U.S. patent number 5,855,576 [Application Number 08/766,154] was granted by the patent office on 1999-01-05 for method for volumetric tissue ablation.
This patent grant is currently assigned to Board of Regents of University of Nebraska. Invention is credited to Randy Fox, Robert F. LeVeen.
United States Patent |
5,855,576 |
LeVeen , et al. |
January 5, 1999 |
Method for volumetric tissue ablation
Abstract
A volumetric tissue ablation apparatus includes a probe having a
plurality of wires journaled through a catheter with a proximal end
connected to the active terminal of a generator and a distal end
projecting from a distal end of the catheter. The probe wire distal
ends are arranged in an array with the distal ends located
generally radially and uniformly spaced apart from the catheter
distal end. A conductor connected to the return terminal of the
generator is located relative to the probe wire array to form a
closed electrical circuit through tissue to be ablated. Preferably,
the probe wire array includes 10 wires, each formed in an arch from
the catheter distal end. The conductor can be either a conventional
ground plate upon which the tissue is supported, or a conductor
wire extending through the probe and electrically insulated from
the probe wires.
Inventors: |
LeVeen; Robert F. (Omaha,
NE), Fox; Randy (Omaha, NE) |
Assignee: |
Board of Regents of University of
Nebraska (Omaha, NE)
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Family
ID: |
23624311 |
Appl.
No.: |
08/766,154 |
Filed: |
December 12, 1996 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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410344 |
Mar 24, 1995 |
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Current U.S.
Class: |
606/41; 606/49;
607/116; 606/50; 607/113; 607/99 |
Current CPC
Class: |
A61N
5/045 (20130101); A61B 18/18 (20130101); A61B
18/1492 (20130101); A61B 18/1477 (20130101); A61B
18/1485 (20130101); A61B 2018/1432 (20130101); A61B
2018/143 (20130101); A61B 18/1402 (20130101); A61B
2018/1425 (20130101); A61B 2018/1475 (20130101); A61B
2018/00214 (20130101) |
Current International
Class: |
A61N
5/02 (20060101); A61N 5/04 (20060101); A61B
18/18 (20060101); A61B 18/14 (20060101); A61B
017/39 () |
Field of
Search: |
;606/41,49,50
;607/98,99,113,116,128 |
References Cited
[Referenced By]
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89 09 492 |
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41 00 422 |
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Jul 1992 |
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DE |
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63-275632 |
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JP |
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US91/08388 |
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WO 93/08757 |
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WO 93/24066 |
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WO |
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WO |
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Feb 1996 |
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WO |
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Other References
Journal of Vascular and Interventional Radiology, "Hepatic Ablation
with Use of Radio-Frequnecy Electrocautery in the Aminal Model",
vol. 3, No. 2, May, 1992..
|
Primary Examiner: Cohen; Lee
Parent Case Text
This is a continuation of application Ser. No. 08/410,344 filed on
Mar. 24, 1995.
Claims
We claim:
1. A method for creating a lesion within tissue, comprising the
steps of:
connecting proximal ends of a plurality of electrically conductive
wires having distal ends to an electrical generator active
terminal;
connecting a proximal end of a conductor to a return terminal on
the generator;
piercing a body of tissue with the distal ends of the plurality of
at least three wires to form the distal ends into an array in a
predetermined location in the tissue, wherein the wires define a
three-dimensional ablation volume surrounding a tissue mass
therebetween;
contacting a distal end of the conductor with the body of tissue to
form a closed electrical circuit through the tissue; and
operating the generator to create a lesion of predetermined size
and shape within the tissue mass at the location of the array.
2. The method of claim 1, further comprising the step of locating
the array at a predetermined location by viewing the array via
ultrasound imaging apparatus.
3. A method for treating a treatment region within solid tissue of
a patient with radio frequency current, said method comprising:
introducing at least three electrodes through tissue to a site
proximate a treatment region;
advancing said at least three electrodes from the site into the
solid tissue proximate the treatment region, wherein the at least
three electrodes define a three-dimensional ablation volume
surrounding a tissue mass therebetween; and
establishing radio frequency current flow among the at least three
electrodes or between said three electrodes and another electrode
to treat the tissue mass.
4. A method as in claim 3, wherein the introducing step comprises
penetrating a sheath-obturator assembly to the site, removing the
obturator from the sheath, and passing the at least three
electrodes through a lumen of the sheath.
5. A method as in claim 4, wherein the at least three electrodes
are disposed in a tube having a central lumen when passed through
the sheath lumen, and wherein the advancing step comprises
advancing said at least three electrodes from the lumen of the tube
into tissue disposed distally of the distal ends.
