U.S. patent application number 12/158831 was filed with the patent office on 2008-11-27 for radiation applicator and method of radiating tissue.
This patent application is currently assigned to MICROSULIS HOUSE. Invention is credited to Nigel Cronin.
Application Number | 20080294155 12/158831 |
Document ID | / |
Family ID | 35841437 |
Filed Date | 2008-11-27 |
United States Patent
Application |
20080294155 |
Kind Code |
A1 |
Cronin; Nigel |
November 27, 2008 |
Radiation Applicator and Method of Radiating Tissue
Abstract
A dipole microwave applicator emits microwave radiation into
tissue to be treated. The applicator is formed from a thin coax
cable having an inner conductor surrounded by an insulator, which
is surrounded by an outer conductor. A portion of the inner
conductor extends beyond the insulator and the outer conductor. A
ferrule at the end of the outer conductor has a step and a sleeve
that surrounds a portion of the extended inner conductor. A tuning
washer is attached to the end of the extended inner conductor. A
dielectric tip encloses the tuning washer, the extended inner
conductor, and the sleeve of the ferrule. The sleeve of the ferrule
and the extended inner conductor operate as the two arms of the
dipole microwave antenna. The tuning washer faces the step in the
ferrule, and is sized and shaped to cooperate with the step in
balancing and tuning the applicator.
Inventors: |
Cronin; Nigel; (Bath,
GB) |
Correspondence
Address: |
COOK ALEX LTD
SUITE 2850, 200 WEST ADAMS STREET
CHICAGO
IL
60606
US
|
Assignee: |
MICROSULIS HOUSE
DENMEAD
GB
|
Family ID: |
35841437 |
Appl. No.: |
12/158831 |
Filed: |
December 15, 2006 |
PCT Filed: |
December 15, 2006 |
PCT NO: |
PCT/EP2006/012144 |
371 Date: |
June 23, 2008 |
Current U.S.
Class: |
606/33 |
Current CPC
Class: |
A61B 2018/00083
20130101; A61B 2018/00178 20130101; A61B 18/18 20130101; A61B
2018/00577 20130101; A61N 5/045 20130101; A61B 2018/1869 20130101;
A61B 18/04 20130101; A61B 2018/00077 20130101; A61B 2018/00023
20130101; A61B 2018/1838 20130101; A61B 2018/1892 20130101; G06T
7/30 20170101; A61B 2018/00029 20130101; A61B 18/1815 20130101 |
Class at
Publication: |
606/33 |
International
Class: |
A61B 18/18 20060101
A61B018/18 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 3, 2006 |
GB |
0600018.6 |
Claims
1. A dipole microwave applicator for emitting microwave radiation
into tissue, the assembly comprising: an outer conductor having an
end; an inner conductor disposed within the outer conductor, and
including a section that extends outwardly beyond the end of the
outer conductor; a ferrule disposed at the end of the outer
conductor, and having a sleeve portion that surrounds a portion of
the outwardly extending section of the inner conductor; and a
dielectric tip surrounding the sleeve portion of the ferrule and
the outwardly extending section of the inner conductor, whereby the
sleeve portion of the ferrule and at least a portion of the
outwardly extending section of the inner conductor operate as
corresponding arms of the dipole microwave applicator.
2. The dipole microwave applicator of claim 1, further comprising a
dielectric spacer disposed within the dielectric tip, the
dielectric spacer surrounding at least a portion of the inner
conductor that extends beyond the sleeve portion of the
ferrule.
3. The dipole microwave applicator of claim 1, wherein the ferrule
has a first end that is attached to the end of the outer
conductor.
4. The dipole microwave applicator of claim 1, further comprising a
tuning element disposed within the dielectric tip, and attached to
an end of the inner conductor.
5. The dipole microwave applicator of claim 4, wherein the ferrule
further includes a step adjacent to the sleeve portion, and the
tuning element and step cooperate to balance the corresponding arms
of the dipole microwave applicator.
6. The dipole microwave applicator of claim 5, wherein the tuning
element is substantially disc shaped.
7. The dipole microwave applicator of claim 5, further comprising a
rigid sleeve adjacent to the ferrule, and surrounding and spaced
from at least a portion of the outer conductor so as to define a
space between the outer conductor and the rigid sleeve.
8. The dipole microwave applicator of claim 7, wherein one or more
holes extend through the rigid sleeve, the one or more holes
providing a fluid communication path from the space within the
rigid sleeve to an area outside of the rigid sleeve.
9. The dipole microwave applicator of claim 1, wherein the ferrule
is formed from copper, and the tip is formed from itrium stabilized
zirconia.
10. The dipole microwave applicator of claim 8, wherein the sleeve
is formed from stainless steel, the ferrule is formed from copper,
and the tip is formed from itrium stabilized zirconia.
11. The dipole microwave applicator of claim 1, wherein microwave
energy at a frequency of approximately 2.45 Gigahertz (GHz) and a
power level of up to 80 watts is applied to the applicator.
12. The dipole microwave applicator of claim 2, further comprising
an insulator disposed between the outer conductor and the inner
conductor, wherein the spacer abuts an end of the sleeve of the
ferrule and the insulator terminates within the sleeve so as to
define a gap within the sleeve of the ferrule around the inner
conductor.
