JPS5822711B2 - Chiyoku Senryu Yusikasoku Souchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to particle accelerator technology, and in particular to
The present invention relates to a linear particle accelerator used in high-energy X-ray equipment such as those used in radiotherapy.

Modern cancer and other related disease treatments require high intensity levels of radiation for deep x-ray treatments.

Therefore, to obtain the desired radiation intensity distribution, high-energy radiation therapy equipment typically uses between 4 million and 25
It operates in the million electron volt range.

In X-ray therapy, in order to obtain maximum clinical benefit from high-energy radiation, it is necessary to direct the radiation with great precision.

Current high-energy x-ray equipment typically includes a charged particle accelerator that forms a charged particle beam and projects it onto a target for x-ray generation.

The accelerated particles are focused and, in some cases, bent by 90° before being directed to the target.

A heavy metal main collimator is generally located downstream of the target and is used to obtain a predetermined x-ray beam configuration.

Flattening filters and ionization chambers are usually placed within the x-ray beam to measure the radiation dose and integrate the total radiation dose to obtain uniform intensity of the beam across a plane perpendicular to the beam path. be done.

An example of such a high-energy X-ray device is J, S
, U.S. Patent No. 33229 to Bailey et al.
It is disclosed in No. 50.

When the charged particle beam impinges on the target at a position displaced from the center of the target, the pattern of emitted X-rays is displaced accordingly.

Additionally, a change in the angle of incidence at which the particle beam impinges on the target causes an angular change in the radiation pattern of the X-rays emanating from the target.

Positional and angular misalignment of the charged particle beam striking the target causes the emitted
It is difficult, if not impossible, to orient the line accurately.

To measure the radiation intensity distribution across the emitted electromagnetic field of charged particles, semicircular or quadrant-shaped radiation-responsive electrodes placed within the ionization chamber are used.

Generally, quadrant electrodes are placed symmetrically about the centerline of the chamber.

Therefore, the ionization chamber is positioned such that its centerline coincides with the central axis of the radiated electromagnetic field.

An example of four such electrodes provides a signal proportional to the integral of the radiation flux passing through each quadrant and can be used to monitor the symmetry of the pattern of the radiated field about the central axis.

In conditions of beam misalignment, this quadrant structure has been found to be unsatisfactory in sensing field asymmetries in planes remote from the ionization chamber itself.

For example, with the positional displacement of the charged particle beam on the target.

Both can result in a change in the angle at which the beam hits the target.

A conventional high-energy X of the type that includes a charged particle beam impinging on a target, a heavy metal collimator located downstream of the target, an electromagnetic flattening filter, and an ionization chamber.

In the ionization chamber, the quadrant-shaped electrodes indicate equilibrium so that the charged particle beam exists only in the plane of the ionization chamber and not in other planes that are remote from the ionization chamber. Dew.

The present invention aims to maintain the desired radiation pattern.

radiation-responsive sensing devices that control the alignment of the valence electron beams for the purpose of eliminating the above-mentioned and other drawbacks of conventional devices.
n responsive detection system
stem).

Based on the principle that the radiation field (or photon field) generated by the collision of charged particles with a target takes the form of a lobe pattern or spindle shape with a front tip. It has been found that a small change in the angle of incidence of the particle beam on the target results in a fairly large tilt of this radiation lobe quintillion turn.

-! In addition, it was confirmed that when the position on the target that the particle beam hits changes, a corresponding displacement of the lobe pattern occurs.

It has therefore been discovered that by placing an outer set of radiation-responsive electrodes at a position monitoring the edge or shoulder of the photon field, the slope of the lobe can be measured with a high degree of accuracy.

Thus, in order to detect changes in the position of the lobes, another set of inner electrodes is arranged to measure the radiation passing through the steepest slope of the flat filter.

Changes in the photon electromagnetic field due to the lobe tilt in the inner part of the lobe are compensated by increased absorption in the flat filter, and therefore the inner electrode set does not respond to changes in the lobe tilt.

Thus, the inner electrodes only provide an indication of the lobe's positional changes.

According to one aspect of the invention, a particle accelerator is provided that includes a device for forming a beam of particles and projecting the same into a substantially straight path.

