U.S. patent application number 11/373710 was filed with the patent office on 2006-07-27 for selective conductive interstitial thermal therapy device.
Invention is credited to Gal Shafirstein.
Application Number | 20060167445 11/373710 |
Document ID | / |
Family ID | 38509965 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060167445 |
Kind Code |
A1 |
Shafirstein; Gal |
July 27, 2006 |
Selective conductive interstitial thermal therapy device
Abstract
An apparatus and method for thermally destroying tumors. A tip
has a plurality of deployable thermal conductive elements whose
temperatures are individually controllable. This allows the shape
of the thermal field to be controlled and for specific areas to be
protected from excessive heat by cooling those specific areas while
ablating other areas. In another embodiment, the deployable thermal
conductive elements are individually deployable to various lengths
to further aid in shaping the thermal field. The temperatures and
the shape of the thermal field may be monitored and controlled by a
data processing device, such as a microprocessor. Further
selectivity in defining the area of tissue to be treated may be
achieved by introducing into the tissue thermal additives that
alter the thermal properties of the tissue.
Inventors: |
Shafirstein; Gal; (Little
Rock, AR) |
Correspondence
Address: |
WRIGHT, LINDSEY & JENNINGS LLP
200 WEST CAPITOL AVENUE, SUITE 2300
LITTLE ROCK
AR
72201-3699
US
|
Family ID: |
38509965 |
Appl. No.: |
11/373710 |
Filed: |
March 10, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11028157 |
Jan 3, 2005 |
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11373710 |
Mar 10, 2006 |
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10336973 |
Jan 6, 2003 |
6872203 |
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11028157 |
Jan 3, 2005 |
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10228482 |
Aug 27, 2002 |
6780177 |
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10336973 |
Jan 6, 2003 |
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Current U.S.
Class: |
606/28 |
Current CPC
Class: |
A61B 2018/00791
20130101; A61B 2017/00084 20130101; A61B 2018/00577 20130101; A61B
18/24 20130101; A61B 2017/00101 20130101; A61B 2017/00867 20130101;
A61B 2018/00011 20130101; A61B 18/082 20130101; A61B 18/20
20130101; A61B 2018/00714 20130101; A61B 2018/2005 20130101 |
Class at
Publication: |
606/028 |
International
Class: |
A61B 18/04 20060101
A61B018/04 |
Claims
1. An apparatus for the thermal treatment of tissues, comprising: a
tip; a plurality of deployable elements operatively connected to
said tip; and temperature providing means associated with each
element of said plurality of deployable elements for providing an
individually controllable temperature from said each element to
said element's respective surrounding tissue.
2. The apparatus of claim 1, further comprising a temperature
sensor associated with said each element.
3. The apparatus of claim 1, where said temperature providing means
further comprises a heat sink.
4. The apparatus of claim 1, wherein said temperature providing
means comprises an electromagnetic field.
5. The apparatus of claim 3, wherein said heat sink comprises a
solid, fluid, gas or mixture of any of the preceding at a
temperature below the maximum temperature of the apparatus.
6. The apparatus of claim 1, wherein said temperature providing
means comprises means for injecting high temperature solids,
liquids, gases or mixtures of the preceding into said respective
surrounding tissue from said deployable elements.
7. The apparatus of claim 1, wherein said deployable elements
comprise means for applying additives that change the thermal
properties of the tissue.
8. The apparatus of claim 7, wherein said additives comprise
particles, solutions containing particles, metals, ceramics,
composites, polymers, organic and inorganic chemicals, and mixtures
of any of the preceding.
9. The apparatus of claim 1, further comprising deployment
providing means associated with each element of said plurality of
deployable elements for deploying said each element to an
individually controllable shape.
10. The apparatus of claim 9, wherein said temperature providing
means further comprises a temperature sensor associated with said
each element.
11. The apparatus of claim 9, where said temperature providing
means further comprises a heat sink.
12. The apparatus of claim 11, wherein said means for cooling
comprises an electromagnetic field.
13. The apparatus of claim 11, wherein said means for cooling
comprises a solid, fluid, gas or mixture of any of the preceding at
a temperature below the maximum temperature of the apparatus.
14. The apparatus of claim 9, wherein said temperature providing
means comprises means for injecting high temperature solids,
liquids, gases or mixtures of the preceding into said respective
surrounding tissue from said deployable elements.
15. The apparatus of claim 9, wherein said deployable elements
comprise means for applying additives that change the thermal
properties of the tissue.
16. The apparatus or claim 15, wherein said additives comprise
particles, solutions containing particles, metals, ceramics,
composites, polymers, organic and inorganic chemicals, and mixtures
of any of the preceding.
