Proton Beam-Based Computed Tomography Device and Its Imaging Method

Abstract

The present invention provides a computer tomography device for a proton beam, comprising an accelerator, an S-band high-gradient proton acceleration structure, an ultrafast proton bunch distribution system, a treatment gantry, and an ultrafast proton bunch scanning system arranged in sequence along the direction of the proton beam current, and a proton CT system installed on the treatment gantry; the accelerator is configured to emit a proton beam current with a proton energy of 70 MeV - 235 MeV; the S-band high-gradient proton acceleration structure is configured to be switchable between an on state and an off state, and when in the on state, the proton energy is increased to 350 MeV. The present invention also provides a corresponding imaging mode. The scanning device of the present invention increases the proton beam current energy from 235 MeV to 350 MeV and uses it on the treatment gantry, ensuring that the proton Bragg peak completely falls outside the human body, reducing the harm to healthy tissues and organs; directly obtaining the RSP value through proton CT technology, reducing the image guidance error and improving the range accuracy.

Description

Technical Field

[0001] The present invention belongs to the field of proton imaging in the field of particle radiation imaging, and particularly relates to a computer tomography device based on a proton beam and an imaging method thereof, aiming to eliminate the proton range error generated during the application of X-ray CT in proton therapy. Background Art

[0002] Currently, proton therapy technologies are all based on X-ray photon CT (Computed Tomography) images for treatment planning and patient positioning. However, due to the different Z / A (ratio of the charge of a charged body to its mass) ratios of substances, a range error of 3% - 5% will occur during the conversion of photon CT from HU unit (Hounsfield unit) to RSP (Relative Stopping Power) in the proton therapy plan, resulting in an error of 3 - 5 mm in the proton range in the treatment plan, which is very likely to affect sensitive cells. Currently, proton therapy technologies are undergoing a leap to a new generation of technologies. Among them, compared with traditional proton therapy, the advanced proton flash therapy (FLASH) can maintain the killing power against tumors while providing excellent protection for normal tissues. At the same time, it also requires the realization of a treatment dose of 30 Gy within 100 ms (the average dose rate is not less than 300 Gy / s). Therefore, higher requirements are put forward for the accuracy of the three-dimensional RSP distribution. There is an urgent need to develop proton CT to meet the technical requirements of proton flash therapy.

[0003] Due to the Bragg Peak effect of protons, when a proton beam enters a deep lesion area, it can instantly release energy to kill cancer cells. For a body with a relatively large irradiation range, there will be more remaining doses. Increasing the energy to 350 MeV can ensure that the Bragg peak falls outside the human body, reducing the remaining dose in the human body. Currently, for accelerators with an energy range of 70 MeV - 235 MeV used for proton therapy, only a section of S-band high-gradient acceleration structure needs to be designed to increase the proton energy to 350 MeV to meet the needs of proton CT, reducing the technical complexity of redesigning a 350 MeV proton accelerator and also reducing the technical cost.

[0004] Proton CT enables patients to complete proton imaging and treatment in the same treatment room. Compared with photon CT (i.e., traditional X-ray CT), it reduces the impact of organ movement during movement on proton therapy. The compression of proton imaging time is also beneficial to reducing the impact of respiratory movement during treatment. Therefore, proton CT and proton therapy devices can be integrated into one to achieve real-time image guidance. With the increasingly significant treatment effect of proton therapy, proton flash therapy technology has attracted much attention in the industry in recent years. The problems of imaging error and organ movement during treatment need to be solved. At the same time, the high dose rate of proton flash therapy poses higher requirements for precise positioning. Based on the existing rotating treatment gantry, projection information detection is achieved through scanning at multiple angles when the proton beam energy is fixed, but the detection time is relatively long and cannot meet the technical requirements of proton flash therapy.

[0005] Both photon CT and proton CT are existing technologies, but there is currently no technology to apply proton CT clinically. In particular, proton CT has not been integrated into the treatment gantry yet.

