JPS6025977B2 - radiation therapy equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a radiation therapy apparatus that accelerates electrons and irradiates them onto an irradiated object for treatment.

This device accelerates electrons emitted from an electron gun using an accelerating tube, deflects the accelerated electrons using a deflection tube installed at the tip of the accelerating tube, and then collides them with a heavy metal target to emit X-rays. This device performs treatment by converting the radiation into radiation and irradiating the lesion with this radiation. By the way, as the acceleration energy increases, the overall length of the accelerator tube becomes longer.On the other hand, in the case of a treatment device, the location of the lesion differs from patient to patient, and the positions that the patient can take are also limited. The acceleration direction of electrons in the accelerating tube cannot be made the same as the radiation irradiation direction, and therefore a deflection magnet (electromagnet) is required to deflect the accelerated electron beam in a predetermined direction.

The deflected electron beam collides with the irradiated object and is converted into X-rays.The X-rays form a radial lacquer cloth from the point of impact on the target and are emitted forward. It is used for treatment by irradiating the affected area. The radiation therapy apparatus is equipped with a collimator made of a heavy metal block to set the radiation field depending on the size of the affected area. In addition, the intensity distribution of radiation within the irradiation field is made uniform so that radiation irradiation can be performed as planned.
A flattening filter is installed below the target. FIG. 1 shows the radiation distribution when a conventional deflection magnet having such a function is used. In the figure, 1 is a pole piece that supplies a magnetic field for deflecting an electron beam using a conventional deflection magnet. 2 is a heavy metal target provided on the electron travel path near the electron sending side exit of this deflection magnet 1; 3 is this target 2;
A flattening filter is provided in front of the target 2 to make uniform the intensity distribution of the radiation converted and emitted by the target 2, 4 is a collimator, and 5 is a collimator that accelerates the radiation with an accelerator tube and returns it to the deflection magnet 1 even on a normal trajectory. This is an incident electron beam.

Here, in order to simplify the analysis, the explanation will be made with the flattening filter 3 removed from FIG. 1.

Now, if the electric charge of an electron is e, its mass is m, its velocity is v, and the magnetic flux density of the deflection magnet 1 is B, then the electron incident on the deflection magnet 1 has a radius of curvature r=m. v/e. It passes through the magnet while drawing a circular orbit B, and when it reaches the end of the deflection magnet 1, it then moves straight in the tangential direction of the circular orbit. At this time, the electron beam whose energy is equal to that set in the normal orbit travels along the orbit shown by 6 and collides with the center of the target 2. The vector points to the center of the irradiation field, and in this case, the distribution of the irradiation field intensity at a distance of about 1 enemy from target 2 is as shown in 7, with the center as the apex. However, because the radiation collides with target 2 and is converted and emitted, it inevitably spreads in a conical shape, so the intensity in the center increases and is not uniform. This results in a concentrated distribution. Therefore, in this type of radiation therapy device, a flattening filter 3 is inserted into the irradiation field according to the intensity distribution of the radiation, and the flattening filter 3 changes the radiation transparency so that the intensity distribution after passing through is uniform. It is set so that

When the flattening filter 3 is inserted, a uniform distribution as shown by the curve 8 is obtained. However, such a distribution can only be obtained when the electrons pass through normal orbits and have uniform energy.For example, when the electrons pass through normal orbits, the energy of the incident electron is Due to the energy higher than that of the electron beam, the electron beam passes through the trajectory shown by the broken line 9a and collides with a point shifted from the center of the target 2, and the vector of the principal axis of the radiation converted and generated by this is shown by the broken line 1.
Tilt the mirror as shown in 0.

Likewise, a low one will pass through the trajectory shown by the broken line 9b. For this reason, the position of the end point on the target 2 and the irradiation field determined by the collimator 4 are shifted, and the vector of the principal axis of the radiation is oblique, so that the radiation intensity distribution becomes asymmetrical as shown at 101. Therefore, when this is passed through the flattening filter 3, as shown at 102, an uneven distribution becomes extremely strong on the right side in the figure.
Moreover, the irradiation field also changes. In general, the electron beam emitted from an accelerator tube does not have a single energy, but includes electron beams with slightly different energies.

That is, it has an energy spectrum. Therefore, the 0 has the following drawbacks in the front magnet deflection method and the main magnet deflection method, which are typical deflection methods of the secondary.

FIG. 2 shows a pre-counterfeit magnet system in which two deflection magnets are installed in series, and the electron beam 12 emitted from the accelerator 11 is deflected at right angles by the two deflection magnets 13 and 14 to the irradiated object 15. Connect your focus.