13. The dipole microwave applicator of claim 10, wherein the gap is
filled with air.
14. The dipole microwave applicator of claim 5, wherein the
dielectric tip has open end that abuts the step in the ferrule and
a closed end opposite the open end, and the closed end is
configured for one of cutting or piercing tissue.
15. The dipole microwave applicator of claim 1, wherein at least
one of the dielectric tip and the ferrule is coated with an inner
layer of polyimide and an outer layer of paralyne.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is related to commonly owned
copending International patent application no. WO 2006/002943,
concerning a Radiation Applicator and Method of Radiating Tissue
and which is hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to medical
technology, and more specifically to microwave radiation
applicators and methods of thermal ablative treatment of tissue
using radiated microwaves.
[0004] 2. Background Information
[0005] Thermal ablative therapies may be defined as techniques that
intentionally decrease body tissue temperature (hypothermia) or
intentionally increase body tissue temperature (hyperthermia) to
temperatures required for cytotoxic effect, or to other therapeutic
temperatures depending on the particular treatment. Microwave
thermal ablation relies on the fact that microwaves form part of
the electromagnetic spectrum causing heating due to the interaction
between water molecules and the microwave radiation. The heat being
used as the cytotoxic mechanism. Treatment typically involves the
introduction of an applicator into tissue, such as tumors.
Microwaves are released from the applicator forming a field around
its tip. Heating of the water molecules occurs in the radiated
microwave field produced around the applicator, rather than by
conduction from the probe itself. Heating is therefore not reliant
on conduction through tissues, and cytotoxic temperature levels are
reached rapidly.
[0006] Microwave thermal ablative techniques are useful in the
treatment of tumors of the liver, brain, lung, bones, etc.
[0007] U.S. Pat. No. 4,494,539 discloses a surgical operation
method using microwaves, characterized in that microwaves are
radiated to tissue from a monopole type electrode attached to the
tip of a coaxial cable for transmitting microwaves. Coagulation,
hemostasis or transaction is then performed on the tissue through
the use of the thermal energy generated from the reaction of the
microwaves on the tissue. In this way, the tissue can be operated
in an easy, safe and bloodless manner. Therefore, the method can be
utilized for an operation on a parenchymatous organ having a great
blood content or for coagulation or transaction on a parenchymatous
tumor. According to the method, there can be performed an operation
on liver cancer, which has been conventionally regarded as very
difficult. A microwave radiation applicator is also disclosed.
[0008] U.S. Pat. No. 6,325,796 discloses a microwave ablation
assembly and method, including a relatively thin, elongated probe
having a proximal access end, and an opposite distal penetration
end adapted to penetrate into tissue. The probe defines an insert
passage extending therethrough from the access end to the
penetration end thereof. An ablation catheter includes a coaxial
transmission line with an antenna device coupled to a distal end of
the transmission line for generating an electric field sufficiently
strong enough to cause tissue ablation. The coaxial transmission
line includes an inner conductor and an outer conductor separated
by a dielectric material. A proximal end of the transmission line
is coupled to a microwave energy source. The antenna device and the
transmission line each have a transverse cross-sectional dimension
adapted for sliding receipt through the insert passage while the
elongated probe is positioned in the tissue. Such sliding
advancement continues until the antenna device is moved to a
position beyond the penetration end and further into direct contact
with the tissue.
[0009] However, a drawback with the existing techniques include the
fact that they are not optimally mechanically configured for
insertion into, and perforation of, the human skin, for delivery to
a zone of soft tissue to be treated. Typically, known radiation
applicator systems do not have the heightened physical rigidity
that is desirable when employing such techniques.
[0010] In addition, some radiation applicators made available
heretofore do not have radiation emitting elements for creating a
microwave field pattern optimized for the treatment of soft tissue
tumors.
[0011] Also, given the power levels employed in some applicators
and treatments, there can be problems of unwanted burning of
non-target, healthy tissue due to the very high temperatures
reached by the applicator or the components attached thereto.
[0012] Further, although small diameter applicators are known, and
liquid cooling techniques have been used, there has been difficulty
in designing a small diameter device with sufficient cooling in
applications employing power levels required to deal with soft
tissue tumors.
[0013] Accordingly, there is a need for methods of treatment of
soft tissue tumors, and for radiation applicators that overcome any
or all of the aforementioned problems of the prior art techniques,
and provide improved efficacy.
SUMMARY OF THE INVENTION
[0014] In accordance with one aspect of the present invention,
there is provided a dipole microwave applicator for emitting
microwave radiation into tissue, the assembly comprising: an outer
conductor having an end; an inner conductor disposed within the
outer conductor, and including a section that extends outwardly
beyond the end of the outer conductor; a ferrule disposed at the
end of the outer conductor, and having a sleeve portion that
surrounds a portion of the outwardly extending section of the inner
conductor; and a dielectric tip surrounding the sleeve portion of
the ferrule and the outwardly extending section of the inner
conductor, whereby the sleeve portion of the ferrule and at least a
portion of the outwardly extending section of the inner conductor
operate as corresponding arms of the dipole microwave
applicator.
[0015] Particular embodiments are set out in the dependent
claims.
