JPH10155921A - Radiotherapeutic equipment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a dose fluctuation per pulse, and irradiate a stable electron dose by applying the constitution that an input part is equipped with a preset dose rate input part for the preset dose rate of an accelerated electron beam, and a device control part controls an electron dose from a cathode part, so as to keep a detected dose rate at the preset dose rate. SOLUTION: A filament power source control part 17, upon the start of an irradiation process, reads a dose rate signal 34 from a dose rate measurement part 20, and grasps an actually irradiated dose rate. Then, the control part 17 computes an actual dose per pulse. Also, a filament power source 16 is controlled and cathode current 22 changing in accordance with the change of filament current 26 is thereby controlled. Furthermore, a DC converted cathode current signal 31 from a cathode current detection part 14 performs filament control in a stable acceleration zone, while always monitoring a cathode current value changing in accordance with a filament current change. Also, when the cathode current 22 is outside the stable acceleration zone, the filament current 26 is immediately controlled, and the cathode current 22 is reset to the stable acceleration zone.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiotherapy apparatus having a microtron, and more particularly, to keeping a radiation dose of an electron beam irradiated from the microtron constant.
The present invention relates to a radiation treatment apparatus including a microtron capable of performing a stable operation by monitoring a reflected wave of a microwave to prevent the energy of the reflected wave from damaging the microtron.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram of a conventional radiotherapy apparatus. As shown in FIG. 7, a conventional dose rate control device includes a set dose rate input unit 19 for inputting an irradiation dose rate to the device.
And a pulse beam repetition frequency control unit 18 that determines a pulse beam repetition frequency according to a preset dose rate 36 set before irradiation, and a pulse beam repetition frequency output by the pulse beam repetition frequency control unit 18 And a high-voltage pulse generator 13 for supplying a high-voltage pulse signal 28 to the cathode 6 and the microwave generator 8 in synchronization with a trigger pulse signal operated by the high-voltage pulse generator 28. It comprises a pulse transformer 11, an accelerating cavity 7 for accelerating electrons in a microwave electric field, a microwave generator 8 for supplying microwaves 24 to the accelerating cavity 7, and a cathode 6 for supplying accelerating electrons to the accelerating cavity 7. ing.

Next, the operation of the above-mentioned conventional device will be described. When the irradiation is started, the pulse beam repetition frequency controller 18 sends a trigger pulse signal 37 having a certain period according to the set dose rate 36 from the set dose rate input unit 19 to the high-voltage pulse generator 13. send. The high-voltage pulse generator 13 boosts the high-voltage pulse signal 28 synchronized with the trigger pulse signal 37 by the high-voltage pulse transformer 11 and sends it to the microwave generator 8 and the cathode 6. The microwave generator 8 and the cathode 6 operate only while the high-voltage pulse signal 28 is being applied. The microwave generator 8 uses the microwave 24, the cathode 6 uses the cathode current 22 which is the electron for acceleration, and the microwave 6. It is supplied to the acceleration cavity 7 in the TRON. Then, the electrons emitted from the cathode 6 to the acceleration cavity 7 are accelerated in the acceleration cavity 7 by the microwave electric field 45 generated by the microwave 24.

The electrons accelerated by the microtron 1 are not continuous beams but are pulse beams accelerated only when a high-voltage pulse signal 28 is applied by a trigger pulse signal 37 as shown in FIG. The dose rate is proportional to the pulse beam repetition frequency and the dose per pulse beam. The dose rate is DR, and the pulse beam repetition frequency is P.
If the dose per RF and the dose per pulse is DPP, a relational expression of DR = PRF × DPP × k (1) holds. k is a conversion coefficient and depends on the irradiation energy.

Conventional dose rate control (mainly in the case of X-rays)
The dose rate is changed by changing the repetition frequency of the pulse beam according to the set dose rate. When the set dose rate 36 is input from the set dose rate input unit 19, the pulse beam repetition frequency control unit 18
According to 6, the repetition frequency of the pulse beam is determined. Assuming that the set dose rate is DRs and the set repetition frequency is PRFs, the set repetition frequency is obtained by the following equation from equation (1): PRFs = DRs / (DPP × k) (2) In the prior art, the irradiation dose DPP per pulse of the formula (2) is adjusted only at the time of installation adjustment and periodic inspection, but is not adjusted during normal use. The dose rate control assumes that the irradiation dose DPP per pulse is constant, and changes the dose rate by setting the repetition frequency of the pulse beam to a certain value according to the set dose rate. .

