A method for determining the structure of a bragg peak based on characteristic x-ray inversion

Abstract

This invention provides a method for retrieving the Bragg peak structure based on characteristic X-rays, belonging to the field of particle radiotherapy technology. The method includes: establishing a first functional relationship between the residual energy of the target charged particle beam and the thickness of the target medium by adjusting the target medium thickness; establishing a second functional relationship between the intensity of characteristic X-rays generated by a tracer element thin target induced by the target charged particle beam at different positions on the target medium and the residual energy, thereby obtaining the secondary fragmentation signal of the nuclear reaction in the Bragg peak tail region; and establishing a third functional relationship between the intensity of characteristic X-rays generated by the particle-induced tracer atoms irradiated on the target surface and the lateral distribution of the particle beam by adjusting the distance between the center of the tracer element thin target and the center of the particle beam. This invention, based on the characteristic X-rays of tracer elements, simultaneously achieves precise characterization of the longitudinal depth and lateral broadening of the Bragg peak generated by the target charged particle beam in the target medium during particle therapy, as well as the detection of the nuclear reaction effect in the tail region.

Description

Technical Field

[0001] This invention relates to the field of particle radiotherapy technology, and in particular to a method based on the inversion of Bragg peak structure using characteristic X-rays. Background Technology

[0002] Proton or heavy ion beams, such as carbon ion beams, form a highly localized dose deposition peak, or Bragg peak, at the end of their range in tissues. This characteristic allows the dose to be highly conformal to the tumor target area during treatment, while avoiding damage to surrounding healthy tissues, even within range of dangerous organs. Therefore, particle therapy has been considered an emerging high-precision radiotherapy method for cancer. However, the realization of this physical advantage is highly dependent on the irradiated anatomical structure and the precise location of the Bragg peak within the body. Currently, treatment planning mainly relies on pre-treatment imaging such as computed tomography (CT) scans, but in actual treatment, problems may arise such as inaccurate patient positioning, changes in anatomical structure due to respiration, organ peristalsis, weight changes, or the growth or decline of the tumor itself. More importantly, the process of converting CT scan values ​​into tissue blocking ability inherently involves uncertainty. Therefore, direct online and precise verification and feedback of the radiation dose applied to the patient during treatment is one of the biggest challenges in the effective implementation of particle therapy.

[0003] To address this challenge, numerous related technologies have explored various approaches. Positron emission tomography (PET), as the earliest proposed and clinically validated therapeutic monitoring technique, indirectly infers ion range by detecting positron annihilation photons generated by the reaction of the beam with tissue nuclei. Another similar method detects the transient gamma rays emitted when incident ions undergo inelastic nuclear reactions with atomic nuclei in tissue. However, these methods suffer from low signal yield, limited spatial resolution, susceptibility to biological clearance effects, and reliance on complex, highly sensitive detection systems, making real-time direct feedback difficult. Although hybrid PET / CT and transient gamma-ray imaging schemes have been proposed in recent years, these limitations have not yet been completely overcome.

[0004] In addition, interaction vertex imaging, ion acoustic imaging, proton computed tomography, and magnetic resonance-guided proton therapy have also shown great application potential. However, they still face core challenges such as weak signals, susceptibility to noise interference, the influence of strong magnetic fields on beam trajectory and dosage, and complex system compatibility and integration. Currently, they are still in the early stages of research and development and are far from routine clinical application. Furthermore, the secondary electron bremsstrahlung and particle-induced X-ray emission analysis techniques proposed in recent years have shown certain potential advantages in in vivo range verification for proton or heavy ion therapy. Secondary electron bremsstrahlung imaging, as an imaging method that detects continuous-energy X-rays emitted when secondary electrons generated by an ion beam in a medium are deflected and decelerated by the Coulomb field of atomic nuclei, derives its signal from the direct interaction between the beam and the medium. Therefore, developing non-invasive detection based on this method shows promising application prospects. Particle-induced X-ray emission analysis is an analytical technique based on the characteristic X-rays generated by the interaction between an ion beam and the inner-shell electrons of atoms. However, this work also faces challenges such as the risk of surgically implanting metal markers and the difficulty in balancing the size of the markers with the requirements of X-ray detection intensity and clinical application. Therefore, there is currently no effective method internationally that can simultaneously characterize the longitudinal depth and lateral broadening of the Bragg peak during particle therapy, as well as reflect the nuclear fragment information in the Bragg peak tail region, for precise online monitoring and control. Summary of the Invention

[0005] This invention provides a method for inverting the Bragg peak structure based on characteristic X-rays. Based on the characteristic X-rays of tracer elements, it accurately characterizes the longitudinal depth and lateral broadening of the Bragg peak of the target charged particle beam in the target medium during particle therapy, and obtains information on the nuclear reaction effect in the tail region of the Bragg peak.

[0006] In a first aspect, the present invention provides a method for retrieving Bragg peak structures based on characteristic X-ray inversion, comprising: By adjusting the thickness of the target medium, the energy deposition of the target charged particle beam in target media of different thicknesses is measured, and a first functional relationship between the remaining energy of the target charged particle beam and the thickness of the target medium is established; wherein, the thickness of the target medium is the penetration depth of the target charged particle beam in the target medium; By adjusting the thickness of the target medium, the intensity of characteristic X-rays generated by the tracer element thin target arranged after the target medium is induced by the target charged particle beam at different characteristic positions of the Bragg peak is measured, and a second functional relationship between the characteristic X-ray intensity and the remaining energy is established by combining the first functional relationship. By adjusting the distance between the center of the tracer element thin target and the center of the target charged particle beam at a preset target medium thickness, the intensity of characteristic X-rays induced by the target charged particle beam irradiating the target surface and generated by the tracer atoms is measured. The relationship between the characteristic X-ray intensity and the target center displacement is obtained, and a third functional relationship between the characteristic X-ray intensity and the lateral distribution of the target charged particle beam is established; wherein, the distance between the center of the tracer element thin target and the center of the target charged particle beam is the target center displacement; Based on the first functional relationship, the first measured data of the characteristic X-ray intensity changing with the thickness of the target medium, the second functional relationship, the second measured data of the characteristic X-ray intensity changing with the displacement of the target center, and the third functional relationship, accurate characterization data of the longitudinal depth and lateral broadening of the Bragg peak of the target charged particle beam in the target medium are obtained, and the secondary fragment signal of the nuclear reaction in the Bragg peak tail region is obtained.

[0007] In some embodiments, establishing the first functional relationship includes: The dose deposition of the target charged particle beam in the target medium of different thicknesses is measured by an ionization device, and the dose deposition is converted into the energy deposition. The remaining energy is calculated by combining the initial energy of the target charged particle beam to obtain the third measured data of the variation of the remaining energy with the thickness of the target medium, and the first functional relationship is established.

[0008] In some embodiments, establishing the second functional relationship and obtaining the secondary fragmentation signal of the nuclear reaction in the Bragg peak tail region includes: Based on the first functional relationship, the adjusted target medium thickness is converted into the corresponding residual energy; The fourth measured data on the variation of characteristic X-ray intensity generated by the tracer element thin target at different positions of the Bragg peak induced by the target charged particle beam with the remaining energy is obtained, and the second functional relationship is established. At the same time, the secondary fragment signal of the nuclear reaction in the tail region of the Bragg peak is obtained.

[0009] In some embodiments, the evolution of the characteristic X-ray intensity with the thickness of the target medium includes plateau region, Bragg peak region, and tail region; In the plateau region, the intensity of the characteristic X-rays first increases gradually and then decreases with the thickness of the target medium. In the Bragg peak region, the intensity of the characteristic X-rays decreases rapidly with the thickness of the target medium and decreases slowly at the end of the range of the target charged particle beam. In the trailing region, following the Bragg peak where the energy of the target charged particle beam is rapidly deposited, the nuclear reaction effect at the tail of the Bragg peak is detected based on the acquired continuous and resolvable characteristic X-ray signals.

[0010] In some embodiments, based on the first functional relationship, first measured data on the variation of characteristic X-ray intensity with the thickness of the target medium, the second functional relationship, second measured data on the variation of characteristic X-ray intensity with the displacement of the target center, and the third functional relationship, precise characterization data of the longitudinal depth and transverse broadening of the Bragg peak of the target charged particle beam in the target medium are obtained, including: Based on the first functional relationship, the first measured data of the characteristic X-ray intensity changing with the thickness of the target medium, and the second functional relationship, accurate characterization data of the longitudinal depth of the Bragg peak of the target charged particle beam in the target medium is obtained, and the secondary fragment signal of the nuclear reaction in the Bragg peak tail region is obtained. Based on the second measured data of the variation of the characteristic X-ray intensity with the displacement of the target center and the third functional relationship, accurate characterization data of the lateral broadening of the Bragg peak of the target charged particle beam in the target medium are obtained.

