U.S. patent application number 10/561701 was filed with the patent office on 2007-02-22 for radiation applicator for microwave medical treatment.
Invention is credited to Nigel Cronin.
Application Number | 20070043346 10/561701 |
Document ID | / |
Family ID | 27637182 |
Filed Date | 2007-02-22 |
United States Patent
Application |
20070043346 |
Kind Code |
A1 |
Cronin; Nigel |
February 22, 2007 |
Radiation applicator for microwave medical treatment
Abstract
A radiation applicator with a dielectric body (2) surrounding
the antenna The dielectric body (2) is comprised of three sections
(3, 4 and 5) with different dielectric constants to provide
broad-band matching of the applicator to surrounding material.
Washers (10) and (11) are mounted on the antenna to act as
reflectors.
Inventors: |
Cronin; Nigel; (Lane Bath,
GB) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA
101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Family ID: |
27637182 |
Appl. No.: |
10/561701 |
Filed: |
June 18, 2004 |
PCT Filed: |
June 18, 2004 |
PCT NO: |
PCT/GB04/02620 |
371 Date: |
August 9, 2006 |
Current U.S.
Class: |
606/33 ; 607/101;
607/156 |
Current CPC
Class: |
A61B 2018/183 20130101;
A61B 2018/1869 20130101; A61B 2018/1892 20130101; A61B 2018/1861
20130101; A61B 18/18 20130101; A61B 18/1815 20130101 |
Class at
Publication: |
606/033 ;
607/101; 607/156 |
International
Class: |
A61B 18/18 20070101
A61B018/18 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 23, 2003 |
GB |
0314631.3 |
Claims
1. A radiation applicator having one end and an opposite distal
end, the radiation applicator comprising: a power input at said one
end, an elongate antenna extending axially of the applicator at
said distal end, and a dielectric body which surrounds the antenna
and serves to emit radiation radially of the dielectric body into
surrounding material, the dielectric body comprising multiple
sections of different dielectric constant which are located axially
relative to one another along the antenna.
2. An applicator as claimed in claim 1 in which, the dielectric
body consists of a second section adapted to emit radiation, and a
first section between the second section and the power input, and
having a lower dielectric constant than the first section.
3. An applicator as claimed in claim 2 in which the dielectric body
has an outer section furthest from the power input having a
dielectric constant lower than that of the second section.
4. An applicator as claimed in claim 3 in which the outer section
has a dielectric constant intermediate that of the first and second
sections.
5. An applicator as claimed in claim 1 in which, the multiple
sections are made as separate components and are assembled to abut
against one another end-to-end.
6. An applicator as claimed in claim 1 in which, a radiation
reflector is provided at the interface between two sections of the
dielectric body so as to modulate the transmission of radiation and
tune the applicator.
7. An applicator as claimed in claim 6 in which, a radiation
reflector is provided each side of a section which is intended to
emit radiation into the surrounding material, a reflector on that
side further from the input end having a larger area so as to
reflect more energy than the reflector nearer the input end,
thereby reducing transmission of radiation to the tip of the
applicator.
8. A radiation applicator having one end and an opposite distal
end, the radiation applicator comprising: a power input at said one
end, an elongate antenna extending axially at said distal end for
emitting radiation into surrounding material, a dielectric body
which surrounds the antenna, and a plurality of radiation
reflectors located axially along the antenna within the dielectric
body to modulate the transmission of radiation, wherein two
radiation reflectors are axially spaced apart with an intermediate
section of the dielectric body disposed between said two radiation
reflectors and intended to emit radiation radially into the
surrounding material, the reflector on one side further from the
input having a larger area so as to reflect more radiation than the
reflector nearer the input end, thereby reducing transmission of
radiation to the tip of the applicator.
9. An applicator as claimed in claim 6 in which, the reflector is
located at an interface between separate sections of the dielectric
body and gives structural support to the applicator.
10. An applicator as claimed in claim 1 in which an outer end of
the dielectric body furthest from the power input is pointed.
11. An applicator as claimed in claim 1 in which the power input
comprises a coaxial conductor having a central conductor and an
outer conductor, and in which the central conductor extends from
the outer conductor to form said elongate antenna.
12. An applicator as claimed in claim 11 in which the dielectric
body has a reduced diameter and which is inserted into an open end
of the outer conductor.
13. A radiation applicator having one end and an opposite distal
end, the radiation applicator comprising: a power input at said one
end, an elongate antenna extending axially at said distal end for
emitting radiation into surrounding material, and a dielectric body
which surrounds the antenna, wherein the antenna extends through a
hole in a section of said dielectric body and through a hole in a
radiation reflector attached to an axial end face of said section
of dielectric body, and said radiation reflector is attached to the
antenna so as to give structural support to the applicator.