[0006]

However, the dose per pulse of the conventional radiotherapy apparatus must be adjusted for each of various radiation irradiation modes, which is complicated. It was adjusted only at the time or during periodic inspections, and was not adjusted during normal use. Therefore, the signal level of the microwaves launched into the body gradually increased due to the use of the microtron, and the actual level per pulse was increased. There is a problem that the dose changes and differs from the set dose rate.

The present invention has been made to solve the above problems, and an object of the present invention is to measure a dose per pulse and feed back the measured amount to control the dose to be constant. It is an object of the present invention to provide a radiotherapy apparatus capable of preventing a dose per pulse from fluctuating and irradiating a stable electron beam.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a microtron for accelerating an electron beam obtained by applying a high voltage to a heated cathode portion by a microwave, and a dose for detecting an irradiation dose of the accelerated electron beam. In a radiotherapy apparatus comprising a rate measurement system, a device control unit for controlling the microtron, and an input unit for inputting control data of the microtron to the device control unit, the input unit sets the acceleration electron beam. A set dose rate input unit for inputting a dose rate; the apparatus control unit controls an amount of the electron beam from the cathode unit such that the dose rate detected by the dose rate measurement system becomes the set dose rate. Is achieved by

The apparatus control section may control a reflected microwave detecting section for detecting a reflected wave of the microwave, and control an amount of the electron beam in accordance with a size of the reflected microwave. Further, the device control unit, an allowable signal level storage unit that stores an allowable signal level of the reflected microwave,
When the signal level of the reflected microwave detected from the reflected microwave detection unit is equal to or higher than the allowable signal level,
The irradiation of the accelerated electron beam may be stopped or interrupted.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a radiotherapy apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the dose rate control device of the radiotherapy apparatus of the present invention.

The radiotherapy apparatus shown here comprises a set dose rate input unit 19 for setting a dose rate in the radiotherapy apparatus, a transmission dosimeter 4 in the irradiation head of the gantry 3 for detecting the irradiation dose. The pulse beam repetition frequency is determined according to the set dose rate signal 36 sent from the set dose rate input unit 4, and the trigger pulse signal 37 having the pulse beam repetition frequency is sent to the high-voltage pulse generator 13. The repetition frequency controller 18 and the high voltage pulse signal 28 synchronized with the trigger pulse signal 37 from the pulse beam repetition frequency controller 18 are transmitted to the microtron 1.
High-voltage pulse generator 13 to be supplied to the power supply, a high-voltage pulse transformer 28 for further boosting the high-voltage pulse signal 28 from the high-voltage pulse generator 13 and applying the same to the cathode 6 and the microwave generator 8 and accelerating the acceleration cavity 7 A cathode 6 for supplying a cathode current 22 which is an electron for use, a filament 5 for heating the cathode with thermoelectrons 23, a microwave generator 8 for supplying a microwave 24 for electron acceleration to the acceleration cavity 7, and a microwave generator A waveguide 9 for guiding microwaves 24 from the cathode 8 to the accelerating cavity, an accelerating cavity 7 for accelerating electrons emitted from the cathode by a microwave electric field from the microwave generator 8, and a microwave in the accelerating cavity 7. Electron acceleration due to electric field is not good, microwave 2
4 is a reflected wave detecting antenna 12 for detecting a microwave (reflected wave) returning to the waveguide 9 because the energy of 4 is not used for electron acceleration, and a reflected wave monitor from the reflected wave detecting antenna 12 A reflected wave signal detector 15 that samples the signal 30 and converts it into a DC signal, a current transformer 10 for detecting a cathode current 22 emitted from the cathode 6 to the acceleration cavity 7, and a cathode current monitor from the current transformer 10. Cathode current detector 14 that samples signal 29 and converts it to a DC signal
A filament power supply 16 for supplying a filament current 26 to the filament 5; a dose measuring unit 20 for detecting an irradiation dose and an irradiation dose rate from a transmission dosimeter signal 35 of the transmission dosimeter 4; It comprises a filament power supply control section 17 for controlling the filament power supply 16 with a dose rate signal 34.