[0011] In some embodiments, obtaining precise characterization data of the lateral broadening of the Bragg peak of the target charged particle beam in the target medium includes: For the characteristic X-ray intensities corresponding to different target center displacements in the second measured data, after eliminating the influence of ionization cross-section factors that depend on the energy of the target charged particle beam, the relationship between the number of charged particles of the experimental target and the target center displacement is obtained.

[0012] In some embodiments, obtaining precise characterization data of the transverse broadening of the Bragg peak of the target charged particle beam in the target medium further includes: The lateral distribution of the pre-defined target charged particle beam conforms to an isotropic two-dimensional Gaussian distribution model; Based on the two-dimensional Gaussian distribution model and the geometric dimensions of the tracer element thin target, the relationship between the theoretical number of charged particles of the target and the displacement of the target center under the two-dimensional Gaussian distribution model is obtained. Based on the relationship between the number of charged particles in the experimental target and the displacement of the target center, the relationship between the number of charged particles in the target and the displacement of the target center under the two-dimensional Gaussian distribution model is fitted and compared to obtain accurate characterization data of the lateral broadening of the Bragg peak of the target charged particle beam in the target medium.

[0013] Secondly, embodiments of the present invention also provide a system based on characteristic X-ray inversion of Bragg peak structures, comprising: A target medium thickness adjustment device is used to contain a target medium and to adjust the thickness of the target medium in the incident direction of a target charged particle beam; wherein, the target medium thickness is the penetration depth of the target charged particle beam in the target medium; A tracer element thin target is disposed behind the target medium and is used to be excited by the beam of charged particles of the target after passing through the target medium to generate characteristic X-rays; An X-ray detector is used to measure the intensity of the characteristic X-rays by maintaining a preset geometric angle and a preset detection distance with the tracer element thin target. A three-dimensional moving platform, carrying the tracer element thin target and the X-ray detector, is used to adjust the tracer element thin target and the X-ray detector to a preset position along the incident direction of the charged particle beam of the target, so as to synchronously adjust the displacement of the target center. A processor for executing the method based on characteristic X-ray inversion of Bragg peak structures as described in the first aspect.

[0014] In some embodiments, the tracer element is selected from at least one element selected from molybdenum, iodine, and gadolinium, and the characteristic X-ray signal generated by the tracer element when excited is different from the background signal generated by the target medium; The target charged particle beam is a proton beam or a carbon ion beam, and the target medium is a water phantom or a human tissue equivalent phantom.

[0015] In some embodiments, the target medium thickness adjustment device is a sub-millimeter-level water phantom stack, and the three-dimensional moving platform is a three-dimensional precision moving platform.

[0016] This invention, while precisely locating the Bragg peak of a charged particle beam, simultaneously acquires the lateral beam broadening and lateral distribution parameters, achieving for the first time comprehensive spatial morphological analysis of the Bragg peak's longitudinal depth and lateral range, as well as detection of nuclear reaction effects in the Bragg peak tail region. Utilizing the unique discrete sharp energy spectral lines of the tracer element's characteristic X-rays as a unique identifier, background scattering interference from the target medium can be effectively avoided, significantly improving the specificity and anti-interference capability of the detection signal. In practical applications, the tracer element can be pre-introduced into the target medium, eliminating the need for any obstructive probes or detectors inserted in the main beam transmission path. The X-ray detector can be placed externally to complete signal acquisition without interfering with the original beam's physical dose field. The characteristic X-rays are generated synchronously at the moment of beam irradiation, with a detection and analysis response time down to the millisecond level, meeting the requirements for online real-time dose verification and beam control during dynamic irradiation. It is also widely applicable to various charged particle and target medium scenarios, including proton beams, heavy ion beams and other heavy ion beams, as well as water phantoms and human tissue phantoms. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced one by one below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating a method for retrieving Bragg peak structures based on characteristic X-rays, as provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of a system based on characteristic X-ray inversion Bragg peak structure provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the dose deposition and residual energy variation curves of a 120MeV / u carbon ion beam in an aqueous phantom medium as provided in an embodiment of the present invention, showing the variation with penetration depth. Figure 4 This is a schematic diagram of the characteristic X-ray spectrum of the K-shell generated by a carbon ion beam with an energy of 120 MeV / u after passing through a 24 mm thick water phantom medium, which induces a thin target of a tracer element. Figure 5 This is a schematic diagram of the variation curve of the intensity of K-shell characteristic X-rays generated by a tracer element thin target after a carbon ion beam with an energy of 120 MeV / u passes through a water phantom medium, as provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the variation curve of the intensity of K-shell characteristic X-rays generated by a carbon ion beam with an energy of 120 MeV / u irradiating a thin target of a tracer element at different penetration depths as a function of the target center displacement. Figure 7 This is a schematic diagram of the change in the number of particles irradiated onto a tracer element thin target at different penetration depths as a function of the target center displacement by a carbon ion beam with an energy of 120 MeV / u, provided in an embodiment of the present invention. Figure 8 This is a three-dimensional spatial evolution cloud map of the lateral distribution of a carbon ion beam with an energy of 120 MeV / u in a water phantom medium at different penetration depths, provided by an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0020] This invention provides a method for retrieving Bragg peak structures based on characteristic X-ray inversion, comprising: adjusting the thickness of the target medium, measuring the energy deposition of a target charged particle beam in target media of different thicknesses, and establishing a first functional relationship between the remaining energy of the target charged particle beam and the thickness of the target medium; wherein the thickness of the target medium is the penetration depth of the target charged particle beam in the target medium; adjusting the thickness of the target medium, measuring the intensity of characteristic X-rays generated by a tracer element thin target arranged after the target charged particle beam induces the target medium at different characteristic positions of the Bragg peak, and establishing a second functional relationship between the intensity of characteristic X-rays and the remaining energy in conjunction with the first functional relationship; adjusting the center of the tracer element thin target and the target charged particle beam at a preset target medium thickness. The distance between the centers of the sub-beams is measured, and the intensity of characteristic X-rays induced by the target charged particle beam irradiating the target surface is measured to obtain the relationship between the characteristic X-ray intensity and the target center displacement. A third functional relationship between the characteristic X-ray intensity and the lateral distribution of the target charged particle beam is established. Among them, the distance between the center of the tracer element thin target and the center of the target charged particle beam is the target center displacement. Based on the first functional relationship, the first measured data of the characteristic X-ray intensity changing with the thickness of the target medium, the second functional relationship, the second measured data of the characteristic X-ray intensity changing with the target center displacement, and the third functional relationship, accurate characterization data of the longitudinal depth and lateral broadening of the Bragg peak of the target charged particle beam in the target medium are obtained, and the secondary fragment signal of the nuclear reaction in the Bragg peak tail region is obtained.

[0021] Figure 1 This is a schematic flowchart illustrating a method for retrieving Bragg peak structures based on characteristic X-ray inversion, provided in an embodiment of the present invention. The method for retrieving Bragg peak structures based on characteristic X-ray inversion can be executed by the system for retrieving Bragg peak structures based on characteristic X-ray inversion provided in this embodiment of the invention. Figure 1 As shown, the method based on characteristic X-ray inversion of Bragg peak structure includes the following steps: S101. Adjust the thickness of the target medium, which is the penetration depth of the target charged particle beam in the target medium. Measure the dose deposition of the target charged particle beam in the target medium of different thicknesses, and convert the dose deposition into energy deposition. Combine the initial energy of the target charged particle beam to obtain the remaining energy of the target charged particle beam, and establish the first functional relationship between the remaining energy of the target charged particle beam and the penetration depth.

[0022] S102. Adjust the thickness of the target medium, measure the intensity of characteristic X-rays generated by the tracer element thin target induced by the target charged particle beam at different positions of the target medium located on the Bragg peak, and establish a second functional relationship between the intensity of characteristic X-rays and the remaining energy of the target charged particle beam in combination with the first functional relationship.

[0023] S103. At the preset penetration depth, adjust the distance between the center of the tracer element thin target and the center of the target charged particle beam, which is the center displacement or target center displacement. Measure the intensity of the characteristic X-rays induced by the target charged particle beam irradiating the target surface to generate tracer atoms, obtain the relationship between the characteristic X-ray intensity and the target center displacement, and establish the third function relationship between the characteristic X-ray intensity and the transverse distribution of the target charged particle beam.

