JP5614679B2 - Feedback system in ion beam irradiation equipment - Google Patents

Description

  The present invention relates to a feedback system for an ion beam irradiation apparatus, and more particularly, to a beam intensity control apparatus such as an RF-KO (Radio Frequency-KnockOut) electrode for controlling an irradiation ion beam to a beam intensity determined by a treatment plan. Regarding control.

  In cancer treatment using an ion beam irradiation apparatus, as disclosed in Patent Document 1 below, in order to shorten the irradiation time of the raster scanning irradiation method, the dose in the spot movement trajectory is predicted and treatment is performed. In order to incorporate in the plan, it is necessary to control the ion beam to be irradiated to the beam intensity (the dose of the ion beam per unit time) determined in the treatment plan.

  Further, as disclosed in Patent Document 2 below, the irradiation target ion beam to be irradiated in the PCR method (Phase Control Rescending), which is capable of scanning irradiation, is used as a treatment plan. It is required to control to a predetermined beam intensity.

However, in beam extraction from the synchrotron, which is a part of the ion beam irradiation apparatus, temporal variations in the beam intensity due to the spatial and energy distribution of the ion beam are inevitable.
Further, the temporal variation of the power source that constitutes the ion beam irradiation apparatus also induces the temporal variation of the beam intensity.
Further, the control unit of the accelerator is in an environment that is easily affected by a noise signal emitted from a high-power power source used to generate a magnetic field for controlling the ion beam.
For these reasons, since the beam intensity of the ion beam irradiation apparatus fluctuates with time, a feedback system for controlling the beam intensity is required (see claim 4 of Patent Document 3 below, paragraph 0020).

  Here, whether or not the beam intensity of the ion beam to be irradiated is kept constant is determined by measuring the dose of the ion beam that passes through it using a dosimeter, and the measured dose value is kept constant. It can be judged by whether or not. A feedback system 200 of the ion beam irradiation apparatus 201 in the prior art shown in FIG. 3 is given as a control system for controlling the beam intensity of the irradiated ion beam using the data of the dose values measured by the dosimeter. It is done.

  Specifically, the feedback system 200 of the ion beam irradiation apparatus 201 shown in FIG. 3 measures a dose of the ion beam irradiated from the ion beam irradiation apparatus 201 and outputs a signal corresponding to the measured value. The I-V converter 220 that receives the signal and outputs an analog signal to which a voltage value proportional to the measured value is input, the A / D converter 230 that converts the analog signal into a digital signal, and the digital signal A difference value is obtained by comparing the beam intensity value of the ion beam and the beam intensity value (command value) scheduled and stored by the treatment plan, and the difference value is obtained by RF-KO as an intensity control device. It comprises a differential amplifier 240 that outputs to the electrode controller 250.

  Then, the RF-KO electrode controller 250 to which the difference value is input controls the voltage applied between the RF-KO electrodes installed in the ion beam irradiation apparatus 201 based on the input difference value, and treatment is performed. The ion beam was irradiated so that the beam intensity determined by the plan was obtained.

JP 2008-136523 A JP 2008-154627 A Japanese Patent Laid-Open No. 2002-334821

T. Furukawa et al., “Global spill control in RF-knockout slow extracution”, Nuclear Instruments and Methods in Physics Research Section A 522-3, (2004) pp.194-204. H. Nakagawa et al., “Slow Extraction Control Using The Digital Feedback System”, Proceedings of EPAC2000, Vienna, (2000) p.1921.

However, in the configuration of the feedback system 200 described above, the dosimeter 210 and the IV converter 220 are usually placed close to each other in order to prevent intrusion of noise. However, the IV converter 220 and the A / D converter are used. The distance 230 is often far away. In this case, since the signal output from the I-V converter 220 is an analog signal that is usually as low as 10 V or less, in an environment where noise is generated, the noise is input to the analog signal, and the waveform of the analog signal Could collapse.
Therefore, the differential amplifier 240 receives not only the measurement value measured by the dosimeter 210 but also a value including noise, and an accurate difference value from the beam intensity value determined by the treatment plan can be obtained. Therefore, there is a problem that the RF-KO electrode controller 250 cannot control the ion beam to the beam intensity determined by the treatment plan.

  On the other hand, although a method of preventing the intrusion of noise by making the distance between the IV converter 220 and the A / D converter 230 close is conceivable, the A / D converter 230 is brought close to the IV converter 220. Accordingly, the distance between the A / D converter 230 and the differential amplifier 240 is increased. That is, there is a problem that a large number of long-distance cables are required to transfer digital data from the A / D converter 230 to the differential amplifier 240.

  In addition, when the measured dose value is low, the analog signal output from the IV converter 220 becomes too small, and the accuracy of the numerical value converted into digital data in the A / D converter 230 deteriorates. There is a problem.

  Therefore, the present invention has a problem that when noise is input to a signal, the measured dose value changes and the differential amplifier cannot output an accurate difference value from the beam intensity value determined by the treatment plan. It is an object of the present invention to provide a feedback system for an ion beam irradiation apparatus that can eliminate the above-mentioned problem.

In order to solve the above problems, a feedback system for an ion beam irradiation apparatus according to the present invention includes a beam intensity control device that controls the intensity of an ion beam irradiated from the ion beam irradiation apparatus, and measures the intensity of the ion beam. A dose measurement unit that outputs a dose signal corresponding to the measurement intensity; receives the output of the dose signal, and obtains a difference value of the beam intensity between the dose signal and the beam intensity value scheduled and stored by the treatment plan And a differential amplifier that outputs the difference value, and the inter-electrode voltage of the beam intensity control device is set according to the magnitude of the difference value so that the difference value falls within a predetermined range across zero. the electrode controller to increase or decrease, in the feedback system of the ion beam irradiation apparatus equipped with, receives the output of the dose signal, the measured該線amount signal A frequency conversion unit for outputting a frequency signal converted into the corresponding frequencies to the amount values, receiving an output of said frequency signal, of the frequency signal, counts the frequency per predetermined time set in advance at the predetermined time interval A counter unit that outputs the count value as the dose signal to the differential amplifying unit, so that the dose signal converted into frequency is input to the differential amplifying unit, so that the transmission accuracy of the dose signal It is characterized by having increased.

According to the above configuration, since the frequency converter converts the dose value of the ion beam measured by the dose measuring unit into a frequency on the signal and outputs it, even if noise is input to the signal, Only the waveform of the signal changes, and the frequency of the signal does not change.
Further, the counter unit can derive the beam intensity as a count value by counting the frequency per predetermined time.
The differential amplifying unit can obtain an accurate difference between the count value (beam intensity) derived from the measured dose value and the intensity value of the beam scheduled and stored by the treatment plan. Difference can be output to the electrode controller.
Therefore, according to the present invention, the electrode controller can determine whether to apply a voltage between the electrodes based on an accurate difference, and can irradiate an ion beam having a beam intensity suitable for a treatment plan. It becomes possible.

  The configuration of claim 2 is characterized in that the waveform of the signal output from the frequency converter is a pulse wave. According to the said structure, since there is little influence by noise, there is little possibility that the measured dose value will change, and an exact measured value can be input into a counter part.

  Further, in the configuration according to claim 3, the counter unit calculates an average count value that is an average value from the counted two or more count values, and uses the calculated average count value as the beam intensity value. It outputs to the said differential amplifier part, It is characterized by the above-mentioned.

  According to the above configuration, an average count value that is an average value can be calculated from count values that precede and follow, and an average count value that approximates the measured value can be input to the differential amplifier, and the measured dose value is low. In this way, it is possible to avoid the measurement failure of the counter section that occurs in the above.

  As described above, according to the present invention, even when noise is input to a signal, the measured value is input to the counter unit without change. Therefore, the electrode controller can provide a feedback system of the ion beam irradiation apparatus that can control the ion beam to be irradiated to the beam intensity determined by the treatment plan.

It is a figure which shows the structure of the ion beam irradiation apparatus and its feedback system in embodiment. FIG. 2A shows the frequency (pulse) in the signal input to the counter unit, and FIG. 2B is a diagram showing the time width of the counter unit of the embodiment counting the pulses. c) is a diagram illustrating the time width of the counter unit of the modification example. It is a figure which shows the structure of the ion beam irradiation apparatus and its feedback system in a prior art.

  Next, a feedback system for an ion beam irradiation apparatus according to an embodiment of the present invention will be described with reference to the drawings.

(Ion beam irradiation apparatus 100)
An ion beam irradiation apparatus 100 of the present embodiment illustrated in FIG. 1 includes an ion source 101 that generates ions, a linear accelerator 102 that performs acceleration at the first stage, an annular synchrotron 103 that accelerates ions to high energy, and an RF − The KO electrode 104 and the treatment irradiation apparatus 105 are included. The ion beam irradiation apparatus 100 is controlled by an RF-KO electrode controller 106 that controls the applied voltage of the RF-KO electrode 104, and a control device (not shown) other than the RF-KO electrode 104 to treat the ion beam. The target is accelerated to the energy required for irradiation.

  The RF-KO electrode 104 is a device that makes it possible to apply a voltage in a direction perpendicular or horizontal to the traveling direction of the ion beam. Then, when the RF-KO electrode 104 applies a voltage in a direction perpendicular or horizontal to the traveling direction of the ion beam, the ion beam is taken out from the synchrotron 103 and irradiated by the irradiation device 105. Whether or not the RF-KO electrode 104 applies a voltage is determined based on a control signal transmitted from the RF-KO electrode controller 106 described later.

  The RF-KO electrode controller 106 is a control unit that determines whether or not to apply a voltage to the RF-KO electrode 104. When a differential value is input from the differential amplifier 40 described later, Based on the difference value, a voltage application between the RF-KO electrodes 104 or a control signal for stopping the voltage application is transmitted to the RF-KO electrodes 104. As a result, the amount of ion beam extracted can be made the intensity of the beam scheduled and stored by the treatment plan.

(Feedback system 1)
The feedback system 1 of the present embodiment includes a dose measurement unit 10 that measures the dose of an ion beam, an IF conversion unit 20 that converts the measured dose value into a frequency, and a counter unit that counts the frequency per predetermined time. 30 and a differential amplifying unit 40 that calculates a difference between two input data.

(Dose measurement unit 10)
The dose measurement unit 10 measures the dose of the ion beam to be irradiated. The dose measurement unit 10 collects the secondary electrons generated by the ionization chamber or ion beam that measures the dose by using the ionization action. Secondary electron monitor that measures Further, the present invention is not limited to this, and any other device may be used as long as it can measure the dose in real time.

(IF conversion unit 20)
The IF conversion unit 20 receives an analog signal such as a current value input from the dose measurement unit 10, generates a frequency proportional to the current value of the analog signal, and outputs the frequency as a signal It is a conversion unit. Further, the waveform of the signal generated and output by the IF converter 20 in the present embodiment is a pulse wave, but the present invention is not limited to this pulse wave. For example, the waveform may show a steep change such as a rectangular wave that is less affected by noise. The IF conversion unit 20 corresponds to a “frequency conversion unit” described in the claims.

(Counter unit 30)
The counter unit 30 counts the frequency per predetermined time input to the signal (pulse) output from the IF conversion unit 20, and outputs a numerical value (count value) of the counted frequency. Here, the predetermined time is not particularly limited, but is assumed to be set to 100 μsec in the present embodiment. Therefore, the counter unit 30 counts the frequency with this 100 μsec as one block.
Therefore, as shown in FIG. 2, when the counter unit 30 receives a signal to which a pulse as shown in FIG. 2A is input, the counter unit 30 of the above-described embodiment is configured as shown in FIG. As shown in FIG. 4, the measurement is performed for each block at intervals of 100 μs, and the measured count values N _{1 to} N ₆ in the respective blocks are transmitted as they are to the differential amplifier 40 described later.

The counter unit 30 may cause variations in frequency measurement when the ion beam amount is small and the beam intensity value is small. In preparation for this case, a threshold value is set in advance, and when the count value falls below that value, the counter unit 30 calculates an average count value that is an average value from two or more count values counted in consecutive blocks. The average count value may be calculated and output to the differential amplifier 40 as a beam intensity value.
Specifically, as shown in FIG. 2C, the counter unit 30 has an average count value of N _{1 to} N ₃ ((N ₁ + N ₂ + N ₃ ) / 3) that is a count value measured in each block. And the average count value ((N ₁ + N ₂ + N ₃ ) / 3) may be transmitted to the differential amplifier 40 as the beam intensity. According to this modification, even if a frequency measurement defect occurs in the counter unit 30, a value approximate to the measurement value can be output as the count value.

(Differential amplifier 40)
The differential amplifying unit 40 is a device that subtracts the command value from the count value input from the counter unit 30 to obtain a difference value, and outputs the difference value to the RF-KO electrode controller 106. Here, the command value input to the differential amplifying unit 40 is a value of the beam intensity to be irradiated to the target scheduled in advance according to the treatment plan and written in the memory (“scheduled and stored in the treatment plan according to the claims”). It is equivalent to the intensity value of the beam that is being applied.), Specifically, the dose value of the ion beam to be irradiated per block unit (100 μsec).

(how to use)
Next, a method of using the feedback system 1 in the ion beam irradiation apparatus 100 according to the embodiment will be described.

  First, the RF-KO electrode controller 106 applies a voltage between the RF-KO electrodes 104 so that the ion beam irradiated from the ion beam irradiation apparatus 100 has a beam intensity to be irradiated based on the treatment plan, and the patient Etc. are irradiated with an ion beam.

  Next, the dose measurement unit 10 measures the dose of the ion beam passing through the ionization chamber, and outputs a current having a magnitude corresponding to the measured dose value to the IF conversion unit 20 as a signal.

  The IF conversion unit 20 generates and outputs a frequency proportional to the current value of the input signal. Further, since the waveform of the signal generated by the IF conversion unit 20 is a pulse, a signal as shown in FIG. 2A is transmitted to the counter unit 30. The counter unit 30 counts the frequency (number of pulses) of the input signal for each block unit (100 μsec) and outputs the count value to the differential amplifier. Here, the count value counted by the counter unit 30 is a dose value in 100 μsec, that is, a beam intensity value per 100 μsec of the measured ion beam.

  Then, the differential amplifying unit 40 calculates the difference value by subtracting the beam intensity value derived by the counter unit 30 by the beam intensity value scheduled and stored by the treatment plan inputted as the command value, The difference value is output to the RF-KO electrode controller 106.

  The RF-KO electrode controller 106 determines that the beam intensity of the ion beam to be irradiated is the same as the beam intensity determined in the treatment plan when the input difference value is within a predetermined range that crosses zero. Then, the RF-KO electrode controller 106 transmits a control signal to the RF-KO electrode 104 so that it is continuously applied without changing the voltage value to be applied. Therefore, the ion beam irradiation apparatus 100 continuously irradiates the ion beam having the ion beam intensity determined in the treatment plan.

  When the input difference value is larger in the plus direction than the predetermined range, the RF-KO electrode controller 106 determines that the beam intensity of the ion beam to be irradiated is higher than the beam intensity determined in the treatment plan. To do. Then, the RF-KO electrode controller 106 transmits a control signal so that the voltage value applied to the RF-KO electrode 104 is lowered and applied.