[0006] In the existing technology, a technology of proton CT combined with photon CT has been proposed. The current implementation of proton CT combined with photon CT only calibrates the conversion curve of HU-RSP, rather than directly reconstructing images, does not eliminate the range error of photon CT, and has a long imaging time. Currently, X-ray CT is used for image guidance in proton therapy, and the HU value is converted into the RSP value in the treatment plan. Since photons and protons are two different substances, there will be an error of 3%-5%.

[0007] Currently, proton CT devices have not been integrated into the existing treatment gantries. On the one hand, it is because proton CT is still in the experimental stage and has not been integrated with the treatment gantry. On the other hand, it is because integrating proton CT devices into the existing traditional treatment gantries for treatment takes a long time to rotate one circle and has a long imaging time. The organ movement caused by respiratory movement during this process has an impact on subsequent treatment, so it cannot meet the requirements of real-time image guidance and cannot be applied clinically.

[0008] Therefore, a proton imaging scheme integrated into a superconducting treatment gantry needs to be proposed, and a device design of proton CT integrated into the treatment gantry is provided to reduce the error generated during the conversion of using photon CT to RSP and improve the range accuracy. Summary of the Invention

[0009] The purpose of the present invention is to provide a computer tomography device based on proton beam and its imaging method to reduce the error generated during the conversion of using photon CT to RSP and improve the range accuracy.

[0010] To achieve the above object, the present invention provides a computer tomography device for proton beams, comprising an accelerator, an S-band high-gradient proton acceleration structure, an ultrafast proton bunch distribution system, a treatment gantry, an ultrafast proton bunch scanning system arranged in sequence along the direction of the proton beam, and a proton CT system installed on the treatment gantry; the accelerator is configured to emit a proton beam with a proton energy of 70 MeV - 235 MeV; the S-band high-gradient proton acceleration structure is configured to be switchable between an on state and an off state, and when in the on state, it raises the proton energy of the proton beam to 350 MeV.

[0011] The accelerator is a cyclotron or a synchrotron, and a bunching structure is provided between the accelerator and the S-band high-gradient proton acceleration structure; or the accelerator is a linear accelerator, and the proton beam emitted by it directly passes through the S-band high-gradient proton acceleration structure.

[0012] The ultrafast proton bunch distribution system is configured to emit proton beams at different energy points to the coil units at the same position on the treatment gantry with the same azimuth angle and different pitch angle beam distribution angles, so that the proton beams converge on the same beam orbit at the outlet of the downstream treatment gantry; the ultrafast proton bunch distribution system is also configured to emit proton beams to the coil units at different positions on the treatment gantry with different azimuth angle beam distribution angles.

[0013] The treatment gantry has a plurality of coil units arranged in rotational symmetry and capable of rotating within a small range around the axis of symmetry to switch positions, or a plurality of stationary symmetrically arranged coil units.

[0014] Each proton CT system corresponds to a coil unit, and includes two position detectors and a residual energy detector; both position detectors are aligned with the outlet of the proton beam of the corresponding coil unit; and the two position detectors include a first position detector arranged in front of the installation position of the object to be scanned and a second position detector arranged behind the installation position of the object to be scanned, and the residual energy detector is located behind the second position detector.

[0015] The position detector of each proton CT system is located inside its corresponding coil unit and is fixed to the inside of the entire treatment gantry through a support structure; the residual energy detector is located outside its corresponding coil unit and is fixed to the outside of the entire treatment gantry through a support structure.

[0016] The treatment gantry has a magnet unit that can rotate to switch positions; the number of proton CT systems is 1, which includes two position detectors and a residual energy detector; both position detectors are aligned with the exits of the proton beam of the corresponding magnet unit; and the two position detectors include a first position detector disposed in front of the installation position of the object to be scanned and a second position detector disposed behind the installation position of the object to be scanned, and the residual energy detector is located behind the second position detector; the position detectors of each proton CT system are located inside the magnet unit; the residual energy detector is located outside the magnet unit.