Next, the operation of the radiotherapy apparatus of the present invention will be described with reference to FIGS. When the irradiation dose rate is set in the set dose rate input unit 19, the set dose rate input unit 1
9 sends the set dose rate signal 36 to the pulse beam repetition frequency controller 18. Upon receiving the set dose rate signal 36, the pulse beam repetition frequency control unit 18 calculates the repetition frequency of the beam using the following equation (3). PRFs = DRs / (DPPs × k) (3) PRFs; pulse beam repetition frequency DRs; set dose rate DPPs; target dose per pulse k; PRFs calculation coefficient (dependent on energy)

Here, DPPs is a target value of the dose per pulse, and is determined by adjustment at the time of adjustment and maintenance. The dose per pulse, which will be described in detail below, changes according to the change in the cathode current. At the time of adjustment, the cathode current is adjusted to the center value of the cathode current variable range, and the dose value per pulse is adjusted.

When the irradiation is started, the pulse beam repetition frequency controller 18 sends a trigger pulse signal 37 having the repetition frequency calculated by the above (Equation 3) to the high-voltage pulse generator 13. The high-voltage pulse generator 13 boosts the high-voltage pulse signal 28 synchronized with the trigger pulse signal 37 with the high-voltage pulse transformer 11 and
To the cathode 6 to drive the microwave generator 8 only during the period when the high-voltage pulse is applied, to generate a microwave signal 24, and to cause the cathode 6 to emit a cathode current 22, which is an electron for acceleration. The microwave 24 output from the microwave generator 8 is transmitted to the acceleration cavity 7 through the waveguide 9 and accelerates electrons emitted from the cathode in the acceleration cavity 7 by the microwave electric field. The accelerated electrons are output from the acceleration cavity 7 into the microtron 1. The electrons output from the acceleration cavity to the microtron 1 are affected by the magnetic field in the microtron 1, draw a circular orbit, and return to the acceleration cavity 7 again.

Then, it is accelerated again by the microwave electric field,
It has greater energy and exits the acceleration cavity 7. Electrons with higher energy return to the accelerating cavity in a circular orbit with a larger radius in the magnetic field as the energy increases. In this way, the electrons are accelerated by the micro electric field in the accelerating cavity 7 each time they enter the accelerating cavity 7 while drawing a circular orbit in the magnetic field in the microtron 1, and gradually increase in energy.

The microtron has a trigger pulse signal 37
The electrons are accelerated as described above only while the high-voltage pulse signal 28 synchronized with the above is generated. The dose rate is proportional to the product of the dose per pulse of the accelerated electron beam and the repetition frequency of the pulse beam of the microtron, which is the trigger pulse signal.

The cathode 6 is heated by thermoelectrons 23 from the filament 5. A voltage of the order of several kilovolts is applied between the filament 5 and the cathode 6. When a filament current 23 flows through the filament 5, thermions 23 are emitted from the filament 5 to the cathode 6. The cathode 6 is heated by the thermoelectrons 23. Then, when a high voltage of several to several tens of kilovolts is applied to the cathode 6, electrons are emitted from the cathode 6 into the acceleration cavity 7. The amount of electrons emitted from the cathode 6 (cathode current 22) depends on the cathode temperature. In general, the higher the cathode temperature, the more electrons are emitted from the cathode 6
Released from

Therefore, when the filament current 22 flowing through the filament 5 is changed, the thermoelectrons 23 emitted from the filament 5 to the cathode 6 change, and the temperature of the cathode 6 changes. Then, since the cathode current 22 emitted from the cathode 6 changes, the filament current 23
, The cathode current 22 can be controlled.

The cathode current 22 and the dose per pulse generally have a relationship as shown in FIG. FIG. 3 is a graph showing the relationship between the cathode current and the dose per pulse. The dose per pulse decreases as the cathode current 22 increases, and increases as the cathode current 22 decreases. However, as shown in FIG.
It can be understood that if the value of 2 is changed too much and the microtron 1 is out of the stable acceleration region, the electrons will not be accelerated at all.

Therefore, by inputting such a stable acceleration region as data in advance and controlling the cathode current 22 in that region, the dose per pulse can be controlled. In the stable acceleration region, the cathode current 2 is changed by changing the filament current 23 manually by the operator.
2, the method of monitoring the state of the dose rate by monitoring the dose rate and checking the stable acceleration region in advance, and automatically changing the amount of the cathode current 22 by changing the filament current 23 by a computer or the like, A method of automatically investigating the dose rate to be irradiated and obtaining a stable region is conceivable.