On the other hand, when the input difference value is larger in the minus direction than the predetermined range, the RF-KO electrode controller 106 determines that the beam intensity of the ion beam to be irradiated is lower than the beam intensity determined in the treatment plan. The control signal is transmitted so that the voltage value applied to the RF-KO electrode 104 is increased by the lower amount and applied.
As described above, in the ion beam irradiation apparatus 100, the RF-KO electrode controller 106 controls the applied voltage of the RF-KO electrode 104 based on the difference value, thereby irradiating the ion beam with the ion beam intensity determined in the treatment plan. It becomes possible to do.

The feedback system of the ion beam irradiation apparatus in the present embodiment has been described above. According to the present embodiment, the measurement data (dose value) measured by the dose measurement unit 10 is converted into a frequency by the IF conversion unit 20. Since it is converted, even if noise is input, only the waveform of the signal changes, and there is no possibility that the frequency will increase or decrease.
That is, according to the feedback system of the ion beam irradiation apparatus of the present embodiment, it is possible to input the measured accurate beam intensity value to the differential amplifier.
Therefore, according to this embodiment, the RF-KO electrode controller obtains an accurate difference value between the derived beam intensity value and the intensity value of the beam scheduled and stored by the treatment plan, and the RF-KO electrode The voltage applied between them can be controlled, and an ion beam having a beam intensity determined by the treatment plan can be irradiated.

  In addition, this invention is not restricted to what is shown to embodiment. For example, in the embodiment, the RF-KO electrode 104 is used. In addition to the RF-KO electrode 104, a betatron tune control method using a quadrupole electromagnet excitation current change is used as a beam intensity control device. It may be a beam intensity control apparatus and a beam intensity control apparatus using a betatron tune control method by changing beam energy. This beam energy change is performed using a beam accelerator such as an induction accelerator or a high-frequency accelerator.

Further, in the beam intensity control apparatus using the betatron tune control method by changing the quadrupole electromagnet excitation current, the excitation current may be changed by controlling the power supply of the quadrupole electromagnet. A plurality of quadrupole electromagnets are generally provided in the synchrotron, but the effect can also be obtained by controlling at least one of them.

DESCRIPTION OF SYMBOLS 1 Feedback system 10 Dose measuring part 20 IF conversion part 30 Counter part 40 Differential amplification part 100 Ion beam irradiation apparatus 101 Ion source 102 Linear accelerator 103 Synchrotron 104 RF-KO electrode 105 Irradiation apparatus 106 RF-KO electrode controller

Claims (3)

A beam intensity control device for controlling the intensity of the ion beam irradiated from the ion beam irradiation device;
A dose measuring unit that measures the intensity of the ion beam and outputs a dose signal corresponding to the measured intensity;
A differential amplifying unit that receives the output of the dose signal and obtains and outputs a difference value of the beam intensity between the dose signal and the intensity value of the beam scheduled and stored by the treatment plan;
An electrode controller that receives the output of the difference value and increases or decreases the inter-electrode voltage of the beam intensity control device according to the magnitude of the difference value so that the difference value falls within a predetermined range across 0 ;
In the feedback system of the ion beam irradiation apparatus equipped with
A frequency converter that receives the output of the dose signal and outputs a frequency signal obtained by converting the dose signal into a frequency corresponding to the measured dose value;
Receiving an output of said frequency signal, of the frequency signal, it counts the frequency per predetermined time set in advance at the predetermined time interval, the counter unit to be output to the differential amplifier section the count value as the dose signal When,
By providing
A feedback system for an ion beam irradiation apparatus, wherein a dose signal converted into a frequency is input to the differential amplification unit to improve a transmission accuracy of the dose signal.   The feedback system of the ion beam irradiation apparatus according to claim 1, wherein the waveform of the frequency signal is a pulse wave.   When the counter unit counts a count value indicating that the beam intensity is smaller than a preset threshold value, the counter unit calculates an average count value of the two or more count values continuously counted, and uses the calculated value as the dose signal. The ion beam irradiation apparatus feedback system according to claim 1, wherein the feedback system outputs the differential amplification unit to the differential amplification unit.

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