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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to improvements in techniques for destroying cells
within the living body and, more particularly, to apparatus and a method
for applying electromagnetic energy to the interior of a tumor within the
body to destroy cells in the tumor.
Hyperthermia, the heating of the body cells to above 41.degree. C. for
therapeutic purposes, particularly to destroy cancer tumors, has been
known and used in the past. It is also known, that, above 46.degree. C.,
irreversible destruction of healthy and diseased body cells occurs. The
purpose of hyperthermia equipment generally is to deliver heat
preferentially to diseased body cells while maintaining adjacent healthy
cells at acceptable temperatures, i.e., below the temperature at which
irreversible cell destruction occurs.
There are three main theories which explain why hyperthermia is successful
in fighting cancerous growths. Some scientists believe that heat produces
a localized fever which causes lymphocytes to congregate (200 lymphocytes
are usually needed to destroy one cancerous cell). Other scientists think
heat improves the flow of blood in the tumor, and this increased blood
flow, in turn, brings more oxygen to the tumor and lowers its PH, thus
starving the tumor cells by reducing nutrients. A third theory contends
that the DNA forces that hold tumorous cells together are weaker than
those of healthy cells and the heat applied to the tumorous cells breaks
them apart and thereby destroys them more easily.
A number of disclosures relating to the method of treating tumors by the
application of electromagnetic radiation to the tumors include U.S. Pat.
Nos. 3,991,770, 4,032,860, 4,095,602, 4,119,102, 4,154,246, 4,230,129,
4,346,715 and 4,397,314. Another disclosure relating to surgical
instruments in the form of an electrically heated hypodermic needle is
U.S. Pat. No. 3,698,394.
A commercial system for producing deep controlled regional hyperthermia has
been made and sold by BSD Medical Corporation, 420 Chipeta Way, Salt Lake
City, Utah 84108. The system uses the principle of phase reinforcement to
create an electrical field within the human body that produces heat
internally. A number of radiating elements surround the patient and direct
radio frequency (RF) energy through the treatment area in the applicator
field. Thus, the sources of electromagnetic energy for the area to be
treated in the patient are external to the patient.
A technique of treating brain tumors by microwave energy has been disclosed
in an article entitled, "Brain Tumors Succumb to New Microwave Probes," in
Microwave Technology, June 19, 1983. In this technique, a hole is drilled
into the skull and a catheter is invasively inserted in the hole to
support a coaxial radiator or antenna. Microwave energy is then applied to
the antenna to cause the brain tumor to be heated to the point at which
cancerous cells in the tumor are destroyed.
The foregoing disclosures relate to hyperthermia equipment which is complex
in construction, expensive to produce and maintain, and requires a
considerable volume of space to accommodate the relatively large size of
such equipment. Because of these drawbacks, a need has arisen for improved
hyperthermia equipment and techniques which simplifies the way internal
body tumors are treated, for example, tumors of the breast. The present
invention satisfies this need.
SUMMARY OF THE INVENTION
The present invention comprises apparatus and a method for applying heat
energy to the interior of a tumor or other body part located on or within
the living body. The heat is applied within the tumor or body part without
excessively heating healthy cells surrounding the tumor or body part.
The apparatus includes an antenna which is constructed in the form of a
hypodermic needle which can be inserted through the skin and into the
tumor with minimal discomfort to the patient. The antenna may be
sufficiently small in diameter so as to be minimally invasive in the
medical sense. It is coupled by way of a coaxial cable to a microwave
generator in a housing or other support structure adjacent to a patient
treatment area. The operating time of the microwave generator can be
varied so that microwave energy can be selectively applied to the tumor
depending upon the condition of the tumor. A typical heating period is 20
to 40 minutes with interruptions of the applied power to the antenna when
predetermined body temperatures near the outer periphery of the tumor are
sensed as hereinafter described.
To assure that healthy body cells surrounding a tumor are not affected by
the heat energy generated by the presence of the radiating antenna in the
tumor, a plurality of temperature sensors are placed in the body at or
near the outer periphery of the tumor. Each sensor is coupled to a
temperature detection and control unit which monitors the temperatures at
each location on the outer periphery of the tumor. If the temperature at
any one location reaches a predetermined value, such as 46.degree. C., the
temperature detection and control unit will deactuate the microwave
generator for a period of time sufficient to allow the temperature at the
specific location to decrease to a second temperature, such as 45.degree.