[0016] Briefly, the present invention is directed to a microwave
applicator for ablating tissue. The applicator is a dipole
microwave antenna that transmits microwave radiation into the
tissue being treated. The applicator is formed from a thin coaxial
cable having an inner conductor surrounded by an insulator, which
is surrounded by an outer conductor or shield. The end of the
coaxial cable is trimmed so that a portion of the insulator and
inner conductor extend beyond the outer conductor, and a portion of
the inner conductor extends beyond the insulator. The applicator
further includes a tubular ferrule defining an aperture
therethrough. One end of the ferrule is attached to the outer
conductor, while the other end, which forms a sleeve, extends out
beyond the end of the insulator and around a portion of the
extended inner conductor. A step is preferably formed on the outer
surface of the ferrule between its two ends. A solid spacer having
a central bore to receive the inner conductor abuts an end of the
ferrule and surrounds the extended inner conductor. A tuning
element is attached to the end of the extended inner conductor, and
abuts an end of the spacer opposite the ferrule. The tuning element
faces the step in the ferrule, and the step and the tuning element
are both sized and shaped to cooperate in balancing and tuning the
applicator. A hollow tip, formed from a dielectric material, has an
open end and a closed end. The tip encloses the tuning element, the
spacer, and the extended inner conductor. The tip also encloses the
sleeve of the ferrule, thus defining outer surface of the ferrule
that is surrounded by the dielectric tip. The open end of the tip
preferably abuts the step in the ferrule. A rigid sleeve surrounds
the coaxial cable and extends away from the ferrule opposite the
tip. The sleeve, which abuts the step of the ferrule opposite the
tip, has an inner diameter that is larger than the coaxial cable,
thereby defining an annular space between the outside of the
coaxial cable and the inner surface of the sleeve. The sleeve
further includes one or more drainage holes, which permit fluid
communication between the annular space around the coaxial cable
and the outside of the applicator.
[0017] In operation, microwave energy from a source is applied to
the coaxial cable, and is conveyed to the tip. The portion of the
inner conductor that extends beyond the end of the ferrule forms
one arm of the dipole, and emits microwave radiation. In addition,
the microwave energy flowing along the inner conductor of the
coaxial cable and in the aperture of the ferrule induces a current
to flow along the outer surface of the sleeve of the ferrule that
is surrounded by the tip. This, in turn, causes microwave radiation
to be emitted from the sleeve of the ferrule, which operates as the
second arm of the dipole. In this way, microwave energy is emitted
along a substantial length of the applicator, rather than being
focused solely from the tip. By distributing the emission of
microwave radiation along a length of the applicator, higher power
levels may be employed.
[0018] To keep the coaxial cable and the applicator from
overheating, a cooling fluid is introduced from a source into the
annular space defined by the outside of the coaxial cable and the
inside of the sleeve. The cooling fluid flows along this annular
space, and absorbs heat from the coaxial cable. The cooling fluid,
after having absorbed heat from the coaxial cable, then exits the
annular space through the one or more drainage holes in the sleeve,
and perfuses adjacent tissue.
[0019] The closed end of the tip is preferably formed into a blade
or point so that the Microwave applicator may be inserted directly
into the tissue being treated. The tip, ferrule, and rigid sleeve,
moreover, provide strength and stiffness to the applicator, thereby
facilitating its insertion into tissue.
[0020] The present invention further provides a method of treating
target tissue, such as a tumor, the tumor being formed of, and/or
being embedded within, soft tissue. The method includes inserting
the microwave applicator into the tumor, and supplying
electromagnetic energy to the applicator, thereby radiating
electromagnetic energy into the tumor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Embodiments of the invention will now be described, by way
of example, with reference to the accompanying drawings, in
which:
[0022] FIG. 1 is a schematic, partial cross-sectional view of a
radiation applicator in accordance with one embodiment of the
invention;
[0023] FIG. 2A shows an axial cross-section, and FIG. 2B shows an
end elevation of the radiating tip of the radiation applicator of
FIG. 1;
[0024] FIG. 3 shows a partial transverse cross-section of the tube
of the radiation applicator of FIG. 1;
[0025] FIG. 4A shows a transverse cross-section, and FIG. 4B shows
an axial cross-section of the tuning washer of the radiation
applicator of FIG. 1;
[0026] FIG. 5A shows an axial cross-section, and FIG. 5B shows an
end elevation of the ferrule of the radiation applicator of FIG.
1;
[0027] FIG. 6A shows an axial cross-section, and FIG. 6B shows a
transverse cross-section of a handle section that may be attached
to the radiation applicator of FIG. 1;
[0028] FIG. 7 illustrates the portion of coaxial cable that passes
through the tube of the radiation applicator of FIG. 1;
[0029] FIG. 8 is a plot of S.sub.11 against frequency for the
radiation applicator of FIG. 1;
[0030] FIG. 9A illustrates the E-field distribution, and FIG. 9B
illustrates the SAR values around the radiation applicator of FIG.
