JP2584665B2 - Microwave radiator for hyperthermia - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a microwave radiator for warming therapy, and is particularly suitable for performing warming therapy by directly piercing a diseased part. The present invention relates to a microwave radiator for hyperthermia.

[Conventional technology]

Conventionally, as this type of applicator for heating therapy, there is one shown in FIGS. 8 (1) (2) to 9 (1) (2).

The conventional example shown in FIG. 8 (1) is similar to a monopole antenna, and has the same structure as that of the coaxial cable in which the outer conductor at the distal end is removed. Specifically, it includes a central conductor 40 provided at the center, a dielectric 41 provided around the central conductor 40, and an outer conductor 42 provided around the dielectric 41. . The outer conductor 42 has a structure in which only a predetermined length A is removed at the tip.

As shown in FIG. 8 (2), this type of heating therapy applicator is provided with a so-called super top (also referred to as a choke) 43 having an opening at the base end of a monopole. The current flowing on the surface of the outer conductor is blocked, and the normal tissue in the outer conductor is prevented from overheating.

In the conventional example shown in FIG. 9 (1), a strip-shaped conductor 50 is spirally wound around the outer surface of the dielectric 41 of the conventional example shown in FIG. 8 (1), thereby forming a helical slit. That is, the feature is that the spiral slit 51 is formed.
The conventional example shown in FIG. 9 (1) is described in, for example,
No. 961 discloses this as a body cavity insertion type. On the other hand, the one disclosed in Japanese Utility Model Publication No. 61-33961 can also be used for puncturing and heating into a lesion tissue by miniaturizing the same.

[Problems to be solved by the invention]

However, the above-mentioned conventional example has a serious drawback in the function of heating a lesion.

 Hereinafter, this will be described in detail.

First, FIGS. 8 (1) (2) to 9 (1)
In the conventional example shown in (2), the length of the center conductor protruding from the coaxial cable portion B is basically set to about "1/4" wavelength. Specifically, in human muscle tissue,
If the frequency used is 400 (MHz), 2.0 (cm); 200
3.1 (cm) at (MHz); 5.5 (cm) at 100 (MHz); 60 (MHz)
Requires a length of 8.5 cm, and if shorter than these,
The matching of the input impedance deteriorates, and the radiation efficiency deteriorates.

On the other hand, in the heating therapy, it is desirable that a single microwave radiator can be used for a wide range of lesions without the heating therapy. This is important because it also reduces the patient's pain caused by inserting many microwave radiators into the body.

By the way, body tissue can be treated as a kind of dielectric loss material including malignant tumor tissue. For this reason, the lower the frequency of electromagnetic waves, the better the permeability.

For example, when microwaves are radiated from the surface to the intramuscular tissue, the penetration depth at which the power is halved is 4
About 1.0 (cm) at 00 (MHz); about 1.4 (cm) at 200 (MHz); 100
It is about 2.2 [cm] at [MHz]; and about 3.0 [cm] at 60 [MHz]. This indicates that it is necessary to select a frequency according to the length of the lesion from the body surface to the depth direction in the heating therapy using the one shown in FIGS. 8 (1) and (2). I have. Therefore, the selection of the working frequency is independent of the lateral spread of the lesion.

Therefore, for flat and laterally expanding lesions, an adapter operating at a high frequency must be used.
Also, high frequencies require a large number of microwave radiators due to poor penetration into tissue. At the same time, this has the disadvantage that the patient requires a lot of puncture and is therefore painful.

9 (1) is originally of a type inserted into a body cavity, but can also be used as a piercing type as described above. In FIG. 9 (1), a spiral continuous slit 51 is provided in an outer conductor 42 of a high-frequency coaxial cable body or the like as described above, and an inner conductor 40 The structure is short-circuited.

The intention of the microwave radiator shown in FIG. 9 (1) is heating by a leak wave from the spiral slit 51. However, in practice it does not work that way.

That is, the helical slit 51 provided in the high-frequency coaxial cable body, which is extremely thin compared to the wavelength, forms a helical antenna in which the circumference of one turn is extremely short compared to the wavelength in the conductor remaining on the outer conductor 42. Due to that. This spiral antenna has little matching with the coaxial line (ie, inner conductor),
Poor emissivity is generally well known.