17. A method for the thermal treatment of tissue, comprising the
steps of (a) determining a spatial shape of a volume of tissue to
be treated; (b) providing a tip having a plurality of deployable
elements comprising temperature providing means associated with
each element of said plurality of deployable thermal conductive
elements for providing an individually controllable temperature
from each said element to said element's respective surrounding
tissue; (c) selecting a temperature for each element whereby a
thermal field is generated having a shape selected to treat the
spatial shape of the volume of tissue; (c) positioning the tip into
the volume of tissue to be treated; (d) generating the temperature
selected for each element; (f) maintaining the tip in the tissue
for a sufficient period of time to treat the tissue; and (g)
removing the tip from the tissue.
18. The method of claim 17, wherein said tip further comprises
deployment providing means associated with each element for
deploying each element to an individually predetermined shape,
further comprising the steps, prior-to step (f), of: selecting a
shape for each element whereby in combination with the selected
temperatures of step (c) a thermal field is generated having a
shape selected to treat the spatial shape of the volume of tissue;
and deploying each element to the selected shape.
19. The method of claim 17, further comprising the step, prior to
step (f), of applying additives to the tissue.
20. The method of claim 19 wherein said additives comprise
particles, solutions containing particles, metals, ceramics,
composites, polymers, organic and inorganic chemicals, and mixtures
of any of the preceding.
21. The method of claim 19, wherein said step of applying additives
comprises introducing said additives by an external applicator.
22. The method of claim 19, wherein said step of applying additives
comprises introducing said additives systemically.
23. The method of claim 18, further comprising the step, prior to
step (f), of applying additives to the tissue.
24. The method of claim 23 wherein said additives comprise
particles, solutions containing particles, metals, ceramics,
composites, polymers, organic and inorganic chemicals, and mixtures
of any of the preceding.
25. The method of claim 23, wherein said step of applying additives
comprises introducing said additives by an external applicator.
26. The method of claim 23, wherein said step of applying additives
comprises introducing said additives systemically.
27. The method of claim 17, wherein step (c) further comprises
providing a separate cooled probe having a temperature selected to
provide, in combination with said selected temperature for each
said element, said thermal field.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of pending U.S.
patent application Ser. No. 11/028,157, filed Jan. 3, 2005, which
is a continuation of U.S. patent application Ser. No. 10/336,973
filed Jan. 6, 2003, now U.S. Pat. No. 6,872,203, which is a
continuation-in-part of U.S. patent application Ser. No. 10/228,482
filed Aug. 27, 2002, now U.S. Pat. No. 6,780,177, all of which are
incorporated herein by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to methods and devices for
treating body tissues such as tumors or lesions with thermal
energy, and in particular, to such methods and devices that deploy
thermally conductive elements to treat a predetermined shape of
tissue.
[0005] 2. Brief Description of the Related Art
[0006] Within the last ten years, interstitial thermal therapy of
tumors has become an accepted method for treating cancerous tumors.
These minimally invasive therapeutic procedures are used to kill
cancer tumors without damaging healthy tissues surrounding it.
Increasing the temperature of the tumor above a threshold level of
about 70-130 C will cause tumor death. Interstitial thermal devices
for thermal tissue ablation including radio frequency ablation
(RFA), microwave and laser based technologies have been developed
and have received 510K FDA clearance. All of these techniques use
radiation to transfer the energy to the tumor, and therefore the
heat in the tumor is generated indirectly through local energy
absorption sites (e.g., blood in the case of a laser or fat in the
case of RFA) could result in a non-homogenous heating of the tumor.
The consequences of a non-uniform heating of the tumor could
include incomplete death of the tumor and/or skin burns and injury
of healthy tissues or organs. Incomplete tumor death will result in
recurrence of multiple small tumors in the treated area.
[0007] Moreover, as most of the heat is transfer by radiation (in
laser, RFA and microwave), it is very difficult to calculate the
temperature distribution without precisely knowing the fine
microstructure (down to the cell level) that cannot be
predetermined with a non-invasive method. In addition the
temperature measurements are also challenging; in these cases,
since the probes could be directly heated by the energy sources and
will show it's own temperature rather than that of the tissue. For
example, in laser or RFA thermocouples may get hot from the source
much quicker than tissue (as they absorb RF and laser energy more
than tissue) and will show temperatures that are higher than the
actual temperature in the lesion. That could result in insufficient
heating and if the operator increases the amount of energy
delivered to the tumor, an overheating may occur which will result
in burning. Another limitation of RFA is that it is not
MRI-compatible.
[0008] The limitations of the prior art are overcome by the present
invention as described below.
BRIEF SUMMARY OF THE INVENTION
[0009] The present invention is an alternative to Laser
Interstitial Thermal Therapy (LLIT) and RFA, which is used to
destroy tumors or lesions through the absorption of radiation by
tissue. However, as discussed above, in the LLIT and RFA processes,
the temperature cannot be predicted or easily controlled due to the
varying light and RF energy absorption properties of different
types of tissue. In addition, RFA will interfere with implants
(such as pacemakers) and the patient with such implants cannot be
treated with RFA.