[0024] S104. Based on the first functional relationship, the first measured data of the characteristic X-ray intensity changing with the penetration depth, the second functional relationship, the second measured data of the characteristic X-ray intensity changing with the target center displacement, and the third functional relationship, the influence of factors such as the ionization cross section dependent on the energy of the target charged particle beam is eliminated from the measured characteristic X-ray intensity. Accurate characterization data of the longitudinal depth and lateral broadening of the Bragg peak of the target charged particle beam in the target medium are obtained, and the secondary fragment signal of the nuclear reaction in the Bragg peak tail region is obtained.

[0025] Specifically, the target medium refers to the main material through which the target charged particle beam is transported, used to simulate or represent the transport characteristics of charged particle beams in biological tissues in real-world applications, such as a water phantom or a human tissue equivalent phantom. The target charged particle beam refers to the stream of charged particles used to generate the Bragg peak, such as a proton beam, carbon ion beam, or other heavy ion beam. The penetration depth refers to the path length of the target charged particle beam along the incident direction within the target medium; this depth can be precisely controlled by adjusting the thickness of the target medium and is denoted by h. The remaining energy of the target charged particle beam refers to the energy retained by the target charged particle beam after passing through a target medium of a specific thickness, denoted by E. res The term "tracer element thin target" refers to a thin target material made of a specific tracer element. When bombarded by a beam of charged particles, the inner-shell electrons of its atoms are ejected, and the outer-shell electrons jump to fill the vacancies, emitting characteristic X-rays. The intensity of the characteristic X-rays indicates the number of characteristic X-ray photons generated by the tracer element thin target when excited by the incident target's charged particle beam. The photon count is expressed in N0.05. x It is indicated that this intensity is related to factors such as the number of incident charged particles, the atomic density of the tracer element thin target, the ionization cross section of the tracer element, and the fluorescence yield.

[0026] In some embodiments, based on a first functional relationship, first measured data on the variation of characteristic X-ray intensity with the thickness of the target medium, a second functional relationship, second measured data on the variation of characteristic X-ray intensity with the displacement of the target center, and a third functional relationship, precise characterization data of the longitudinal depth and transverse broadening of the Bragg peak of the target charged particle beam in the target medium are obtained, including: Based on the first functional relationship, the first measured data of the characteristic X-ray intensity changing with the thickness of the target medium, and the second functional relationship, the precise characterization data of the longitudinal depth of the Bragg peak of the target charged particle beam in the target medium is obtained, and the secondary fragment signal of the nuclear reaction in the Bragg peak tail region is obtained. Based on the second measured data and the third functional relationship of the characteristic X-ray intensity variation with the target center displacement, accurate characterization data of the lateral broadening of the Bragg peak of the target charged particle beam in the target medium are obtained.

[0027] The first stage establishes a primary functional relationship between the remaining energy of the target charged particle beam and the thickness of the target medium. Specifically, by adjusting the penetration depth h of the target charged particle beam in the target medium, the dose deposition value of the target charged particle beam in the target medium of different thicknesses is measured point by point using equipment such as a Markus ionization chamber. The dose deposition is then converted into energy deposition, and combined with the initial energy of the target charged particle beam, the remaining energy E of the target charged particle beam is obtained. res Furthermore, the penetration depth h can be achieved by changing the thickness of the target medium. For example, a stack of water phantoms with adjustable number of pieces can be used, where the thickness of each piece is known, with a minimum thickness of 0.1 mm. The total thickness can be precisely controlled by increasing or decreasing the number of pieces.

[0028] In some embodiments, establishing a first functional relationship includes: measuring the dose deposition of the target charged particle beam in a target medium of different thicknesses using an ionization device, converting the dose deposition into energy deposition, calculating the remaining energy by combining the initial energy of the target charged particle beam, obtaining third measured data on the variation of the remaining energy with the thickness of the target medium, and establishing the first functional relationship.

[0029] The dose deposition of a charged particle beam in target media of varying thicknesses can be measured using advanced equipment such as the Markus ionization chamber. The ionization chamber consists of an entrance window, an air-sensitive cavity, high-voltage electrodes, a collecting electrode, and an electrostatic readout meter. The charged particle beam passes through the entrance window into the air-sensitive cavity, ionizing air molecules and generating numerous electron-positron pairs. A polarized high voltage of several hundred volts is applied to both electrodes of the ionization chamber, creating a uniform electric field. This field drives electrons and ions to drift towards the collecting electrode and the high-voltage electrode, respectively, where they are collected before complete recombination, generating a weak ionization current. The magnitude of this current is proportional to the absorbed dose deposited within the sensitive cavity. The current is read by the electrostatic readout meter, and the radiation dose deposition value is calculated. After obtaining the dose deposition values ​​of the charged particle beam in target media of varying thicknesses, the dose deposition is converted into energy deposition. Combined with the initial energy E0 of the charged particle beam, the remaining energy E of the charged particle beam is then obtained. res At multiple different penetration depths h1, h2, h3..., the dose deposition value of the target charged particle beam at the corresponding target medium thickness was measured, and the residual energy E of the target charged particle beam at the corresponding penetration depth was obtained according to the above formula. res1 E res2 E res3 ... to obtain a set of discrete (h, E) resThe data points, namely the third measured data showing the change of the remaining energy of the target charged particle beam with the penetration depth, i.e., the thickness of the target medium, establish the first functional relationship between the remaining energy of the target charged particle beam and the thickness of the target medium. This functional relationship describes the evolution of the energy decay of the target charged particle beam in the target medium, providing a benchmark for subsequent quantitative measurements based on the inversion of the Bragg peak structure using the characteristic X-rays of the tracer element iodine.

[0030] In some embodiments, establishing a second functional relationship and obtaining secondary fragment signals of nuclear reactions in the Bragg peak tail region includes: converting the adjusted target medium thickness into corresponding residual energy according to a first functional relationship; acquiring fourth measured data on the variation of characteristic X-ray intensity generated by a tracer element thin target at different positions of the target medium induced by a target charged particle beam with residual energy, and establishing a second functional relationship while obtaining secondary fragment signals of nuclear reactions in the Bragg peak tail region.

[0031] The second stage establishes a second functional relationship between the intensity of characteristic X-rays and the remaining energy of the target charged particle beam. Specifically, the intensity of characteristic X-rays induced by the target charged particle beam and generated by a thin tracer target located behind the target medium is measured at multiple different penetration depths h. After the tracer target is bombarded by the charged particle beam, the inner-shell electrons of its atoms are excited, and the outer-shell electrons emit characteristic X-rays when they jump to fill the holes. This characteristic X-ray is collected using an X-ray detector, such as a silicon drift (SDD) detector, and the photon count N is recorded. x At each penetration depth h, the corresponding characteristic X-ray intensity, i.e., the photon count N, is measured. x To obtain a discrete set of (h, N) x The data points are obtained based on the first functional relationship between the remaining energy of the target charged particle beam and the thickness of the target medium, and also yield a set of discrete (E) data points. res N x The data points are either the first measured data of the characteristic X-ray intensity changing with the thickness of the target medium, or the fourth measured data of the characteristic X-ray intensity changing with the remaining energy, and then a second functional relationship between the characteristic X-ray intensity and the remaining energy is established.

[0032] Furthermore, based on the continuous variation of characteristic X-ray intensity with the thickness of the target medium or the remaining energy, the secondary fragment signal of the nuclear reaction in the Bragg peak tail region can be further obtained. Specifically, when the thickness of the target medium, i.e., the penetration depth of the target charged particle beam in the target medium, exceeds the range of the target charged particle beam, the kinetic energy of the target charged particle beam is completely exhausted and it stops. However, due to the high dose deposition of the target charged particle beam, such as a high-energy charged particle beam, at the end of its range, and the inelastic nuclear reaction with the target medium such as the water phantom, various secondary light fragments are generated, mainly including B, Be, Li, He, and H ions. These secondary light fragments have a longer range, can penetrate deeper into the target medium, and bombard the tracer element thin target, inducing the tracer element to emit characteristic X-rays. By continuously acquiring the characteristic X-ray signal generated by the secondary light fragments in deeper regions, the count intensity of this signal and its variation with the penetration depth are obtained, thereby realizing the detection and characterization of the nuclear reaction effect in the Bragg peak tail region.

[0033] Thus, the second functional relationship describes the intensity variation law of the tracer element induced to produce characteristic X-rays under different penetration depths or remaining energies of the target charged particle beam under this specific condition. This enables the accurate characterization of the longitudinal depth of the Bragg peak of the target charged particle beam in the target medium, and at the same time, the secondary fragment signal of the nuclear reaction in the Bragg peak tail region is obtained.

[0034] In some embodiments, obtaining accurate characterization data of the transverse broadening of the Bragg peak of the target charged particle beam in the target medium includes: for the characteristic X-ray intensities corresponding to different target center displacements in the second measured data, after eliminating the influence of ionization cross-section factors that are dependent on the energy of the target charged particle beam, obtaining the relationship between the number of experimental target charged particles and the target center displacement.