6. A method as in claim 3, wherein the introducing step comprises
penetrating an elongate member through solid tissue to the
treatment region and wherein the advancing step comprises extending
the electrodes from the elongate member.
7. A method as in claim 3, wherein the advancing step comprises
introducing an elongate member having a distal tip to the site and
extending the at least three electrodes in a diverging pattern from
the distal tip of the elongate member, wherein said at least three
electrodes are disposed symmetrically about an axis extending from
the site into the treatment region.
8. A method as in claim 7, wherein the establishing step comprises
applying a radio frequency potential between said at least three
electrodes and a common electrode disposed on the elongate
member.
9. A method as in claim 3, wherein the establishing step comprises
applying a radio frequency potential between said at least three
electrodes and a common dispersive plate located externally on the
patient.
10. A method as in claim 3, wherein the establishing step comprises
applying a radio frequency potential between said at least three
electrodes.
11. A method for treating a treatment region within solid tissue of
a patient with radio frequency current, said method comprising:
advancing at least three electrodes into the solid tissue from a
site adjacent the treatment region, wherein the electrodes assume a
three-dimensional pattern in the treatment region, wherein the
distal tips of the electrodes are aligned generally in parallel to
each other to define a three-dimensional treatment volume
therebetween; and
establishing radio frequency current flow among the at least three
electrodes or between said at least three electrodes and a common
electrode.
12. A method as in claim 11, wherein the advancing step comprises
positioning the at least three electrodes symmetrically about an
axis extending from the site into the tissue.
13. A method as in claim 12, wherein the at least three electrodes
are evenly spaced from each other as they are advanced.
14. A method as in claim 11, wherein the establishing step
comprises applying a radio frequency potential between said at
least three electrodes and a common dispersion plate located
externally on the patient.
15. A method as in claim 11, wherein the establishing step
comprises applying a radio frequency potential between said at
least three electrodes and a common electrode.
16. A method as in claim 11, wherein the establishing step
comprises applying a radio frequency potential between said at
least three electrodes.
17. A method as in claim 11, further comprising introducing an
elongate member having a distal end through solid tissue to the
target site, wherein the electrodes are carried to the target site
by the elongate member.
18. A method as in claim 17, wherein the introducing step comprises
penetrating a sheath-obturator assembly to the target site,
removing the obturator from the sheath, and passing the at least
three electrodes through a lumen of the sheath.
19. A method as in claim 17, wherein the at least three electrodes
are disposed in a tube having a central lumen, wherein the
advancing step comprises advancing said at least three electrodes
from the lumen of the tube into tissue disposed distally of the
distal end of the elongate member.
20. A method as in claim 17, wherein the introducing step comprises
penetrating the distal end of the elongate member through solid
tissue to the target site within the treatment region and wherein
the advancing step comprises extending the electrodes from the
elongate member after said member has penetrated to the target
site.
Description
TECHNICAL FIELD
The present invention relates generally to radio frequency
electrodes for tissue ablation, and more particularly to an
improved RF electrode having a spreading array of wires to ablate
large volumes of tissue.
BACKGROUND OF THE INVENTION
The liver is a common repository for metastasis from many cancers,
including those of the stomach, bowel, pancreas, kidney, and lung.
In colorectal cancer the liver is the initial site of spread in
more than one-third of patients, and is involved in more than
two-thirds at the time of death. While patients with untreated
colorectal metastasis to the liver have no five year survival,
patients undergoing surgical resection have approximately a 25-30%
five year survival. Unfortunately, only a limited number of
patients are candidates for surgical resection.
Cryosurgery is also used for the treatment of hepatic metastasis.
Cryosurgery, which relies on a freeze-thaw process to
nonselectively kill cells, has been found equally effective as
surgical resection but is more tissue sparing. While an improvement
over open surgical tissue resection, cryosurgery still suffers from
disadvantages. It is an open surgical procedure, requires placement
of up to five relatively large probes, and can only be applied to a
limited number of lesions. While percutaneous probes are being
developed, they are currently capable only of treatment of smaller
lesions. Typical lesions common to colorectal metastasis, however,
are relatively large. Therefore, the outlook for percutaneous
cryotherapy is guarded.