[0010] The present invention also destroys tumors thermally, but
the heat is generated directly by heat, such as by electrical
resistance heating, conducted to the tissue rather than through the
absorption of non-ionized radiation by the tissue. A process of the
present invention may involve digital imaging (x-ray, ultrasound)
and/or computerized scanning (CAT, CT, PET, or MRI) to
mathematically determine the location and shape of the tumor. The
information derived from the scan allows a stereotactic frame or
other technique such as ultrasound to be used to position a probe
within the tumor.
[0011] In one embodiment, the probe comprises a thermally
conductive tip containing an electrical resistance heating element.
The thermally conductive tip is mounted on the end of a fiber which
is separated from the tip by a heat sink to avoid thermal
conduction down the fiber. The fiber contains the electrical power
leads and other electrical leads connecting to monitoring devices
associated with the tip. The tip is coated with a thin
biocompatible coating, such as diamond-like coating, ceramic,
polymers and the like, to avoid coagulated tissue sticking to the
tip.
[0012] The area of tissue treated by the tip is determined by the
addition of one or more thin, thermal conductive elements, which
may be formed of shape memory material, such as nitinol. The shape
memory elements are desirably in the form of thin wires or pins
which are folded against the tip at lower temperatures and which
deploy at selected higher temperatures. The shape memory elements
may be deployed in multiple stages at succesively higher
temperatures so that succesive layers of the tumor are exposed to
specific temperatures during treatment. Coagulating the tumor in
successive layers is desirable to avoid hemoraging. By selecting
the number, size and placement of the shape memory elements, tumors
of varying sizes and shapes may be treated in a predictable,
controllable fashion.
[0013] In order to control the process, the tip may also be
provided with a miniature thermocouple or the like to provide
temperature feedback information to control the temperature of the
tip. Through knowledge of the shape and location of the tumor
obtained from computerized imaging, the design of the tip and
thermal conductive elements, and the temperature feedback
information, information can be presented to the operator showing
the specific progress of the treatment of a tumor and allowing
predictable control of the process.
[0014] In alternative embodiments, deployable pivoted razorblades
rather than thin wires are employed to conduct the thermal energy
to the tumor. The razorblades are deployed mechanically rather than
being deployed due to temperature dependent shape memory effects.
In one embodiment, a linear actuator, comprising a threaded shaft
operated by a motor, deploys the razorblade thermal conductive
elements. In another embodiment, a nitinol spring is heated so as
to extend and deploy the razorblade elements.
[0015] In some embodiments, a pyrolytic graphite element may be
used to provide the heat source. Pyrolytic graphite has unique
thermal properties in that it acts as a resistor axially but is
conductive radially.
[0016] In a further embodiment, the deployable razorblades are
deployed mechanically by a spring-biased copper conductor that
serves a dual function--as a plunger to push deploying arms on the
razorblades and also as a conductor for the power supply for the
pyrolytic graphite heater element. The plunger is housed in a shaft
which is coated with an electrically conductive material, for
example, gold, to act as the power return or ground so as to
complete the electrical circuit supplying power to the
heater-element. When the plunger moves forwardly to push the arms
on the razorblades, it may also extend a needle which helps to hold
the probe in place when the razorblades deploy.
[0017] The deployable razorblades may be deployed in stages to
treat the tumor layer by layer. The deployment may be triggered at
specified temperatures as measured by temperature feedback elements
in the probe tip.
[0018] The present invention uses thermal conduction, as opposed to
radiation absorption, to heat the tumor/lesion volume. Since the
thermal properties of tissue are relatively homogenous, the results
can be predicted. The shape of the probe tip in the form of the
deployable thermal conductive elements may be altered during
treatment. The combination of shape and activation temperature can
be predetermined for any specific tumor/lesion geometry. This
offers the following advantages: highly predictable temperature
distribution; larger areas can be effectively treated, in a
controlled manner, since the heat is dissipated primarily by
conduction; localized carbonization will not result in tunneling
and the process is safer than LLIT or RFA; the maximum temperature
in the treatment zone will never exceed the temperature at the tip
of the probe, and therefore, one can easily control the maximum
temperature within the tumor/lesion and adjacent tissues; and
temperature may be actively controlled via closed loop feedback
system, where the maximum temperatures are measured during the
process by placing miniature thermocouples at the end of the
thermal probe.
[0019] In an alternative embodiment, the tip is provided with a
plurality of deployable elements whose temperatures are
individually controllable to provide heat to the elements and
surrounding tissue. This allows the shape of the thermal field to
be controlled and for specific areas to be protected from excessive
heat by cooling those specific areas while ablating other areas.
