A high intensity pulsed x-ray beam monitoring device and method

Abstract

This invention relates to a high-intensity pulsed X-ray beam monitoring device and method, applicable to flash therapy. The high-intensity pulsed X-ray beam monitoring device of this invention uses a conversion target to convert a high-intensity pulsed X-ray beam into low-intensity electron-positron annihilation gamma rays. A ring detector array is set around the conversion target to capture the electron-positron annihilation gamma rays and calculate and determine their emission positions. The intensity of the X-ray beam under test is estimated by the intensity of the electron-positron annihilation gamma rays and the conversion efficiency of the conversion target; valid coincidence events are screened, and the coordinates of the annihilation positions are reconstructed using filtered back projection based on the signals of multiple coincidence events, obtaining the shape distribution of the X-ray beam and the intensity distribution of the beam interface.

Description

Technical Field

[0001] This invention relates to the field of gamma monitoring technology, and in particular to a high-intensity pulsed X-ray beam monitoring device and method. Background Technology

[0002] Radiation therapy has become one of the main methods for treating cancer. Statistics show that over 70% of cancer patients require radiation therapy alone or in combination with other treatments. Currently, the primary method of tumor radiation therapy is flash therapy, which can reduce damage to normal tissues while maintaining its tumor-killing ability. Clinical trials based on electron, X-ray, and proton flash therapy have been successfully conducted. The ultra-high dose rate of flash therapy presents unique challenges to dose measurement, beam control and validation, and treatment planning systems. In flash therapy, dose measurement typically requires excellent ultra-high dose rate independence, excellent spatiotemporal resolution, and tissue equivalence.

[0003] As flash therapy continues its clinical translation, high dose rates and large radiation fields are required, and the spatial distribution of the dose rate can only be measured through imaging techniques or detector arrays. Therefore, to avoid volume averaging effects, high-resolution detector arrays with small detector spacing are needed to accurately measure the two-dimensional spatial distribution of the dose rate. Furthermore, accelerator output dose verification, single-pulse dose, and real-time dose rate are also urgent requirements in flash therapy dosimetry. Real-time dose monitoring is extremely difficult for high dose rates and single-pulse doses. Flash therapy dosimeters not only need to be dose rate independent but also require sufficiently high temporal resolution and bandwidth for dose information readout. Dosimeters such as film and thermoluminescent dosimeters (TLDs) have dose rate independent responses but can only provide passive dose monitoring. Moreover, although some dosimeters can provide online dose monitoring, they encounter other problems at ultra-high dose rates, limiting their application in flash therapy. Linear accelerators employ ionization chambers at the gantry head to record the machine's output dose in real time and output a signal to shut down the accelerator after the expected dose is reached. However, most commercial ionization chambers exhibit saturation or reduced ion collection efficiency at the onset of high-dose-rate pulses. Existing dose monitoring devices suffer from sensitivity variations, nonlinear responses, and saturation at high dose rates; therefore, there is a need for an online dose monitoring device at flash therapy dose rates. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the problems of sensitivity changes, nonlinear response and saturation phenomena that occur in the dose monitoring device under high dose rates in the prior art.

[0005] To address the aforementioned technical problems, this invention provides a high-intensity pulsed X-ray beam monitoring device and method.

[0006] A high-intensity pulsed X-ray beam monitoring device, comprising:

[0007] A conversion target that converts the incident X-ray beam into low-intensity electron-positron annihilation gamma rays;

[0008] A ring detector array, wherein the ring detector array consists of multiple scintillation crystals connected in sequence, the multiple scintillation crystals being coplanar with the conversion target and arranged on a circumference centered on the conversion target;

[0009] In this process, the X-ray beam to be tested is incident on the conversion target and interacts to generate multiple pairs of positive and negative electron annihilation gamma rays with opposite propagation directions. Each pair of positive and negative electron annihilation gamma rays is received by two detectors in the ring detector array and its energy is measured. The intensity of the X-ray beam to be tested can be known based on the measured energy and the conversion efficiency of the conversion target. The position distribution of the X-ray beam is determined based on the connection between the two detectors, the time difference between the two signals, and the speed of light.

