Surgery – Magnetic field applied to body for therapy – Electromagnetic coil
Reexamination Certificate
2001-01-18
2003-10-21
Leung, Philip H. (Department: 3742)
Surgery
Magnetic field applied to body for therapy
Electromagnetic coil
C600S009000, C607S103000, C607S115000, C219S632000, C219S670000, C219S677000, C336S060000
Reexamination Certificate
active
06635009
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a magnetic field applicator for heating magnetic substances in biological tissue for use in administering hyperthermia and thermo-ablation procedures, as well as having other medical and industrial applications.
Cancer diseases are treated in a generally known manner through surgical removal, chemotherapy, radiation therapy or a combination of these methods. Each of these methods is subject to certain limitations, especially at advanced stages following metastasis, when the tumor is located close to critical body areas. In cases of diffused tumor growth with uncertain localization, surgical removal of the tumor is either not possible or offers only minimal chances for a cure. For this reason, surgical intervention is generally combined with radiation therapy and chemotherapy. Radiation therapy is only as precise as the localization of the tumor by means of an image-producing processes, with the utmost care taken to avoid the destruction of healthy tissue. Chemotherapeutic means on the other hand, act systemically over the entire body. With this method, bone marrow toxicity or lack of specificity of the therapy limit the treatment ability. Undesirable side effects and damage to healthy tissue are often the unavoidable consequences with these therapy methods using the present state of the art. Improvement is therefore needed.
Over the last few years, hyperthermia has gained significance as an alternative procedure, which works by heating the tumor tissue to temperatures above 41° C. This process provides an increased success in cancer treatment due to the increased local control, and in combination with surgery, radiation therapy and chemotherapy, improves the chance of survival. With temperatures between 41 and 46° C., and with the natural assistance of the body, a controlled and rather slow reduction of the tumor tissue takes place. Acute destruction of cells starts to take place at higher temperatures starting at 47° C. Depending on temperature, the form of necrosis, coagulation or carbonization, is either called hyperthermia (between 41 and 46° C.) or thermo-ablation (above 47° C.). Until the present invention, hyperthermia systems were considered to be suitable only for the above-mentioned hyperthermia or thermo-ablation procedures, having no other medial applications.
One general problem with hyperthermia systems according to the state of the art, is that no precisely localized and homogenous heating of a target region of a body is, as a general rule, possible. This was possible under certain physiological conditions (e.g. oxygen deprivation, low pH), when the tumor cells become sensitive to hyperthermia, but this only applies in a few isolated circumstances. Hyperthermia by itself is not any more effective on tumor cells than on normal tissue. For this reason, limiting the heating of tissue to the area indicated for treatment (which need not necessarily be confined to the tumor) is especially important, and not realized according to the state of the art. Thus, there is need for improvement.
According to the state of the art, systems dominated by electrical fields, radiate the electromagnetic waves in the megahertz range from antennae or other antenna-shaped objects or arrays of antennae, for regional hyperthermia. For so-called interstitial hyperthermia the electrical field of individual electrical-field applicators is used, and for deep hyperthermia the interference from an antenna array is used. It is a difficulty common to all of these electrical-field-dominated systems that the power consumption of target tissue can only be regulated by means of complex and expensive controls over the electrical field. Furthermore, the heating depends on the electrical conductivity of the applicable target tissue, which is by its very nature heterogeneous, so that an uneven heating of the electrical field is the likely result, even with homogenous radiation. Especially at the transition points of body regions, there is very different electrical conductivity. Excessive power can create “hot spots” that result in pain and burns inflicted on the patient. The consequence is a reduction of the total emitted power necessary for proper treatment of the patient, so that as a result the temperature required to irreversibly damage the tumor tissue (41-42° C.) is not reached in the target region, and the therapy is not successful. Furthermore, due to the interference of dipole arrays, the production of a second electrical field maximum is only possible in areas further inside the body. For physical reasons, the greatest power consumption always takes place at the surface of the body, i.e. at the maximum radius. Added to this is the fact that the blood flow through the tumor and the surrounding normal tissue often changes under hyperthermia, and that this change cannot be compensated for by means of systems dominated by electrical fields from the outside because of the rather low control possibilities over the field.
Other processes according to the state of the art are ultrasound, preferably for thermo-ablation, and interstitial microwave applicators. The latter possess low penetration depth because of the frequency and can therefore only be used in the form of interstitial antennae. In addition, infrared for whole-body hyperthermia is used, as well as extra-corporeal systems to heat body fluids.
Furthermore, a hyperthermia process for the therapy of prostate cancer is disclosed in U.S. Pat. No. 5,197,940, hereinafter the '940 patent, in which “thermoseeds” consisting of magnetic, in particular ferromagnetic or magnetizable material or containing such material, are implanted in the area of the tumor. These thermoseeds are typically several centimeters long, with a diameter in the millimeter range. It is necessary to implant such thermoseeds surgically, and at great cost. During treatment, the thermoseeds are subjected to an alternating magnetic field produced outside a patient's body, whereby heat in the thermoseeds is produced by known hysteresis effects in form of hyperthermia.
These seeds are heated according to the “hot source” principle that while the seeds are heated, the temperatures in the surroundings of the seed drop exponentially, so that the distance between the seeds may not be more than 1 cm in clinical application. In case of greater or uneven distances, thermal under-dosing occurs, which can prevent the success of the therapy. Especially with larger tumors, a very narrow implantation of the seed becomes necessary and the method becomes surgically expensive and stressful to the patient. Aside from the small distance, the seeds must be oriented parallel to the magnetic alternating field for optimal power consumption. The Curie temperature in so-called self-regulating thermoseeds prevents overheating by stopping further power consumption when the ferrite passes into a non-magnetizable state after the Curie temperature has been reached.
The '940 patent discloses the use of a magnetic coil with an oscillatory circuit as the magnetic field applicator for the magnetic alternating field. A patient's body region with the implanted thermoseeds can be placed in the axis of this oscillatory circuit. In practice, air coils are used in the central area where a patient is sifting on a non-magnetizable supporting plate during treatment.
In hyperthermia using thermoseeds, the high cost of surgery and the high intensity of the method, the risk of an imprecise orientation or a change in position of the seeds, the ensuing risk of thermal under-dosing, as well as a limitation of using this treatment method on tumors of smaller size are all disadvantages of this system.
In another known hyperthermia process disclosed in WO 97/43005 for tumor therapy, magnetizable microcapsules are proposed which reach the area of the tumor through the blood stream. In this way surgical implantation of magnetizable elements can be avoided, since with implantation, the danger exists that malignant tumor cells may be dispersed into healthy tissue w
Flint Cort
Leung Philip H.
McNair Law Firm, P.A.
MFH Hyperthermiesysteme GmbH
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