Treatment areas can be targeted more effectively and particularly
sensitive areas can be protected from ablation. Thus, it is
possible to ablate targeted areas of tissue near the chest wall, in
the head and neck, liver, pancreas and other regions where portions
of the tissue require ablation, but nearby portions must be
protected from ablation to avoid life threatening injury. The
deployable elements may be heated or cooled by any of various
techniques known to those skilled in the art. For example, heat may
be supplied from a miniature resistance heating coil in each
deployable element. Cooling may be accomplished by Peltier effect
devices. Heating and/or cooling may be applied by introducing
heated or chilled fluid, either liquid such as water or gas such as
argon, to a hollow space within the deployable thermal conductive
elements.
[0020] The temperature of the thermal conductive elements may be
monitored by thermal sensors at the ends of the elements. The
thermal sensors may be miniature thermocouples located within the
end of each element. The temperatures may be monitored and
controlled by a data processing device, such as a
microprocessor.
[0021] In a further alternative embodiment, the tip is provided
with a plurality of deployable elements that are individually
deployable to various shapes. The deployable elements remain
retracted in the tip during insertion into the tissue to be
treated. The tip may be heated by joule heating using a miniature
heating coil and/or the individual elements may be separately
heated. Each element is individually connected to means for
deploying the elements. The deploying means may a direct mechanical
connection from the elements to an external mechanical control or
the deploying means may be associated with each individual
deployable element. Other techniques to deploy the elements to a
specified length would be known to those skilled in the art. These
technique could include electromechanical or pneumatic means. Other
techniques could include the application of temperature to induce a
shape change in bimetallic elements. Over- or under-treatment of
the tissue may be avoided by deploying the deployable elements to
individually predetermined lengths to generate a thermal field that
approximates the shape of the spatial volume of the tissue to be
treated.
[0022] Each deployable element may include its individual
temperature and/or shape controller in an associated modular
package. The tip may be connected by a hollow fiber to external
control devices, such as a microprocessor, mechanical actuator,
heating and/or cooling fluid supply, thermal additive supply, and
electrical power. Each modular package may be connected via control
lines through the hollow fiber to the respective external control
devices.
[0023] Any number of deployable elements could be used depending
upon the application. Although the present invention is not limited
thereto, it has been found that eight (8) deployable elements allow
the creation of a thermal field that can conform to various shapes
of tissues to be treated, for example, spherical, ellipsoidal or
oblong. Various sizes and shapes of the tip and the deployable
elements may be used to fit various shapes of tissue to be treated.
The tip, the deployable elements and the associated temperature
and/or shape controllers may be replaceable and disposable.
[0024] Further selectivity in defining the area of tissue to be
treated may be achieved by introducing into the tissue thermal
additives that alter the thermal properties, such as thermal
diffusivity, specific heat capacity, density or thermal
conductivity, of the tissue. Such additives are known to those
skilled in the art and may include carbon particles (from 1 nm to
5000 .mu.m) and metal particles including gold nano-particles.
Various chemicals are known in the art that bind selectively to
tumor cells or that otherwise accumulate in tumors and that can
alter the thermal properties of the tumor. It is also known that
glucose will increase the thermal conductivity of a tumor into
which it is introduced.
[0025] The thermal additives may be introduced into the tissue to
be treated by various means, for example, by intralesional
injection or by intravenous injection. Further, the deployable
elements may be employed to spray such additives onto the tissue
during or before treatment. A hollow duct in the deployable element
may be connected through control lines in the hollow fiber to a
source of the additive. The additive is than sprayed from one or
more ports opening into the hollow duct.
[0026] These and other features, objects and advantages of the
present invention will become better understood from a
consideration of the following detailed description of the
preferred embodiments and appended claims in conjunction with the
drawings as described following.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0027] FIGS. 1A, 1B and 2 are views of an embodiment of the present
invention in which the deployable thermal conductive elements are
shape memory wires. FIG. 1A is a perspective view showing the first
stage deployment of the shape memory wires. FIG. 1B shows the
second stage deployed. FIG. 2 is a sectional view of the device of
FIGS. 1A and 1B along the lines 2-2 of FIGS. 1A and 1B with the
shape memory wires in the non-deployed configuration.
[0028] FIGS. 3-5 are views of an alternative embodiment of the
present invention in which the deployable thermal conductive
elements are pivoted razorblades deployed by a linear actuator.
FIG. 3 is a perspective view of the present invention in which the
pivoted razorblades are shown by broken lines in the deployed
configuration. FIG. 4 is a sectional view along the line 3-3 of
FIG. 3. FIG. 5 is a sectional view along the line 5-5 of FIG.
3.
[0029] FIG. 6 is a sectional view of a further alternative
embodiment of the present invention in which the deployable thermal
conductive elements are pivoted razorblades deployed by a nitinol
muscle wire.