A number of investigators have used radio frequency hyperthermia
with placement of external electrodes, for the treatment of liver
cancers. Tumor cells are known to be more sensitive to heat than
normal cells, and externally applied regional hyperthermia
delivered with radio frequency tends to ablate the tumor while
sparing the normal tissue of significant damage. While this therapy
improves the response to systemic chemotherapy, it has uncertain
benefit for long-term survival. One limitation of hyperthermia is
that it is difficult to heat the tumors to a lethally high
temperature. Moreover, tumor cells tend to become thermoresistant
if they survive early treatments.
Percutaneous laser hyperthermia has also been used for primary and
metastatic liver cancer. Laser fibers are introduced through
needles, under ultrasound guidance. The lesions generated by laser
are represented by hyperechoic foci on the real time ultrasound
images, which can be used to monitor the size of the lesion. Low
energy single fiber systems, which do not require a cooling system
along the fiber, can generate areas of necrosis limited to
approximately 15 mm diameter. Such small diameters are insufficient
for the vast majority of lesions encountered clinically thus
requiring multiple fiber placement and prolonged procedure
times.
Radio frequency (RF) hyperthermia, using a standard electrosurgical
generator and a fine needle partially sheathed in plastic, has also
been proposed for the treatment of liver and other solid tumors. In
one system, the apparatus was capable of generating lesions of
approximately 1.times.2 cm in a pig liver. In order to produce
larger treatment volumes with a single needle, high currents and
temperatures have been employed, but produce charred and carbonized
tissue, without enlarging the tissue volume being treated. To treat
a larger lesion, multiple needle passes in different locations
would be needed. In preliminary testing, this system established a
75% survival at 40 months.
It can therefore be seen that the treatment of primary and
metastatic liver tumors and other solid tumors elsewhere in the
body, remains problematic. Surgery is effective, but only a small
percentage of affected patients are candidates. Cryotherapy has had
improved results, but its applicable patient population is
essentially the same as that for surgery. The percutaneous methods
have the virtue of being less invasive, so they can be
appropriately used for a larger spectrum of patients, but current
percutaneous methods all suffer from a limited ability to ablate a
large volume of tissue in a single procedure with a single probe
passage.
SUMMARY OF THE INVENTION
It is therefore a general object of the present invention to
provide an improved electrosurgical method and probe deployable in
a percutaneous procedure that will produce a large volume of
thermally ablated tissue with a single deployment.
It is a further object that such methods and probes should be
useful in open surgical as well as percutaneous procedures.
Another object is to provide an electrosurgical probe which will
provide uniformly treated tissue within a large volumetric
lesion.
Still another object of the present invention is to provide a
percutaneous electrosurgical probe which requires only a small
access hole but provides for large volumetric tissue ablation.
Still another object is to provide an electrosurgical probe which
avoids the problems of charring and carbonization common with
single needle probes.
These and other objects will be apparent to those skilled in the
art.
The present invention provides both methods and apparatus for the
radio frequency (RF) treatment of a specific region within solid
tissue, referred to hereinafter as a "treatment region". The
methods and apparatus rely on introducing at least two electrodes,
and usually at least three electrodes to a target site within the
treatment region. After reaching the target site, the plurality of
electrodes are deployed within the solid tissue, usually in a
three-dimensional array and preferably in a configuration which
conforms to or encompasses the entire volume of the treatment
region, or as large a portion of the volume of the treatment region
as possible. More preferably, the adjacent electrodes are evenly
spaced-apart from each other (i.e., pairs of adjacent electrodes
will be spaced-apart in repeating pattern) so that application of
RF current through the electrodes will result in generally uniform
heating and necrosis of the entire tissue volume being treated.
Advantageously, the use of multiple electrodes to treat a
relatively large tissue volume allows the RF energy to be applied
with a lower current density (i.e., from a larger total electrode
area) and therefore at a lower temperature in the tissue
immediately surrounding the electrode. Thus, charring and
carbonization of tissue (which has heretofore been associated with
the use of single electrode systems) is reduced. The uniform
treatment of a large volume of tissue reduces the number of
electrode deployments which are necessary for treating a tissue
region of any given size.
In a first particular aspect, the method of the present invention
comprises introducing at least two electrodes through solid tissue
to a target site within a treatment region. The at least two
electrodes are maintained in a radially constrained or collapsed
configuration as they are advanced through the tissue to the target
site and are then deployed from the target site further into the
treatment region in a desired divergent pattern. RF current flow is
then established between the at least two electrodes (i.e.,
bipolar) or among at least the two electrodes and a separate return
electrode (i.e. monopolar). The monopolar return electrode will
have a surface area which is sufficiently large to dissipate any
electrosurgical effect. The at least two electrodes may be deployed
by a variety of specific techniques. For example, a sheath may be
initially placed using an obturator or stylet to the target site in
a conventional manner. After removing the obturator or stylet, the
electrodes can be introduced through the sheath and advanced from
the distal end of the sheath into the solid tissue. Optionally, the
electrodes may be disposed in or on an elongate member, such as a
tube which reciprocatably receives the electrodes. The electrodes
may then be advanced from the tube, or alternatively the tube may
be withdrawn proximally from over the electrodes prior to
advancement of the electrodes from the sheath into the tissue.
