JPH0221274B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a microwave radiator for heating therapy, and particularly to a microwave radiator for high-frequency dielectric heating that increases the temperature inside a living body by utilizing dielectric loss caused by microwaves. It is known that heating malignant tumors such as cancer at 43 to 45°C for a certain period of time kills cancer cells and makes other treatments more effective. For this reason, a microwave radiator has been proposed as a device for warming a patient inside a living body.
This microwave radiator performs high-frequency dielectric heating that radiates microwaves toward an affected area inside a living body and uses dielectric loss caused within the living body to heat the affected area. For this type of heating treatment,
It is desirable to warm the affected area to a uniform temperature. However, in the case of conventional devices, since microwaves are uniformly radiated toward the affected area, the temperature near the center of the affected area increases too much, which is not desirable. The present invention was made in view of such conventional problems, and its purpose is to provide a microwave radiator for heating therapy that can heat an affected area in a living body to a uniform temperature, for example. . In order to achieve the above object, the present invention is characterized in that microwaves having a donut-shaped spread are radiated toward an object to be heated. In other words, it is a heating treatment microwave that emits microwaves from a radiator supplied with high-frequency power via a coaxial cable toward a patient inside the body, and uses the dielectric loss caused inside the body to heat the patient. In the wave radiator, the radiator has a generally conical outer cone connected to a shielded wire of the coaxial cable and a power supply wire of the coaxial cable, the outer cone having a diameter smaller than the diameter of the outer cone. A substantially conical inner cone inserted into the outer cone is formed of a conductive material, and has a donut-shaped opening formed by a gap between the outer cone and the inner cone, It is characterized by emitting microwaves from the opening toward the affected area in a donut-shaped spread, thereby uniformly warming the affected area. Further, by adjusting the diameter ratio of the outer cone and the inner cone, the coaxial impedance at the connection point between each cone and the coaxial cable is set equal to the impedance of the coaxial cable, and the coaxial impedance at the opening is set to be equal to the impedance of the coaxial cable. It is characterized by setting a value that allows microwaves to be efficiently transmitted to the affected area. Furthermore, a dielectric material having a high dielectric constant is filled between the outer cone and the inner cone. Next, preferred embodiments of the present invention will be described based on the drawings. FIGS. 1 and 2 are detailed explanatory diagrams of the microwave radiator for heating treatment of the present invention. In the figure,
10 is a connector, 12 is this connector 10
This is a microwave radiator for heating treatment that is connected to a coaxial cable 11 via a coaxial cable 11. The microwave radiator 12 includes a substantially conical external cone 14 made of a conductive material and coaxially provided.
and a substantially conical inner cone 16 which has a smaller diameter than the outer cone 14 and is housed in the outer cone 14, and the outer cone 14 is connected to the shielded wire side of the coaxial cable 11 via the connector 10. The inner cone 16 is connected to the core wire of the coaxial cable 11, ie, the power supply line, via the connector 10. And coaxial cable 11
The electric power transmitted through the inner cone 16 converts the electric power into microwaves, and emits the microwaves from a donut-shaped opening 18 formed between the outer cone 14 and the inner cone 16. do. The present invention has the above configuration, and its operation will be explained next. When performing heating treatment on the affected area of a living body using the microwave radiator 12 of the present invention, first, the opening of the microwave radiator 12 is brought into close contact with the living body, and
Position the affected area in the center of the donut shape, and apply power to the internal cone 16 by power supply from the coaxial cable 11.