[0030] FIG. 7 is a sectional view of a further alternative
embodiment of the present invention in which the deployable thermal
conductive elements are pivoted razorblades deployed by a plunger.
The activation of the plunger also deploys a needle through the
forward end of the tip.
[0031] FIG. 8 is a block diagram of a method of the present
invention.
[0032] FIGS. 9 and 10 are views of an embodiment of the present
invention in which the deployable thermal conductive elements are
shape memory wires in the form of coils. FIG. 9 is a perspective
view showing the deployment of the shape memory wires. FIG. 10 is a
sectional view of the device of FIG. 9 along the lines 10-10 with
the shape memory wires in the non-deployed configuration.
[0033] FIGS. 11A and 11B are sectional views of an alternative
embodiment of the embodiment of FIG. 7 wherein the deployed
razorblades are spring biased to aid in retraction of the
razorblades from the deployed position. FIG. 11A is an embodiment
in which the biasing spring is located to the proximal side of the
probe and FIG. 11B is an embodiment in which the biasing spring is
located to the distal side of the probe.
[0034] FIG. 12 is a schematic view of an embodiment of the
invention in which the tip of the device is a metal tip heated by a
remote laser through a waveguide.
[0035] FIG. 13 is a schematic diagram of a cross section of an
embodiment of a probe, including a tip, a plurality of deployable
thermal conductive elements, and associated temperature and/or
length controllers.
[0036] FIG. 14 is a schematic diagram of an individual deployable
thermal conductive element and its associated temperature and/or
length controller with connections via control lines to external
controllers.
[0037] FIGS. 15A and 15B illustrate a thermal field generate by a
probe. FIG. 15A illustrates the situation where some of the thermal
conductive element are heated and some cooled. FIG. 15B illustrates
the effect on the thermal field of extending the thermal conductive
elements to various lengths.
[0038] FIG. 16 is a partial cross section of the end of a thermal
conductive element showing a miniature thermocouple in the end.
[0039] FIG. 17 is a partial cross section of the end of a thermal
conductive element showing a hollow duct and ports for spraying
thermal additives.
DETAILED DESCRIPTION OF THE INVENTION
[0040] With reference to FIGS. 1A-12, the preferred embodiments of
the present invention may be described as follows.
[0041] The present invention is a miniature thermal apparatus for
the controlled destruction of malignant and benign tumors/lesions
and abnormal or excess tissue. As used herein, the terms tumors and
lesions may be used interchangeably to indicate tissue to be
thermally treated by the device and method of the present
invention. The present invention comprises a tip 10 mounted onto a
fiber 11 that can be inserted through a catheter that has been
accurately placed within the tumor/lesion. The tumor/lesion is
destroyed via heat generation originating from the specifically
designed tip 10 that matches the tumor/lesion geometry. The tip 10
comprises a plurality of deployable thermal conductive elements
that may be customized by the number, size and arrangement to be
deployable into a geometry that matches the geometry of the
tumor/lesion to be thermally treated. The temperature distribution
around the tip 10, within the tumor/lesion and in the adjacent
tissue may be predicted by mathematical models of the heat transfer
equations. Software may be employed in conjunction with the
mathematical models of the heat transfer to provide (1) process
monitoring and control, (2) custom probe design, and (3) process
simulation. Additionally, using this predictive ability, the
process may be monitored and controlled with a closed loop feedback
system utilizing sensors in the tip 10. The geometry of the tip 10
may be changed as a function of temperature to increase the volume
of irreversibly damaged tissue in the tumor/lesion.
[0042] As shown in FIG. 8, a process of the present invention
involves the step of computerized scanning (CAT, CT, PET, or MRI)
to mathematically determine the location and shape of the tumor 20.
The information derived from the scan allows the geometry of the
tip to be customized to treat the specific shape of the tumor 21
and also allows a stereotactic frame to be used to position the
probe within the tumor 22. Ultrasound or the like may be also used
to position the probe. The probe is inserted into the tumor 23, and
the heating element is activated to a predetermined temperature to
treat the tumor 24. Alternatively, the temperature may be increased
in a stepwise fashion to treat the tumor in layers 25. Finally, the
probe is cooled and withdrawn from the treated tumor 26. As an
adjunct to the treatment process, the coagulation of the tumor may
be enhanced by the use of a drug effective in reducing bleeding
from vascular damage, such as NovoSeven (recombinant factor VIIa)
or other coagulant enhancement drug such as Aminocaproic acid
(Amicar). NovoSeven is used to stop bleeding in various surgical
procedures. The drug is delivered systemically but only works in
regions of the body in which vascular damage has taken place. In
the procedure of the present invention, the drug would be
administered approximately ten minutes prior to the procedure.