In a second specific aspect, the method of the present invention
comprises advancing at least three electrodes from a target site
within the treatment region. The electrodes diverge in a
three-dimensional pattern, preferably with individual electrodes
being evenly spaced-apart to provide for uniform volumetric
treatment, as discussed above. Treatment is then performed by
passing RF current among the at least three electrodes or between
said three electrodes and a return electrode. Preferably, the
method will employ more than three electrodes, often deploying at
least five electrodes, preferably employing at least six
electrodes, frequently employing at least eight electrodes, and
often employing at least ten electrodes or more. It will be
appreciated that a larger number of individual electrodes can
enhance the uniformity of treatment while limiting the amount of
power (current density) emitted from any single electrode, thus
reducing the temperature in the immediate region of the
electrode(s). Optionally, the at least three electrodes may be
everted, i.e. turned first in a radially outward direction and then
in a generally proximal direction, as they are advanced from the
target site. The use of such multiple, everted electrodes provides
a preferred array for treating relatively large tissue volumes. In
particular, arrays of everted electrodes will provide current and
heating in generally spherical volumes which will more closely
match the spherical or ellipsoidal geometries of the typical tumor
or other lesion to be treated. In contrast non-everted electrode
arrays will often effect a conical or irregular treatment volume
which may have less widespread applicability.
In a first aspect of the apparatus of the present invention, a
probe system comprises an elongate member having a proximal end and
a distal end. At least two solid-tissue-penetrating electrode
elements are reciprocatably disposed on or in the elongate member
so that they may be advanced into tissue after the elongate member
has been introduced through solid tissue to a target site in or
near the treatment region. A means for introducing the elongate
member through tissue to the target site is also provided. The
means may take a variety of forms, including a sheath and obturator
(stylet) assembly which may be used to provide the initial
penetration. Alternatively, a self-penetrating element may be
provided directly on the elongate member. Other conventional
devices and techniques of the type used for introducing shafts and
other elongate members to solid tissue may also be employed.
The tissue-penetrating electrode elements may comprise wires which
are received within an axial lumen of the elongate member. For
example, the wires may be bundled together over a proximal portion
thereof, but remain separate and shaped over their distal portion
so that they diverge in a selected pattern when advanced into
tissue. Usually, the wires will be advanced directly from the
elongate member (when the elongate member is left inside the sheath
or the sheath is withdrawn), but could alternatively be advanced
from the sheath when the elongate member is withdrawn proximally
from over the electrodes prior to penetration of the electrodes
into the tissue.
In a second aspect of the apparatus of the present invention, a
probe system comprises an elongate member having a proximal end and
a distal end, and at least three solid-tissue penetrating electrode
elements reciprocatably attached to the elongate member. The at
least three electrodes are configured to diverge in a
three-dimensional pattern as they are advanced in a distal
direction from the elongate member. Usually, the elongate member is
a tube having an axial lumen which reciprocatably receives the
tissue-penetrating electrode element, and the electrode elements
comprise individual wires which may be bundled as described above.
The distal ends of the wires or other electrode elements are
preferably shaped so that they will assume a radially constrained
configuration while present in the axial lumen of the tube and will
assume a radially divergent configuration when axially extended
from the tube. In a preferred configuration, the distal ends of at
least some of the wires are shaped so that they assume outwardly
everted configuration as they are axially extended from the tube or
other elongate member. The probe system may include one, two, or
more groups of at least three electrodes which are axially
spaced-apart from each other. In particular, such axially
spaced-apart groups of electrodes may extend from the distal end of
the elongate member or may be distributed along the elongate member
and individually extendable to assume the desired three-dimensional
configuration. Preferably, each group of tissue-penetrating wires
or other electrode elements will include more than three
electrodes, as described generally above.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view of the tissue ablation apparatus
of the present invention;
FIG. 2 is an end view of the apparatus of FIG. 1;
FIG. 3 is a sectional view through tissue, showing the prior art
affects of a single needle probe;
FIG. 4 is a sectional view through tissue showing the results of
the probe of the present invention;
FIG. 5 is a side perspective view of a second embodiment of the
probe of the present invention;
FIG. 6 is a side perspective view of a bipolar embodiment of the
invention;
FIG. 7 is a side perspective view of a second bipolar probe;
and
FIG. 8 is a side perspective view of a third bipolar probe.