[0035] The third stage establishes a third functional relationship between the characteristic X-ray intensity and the lateral distribution of the target charged particle beam. Specifically, by adjusting the distance between the center of the tracer element thin target and the center of the target charged particle beam at a preset penetration depth (i.e., the center displacement or target center displacement), the intensity of the characteristic X-rays induced by the charged particles irradiating the target surface to the tracer atoms is measured to obtain the relationship between the characteristic X-ray intensity and the target center displacement. Furthermore, the influence of factors such as the ionization cross-section, which are related to or dependent on the energy of the target charged particles, is eliminated to obtain the relationship between the number of experimental target charged particles and the target center displacement.

[0036] Specifically, the center displacement or target center displacement refers to the distance between the center of the tracer element thin target and the center of the target charged particle beam, or the displacement of the target center relative to the target charged particle beam center. The target center displacement is denoted by D. The target center displacement is measured by a three-dimensional precision moving platform, which moves the tracer element thin target gradually along the beam direction perpendicular to the beam direction in preset steps, such as 3 mm, including both positive and negative directions. When the center of the tracer element thin target coincides with the beam center, the target center displacement is 0. At a preset penetration depth, such as a depth position that represents the structural characteristics of the Bragg peak, the intensity of characteristic X-rays induced by charged particles irradiating the target surface at the corresponding target center displacement D is measured by gradually moving the tracer element thin target laterally, i.e., the photon count N. x The set of discrete data points showing the variation of characteristic X-ray intensity with the displacement of the target center is obtained, denoted as (D, N). x This refers to the second measured data on the change of characteristic X-ray intensity with the displacement of the target center, thereby establishing the correspondence between characteristic X-ray intensity and target center displacement.

[0037] However, at a predetermined penetration depth, the intensity of the characteristic X-rays induced by the target charged particle beam irradiating the target surface and generating tracer atoms depends not only on the number of charged particles irradiating the target, but also directly on the size of the collision ionization cross section between the target charged particle beam and the tracer element. Therefore, in order to further obtain the relationship between the number of charged particles irradiating the target at a specific penetration depth and the displacement of the target center, the intensity of the measured characteristic X-rays, i.e., the photon count N, is analyzed. x Eliminating the influence of energy-related factors such as ionization cross-section, the number N of the target charged particles in the experiment was obtained. p The set of discrete data points that vary with the displacement of the target center is denoted as (D, N). p This leads to the establishment of a correspondence between the number of charged particles in the experimental target and the displacement of the target center.

[0038] In some embodiments, obtaining accurate characterization data of the lateral broadening of the Bragg peak of the target charged particle beam in the target medium further includes: presupposing that the lateral distribution of the target charged particle beam conforms to an isotropic two-dimensional Gaussian distribution model; obtaining the theoretical relationship between the number of target charged particles and the displacement of the target center under the two-dimensional Gaussian distribution model based on the two-dimensional Gaussian distribution model and the geometric dimensions of the tracer element thin target; and fitting and comparing the experimental relationship between the number of target charged particles and the displacement of the target center with the theoretical relationship between the number of target charged particles and the displacement of the target center under the two-dimensional Gaussian model to obtain accurate characterization data of the lateral broadening of the Bragg peak of the target charged particle beam in the target medium.

[0039] After obtaining the above functional relationship, in order to further obtain the lateral distribution characteristics of the target charged particle beam from the correspondence between the number of charged particles in the experimental target and the displacement of the target center, that is, the evolution relationship of the lateral distribution of the target charged particle beam with the thickness of the target medium, the specific method includes: assuming that the lateral distribution of the target charged particle beam follows an isotropic two-dimensional Gaussian distribution, and σ is the Gaussian distribution parameter to be solved, then the full width at half maximum (FWHM) of the beam is... Based on the pre-defined Gaussian distribution model, the geometry of the tracer element thin target, and the spatial position of the tracer element thin target relative to the target medium, the theoretical number of charged particles N corresponding to the overlapping area between the target charged particle beam and the tracer element thin target at different target center displacements under different assumed Gaussian distribution parameters σ is calculated through numerical integration. P’ (D, σ). Furthermore, the number N of the target charged particles obtained from the above experiment... p Compared with the theoretical target number of charged particles N P’ By fitting and comparing (D, σ), the optimal σ is obtained, which is the lateral distribution parameter of the target charged particle beam at that penetration depth. Repeating the above process for multiple penetration depths, the complete evolution law of the beam lateral distribution with penetration depth can be obtained, clearly reflecting the physical process of the target charged particle beam, i.e., the ion beam, gradually diverging with the transmission depth.

[0040] Therefore, this invention proposes for the first time a method for retrieving the Bragg peak structure of a particle beam based on the characteristic X-rays of tracer elements. Based on the first functional relationship between the remaining energy of the target charged particle beam and the thickness of the target medium, the first measured data showing the variation of characteristic X-ray intensity with the thickness of the target medium, the second functional relationship between characteristic X-ray intensity and the remaining energy, the second measured data showing the variation of characteristic X-ray intensity with the displacement of the target center, and the third functional relationship between characteristic X-ray intensity and the lateral distribution of the target charged particle beam, the method simultaneously achieves accurate characterization of the longitudinal depth and lateral broadening of the Bragg peak of the target charged particle beam in the target medium, and obtains the secondary fragment signal of the nuclear reaction in the Bragg peak tail region.

[0041] The embodiments of this invention have the following characteristics: Precise positioning; the characteristic X-rays generated by the tracer element have unique energy identifiers and high specificity, accurately distinguishing background signals generated by the target medium. Combined with the established first and second functional relationships, accurate characterization of the longitudinal depth of the Bragg peak in the target medium, as well as detection of nuclear reaction effects in deeper regions after the peak, can be achieved. High real-time performance; the characteristic X-ray signal generated by the interaction between charged particles and the inner shell electrons of the tracer element is generated synchronously with the transmission of the charged particle beam. The X-ray detector can acquire and analyze the signal in real time, with a fast response speed, meeting dynamic monitoring requirements and enabling real-time online monitoring and adjustment of the beam irradiation. High detector adaptability; the tracer element can be pre-introduced or placed in the lesion area, and the X-ray detector can be placed outside the body or outside the medium to complete the measurement without interfering with the original charged particle beam and the target medium. It can be adapted to various charged particle beams such as protons and carbon ions, and is compatible with different target media such as water phantoms and human tissue equivalent phantoms. It is suitable for multiple high-precision application fields such as proton and heavy ion radiotherapy and semiconductor material modification, possessing good versatility and promotional value.

[0042] This invention also provides a system based on characteristic X-ray inversion of Bragg peak structures, including a target medium thickness adjustment device for accommodating the target medium and adjusting the thickness of the target medium in the incident direction of the target charged particle beam; wherein the target medium thickness is the penetration depth of the target charged particle beam in the target medium; a tracer element thin target, disposed behind the target medium, for being excited by the target charged particle beam after passing through the target medium to generate characteristic X-rays; an X-ray detector, maintaining a preset geometric angle and a preset detection distance with the tracer element thin target, for measuring the intensity of characteristic X-rays; a three-dimensional moving platform, carrying the tracer element thin target and the X-ray detector, for adjusting the tracer element thin target and the X-ray detector at a preset position along the incident direction of the target charged particle beam to synchronously adjust the target center displacement; and a processor for executing the method based on characteristic X-ray inversion of Bragg peak structures as described in the foregoing embodiments.

[0043] The method based on characteristic X-ray inversion of Bragg peak structure can be executed by a system based on characteristic X-ray inversion of Bragg peak structure. Figure 2 This is a schematic diagram of a system based on characteristic X-ray inversion of Bragg peak structure provided in an embodiment of the present invention. Figure 2As shown, the system based on the characteristic X-ray inversion Bragg peak structure includes a target medium thickness adjustment device 100, a tracer element thin target 200, an X-ray detector 300, a three-dimensional moving platform 400, and a processor. The target medium thickness adjustment device 100 is used to accommodate the target medium and can adjust the thickness of the target medium in the incident direction of the target charged particle beam, i.e., the penetration depth of the target charged particle beam in the target medium. The target medium thickness adjustment device 100 is placed at the front end of the beam path of the target charged particle source 700 and can add or remove sub-millimeter-level water phantom stacks to achieve precise adjustment of the penetration depth of the target charged particle beam in the target medium. The tracer element thin target 200 is set behind the target medium and is used to excite the characteristic X-rays generated after the target charged particle beam passes through the target medium. The X-ray detector 300 and the tracer element thin target... The X-ray detector 200 maintains the optimal geometric angle and detection distance for measuring characteristic X-ray intensity. For example, the X-ray detector 300 forms a 45° detection angle with the beam direction of the tracer element thin target 200 and is 12.5 cm away from the target surface. This is used to synchronously acquire characteristic X-ray signals and transmit them to the processor to perform inversion calculations of the Bragg peak position and lateral broadening of the target charged particle beam. The three-dimensional moving platform 400 carries the tracer element thin target 200 and the X-ray detector 300. It is used to adjust the tracer element thin target 200 and the X-ray detector 300 to a suitable position along the incident direction of the target charged particle beam, and to synchronously adjust the tracer element thin target 200 and the X-ray detector 300, etc., to precisely control the target center displacement. The processor is used to execute the method for inverting the Bragg peak structure based on characteristic X-rays as described in the above embodiments.