Thereafter, the apparatus of the present invention is introduced
into the tumor. Once the temperature of the tissue has increased to
the point that the endothelial cells in the blood vessels are
damaged, coagulation is initiated by NovoSeven in the areas of the
damaged vessels. The process aids in heat transfer and may aid in
the destruction of the tumor by nutrient deprivation. An ancillary
advantage to using NovoSeven is that it will decrease the risk of
bleeding along the track of the apparatus. The drug is metabolized
in about two hours.
[0043] The thermally conductive tip 10 contains an electrical
resistance heating element 13. The thermally conductive tip 10 is
mounted on the end of fiber 11 which is separated from the tip 10
by a heat sink 12 to avoid thermal conduction down the fiber 11.
The fiber 11 contains the electrical power leads 14 and may also
contain other electrical leads connecting to monitoring devices
associated with the tip 10. The tip 10 is coated with a thin
biocompatible coating 15 to avoid coagulated tissue sticking to the
tip 10. The thin biocompatible coating 15 may be diamond-like
coatings, ceramic, polymers and the like.
[0044] The area of tissue treated by the tip 10 can be adjusted by
the addition of one or more deployable, thermal conductive
elements. The deployable elements may be shape memory elements 16
made of shape memory materials, such as nitinol. The shape memory
elements 16 are desirably in the form of thin wires or pins which
are folded against the tip 10 at lower temperatures as shown in
FIG. 2 and which deploy at selected higher temperatures. The shape
memory elements 16 may be deployed in multiple stages at
succesively higher temperatures so that succesive layers of the
tumor are exposed to specific temperatures during treatment. For
example, a set of short shape memory elements 17 may be deployed at
a first temperature and a set of longer shape memory elements 18
may be deployed at a higher second temperature. Coagulating the
tumor in successive layers is desirable to avoid hemoraging. By
selecting the number, size and placement of the shape memory
elements 16, tumors of varying sizes and shapes may be treated in a
predictable, controllable fashion.
[0045] In order to control the process, the tip 10 may also be
provided with a miniature thermocouple to provide temperature
feedback information to control the temperature of the tip 10.
Through knowledge of the shape and location of the tumor obtained
from computerized imaging, the design of the tip 10 and shape
memory elements 16, and the temperature feedback information,
information can be presented to the operator showing the specific
progress of the treatment of a tumor and allowing predictable
control of the process.
[0046] As shown in FIGS. 9 and 10, an alternative design of shape
memory elements 30 employs shape memory material, such as nitinol,
in the form of coils which expand to a deployed configuration as
shown in FIG. 9 from a non-deployed configuration as shown in FIG.
10.
[0047] Alternative embodiments as shown in FIGS. 3-7 use deployable
pivoted razorblades 30 rather than thin shape memory wires as the
thermal conductive elements to conduct the thermal energy to the
tumor. Desirably, the pivoted razorblades 30 may be made of
biocompatible materials, such as composite materials including
aluminum silicon carbide, titanium boride and the like. The pivoted
razorblades 30 may be deployed mechanically rather than being
deployed by a nitinol shape memory wire element. In one embodiment
shown in FIG. 4, a linear actuator, comprising a threaded shaft 31
operated by a motor (not shown), deploys the razorblade 30. In
another embodiment shown in FIG. 6, a nitinol spring 32 is heated
so as to extend and deploy the razorblade elements 30. In both
embodiments, a pyrolytic graphite element 33 may be used to provide
the heat source. Pyrolytic graphite has unique thermal properties
in that it acts as a resistor axially but is conductive
radially.
[0048] In a further embodiment shown in FIG. 7, the deployable
razorblades 30 are deployed mechanically by a spring-biased copper
conductor that serves as a plunger 34 to push deploying arms 35 on
the razorblades 30. The plunger 34 also acts as a conductor for the
power supply for the pyrolytic graphite heater element 33. The
copper conductor is housed in a shaft 36 which is coated with an
electrically conductive material such as gold to act as the power
return or ground so as to complete the electrical circuit supplying
power to the heater element 33. When the copper conductor plunger
34 moves forwardly to push the arms 35 on the razorblades 30, it
may also extend a needle 36 which helps to hold the probe in place
when the razorblades 30 deploy.
[0049] FIGS. 11A and 11B are sectional views of an alternative
embodiment of the embodiment of FIG. 7 wherein the deployed
razorblades 30 are biased by spring 40, 42 to aid in retraction of
the razorblades 30 from the deployed position. FIG. 11A is an
embodiment in which biasing spring 40 is located to the proximal
side of tip 10. Spring 40 is fixed at one end in a bore 43 and at
the other end to deploying arm 35. As razorblade 30 is extended,
spring 40 also extends and exerts a force tending to retract
razorblade 30. FIG. 11B is an embodiment in which the biasing
spring 42 is located to the distal side of tip 10. Spring 42 bears
against pin 41 which in turn bears against deploying arm 35. As
razorblade 30 is deployed, spring 42 is compressed and thereby
exerts a force tending to retract razorblade 30. Biasing springs
40, 42 may also be used in the embodiments of FIGS. 4 and 6 as well
as FIG. 7.