Generates microwaves with a frequency around 2450MHz. This microwave is radiated from a donut-shaped opening 18 between the outer cone 14 and the inner cone 16 toward the affected area inside the living body with a donut-shaped spread. In this way, the affected area to which the microwave is radiated is dielectrically heated, making it possible to highly effectively treat cancer cells and the like existing in the affected area. Here, since the microwave radiator of the present invention emits microwaves with a donut-shaped spread toward the affected area, the affected area is heated gradually from the periphery toward the center. will be heated to a uniform temperature. That is, a high-frequency alternating electric field is gradually applied from the surroundings of the body to the affected area inside the body, and the heat generated by power loss, that is, dielectric loss, generated in the affected area is used to uniformly dielectrically heat the affected area. Next, the effects of radiating microwaves in a donut shape will be explained in detail using FIGS. 5 to 7 as an example. The fifth reason for dielectric heating in the donut shape of the present invention is as follows.
An explanation will be given by taking as an example the model of the object to be heated and the blood flow shown in the figure. In FIG. 5, a tumor tissue X is shown as a body to be heated with a radius a in contrast to a normal tissue Y. In this tumor tissue X, for example, as shown in FIG. 6, the blood flow within the tumor is large in the peripheral portion (near radius a) and is almost zero in the central portion. Here, conventionally, when the tumor tissue X is irradiated with microwaves, the tissue temperature distribution is calculated as follows.
The temperature distribution is determined by the following heat conduction equation. That is, ρcdT′/dt=kΔ ² T′−Vs(T′−To)+Q...(1) where T′ is temperature, To is temperature of blood flow, ρ is tissue density, c is tissue specific heat, k is tissue thermal conductivity, Vs
represents blood flow and Q represents fever. Therefore, according to the above equation (1), when the tumor tissue X shown in FIG. 5 is dielectrically heated uniformly by microwave radiation in the conventional method, the temperature distribution is expressed by the following equation due to heat conduction. That is, T=To-Q/4( _r2 - _a2 )...(2). The temperature distribution characteristic shown by this equation (2) has a high temperature at the center as shown in Figure 7, and
It becomes a characteristic that decreases with the power of As a result, in the conventional microwave radiator, since the blood flow is small in the central part, the transfer of heat due to the blood flow is small, and it is easy to locally heat only this central part. From the above, the tumor tissue X shown in FIG.
When heating dielectrically, in order to obtain a more uniform temperature distribution, it was necessary to avoid heating only the central portion shown in FIG. For this reason, the microwave radiator of the present invention radiates microwaves to the affected area in a doughnut-shaped heating pattern 18' as shown in FIG. By this donut-shaped heating pattern 18',
This makes it possible to heat the affected area more effectively and uniformly than before. Of course, in the present invention, the donut-shaped microwave radiation gradually warms the affected area from around it, but it does radiate to the outside. However, it is also possible to provide the amount of heat generated by the divergence using, for example, another high-frequency oscillator.
Further, since the outside is heated only by heat conduction from the affected area, the outside cannot reach a higher temperature than the affected area, and the affected area can be heated evenly. Therefore, unlike when using a conventional microwave radiator, there is no problem of the temperature at the center of the affected area rising too much, and it is possible to obtain an effective therapeutic effect. By the way, in the microwave radiation as described above, reflection at the connection part of the coaxial cable 11 and reflection at the contact interface with the living body pose problems. In this embodiment, such a problem of reflection is solved by taking the following measures. First, if the radius of the outer cone 14 is b and the radius of the inner cone 16 is a, then the coaxial impedance Z of the microwave radiator 12 is It is expressed as However, μ is magnetic permeability, ε is dielectric constant,