[0044] Specifically, the target medium thickness adjustment device 100 refers to a mechanical device used to accommodate the target medium and precisely adjust the thickness of the target medium in the incident direction of the charged particle beam. The core function of this device is to adjust the penetration depth of the charged particle beam in the target medium. The tracer element thin target 200 refers to a thin target material made of a specific tracer element, placed behind the target medium, used to excite characteristic X-rays generated after the charged particle beam passes through the target medium. The X-ray detector 300 refers to a device used to measure the intensity of the characteristic X-rays generated by the tracer element thin target 200. This detector maintains an optimal geometric angle and detection distance with the tracer element thin target 200 to ensure optimal detection efficiency. The three-dimensional moving platform 400 refers to a mechanical device that carries the tracer element thin target 200 and the X-ray detector 300 and enables precise position control. The platform needs to have the ability to move in two directions: moving along the incident direction of the target charged particle beam to adjust the tracer element thin target 200 and X-ray detector 300 to a suitable position along the incident direction of the target charged particle beam; and moving along a horizontal plane perpendicular to the incident direction of the target charged particle beam to synchronously adjust the tracer element thin target 200 and X-ray detector 300 and other equipment, and precisely control the displacement of the target center.

[0045] The target medium thickness adjustment device 100 is placed at the front end of the beam path of the target charged particle source 700 and contains the target medium. This device can precisely adjust the thickness of the target medium in the incident direction of the target charged particle beam within a sub-millimeter range, which is the penetration depth of the target charged particle beam in the target medium. The minimum adjustment unit can reach 0.1mm. This device is composed of multiple sub-millimeter-level water phantom sheets stacked together to simulate the transmission characteristics of target charged particles in human tissue. The ionization chamber 500 is located behind the target medium thickness adjustment device 100 and is used to measure the dose deposition of the target charged particle beam through target media of different thicknesses during the calibration stage, thereby obtaining the correspondence between the remaining energy of the target charged particle beam and the thickness of the target medium. The tracer element thin target 200 is located behind the target medium thickness adjustment device 100 and is a thin target material made of a specific tracer element. It is used to excite the target charged particle beam to generate characteristic X-rays after it passes through the target medium. The X-ray detector 300 maintains the optimal geometric angle and detection distance with the tracer element thin target 200 to measure the intensity of the characteristic X-rays. The three-dimensional moving platform 400, carrying the tracer element thin target 200 and the X-ray detector 300, is positioned behind the target medium thickness adjustment device 100. It is used to adjust the tracer element thin target 200 and the X-ray detector 300 to appropriate positions along the incident direction of the target charged particle beam, and to synchronously adjust the tracer element thin target 200 and the X-ray detector 300, precisely controlling the target center displacement. The processor is connected to the X-ray detector 300 and other equipment, receiving measurement data and performing Bragg peak structure inversion calculations for the target charged particle beam in the target medium. The Faraday cylinder 600, positioned behind the three-dimensional moving platform 400, is used to detect the intensity of the target charged particle beam and collect remaining charged particles.

[0046] In this embodiment of the invention, the target medium thickness adjustment device 100 has a minimum adjustment unit of 0.1 mm, which can accurately adjust the target medium thickness, that is, the target medium thickness of the target charged particle beam in the target medium; the three-dimensional moving platform 400 has high stepping accuracy, with a minimum step size of 0.1 mm, which can achieve fine scanning conditions in different directions; the X-ray detector 300 and the tracer element thin target 200 maintain the optimal geometric angle and detection distance to ensure the best detection efficiency.

[0047] In some embodiments, the tracer element is selected from high-Z elements such as molybdenum, iodine, and gadolinium. The characteristic X-ray signal generated by the tracer element when excited is different from the background signal generated by the target medium. The target charged particle beam is a proton beam, a carbon ion beam, or other heavy ion beam, and the target medium is a water phantom or a human tissue equivalent phantom.

[0048] Specifically, tracer elements refer to specific chemical elements used to generate characteristic X-rays, selected from high-Z elements such as molybdenum, iodine, and gadolinium. These elements share the following characteristics: unique characteristic X-ray energy, high resolution, and a large emission cross-section; good biocompatibility and targeted enrichment ability; non-toxic and harmless to normal tissues; and high characteristic X-ray energy, enabling them to penetrate the target medium and be effectively received by X-ray detectors to ensure detectable signal strength. A proton beam refers to a beam of charged particles composed of protons, used in proton radiotherapy and proton material modification. Protons have relatively small masses, resulting in a long range in the target medium and a sharp Bragg peak. A carbon ion beam refers to a beam of charged particles composed of carbon ions, commonly used in heavy ion radiotherapy and heavy ion material modification. Carbon ions have relatively large masses, resulting in a shorter range in the target medium, a sharper Bragg peak, and a tail effect.

[0049] A water phantom is a solid material used to simulate the transport properties of water or human tissue. It is composed of polymers and other materials, and its density and effective atomic number are similar to those of water or human tissue. It is used for dose verification and experimental research in radiotherapy. A human tissue equivalent phantom is a material or device used to simulate the transport properties of human tissue. Its density, effective atomic number, and radiation absorption characteristics are similar to those of real human tissue. It is used for planning verification and dose measurement in radiotherapy.

[0050] Therefore, this invention selects a tracer element with characteristic X-rays possessing unique energy, ensuring that its energy avoids background signals generated by the target medium, thus achieving high specificity in the measurement signal. This system is compatible with major charged particle beam types such as proton beams, carbon ion beams, and other heavy ion beams, covering the mainstream particle types in current radiotherapy and materials modification fields. Simultaneously, the system is compatible with various target media, including water phantoms and human tissue equivalent phantoms, meeting diverse needs from basic research to clinical applications.

[0051] In some embodiments, the target medium thickness adjustment device 100 is an addable or subtractable sub-millimeter-level water phantom stack, and the three-dimensional moving platform 400 is a three-dimensional precision moving platform.

[0052] Specifically, the sub-millimeter-level water phantom stack refers to a device composed of multiple sub-millimeter-level water phantom sheets stacked together, which can adjust the thickness of the target medium in the incident direction of the target charged particle beam. It is a specific implementation of the target medium thickness adjustment device 100. The thickness of each water phantom sheet is precise and uniform, such as 0.1mm. The total thickness can be precisely controlled by increasing or decreasing the number of sheets, realizing continuous adjustment of the target medium thickness of the target charged particle beam in the target medium. The three-dimensional precision moving platform refers to a mechanical platform that can achieve precise position control in three orthogonal directions. It is a specific implementation of the three-dimensional moving platform 400. The Z direction corresponds to the ion beam incident direction and is used to adjust the precise position of the tracer element thin target and X-ray detector along the incident direction of the target charged particle beam. The X and Y directions correspond to the horizontal plane perpendicular to the incident direction and are used to synchronously adjust the tracer element thin target and X-ray detector, etc., and precisely control the target center displacement.

[0053] Submillimeter-scale water phantom stacks are composed of multiple water phantom sheets. Key design considerations include: each sheet has a uniform and known thickness, e.g., 0.1 mm. The sheet dimensions should be large enough to completely cover the transverse cross-section of the target charged particle beam, preventing it from escaping through the edges of the water phantom sheet. The material composition of the water phantom must be consistent with the target medium, such as using a specialized water phantom material with transport characteristics equivalent to human tissue. Its density, effective atomic number, and stopping power should be precisely calibrated. The number of sheets can be freely increased or decreased, with the total thickness controlled by the number of stacked sheets. During stacking, tight contact between sheets should be ensured to prevent air gaps from introducing additional energy loss. The total stack thickness should cover a range from zero to exceeding the target charged particle beam's range, e.g., 0 mm to 40 mm, to meet the measurement requirements of charged particle beams with different energies. Figure 2 In the illustrated embodiment, a sub-millimeter-scale water phantom stack is positioned 1.1m from the charged ion beam emission port, with a minimum adjustable thickness of 0.1mm, enabling precise adjustment of the penetration depth of the target charged particle beam in the target medium. Figure 2 In the embodiment shown, the three-dimensional precision moving platform carries the tracer element thin target 200 and the X-ray detector 300. The platform has the ability to move in three orthogonal directions, and the adjustment accuracy is 0.1 mm, which can meet the sub-millimeter level measurement requirements.