[0050] The device may require increasing the minimum size of the
catheter since the tip 10 of the probe may be larger than a
standard laser tip.
[0051] This limitation is not serious, however. Although the size
of the thermal tip 10 is expected to be larger than a standard
laser tip, the maximum size could be limited to 1.6-5 mm in
diameter, which is still acceptable for interstitial procedures.
Also, as shown in FIG. 12, the size of the tip 10 could be reduced
to LITT size, by using a laser 50 as an energy source to heat up a
metal tip 10.
[0052] When using a laser 50 as an energy source, the laser 50 is
remotely located from the metal tip 10 and the laser radiation is
transmitted through a wave guide fiber 51 to the metal tip 10. The
metal tip 10 is desirably stainless steel. The metal tip 10 absorbs
the laser radiation and is heated thereby to a high temperature,
e.g., 150.degree. C. The heat of the heated metal tip 10 is
dissipated to the surrounding tissue through conduction, thereby
causing blood coagulation and tissue necrosis around the metal tip
10 in a well defined region. In order to limit the heat flow from
the metal tip 10 to the wave guide fiber 51, a heat conductive
barrier 52 in the form of insulation or a heat sink may be placed
between the metal tip 10 and the wave guide fiber 51. Further, the
wave guide fiber 51 may have an insulating jacket 53. The wave
guide fiber 51 may also be cooled by cool air flowing through the
wave guide fiber 51. A portion of the wave guide fiber 51 adjacent
to the metal tip 10 may be in the form of a tube 54 through which
the cool air flows. The tube 54 may be formed from a metal, such as
copper, a composite material or a ceramic material.
[0053] The laser 50 is desirably a CO.sub.2 laser. Although there
is low absorption (around 9%) of CO.sub.2 laser radiation by
stainless steel, the amount of energy required to heat stainless
steel is low due to the low heat capacity of stainless steel (0.46
Jgr.sup.-1C.sup.-1) compared to blood (3.6 Jgr.sup.-1C.sup.-1).
Therefore, a stainless steel metal tip 10 of 1 gram could be heated
to high temperatures of up to 300-500.degree. C. by a 50 Watt
CO.sub.2 laser.
[0054] To avoid tissue sticking, the metal tip 10 is desirably
coated with a thin layer, e.g., 5 .mu.m, of biocompatible ceramic,
such as alumina or titanium nitride, or a biocompatible polymer,
such as Teflon.RTM.. A ceramic coating may be applied by physical
vapor deposition, a standard process in the industry.
[0055] Since the heat of the metal tip 10 is dissipated by
conduction, the temperature profile can be calculated using known
finite difference or finite element methods. Since the thermal
properties of all human tissues are similar, accurate temperatures
predictions are possible. Since the critical temperatures are not a
strong function of time, the irreversible thermal damage of tissues
can be controlled through the heating time. To limit necrosis of
tissues to a well defined region, the size of the metal tip 10 can
be minimized. Deployable thermally conductive elements, as
described heretofore, may be added to the metal tip 10 to determine
the shape of the thermally treated tissue. Such deployable thermal
elements may be deployed in stages.
[0056] With reference to FIGS. 13-17, an alternative embodiment of
the present invention is described. In this alternative embodiment,
the tip 60 is provided with a plurality of deployable elements 61
with temperature providing means for providing for providing an
individually controllable temperature to said each deployable
element and its surrounding tissue. This allows the shape of the
thermal field 66 to be controlled and for specific areas to be
protected from excessive heat by cooling those specific areas while
ablating other areas. For example, as shown in FIG. 15A, elements
61 are heated and element 80 is cooled, producing the thermal field
66. Treatment areas can be targeted more effectively and
particularly sensitive areas can be protected from ablation. Thus,
it is possible to ablate targeted areas of tissue near the chest
wall, in the head and neck, liver, pancreas and other regions where
portions of the tissue require ablation, but nearby portions must
be protected from ablation to avoid life threatening injury. The
deployable elements may be heated or cooled by any of various
techniques known to those skilled in the art. For example, heat may
be supplied from a miniature resistance heating coil in each
deployable element. Cooling or heating may be supplied the action
of an electromagnetic field, such as Peltier effect devices.
Heating and/or cooling may be applied by introducing heated or
chilled fluid, either liquid such as water or gas such as argon, to
a hollow space (not shown) within the deployable elements 61.