[Formula] is 120π in the case of air. Then, by adjusting the radii b and a of each of the cones 14 and 16, the coaxial impedance Z of the microwave radiator at the connection part with the connector 10 is set equal to the impedance of 50Ω of the coaxial cable 11, and the Matching is achieved, and the coaxial impedance Z of the opening 18 of the microwave radiator is set to a value (18Ω in this embodiment) that allows microwaves to be efficiently transmitted to the living body, thereby achieving matching between both members. With the above structure, when microwave energy is supplied from the coaxial cable 11 to the microwave radiator 12, reflection that occurs at the connection part can be significantly suppressed, and further, the When emitting microwaves toward the body, reflection that occurs at the interface between the opening 18 and the living body can be significantly suppressed. Note that the gap 20 between the outer cone 14 and the inner cone 16
The above-mentioned matching can be made even better by filling the substrate with a dielectric material having a high dielectric constant, such as alumina haica cement (dielectric constant ε _r =8). In this case,
√ in the first equation is

[Formula] becomes. In Figure 3, the wavelength of the emitted microwave is λ,
The length l of the external cone 14 was set to l = λ/4, and a microwave radiator was used that gently reduced the coaxial impedance Z from 50Ω to 9Ω from the connector joint portion toward the opening 18, and was brought into close contact with the opening 18. It is a reflection coefficient characteristic diagram when microwaves are radiated toward a hand. FIG. 4 is a reflection coefficient characteristic diagram when microwaves are emitted from the same microwave radiator toward a hand with a thin vinyl film in between. As is clear from the figure, microwaves are emitted by directly touching the opening 18 and the microwave frequency is emitted.
It is understood that when varied between 2100 and 2500 MHz, the reflection coefficient of microwave energy is -10 dB or less (transmission rate of 90% or more). Similarly, when a hand is placed in close contact with the opening 18 through a thin vinyl film, the reflection coefficient of microwave energy is -
It can be set to 10 dB or less, and at most -27 dB or less (transmission rate of 99.8% or more). The following table is obtained from the data in FIGS. 3 and 4.

[Table] Tables 2 and 3 show the actual measured values of the reflection coefficient of microwave energy obtained by changing the coaxial impedance Z in the opening 18. 1
Table 3 shows the measured values when the voids 20 in No. 2 were filled with air, and Table 3 shows the measured values when the voids 20 were filled with alumina haica cement. Table 2 and 3
From the table, it is understood that good characteristics can be obtained when the void 20 is filled with alumina Hica cement and the coaxial impedance Z of the opening 18 of the microwave radiator 12 is set to 9Ω.

【table】

[Table] When performing actual heating treatment using such a microwave radiator, it is conceivable to cover the opening 18 with Teflon, silicone rubber, etc. for insulation. Even in this case, the same characteristics as described above can be obtained by adjusting the length l of the external cone 14 and the coaxial impedance Z of the microwave radiator. Furthermore, by filling the void 20 with a dielectric material having a high dielectric constant, it is possible to reduce the dimensions, for example, length l and diameters a and b of the outer cone 14 and the inner cone 16 as conductive materials. Further, the microwave radiator 12 of this embodiment is effective as a lateral irradiation type for the coaxial cable 11. As described above, according to the present invention, it is possible to heat an object to be heated, such as an affected part of a living body, to a uniform temperature by emitting microwaves with a doughnut-shaped spread toward the object. In particular, it is possible to effectively treat cancer and the like.

[Brief explanation of drawings]

Fig. 1 is a side view of the microwave radiator for heating treatment according to the present invention, Fig. 2 is a front view thereof, and Fig. 3 is an explanatory side view of the microwave radiator for heating treatment according to the present invention. Reflection coefficient characteristic diagram when
The figure shows the reflection coefficient characteristics when the hand is closely attached to the microwave radiator through vinyl and microwaves are emitted toward the hand. Figure 5 shows the affected area as the object to be heated and the donut-shaped heating pattern. An explanatory diagram showing the positional relationship as an example, FIG. 6 is a characteristic diagram showing the blood flow inside the affected area, and FIG. 7 is a characteristic diagram showing the temperature distribution when the affected area is heated. Corresponding members in each figure are designated by the same reference numerals, and 12
is a microwave radiator, 14 is an external cone, 16 is an internal cone, 18 is an opening, and 20 is a void.

Claims (1)

[Claims] 1. Microwaves are emitted from a radiator supplied with high-frequency power via a coaxial cable toward an affected area inside a living body, and the affected area is treated by heating using dielectric loss caused within the living body. In a microwave radiator for heating therapy, the radiator includes a substantially conical external cone connected to a shielded wire of the coaxial cable, and a substantially conical external cone connected to a power supply line of the coaxial cable and having a diameter larger than the diameter of the external cone. a generally conical inner cone with a small diameter inserted into the outer cone; and a donut-shaped opening formed by a conductive material between the outer cone and the inner cone. A microwave radiator for heating treatment, characterized in that it radiates microwaves with a doughnut-shaped spread toward a living body from the opening to uniformly warm an affected area within the living body. 2. In the radiator according to claim 1, by adjusting the diameter ratio of the outer cone and the inner cone, the coaxial impedance at the connection point between each cone and the coaxial cable can be adjusted to the impedance of the coaxial cable. A microwave radiator for heating treatment, characterized in that the coaxial impedance at the opening is set to a value that allows microwaves to be efficiently transmitted to the affected area. 3. A microwave radiator for heating therapy according to claims 1 and 2, characterized in that a dielectric material having a high dielectric constant is filled between the outer cone and the inner cone. .