1, in use;
[0031] FIGS. 10A-E show a preferred sequential assembly of the
radiation applicator of FIG. 1;
[0032] FIG. 11 schematically illustrates a treatment system
employing the radiation applicator of FIG. 1;
[0033] FIG. 12 is an exploded, perspective view of another
embodiment of the present invention;
[0034] FIGS. 13-18 show a preferred sequential assembly of the
radiation applicator of FIG. 12; and
[0035] FIG. 19 is a schematic, partial cross-sectional view of the
radiation applicator of FIG. 12.
DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT
[0036] In the following description, like references are used to
denote like elements, and where dimensions are given, they are in
millimeters (mm). Further, it will be appreciated by persons
skilled in the art that the electronic systems employed, in
accordance with the present invention, to generate, deliver and
control the application of radiation to parts of the human body may
be as described in the art heretofore. In particular, such systems
as are described in commonly owned published international patent
applications W095/04385, W099/56642 and WOOO/49957 may be employed
(except with the modifications described hereinafter). Full details
of these systems have been omitted from the following for the sake
of brevity.
[0037] FIG. 1 is a schematic, partial cross-sectional view of a
radiation applicator in accordance with one embodiment of the
invention. The radiation applicator, generally designated 102,
includes a distal end portion of a coaxial cable 104 that is used
to couple to a source (not shown) of microwaves, a copper ferrule
106, a tuning washer 108 attached on the end 110 of the insulator
part of the coaxial cable 104, and a tip 112. Preferably, the
applicator 102 further includes a metal tube 114. Tube 114 is
rigidly attached to the ferrule 106. An annular space 116 is
defined between the outer conductor 118 of the cable 104 and the
inner surface of the tube 114, enabling cooling fluid to enter (in
the direction of arrows A), contact the heated parts of the
applicator 102 and exit in the direction of arrows B through radial
holes 120 in the tube 114, thereby extracting heat energy from the
radiation applicator 102.
[0038] In assembly of the applicator 102, the washer 108 is
soldered to a small length 122 of the central conductor 124 of the
cable 104 that extends beyond the end 110 of the insulator 126 of
the cable 104. The ferrule 106 is soldered to a small cylindrical
section 128 of the outer conductor 118 of the cable 104. Then, the
tube 114, which is preferably stainless steel, but may be made of
other suitable materials, such as titanium or any other medical
grade material, is glued to the ferrule 106 by means of an
adhesive, such as Loctite 638 retaining compound, at the contacting
surfaces thereof, indicated at 130 and 132. The tip 112 is also
glued preferably, using the same adhesive, on the inner surfaces
thereof, to corresponding outer surfaces of the ferrule 106 and the
insulation 126.
[0039] When assembled, the applicator 102 forms a unitary device
that is rigid and stable along its length, which may be of the
order of 250 or so millimeters including tube 114, thereby making
the applicator 102 suitable for insertion into various types of
soft tissue. The space 116 and holes 120 enable cooling fluid to
extract heat from the applicator 102 through contact with the
ferrule 106, the outer conductor 118 of the cable 104 and the end
of the tube 114. The ferrule 106 assists, among other things, in
assuring the applicator's rigidity. The exposed end section 134 of
cable 104 from which the outer conductor 118 has been removed, in
conjunction with the dielectric tip 112, are fed by a source of
radiation of predetermined frequency. The exposed end section 134
and dielectric tip 112 operate as a radiating antenna for radiating
microwaves into tissue for therapeutic treatment. The applicator
102 operates as a dipole antenna, rather than a monopole device,
resulting in an emitted radiation pattern that is highly beneficial
for the treatment of certain tissues, such as malignant or tumorous
tissue, due to its distributed, spherical directly heated area.
[0040] FIG. 2A shows an axial cross-section, and FIG. 2B shows an
end elevation of the tip 112 of the radiation applicator 102 of
FIG. 1. As can be seen, the tip 112 has inner cylindrical walls
202, 204, and abutting walls 206, 208, for receiving and abutting
the washer 108 and the ferrule 106, respectively, during assembly.
Suitably, the tip 112 is made of zirconia ceramic alloy. More
preferably, it is a partially stabilized zirconia (PSZ) having
yttria as the stabilizing oxidizing agent. Even more preferably,
the tip 112 is made of Technox 2000, which is a PSZ commercially
available from Dynamic Cerarnic Ltd. of Staffordshire, England,
having a very fine uniform grain compared to other PSZs, and a
dielectric constant (k) of 25. As understood by those skilled in
the art, the choice of dielectric material plays a part in
determining the properties of the radiated microwave energy.
[0041] It will be noted that the transverse dimensions of the
applicator 102 are relatively small. In particular, the diameter of
applicator 102 is preferably less than or equal to about 2.4 mm.
The tip 112, moreover, is designed to have dimensions, and be
formed of the specified material, so as to perform effective tissue
ablation at the operating microwave frequency, which in this case
is preferably 2.45 Gigahertz (GHz). The applicator 102 of the
present invention is thus well adapted for insertion into, and
treatment of, cancerous and/or non-cancerous tissue of the liver,
brain, lung, veins, bone, etc.
[0042] The end 210 of the tip 112 is formed by conventional
grinding techniques performed in the manufacture of the tip 112.
The end 210 may be formed as a fine point, such as a needle or pin,
or it may be formed with an end blade, like a chisel, i.e. having a
transverse dimension of elongation. The latter configuration has
the benefit of being well suited to forcing the tip 112 into or
through tissue, i.e. to perforate or puncture the surface of
tissue, such as skin.
