JP2578539B2 - Radiotherapy equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation therapy apparatus, and more particularly to a radiation therapy apparatus capable of interpolating a radiation output of a medical linac by integrating a pulse output at a high speed and monitoring the radiation output.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing an output monitor system of a conventional radiotherapy apparatus disclosed in Japanese Patent Application Laid-Open No. Sho 56-83362. In FIG. A radiation output monitoring ionization chamber chamber 3 provided in the irradiation section of the treatment apparatus main body 1 for monitoring the radiation output is electrically connected to the ionization chamber chamber 2, and a pulse current output from the ionization chamber chamber 2. To an integrated preamplifier that converts
A main amplifier 4 is connected to the integral preamplifier 3, amplifies the output voltage thereof, and outputs a radiation output dose monitor signal.
This is a master oscillator that generates electric pulses necessary for generating pulsed radiation from the radiation therapy apparatus main body 1.

Next, the operation will be described. The master oscillator 5 has a pulse repetition frequency of an electric pulse controlled by its external volume 5a, and its output pulse includes a trigger pulse for driving each pulse power supply (not shown) necessary for generating pulsed radiation. Become. The trigger pulse from the master oscillator 5 is sent to the main body 1 of the radiotherapy apparatus, whereby pulsed radiation is generated. The pulsed radiation is applied to the irradiation target from the irradiation unit of the radiation therapy apparatus main body 1 through the ionization chamber 2. The ionization chamber 2 measures the amount of radiation generated by detecting the amount of ionization current ionized in a fixed volume by utilizing the ionization effect in the atmosphere. The ionization chamber chamber 2 outputs the pulse current I ₀ which is synchronized with the trigger pulse V _T from the master oscillator 5 as shown in FIG. The pulse current I ₀ is input to the integrating preamplifier 3, and the integrating preamplifier 3 converts the input pulse current I ₀ into a pulse voltage. At this time, the integration type preamplifier 3 is given a certain time constant by connecting an impedance to its feedback loop, and thereby converts the pulse current I ₀ into a smoothed voltage signal V ₀ . The relationship between the input and output signals of the integrating preamplifier 3 is as follows.

[0004] _{V 0ave ≒ -R 1 I P (} τ W / τ R) ··· (1)

V ₀ ≒ (τ _R / R ₁ C ₁ ) V _0ave (2) where τ _W ≪τ _R , τ _R ≪R ₁ C ₁ , where τ _W is the ionization current pulse width, τ _R is the pulse repetition period, I _P is the ionization current peak value, V ₀ is the integral preamplifier (ie, the output voltage of the current-voltage conversion amplifier 3, V _0ave is the output average voltage of the integral preamplifier 3, and ΔV ₀ is the integral preamplifier. 3 is a P-P value of the output ripple voltage. output voltage supplied in this way the integral form preamplifier 3 is inputted to the main amplifier 4, where it is amplified. the main amplifier 4 changes the variable resistor R ₂ As a result, the output voltage V _A becomes as follows: V _A = − (R ₃ / R ₂ ) V ₀ (3) However, R ₂ and R ₃ are the input resistance and the input of the main amplifier 4 in FIG. The output voltage _VA from the main amplifier 4 is displayed on a meter as a radiation output dose monitor signal or used as a feedback signal of an output dose automatic control circuit.

[0006]

Since the conventional radiotherapy apparatus is configured as described above, the pulse signal is converted to a CR signal.
It has been changed to a DC signal by the integration circuit, so that the ripple voltage △ V ₀ of the output of the integration type preamplifier cannot be completely removed, and the pulse repetition period τ _R becomes larger than the ionization current pulse width τ _W. ripple voltage △ V ₀ becomes large, the vibration of the resulting output dose meter there problem causing degradation of controllability of the output dose rate automatic control circuit with increased. On the other hand, if the time constant C ₁ R ₁ is increased in order to reduce the ripple voltage ΔV ₀ , the vibration of the output dose meter also increases as described above,
There was also a problem that the response of the output dose rate automatic control circuit deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and eliminates the vibration of the output dose meter due to ripples, thereby improving the responsiveness and controllability of the output dose rate automatic control circuit. It is an object of the present invention to provide a radiotherapy apparatus capable of improving safety by interlocking the apparatus and stopping irradiation in an abnormal situation.