On the other hand, in this case, since the inner conductor of the high-frequency coaxial cable body exists at the position of the helical axis, this structure also propagates a wave whose phase speed is very close to the speed of light (3 × 10 ⁸ [m / sec]). Let me know. That is, the surface wave propagates. Then, compared with the case of using only a spiral antenna having an extremely small wavelength as compared with the above-mentioned structure, the matching of the input impedance is somewhat improved. The reason is that the presence of the inner conductor acts as a surface wave transmission path. However, this surface wave rapidly attenuates (see FIG. 9 (2)) as it goes away from the axis of the transmission line (the direction of the inner conductor). For this reason, the heating region is limited to a transmission line, that is, a very close vicinity of the microwave radiator. Therefore, in the conventional example shown in FIG. 9 (1), almost the same effects as those shown in FIGS. 8 (1) and (2) can be obtained.

[Object of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a microwave radiator for hyperthermia, which can solve the disadvantages of the conventional example and in particular can spread electromagnetic energy widely into a lesion.

[Means for solving the problem]

Therefore, in the present invention, a relatively thin high-frequency coaxial cable body including a relatively thin inner conductor disposed at the center and an outer conductor disposed around the inner conductor via a dielectric is provided. I have. An inner conductor and a dielectric are respectively extended on an extension of the same center line of the high-frequency coaxial cable body. Then, a plurality of annular conductors are mounted on the outer peripheral surface of the extended dielectric portion at equal intervals. This aims to achieve the above-mentioned object.

(Example of the invention)

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

The embodiment shown in FIG. 1 has a relatively thin inner conductor 1 disposed at the center and an outer conductor 3 disposed around the inner conductor 1 via a dielectric 2. The high-frequency coaxial cable body 10 is provided.

On the extension of the same center line of the high-frequency coaxial cable body 10, an inner conductor 1 and a dielectric 2 extend respectively.
Among them, a plurality of annular conductors 4, 4,... Are provided at equal intervals on the outer peripheral surface of the extended dielectric portion 2A. Reference numeral l ₀ denotes the distance (slit width) between each other in each annular conductor 4.

Further, a conductive member 5 is provided between the inner conductor 1 and the annular conductor 4 located at the foremost end of each of the aforementioned annular conductors 4. Reference numeral 9 denotes a protective film. This protective film 9
Uses a polymer compound coating harmless to human tissues. Symbol d indicates the diameter of the outer conductor 3 described above. The diameter d of the outer conductor 3 is set, for example, to 0.5 [mm] to 1.0 [mm]. The distance (slit width) l ₀ between mutual extension設誘material portion length of 2A A and each annular conductor 4 is arranged to be specified in advance in accordance with the use frequency. FIG. 2 is a sectional view taken along the line II-II of FIG.

Next, the operation of the embodiment shown in FIGS. 1 and 2 will be described.

First, a plurality of annular conductor 4 that is provided on the extension設誘material portion 2A is annular slit with a distance l ₀ between their mutual
Forming an array. For this reason, this annular slit
The array is represented by an equivalent circuit as shown in FIG.

In FIG. 3, _Vf indicates a high-frequency voltage applied to the coaxial cable. Further, C _{1 to} C _n indicate equivalent capacitances generated by the high-frequency current flowing on the outer conductor being cut by the slit and being converted into a displacement current, and R _{1 to} R _n are:
At this time, the radiation resistance indicates the magnitude of the electromagnetic wave radiated by the slit. Furthermore, Z _L
Shows the load attached to the end of the array. In the case of FIG.
The load Z _L is set to “Z _L = 0” by the action of the conductive member 5.
[Ω] ”.

Next, a specific operation will be described. The high-frequency voltage applied to the high-frequency coaxial cable body 10 derives a current determined by the characteristic impedance of the cable body 10 to the inner and outer conductors 1 and 3. The transmission mode transmitted to the coaxial cable body 10 is, as is well known, the TEM ₁ mode, which generates a current on the outer conductor 3 of the coaxial cable body 10 in the length direction. Therefore, this current crosses the annular slit disposed on the outer conductor 3 at right angles. In this case the capacity and the radiation resistance is changed according to the width l ₀ of the slit. That is, if the width l _{0 of} the slit is too wide, the high-frequency coaxial cable body 10 is in an open state, and if the width is too narrow, the capacity is equivalently large, so that the slit is short-circuited and the radiation resistance is “0 [Ω ]] ”.

Therefore, slit width l ₀ is determined according to the frequency of the electromagnetic wave that excites the slit portion.

Here, the embodiment shown in FIG. 1 is used in a state of being inserted into a lesion in the body. For this reason, the diameter is as thin as 0.5 [mm] to 1.0 [mm] as described above.