[0017] The proton beam-based computed tomography device of the present invention increases the proton beam energy from 235 MeV to 350 MeV and is used on a treatment gantry to ensure that the proton Bragg Peak completely falls outside the human body, reducing damage to healthy tissues and organs; on this basis, the RSP value is directly obtained through proton CT technology, reducing the RSP error in the treatment plan to 1%. Compared with using X-ray CT for image guidance in existing proton therapy and converting the HU value into the RSP value in the treatment plan, the error is lower, reducing the image guidance error, and the image resolution reaches 1 mm, improving the range accuracy.

[0018] The proton beam-based computed tomography device of the present invention integrates proton CT on a superconducting treatment gantry, greatly shortening the scanning time, controlling the imaging time within seconds, reducing the influence of organ movement, achieving accurate image positioning and dynamic image guidance in proton therapy, and at the same time solving the technical problem of real-time image guidance for proton CT, providing a feasible technical solution for realizing proton flash therapy (FLASH), thus completing a substantial leap from scientific experiments to true clinical use.

[0019] The three proton imaging modes proposed by the present invention propose different imaging modes for existing treatment gantries and superconducting treatment gantries respectively. All three imaging modes can directly obtain the RSP value through proton imaging. Integrating proton CT on traditional treatment gantries and rotatable superconducting treatment gantries, proton imaging is realized based on incomplete projection, thereby reducing the imaging time; for the imaging mode of integrating proton CT on a static superconducting treatment gantry, the superconducting coil does not rotate, only the proton beam rotates around the irradiated object, thereby reducing the scanning time, and using photon CT as a prior image, directly irradiating with a small number of angles of proton beams for image reconstruction, thereby realizing real-time image guidance.

[0020] The proton beam-based computed tomography device of the present invention can integrate proton CT onto a superconducting treatment gantry and can achieve two imaging modes corresponding to two types of gantries. Among them, for the imaging mode based on a static superconducting treatment gantry, proton CT is combined with X-ray CT, and the RSP distribution obtained by converting X-ray CT is used as a prior image. Under the condition of a small number of scanning angles, an ultra-fast proton beam scanning projection with a fixed energy is performed to achieve high-precision proton CT imaging, obtain three-dimensional RSP distribution information, and thus achieve secondary proton CT imaging, greatly shortening the proton CT imaging time, thereby reducing the influence caused by respiratory movement and organ movement, reducing range errors, and improving image quality. It is the only proposed solution that can truly be used clinically. Previous solutions had extremely long imaging times and could not be used for actual clinical applications, but only for scientific research. At the same time, the function of real-time image-guided proton CT is realized, providing a feasible technical solution for the development of FLASH radiotherapy.

[0021] The present invention can not only realize the clinical application of proton CT, but also be integrated with a proton treatment gantry to achieve proton treatment technology based on real-time image-guided proton CT, and provide a feasible technical solution for future proton FLASH radiotherapy technology. The present invention relates to S-band high-gradient proton linac technology, beam distribution systems, treatment gantries, ultra-fast proton scanning technology, and proton detection and imaging technology. The proton energy is increased from 235 MeV to 350 MeV, and protons are used as the detection medium to penetrate the object to be scanned, achieving three different imaging modes based on two types of proton treatment gantries. The first type of gantry is based on a traditional rotating treatment gantry. Based on this gantry, the first imaging mode is proposed. In this mode, a 350 MeV proton beam is used to perform multiple uniform angle scans of the object to be scanned within 180 degrees, and then three-dimensional tomographic information is obtained using image reconstruction technology to achieve high-precision proton CT images. The second type of gantry is based on a superconducting coil treatment gantry. Based on this gantry, two imaging modes are proposed: the second imaging mode is achieved based on a rotatable superconducting coil treatment gantry. The superconducting coil gantry can perform multiple small-angle rotations within a small range, and a 350 MeV proton beam is used for scanning projection to obtain projection information at multiple non-uniform angles, and then an incomplete projection angle algorithm is used to achieve high-precision proton CT image reconstruction. In the third imaging mode, it is achieved based on a static superconducting coil treatment gantry. The superconducting coil gantry is in a fixed static mode. Based on the RSP distribution of photon CT as a prior image, an ultra-fast proton beam scanning projection at a small number of angles is used for secondary back-projection iterative imaging to reconstruct a high-precision three-dimensional RSP distribution imaging of proton CT, providing a feasible solution for realizing clinically significant proton CT imaging and proton treatment technology based on real-time image guidance. Brief Description of the Drawings