[0054] Figure 3 This is a schematic diagram illustrating the dose deposition and residual energy variation with penetration depth of a 120 MeV / u carbon ion beam in an aqueous phantom medium, as provided in an embodiment of the present invention. Figure 3As shown, the left ordinate represents relative dose, the right ordinate represents remaining energy, and the horizontal axis represents penetration depth. The black dots with error bars represent the relative dose deposition curve obtained from actual measurements in the ionization chamber, corresponding to the third measured data point; the blue solid line represents the relative dose deposition curve obtained from theoretical simulations, such as Monte Carlo simulations; and the red dotted line represents the curve of remaining carbon ion beam energy versus penetration depth, calculated based on dose deposition. (Refer to...) Figure 3 The relative dose deposition curve in the image divides the penetration range of the target charged particle beam in the target medium, such as a water phantom, into three segments: the orange shaded area indicates the region where the relative dose deposition of carbon ions ranges from 10% to 90%, i.e., the Bragg peak region; the area before the orange shaded area indicates a plateau region where the relative dose deposition of carbon ions is relatively low and changes gradually; and the area after the orange shaded area partially indicates a tail region where the carbon ions have exhausted their kinetic energy and reached the end of their range, but there is still a small dose tail caused by secondary debris from nuclear reactions. The ionization chamber measurement data generally agrees well with the theoretical simulation curves, providing a reliable benchmark for characteristic X-ray inversion. (Reference) Figure 3 The curve showing the variation of the residual energy of the carbon ion beam with penetration depth reveals a gradual and monotonically decreasing trend within the plateau region. However, in the Bragg peak region, the residual energy decreases sharply with increasing penetration depth, reaching zero at the end of the range. By measuring the dose deposition values ​​of the carbon ion beam in water phantom media of varying thicknesses, the dose deposition is converted into energy deposition, and combined with the initial energy of the target charged particle beam, the residual energy E of the target charged particle beam is obtained. res The specific calculation formula is shown below: Where E0 is the initial energy of the carbon ion beam, E air The initial carbon ion beam energy loss in air is represented by dE / dh, which represents the energy deposition per unit thickness of the water phantom medium. Alternatively, independent experiments can be designed using software such as SRIM or Geant4, inputting parameters such as air composition, density, temperature, and the energy of the target charged particles to simulate and calculate the variation of the remaining energy of the target charged particle beam with penetration depth.

[0055] Therefore, the embodiments of the present invention offer flexibility in implementation. The theoretical simulation method requires no actual experimental equipment and can quickly obtain the first functional relationship between the remaining energy of the target charged particle beam and the thickness of the target medium during the design phase, making it suitable for preliminary scheme verification and parameter optimization. The experimental calibration method, based on real measurement data, can obtain a more accurate functional relationship, suitable for precise calibration in practical application scenarios. The two methods can verify and complement each other, ensuring the accuracy and reliability of the first functional relationship. Taking experimental calibration as an example, by precisely adjusting the thickness of the target medium, i.e., the penetration depth of the target charged particle beam in the target medium, using a high-precision ionization chamber to measure the dose deposition of the target charged particle beam at different penetration depths in the target medium, and converting the dose deposition into energy deposition, combined with the initial energy of the target charged particle beam, the remaining energy of the target charged particle beam is calculated. The theoretical simulation method is applicable to any particle type and medium material combination, and is not limited by experimental conditions; the experimental calibration method can be customized for specific application scenarios.

[0056] Figure 4 This is a schematic diagram of the characteristic X-ray spectrum of a K-shell generated by a tracer element thin target after a carbon ion beam with an energy of 120 MeV / u passes through a 24 mm thick water phantom medium, according to an embodiment of the present invention. Figure 4 As shown, the horizontal axis represents X-ray energy, and the vertical axis represents photon count. When the carbon ion beam passes through a 24 mm thick water phantom medium, it bombards the iodine target, producing characteristic X-rays. Clearly, three significant characteristic energy peaks can be observed in the spectrum acquired by the X-ray detector. The first peak is the L-shell characteristic X-ray spectrum induced by the carbon ion beam through the target medium, producing tracer iodine atoms. The second and third peaks are the Kα and Kβ characteristic X-ray spectra induced by the carbon ion beam through the target medium, respectively. This spectrum exhibits extremely high energy resolution and low background noise, enabling precise differentiation between the characteristic X-ray peaks induced by the charged particle beam at different positions on the Bragg peak within the target medium and the background signal generated by the target medium. This ensures the specificity and high signal-to-noise ratio of subsequent X-ray spectral acquisition and intensity calculation.

[0057] In some embodiments, the evolution of characteristic X-ray intensity with the thickness of the target medium includes a plateau region, a Bragg peak region, and a tail region; wherein, in the plateau region, the characteristic X-ray intensity first increases gradually with the thickness of the target medium and then decreases; in the Bragg peak region, the characteristic X-ray intensity decreases rapidly with the thickness of the target medium and then decreases slowly at the end of the range of the target charged particle beam; in the tail region, after the Bragg peak where the energy of the target charged particle beam is rapidly deposited, the nuclear reaction effect at the tail of the Bragg peak is detected based on the acquired continuous and resolvable characteristic X-ray signal.

[0058] Figure 5This is a schematic diagram illustrating the variation of the intensity of K-shell characteristic X-rays generated by a tracer element thin target after a 120 MeV / u carbon ion beam passes through a water phantom medium, as provided in an embodiment of the present invention, with the effect of penetration depth. Figure 5 As shown, the vertical axis represents the characteristic X-ray intensity of the K-shell, i.e., the X-ray count, and the horizontal axis represents the penetration depth. Figure 3 Correspondingly, Figure 5 The penetration range is also divided into the plateau region, the Bragg peak region, and the tail region. Within the plateau region, as the penetration depth of the carbon ion beam in the water phantom medium gradually increases, the intensity of the characteristic X-rays induced by the iodine target of the tracer element initially increases gradually to a maximum due to the decrease in carbon ion energy, and then gradually decreases. This trend is completely consistent with the variation trend of the ionization cross-section of the K-shell of the tracer iodine atom. During this stage, the incident beam energy is high and the particle flux remains stable. In the Bragg peak region, as the remaining energy rapidly decays and the number of carbon ions irradiating the thin target of the tracer element decreases rapidly, the intensity of the characteristic X-rays shows a rapid decreasing trend. In the tail region, i.e., the region further beyond the Bragg peak, a characteristic X-ray signal stronger than the background can still be clearly measured, and this signal gradually weakens and disappears after traveling a certain distance.

[0059] Figure 6 This is a schematic diagram showing the variation of the intensity of K-shell characteristic X-rays generated by a carbon ion beam with an energy of 120 MeV / u irradiating a thin target of a tracer element at different penetration depths as a function of the target center displacement. Figure 6 The horizontal axis represents the target center displacement D, and the vertical axis represents the X-ray count. Different types of experimental points and guide dashed lines correspond to six representative penetration depths: 15mm, 20mm, 24mm, 28mm, 30mm, and 32mm, respectively, showing the relationship between characteristic X-ray intensity and target center displacement. Figure 6As shown, at each selected penetration depth, the characteristic X-ray intensity exhibits a fairly symmetrical spatial distribution with the displacement of the target center. When the center of the tracer element thin target coincides with the beam center, i.e., the target center displacement is 0, the overlap area between the beam and the tracer element thin target is the largest, resulting in a larger number of carbon ions irradiating the tracer element thin target and the strongest characteristic X-ray intensity. As the three-dimensional moving platform gradually moves the tracer element thin target laterally and the target center displacement increases, the overlap area shrinks, the number of carbon ions irradiating the tracer element thin target continuously decreases, and the characteristic X-ray intensity weakens synchronously. When the target center displacement exceeds the sum of the beam radius and the tracer element thin target radius, the beam and iodine target are almost completely separated, with only a very small number of ions acting on the iodine target, and the X-ray intensity also weakens significantly. Furthermore, comparing the curve changes at different penetration depths shows that as the longitudinal penetration depth increases, the characteristic X-ray intensity first increases and then decreases, which is closely related to the collision ionization cross section of carbon ions and iodine atoms. In particular, near the end of the ion beam range, the curve of characteristic X-ray intensity changing with the displacement of the target center becomes significantly flatter and wider, which intuitively reflects the beam divergence phenomenon caused by the accumulation of multiple small-angle Coulomb scatterings when the charged particle beam propagates in the medium.