[0043] In use, the tip 112 is preferably coated with a non-stick
layer such as silicone or paralene, to facilitate movement of the
tip 112 relative to tissue.
[0044] FIG. 3 shows a partial transverse cross-section of the tube
114. As mentioned above, the tube 114 is preferably made of
stainless steel. Specifically, the tube 114 is preferably made from
13 gauge thin wall 304 welded hard drawn (WHD) stainless steel. The
tube 114 is also approximately 215 mm in length. As can be seen,
two sets of radial holes 120, 120' are provided at 12 mm and 13 mm,
respectively, from the end 302 of the tube 114. These radial holes
120, 120', as mentioned, permit the exit of cooling fluid. Although
two sets of holes are shown, one, three, four or more sets of holes
may be provided, in variants of the illustrated embodiment. In
addition, although two holes per set are shown, three, four, five,
or more holes per set may be provided, so long as the structural
rigidity of the tube 114 is not compromised. In this embodiment,
the holes 120, 120' are of 0.5 mm diameter, but it will be
appreciated that this diameter may be quite different, e.g. any
thing in the range of approximately 0.1 to 0.6 mm, depending on the
number of sets of holes and/or the number of holes per set, in
order to provide an effective flow rate. Although the illustrated
distance from the end 302 is 12 or 13 mm, in alternative
embodiments, this distance may range from 3 mm to 50 mm from the
end 302, in order to control the length of track that requires
cauterization.
[0045] Further, in an embodiment used in a different manner, the
tube 114 may be omitted. In this case the treatment may comprise
delivering the applicator to the treatment location, e.g., to the
tumorous tissue, by suitable surgical or other techniques. For
example, in the case of a brain tumor, the applicator may be left
in place inside the tumor, the access wound closed, and a sterile
connector left at the skull surface for subsequent connection to
the microwave source for follow-up treatment at a later date.
[0046] FIG. 4A shows a transverse cross-section, and FIG. 4B shows
an axial cross-section of the tuning washer 108. The washer 108 is
preferably made of copper, although other metals may be used. The
washer 108 has an inner cylindrical surface 402 enabling it to be
soldered to the central conductor 124 of the cable 104 (FIG. 1).
Although the washer is small, its dimensions are critical. The
washer 108 tunes the applicator 102, which operates as a dipole
radiator, i.e., radiating energy from two locations, so that more
effective treatment, i.e., ablation, of tissue is effected.
[0047] FIG. 5A shows an axial cross-section, and FIG. 5B shows an
end elevation of the ferrule 106. The ferrule 106 is preferably
made of copper, and is preferably gold plated to protect against
any corrosive effects of the cooling fluid. The ferrule 106 may be
produced by conventional machining techniques, such as CNC
machining.
[0048] FIG. 6A shows an axial cross-section, and FIG. 6B shows a
transverse cross-section at line B-B of a handle section 602 that
may be attached to the tube 114 of the radiation applicator 102.
The handle section 602 is preferably made from the same material as
the tube 114, i.e., stainless steel. The handle section 602
includes a forward channel 604 enabling insertion of the tube 114,
and a rear channel 606 enabling insertion of the coaxial cable 104
during assembly. A transverse port 608 having an internal thread
610 enables the connection, through a connector, to a source of
cooling fluid, discussed later. The connector may be formed from
plastic. Once assembled, the arrangement of handle section 602
enables cooling fluid to pass in the direction of arrow C into the
tube 114 (not shown).
[0049] FIG. 7 illustrates the portion of coaxial cable 104 that
passes through the tube 114. The cable 104 suitably comprises a
low-loss, coaxial cable such as SJS070LL-253-Strip cable. A
connector 702, preferably a SMA female type connector permits
connection of the cable 104 to a microwave source (not shown), or
to an intermediate section of coaxial cable (not shown) that, in
turn, connects to the microwave source.
[0050] FIG. 8 is a plot of S11 against frequency for the radiation
applicator 102 of FIG. 1. This illustrates the ratio of reflective
microwave power from the interface of the applicator 102 and
treated tissue to total input power to the applicator 102. As can
be seen, the design of the applicator 102 causes the reflected
power to be a minimum, and therefore the transmitted power into the
tissue to be a maximum, at a frequency of 2.45 GHz of the delivered
microwaves.
[0051] FIG. 9A shows the E-field distribution around the radiation
applicator 102 of FIG. 1, in use. Darker colors adjacent to the
applicator 102 indicate points of higher electric field. In FIG.
9A, the position of the washer 108 is indicated at 902, and the
position of the tip-ferrule junction is indicated at 904. Two
limited, substantially cylindrical zones 906, 908, of highest
electric field are formed around the applicator 102 at the
positions 902 and 904 respectively.
[0052] FIG. 9B shows the specific absorption rate (SAR) value
distribution around the radiation applicator 102 of FIG. 1, in use.
Darker colors adjacent the applicator 102 indicate points of SAR.