If the cathode current 22 is controlled by controlling the filament current 23 in the stable acceleration region obtained as described above, it is possible to control the dose per pulse to be constant. is there.

Next, the filament power controller 17 will be described. FIG. 2 is a block diagram showing a configuration example of the filament power supply control unit in FIG.

The filament power supply control unit 17 performs various arithmetic processing for controlling the filament power supply 16.
U38, a memory 39 as a storage unit for various programs and data, and a set dose rate 3 from the set dose rate input unit 19
Set dose rate input interface 41 for reading 6
And a dose rate input interface 4 for reading a dose rate signal 34 actually irradiated from the dose measuring unit 20
0 and an A / D converter 4 for reading the cathode current signal 31 converted into a DC signal by the cathode current detection unit 14.
2 (A / D1), an A / D converter 43 (A / D2) for reading the reflected wave signal 32 converted into a DC signal by the reflected wave current detector 15, and a D / A for controlling the filament power supply 16. The interface between the converter 44 (D / A) and other peripheral devices (filament power supply:
It is composed of an A / D converter group (A / D3) connected to serial communication, parallel communication, and other general interfaces.

The CPU 38 of the filament control section 17 configured as described above reads the set dose rate 36 from the set dose rate input section 19, and calculates a target dose per pulse from the following equation (4). DPPs = DRs / (PRFs × k) (4) DPPs; target dose per pulse DRs; set dose rate PRFs; pulse beam repetition frequency k; conversion factor (dependent on radiation energy)

The pulse beam repetition frequency is set by the pulse beam repetition frequency controller 18 to a set dose rate of 3
6 is determined.

When the irradiation is started, a cathode current 22 is emitted from the cathode 6. This cathode current 22
Can be monitored by the current transformer 10 installed at the output of the high-voltage pulse transformer 11. The monitor signal of the cathode current 22 is generally a waveform signal as shown in FIG. FIG. 4 is a diagram showing a device around the cathode. This waveform signal is sampled by the cathode current detector at the center of the waveform as shown in FIG. FIG. 5 is a diagram showing a manner of sampling the cathode current. The sampled signal is converted into a DC signal and sent to the filament power control unit 17. Filament power controller 17
Converts the DC-converted cathode current signal 31 into an A / D signal.
Reading from the converter, the cathode current 22 is grasped.

CPU 38 of filament power supply controller 17
When the irradiation is started, the dose rate signal 34 transmitted from the dose rate
Reading from 0, the dose rate actually irradiated is grasped. Then, the actual dose per one pulse is calculated from the following equation (5). DPPa = DRa / (PRF × k) (5) DPPa; actual dose per pulse DRa; actual dose rate PRF; pulse beam repetition frequency k; conversion coefficient (dependent on radiation energy) From the actual dose per pulse and the target dose per pulse DPPs determined by equation (3), an error signal ε as in equation (6) is calculated. ε = DPPs-DPPa (6)

Then, the filament power supply 16 is controlled so that the ε becomes 0, and the filament current 26 is controlled, thereby controlling the cathode current 22 that changes with the filament current 26.

The DC current-converted cathode current signal 31 from the cathode current detector 14 is used to confirm that the cathode current value is within the stable acceleration region of the microtron, and the cathode current signal changes according to the filament current change. The filament control is performed in the stable acceleration region while constantly monitoring the value. Then, when the cathode current 22 goes out of the stable region, the filament current 26 is immediately controlled to return the cathode current 22 to the stable region. As described above, the cathode current control is performed by the filament current control using the feedback signal of the actually irradiated dose rate.
By controlling the dose per pulse, the dose per pulse is kept constant and the dose rate is stabilized.