[0060] Figure 7 This is a schematic diagram showing the change in the number of particles irradiated onto a thin target of a tracer element by a carbon ion beam with an energy of 120 MeV / u at different penetration depths as a function of the target center displacement, according to an embodiment of the present invention. Figure 7 The horizontal axis represents the target center displacement D, and the vertical axis represents the particle count, i.e., the number of carbon ions. The colored dots with error bars represent the carbon ion count as a function of target center displacement, obtained after eliminating the energy dependence of the ionization cross-section by experimentally measuring the characteristic X-ray intensity. This corresponds to the relationship between the number of charged particles in the experimental target and the target center displacement described in the aforementioned embodiments. The colored dashed lines represent the carbon ion count as a function of target center displacement calculated under an isotropic two-dimensional Gaussian distribution model, corresponding to the theoretical relationship between the number of charged particles in the target and the target center displacement described in the aforementioned embodiments, with corresponding penetration depths of 15mm, 20mm, 24mm, 28mm, 30mm, and 32mm. The relationship between the number of charged particles in the experimental target and the target center displacement is fitted and compared with the theoretical relationship under the two-dimensional Gaussian distribution model. Figure 7 The experimental structure shown is highly consistent with the theoretical results. Under these conditions, the optimal Gaussian distribution parameter σ can be solved, thereby obtaining accurate characterization data of the transverse broadening of the Bragg peak of the target charged particle beam in the target medium. Clearly, with... Figure 6 Compared to the curve showing the variation of characteristic X-ray intensity with target center displacement, the curve showing the variation of carbon ion number with target center displacement after eliminating the influence of ionization cross-section in the central position and its vicinity exhibits a monotonically decreasing characteristic as the penetration depth gradually increases. This is consistent with... Figure 6The nonlinear peak reversal at a depth of 20 mm in the center displacement of the target contrasts sharply with this. However, in terms of lateral distribution pattern, Figure 6 and Figure 7 It maintained a high degree of consistency, and as the penetration depth increased, the full width at half maximum (FWHM) of the lateral distribution curve increased significantly, which intuitively showed that the beam pattern of the charged particle beam gradually widened with the increase of penetration depth.

[0061] Figure 8 This is a three-dimensional spatial evolution cloud map showing the lateral distribution of a 120 MeV / u carbon ion beam at different penetration depths in a water phantom medium, provided by an embodiment of the present invention. Figure 8 As shown, the horizontal axis represents the penetration depth, the X and Y axes perpendicular to the plane represent the spatial dimensions of the beam cross-section, and the color scale on the right represents the charged particle density. Figure 8 As shown, in the Bragg plateau region, the carbon ion beam exhibits high particle kinetic energy, weak multiple Coulomb scattering, a compact beam spot morphology, and high-density ions concentrated in the central region, corresponding to the red highlight area. The spatial size of the beam cross-section shows a slow expansion trend. With further increases in penetration depth, the carbon ion kinetic energy continues to deplete, the cumulative effect of multiple small-angle Coulomb scattering significantly enhances, the beam spot gradually widens, and the central ion density decreases synchronously. When the penetration depth reaches near the end of the Bragg peak, beam divergence becomes significant, exhibiting a substantial reduction in the central high-density region and a significant expansion of the peripheral low-density distribution region. This invention, based on the spatial distribution characteristics of tracer element characteristic X-ray intensity with penetration depth and target center displacement, fully reconstructs the spatial distribution evolution characteristics of charged particle beams during transmission in the target medium.

[0062] Therefore, the method for retrieving the Bragg peak structure based on the characteristic X-rays of tracer elements includes obtaining precise characterization parameters of the longitudinal depth and lateral broadening of the Bragg peak in the target medium based on the first functional relationship between the residual energy of the target charged particle beam and the thickness of the target medium, the first measured data of the characteristic X-ray intensity changing with the penetration depth, the second functional relationship between the characteristic X-ray intensity and the residual energy, the second measured data of the characteristic X-ray intensity changing with the displacement of the target center, and the third functional relationship between the characteristic X-ray intensity and the lateral distribution of the target charged particle beam. It also obtains the secondary fragment signal of the nuclear reaction in the tail region of the Bragg peak. Specifically, using a target medium with precisely adjustable thickness as a carrier, and targeting the Bragg peak structure generated by the target charged particle beam in the target medium, the dose deposition values ​​of the target charged particle beam in the target medium of different thicknesses are measured point by point in an ionization chamber. The dose deposition is converted into energy deposition, and combined with the initial energy of the target charged particle beam, the remaining energy of the target charged particle beam is calculated. Data on the variation of the remaining energy of the target charged particle beam with the thickness of the target medium is obtained, and a first functional relationship between the remaining energy of the target charged particle beam and the thickness of the target medium is established. Furthermore, a tracer element with specific characteristic X-rays is selected to form a tracer element thin target, which is then placed at the target medium position. A high-resolution X-ray detector is used to maintain the optimal geometric angle and detection distance with the tracer element thin target. By adjusting the thickness of the target medium and collecting the intensity of characteristic X-rays generated by the tracer element thin target at different positions of the Bragg peak induced by the target charged particle beam, a relationship between the intensity of characteristic X-rays and the remaining energy of the target charged particle beam is established. The second functional relationship of residual energy is obtained, and the secondary fragment signal of nuclear reaction in the Bragg peak tail region is obtained. At the selected target medium thickness, the distance between the center of the tracer element thin target and the center of the target charged particle beam is adjusted with preset precision along the lateral direction perpendicular to the charged ion beam by a three-dimensional moving platform, i.e., the target center displacement. The intensity of characteristic X-rays induced by the charged particles irradiated on the tracer element thin target surface is measured, and the correspondence between the characteristic X-ray intensity and the target center displacement is obtained. Furthermore, by eliminating the influence of factors such as ionization cross-section related to the energy of the target charged particles, the relationship between the number of target charged particles and the target center displacement is obtained, and a third functional relationship between the characteristic X-ray intensity and the lateral distribution of the target charged particle beam is established. Based on the above relationship, combined with the embodiments of the present invention, not only is the accurate characterization of the longitudinal depth and lateral broadening of the Bragg peak of the target charged particle beam in the target medium simultaneously realized, but also the secondary fragment signal of nuclear reaction in the Bragg peak tail region is obtained.

[0063] In summary, this invention discloses a method for retrieving the Bragg peak structure based on tracer element characteristic X-rays, aiming to solve the technical challenge of precise positioning and real-time verification of the Bragg peak in existing particle therapy. The method includes: using a precisely adjustable-thickness water phantom as the target medium, establishing a quantitative relationship between the energy loss of the particle beam in the Bragg peak region of the target medium and the medium thickness, i.e., the quantitative relationship between the remaining energy of the particle beam after passing through target media of different thicknesses and the target medium thickness; arranging tracer element thin targets 200 and X-ray detectors 300 behind the target medium at different positions of the Bragg peak, constructing a correlation model between the intensity of characteristic X-rays induced by the particle beam and the remaining energy generated by the tracer element thin targets behind the target medium at different positions of the Bragg peak; establishing a correlation model between the intensity of characteristic X-rays induced by the particle irradiating the target surface and the target center displacement, as well as the lateral distribution of the particle beam, by precisely moving the tracer element thin target laterally at a preset target medium thickness; and achieving precise characterization of the depth position and lateral range of the particle beam Bragg peak based on the evolution law of characteristic X-rays and the thickness and lateral distribution of the target medium. This invention uses the Bragg peak structure generated by a 120 MeV / u carbon ion beam in a water phantom as an example. It simultaneously achieves high-precision quantitative characterization of the longitudinal range and transverse beam profile of the Bragg peak, and visually observes the X-ray signal induced by secondary light debris from the nuclear reaction in the Bragg peak tail region. This technical solution provides a reliable approach for comprehensive, real-time, and high-resolution online characterization of dose deposition characteristics within the beam fluid during particle therapy.

