cancerous tissue and the recurrence of cancer. Alternatively, radiation can be applied to other areas of the body to inhibit tissue growth, for example the growth of new blood vessels inside the eye that can cause macular degeneration.
Conventional radiation treatments systems, such as the LINAC used for medical treatment, utilize a high power remote radiation source and direct a beam of radiation at a target area, such as tumor inside the body of a patient. This type of treatment is referred to as teletherapy because the radiation source is located a predefined distance, approximately one meter, from the target. This treatment suffers from the disadvantage that tissue disposed between the radiation source and the target is exposed to radiation.
An alternative treatment system utilizing a point source of radiation is disclosed in U.S. Pat. No. 5,153,900 issued to Nomikos et al., U.S. Pat. No. 5,369,679 to Sliski et al., and U.S. Pat. No. 5,422,926 to Smith et al., all owned by the assignee of the present application, all of which are hereby incorporated by reference. This system includes a miniaturized, insertable probe capable of producing low power radiation in predefined dose geometries disposed about a predetermined location. This type of treatment is referred to as brachytherapy because the source is located close to or in some cases within the area receiving treatment. One advantage of brachytherapy is that the radiation is applied primarily to treat a predefined tissue volume, without significantly affecting the tissue adjacent to the treated volume.
Typical radiation therapy treatment involves positioning the insertable probe into or adjacent to the tumor or the site where the tumor or a portion of the tumor was removed to treat the tissue adjacent the site with a “local boost” of radiation. In order to facilitate controlled treatment of the site, it is desirable to support the tissue portions to be treated at a predefined distances from the radiation source. Alternatively, where the treatment involves the treatment of surface tissue or the surface of an organ, it is desirable to control the shape of the surface as well as the shape of the radiation field applied to the surface.
The treatment can involve the application of radiation, either continuously or intermittently, over an extended period of time. Therefore, it is desirable that the insertable probe be adjustably supported in a compliant manner to accurately position the radiation source with respect to the treated site and accommodate normal minor movements of the patient, such as movements associated with breathing.
In many x-ray therapeutic procedures, x-ray probes of the type generally disclosed in U.S. Pat. No. 5,153,900 incorporate a relatively rigid tube enclosing an electron beam directed to an x-ray emitting target at its distal end. For example, in treatment of brain tumors, an x-ray probe having a rigid tube is used with a stereotactic frame affixed to the patient's skull, where the tube is advanced into a biopsy hole to the tumor location, as disclosed in U.S. Pat. No. 5,369,679. The rigidity of the tube is useful in ensuring that the x-ray emitting target is properly located. In other cases, it is desirable to have a flexible tube leading to the x-ray emitting target, for example, where it is desirable to pass the probe up the urethra to the bladder, for treatment of the bladder. Such a flexible probe is disclosed in U.S. Pat. No. 5,248,658.
However, it has been difficult to effectively treat tissue using the flexible probe of the latter patent.
Accordingly, it is an object of the present invention to provide an improved system for delivering radiation to a localized area.
It is a further object of the present invention to provide an improved highly miniaturized radiation source with a flexible probe.
SUMMARY OF THE INVENTION
The present invention is directed to a miniaturized radiation source at the end of a flexible probe or catheter. The flexible catheter extends along a probe axis between a proximal end and a distal end of the catheter. The radiation source, at the distal end of the catheter, includes a substantially rigid housing disposed about a substantially evacuated interior region extending along a beam axis from an electron source at an input end of the housing to a radiation transmissive window at an output end of the housing. The housing also may include, depending on the current capability of the electron source's electron emitter, a channel electron multiplier adapted for receiving electrons from the electron source and for producing free electrons at an output end of the channel electron multiplier and an electron accelerator adapted for establishing a potential difference in the interior region of the housing whereby the free electrons produced at the output end of the channel electron multiplier are accelerated toward a target at or near the window. The target produces x-radiation in response to incident accelerated free electrons.
Preferably, the electron accelerator includes a surface disposed about the beam axis between the electron source and the target on a ceramic and preferably monolithic, substrate. In one embodiment, the surface bears a semiconductor coating. The surface may be substantially conical in shape wherein the distance from the beam axis increases as a function of the distance from the electron source. The electron source can be a photocathode illuminated by laser energy, a field emitter or a thermionic emitter. The target and outer surface of the probe is preferably maintained at ground potential to reduce the risk of shock.
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Church Craig E.
McDermott & Will & Emery
Photoelectron Corporation
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