[0010] Preferably, the scintillation crystal is an LYSO:Ce crystal.

[0011] Preferably, the high-intensity pulsed X-ray beam monitoring device further includes an electronics module connected to the ring detector array for receiving and processing signals transmitted by the ring detector array.

[0012] Preferably, the high-intensity pulsed X-ray beam monitoring device further includes a support structure for fixing the conversion target and the ring detector array.

[0013] Preferably, the high-intensity pulsed X-ray beam monitoring device further includes a base plate, which is used to support the conversion target, the ring detector array, the support structure, and the electronic components.

[0014] Preferably, the conversion target is made of aluminum, iron, copper, or tungsten.

[0015] Preferably, the conversion target material is tungsten.

[0016] Preferably, the tungsten conversion target has a diameter of 15 cm and a thickness of 1 mm.

[0017] A method for monitoring high-intensity pulsed X-ray beams, employing the high-intensity pulsed X-ray beam monitoring device described above, includes the following steps:

[0018] S1: When the X-ray beam to be tested is incident on the conversion target, multiple electron-electron pairing effects occur. Each electron-electron pairing effect produces one positron and one electron, where the positron has a certain kinetic energy.

[0019] S2: After moving a certain distance, the positron gradually decelerates due to electromagnetic interaction. When the positron's speed decelerates to near 0, it annihilates with the electron to produce gamma rays, which are then received by the ring detector array.

[0020] S3: A valid coincidence event is defined as the signal energy detected by both detectors being within the range of 500-515keV.

[0021] S4: Determine the flight paths of the two gammas by connecting the center coordinates of the two detectors in a coincidence event; the annihilation location of the positron lies on this line.

[0022] S5: Determine the annihilation location of positrons along this line based on the time difference between the two signals and the speed of light;

[0023] S6: Based on the signal from multiple coincidence events, the coordinates of the annihilation location are reconstructed using filtered back projection, thus obtaining the shape distribution of the X-ray beam and the intensity distribution of the beam interface.

[0024] Preferably, in step S2, there is a greater than 99% probability that two gamma rays in opposite directions are generated when positive and negative electrons annihilate, and these rays are detected by two detectors.

[0025] The technical solution of the present invention has the following advantages compared with the prior art:

[0026] The high-intensity pulsed X-ray beam monitoring device of this invention uses a conversion target to convert a high-energy pulsed X-ray beam into low-intensity electron-positron annihilation gamma rays. A ring detector array is set around the conversion target to capture the electron-positron annihilation gamma rays and calculate and determine their emission positions. The intensity of the X-ray beam under test is estimated by the intensity of the electron-positron annihilation gamma rays and the conversion efficiency of the conversion target. Valid coincidence events are screened, and the coordinates of the annihilation positions are reconstructed by filtered back projection based on the signals of multiple coincidence events, thus obtaining the shape distribution of the X-ray beam and the intensity distribution of the beam interface. Attached Figure Description

[0027] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0028] Figure 1 This is a schematic diagram showing the positions of the conversion target and the ring detector array of the present invention.

[0029] Figure 2 This is a schematic diagram of the high-intensity pulsed X-ray beam monitoring device of the present invention.

[0030] Figure 3 This is a schematic diagram of the operation of the conversion target and the ring detector array of the present invention.

[0031] Figure 4 This is a schematic diagram showing the shift of positrons in different materials according to the present invention.

[0032] Figure 5 This is a schematic diagram of the X-ray energy distribution after the X-ray beam to be tested passes through tungsten conversion targets of different thicknesses according to the present invention.

