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CROSS REFERENCE TO RELATED APPLICATION
Of interest is the following pending U.S. Pat. application: Ser. No.
840,036 filed Oct. 6, 1977 by R. W. Paglione, entitled, "A Temperature
Controller For a Microwave Heating System."
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to hyperthermia treatment of living tissues and more
particularly to radiation of microwave energy and simultaneous measurement
of the temperature at the site of treatment.
2. Description of the Prior Art
Medical practitioners have known that a patient with a cancerous tumor can
be successfully treated, by a process which raises the temperature of the
tumor. This treatment is generally referred to as hyperthermia. One method
of hyperthermia treatment utilizes microwave radiation energy. The
temperature of the tissue irradiated by the microwave energy is a function
of the power or intensity of the microwave signal applied to the body
tissue. The depth of penetration of a microwave signal into the tissue is,
in general, an inverse function of the signal frequency employed. The
volume of the tissue to be treated is controlled by the electrical and
geometrical design of the microwave applicator.
The microwave radiation may be controlled to elevate the temperature of a
known volume of tissue. During microwave radiation, it is desirable to
prevent overheating of the tissue as well as the surrounding tissues. It
is correspondingly desirable to provide an accurate measurement of the
temperature of the tissue being treated, particularly at the site of the
tumor. Prior methods for measuring the temperature of the treated tissue
employ thermocouples, thermometers or radiometers. One such method
utilizing a radiometer is described in U.S. Pat. application, Ser. No.
808,272, filed on June 20, 1977 entitled "Apparatus for Hyperthermia
Treatment" by Fred Sterzer.
Thermocouples for measuring the temperature of the treated tissue may be
either attached to the surface of the skin or invasively positioned
beneath the skin at or near the site of the tumor to be treated.
Thermocouples are used while measuring temperature during treatment to
switch off the microwave radiation to the tissue upon sensing a
predetermined temperature. However, thermocouples positioned near or in
close proximity to the irradiating signal distort the applied microwave
signal inducing anomalous heating effects which contribute to inaccurate
temperature control. It is known to measure the tissue temperature with a
thermocouple only at a time when the irradiation signals are removed. Such
an arrangement is described in the above-identified U.S. Pat. application,
Ser. No. 840,036.
It is further known to utilize a thermometer disposed within a radio
frequency radiating electrode to measure the temperature within the
electrode, as described in U.S. Pat. No. 2,126,257, entitled
"Electromedical Instrument," issued Aug. 9, 1938, to Frank E. Hird.
SUMMARY OF THE INVENTION
According to this invention, hyperthermia treatment of tissue is provided
by irradiating tissue with microwave signals while simultaneously
measuring the temperature of the irradiated tissues at the site of the
applied microwave signals.
A coaxial applicator, having a shielded thermocouple, within the inner
conductor, radiates the microwave signals to the treated tissue. The
thermocouple is positioned at the site of the applied radiation
continuously measuring the temperature of the treated tissue.
The voltage corresponding to the temperature of the treated tissue is
compared to a voltage that corresponds to the temperature to control the
application or interruption of the microwave signals.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block schematic of an apparatus utilizing the preferred
embodiment of the invention.
FIG. 2 is a detailed elevation view of the connector 80 of FIG. 1.
FIGS. 3a and 3b are sectional schematics of the coaxial cable applicator of
the invention.
FIG. 4 is a schematic of a preferred controller circuit utilized in FIG. 1.
FIGS. 5a and 5b are sectional schematics of a coaxial applicator modified
to produce a directional radiator.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in FIG. 1, microwave source 10 supplies a cw or pulsed microwave
signal 14 for irradiation of tumor 104 during hyperthermia treatment.