In FIG. 9B, the position of the washer 108 is indicated at 902, the
position of the tip-ferrule junction is indicated at 904, and the
position of the ferrule-tube junction is indicated at 905. Two
limited, substantially cylindrical zones 910, 912, of highest SAR
are formed around the applicator 102 at the positions 902 and
between 904 and 905, respectively.
[0053] FIGS. 10A-E show a preferred sequential assembly of
components forming the radiation applicator 102 of FIG. 1. In FIG.
10A, the coaxial cable 104 is shown with the outer conductor 118
and the inner insulator 126 trimmed back, as illustrated earlier in
FIG. 7.
[0054] As shown in FIG. 10B, the tube 114 is then slid over the
cable 104. Next, the ferrule 106 is slid over the cable 104 (FIG.
10C), and fixedly attached to the tube 114 and to the cable 104, as
described earlier. Then, the washer 108 is attached to the inner
conductor 124 by soldering, as shown in FIG. 1D. Finally, the tip
112 is slid over the cable 104 and part of the ferrule 106, and
affixed thereto, as described earlier. The completed applicator is
shown in FIG. 10E. This results in a construction of great rigidity
and mechanical stability.
[0055] FIG. 11 schematically illustrates a treatment system 1102
employing the radiation applicator 102 of FIG. 1. Microwave source
1104 is couple to the input connector 1106 on handle 602 by coaxial
cable 1108. In this embodiment, the microwave power is supplied at
up to 80 Watts. However this could be larger for larger size
applicators, e.g., up to 200 Watts for 5 mm diameter radiation
applicators.
[0056] Syringe pump 1110 operates a syringe 1112 for supplying
cooling fluid 1114 via conduit 1116 and connector 1118 attached to
handle 602, to the interior of the handle section 602. The fluid is
not at great pressure, but is pumped so as to provide a flow rate
of about 1.5 to 2.0 milliliter(ml)/minute through the pipe 114 in
the illustrated embodiment. However, in other embodiments, where
the radiation applicator 102 is operated at higher powers, higher
flow rates may be employed, so as to provide appropriate cooling.
The cooling fluid is preferably saline, although other liquids or
gases may be used, such as ethanol. In certain embodiments, a
cooling liquid having a secondary, e.g., cytotoxic, effect could be
used, enhancing the tumor treatment. In the illustrative
embodiment, the cooling fluid 1114 exits the tube 1114, as shown by
arrows B in FIG. 1, at a temperature on the order of 10.degree. C.
higher than that at which it enters the tube 114, as shown by
arrows A in FIG. 1. Thus, substantial thermal energy is extracted
from the coaxial cable. The cooling fluid 1114 may, for example,
enter the tube 114 at room temperature. Alternatively, the cooling
fluid 1114 may be pre-cooled to a temperature below room
temperature by any suitable technique.
[0057] As shown, the cooling system is an open, perfusing cooling
system that cools the coaxial cable connected to the radiation
applicator 102. That is, after absorbing heat from the coaxial
cable, the cooling fluid perfuses the tissue near the radiation
applicator 102.
[0058] The methodology for use of the radiation applicator 102 of
the present invention may be as conventionally employed in the
treatment of various soft tissue tumors. In particular, the
applicator 102 is inserted into the body, laparoscopically,
percutaneously or surgically. It is then moved to the correct
position by the user, assisted where necessary by positioning
sensors and/or imaging tools, such as ultrasound, so that the tip
112 is embedded in the tissue to be treated. The microwave power is
switched on, and the tissue is thus ablated for a predetermined
period of time under the control of the user. In most cases, the
applicator 102 is stationary during treatment. However, in some
instances, e.g., in the treatment veins, the applicator 102 may be
moved, such as a gentle sliding motion relative to the target
tissue, while the microwave radiation is being applied.
[0059] As described above, and as shown in FIGS. 9A and 9B,
radiation applicator 102, is a dipole antenna. The portion of the
inner conductor 124 that extends beyond the ferrule 106 operates as
one arm of the dipole antenna. In addition, the transmission of
microwave energy along the inner conductor 124 and in the aperture
of the ferrule induces a current to flow on that portion of the
outer surface of the ferrule 106 that is located underneath the tip
112. This induced current causes this enclosed, outer surface of
the ferrule 106 to emit microwave radiation, thereby forming a
second arm of the dipole antenna. The bipolar configuration of the
applicator effectively spreads the microwave radiation that is
being transmitted by the applicator 102 along a greater transverse,
i.e., axial, length of the antenna 102, rather than focusing the
radiation transmission solely from the tip 112 of the applicator
102. As a result, the applicator 102 of the present invention may
be operated at much higher power levels, e.g., up to approximately
80 Watts, than prior art designs.
[0060] An alternative embodiment of the present invention is shown
in FIGS. 12-19. FIG. 12 is an exploded, perspective view of an
alternative radiation applicator 1202. As shown, the applicator
1202 includes a coaxial cable 1204 having an outer conductor 1206
that surrounds an insulator 1208 that, in turn, surrounds an inner
or central conductor 1210. The applicator 1202 further includes a
ferrule 1212. The ferrule 1212 is generally tubular shaped so as to
define an aperture therethrough, and has first and second ends
1212a, 1212b. The ferrule 1212 also has three parts or sections. A
first section 1214 of the ferrule 1212 has an inner diameter sized
to fit over the outer conductor 1206 of the coaxial cable 1204. A
second section 1216 of the ferrule 1212 has an inner diameter that
is sized to fit over the insulator 1208 of the coaxial cable 1204.