[0033] Explanation of reference numerals in the accompanying drawings: 1. Conversion target; 2. Ring detector array; 3. Electronic components; 4. Support structure; 5. Base plate. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0035] like Figure 1-2 As shown, this invention provides a high-intensity pulsed X-ray beam monitoring device for use in flash therapy, comprising:

[0036] The conversion target 1 converts the incident X-ray beam into low-intensity electron-positron annihilation gamma rays.

[0037] A ring detector array 2 is formed by sequentially connecting multiple scintillation crystals. These crystals are coplanar with the conversion target 1 and arranged on a circumference centered on the conversion target 1. The crystals can be NaI:Tl crystals, BGO crystals, or LYSO:Ce crystals. Preferably, the scintillation crystal is an LYSO:Ce crystal with a density of 7.1 g / cc and a light yield of 32,000 photons / MeV. Its physical properties give the LYSO:Ce crystal better gamma-ray detection efficiency and energy resolution than NaI:Tl crystals and BGO crystals, and its time resolution is also superior, with a light decay time of 45 ns.

[0038] like Figure 3As shown, when the high-intensity pulsed X-ray beam monitoring device is working, the X-ray beam to be measured is incident on the conversion target 1, resulting in multiple electron-electron pair effects. Each electron-electron pair effect produces one positron and one electron, where the positron has a certain kinetic energy. After moving a certain distance, the positron gradually decelerates due to electromagnetic interaction. When the positron's velocity decelerates to near zero, it annihilates with the electron, producing one, two, or three gamma rays. Preferably, the probability of producing two positron-electron annihilation gamma rays is greater than 99%. The energy of the positron-electron annihilation gamma rays is approximately 511 keV. Since the system momentum before annihilation is close to zero, the momentum directions of the two gamma rays are opposite, with an angle of 180 degrees. In special cases where the system momentum is not zero, the angle is slightly less than 180 degrees, but it can generally be treated as 180 degrees. The two positron-electron annihilation gamma rays move in opposite directions, pass through the air, and interact with the ring detector array 2, mainly through Compton scattering. When electron-positron annihilation gamma rays propagate through air, they may interact with atmospheric matter and lose some energy. Furthermore, during Compton scattering, the ring detector array 2 may not be able to deposit all the energy. Therefore, a threshold of 500 keV is set for the energy deposition generated by the detectors. Simultaneously, interference from scattering by the incident X-ray beam needs to be eliminated, requiring an upper threshold of 515 keV. That is, a valid coincidence event is only considered complete when the signal energy detected by both detectors is within the 500-515 keV range. As described above, the high-intensity pulsed X-ray beam monitoring device provided by this invention can convert a high-intensity pulsed X-ray beam into low-intensity electron-positron annihilation gamma rays, thereby indirectly measuring the energy and positional distribution of the high-intensity pulsed X-ray beam using these low-intensity electron-positron annihilation gamma rays.

[0039] In one specific embodiment, the high-intensity pulsed X-ray beam monitoring device further includes an electronics module 3. The electronics module 3 is connected to the ring detector array 2 to receive and process the signals transmitted by the ring detector array 2, thereby determining the annihilation positions of the positrons and electrons. Specifically, the electronics module 3 can determine the flight paths of two gamma rays based on the line connecting the center coordinates of the two detectors in a single coincidence event. The annihilation position of the positron lies on this line, and the position of the annihilation point on this line can be determined based on the time difference between the two signals and the speed of light. Since gamma rays can interact at any position on the detector, the flight distance is not necessarily equal to the center distance between the two detectors. Furthermore, the time resolution of the detector is limited. Therefore, a single coincidence event can only determine a probability region with a length of approximately 100 mm. Using the coordinates of the calculated line as the center, a probability distribution is set at both ends according to the calculated position resolution. Based on the signals from multiple coincidence events, the coordinates of the annihilation position are reconstructed using filtered back projection, thus obtaining the shape distribution of the X-ray beam and the intensity distribution of the beam interface. The intensity value of the X-ray beam to be measured can be obtained from the intensity of the annihilation of positive and negative electron gamma rays and the conversion efficiency of conversion target 1.