Signal 14 is coupled to control circuit 20 via coaxial connector 12,
coaxial cable 16, and coaxial connector 22. Control circuit 20 couples the
microwave signal 14 to tumor 104 via connector 24, coaxial cable 29 and
coaxial right angle connector 80. The right angle connector 80 is a
modified Model 1037-5002 connector manufactured by Omni-Spectra/Americon
of Waltham, Mass. Coaxial cable 29 is attached to right angle connector 80
in a conventional manner whereby its center coaxial conductor 29a is
extended into connector 80 (shown in detail in FIG. 2) and attached to
hollow center conductor 94a of coaxial cable 20. Within the hollow
conductor 94a of cable 90 (shown in detail in FIG. 3 to be described) are
a pair of thermocouple wires 94 formed at one end into a thermocouple 100
and connected at the other end of the input connector 112 of a digital
thermometer 110. Outer conductor 98 of coaxial cable 90 is separated from
the central portion and slipped over a hollow nose portion 80a of
connector 80, the center conductor 94a being extended into and through the
connector 80 for connection to extension pin 80e as by soldering at 80c
and thence to the center conductor 29a of coaxial cable 29. The soldering
access hole 80g is suitably sealed after soldering the inner conductors. A
male threaded coaxial coupler 29b attached to coax 29 couples center
conductor 29a of coax 29 to connector 80 via a female rotatable threaded
sleeve 80d. The thermocouple wire pair 94 and center conductor 94a are
extended out through a suitable access hole 80b of connector 80 for
connection to digital thermometer 110. A hollow telescopic brass slideable
tuner slug 83 is fit within a hollow brass sleeve 82 attached to connector
housing 80 in registration with ahole therein and over conductor 94a and
the wire pair 94. Slug 83 is slideably adjusted within sleeve 82 as by
knob 84 between the connector 80 and the digital thermometer 119 to reduce
reflections produced by the thermocouple sleeve 94a extending out through
the connector 80 and within the hollow sleeve 82 and other reflections
generated at the right angle connector. Thus, the microwave energy from
source 10 via cable 29 is efficiently coupled to cable 90 and thence the
treated tumor tissue is decoupled from the thermocouple signal (to be
described) conducted by the thermocouple wire pair 94.
As shown in FIG. 1, microwave signal 14 is radiated into tumor 104 via an
unshielded end 96 of the coaxial cable applicator 90. Unshielded end 96 is
positioned at the site of the tumor to be treated within tissue 102. The
unshielded end 96 is invasively positioned within a subcutaneous tumor 104
beneath surface 106. The unshielded end 96 functions as a monopole antenna
converting microwave signal 14 into irradiation fields within tumor 104.
Located near the tip of the unshielded end 96 is thermocouple 100.
Thermocouple 100 measures the temperature of tissue in contact with the
end 96, in the known manner, the temperature of the tissue being
manifested as a D.C. voltage developed by the thermocouple 100. This D.C.
voltage is coupled to digital thermometer 110 via the thermocouple wire
pair 94. Digital thermometer 110 is suitably a Model No. BAT-8
manufactured by the Bailey Instrument Co. of Saddle Brook, New Jersey.
Digital thermometer 110 includes suitable circuits and logic to display
digitally the temperature sensed by the thermocouple 100. Digital
thermometer 100 provides a proportional D.C. voltage, suitably in a range
of 0-3.0V, indicative of the thermocouple temperature, which is coupled to
the control circuit 20 via signal path 114.
FIG. 3a illustrates in section a portion of the coaxial applicator 90, FIG.
3b being an end view thereof. Applicator 90 comprises a suitable vinyl
jacket 97, outer conductor 98 formed of a suitable braided wire. The space
between outer conductor 98 and center conductor 94a is filled with a
suitable dielectric material 95 such as teflon. The thermocouple 100 is
suitably an ungrounded, 304ss (stainless steel) sheathed,
copper-constantan, Model Number SCPSS-02OU-6, manufactured by Omega
Engineering, Inc. of Waltham, Mass. An end gap 108 is provided by the
manufacturer to prevent the thermocouple 100 from being grounded to the
inner conductor 94a. The center conductor 94a may be gold plated to
improve its conductivity and reduce the eddy current effect in the
thermocouple sleeve 94a produced by the microwave signal 14. The
characteristics impedance (Zo) of coaxial applicator 90 can be represented
by the formula:
Zo=138/.sqroot..epsilon.log.sub.10 (b/a) (1)
where .epsilon. is the dielectric constant of the medium between the center
(94a) and outer (98) conductor and a and b are respectively the center and
outer conductor diameters. For a characteristic impedance of 50 ohnms,
1/.sqroot..epsilon. is 0.69 for teflon, "a" equals 0.020 inches and "b"
inches 0.067 inches.