The electron beam emitted from the accelerator 11 does not have a single energy as described above, but contains electron beams with slightly different energies. Those with a deflection angle smaller than the center energy take a trajectory 16 with a slightly smaller deflection angle, and those with a larger deflection angle take a trajectory 17 with a slightly larger deflection angle, and are incident on the same point on the object 15 to be irradiated. In this way, with the previous magnet method, it is possible to focus beams of different energies on the irradiated object, but the beams other than the center energy are not incident perpendicularly to the irradiated object, and are incident at different angles for each energy. There are drawbacks to doing so. Next, in the main magnet system shown in FIG. 3, the electron beam 12 emitted from the accelerator 11 is deflected in a right angle direction by a deflection magnet 18 that deflects it over 2700 degrees, and is made to enter the object 15 to be irradiated. Then, those smaller than the center energy follow a trajectory 16 with a small radius of rotation, and those larger than the center energy follow an orbit 17 with a large radius of rotation, and are then ejected in a right-angled downward direction. Therefore, this method does not have the disadvantages of the above-mentioned pre-layer magnet method, and allows objects with different energies to be incident perpendicularly on the irradiated object 15, while the advantage of the pre-layer magnet method is that they are emitted as parallel beams. I can't focus on something. Therefore, either method has the drawback that X-rays of uniform quality cannot be emitted.

The present invention has been made in view of the above circumstances, and eliminates the drawbacks of conventional deflection methods, and enables even electron beams with various energies to be focused on an object to be irradiated. It is an object of the present invention to provide a radiation therapy device that can deflect radiation so that it is incident perpendicularly to an object.

An embodiment of the present invention will be described below with reference to FIGS. 4 to 9. First, the principle of the present invention will be explained.

The deflection theory of the front layer magnet system is as follows.

That is, as shown in FIG. 4, core-shaped magnets MG1 and MG2 of the same standard are arranged with a distance of 1 apart. These magnets MG1 and MG2 have a constant magnetic flux density Bo
Apply magnetic fields in opposite directions. Also magnet MG
1. The width of MG2 is D. Now, consider an electron with energy E exposed to a magnetic flux with a constant magnetic flux density Bo.

This electron has a radius of curvature ro:r in a magnetic flux of &.

= 3.36 no E (E11.02)/B.・・・・・・
・Since the magnets move in the circular orbit of [1], the deviation h,, for a pair of magnets in FIG. 4 is h. =r.

-Noryo-d2 ...{21 Injection angle mao nine n-1 (d/Nor.

21) ...(will be subject to the deflection of 3l).

Therefore, the deviation date for the whole front pupil magnet is H=water,
10ltan8=2(r.

No r. 2-ra) 10 ld/nor.

21d2. ．．・…■ It can be expressed as
4} is subject to the deviation of Eq.

FIG. 5 shows a curve of deviation and radius of curvature given by equation [4}.

Next, in the main magnet system, as shown in Figure 6, the electron beam is incident at an oblique angle of a, and the entrance and exit surfaces of the magnet are beveled so that the electron beam enters at an oblique angle of a and is emitted. A magnet MG3 that emits light by deflecting it in a direction almost perpendicular to the corner is used, but an electron beam is incident on the upper end of the magnet MG3 as shown in FIG. 5 so that the incident beam and the emitted beam of this magnet MG3 do not intersect. It is made to emit from the lower end side after being deflected approximately 900 degrees inside.

In this case, if a magnetic flux with a constant magnetic flux density B is generated in the magnet MG3, the electrons with energy E added to this density magnetic flux B will have a radius of curvature ro
is r.

The electron moves on a circular orbit of =3.36°E (E11.02)/B, but as shown in FIG.

At that time, the distance D between the incident position and the emission position is D=distance.

si〆8 ……It is given by ■. Therefore, assuming that the deflection angle 28 of the electron beam within the magnet MG3 is constant, D becomes a straight line with respect to the radius of curvature ro as shown in FIG. In other words, if the incident position with respect to magnet MG3 is changed depending on the energy of the electron beam, the emission positions can be aligned because ro and D are in a proportional relationship.Moreover, in the main magnet method, the energy of the electron beam is Since only the curvature of the deflection locus changes depending on the magnitude, the emission angles are all the same.

As mentioned above, in the front layer magnet method, depending on the energy level of the electron beam, some of the energy is largely deflected, and large ones are deflected small, so the front layer magnet method is used to deflect the electron beam. If the final deflection is performed using the main magnet method after adding , the larger energy will be incident on the upper end of the main magnet, and the smaller energy will be incident on the center, so that the same ejection position will eventually be emitted directly. The electron beam can be emitted at the same emission angle from both sides, and the object to be irradiated can be focused.

FIG. 8 is a schematic configuration diagram showing one embodiment of the present invention, in which reference numeral 21 is an acceleration tube that accelerates the lint beam, and 22 and 23 are constructed of the same standard and generate magnetic flux in opposite directions. These are core-shaped deflection magnets that are connected to the acceleration tube 21.
They are arranged in parallel at an appropriate distance 1 so that electron beams accelerated and emitted from the electron beams can be deflected and emitted one after another.