On the other hand, the annular slit completely cuts off the actual current flowing through the outer conductor 3 of the high-frequency coaxial cable body 10, so that the surface current flows along the spiral conductor 50 as in the conventional example of FIG. No transmission mode occurs. For this reason, radiation waves are generated effectively, and dielectric loss in the body tissue causes
The surroundings are effectively warmed as a whole.

 Next, another embodiment will be described.

FIG. 4 shows an embodiment shown in FIG.
Shows the case where is removed. In this case, in the equivalent circuit of FIG. 3, “Z _L ≒ ∞”, which means that the tip is set to the open state. Even in this case, radiant energy is effectively output.

FIG. 5 shows the slit width in the embodiment shown in FIG.
The feature is that the width of l ₀ is sequentially changed to “l ₁ ≠ l ₂ ≠ l ₃ ... ≠ l _n ”.

In this case, all the annular conductors 4 have the same width.

In FIG. 6, the slit width is changed to “l ₁ ≠ l ₂ ≠ l ₃ ... ≠ l _n ” as in the case of FIG.
At the same time, adjust the width of the annular conductor according to the change in slit width.
The feature is that it is changed like 4 ₁ , 4 ₂ , 4 ₃ ... 4 _n .

Even in this case, in addition to the function equivalent to that of FIG. 1, there is an advantage that the width of the heating depth (heating depth region) can be changed by changing the frequency.

Further, FIG. 7 is characterized in the embodiment shown in FIG. 1, the point equipped with load Z _x having the same impedance value and the characteristic impedance of the high-frequency coaxial cable 10 described above in place of the conductive member 5 have.

This eliminates reflection at the terminal end, so that a microwave radiator with good energy efficiency can be obtained.

〔The invention's effect〕

As described above, according to the present invention, the high-frequency current flowing on the outer conductor can be effectively suppressed, whereby the microwave energy can be effectively radiated.
To provide an unprecedented superior microwave radiator for warming therapy in which, when the microwave radiator is inserted into a heated portion, the surrounding area can be effectively heated over a relatively high range. Can be.

[Brief description of the drawings]

FIG. 1 is a partially sectional front view showing one embodiment of the present invention,
2 is a sectional view taken along the line II-II in FIG. 1, FIG. 3 is a circuit diagram showing an equivalent circuit when FIG. 1 is generalized, and FIGS. FIGS. 8 (1) (2) to 9 (1) (2) are explanatory views showing examples of the related art. 1 ... Inner conductor, 2 ... Dielectric, 2A ... Extended dielectric part, 3
…… Outer conductor, 4,4 ₁ , 4 ₂ , 4 ₃ , ～ 4 _n …… Circular conductor, 5 ……
Conducting member, 10 ... High-frequency coaxial cable body, l ₀ , l ₁ , l ₂ , l ₃ ,
~ L _n ... slit width.

Claims (5)

(57) [Claims] 1. A relatively thin inner conductor disposed at the center,
A relatively thin high-frequency coaxial cable body composed of an outer conductor disposed around the inner conductor via a dielectric is provided. On the extension of the same center line of the high-frequency coaxial cable body,
The inner conductor and the dielectric are respectively extended, and a plurality of annular conductors of the same length are attached at equal intervals on the outer peripheral surface of the extended dielectric portion, for heating therapy. Microwave radiator. 2. The microwave radiator for heating therapy according to claim 1, wherein intervals between said plurality of annular conductors are set to different intervals. 3. The microwave radiator for warming therapy according to claim 1, wherein the width of the plurality of annular conductors is gradually reduced from one to the other. 4. A relatively thin inner conductor disposed at the center,
A relatively thin high-frequency coaxial cable body composed of an outer conductor disposed around the inner conductor via a dielectric is provided. On the extension of the same center line of the high-frequency coaxial cable body,
The inner conductor and the dielectric are respectively extended, and a plurality of annular conductors are mounted at equal intervals on the outer peripheral surface of the extended dielectric portion. A microwave radiator for heating therapy, wherein a conductive member is provided between the located annular conductor and the inner conductor. 5. A relatively thin inner conductor disposed at the center,
A relatively thin high-frequency coaxial cable body composed of an outer conductor disposed around the inner conductor via a dielectric is provided. On the extension of the same center line of the high-frequency coaxial cable body,
The inner conductor and the dielectric are respectively extended, and a plurality of annular conductors are mounted at equal intervals on the outer peripheral surface of the extended dielectric portion. A microwave radiator for heating therapy, wherein a non-reflective end is provided between the annular conductor and the inner conductor.