[0040] In one specific embodiment, the high-intensity pulsed X-ray beam monitoring device further includes a support structure 4 and a base plate 5. The support structure 4 is used to fix the conversion target 1 and the ring detector array 2; the base plate 5 is used to support the conversion target 1, the ring detector array 2, the electronic plug-in 3, and the support structure 4.

[0041] In an optional embodiment, the conversion target 1 of the present invention can be made of aluminum, iron, copper, or tungsten. To select the optimal conversion target 1 material, simulations were performed on the positron shift in the aforementioned different materials, and the simulation results are as follows: Figure 4 As shown in the figure, the horizontal axis represents the positron deflection distance, and the vertical axis represents the number of X-ray beams to be measured. It can be seen from the figure that the positron deflection is greatest in the aluminum conversion target and smallest in the tungsten conversion target. In a preferred embodiment, the conversion target material is tungsten.

[0042] Tungsten, as a shielding material for X-ray beams, directly affects the energy attenuation of the X-ray beam after it passes through. Therefore, to select suitable tungsten conversion target thickness parameters, a simulation study was conducted on the energy distribution of a 1 million 6 MeV X-ray beam after passing through tungsten conversion targets of different thicknesses. The results are as follows: Figure 5As shown in the figure, the horizontal axis represents the energy of the X-ray beam to be tested, and the vertical axis represents the number of X-ray beams to be tested. The figure shows that the majority of the X-ray beams to be tested do not experience energy attenuation after passing through the tungsten conversion target. Specifically, the number of 1,000,000 6 MeV X-ray beams to be tested after passing through a 4 mm thick tungsten conversion target accounts for 80% of the number before incident; the number of 1,000,000 6 MeV X-ray beams to be tested after passing through a 2 mm thick tungsten conversion target accounts for 90% of the number before incident; and the number of 1,000,000 6 MeV X-ray beams to be tested after passing through a 1 mm thick tungsten conversion target accounts for 95% of the number before incident. Considering the energy attenuation of some X-ray beams, the total current attenuation of the X-ray beams to be tested after entering the tungsten conversion target is controlled within 8%. In one specific embodiment, a 1mm thick tungsten beam is selected as the tungsten conversion target. This configuration avoids excessive shielding of the X-ray beam by the tungsten conversion target, which could lead to excessive attenuation of the X-ray beam and prevent the energy of the X-ray beam used for treatment from falling short of the actual treatment requirements. Simultaneously, to match the 10*10cm... 2 The size of the X-ray beam to be measured was determined, and a tungsten conversion target with a diameter of 15 cm was selected. It should be noted that the diameter and thickness settings of the tungsten conversion target mentioned above are only examples in the embodiments of this application. In fact, the diameter and thickness settings of the tungsten conversion target should be based on the actual operational needs, and the diameter and thickness of the tungsten conversion target are not specifically limited in the embodiments of this application.

[0043] In one specific embodiment, the ring detector array 2 uses LYSO:Ce crystals as detectors. The ring detector array 2 is uniformly distributed outside a 700mm diameter ring, meaning the end face of the crystal is 350mm from the center of the ring. The tungsten conversion target is positioned at the center of the circular plane. The crystals are 82 cubes with an edge length of 1 inch each, and the crystal thickness is chosen to be 1 inch, which improves the detector position resolution while ensuring sufficient full-energy peak detection efficiency at 511keV.

[0044] The present invention also provides a method for monitoring high-intensity pulsed X-ray beams, employing the high-intensity pulsed X-ray beam monitoring device described above, comprising the following steps:

[0045] S1: When the X-ray beam to be tested is incident on the conversion target 1, the electron-electron pair effect occurs, producing one positron and one electron, wherein the positron has a certain kinetic energy;

[0046] S2: After moving a certain distance, the positron gradually decelerates due to electromagnetic interaction. When the positron's speed decelerates to near 0, it annihilates with an electron to produce gamma rays, which are received by the ring detector array 2. Among them, there is a greater than 99% probability of producing two gamma rays in opposite directions, which are detected by two detectors.