C., whereupon, the microwave generator will once again be actuated. The
on-off condition of the microwave generator continues until the preset
heating time has elapsed. In this way, the heat energy necessary to
destroy cancer cells is confined to the body region in which the tumor is
located. Thus, healthy body cells are substantially kept below the
temperature at which their destruction would ordinarily occur.
The apparatus of the present invention includes a video system which
permits a video image of a cancerous tumor to be displayed on a video
monitor. This image is formed by directing an intense light onto a body
part suspected of containing a tumor. The light passing through body from
the light source will present an image of a tumor if a tumor is present.
This image will be sensed by a video camera and can be viewed on a video
monitor. The video image on the monitor can be observed and used to assist
in inserting the antenna and temperature sensors into the body and into
the proper locations with respect to the tumor itself.
The apparatus of the present invention is simple and rugged in
construction, is inexpensive to produce and maintain, and can be used with
clinicians with minimal expertise in the operation and handling of the
electronic equipment. Since the antenna has the construction of a
hypodermic needle, microwave energy can readily and easily be applied to a
tumor without elaborate preparation of a patient, such as by the use of
local anesthesia or other procedures. Moreover, the video system of the
apparatus includes a video recorder so that a record of the progress in
the destruction of a cancerous tumor can be made.
The primary object of the present invention is to provide an improved
apparatus and method for applying heat to the interior of a tumor within
the living body wherein an antenna similar in construction to a hypodermic
needle inserted into the body and into the tumor can radiate microwave
energy into the tumor to heat the tumor while the temperature at the outer
periphery of the tumor can be continuously monitored by sensors inserted
into the body to thereby permit the destruction of cancerous cells in the
tumor without destruction of healthy cells in the body surrounding the
tumor.
Another object of the present invention is to provide an improved antenna
for use in applying microwave energy within a tumor wherein the antenna is
constructed in the form of a hypodermic needle provided with a center
conductor within and spaced from an outer tubular barrel and the antenna
itself can be impedance matched with human tissues and can be of a
diameter less than that considered to be minimally invasive of the body to
thereby allow the heating of a tumor within the body without elaborate
preparation of the patient as might be required for more invasive
penetration of the body.
Other objects of this invention will become apparent as the following
specification progresses, reference being had to the accompanying drawing
for an illustration of the invention.
In the drawing:
FIG. 1 is a schematic view of the apparatus for use in destroying tumors
and other cancerous growths in the living body;
FIG. 2 is a schematic view, partly in section, of one embodiment of an
antenna and a microwave generator coupled with the antenna for applying
microwave energy to a tumor to heat it;
FIG. 3 is a fragmentary, cross-sectional view of another embodiment of the
antenna;
FIG. 4 is a fragmentary, cross-sectional view of a prior art coaxial cable
for radiating microwave energy into human or animal tissue, the coaxial
cable being in an air-filled catheter; and
FIG. 5 is a cross-sectional view of an improved antenna of the present
invention having impedance matching characteristics.
The apparatus of the present invention is broadly denoted by the numeral 10
and is illustrated schematically in FIG. 1. Apparatus 10 includes a
housing 12 containing a number of components, including a microwave power
generator 14, a temperature detector and control unit 16 and a video
system 18 provided with a video recorder and playback device 19, a video
monitor 21, and a video camera 27. Apparatus 10 further includes a
microwave antenna 20 coupled by a coaxial cable 22 having leads 23 and 25
to power output terminals 24 of microwave generator 14. Antenna 20 is
shown in more detail in FIG. 2 and will be described hereinafter.
Antenna 20 is adapted to be inserted into a tumor 24 in the living body 26
so that microwave energy can be imparted to the tumor to heat the tumor
and to destroy cancerous cells therein. Temperature detection and control
unit 16 is provided to sense temperatures at various locations at the
outer periphery of tumor 24 and to control the actuation and deactuation
of the microwave generator as a function of such temperatures.