The unshielded end 96 of center conductor 94a extends for a distance equal
to .lambda.g/2, or an integer multiple of .lambda.g/2, .lambda.g being
defined by the following relation:
.lambda.g=C/f.sqroot..epsilon. (2)
where C is the speed of light in vacuum equal to 11.802874 inch-GHz, f is
the microwave frequency in Gigahertz and .epsilon. is the dielectric
constant of the area being irradiated.
In operation, microwave signal 14 is propagated in a radial direction about
the unshielded end 96. In practice the braided wire 98 is completely
removed or cut back from the circumference of unshielded end 96 allowing
the microwave signal 14 to irradiate the tumor 104 located about
unshielded end 96. Unshielded end 96 being essentially a probe functions
as an omnidirectional antenna in the radial plane. Since the end 96 has an
electrical length of .lambda.g/2 or an integer multiple thereof, it
functions to provide maximum radiation efficiency at frequency f.
FIG. 4 is a schematic of control circuit 20, which interconnects the
severed components of the system for the hyperthermia treatment. Coaxial
switch 60 connects microwave signal 14 to either connector 80, for further
transfer to tumor 104, or to the dummy load 70. Coaxial switch 60 is
suitably a Hewlett-Packard switch part number 8761A. Switch 60 includes an
input coaxial connector 22 and two output coaxial connectors 24 and 26,
and a flexible reed contact 64 that is magnetically coupled to a winding
68. Each of the coaxial connectors 22, 24, and 26 have inner conductors
62, 65, and 66, respectively. Reed contact 64 is connected at one end to
the center conductor 62 of the input connector 22, while the other end
thereof is positionable in response to signals passing through the winding
68 to be electrically connected with either center conductor 65 or 66. The
polarity of voltage applied to winding 68 determines the position to which
reed contact 64 is connected. Thus, a positive voltage applied to winding
68 positions reed contact 64 to inner conductor 65 of the coaxial
connector 24 and thus connects microwave signal 14 to applicator 90 via
connector 80 for irradiation of tumor 104. A negative voltage applied to
winding 68 positions reed contact 64 to inner conductor 66 and thus
connects microwave signal 14 to dummy load 70. The application of a
positive or negative energizing signal to winding 68 is controlled by a
differential amplifier 30 operating with transistors 52 and 54.
Differential amplifier 30 is suitably type RCA CA-741. Transistor 52 is a
NPN type and transistor 54 is a PNP type.
Differential amplifier 30 has two inputs, one a non-inverting input on
signal path 34 and the other an inverting input on signal path 36. The
input on path 34 is preset to a D.C. value indicative of a predetermined
temperature that is to be maintained during a hyperthermia treatment;
e.g., 43.degree. C. The preset value is set by adjusting potentiometer 32.
The potentiometer 32 is connected between a voltage source having a
particular polarity, such as a positive D.C. voltage, at terminal 48 and a
reference voltage such as ground, such that the preset value is adjustable
therebetween. The input voltage to amplifier 30 on path 36 is suitably a
voltage within a range of 0 to 3 volts D.C. from digital thermometer 110
coupled to control circuit 20 via signal path 114, terminal 33, and
resistor 50. The voltage is indicative of the temperature of the treated
tumor 104 as measured by the thermocouple internal to center conductor 94a
of coaxial applicator 90 at the site of the treatment. Differential
amplifier 30 is connected to positive (48) and negative (44) supply
voltages via paths 41 and 43, respectively.