14. A radiation applicator having one end and an opposite distal
end, the radiation applicator comprising: a power input at said one
end, an elongate antenna extending axially of the applicator at
said distal end, and a dielectric body which surrounds the antenna
and serves to emit radiation radially of the antenna into
surrounding material, wherein the dielectric body comprises
multiple sections of different dielectric constant which are
located axially relative to one another along the antenna.
Description
TECHNICAL FIELD
[0001] This invention relates to radiation applicators and, in
particular, to microwave medical treatment devices.
PRIOR ART
[0002] A known radiation applicator used for microwave medical
treatment is shown in PCT/GB00/00682 and comprises a generator
which supplies microwave energy via a coaxial conductor to a tip
region at the distal end of the conductor. Dielectric packing is
provided between the inner and outer conductors of the coaxial
conductor but a length of the inner conductor at the tip projects
beyond the outer conductor so as to form an antenna to emit
radiation. The antenna is embedded axially in a cylindrical body of
dielectric which has the same outer diameter as the coaxial
conductor. A pointed tip at the end of the dielectric body serves
to assist penetration into biological matter, such as a liver to
perform ablation on a tumour.
DISCLOSURE OF THE INVENTION
[0003] According to one aspect of the invention, a radiation
applicator has a power input at one end, an elongate antenna
extending axially at its distal end for emitting radiation into
surrounding material, and a dielectric body which surrounds the
antenna, characterised in that the dielectric body consists of
multiple sections of different dielectric constant which are
located axially relative to one another along the antenna.
[0004] The dielectric constant of each section of the dielectric
body is selected so as to tune the applicator to operate at a
particular frequency or range of frequencies for optimum
performance in transferring energy to the surrounding material of
predetermined dielectric constant. For example, energy transfer
from the applicator to the surrounding material may change the
physical properties of that material and the sectioned nature of
the dielectric body may, in some embodiments, permit a broadband
match of the applicator to the surrounding material so as to allow
efficient energy transfer to the material to continue despite
changes in the properties of the material.
[0005] Preferably, the dielectric body consists of three
consecutive sections: a first section adjacent the power unit, a
second first section adapted to be the major emitter of radiation,
and a third tipsection. The second section has a higher dielectric
constant than the first section. The higher dielectric constant of
the second section allows the overall length of the dielectric body
to be made shorter than would otherwise be required if the
dielectric body was composed entirely of the material of the first
dielectric, the length being related to the wavelength of the
radiation in the dielectric. The third, tip section, is composed
entirely of a material with a dielectric value from the other two
sections and is chosen as a match to the surrounding material. The
use of multiple sections of different dielectric constant allows
the reflections from the dielectric interfaces to be used for
matching or turning at the power input to ensure optimum power
transfer.
[0006] Preferably, the dielectric body has a tip section furthest
from the power input which is pointed so as to penetrate the
surrounding material in use. The fact that the tip is composed of a
dielectric material and not an electrical conductor serves to avoid
local surface heating. Preferably, the dielectric constant of the
tip is less than that of the second section, and is preferably
intermediate that of the first and second sections.
[0007] The multiple sections could be made as an integral body, or
made as separate components assembled together to abut against one
another end-to-end.
[0008] According to a further feature of the invention, a radiation
reflector is provided at the interface between sections of the
dielectric body so as to modulate the transmission of radiation and
further tune the applicator. Preferably, a radiation reflector is
provided each side of the section which is intended to emit
radiation into the surrounding material, a reflector on that side
further from the input end having a larger area so as to reflect
more energy than the reflector nearer the input end, thereby
reducing transmission of radiation to the tip of the applicator.
The emission of radiation from the dielectric body can therefore be
more localised in one section. Preferably, the invention is
designed to radiate more energy from the second section.
[0009] According to a second aspect of the invention, a radiation
applicator has a power input at one end, an elongate antenna
extending axially at its distal end for emitting radiation into
surrounding material, and a dielectric body which surrounds the
antenna, characterised in that one or more radiation reflectors are
located axially along the antenna within the dielectric body to
modulate the transmission of radiation.
[0010] Preferably, two radiation reflectors are spaced apart with
the intermediate section of the dielectric body being intended to
emit radiation into the surrounding material, the reflector on one
side further from the input having a larger area so as to reflect
more radiation than the reflector nearer the input end, thereby
reducing transmission of radiation to the tip of the
applicator.
[0011] Preferably, the reflectors, as used in connection with
either the first or second aspect of the invention, are located at
the interface between separate abutting sections of the dielectric
body and help give structural support to the applicator. For
example, the reflectors can be soldered or otherwise bonded to
sections of the dielectric body and antenna
DESCRIPTION OF THE DRAWINGS
[0012] The invention will now be described by way of example with
reference to the accompanying drawings in which:
[0013] FIG. 1 shows an axially section through the tip of the
radiation applicator according to the invention, and
[0014] FIG. 2 shows a graph of reflected radiation at the input of
the radiation applicator of FIG. 1 against the input frequency.