The second section 1216 thus defines an annular surface or flange
(not shown) around the inside the ferrule 1212. The outer diameter
of the second section 1216 is preferably larger than the outer
diameter of the first section 1214, thereby defining a step or
flange around the outside of the ferrule 1212. A third section 1218
of the ferrule 1212 has an inner diameter also sized to fit around
the insulator 1208 of the coaxial cable 1204. The third section
1218 has an outside diameter that is less than the outside diameter
of the second section 1216. The third section 1218 thus defines an
outer, cylindrical surface or sleeve.
[0061] Applicator 1202 further includes a spacer 1220. The spacer
1220 is preferably cylindrical in shape with a central bore 1222
sized to receive the inner conductor 1210 of the coaxial cable
1204. The outer diameter of the spacer 1220 preferably matches the
outer diameter of the third section 1218 of the ferrule 1212.
Applicator 1202 also includes a tuning element 1224 and a tip 1226.
The tuning element 1224, which be may be disk-shaped, has a central
hole 1228 sized to fit around the inner conductor 1210 of the
coaxial cable 1204. The tip 1226 is a hollow, elongated member,
having an open end 1230, and a closed end 1232. The closed end 1232
may be formed into a cutting element, such as a trocar point or a
blade, to cut or pierce tissue. Applicator 1202 also includes a
rigid sleeve 1234. The sleeve 1234 has an inner diameter that is
slightly larger than outer diameter of the coaxial cable 1204. As
described below, an annular space is thereby defined between the
outer surface of the coaxial cable 1204 and the inner surface of
the sleeve 1234. The sleeve 1234 further includes one or more
drainage holes 1236 that extend through the sleeve.
[0062] FIGS. 13-18 illustrate a preferred assembly sequence of the
applicator 1202. As shown in FIG. 13, the coaxial cable 1204 is
trimmed so that there is a length "m" of insulator 1208 that
extends beyond an end 1206a of the outer conductor 1206, and a
length "l" of inner conductor 1210 that extends beyond an end 1208a
of the insulator 1208. The ferrule 1212 slides over the exposed
inner conductor 1210 and over the exposed insulator 1208 such that
the first section 1214 surrounds the outer conductor 1206, and the
second and third sections 1216, 1218 surround the exposed portion
of the insulator 1208. The inner surface or flange formed on the
second section 1216 of the ferrule 1212 abuts the end 1206a of the
outer conductor 1206, thereby stopping the ferrule 1212 from
sliding any further up the coaxial cable 1204. The ferrule 1212 is
preferably fixedly attached to the coaxial cable 1204, such as by
soldering the ferrule 1212 to the outer conductor 1206 of the
coaxial cable 1204. In the preferred embodiment, the third section
1218 of the ferrule 1212 extends past the end 1208a of the exposed
insulator 1208 as shown by the dashed line in FIG. 14.
[0063] Next, the spacer 1220 is slid over the exposed portion of
the inner conductor 1210, and is brought into contact with the
second end 1212b of the ferrule 1212. In the preferred embodiment,
the spacer 1220 is not fixedly attached to the ferrule 1212 or the
inner conductor 1210. The spacer 1220 is sized so that a small
portion 1210a (FIG. 15) of the inner conductor 1210 remains
exposed. The tuning element 1224 is then slid over this remaining
exposed portion 1210a of the inner conductor 1210. The tuning
element 1224 is preferably fixedly attached to the inner conductor
1210, e.g., by soldering. The tuning element 1224, in cooperation
with the ferrule 1212, thus hold the spacer 1220 in place.
[0064] With the tuning element 1224 in place, the next step is to
install the tip 1226 as shown in FIG. 16. The open end 1230 of the
tip 1226 is slid over the tuning element 1224, the spacer 1224 and
the third section 1218 of the ferrule 1212. The open end 1230 of
the tip 1226 abuts the second section or step 1216 of the ferrule
1212. The tip 1226 is preferably fixedly attached to the ferrule
1212, e.g., by bonding. With the tip 1226 in place, the next step
is to install the sleeve 1234 (FIG. 17). The sleeve 1234 is slid
over the coaxial cable 1234, and up over the first section 1214 of
the ferrule 1212. The sleeve 1234 abuts the step 1216 in the
ferrule 1212 opposite the tip 1226.
[0065] Those skilled in the art will understand that the applicator
1202 may be assembled in different ways or in different orders.
[0066] As illustrated in FIG. 18, upon assembly, the tip 1226,
second section 1216 of the ferrule 1212, and sleeve 1234 all
preferably have the same outer diameter, thereby giving the
applicator 1202 a smooth outer surface.