[0022] Figure 1 It is a schematic diagram of the overall connection of the proton beam computed tomography device of the present invention.

[0023] Figure 2 It is a schematic diagram of the installation position of the S-band high-gradient proton acceleration structure of the proton beam computed tomography device of the present invention.

[0024] Figure 3 It is a schematic diagram of the working principle of the ultrafast proton bunch distribution system of the proton beam computed tomography device of the present invention.

[0025] Figure 4 Shown is the working principle and the scanning path diagram of the lateral position of the ultrafast proton bunch scanning system of the proton beam computed tomography device of the present invention.

[0026] Figure 5 It is a schematic diagram of the structure of a rotatable superconducting treatment gantry and the corresponding proton scanning projection.

[0027] Figure 6 It is a schematic diagram of the structure of a static superconducting treatment gantry and the corresponding proton scanning projection.

[0028] Figure 7 It is a schematic diagram of the principle structure of a proton CT system. Detailed implementation manners

[0029] The following combines the accompanying drawings to give the preferred embodiments of the present invention and describes them in detail.

[0030] As Figures 1 to 5 Shown is the proton beam computed tomography device of the present invention, which is realized by integrating a proton CT imaging device based on a treatment gantry, and is used to reduce the range error generated in the process of indirectly calculating the RSP using a photon CT and achieve accurate positioning of the lesion. As Figure 1 Shown, the proton beam computed tomography device includes an accelerator 10, an S-band high-gradient proton acceleration structure 20, an ultrafast proton bunch distribution system 30, a treatment gantry 40, and an ultrafast proton bunch scanning system 50 arranged in sequence along the direction of the proton beam, and a proton CT system 60 installed on the treatment gantry 40, and the ultrafast proton bunch distribution system 30, the treatment gantry 40, the ultrafast proton bunch scanning system 50, and the proton CT system 60 are located in a proton treatment room 70.

[0031] The accelerator 10 can be a linear accelerator, a cyclotron or a synchrotron, which is set to emit a proton beam with a proton energy of 70 MeV - 235 MeV. The S-band high-gradient proton acceleration structure 20 belongs to the energy-increasing part of the proton CT input energy of the entire device of the present invention. The S-band high-gradient proton acceleration structure 20 receives the proton beam and is set to be switchable between an on state and an off state. When in the on state, it increases the proton energy of the proton beam from 235 MeV to 350 MeV, while when in the off state, it does not change the proton energy of the proton beam. Thus, the present invention enables the switching of the proton energy of the proton beam between the proton energy during proton CT scanning and the proton energy required for proton therapy by turning on and off the S-band high-gradient proton acceleration structure 10.

[0032] The acceleration gradient of the S-band high-gradient proton linear accelerator 10 is not less than 50 MV / m, so as to increase the proton beam energy from 235 MeV to 350 MeV. Thus, the proton energy during proton CT scanning is 350 MeV, and the proton CT energy range is between 300 MeV - 350 MeV, which can ensure that the Bragg Peak of the proton beam falls outside the human body, thereby reducing the residual dose in the human body and protecting healthy tissues and organs. The proton energy during the proton therapy process is in the range of 70 MeV - 235 MeV and does not need to be accelerated by the S-band high-gradient proton acceleration structure 20.