Antenna 20 is constructed in the form of a hypodermic needle and includes a
tubular member or barrel 29 having a pointed end 30 for penetration of the
skin and insertion into the body 26 and into a tumor 24 within the body as
shown in FIG. 1. Barrel 29 has an internal circular bore 32 and an
electrical conductor 34 is located concentrically within bore 32, and
uniform spacing is maintained by a dielectric material 33, the conductor
and dielectric material extending to the pointed end 30 as shown in FIG.
2. Antenna 20 comprises a transmission line for microwave energy from
microwave generator 14 by way of coaxial cable 22. Lead 23 of cable 22 is
coupled to conductor 34 and lead 25 is secured to barrel 29. The output
end of antenna 20 is "open circuited" to allow incoming microwave energy
to be broadcast or radiated in all directions from the antenna. The design
of antenna 20 is such that there is impedance matching between the antenna
and the human tissue in which the energy is radiated. By selecting the
proper electromagnetic mode of operation, broadband frequency of operation
in the antenna (transmission line) is readily achieved.
Typically, the diameter of barrel 29 is less than 16 gauge (0.065 inch
O.D.). This gauge is chosen because the use of a hypodermic needle above
this gauge is considered to be minimally invasive in the medical sense.
The length of the needle typically is of a value sufficient to cause the
needle to penetrate the skin and then penetrate a tumor so that the needle
point 30 is substantially at the center of the tumor itself. Thus, the
microwave energy radiated from the antenna will radiate in all directions
and substantially uniformly heat the tumor so as to destroy the cancerous
cells therein.
Microwave generator 14 can be of any desired construction. It can be a
commercially available product, such as one made by Matsushita Electric
Industries, Ltd. of Tokyo, Japan and identified as Magnetron 2M157. Such a
microwave generator is rated at a frequency of 2450 MHz and 600 watts
(continuous wave). This generator can be modified so as to produce lower
power output levels such as 100 to 400 watts which is considered to be
sufficient for the purposes to which the present invention is to be
placed.
Microwave generator 14 typically is provided with an elapsed time clock 40
which times the delivery of output power applied to antenna 20
particularly after the tissue has reached a preset temperature. A keyboard
42 or other switching means is provided to permit the setting of operating
times, depending upon the amount of microwave energy to be applied to a
tumor by way of antenna 20. Typically, operating times of 20 minutes to 45
minutes are used, and a tumor is heated to a temperature in the rage of
43.degree. to 46.degree. C. for destroying cancerous cells in a tumor.
Elapsed time at temperature is referred to as a dosage. Other operating
times can be used, depending upon the condition of the tumor and the need
for applying a greater or lesser dosage of heat thereto.
Temperature detector and control unit 16 is provided to detect temperatures
at various locations around the outer periphery of a tumor as microwave
energy is being imparted to the tumor by way of antenna 20. To this end, a
plurality of temperature sensors 42 are inserted in body 56 at the outer
periphery of tumor 24, and these sensors are coupled to respective leads
44 to a common lead 46 coupled with unit 16. When signals from sensors 42
are directed to unit 16, the signals are used to indicate relative
temperature values at the outer periphery of the tumor. If the temperature
determined by unit 16 approaches a maximum value, such as 46.degree. C.,
the unit 16 actuates a switching network coupled with microwave generator
14, the switching network de-energizes microwave generator 14 for a period
of time until the temperature at the outer periphery of the tumor is
reduced to a certain value, such as 45.degree. C. In this way, the heat
energy necessary to kill cancer cells in a growth does not exceed a level
which might possibly harm healthy cells in the region surrounding the
tumor. Yet, once power is again applied to antenna 20, the antenna can
radiate the energy so as to continue to heat the tumor for a time deemed
necessary to kill the cancerous growth therein.
Suitable sensors for use in the present invention may be those made by
Luxtron Corporation, Mountain View, Calif. and identified as Model 1000B
biomedical thermometer.