This linear accelerator also has a device that deflects the particle beam, such as an angular error symmetric servomechanism fill (angular
error symmetryservomecha
nism coil ) and positional error symmetric servomechanism coil (positional errnr sy
mm-etry servomechanism e
oil).

A target is placed in the path of the particle beam that emits x-rays upon particle impact.

A radiation detection device measuring some parameters of the radiation pattern is placed within the radiating electromagnetic field, and a control circuit is provided between the radiation detection device and the beam deflection device to compensate for angular and positional displacements of the particle beam. are combined.

According to other features of the invention, the detection device includes a radiation-responsive electrode for monitoring the radiation intensity at the outer edge of the radiated electromagnetic field, and a radiation-responsive electrode for monitoring the radiation intensity at the outer edge of the radiated electromagnetic field, and a radiation-responsive electrode for monitoring the radiation intensity at the outer edge of the radiated electromagnetic field, and a symmetry of the radiated electromagnetic field for producing a signal that acknowledges changes in two parameters of the radiation pattern. It includes an electrode positioned near the axis to monitor radiation intensity.

According to another feature of the invention, a set of four inner electrodes, each arranged in one of the quadrants around the axis of symmetry of the radiated electromagnetic field, and a set of four inner electrodes arranged further from the axis than the inner electrodes; A set of four outer electrodes are provided, each located in one of the quadrants.

According to another feature of the invention, by monitoring the slope and position changes of the lobed radiation pattern formed when the particles hit the target, both with respect to angular changes in the longitudinal axis and changes in the displacement of the beam. A method of aligning a charged particle beam is provided.

Objects and advantages of the invention will be understood from the description of the preferred embodiments that follows with reference to the drawings.

FIG. 1 shows a high-energy x-ray system that includes a particle accelerator 10 that accelerates charged particles and projects them onto a target 12.

The collision of charged particles causes the target 12 to emit high-energy X-rays.

A heavy metal main collimator 14 is located downstream of the target 12, which is used to obtain the desired x-ray beam configuration.

The flat filter 16 and the ionization chamber 18 are the main collimator 1
4 and aligned with the collimator aperture.

The ionization chamber 18 measures the radiation dose (dose rate)
) is placed within the radiating electromagnetic field to measure the total number of rays and to generate an electrical signal that is used to integrate the total number of rays and maintain alignment of the particle beam.

A jaw-shaped movable collimator 20 is located downstream from the flattening filter and ionization chamber to vary the size of the radiated electromagnetic field.

More specifically, particle accelerator 10 includes a charged particle accelerator 22 that forms charged particles, accelerates the particles, and focuses the particles into a beam.

Angular error symmetry servomechanism coil 24 combined with particle accelerator 22
etry 5ervo-mechanism coi
l) is mainly because the charged particle beam is the target 12.
It has the effect of changing the angle of incidence at which it hits.

The beam of particles generated by the accelerator 22 passes through a beam delivery device 26 and passes through a positional error symmetrical servomechanism coil 2.
8 (position error symmeter
yservomechanism coil).

Beam transmission device 26 includes deflection and focusing coils and various slits for particle beam shaping.

The position error servomechanism coil 28 primarily functions to vary the location on the target 12 at which the particle beam impinges on the target.

A beam bending magnet 30 is positioned between the position servomechanism coil 28 and the target 120, which serves to bend the beam of charged particles by 90 degrees.

An example of an electron accelerator using a 90° beam bending technique is U.S. Patent No. 3 to R.T. Avery.
Reference can be made to No. 360647.

However, it should be understood that such beam bending is not necessary for the practice of the present invention.

Figure 2 shows the photon electromagnetic field (photon f) generated in the target when charged particles collide with the target.
1eld).

In the illustration, the photon electromagnetic field in the form of a lobe pattern or spindle shape 36 with a front tip is shown as a separate figure, but this lobe pattern is actually
must be understood to exist within the line equipment.

As shown, the beam of charged particles reaches the target 1 at a point corresponding to the center of the target as indicated by solid line 32.
2, the axis of symmetry 34 of the lobe 36, shown as a solid line, extends perpendicular to the plane of the target 120.