[0067] Preferably, the sleeve 1234 is formed from stainless steel,
and the ferrule 1212 is formed from gold-plated copper. The tip
1226 and the spacer 1220 are formed from dielectric materials. In
the illustrative embodiment, the tip 1226 and the spacer 1220 are
formed from an itrium stabilized zirconia, such as the Technox
brand of ceramic material commercially available from Dynamic
Ceramic Ltd. of Stoke-on-Trent, Staffordshire, England, which has a
dielectric constant of 25. The tip 1226 may be further provided
with a composite coating, such as a polyimide undercoat layer, for
adhesion, and a paralyne overcoat layer, for its non-stick
properties. Alternatively, silicone or some other suitable material
could be used in place of paralyne. The composite coating may also
be applied to the ferrule and at least part of the stainless steel
sleeve, in addition to being applied to the tip.
[0068] Those skilled in the art will understand that alternative
materials may be used in the construction of the radiation
applicator 1202.
[0069] FIG. 19 is a schematic, partial cross-sectional view of the
radiation applicator 1202. As shown, at least part of the first
section 1214 of the ferrule 1212 overlies and is attached to the
outer conductor 1206. The insulator 1208 extends partially through
the inside of the ferrule 1212. In particular, the end 1208a of the
insulator 1208 is disposed a predetermined distance back from the
second end 1212b of the ferrule 1212. The inner conductor 1210
extends completely through and beyond the ferrule 1212. The sleeve
1234 slides over and is bonded to the first section 1214 of the
ferrule 1212. As shown, the inside diameter of the sleeve 1234 is
greater than the outside diameter of the coaxial cable 1204,
thereby defining an annular space 1238 between the outside of the
coaxial cable 1204 and the inside of the sleeve 1234. Cooling
fluid, such as saline, is pumped through this annular space 1238,
as shown by arrows A. The cooling fluid absorbs heat from the
coaxial cable that feeds radiation to applicator 1202. The cooling
fluid is then discharged through holes 1236 in the sleeve 1234, as
shown by arrows B.
[0070] In the preferred embodiment, the holes 1236 are placed far
enough behind the closed end 1232 of the tip 1226 such that the
discharged cooling fluid does not enter that portion of the tissue
that is being heated by the radiation applicator 1202. Instead, the
discharged cooling fluid preferably perfuses tissue outside of this
heated region. Depending on the tissue to be treated, a suitable
distance between the closed end 1232 of the tip 1226 and the holes
1236 may be approximately 30 mm.
[0071] A first end 1220a of the spacer 1220 abuts the second end
1212b of the ferrule 1212, while a second end 1220b of the spacer
1220 abuts the tuning element 1224. Accordingly a space, designated
generally 1240, is defined within the ferrule 1212 between the end
1208a of the insulator and the second end 1212b of the ferrule. In
the illustrative embodiment, this space 1240 is filled with air.
Those skilled in the art will understand that the space may be
filled with other materials, such as a solid dielectric, or it may
be evacuated to form a vacuum. The inside surface of the tip 1226
preferably conforms to the shape of the tuning element 1224, the
spacer 1220, and the third section 1218 of the ferrule 1212 so that
there are no gaps formed along the inside surface of the tip
1226.
[0072] As indicated above, operation of the radiation applicator
1202 causes a current to be induced on the outer surface of the
third section 1218 of the ferrule 1212, which is enclosed within
the dielectric material of the tip 1226. This induced current
results in microwave energy being radiated from this surface of the
ferrule 1212, thereby forming one arm of the dipole. The section of
the inner conductor 1210 that extends beyond the ferrule 1212 is
the other arm of the dipole. Both the length of the inner conductor
1210 that extends beyond the ferrule 1212, and the length of the
third section 1218 of the ferrule 1212, which together correspond
to the two arms of the dipole, are chosen to be approximately 1/4
of the wavelength in the dielectric tip 1226, which in the
illustrative embodiment is approximately 6 mm. Nonetheless, those
skilled in the art will understand that other factors, such as
tissue permittivity, the action of the tuning element, etc., will
affect the ultimate lengths of the dipole arms. For example, in the
illustrative embodiment, the two arms are approximately 5 mm in
length.
[0073] The tuning element 1224, moreover, cooperates with the
second section or step 1216 of the ferrule to balance the radiation
being emitted by the two arms of the dipole. In particular, the
size and shape of the tuning element 1224 and the step 1216 are
selected such that the coherent sum of the microwave power
reflected back toward the cable at the aperture of the ferrule is
minimized. Techniques for performing such design optimizations are
well-known to those skilled in the relevant art.
[0074] In use, the radiation applicator 1202 is attached to a
source of microwave radiation in a similar manner as described
above in connection with the applicator 102 of FIG. 1. The coaxial
cable is also attached to a source of cooling fluid in a similar
manner as described above. With the present invention, it is the
dielectric tip, ferrule and stainless steel sleeve that cooperate
to provide the necessary stiffness and mechanical strength for the
applicator to be used in treatment procedures. The applicator does
not rely on the coaxial cable for any of its strength. Indeed, a
flexible coaxial cable, having little or no rigidity, could be used
with the radiation applicator of the present invention.
[0075] The foregoing has been a detailed description of
illustrative embodiments of the invention. Various modifications
and additions can be made without departing from the spirit and
scope thereof. For example, the materials described herein are not
exhaustive, and any acceptable material can be employed for any
component of the described system and method. In addition,
modifications can be made to the shape of various components.
Accordingly, this description is meant to be taken only by way of
example, and not to otherwise limit the scope of the invention.
* * * * *