Video system 18 is coupled by cable means 52 to video camera 27 which is to
be used to insert the antenna 20 into a tumor 24 and to insert temperature
sensors 42 into the body 26 at the outer periphery of the tumor. To this
end, camera 27 is mounted on one side of the body 26 in alignment with
tumor 24 therein. A strong light source 56 on the opposite side of tumor
24 directs light onto body 26. This will present an image capable of being
sensed by camera 27, the image showing the presence of the tumor 24. This
image in the form of video signals is directed to system 18 where it is
displayed on monitor 21. Thus, a clinician, while viewing monitor 21, can
insert antenna 20 into body 26 and then into tumor 24, so that the pointed
end 30 of the antenna is substantially at the center of the tumor. Then,
while viewing monitor 21, the clinician can insert the temperature sensors
42, one by one, so that the sensors will be at the outer periphery of the
tumor for sensing the temperature immediately after heating of the tumor
commences.
A video record can simultaneously be made with recorder 19 during the
insertion of the antenna and sensors into the body. The record can also
show the progress in the reduction of the size of the tumor. In this way,
a permanent record of the procedure for a particular patient can be
obtained and stored for future reference.
Generally, the presence or location of a tumor 24 in body 26 is determined
by palpations; however, camera 27 and light source 56 can be used for the
same purpose, if deemed desirable or necessary.
In operation, apparatus 10 is assembled as shown in FIG. 1. A person found
to have a cancerous tumor, such as in the breast, is placed adjacent to
camera 27 so that light 56 can illuminate the portion of the body
containing the tumor. The camera then senses the image of the light
passing through the body from light source 56 and this image will include
a view of tumor 24. The image of the tumor will be displayed on monitor 21
and a continuous video record of the image can be obtained with recorder
19 while the camera is receiving light images from body 26.
With an image properly displayed on monitor 21, a clinician will then
insert antenna 20 into body 26, the antenna being readily capable of
penetrating the skin and entering tumor 24 because of the sharpened
pointed end 30 of the needle-like construction of the antenna. The
clinician will be able to determine, while viewing monitor 21, when the
pointed end 30 of the antenna is substantially at the center of the tumor.
Following the placement of the antenna in the tumor, the clinician then
inserts one or more sensors 42 into body 26 so that the sensor or sensors
are at the outer periphery of the tumor. When the sensors are properly
located, apparatus 10 is ready for the application of microwave energy to
the antenna.
The clock-setting device 42 is then actuated to provide a specific
operating time for operation of microwave generator 14. Then, the
microwave generator is energized to cause microwave energy to be applied
to antenna 20 which radiates the energy in substantially all directions
throughout the tumor to heat the cells of the tumor. As the energy is
applied, the temperature at the various locations on the periphery of the
tumor are continuously sensed by sensors 42, and signals from these
sensors are directed to unit 16 which monitors the magnitudes of the
temperatures. If any one sensor senses a temperature above a predetermined
maximum value, unit 16 will de-energize microwave generator 14, causing
removal of power from antenna 20. This power interruption continues until
the temperature at the outer periphery of the tumor once again drops to a
pre-set value, whereupon power is once again restored to the antenna since
unit 16 will again energize microwave generator 14 after the lower
temperature is reached. This pattern of operation continues until the
requisite amount of microwave energy has been applied for the preset time
as determined by the setting on clock 40.
Apparatus 10 provides a means to develop and deliver microwave energy to a
tumor in a simple and expeditious manner so as to provide an effective
tool for the precise heating of a tumor with minimum discomfort to the
patient. Apparatus 10 provides an integrated instrument characterized by
reliability and simplicity of construction. The apparatus is especially
suitable for treating tumors in the living breast, on or near the surface
of the body and those locations that can be reached by the hypodermic
needle antenna.
In the normal course of treatment of a tumor, if a tumor is detected, a
physician can order a biopsy. Then, depending upon the results of the
biopsy, the physician can select a course of treatment, such as surgery,
chemotherapy, radiation therapy or combinations of these approaches.
Apparatus 10 provides another option, namely, hyperthermia, which can be
used alone or in combination with the other approaches.
If a physician prescribes hyperthermia, he will typically prescribe a
temperature of about 44.5.degree. C. and a duration of exposure at that
temperature level, usually 20 to 40 minutes, as a function of the size of
the tumor. Apparatus 10 will then be used to deliver enough microwave
energy at a given frequency, such as 2450 MHz, an FCC approved frequency
for medical applications, to elevate the tissue temperature to the
prescribed level. However, other microwave frequencies may be selected as
is determined by medical efficacy. Using this needle-like antenna
eliminates the stray frequency broadcasting which would require RF
shielding if other external transmission methods were used.
In FIG. 3, another antenna embodiment is shown. Antenna 20a has a pointed
end formed by a conductor 34a which is longer than barrel 29a. The outer
end of conductor 34a is pointed, and dielectric spacer material 33a is
pointed between the outer end of barrel 29a and the outer end of conductor
34a.
An antenna which can be used in the present invention as one shown FIG. 5
or hyperthermia application, typically in the treatment of tumors. The
antenna shown in FIG. 5, broadly denoted by the numberal 50, is designed
to solve the problem of impedance matching that exists when a coaxial
cable is inserted into an air-filled plastic catheter that has been placed
into human or animal tissue, such as a tumor which is about 80% water.
The impedance of prior art coaxial cable used in these applications is
typically 50 ohms while air is approximately 377 ohms and moist tissues
about 50 ohms. Without impedance matching, a mismatch occurs, causing a
significant reflection of the microwave power in the opposite direction of
propagation. This is detrimental to the application as the reflected power
will be additive to the forward moving power and as a result, over-heating
will occur in the cable and in the patient's tissue. Over-heating can
become significant enough to cause pain in the patient.
In the prior arts embodiment of FIG. 4, a coaxial cable 52 is inserted into
a tubular catheter 54 placed in a mass 56 of human or animal tissue which
is moist. The catheter is air filled and the direction of forward power
propagation from the coaxial cable 52 is in the direction of arrow 58.
Reflective power denoted by the arrow 60 is caused because of the
mis-match in the impedance of the air in the space 62 surrounding the end
64 of the coaxial cable 52, such space 62 being within catheter 54 since
the impedance of coaxial cable 52 and the tissue 56 is approximately 50
ohms and beacause the impedance of the air is approximately 377 ohms there
is a mismatch which gives rise to a considerable amount of reflection
denoted by the arrow 60 in the opposite direction of the desired
propagation direction indicated by the arrow 62.
The purpose of antenna 50 (FIG. 5) is to significantly reduce or eliminate
the air space 62 of the prior art embodiment of FIG. 4. This is
accomplished in antenna's 50 by placing the concentric cable 50 thereof
(FIG. 5) into a concentric plastic tube 67 that is sealed at both ends and
is filled with an appropriate fluid, such as distilled water, denatured
alcohol or an optimized molal solution of water and salt. By selecting the
appropriate fluid for the diameters and thickness of tube 67, impedance
matching is achieved and maximum forward transmission of the microwave
energy is obtained. With the reflected power reduced to a few percent,
transmission line heating is eliminated and patient comfort is assured.
As shown in FIG. 5, a space 68 surrounding the electrically non-conductive
layer 69 of the antenna 50, space 68 being surrounded by tubing 67. Space
68 is filled with the appropriate fluid for impedance matching.
The rear end of tube 67 is sealed and press fitted in the forward, tubular
end of a tubular member 70. The front end of tube 67 is press fitted on
the rear boss 71 of an end plug 72.
Antenna 50 is terminated typically with a type SMA (male) connector or SMA
(female) connector to assure compatability with a typical cable
transmission lines from the source of microwave power. The male connector
with its rotating collar allows the assembly to remain stationary during
the connecting operation although this in itself is not a critical aspect.
End plug 72 is smooth and rounded to facilitate the insertion of the
antenna into the catheter 73. The end plug also serves to center the
coaxial cable within the concentric tubing, assuring optimum impedance
matching characteristics. The outer diameter of the end plug is determined
by the inner diameter of the catheter into which the end plug is to be
inserted.
The length of the assembly from this from the SMA connector 75 to the end
plug is not electrically important and will be set to be convenient to the
user. A calibration may be added to assist in noting the depth of
penetration of the assembly into the catheter which typically will have
been previously inserted into the patient's tumor.
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