Fluids, solids, gases or mixtures of the same at temperatures below
the maximum temperature of the probe may be used to cool the
deployable elements 61 and their surroundings. Cooling may also be
provided by the interaction of an electromagnetic field with a gas,
liquid, solid or a mixture of any of the preceding. Other cooling
means could include the use of chemical or biological endothermic
reactions induced by mixing one or more solids and/or one or-more
liquids. In addition, a separate cooled probe may be provided such
that its temperature in combination with selected temperatures for
each deployable element provide the desired thermal field. All
means for cooling the deployable elements 61 are encompassed herein
by the term "heat sink." The thermal treatment of the tissue may
occur by the thermal conduction of heat from the individual
elements or may be from high temperature solids, liquids, gases or
mixtures of the preceding injected from the deployable elements or
the tip into the target tissue. Injection may be accomplished as
described below with respect to the injection of additives to alter
the thermal properties of the tissue.
[0057] The temperature of the deployable elements 61 may be
monitored by thermal sensors at the ends of the elements. The
thermal sensors may be miniature thermocouples 62 located within
the end of each element 61. The temperatures may be monitored and
controlled by a data processing device, such as a microprocessor
63.
[0058] In a further alternative embodiment, the tip 60 is provided
with a plurality of deployable elements 61 that are individually
deployable to various shapes. The deployable elements remain
retracted in the tip during insertion into the tissue to be
treated. The tip 60 may be heated by joule heating using a
miniature heating coil and/or the individual elements may be heated
separately. Each element 61 is individually connected to means for
deploying the elements. The deploying means may a direct mechanical
connection from the thermal conductive elements 61 to an external
mechanical control 64 or the deploying means may be associated with
each individual deployable element 61 as described below. Other
techniques to deploy the elements 61 to a specified shape would be
known to those skilled in the art. These techniques could include
electromechanical or pneumatic means. Other techniques could
include the application of temperature to induce a shape change in
bimetallic elements. Over- or under-treatment of the tissue may be
avoided by deploying the deployable conductive elements 61 to
individually controllable shapes to generate a thermal field 70
that approximates the shape of the spatial volume of the tissue to
treated. As shown in the example of FIG. 15B, the thermal field 70
is generated by elements 61 having the same extended shape and
element 81 having a shorter extended shape. The deployable elements
themselves may comprise sub-elements or materials that deploy to
form various shapes.
[0059] Each deployable element 61 may include its individual
temperature and/or shape controller in a modular package 65. The
tip 60 may be connected by a hollow fiber 66 to external control
devices, such as a microprocessor 63, mechanical actuator 64,
heating and/or cooling fluid supply 67, thermal additive supply 68,
and electrical power 69. Each modular package 65 may be connected
via control lines 71 through the hollow fiber 66 to the respective
external control devices 63, 64, 67, 68, 69.
[0060] Any number of deployable elements 61 could be used depending
upon the application. Although the present invention is not limited
thereto, it has been found that eight (8) deployable elements 61
allow the creation of thermal fields 66, 70 that can conform to
various shapes of tissue to be treated, for example, spherical,
ellipsoidal or oblong. Various sizes and shapes of the tip 60 and
the deployable elements 61 as described herein may be used to fit
various shapes of tissue to be treated. The tip 60 and the
deployable elements 61 may be replaceable and disposable.
[0061] Further selectivity in defining the area of tissue to be
treated may be achieved by introducing into the tissue thermal
additives that alter the thermal properties, such as thermal
diffusivity, specific heat capacity, density or thermal
conductivity, of the tissue. Such additives are known to those
skilled in the art and may include carbon particles (1 nm to 5000
.mu.m) and metal particles including gold nano-particles. Various
chemicals are known in the art that bind selectively to tumor cells
or that otherwise accumulate in tumors and that can alter the
thermal properties of the tumor. It is also known that glucose will
increase the thermal conductivity of a tumor into which it is
introduced. Any particles, solutions containing particles, metals,
ceramics, composites, polymers, organic and inorganic chemicals,
solids, liquids, gases and mixtures of the preceding that alter the
thermal properties of the tissue (either normal or abnormal tissue)
are considered to be additives as encompassed within the scope of
the present invention.
[0062] The thermal additives may be introduced to the tissue to be
treated by various means, for example, by intralesional injection
or by intravenous injection. More generally, the present invention
encompasses the introduction of additives by an external
applicator. The thermal additives may also be introduced
systemically to change or affect the properties of the target
tissue and boundary in order to make the target tissue more
susceptible to thermal treatment. Further, the deployable elements
may be employed to spray such additives onto the tissue during or
before treatment. A hollow duct 72 in the deployable element 61 may
be connected through control lines 71 in the hollow fiber 66 to a
source of the additive 68. The additive is than sprayed from one or
more ports 73 opening into the hollow duct 72.
[0063] The present invention has been described with reference to
certain preferred and alternative embodiments that are intended to
be exemplary only and not limiting to the full scope of the present
invention as set forth in the appended claims.
* * * * *