That is, the above-mentioned front-direction magnet system is configured. In order to further deflect the electron beam EB deflected and emitted by the deflection magnets 22 and 23 by about 90 degrees, a deflection magnet 24 used in the main magnet method is provided on the electron beam emission side of the deflection magnet 23 on the rear stage side. . Reference numeral 25 denotes an object to be irradiated, such as a target, which converts the electron beam EB deflected and emitted by the deflection magnet 24 into X-rays.

With this configuration, the electron beam EB emitted from the accelerator 21 is dispersed in parallel according to the magnitude of energy by the deflection magnets 22 and 23 of the front layer magnet type.

The dispersed electron beam EB is deflected by 90 degrees by a main magnet type deflection magnet 24 with a radius of curvature corresponding to each energy, focused on the east, and incident on the object 25 to be irradiated perpendicularly. That is, the electron beams EB have smaller energy than the center energy, and the electron beams EB pass through the orbit La, and the electron beams EB, which are larger, pass through the orbit Lb, converge on the same point, and are parallel to each other. Let me explain the rationale in a little more detail.

Let Ec be the center energy of the electron beam EB having an energy spectrum emitted from the accelerating tube 21, and this Ec
Let Hc be the deviation due to the magnets 22 and 23 of the front-direction magnet system for an electron beam having an energy of When is day and D, it is always day and day c
=Dc-D If the following relationship holds true, the electron beam EB having an energy range as shown in FIG. 8 can be concentrated at one point.

However, in reality, as shown in Figures 5 and 7, the day is r.
D changes along a curve with respect to r, and D changes along a straight line with respect to r.

Moreover, r is rqzoE(B+1.02) as shown in the mth equation.
However, it is not a linear relationship with energy. However, in practice, the effective energy width is preferably 90% to 105% of the central energy, and the beam focus only needs to be within a certain effective value.

Moreover, within this energy range, it can be regarded as r wide E.
Fig. 9 shows the calculation of o and Do-D for each day under the assumption of a uniform magnetic field. In the front layer magnet method, the conditions are 1 = 90 feet, d: 35 arcs, r = 130 feet,
In the main magnet system, r=40. That is, in the energy range of 90% to 105%, it is possible to focus within ±1. In this way, after dividing the electron beam by energy using the front magnet method, the main magnet method is used to deflect the electron beam by 900 degrees with a curvature according to each energy, so even if the electron beam has an energy spectrum, it can be deflected by 900 degrees. Afterwards, the electron beam can be focused on one point, and since they can be emitted at the same emission angle, when this deflected electron beam is irradiated onto an object such as a target, the incident electron beam will be concentrated at one point at the same angle. It is possible to provide a radiation therapy apparatus that can obtain X-rays with a linear intensity distribution and, therefore, can easily obtain homogeneous X-rays by passing them through a filter or the like. The present invention is not limited to the examples, and may be modified and implemented as appropriate without changing the gist of the present invention.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a conventional device using a basic deflection magnet and its radiation distribution when the single energy is different.
Figure 2 is a diagram to explain the front layer magnet system, Figure 3
The figure is a diagram to explain the main magnet system, and Figure 4 is a diagram to explain the deflection theory of the front layer magnet system.
Figure 5 is a diagram showing the relationship between the deflection and radius of curvature, Figure 6 is a diagram explaining the deflection theory of the main magnet system,
Figure 7 is a diagram showing the relationship of deflection in the magnet.
FIG. 8 is a diagram showing an embodiment of the present invention, and FIG. 9 is a diagram showing the degree of deflection and the variation in the distance between the incident and emission positions with respect to the energy bias of the electron beam in the present apparatus. 21...Acceleration tube, 22, 23, 24...
- Deflection magnet, EB...Electron beam. 1st
Figure 2 Figure 3 Figure 6 Figure 5 Figure 8 Figure 7 Figure 9

Claims (1)

[Claims] 1. In a radiation therapy apparatus that obtains radiation used for treatment by deflecting and focusing an electron beam having an energy spectrum accelerated in an acceleration tube using a deflection magnet, the electron beam is divided into a plurality of beams at different deflection angles depending on the energy. a first deflection means for generating a first magnetic field for separation; and a first deflection means for deflecting each electron beam separated by the first deflection means into a state parallel to each other. A front magnet comprising a second deflection means for generating a second magnetic field is placed in the front stage, and each electron beam emitted from the front magnet is incident on the front magnet, and each electron beam is A main magnet for deflecting and focusing the incident electron beam, which has an entrance surface and an exit surface inclined with respect to the separation direction of the electron beam, and has a shorter trajectory length as the energy of the electron beam becomes lower, is disposed at a subsequent stage to form a main magnet for deflecting and focusing the incident electron beam. A radiation therapy device comprising: