Beam transportation control system

Abstract

The invention discloses a beam transportation control system, and belongs to the technical field of nuclear medicine radiotherapy. The control system comprises an energy adjusting system and a beam transport system. The energy adjusting system is composed of a magnet system, an energy reducer system, a beam measuring system, a vacuum system and a water cooling system. The beam conveying system is composed of a magnet system, a beam measuring system, a vacuum system and a water cooling system. The control system of the energy selection section and the control system of the beam section are connected in series to form the whole beam transport control system. According to the system, through compact beam optical design, the number of magnets is greatly reduced, meanwhile, high-quality continuous beams are guaranteed, beam parameters can be accurately controlled, the transmission efficiency and quality are kept, the beam transportation cost is saved, and meanwhile energy consumption is reduced.

Description

Technical Field

[0001] The invention discloses a beam transport control system, belonging to the technical field of nuclear medicine radiotherapy. Background Art

[0002] Nuclear medicine radiotherapy technology is currently an important research field in modern oncology. Protons in nuclear medicine radiotherapy have the characteristics of strong penetration, concentrated energy distribution, and controllable dose distribution; therefore, during the treatment process, they can protect the normal cells around the lesion to the greatest extent and use most of the energy to kill cancer cells.

[0003] As an important component and key system in nuclear medicine radiotherapy technology, the beam transport control system is mainly used to transport the accelerator's extracted beam to the treatment room according to certain requirements, and monitor and modify the beam according to terminal requirements. Ensure the stability and uniformity of the beam during transmission. In addition, the beam delivery system must be designed with strict safety control measures, including radiation protection, emergency stop mechanism, and automatic monitoring system to ensure the safety of patients and operators.

[0004] At present, the beam transport system of large nuclear medicine radiotherapy equipment has no unified specifications, and the various subsystems are chaotic. This leads to high costs and has been detrimental to system maintenance and operational efficiency for a long time. It also leads to a decrease in stability and quality during beam transport. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems and provide a beam transport control system to solve the problem that the various subsystems mentioned in the above background technology have no unified specifications and the subsystem equipment is chaotic.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions.

[0007] A beam transport control system includes an energy regulation system and a beam transport system. The energy regulation system and the beam transport system are mainly composed of a magnet system, an energy degrader system, a beam measurement system, a vacuum system, and a water cooling system. The various systems are respectively composed of a quadrupole iron, a dipole iron, a correction iron, an energy degrader, a collimator, a slit, a Faraday cup, a fluorescent target, a striped ionization chamber, an ionization chamber, and a vacuum pump. The control system of the energy selection section and the control system of the beam line section are connected in series to form the overall beam transport control system. This system greatly reduces the number of magnets while ensuring high-quality continuous beams through a compact beam optical design. It can accurately control beam parameters and maintain transmission efficiency and quality, saving beam transportation costs and reducing energy consumption.

[0008] Preferably, the magnet system includes a quadrupole magnet power supply, a correction magnet power supply, a dipole magnet power supply and a deflection magnet power supply, and a digital power supply is used to control the magnet power supply by interfacing with the control system through a communication port, and the temperature switch and flow switch in the magnet system are connected in series into a signal to form a safety interlock with the magnet power supply.

[0009] Preferably, the degrader in the degrader system is composed of a pair of split wedge-shaped graphite. After the particles in the beam enter the degrader, they collide with the atoms in the degrader multiple times. The energy reduction process reconstructs the phase space distribution of the beam, which will lead to a rapid increase in the size and emittance of the beam. FLUCK is used to simulate the movement of particles in the medium. For the 220MeV beam required for treatment, the thickness of the degrader is 21mm, and for the 70MeV beam, the thickness of the degrader is 179mm. The effect of the medium on the beam particles is divided into three aspects: change in energy, change in position and change in divergence angle.

[0010] Preferably, the collimator is used because emittance control needs to be completed through the collimator. The collimator is a double-hole collimator with an effective length of 0.35m and an adjustable aperture size. For an exit emittance of 10π, the collimator aperture size is required to be 2.64mm; for an exit emittance of 20π, the collimator aperture size is required to be 3.32mm. According to the needs of the treatment end, this system designs a collimator with an aperture of 10π~20π, which can be infinitely adjusted through motor control. It can meet the different requirements of the treatment end for beam emittance.

[0011] Preferably, the slit acts as a selective barrier, allowing only particles that meet specific energy standards to pass through. By precisely setting the slit opening to 4 mm, particles whose energies are higher or lower than the energy window required for the set treatment course can be effectively eliminated. Only particles whose momentum meets the slit setting range can pass through, thereby achieving energy selection and momentum control of the beam.

[0012] Preferably, the beam measurement system includes a fluorescent target, a Faraday bucket, an ionization chamber and a multi-wire proportional chamber. The fluorescent target is made of a material called Lafarin deposited on glass or ceramic. When the beam hits the fluorescent target, it will emit light. The image information can be transmitted to the central control system through a dedicated PoE camera, so that the approximate envelope information of the beam can be observed. The Faraday bucket has two states: inserted and withdrawn. In the inserted state, the beam current intensity of the proton beam is measured and it serves as a beam junk target. Its output signal is current, which is connected to the beam measurement electronics system after current / voltage conversion (I / V conversion). The dose ionization chamber mainly monitors the irradiation dose, which is connected to the beam measurement electronics system through an ionization chamber probe after current / voltage conversion (I / V conversion). IV conversion is generally transimpedance amplification and integral amplification. The multi-wire proportional chamber mainly monitors the beam position.

[0013] Preferably, the vacuum system includes vacuum pumps (dry pumps, molecular pumps), valves, vacuum gauges and other equipment, and the monitoring and control of the vacuum subsystem is completed by PLC. The main functions of the control system include pump power supply indication, start / stop control, fault status display; vacuum gauge vacuum degree display and vacuum interlock; gate valve open / close control and status display; interlock bypass start, protection and status display. An efficient vacuum system reduces the interaction between the beam and air molecules, thereby reducing beam loss and maintaining transmission efficiency and quality.

[0014] Preferably, the water cooling system equipment mainly includes a water temperature sensor, a water pressure sensor and a water flow sensor. The system mainly completes water temperature, water pressure and water flow monitoring and corresponding interlocking. The interlocking threshold can be set.

[0015] Compared with the prior art, the present invention has the following beneficial effects: Magnets of the same type should adopt unified specifications as much as possible to avoid duplication of design schemes and processing and mold-making costs for proton therapy equipment in advanced particle equipment research and development projects; through accurate simulation and calculation of the spatial arrangement of quadrupole magnets and the magnetic field gradient, the beam envelope size is made as small as possible to reduce key parameters such as the good field area and aperture of the magnet, thereby reducing the production cost of the magnet.

[0016] The beam current intensity requirement of unified specifications is 0.47nA~3nA to adapt to the dose requirements of different treatment plans; as well as the management of phase space distribution, the collimator aperture 10π~20π is continuously adjustable to ensure the stability and uniformity of the beam during transmission.

[0017] To ensure the functionality of the beam delivery system, the overall size of the beam delivery system must be controlled, and the requirements of radiation protection must also be met. The total length of the unified beam transmission line is about 118.9m. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of the structural design of a beam transport control system of the present invention; Figure 2 A schematic diagram of a magnetic field distribution curve of a 90° magnet center trajectory of a beam transport control system of the present invention; Figure 3 A schematic diagram of a magnetic field distribution curve of a 60° magnet center trajectory of a beam transport control system of the present invention; Figure 4 A magnetic field distribution diagram of a 30° magnet center trajectory magnetic field distribution curve of a beam transport control system of the present invention; Figure 5 A 2D model of horizontal correction of a correction magnet and a schematic diagram of magnetic field line distribution of a beam transport control system of the present invention; Figure 6A schematic diagram of the magnetic field distribution along the X-axis of a quadrupole magnet of a beam transport control system of the present invention; Figure 7 It is a schematic diagram of a cross section of a 1 / 8 core of a correction magnet of a beam transport control system of the present invention; Figure 8 A two-dimensional schematic diagram of an energy degrader of a beam transport control system of the present invention; Fig. 9 A schematic diagram of the working principle of a striped ionization chamber of a beam transport control system of the present invention; Fig.10 A schematic diagram of the working principle of a fluorescent target of a beam measurement system of a beam transport control system of the present invention; Fig.11 It is a schematic diagram of the structure of a fluorescent target of a beam measurement system of a beam transport control system of the present invention; Fig.12 A schematic diagram of the working principle of a Faraday cup of a beam transport control system of the present invention; Fig.13 This is a schematic diagram of the vacuum pump distribution structure of a beam transport control system of the present invention.

[0019] Fig.14 This is a schematic diagram of the structure of a water cooling system of a beam transport control system of the present invention. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, which are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0021] Figure 1 This is the structure diagram of the beam transport control. The control system consists of two parts: hardware and software. The hardware of the control system mainly uses Beckhoff PLC. PLC is connected to each subsystem via Ethernet. The subsystems are the magnet system, energy degrader system, beam measurement system, vacuum system and water cooling system.

[0022] The software part is the IOC and OPI interface. The connection between IOC and OPI is realized through the communication mechanism provided by EPICS (Channel Access). Channel Access allows OPI to read data from IOC and send control commands to it. EPICS PV (Process Variable) is configured on OPI to correspond to the records and fields in IOC. PV is an abstraction used in the EPICS system to transfer data between IOC and OPI. After the connection is established, testing and debugging are carried out to ensure that the data is transmitted correctly and the system is operating normally. The monitoring tools provided by EPICS can be used to verify the value and status of PV.

[0023] The design of dipole magnets includes 90°, 60° and 30° dipole magnets, where the angles represent the deflection angles. The central magnetic field of the three different dipole magnets is 0.75-1.5T, the pole gap is 60mm, and the central orbit deflection radius is 1600mm. In addition to the different deflection angles, the effective length parameters are greater than 2530mm, 1670mm, and 837.758mm, respectively, and the incident and exit edge angles are 23.5°, 18°, and 10°.

[0024] In the three-dimensional structure design of the secondary magnets at 90°, 60° and 30°, the focus is on the integral distribution. Figure 2 , Figure 3 , Figure 4 It is the center track magnetic field distribution curve. The integral field uniformity distribution of ±25mm in the good field area is better than ±0.1%, and the high-order field error distribution is better than 0.1%. It can be judged that the effective lengths of the integral field are 2537.2mm, 1688.6mm, and 859.2mm respectively, which meet the design requirements, and the magnetic field uniformity and high-order field error also meet the design requirements.

[0025] The two-dimensional parameter design of the correction magnet is based on the characteristics of the magnetic field pulse change. The core is made of 0.5mm thick non-oriented silicon steel sheets, and the end plate is non-magnetic stainless steel with a thickness of 8mm. In order to increase the overall rigidity and reduce vibration, it is necessary to add a through-core screw at the appropriate position of the yoke. The two-dimensional model simulation uses OPERA / 2D software to determine the magnet aperture of 120mm. The horizontal correction 2D model and the magnetic line distribution are as follows Figure 5 .

[0026] When the ampere-turns are 4610.62AT, the By magnetic field is calculated to be distributed along the X direction, and the corresponding central magnetic field is 300Gs. According to the error of the horizontal distribution of the central plane magnetic field, within the range of X=±40mm, the magnetic field uniformity error is ≤10%.

[0027] Since the magnetic field of the quadrupole magnet is highly symmetric about X and Y, we only need to calculate the magnetic field in one direction to obtain the field distribution in the other directions through symmetry. The calculated magnetic field distribution along the X direction is as follows: Figure 6 As shown, the magnetic field gradient is 16T / m. The gradient uniformity is calculated based on the two-dimensional magnetic field distribution, and the integral field error is within 0.5%, which is lower than the integral field uniformity requirement of 1%. After that, three-dimensional modeling is performed based on the two-dimensional simulation results. The cross section of the quadrupole magnet modeling is shown in Figure 7 shown.

[0028] The degrader system includes degrader and collimator components. The degrader is responsible for adjusting the energy of the proton beam, but this process may lead to an increase in energy divergence and emittance, as well as a decrease in transmission efficiency. Therefore, optimizing the performance of the degrader is one of the key points of this system research. The collimator is located after the degrader and is used to suppress the increase in emittance caused by the degrader to ensure that the emittance of the beam meets the needs of clinical treatment.

[0029] The degrader adopts a wedge-shaped structure and uses graphite as the blocking material. The main design parameters include the number of teeth, the length of the teeth, the angle of the teeth, the thickness of the teeth, etc. Through thermodynamic and mechanical analysis, it was decided that the degrader adopts a three-tooth structure. The beam envelope of the accelerator beam before entering the degrader is ±10mm, and a margin of 5mm is reserved. For the case of a central energy of 225MeV, the overlapping part of the teeth is ±15mm, and its thickness is 21mm, so the angle of the teeth is 13°. For the case of a central energy of 65MeV, the total thickness of the degrader is 179mm, and the total length of the teeth needs to be 130mm. With a certain margin, the length of the teeth is selected to be 140mm. Considering symmetry, the length of the teeth is 280mm. For the thickness of the teeth, the design is 40mm, mainly considering the beam envelope and strength. The mechanical structure of the degrader is designed based on the above basic parameters, such as Figure 8 shown.

[0030] In order to precisely control the position of the existing wedge-shaped graphite block degrader and collimator so as to adjust the energy and emittance of the beam, a special drive device is added behind the wedge-shaped graphite block and collimator. The drive device is designed independently to meet the physical design and functional requirements. Specifically, the drive device has a stroke of 300mm, a repeatability of ±0.012mm, and can guarantee a life of at least 100,000 reciprocating motions. These parameters ensure that the energy degrader and collimator can be adjusted with high precision and reliability, so as to achieve the purpose of finely controlling the properties of the beam.

[0031] Fig. 9The working principle diagram of the stripe ionization chamber is shown in Figure 1. When charged particles pass through the working gas in the ionization chamber, they cause the ionization of gas molecules and form electron-ion pairs. The number of electron-ion pairs is proportional to the energy loss of the charged particles in the ionization chamber. By adding an electric field to collect electrons or ions, a current signal proportional to the number of charged particles can be obtained. The absolute current value can be obtained by calibrating with a known beam current intensity. The collector adopts a stripe structure, which can give the projection distribution of the beam profile. The main components of the ionization chamber are two mutually insulated flat electrodes, which are connected to the high voltage end and the ground end of the power supply respectively. The space between the electrodes is filled with gas. When charged particles pass through the working gas in the ionization chamber, they cause the ionization of gas molecules and form electron-ion pairs. The number of electron-ion pairs is proportional to the energy loss of the charged particles in the ionization chamber. By adding an electric field to collect electrons or ions, a current signal proportional to the number of charged particles can be obtained. The absolute current value can be obtained by calibrating with a known beam current intensity. Fig.10 This is the working principle of the fluorescent target. The fluorescent target is used for interception measurement of the beam profile. The beam bombards the fluorescent target to produce visible light and form a beam bright spot. There is an observation window in the vertical direction of the beam. The beam spot image can be obtained through the observation window using CCD. After mathematical processing, the lateral distribution information of the beam can be obtained. Fig.11 It is a fluorescent target structure. Fig.12 This is the working principle of the Faraday cup. The Faraday cup is used to measure beam current intensity. Compared with the beam transformer, the Faraday cup can be used to measure weak current. The beam hits an independent metal cup to generate current. The metal cup is connected to a current-to-voltage converter (IUC). The IUC consists of a low-noise operational amplifier with high input impedance and high sensitivity. It converts weak current signals into voltage signals, and the measured current value I can be obtained.

[0032] The monitoring and control of the vacuum subsystem is completed by PLC. The main functions of the control system include pump power supply indication, start / stop control, fault status display; vacuum gauge vacuum degree display and vacuum interlock; gate valve open / close control and status display; interlock bypass start, protection and status display. The vacuum control software runs in PLC and vacuum control IOC to realize remote control of the vacuum unit. The vacuum unit control mode has two modes: manual control and automatic control. Manual control is to click the button on the vacuum interface of the main control room to operate the vacuum equipment separately; automatic control is that the vacuum equipment acts according to the designed interlock conditions until the vacuum start / stop operation is completed or a fault occurs and exits.

[0033] The devices connected to the water cooling system control system are mainly water temperature sensors, water pressure sensors and water flow sensors. The control system mainly completes water temperature, water pressure and water flow monitoring and corresponding interlocking. The interlocking threshold can be set. The control principle of the water cooling system is as follows Fig.14As shown. The water temperature sensor, water pressure sensor and water flow sensor are controlled by PLC. IOC exchanges data with Twincat3.0 PLC through ADS protocol and transmits the content to be displayed to OPI through CA protocol. The above monitored water cooling status values ​​are mainly processed by manual intervention at the OPI level. When the monitored value exceeds the warning value, OPI will issue an audible and visual warning signal, and manual intervention is required. When the measured data exceeds the alarm value, an alarm signal will be sent to the interlocking protection system at the same time as the audible and visual alarm, and the interlocking protection system will perform the corresponding protection action according to the alarm type. If the signal is in the form of dry contact, it will be connected to the PLC controller of the water cooling subsystem, and then sent by the water cooling PLC to the main PLC. If it is sent in the form of communication, it will be sent to the main control through the communication protocol. After receiving the water cooling alarm signal, the main control will immediately stop the beam flow, issue an audible and visual alarm, and execute the interlocking plan according to different operation modes.

