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.

Claims

1. A method of treating tissue using microwave, comprising: gaining access to the body using a radiation applicator, the applicator comprising: a sharp end to pierce through tissue, the applicator comprising an outer conductor having a proximal end and a distal end; an inner conductor having a proximal end and a distal end; a first dielectric body having a proximal end and a distal end, the first dielectric body is comprised of a first dielectric material having a first dielectric constant, the proximal end of the first dielectric body extends coaxially within the outer conductor; a second dielectric body having a proximal end and a distal end, the second dielectric body is comprised of a second dielectric material having a second dielectric constant, the second dielectric body has a sharp end capable of piecing through tissue, the second dielectric body having a cavity; a tuning reflector having a proximal end and a distal end, the distal most end and the proximal most end of the tuning reflector are both inside the cavity of the second dielectric body, the tuning reflector is comprised of a third dielectric material having a third dielectric constant; the first dielectric constant, the second dielectric constant, and the third dielectric constant are different; and applying microwave energy to the affected tissue.

2. The method of claim 1, wherein the applicator further comprises the inner conductor extending a distance past the distal end of the outer conductor.

3. The method of claim 1, wherein the applicator further comprises a tuning reflector directly connected to the distal end of the inner conductor.

4. The method of claim 3, wherein the applicator further comprises the tuning reflector being soldered to the inner conductor.

5. The method of claim 1, further comprising the step of transferring energy to the second dielectric body at a frequency of up to 10 GHz.

6. The method of claim 1, further comprising the step of inserting the radiation applicator into a human.

7. The method of claim 6, further comprising the step of piercing the tissue with a tapered end the proximal end of the first dielectric body.

8. The method of claim 1, wherein the applicator further comprises a rigid outer conductor.

9. The method of claim 1, wherein the applicator further comprises a flexible outer conductor.

10. The method of claim 7, wherein the applicator further comprises the proximal end of the first dielectric body coaxially extending the distal most end of the outer conductor.

Description

DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described by way of example with reference to the accompanying drawings in which:

(2) FIG. 1 shows an axially section through the tip of the radiation applicator according to the invention, and

(3) 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

(4) 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.

(5) 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.

(6) 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.

(7) 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.

(8) 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.

(9) 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.

(10) 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.

(11) 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.

(12) 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 nacre. 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.

(13) 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.