FIGS. 9-14 illustrate use of an exemplary probe system according to
the present invention in RF treatment of a target region of solid
tissue.
GENERAL DESCRIPTION OF THE SYSTEM OF THE PRESENT INVENTION
Systems according to the present invention will be designed to
introduce a plurality of electrode elements to a treatment region
within patient solid tissue. The treatment region may be located
anywhere in the body where hypothermic exposure may be beneficial.
Most commonly, the treatment region will comprise a solid tumor
within an organ of the body, such as the liver, kidney, pancreas,
breast, prostate (not accessed via the urethra), and the like. The
volume to be treated will depend on the size of the tumor or other
lesion, typically having a total volume from 1 cm.sup.3 to 150
cm.sup.3, usually from 1 cm.sup.3 to 50 cm.sup.3, and often from 2
cm.sup.2 to 35 cm.sup.2. The peripheral dimensions of the treatment
region may be regular, e.g. spherical or ellipsoidal, but will more
usually be irregular. The treatment region may be identified using
conventional imaging techniques capable of elucidating a target
tissue, e.g. tumor tissue, such as ultrasonic scanning, magnetic
resonance imaging (MRI), computer-assisted tomography (CAT),
fluoroscopy, nuclear scanning (using radiolabeled tumor-specific
probes), and the like. Preferred is the use of high resolution
ultrasound which can be employed to monitor the size and location
of the tumor or other lesion being treated, either intraoperatively
or externally.
Systems according to the present invention will employ a plurality
of tissue-penetrating electrodes, typically in the form of
sharpened, small diameter metal wires which can penetrate into
tissue as they are advanced from a target site within the treatment
region, as described in more detail hereinafter. The electrode
elements, however, can also be formed in other manners, such as
blades, helices, screws, and the like. The primary requirement of
such electrode elements is that they can be deployed in an array,
preferably a three-dimensional array, emanating generally from a
target site within the treatment region of the tissue. Generally,
the electrode elements will be first introduced to the target site
in a radially collapsed or other constrained configuration, and
thereafter advanced into the tissue from a delivery element in a
divergent pattern to achieve the desired three-dimensional array.
Preferably, the electrode elements will diverge radially outwardly
from the delivery element (located at the target site) in a uniform
pattern, i.e. with the spacing between adjacent electrodes
diverging in a substantially uniform and/or symmetric pattern. In
the exemplary embodiments, pairs of adjacent electrodes will be
spaced-apart from each other in similar or identical, repeated
patterns and will usually be symmetrically positioned about an axis
of the delivery element. The electrode elements may extend or
project along generally straight lines from the target site, but
will more usually be shaped to curve radially outwardly and
optionally to evert proximally so that they face partially or fully
in the proximal direction when fully deployed. It will be
appreciated that a wide variety of particular patterns can be
provided to uniformly cover the region to be treated.
A preferred form of the individual electrode element of an
electrode array is a single wire having a shaped distal portion
which can be extended from the delivery element at the target site
in the tissue to diverge in a desired pattern. Such wires can be
formed from conductive metals having a suitable shape memory, such
as stainless steel, nickel-titanium alloys, spring steel alloys,
and the like. The wires may have circular or non-circular
cross-sections, with circular wires typically having a diameter in
the range from about 0.1 mm to 2 mm, preferably from 0.2 mm to 0.5
mm, often from 0.2 mm to 0.3 mm. The non-circular wires will
usually have equivalent cross-sectional areas. Optionally, the
distal ends of the wires may be honed or sharpened to facilitate
their ability to penetrate tissue. The distal ends of such wires
may be hardened using conventional heat treatment or other
metallurgical processes. Such wires may be partially covered with
insulation, although they will be at least partially free from
insulation over their distal portions which will penetrate into the
tissue to be treated. In the case of bipolar electrode arrays, it
will be necessary to insulate the positive and negative electrode
wires in any regions where they would be in contact with each other
during the power delivery phase. In the case of monopolar arrays,
it may be possible to bundle the wires together with their proximal
portions having only a single layer of insulation over the entire
bundle. Such bundled wires may be brought out directly to a
suitable RF power supply, or may alternatively be connected via
other (intermediate) electrical conductors, such as coaxial cable,
or the like.