[0034] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0035] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A beam transport control system, comprising an energy regulation system and a beam delivery system, wherein the beam is first regulated by the energy regulation system and then transported to a treatment terminal by the beam delivery system; the energy regulation system is composed of a magnet system, an energy degrader system, a beam measurement system, a vacuum system, and a water cooling system; the beam delivery system is composed of a magnet system, a beam measurement system, a vacuum system, and a water cooling system; the beam measurement system monitors the energy and position of the beam in real time; the vacuum system maintains a vacuum environment to reduce energy loss; the water cooling system ensures that the equipment operates at an appropriate temperature; the magnet system guides the beam to adjust its energy through the energy degrader system and then continues to guide the beam to the treatment terminal.

2. A beam transport control system according to claim 1, characterized in that: The magnet system includes a quadrupole magnet power supply, a correction magnet power supply, a dipole magnet power supply and a deflection magnet power supply. A digital power supply is used to control the magnet power supply by interfacing with a control system through a communication port. A temperature switch and a flow switch in the magnet system are connected in series into a signal to form a safety interlock with the magnet power supply.

3. A beam transport control system according to claim 1, characterized in that: The degrader system includes a degrader, a collimator, and a slit. The degrader is composed of a pair of split wedge-shaped graphite. After the particles in the beam enter the degrader, they collide with the atoms in the degrader multiple times. The energy reduction process reconstructs the phase space distribution of the beam, which will lead to a rapid increase in the size and emittance of the beam. FLUCK is used to simulate the movement of particles in the medium. For the 220MeV beam required for treatment, the thickness of the degrader is 21mm, and for the 70MeV beam, the thickness of the degrader is 179mm. The effect of the medium on the beam particles is divided into three aspects: change in energy, change in position, and change in divergence angle.

4. A beam transport control system according to claim 3, characterized in that: The collimator is a double-hole collimator with an effective length of 0.35m and an adjustable aperture size. For an exit emittance of 10π, the collimator aperture size is required to be 2.64mm; for an exit emittance of 20π, the collimator aperture size is required to be 3.32mm. According to the needs of the treatment end, this system is designed to adjust the aperture in the range of 10π to 20π.

5. A beam transport control system according to claim 3, characterized in that: The slit acts as a selective barrier, allowing only particles that meet specific energy standards to pass through. By precisely setting the slit opening to 4 mm, particles whose energies are higher or lower than the energy window required for the set treatment course can be effectively eliminated. Only particles whose momentum meets the slit setting range can pass through, thereby achieving energy selection and momentum control of the beam.

6. A beam transport control system according to claim 1, characterized in that: The beam measurement system includes a fluorescent target, a Faraday bucket, an ionization chamber and a multi-wire proportional chamber. The fluorescent target is made of a material called Lafarin deposited on glass or ceramic. When the beam hits the fluorescent target, it will emit light. The image information is transmitted to the central control system through a dedicated PoE camera, so that the approximate envelope information of the beam can be observed. The Faraday bucket has two states, insertion and withdrawal. In the insertion state, the beam current intensity of the proton beam is measured and it serves as a beam garbage target. Its output signal is current, which is connected to the beam measurement electronics system after current / voltage conversion. The dose ionization chamber completes the monitoring of the irradiation dose. They are all connected to the beam measurement electronics system through the ionization chamber probe after current / voltage conversion. The IV conversion is transimpedance amplification and integral amplification. The multi-wire proportional chamber completes the monitoring of the beam position.

7. A beam transport control system according to claim 1, characterized in that: The vacuum system includes a dry pump, a molecular pump, a valve and a vacuum gauge. The monitoring and control of the vacuum subsystem are completed by a PLC. The functions of the control system include pump power supply indication, start / stop control, and fault status display; vacuum gauge vacuum degree display and vacuum interlock; gate valve open / close control and status display; interlock bypass start-up, protection and status display. The efficient vacuum system reduces the interaction between the beam and air molecules.

8. A beam transport control system according to claim 1, characterized in that: The water cooling system equipment includes a water temperature sensor, a water pressure sensor and a water flow sensor. The system mainly completes water temperature, water pressure and water flow monitoring and corresponding interlocking, and the interlocking threshold can be set.

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