However, if the charged particle beam impinges on the target 12 at a different angle of incidence from 90° at a point displaced from the center of the target as indicated by dashed line 38, the resulting lobe pattern 40 corresponds to the change in the angle of incidence of the particle beam. tilted by the amount.

This change is indicated by the change in strength at the shoulder of the lobe, designated Δφ.

Dashed line 42 indicates the axis of symmetry of inclined lobe pattern 40.

FIG. 3 shows the ionization chamber 18 in detail.

Specifically, the ionization chamber 18 exhibits an arrangement of electrodes that measure parameters of the radiation lobe pattern to detect both changes in the angle of incidence of the particle beam and changes in the point at which the particle beam strikes the target.

The electrodes take the form of four plate-shaped electrodes 44, 46, 48.50, each located in one of the quadrants of the disc-shaped ionization chamber.

The electrodes 44, 46°48.50 constitute an inner set of electrodes, each having a small distance from the central axis of the disc-shaped ionization chamber 18, each of which has a radial length ρ of the ionization chamber 18. is so 4
It extends outward by a distance of 1/2.

As shown at 1 in FIG. 1, the inner quadrant electrode is located below the flattening filter 16 at a location just below the steepest slope of the flattening filter.

By positioning the electrodes in this manner, the slope of the lobe pattern within this area of the flattening filter is compensated for by increased absorption in the flattening filter.

These electrodes thus respond only to changes in the position of the radiation lobe.

Each of the inner electrodes 44, 46° 48.50 is connected to a corresponding one of the four output terminals 52, 54° 56.58.

In addition, the ionization chamber 18 has four flat electrodes 60°62.64
, 66, each of which has an inner electrode 44,
It is located in the same quadrant as one of 46, 48, and 50.

The outer set of electrodes has an arcuate rim, and the center of curvature of this curved portion is located at the central axis of the disk-shaped ionization chamber 18.

The outer set of electrodes are further apart than the inner electrodes and are radially spaced from the central axis of the ionization chamber.

an outer set of electrodes positioned to detect the intensity of the radiation lobe pattern at the outer edge or shoulder of the lobe;
This measures the slope of the lobe.

Each of the outer electrodes 60.62, 64, 66 is electrically connected to a corresponding one of the four output terminals 6B, 70, 72.74.

Flat electrodes 44, 46, 48, 50, 60°62.6
4 and 66 are all placed in a single plane within the ionization chamber 18, and are supported by an insulating plate located within a disc-shaped housing member.

A plate-shaped high voltage electrode (not shown) is arranged in spaced parallel relationship with other electrodes, and the ionization chamber 18 is filled with an ionizable gas.

Thus, each sensing electrode collects an ionic current proportional to the strength of the radiated field averaged over the electrode area.

As shown in FIGS. 4 and 5, the inner electrode 46.4
8 is connected to the input terminal of a differential servo amplifier type 760, and the output terminal of the servo amplifier is connected to -1 of the terminals of the coil 78 of the position error symmetric servomechanism.

The other terminal of this coil is connected surface-wise to ground.

A meter 80 is also connected between the output terminal of differential servo amplifier 76 and ground to provide an indication of the value of the compensation signal applied to position servomechanism coil 78.

Similarly, the other inner set of electrodes 44,50 are connected to the input terminals of a differential servo amplifier 82, whose output terminals are connected to one terminal of the coil 840 of another position error symmetric servomechanism.

The other terminal of this coil is connected surface-wise to ground.

Further, the other output of the differential servo amplifier 82 is connected to ground via a meter 86.

Thus, the electrodes 46,48 reduce the displacement of the radiation lobe at which the particle beam impinges the target 12 by 1.
It functions to monitor along two coordinate axes.

Electrodes 44.50 serve to sense changes in beam position along a second coordinate axis perpendicular to the first coordinate axis.

Thus, the signals generated by the electrodes 44, 46, 48.50, when applied to the coils 78, 84 of the position servomechanism, primarily compensate for changes in the position at which the particle beam impinges on the target.

The outer electrodes 62,64 are connected to the input terminals of another differential servo amplifier 88, the output terminal of which is connected to one of the terminals of the coil 90 of the angular error symmetry servomechanism.

The other terminal of this coil is connected directly to ground.