[0008]

A radiotherapy apparatus according to the present invention is provided with a radiation irradiator for irradiating a patient with therapeutic pulse radiation based on a trigger signal, and between the radiation irradiator and the patient, An ionization chamber for detecting the intensity of therapeutic pulse radiation and outputting a pulsed ionization current, a preamplifier connected to the ionization chamber and for pulse-integrating the pulsed ionization current, and connected to the preamplifier for pulse integration. A peak hold circuit for peak-holding the output current, and a timing controller for driving and controlling the hold circuit based on the trigger signal. Further, the radiation therapy apparatus according to the present invention is further connected to the hold circuit, a comparator for determining whether the hold value of the hold circuit is within a specified value, and connected to the comparator, the output of which An interlock circuit for stopping irradiation of the radiation when the hold value does not fall within a specified value based on a signal.

[0009]

According to the present invention, the pulse-like ionization current is converted into a direct current by a preamplifier and a hold circuit, and a ripple is eliminated. In addition, the comparator provided on the output side of the hold circuit determines whether the output level of the hold circuit is within the specified value or not. If not, the irradiation of radiation is stopped by the interlock circuit. You.

[0010]

【Example】

Embodiment 1 FIG. Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, 1 to 3 are the same as those in the conventional example, 6 is connected to the output side of the integrating preamplifier 3,
A peak hold circuit 7 for peak-holding the integrated output value is connected to the output side of the peak hold circuit 6, an A / D converter for converting the output signal into a digital signal, and 8 is an A / D converter 7 I connected to the output side of
An I / O interface 9 is an I / O interface 8
Microprocessor (hereinafter referred to as CPU)
10 and 11 are ROM and RAM connected to the system bus of the CPU 9, and 12 is a CP similarly.
Connected to a system bus of U9 the E ² -ROM, 13 is connected to the peak hold circuit 6, A / D converter 7, CPU 9, and the master Oshi' regulator, the peak-hold circuit receives the trigger pulse from the master oscillator 6 and a timing controller for outputting an operation timing pulse to the A / D converter 7; 14 and 15 are connected to the output side of the peak hold circuit 6 and detect an upper limit level and a lower limit level of the peak hold output; A comparator and an analog comparator for detecting a lower limit level.
4, an interlock circuit for instructing the radiation therapy apparatus to continue or stop irradiation based on the output of the apparatus.