The above described electrode characteristics apply only to active
electrodes intended to have the desired surgical effect, i.e.
heating of the surrounding tissue. It will be appreciated that in
monopolar operation, a passive or dispersive "electrode" must also
be provided to complete the return path for the circuit being
created. Such electrodes, which will usually be attached externally
to the patient's skin, will have a much larger area, typically
about 130 cm.sup.2 for an adult, so that current flux is
sufficiently low to avoid significant heating and other surgical
effects. It may also be possible to provide such a dispersive
return electrode directly on a portion of a sheath or elongate
member of the system of the present invention, as described in more
detail below (generally, when the return electrode is on the
sheath, the device will still be referred to as bipolar).
The RF power supply may be a conventional general purpose
electrosurgical power supply operating at a frequency in the range
from 400 kHz to 1.2 MHz, with a conventional sinusoidal or
non-sinusoidal wave form. Such power supplies are available from
many commercial suppliers, such as Valleylabs, Aspen, Bovie, and
Birtcher.
The plurality of electrode elements will usually be contained by or
within an elongate member which incorporates the delivery element,
typically a rigid, metal or plastic cannula. The elongate member
serves to constrain the individual electrode elements in a radially
collapsed configuration to facilitate their introduction to the
tissue target site. The electrode elements can then be deployed to
their desired configuration, usually a three-dimensional
configuration, by extending distal ends of the electrode elements
from the elongate member into the tissue. In the case of the
tubular cannula, this can be accomplished simply by advancing the
distal ends of the electrode elements distally forward from the
tube so that they emerge and deflect (usually as a result of their
own spring memory) in a radially outward pattern. Alternatively,
some deflection element or mechanism could be provided on the
elongate member to deflect members with or without shape memory in
a desired three-dimensional pattern.
A component or element will be provided for introducing the
elongate member to the target site within the treatment region to
be treated. For example, a conventional sheath and sharpened
obturator (stylet) assembly can be used to initially access the
target site. The assembly can be positioned under ultrasonic or
other conventional imaging, with the obturator/stylet then being
removed to leave an access lumen through the sheath. The electrode
elements can then be introduced through the sheath lumen, typically
while constrained in the elongate member. The electrode elements
are then extended distally beyond the distal end of the sheath into
the treatment region of tissue, and the elongate member can
subsequently be withdrawn or left in place. RF current can then be
applied through the electrodes in either a monopolar or bipolar
fashion. With monopolar treatment, a dispersive plate attached
externally to the patient is attached to the other lead from the RF
power supply. Alternatively, a return electrode having a relatively
large surface area can be provided on the elongate member, or the
sheath. In bipolar operation, the individual electrode elements can
be connected alternately to the two poles of the RF power supply.
Alternatively, one or more additional electrode elements can be
penetrated into the tissue and serve as a common electrode
connected at the second pole.
Description of the Preferred Embodiment
Referring now to the drawings, in which similar or corresponding
parts are identified with the same reference numeral, and more
particularly to FIG. 1, the volumetric tissue ablation apparatus of
the present invention is designated generally at 10 and includes a
probe 12 electrically connected to a generator 14.
In experiments with a prototype of the present invention, the
inventor utilized a Bovie.RTM. X-10 electrosurgical unit for
generator 14, to generate radio frequency current at specific
energies, using the probe 12 as the active electrode and placing
the tissue sample on a dispersive or ground plate. Thus, generator
14 includes at least an active terminal 16 and a return terminal
18, with a dispersive or ground plate 20 electrically connected by
conductor 22 to terminal 18.
Probe 12 is comprised of a plurality of electrically conductive
wires 24 which are bundled at a proximal end and connected to
terminal 16 to conduct RF current therefrom. Wires 24 are threaded
through an electrically insulated or non-conductive tube or
catheter 26.
Wires 24 are preferably formed of spring wire or other material
which will retain memory. As shown in FIG. 1, a 10-wire array 28 is
formed with each wire 24 arching from catheter 26 in a general "U"
shape with each wire substantially uniformly separated, as shown in
FIG. 2. Thus, array 28 is formed of a plurality of wires 24 curving
radially outwardly from the axis of distal end 26a of catheter 26.
Wires 24 all extend a length such that a portion of each wire 24 is
perpendicular to the axis of tube 26, and preferably continue
curving rearwardly back upon themselves such that wire distal ends
24a are oriented generally parallel to the axis of the tube distal
end 26a. As shown in FIG. 1, wire distal ends 24a generally lay
within a plane orthogonal to the tube distal end 26a, and uniformly
spaced-apart from one another.