Differential amplifier 30 produces an output voltage on path 38
proportional to a differential voltage existing between input paths 34 and
36. When the voltage signal on path 36 is less than the preset value at
input 34, differential amplifier 30 produces a positive voltage on path 38
rendering transistor 52 conductive. Transistor 52 being conductive
provides a positive voltage to winding 68 of coaxial switch 60 thereby
providing the path for connecting microwave signal 14 to tumor 104. When
the voltage signal on path 36 exceeds the preset value at input 34, a
negative voltage is generated on path 38, turning off transistor 52 and
allowing transistor 54 to be conductive. Transistor 54 being conductive
provides a negative voltage to winding 68 of coaxial switch 60 thereby
removing microwave signal 14 from tumor 104 and further connecting the
microwave signal 14 to the dummy load 70. Resistor 40 and capacitor 42
connected between the inverting input path 36 and the output path 38 of
amplifier 30 forms a feedback network that determines the gain of the
differential amplifier in response to the differential signal between 34
and 36.
In operation, when the temperature of the treated tumor 104 as measured by
the thermocouple 100 at the site of the treatment, is below the preset
value as established by the potentiometer 32, the microwave signal 14 is
coupled via switch 60 to irradiate tumor 104. The irradiation by signal 14
continues until the temperature of the treated tissue equals the preset
value. This action is repeated as the switch 60 applies and disconnects
signal 14 from the tumor 104 in response to the temperature of the tumor
as sensed by the thermocouple 100.
Another embodiment for radiating the microwave signal 14 to tissue, but in
a selected direction is illustrated in FIGS. 5a and 5b. FIG. 5a is a plan
view of the end portion of coaxial applicator 90 while FIG. 5b is a
sideview thereof. The braided wire outer conductor 98 is cut out to
provide a generally semicylindrical unshielded area 93 having a length in
accordance with formula (2) given for unshielded end 96. The unshielded
end portion 93 functions as a directional antenna for radiating microwave
signal 14 in one general direction. The unshielded end 93 may be formed by
removing only a portion of the braided wire at the end of applicator 90 as
shown in FIGS. 5a and 5b. The braided wire 98 suitably covers the end of
the coaxial applicator 90 as at 98a to prevent longitudinal propagation of
microwave signal 14. Therefore, the center conductor 94a is shortened a
distance to prevent it from touching the braided wire 98 as by gap 109. A
gap 108 between the thermocouple and conductor 94a being similarly
provided by the manufacturer as that for the applicator of FIG. 3a.
If desired a directive radiator can be fabricated by merely cutting back
the shielded conductor 98 a sufficient distance to provide the desired
radiator length for conductor 94a andd suitably forming a semi-cylindrical
metallic reflector over the radiator portion to provide an unshielded
portion similar to that shown in FIGS. 5a and 5b.
In practice the use of an unshielded end as an omnidirectional (FIGS. 3a
and 3b) or directional antenna (FIGS. 5a and 5b) is dependent upon the
form or location of the tumor to be treated. If it is desired to confine
the microwave signal 14 to a particular direction for irradiation of a
tumor, as existing in a surface portion, then partially shielded end 93
(FIGS. 5a and 5b) is used. If it is desired to radiate in a cylindrical
volume, to treat a tumor 104, then unshielded end 96 (FIGS. 3a and 3b) is
invasively positioned within the tissue.
It should now be appreciated that this invention provides an applicator for
hyperthermia treatment for continuous irradiation of a microwave signal
(14) into tissue (104) and concurrent measurement of the temperature at
the site of the irradiated tissue (104). The temperature of the heat
treated tissue is automatically controlled in response to the temperature
being sensed by the thermocouple within the applicator. Since the
thermocouple is isolated from microwave signals and yet thermally
sensitive to the ambient tissue temperature, the invention overcomes the
problem of thermocouples used in the prior art interfering with the
irradiating microwave signals. Furthermore, since the thermocouple
provided in the present applicator is in the radiator, it measures the
temperature of the tissue continuously during the irradiation process. It
should be further understood that the microwave signals used to practice
the invention include electromagnetic signals in the radio frequency
spectrum comprising, for example, 100 to 10,000 MHz.
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