[0047] S3: A valid coincidence event is defined as the signal energy detected by both detectors being within the range of 500-515keV.

[0048] S4: Determine the flight paths of the two gammas by connecting the center coordinates of the two detectors in a coincidence event; the annihilation location of the positron lies on this line.

[0049] S5: Determine the annihilation location of positrons along this line based on the time difference between the two signals and the speed of light;

[0050] S6: Based on the signal from multiple coincidence events, the coordinates of the annihilation location are reconstructed using filtered back projection, thus obtaining the shape distribution of the X-ray beam and the intensity distribution of the beam interface.

[0051] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A high intensity pulsed X-ray beam monitoring device, characterized by, Applications in flash therapy include: A conversion target, which converts the incident X-ray beam into low-intensity electron-positron annihilation gamma rays, is made of tungsten and has a diameter of 15 cm and a thickness of 1 mm. A ring detector array, wherein the ring detector array consists of multiple scintillation crystals connected in sequence, the multiple scintillation crystals being coplanar with the conversion target and arranged on a circumference centered on the conversion target; In this process, the X-ray beam to be tested is incident on the conversion target and interacts to generate multiple pairs of positive and negative electron annihilation gamma rays with opposite propagation directions. Each pair of positive and negative electron annihilation gamma rays is received by two detectors in the ring detector array and its energy is measured. The intensity of the X-ray beam to be tested can be known based on the measured energy and the conversion efficiency of the conversion target. The position distribution of the X-ray beam is determined based on the connection between the two detectors, the time difference between the two signals, and the speed of light.

2. The high intensity pulsed X-ray beam monitoring device of claim 1, wherein, The scintillation crystal is an LYSO:Ce crystal.

3. The high intensity pulsed X-ray beam monitoring device of claim 1, wherein, The high-intensity pulsed X-ray beam monitoring device also includes an electronics module connected to the ring detector array for receiving and processing signals transmitted by the ring detector array.

4. The high intensity pulsed X-ray beam monitoring device of claim 3, wherein, The high-intensity pulsed X-ray beam monitoring device also includes a support structure for fixing the conversion target and the ring detector array.

5. The high intensity pulsed X-ray beam monitoring device of claim 4, wherein, The high-intensity pulsed X-ray beam monitoring device also includes a base plate, which is used to support the conversion target, the ring detector array, the support structure, and the electronic components.

6. A method of high intensity pulsed X-ray beam current monitoring, characterized by, The high-intensity pulsed X-ray beam monitoring device as described in any one of claims 1 to 5 includes the following steps: S1: When the X-ray beam to be tested is incident on the conversion target, multiple electron-electron pairing effects occur. Each electron-electron pairing effect produces one positron and one electron, where the positron has a certain kinetic energy. S2: After moving a certain distance, the positron gradually decelerates due to electromagnetic interaction. When the positron's speed decelerates to near 0, it annihilates with the electron to produce gamma rays, which are then received by the ring detector array. S3: A valid coincidence event is defined as the signal energy detected by both detectors being within the range of 500-515keV. S4: Determine the flight paths of the two gammas by connecting the center coordinates of the two detectors in a coincidence event; the annihilation location of the positron lies on this line. S5: Determine the annihilation location of positrons along this line based on the time difference between the two signals and the speed of light; S6: Based on the signal from multiple coincidence events, the coordinates of the annihilation location are reconstructed using filtered back projection, thus obtaining the shape distribution of the X-ray beam and the intensity distribution of the beam interface.

7. The high intensity pulsed X-ray beam monitoring method of claim 6, wherein, In step S2, there is a greater than 99% probability that two gamma rays in opposite directions are generated when positive and negative electrons annihilate, and these rays are detected by two detectors.

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