The error signal used for control is
The same control can be performed by obtaining from the difference between the set dose rate and the actually applied dose rate as in the following equation (7) and performing control so that this error signal becomes 0. εd = DRs−DRa (7) DRs; set dose rate DRa; actual dose rate

Also, electrons are generated in the acceleration cavity 7 in the microtron.
It can also be determined by examining the state of the reflected wave from the acceleration cavity 7 whether or not the acceleration is stable. The energy of the microwave 24 transmitted from the microwave generator 8 through the waveguide 9 to the acceleration cavity 7 is used to accelerate electrons in the acceleration cavity 7. However, if the electron acceleration is not successful in the acceleration cavity 7 and the microwave energy is not absorbed by the electrons, the microwave 24 returns to the waveguide 9. The microwave returning from the acceleration cavity 7 is a reflected wave. The reflected wave usually has a concave portion at the center as shown in FIG.

However, when the number of reflected waves increases due to insufficient electron acceleration in the accelerating cavity 7, the shape of the central dent rises as shown in FIG. 6B. By sampling the middle part of this reflected wave and converting it into a DC signal, the amount of the reflected wave can be measured.

When the cathode current greatly changes from the stable acceleration region, the electrons are not sufficiently accelerated, or the sampled reflected wave signal increases. By controlling the cathode current by recognizing the generation of this reflected wave signal, it is possible to recognize the abnormal acceleration faster than controlling using the dose rate, and to respond faster to the dose rate fluctuation. Becomes possible.

The generation of such a reflected wave is caused by the waveguide 9
In addition, there is a possibility that a natural frequency that damages a microwave generation system such as the microwave generator 8 may be obtained. To prevent this, when the reflected wave signal increases, the repetition frequency control unit 18 of the pulse beam supplies the trigger pulse stop signal 4
7 and the trigger pulse 37 sent from the pulse beam repetition frequency controller 18 to the high-voltage pulse generator 13.
Is temporarily stopped, and the electron acceleration of the microtron 1 is temporarily stopped. The filament current value is returned to the filament current value flowing so that the cathode current 22 is around the center value of the stable acceleration region, the trigger pulse 37 is restarted again, and irradiation is started. It is possible to irradiate electron beams continuously without stopping the entire device when a problem occurs due to a reflected wave in a conventional radiotherapy device, because it can be prevented beforehand and the device can be returned without stopping the device completely. Becomes possible.

[0035]

The present invention has the above-described configuration, and since each configuration operates, the dose per pulse is measured, and the measured amount is fed back to control the dose to be constant. It is effective in providing a radiation therapy apparatus which can prevent the dose per pulse from fluctuating and can irradiate a stable electron beam.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing one embodiment of a control unit of the present invention.

FIG. 3 is a graph showing a relationship between a cathode current and a dose per pulse.

FIG. 4 is a diagram showing a device around a cathode.

FIG. 5 is a diagram showing a manner of sampling a cathode current.

FIG. 6 is a diagram showing a reflected wave signal at the time of normal acceleration and a reflected wave signal at the time of insufficient acceleration.

FIG. 7 is a block diagram of a conventional device.

FIG. 8 is a diagram showing a state of a pulse beam.

[Explanation of symbols]

 Reference Signs List 40 Dose rate input interface 41 Set dose rate input interface 42 A / D converter for reading cathode current signal 43 A / D converter for reading reflected wave signal 44 D / A converter for filament power supply control 45 A / D converter for filament power supply monitoring

Claims (3)

[Claims] 1. A microtron for accelerating an electron beam obtained by applying a high voltage to a heated cathode portion by a microwave, a dose rate measuring system for detecting an irradiation dose of the accelerated electron beam, and the microtron. A device control unit for controlling the radiotherapy apparatus having an input unit for inputting the control data of the microtron to the device control unit;
The input unit includes a set dose rate input unit for inputting a set dose rate of the accelerating electron beam, and the apparatus control unit controls the cathode so that a dose rate detected by the dose rate measurement system becomes the set dose rate. A radiation therapy apparatus characterized by controlling the amount of an electron beam from a part. 2. The apparatus according to claim 1, wherein the apparatus control section controls a reflected microwave detecting section for detecting a reflected wave of the microwave, and controls an amount of the electron beam in accordance with a magnitude of the reflected microwave. Item 7. A radiotherapy apparatus according to Item 1. 3. An apparatus according to claim 2, wherein said apparatus control section stores an allowable signal level of said reflected microwave;
When the signal level of the reflected microwave detected from the reflected microwave detection unit is equal to or higher than the allowable signal level,
The radiation therapy apparatus according to claim 2, wherein the irradiation of the accelerated electron beam is stopped or interrupted.