Because wires 24 are formed of spring steel, they may be drawn
within catheter 26, for percutaneous insertion. Once distal end 26a
of catheter 26 is in position, sliding wires 24 through catheter 26
will permit the memory of the wires to take the radially disposed
shape of the array 28 shown in FIGS. 1 and 2.
FIG. 3 is a sectional view taken through a liver sample 30, showing
the results of a prior art 18 gauge straight needle 31 with 1.2 cm
of exposed metal when inserted in liver 30 and operated at 20 watts
of power, with 100% coagulation current, for a period of 5 minutes.
As can be seen in FIG. 3, the lesion 32 produced by the single
needle has a narrow elliptical (nearly cylindrical) shape with a
diameter of approximately 1.2 cm and a length of approximately 2
cm. FIG. 3 also shows the effects of very high temperatures near
the probe tip with gas formation common with single needle
electrosurgical sources, resulting in charred and carbonized tissue
34 immediately around the needle. The charring and associated gas
formation at the site of the single needle probes significantly
limits the power which may be applied.
FIG. 4 is a sectional view through a liver sample 30' showing the
necrotic lesion 32' produced by the 10 wire array 28 of probe 12 of
the present invention. Probe 12 is located in tissue sample 30'
with tube distal end 26a positioned generally centrally at the site
at which a lesion is desired. Various methods, known in the art,
may be utilized to position probe 12, prior to deployment of wires
24 (shown deployed in hidden lines). Preferably, positioning of
tube distal end 26a is confirmed by ultrasound or other imaging
techniques. Once tube 26 is appropriately positioned, wires 24 are
deployed into tissue 30', the memory of the wire material causing
the wire deployment to take a predetermined array shape.
The applicants utilized the same generator 14 at a power of 60
watts, with 100% coagulation current, for a period of 5 minutes. It
can be seen that the necrotic lesion produced by probe 12 is
roughly spherical in shape and has a diameter of approximately 3.5
cm. Furthermore, there is no charring evident, indicating no
sparking, and a more uniform temperature distribution within the
volume of tissue being treated. During testing, it was found that
the temperature of the tissue 2 cm away from the access of probe 12
at the end of the 5 minutes was 51.4.degree. C. The same 10 wire
probe 12 was used repeatedly at the same settings and produced
substantially identical lesions. It was also found that the area of
lethal heating may extend at least another centimeter beyond the
visible lesion shown in FIG. 4, after thermistor measurements were
taken during repeated experiments with probe 12.
While FIGS. 1 and 2 show a general "fountain" shaped array 28 with
10 wires 24, various other array designs are equally suitable,
utilizing uniform spacing of the wire distal ends 24a from catheter
distal end 26a to produce a symmetrical lesion, or with non-uniform
spacing to produce an assymetric lesion. For example, as shown in
FIG. 5, multiple arrays 28' may be formed spaced longitudinally
from one another. This embodiment of the monopolar tissue ablation
apparatus is designated generally at 110 and includes a probe 112
electrically connected to generator 14. Probe 112 includes a first
wire bundle 124 journaled through a tube 126 with wire distal ends
124a deployable to form a first array 28'a extending from tube
distal end 126a. A second wire bundle 125 surrounds tube 126 within
an outer tube 127, with wire distal ends 125a deployable to form a
second array 28'b projecting from outer tube distal end 127a. The
proximal ends 124b and 125b of wire bundles 124 and 125 are
electrically connected in common to active terminal 16.
In operation, outer tube 127 is positioned with distal end 127a
located at the predetermined site for the lesion. The second array
28'b is then formed by deploying wire ends 125a of second wire
bundle 125. Inner tube 126 is then moved axially such that tube
distal end 126a is spaced longitudinally from tube distal end 127a.
First wire bundle 124 is then deployed such that wire ends 124a
form array 28'a longitudinally spaced from array 28'b.
Referring now to FIG. 6, a bipolar embodiment of the tissue
ablation apparatus is designated generally at 210 and includes a
probe 212 electrically connected to a generator 14. Wires 224 are
electrically connected to terminal 16 on generator 14 and terminate
distally in an array 228 in the same fashion as the array 28 of the
first embodiment. However, apparatus 210 includes an integral
return path consisting of a return wire 238 coated with an
electrically nonconductive material 236, which extends through
catheter 226 within the bundle of wires 224, and has a distal end
238a projecting generally centrally within array 228. The proximal
end 238b of wire 238 is connected to return terminal 18, to provide
an electrical circuit when probe 212 is deployed within tissue.