Next, the operation will be described. FIG. 2 is a time chart for explaining the operation of this embodiment. 2A shows a trigger signal from a master oscillator for generating pulsed radiation, such as a linac trigger, and FIG. 2B shows a waveform of a radiation output emitted in synchronization with the linac trigger. This radiation output is detected as a current signal in the ionization chamber 2, and this detected current is pulse-integrated by the integrating preamplifier 3, as shown in FIG. And the peak hold circuit 6
Is driven by the timing controller 13 controlled by the CPU 9 at a fixed timing with the linac trigger, and holds the integrated value of the preamplifier 3. By the way, the integral waveform by the integrator is determined by the integral time constant. When the integral time constant τ = C ₁ R ₁ is sufficiently smaller than the pulse repetition time width T shown in FIG. Becomes almost the same as the integral value of the integral type preamplifier 3. Therefore, this integrated value is stored in the peak hold circuit 6
, The integrated value of each pulse can be held constant until the next pulse is generated, and the pulse-like signal is converted to a direct current. (D) shows the peak hold output which is thus peak-held and converted into DC for each pulse. This peak hold output is converted into a digital signal by the A / D converter 7.
(E) is commanded by the timing controller 13,
5 shows an A / D converter start signal of the A / D converter 7 which starts in synchronization with a linac trigger. (D)
As is clear, the hold value V _PH of the peak hold circuit 6 is a DC signal that does not include the ripple component due to the influence of the integrator as in the conventional example. Therefore, if this hold value is used as a feedback signal for controlling the radiation output for each pulse, stable control that is not affected by circuit constants, pulse repetition frequencies, or the like is realized. Normal,
It is necessary for the stability of the device that the dose per radiation pulse be constant depending on the operating mode, while at the same time ensuring safety for the patient. The analog comparator 14 for detecting the upper limit level and the analog comparator 15 for detecting the lower limit level are each provided with a peak hold circuit 6.
Is compared with the upper limit voltage V _up and the lower limit voltage V _Lo . If the integrated value is not within these specified voltages, a signal is output to the interlock circuit 16. That is, the comparators 14 and 15 can detect an abnormal change in the radiation output for each pulse, and when an abnormality occurs, the abnormality can be immediately detected by a signal of the first pulse. Then, the interlock circuit 16 to which this signal has been input can immediately activate the interlock to stop the irradiation of radiation. Then, the CPU9 is inputted digital data from the A / D converter 7, the data E ² -R
Stored in the OM 12. Unlike the RAM used for normal data storage, the E ² -ROM 12 does not lose its stored data even when the power is turned off, and stores the stored data semi-permanently until the same address is rewritten. Therefore, it is possible to trace changes over time by storing the daily dose per pulse of radiation output, and to easily record the stability of this radiation therapy device without using other measuring instruments. As a result, abnormalities are detected before the parts necessary for radiation generation are damaged,
Preventive maintenance can be performed.

In the above embodiment, the peak hold circuit is provided to hold the integrated pulse from the integrating preamplifier at the peak. However, the sample / hold circuit may be provided to sample and hold the integrated pulse. Good. Also, it is caused to operate the RAM constantly by battery backup in place of the E ² -ROM the same effect.

[0013]

As described above, according to the present invention, a hold circuit for peak-holding an integrated pulse obtained by integrating a detection current of pulse radiation per pulse and converting the hold pulse into a direct current is provided. A timing controller for controlling the driving; a comparator for determining whether an output value of the hold circuit is within a specified value; and a hold value of the hold circuit within the specified value based on an output signal of the comparator. The provision of the interlock circuit that stops the irradiation of radiation when not entering the device provides an effect that the stable operation of the output dose control can be realized and the safety for the patient can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a radiotherapy apparatus according to the present invention.

FIG. 2 is a timing chart for explaining the operation of the embodiment of FIG. 1;

FIG. 3 is a schematic configuration diagram showing a conventional radiotherapy apparatus.

FIG. 4 is a timing chart for explaining the operation of the conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Radiotherapy apparatus main body 2 Ionization chamber 3 Integrating type preamplifier 6 Peak hold circuit 13 Timing controller 14 Analog comparator for upper limit level detection 15 Analog comparator for lower limit level detection 16 Interlock circuit

Claims (2)

(57) [Claims] 1. A radiation irradiator for irradiating a patient with therapeutic pulse radiation based on a trigger signal, and a pulse ionization current provided between the radiation irradiator and the patient for detecting the intensity of the therapeutic pulse radiation. , A preamplifier connected to the ionization chamber and pulse-integrating the pulsed ionization current, a peak hold circuit connected to the preamplifier and peak-holding the pulse-integrated output current, A radiation controller, comprising: a timing controller that drives and controls a hold circuit based on the trigger signal. 2. A radiation irradiator for irradiating a patient with therapeutic pulse radiation based on a trigger signal, and a pulse-like ionization current provided between the radiation irradiator and the patient for detecting the intensity of the therapeutic pulse radiation. , A preamplifier connected to the ionization chamber and pulse-integrating the pulsed ionization current, a peak hold circuit connected to the preamplifier and peak-holding the pulse-integrated output current, A timing controller that drives and controls a hold circuit based on the trigger signal; a comparator that is connected to the hold circuit and determines whether a hold value of the hold circuit is within a specified value; and a comparator that is connected to the comparator. When the hold value is not within a specified value based on the output signal, A radiotherapy apparatus comprising: an interlock circuit for stopping irradiation of radiation.