Additionally, a meter 92 is connected between the output terminal of the servo amplifier 88 and ground.

Similarly, another set of outer electrodes 60, 66 is connected to the input terminal of yet another differential servo amplifier 94 whose output terminal is one of the terminals of the coil 96 of another angular error symmetric servomechanism. connected to.

The other terminal of this coil is connected face-to-face to ground, and a meter 98 is connected between the output terminal of differential servo amplifier 94 and ground.

Thus, the outer pair of electrodes 62,64 will respond to large changes in intensity at the shoulders of the lobe pattern.

Changes in the intensity of the lobe pattern reflect changes in the angle of incidence of the particle beam on the target.

Thus, the electrical signals generated by these electrodes, when applied through differential servo amplifier 88, are used to control the energization of coil 90 of the angular error symmetry servomechanism.

An indication of angular compensation is provided by meter 92.

Other pairs of outer electrodes 60.66 provide similar compensation for angular errors along axes perpendicular to the axes of electrodes 62.64.

Thus, the present invention provides both angular and positional beam alignment at the point where the particle beam strikes the target.

Therefore, according to the invention it is possible to maintain a constant axis of symmetry for the radiation pattern emitted by the target.

Having described the invention in terms of preferred embodiments,
It will be readily understood by those skilled in the art that various modifications to the form and arrangement of parts can be made to meet various requirements without departing from the technical scope of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing the basic form of a high-energy X-ray apparatus including a beam alignment device according to the present invention. FIG. 2 is a schematic diagram illustrating a lobe pattern with a front tip caused by changes in the alignment of the charged particle beam. FIG. 3 is a plan view showing the structure of the electrode for monitoring radiation patterns. FIG. 4 is a sectional view of the electrode assembly taken along line 4--4 in FIG. 3, and the circuit of the electric servo mechanism combined therewith. shows. FIG. 5 shows a sectional view of the electrode assembly taken along line 5--5 in FIG. 3 and a circuit of an electric servo mechanism combined therewith. 10...Particle accelerator, 12...Target, 14
... collimator, 16 ... filter, 18 ... ionization chamber, 20 ... movable collimator, 22 ... charged particle accelerator, 24 ... internal error symmetrical servo mechanism coil,
26... Beam transmission device, 28... Coil of positional error symmetry servomechanism, 30... Beam bending magnet, 32... Beam of charged particles, 34... Axis of symmetry, 3
6... Lobe pattern, 38... Beam of charged particles, 40... Lobe pattern, 42... Axis of symmetry, 4
4, 46, 48° 50...inner electrode, 52, 54,
56, 58...output terminal, 60, 62, 64, 66...
...Outer electrode, 68.70. γ2, 74... Output terminal, 76... Differential servo amplifier, 78... 9 coils of position error symmetrical servo mechanism, 80... Meter, 82...
・Differential servo amplifier, 84... Coil of position error symmetric servo mechanism, 86... Instrument, 88... Differential servo amplifier, 90... Coil of internal error symmetric servo mechanism ,
92... Instrument, 94... Differential servo amplifier, 96.
... Coil of internal error symmetrical servo mechanism 5, 98... Instrument.

Claims (1)

[Claims] 1 A device that projects a beam of charged particles along a linear path, a deflection device that deflects the beam, and a collision L7 of charged particles.
A target in the beam path that emits radiation that spreads out in a spindle shape, and a target that is placed near the axis of symmetry of the spindle and on both sides of the axis of symmetry to monitor the magnitude of the radiation near the center of the radiation and indicate the location of the beam impact. a first sensing means comprising four electrodes generating a signal of 1 and arranged on either side of said axis of symmetry further from said axis of symmetry than the four electrodes of said first sensing means, close to the outer edge of the radiation; a sensing means comprising four electrodes for monitoring the magnitude of the radiation and generating a second signal representative of the angle of incidence of the beam; said first and second sensing means and said deflection device; a control signal connected between the first and second signals to apply a control signal to the deflection device according to the values of the first and second signals, thereby adjusting the deviation in the position where the beam impinges on the target and the change in the angle at which the beam is incident on the target. A linear particle accelerator comprising a dexterity circuit that deflects a beam in response.