Thus, a dispersive plate is unnecessary.
Referring now to FIG. 7, a second bipolar embodiment of the tissue
ablation apparatus is designated generally at 310 and includes a
probe 312 with wires 324 connected to active terminal 16 of
generator 14. Wires 324 project from distal end 326a of tube 326 to
form an array 328.
Bipolar apparatus 310 differs from bipolar apparatus 210 of FIG. 6,
in two ways. First, a collar 340 is attached to the exterior of
tube distal end 326a and is electrically connected to return
terminal 18 by a conductor 342, to form an electrical return for
current supplied by wires 324. Conductor 342 may be affixed to the
outside of tube 326, or threaded through tube 326 while
electrically insulted from wires 324.
Second, wires 324 have portions 344 which are coated with an
electrically insulative material. Portions 344 are spaced-apart
along a plurality of wires 324 in order to restrict current flow
from selected portions of wires 324 in order to create a more
uniform distribution of heat from the remaining exposed portions of
wires 324.
A third bipolar embodiment of the tissue ablation apparatus is
designated generally at 410 in FIG. 8. Bipolar apparatus 410
includes a probe 412 with one set of wires 424 of wires 424
connected to one terminal 16' of a current generator 14', and a
second set of wires 425 connected to the opposite terminal 18'. The
individual wires of wire bundles 424 and 425 have an electrically
insulative coating through tube 426, to prevent electrical contact
with one another. Wires 424 and 425 preferably alternate throughout
array 428, such that current flows between wires 424 and wires
425.
Description of the Method of the Present invention
Referring now to FIGS. 9-14, a treatment region TR within tissue T
is located beneath the skin S of a patient. The treatment region
may be a solid tumor or other lesion where it is desired to treat
the region by RF hyperthermia. The treatment region TR prior to
treatment is shown in FIG. 9.
In order to introduce an electrode array according to the method of
the present invention, a conventional sheath and obturator/stylet
assembly 500 is introduced percutaneously (through the skin) so
that a distal end of the sheath lies at or within a target site TS,
as shown in FIG. 10. Obturator/stylet 504 is then withdrawn from
sheath 502, leaving an access lumen to the target site, as shown in
FIG. 11. A delivery probe 510 incorporating the features of the
present invention is then introduced through the access lumen of
the sheath 502 so that a distal end 512 of an outer cannula 515 of
the probe lies near the distal end 514 of the sheath 502, as shown
in FIG. 12. Individual electrodes 520 are then extended distally
from the distal end 512 of the probe 510 by advancing cable 516 in
the direction of arrow 519, as shown in FIG. 13. The electrodes 520
are advanced so that they first diverge radially outwardly from
each other (FIG. 13), eventually everting backward in the proximal
direction, as shown in FIG. 14. If desired, the cannula 515 of
probe 510 is then withdrawn proximally over electrode cable 516,
and the electrode cable is then attached to an RF power supply 518
in a monopolar manner, also as shown in FIG. 14. Radio frequency
current may then be applied from the power supply 518 at a level
and for a duration sufficient to raise the temperature of the
treatment region TR by a desired amount, typically to a temperature
of at least 42.degree. C., usually to at least 50.degree. C., for
10 minutes or longer. Higher temperatures will generally require
much shorter treatment times.
While the method and system just described employs a separate
sheath and obturator/stylet assembly 500 for introducing the
treatment electrodes, it will be appreciated that the use of such a
separate introducer is not necessary. Alternatively, the electrodes
could be introduced through the elongate member, where the elongate
member is provided with a self-penetrating element, such as a sharp
tip or an electrosurgical tip, to enhance tissue penetration. As a
further alternative, a bundle of electrodes could be introduced in
any constrained fashion (e.g. a removable ring, soluble sheath,
etc.), with the constraint selectively released after they have
reached the target site within the treatment region. The present
invention thus will encompass use of a variety of specific systems
for introducing a plurality of electrodes to the target site in
solid tissue, and thereafter releasing and diverging the individual
electrode elements into a treatment region surrounding the target
site in a desired three-dimensional array or other configuration or
geometry.
Whereas the invention has been shown and described in connection
with the preferred embodiments thereof, many modifications,
substitutions and additions may be made which are within the
intended broad scope of the appended claims. It can therefore be
seen that the volumetric tissue ablation apparatus of the present
invention provides an effective and desirable electrosurgical
ablation system which is suitable for percutaneous and open
surgical introduction, produces uniform lesions, and produces
lesions large enough to treat a large spectrum of patients.
* * * * *