EMBODIMENTS OF THE INVENTION
[0015] The radiation applicator illustrated in FIG. 1 comprises a
coaxial conductor 1, which may be rigid or flexible, and which is
connected to a microwave power supply at one end (not shown) and
terminates at its other end in a radiation emitting tip 2. The tip
2 consists of a cylindrical dielectric body composed of three
sections 3,4,5, coaxially aligned and abutting one another at
interfaces between them so as to form a continuous body. One outer
section 3 is connected to the end of the coaxial conductor 1. A
portion 6 of the section 3 at one end is of reduced diameter and is
inserted a short distance into the outer conductor 7 of the coaxial
conductor to make a secure connection. The central conductor 8 of
the coaxial conductor extends through an axial hole 9 in the body
2, through all three sections but terminating within the outer
third section 5. During assembly, a metal washer 10 is soldered to
the section 3 at the interface with section 4, and is soldered to
the central conductor 8; and a second metal washer 11 is soldered
to the middle section 4 at the interface with the third section 5,
and is soldered to the central conductor 8. The washers 10 and 11
therefore serve to secure the two sections 3 and 4 of the
dielectric body to the end of the coaxial conductor 1 via the
central conductor 8. The third section 5 is then bonded to the
second washer 11 and central conductor 8.
[0016] The third section 5 of the applicator has a pointed shape to
assist insertion into material to be treated, and this will be made
as sharp as is necessary for the application, for example, the
treatment of liver cancer.
[0017] In operation, that portion of the central conductor 8 that
extends from the outer conductor 7, acts as an antenna to emit
radiation. The wavelength of the radiation within the dielectric
body is determined by the frequency of the power supply and the
dielectric constant of the various components. Thus the wavelength
of the radiation is different in each of the three sections 3, 4
and 5. By appropriate selection of the dielectric constant of these
three sections relative to one another and to the surrounding
material in which the applicator is to be used, it is possible to
tune the applicator to give optimum performance.
[0018] Another factor which affects the tuning of the applicator is
the metal gaskets 10 and 11 which act as radiation reflectors. Both
gaskets serve to reflect radiation back to the input, and with
appropriate matching at the input ensures a maximum transfer of
energy to the tip 2. The gasket 11 has a larger surface area than
the gasket 10 so as to reduce the amount of energy transmitted to
the third section 5.
[0019] Other factors which affect tuning are the length of the
central conductor 8 extending beyond the outer conductor 7, the
diameter and axial length of the individual dielectric sections 3,
4 and 5, and the thickness and diameter of the washers 10,11.
[0020] It will be appreciated that the choice of dielectric
materials and dimensions of the various components allows great
flexibility in designing a radiation applicator to suit a wide
range of applications and performance requirements, bearing in mind
that the dielectric constant of the surrounding material when the
device is in use, will effect performance.
[0021] For example, a radiation applicator designed for medical use
has the dimensions shown in FIG. 1 and the following further
specifications: the washer 10 has an outer diameter of 1.9 mm; the
washer 11 has an outer diameter of 2.7 mm; the central conductor 8
protrudes beyond the outer conductor by 8.5 mm; and the dielectric
sections 3,4,5 are composed, respectively, of alumina with
dielectric constant 10, titanium oxide with dielectric constant 100
and a Ca--Ti--Nd--Al dielectric with dielectric constant 47. The
applicator of this example is capable of operating well at
frequencies in the vicinity of 3 GHz. In particular, the applicator
of this example is especially suited to operation at a frequency of
2.45 GHz and a power of 50 W.
[0022] The performance of the applicator of the above example is
illustrated in FIG. 2. This shows the power reflected from the tip
of the applicator against the operating frequency, and shows that
there is a dip in the reflected power at about 2.45 GHz, which
corresponds to a maximum transfer of energy to the tip at this
frequency. The width of the dip in FIG. 2, which is about 0.6 GHz,
gives the applicator a broadband characteristic which allows it to
better accommodate use with surrounding materials with a range of
dielectric constant values.
[0023] In alternative embodiments of the invention, other
dielectric materials may be used, including air, and instead of
three dielectric sections there may be just two or may be four or
more. Grooves may be formed in the outer surface of each or any of
the dielectric section circumferentially. Also, the dielectric
sections may be tapered longitudinally.
[0024] Also, an imaging process could be used to guide the
applicator to the desired location. The applicator may be of small
enough diameter to be inserted through a guidewire, such as used in
ultrasound imaging techniques, so as to ensure accurate treatment
in use.
* * * * *