[0064] It should be noted that the embodiments of the present invention may also include the following extended schemes, all of which fall within the protection scope of the present invention. First, the method of the present invention can also be organically integrated with secondary electron bremsstrahlung imaging technology. During charged particle beam irradiation, continuous secondary electron bremsstrahlung X-rays and discrete tracer element characteristic X-rays are simultaneously acquired. The characteristic X-ray peaks with unique energy identifiers are used to perform in-situ precise calibration of the continuous energy spectrum of secondary electron bremsstrahlung, establishing a quantitative mapping relationship between the integrated intensity, average energy, and peak energy of the secondary electron bremsstrahlung energy spectrum and the intensity and depth position of the characteristic X-rays. The high signal-to-noise ratio and strong anti-interference characteristics of the characteristic X-rays overcome the shortcomings of non-intuitive secondary electron bremsstrahlung characteristics and strong signal background, thereby achieving non-invasive, highly sensitive real-time online beam range monitoring and verification. Second, the tracer element thin target can be replaced with a high-Z element tracer carrier enriched in the tumor target area, such as iohexol contrast agent solution, polymers or nanoparticles containing high-Z elements. When the charged particle beam passes through the medium to reach the tumor target area, it not only deposits the main physical dose through the Bragg peak, but also excites the tracer atoms enriched in the lesion area to generate local characteristic X-rays. While monitoring the beam range based on characteristic X-rays, local X-ray-assisted radiotherapy can be realized, achieving the organic integration of particle therapy, local X-ray-assisted radiotherapy, and online X-ray diagnosis, providing a new technical path for the development of integrated particle tumor diagnosis and treatment technology. Third, in response to the edge divergence characteristics of the lateral profile of the charged particle beam caused by multiple small-angle Coulomb scattering, in the aforementioned inversion process, the preset lateral distribution model is extended from a single Gaussian model to a composite distribution model of double Gaussian or multi-Gaussian superposition. Fourth, the X-ray detector system is further optimized into a detector array or a multi-angle moving detection system surrounding the target medium and tracer carrier. By synchronously acquiring the spatial distribution characteristics of the characteristic X-rays generated by the tracer elements from multiple angles, and combining it with a three-dimensional reconstruction algorithm, the dose deposition characteristics and spatial beam spot morphology of the charged particle beam in the complex heterogeneous medium are obtained, overcoming the geometric errors caused by single-angle detection for asymmetric anatomical structures.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for retrieving Bragg peak structure based on characteristic X-ray inversion, characterized in that, include: By adjusting the thickness of the target medium, the energy deposition of the target charged particle beam in target media of different thicknesses is measured, and a first functional relationship between the remaining energy of the target charged particle beam and the thickness of the target medium is established; wherein, the thickness of the target medium is the penetration depth of the target charged particle beam in the target medium; By adjusting the thickness of the target medium, the intensity of characteristic X-rays generated by the tracer element thin target arranged after the target medium is induced by the target charged particle beam at different characteristic positions of the Bragg peak is measured, and a second functional relationship between the characteristic X-ray intensity and the remaining energy is established by combining the first functional relationship. By adjusting the distance between the center of the tracer element thin target and the center of the target charged particle beam at a preset target medium thickness, the intensity of characteristic X-rays induced by the target charged particle beam irradiating the target surface and generated by the tracer atoms is measured. The relationship between the characteristic X-ray intensity and the target center displacement is obtained, and a third functional relationship between the characteristic X-ray intensity and the lateral distribution of the target charged particle beam is established; wherein, the distance between the center of the tracer element thin target and the center of the target charged particle beam is the target center displacement; Based on the first functional relationship, the first measured data of the characteristic X-ray intensity changing with the thickness of the target medium, the second functional relationship, the second measured data of the characteristic X-ray intensity changing with the displacement of the target center, and the third functional relationship, accurate characterization data of the longitudinal depth and lateral broadening of the Bragg peak of the target charged particle beam in the target medium are obtained, and the secondary fragment signal of the nuclear reaction in the Bragg peak tail region is obtained.

2. The method based on characteristic X-ray inversion of Bragg peak structure according to claim 1, characterized in that, Establishing the first functional relationship includes: The dose deposition of the target charged particle beam in the target medium of different thicknesses is measured by an ionization device, and the dose deposition is converted into the energy deposition. The remaining energy is calculated by combining the initial energy of the target charged particle beam to obtain the third measured data of the variation of the remaining energy with the thickness of the target medium, and the first functional relationship is established.

3. The method based on characteristic X-ray inversion of Bragg peak structure according to claim 1, characterized in that, Establish the second functional relationship and obtain the secondary fragmentation signal of the nuclear reaction in the Bragg peak tail region, including: Based on the first functional relationship, the adjusted target medium thickness is converted into the corresponding residual energy; The fourth measured data on the variation of characteristic X-ray intensity generated by the tracer element thin target at different positions of the Bragg peak induced by the target charged particle beam with the remaining energy is obtained, and the second functional relationship is established. At the same time, the secondary fragment signal of the nuclear reaction in the tail region of the Bragg peak is obtained.

4. The method based on characteristic X-ray inversion of Bragg peak structure according to claim 1, characterized in that, The evolution of the characteristic X-ray intensity with the thickness of the target medium includes plateau region, Bragg peak region, and tail region; In the plateau region, the intensity of the characteristic X-rays first increases gradually and then decreases with the thickness of the target medium. In the Bragg peak region, the intensity of the characteristic X-rays decreases rapidly with the thickness of the target medium and decreases slowly at the end of the range of the target charged particle beam. In the trailing region, following the Bragg peak where the energy of the target charged particle beam is rapidly deposited, the nuclear reaction effect at the tail of the Bragg peak is detected based on the acquired continuous and resolvable characteristic X-ray signals.

5. The method based on characteristic X-ray inversion of Bragg peak structure according to claim 1, characterized in that, Based on the first functional relationship, the first measured data of the characteristic X-ray intensity varying with the thickness of the target medium, the second functional relationship, the second measured data of the characteristic X-ray intensity varying with the displacement of the target center, and the third functional relationship, precise characterization data of the longitudinal depth and lateral broadening of the Bragg peak of the target charged particle beam in the target medium are obtained, including: Based on the first functional relationship, the first measured data of the characteristic X-ray intensity changing with the thickness of the target medium, and the second functional relationship, accurate characterization data of the longitudinal depth of the Bragg peak of the target charged particle beam in the target medium is obtained, and the secondary fragment signal of the nuclear reaction in the Bragg peak tail region is obtained. Based on the second measured data of the variation of the characteristic X-ray intensity with the displacement of the target center and the third functional relationship, accurate characterization data of the lateral broadening of the Bragg peak of the target charged particle beam in the target medium are obtained.

6. The method for retrieving Bragg peak structure based on characteristic X-rays according to claim 5, characterized in that, Obtain precise characterization data of the transverse broadening of the Bragg peak of the target charged particle beam in the target medium, including: For the characteristic X-ray intensities corresponding to different target center displacements in the second measured data, after eliminating the influence of ionization cross-section factors that depend on the energy of the target charged particle beam, the relationship between the number of charged particles of the experimental target and the target center displacement is obtained.

7. The method for retrieving Bragg peak structure based on characteristic X-rays according to claim 6, characterized in that, Obtaining precise characterization data of the transverse broadening of the Bragg peak of the target charged particle beam in the target medium also includes: The lateral distribution of the pre-defined target charged particle beam conforms to an isotropic two-dimensional Gaussian distribution model; Based on the two-dimensional Gaussian distribution model and the geometric dimensions of the tracer element thin target, the relationship between the theoretical number of charged particles of the target and the displacement of the target center under the two-dimensional Gaussian distribution model is obtained. Based on the relationship between the number of charged particles in the experimental target and the displacement of the target center, the relationship between the number of charged particles in the target and the displacement of the target center under the two-dimensional Gaussian distribution model is fitted and compared to obtain accurate characterization data of the lateral broadening of the Bragg peak of the target charged particle beam in the target medium.

8. A system based on characteristic X-ray inversion of Bragg peak structure, characterized in that, include: A target medium thickness adjustment device is used to contain a target medium and to adjust the thickness of the target medium in the incident direction of a target charged particle beam; wherein, the target medium thickness is the penetration depth of the target charged particle beam in the target medium; A tracer element thin target is disposed behind the target medium and is used to be excited by the beam of charged particles of the target after passing through the target medium to generate characteristic X-rays; An X-ray detector is used to measure the intensity of the characteristic X-rays by maintaining a preset geometric angle and a preset detection distance with the tracer element thin target. A three-dimensional moving platform, carrying the tracer element thin target and the X-ray detector, is used to adjust the tracer element thin target and the X-ray detector to a preset position along the incident direction of the charged particle beam of the target, so as to synchronously adjust the displacement of the target center. A processor for performing the method based on characteristic X-ray inversion of Bragg peak structure as described in any one of claims 1-7.

9. The system based on characteristic X-ray inversion of Bragg peak structure according to claim 8, characterized in that, The tracer element is selected from at least one element selected from molybdenum, iodine, and gadolinium, and the characteristic X-ray signal generated by the tracer element when excited is different from the background signal generated by the target medium. The target charged particle beam is a proton beam or a carbon ion beam, and the target medium is a water phantom or a human tissue equivalent phantom.

10. The system based on characteristic X-ray inversion of Bragg peak structure according to claim 8, characterized in that, The target medium thickness adjustment device is a sub-millimeter level water phantom stack, and the three-dimensional moving platform is a three-dimensional precision moving platform.

Images