[0033] As Figure 2 shown, in this embodiment, the accelerator 10 is a cyclotron or a synchrotron. Therefore, a bunching structure 21 is provided between the accelerator 10 and the S-band high-gradient proton acceleration structure 20, so that the proton beam 11 in the form of a continuous beam generated by the accelerator 10 becomes a proton beam 22 in the form of microbunches after being accelerated by the bunching structure 21, and then is accelerated by the S-band high-gradient linear accelerator 20 to be input into the proton therapy room 70.

[0034] In other embodiments, if the accelerator 10 is a linear accelerator, the emitted proton beam does not need to pass through the bunching structure 21 and is directly accelerated by the S-band high-gradient proton acceleration structure 20 and then input into the proton therapy room 70.

[0035] The outlet of the S-band high-gradient proton linear accelerator 20 is directly opposite to the ultrafast proton bunch distribution system 30. The ultrafast proton bunch distribution system 30 is located downstream of the S-band high-gradient proton linear accelerator 20.

[0036] As Figure 3As shown, the ultrafast proton bunch distribution system 30 is also located upstream of the treatment gantry 40, which has at least one coil unit 41 (or the treatment gantry 40 has at least one magnet unit). Hereinafter, only the coil unit 41 will be taken as an example for illustration.

[0037] The number of the ultrafast proton bunch distribution systems 30 is one, that is, regardless of the number of coil units 41 of the treatment gantry 40, they share the same ultrafast proton bunch distribution system 30.

[0038] Based on the radio frequency deflection cavity technology with variable polarization direction, the ultrafast proton bunch distribution system 30 can complete the solid angle distribution of the proton beam current, and make the proton beam current transmit to the subsequent treatment gantry 40 at different azimuth angles and pitch angles according to the requirements of proton CT.

[0039] The ultrafast proton bunch distribution system 30 includes a power source system, and a radio frequency deflection structure and a low-level system connected to the power source system. Among them, the low-level system is connected to the power source system through a cable. The number of the power source systems is two sets, and each power source system corresponds to a polarization direction (that is, one horizontal and one vertical direction), and is set to provide the pulsed microwave power corresponding to a polarization direction.

[0040] The radio frequency deflection structure has two independent and orthogonal polarization directions, and is set to generate independent and orthogonal microwave electromagnetic fields through the pulsed microwave power provided by the power source system, and provide two independent and orthogonal transverse deflection forces (that is, kick forces) for the proton beam current through the microwave electromagnetic fields. Through the vector superposition of the two generated independent and orthogonal transverse deflection forces, the proton beam current deflects by a beam distribution angle under the action of the transverse deflection force and is emitted to the treatment gantry 40, thereby completing the solid angle distribution of the proton beam current.

[0041] The beam distribution angle is a solid angle, which is synthesized by the pitch angle and the azimuth angle.

[0042] The pitch angle is determined by the energy of the proton beam current. The ultrafast proton bunch distribution system 30 is set to make the proton beam currents at different energy points emit to the coil unit 41 at the same position of the treatment gantry 40 with the same azimuth angle and different pitch angles as shown in Figure 3 so that the proton beam currents converge on the same beam orbit at the outlet of the downstream treatment gantry 40, and thus are transmitted to the ultrafast proton bunch scanning system 50 downstream of the treatment gantry 40. As shown in Figure 3 Low-energy proton bunches pass through the corresponding internal α orbit, and high-energy proton bunches pass through the corresponding external α orbit. The α-shaped orbit design can effectively increase the treatment area space and enhance the flexibility of the treatment process.

[0043] In addition, the ultrafast proton bunch distribution system 30 is also configured to emit the proton beam current to the coil units 41 located at different positions of the treatment gantry 40 at beam distribution angles with different azimuth angles.

[0044] Thus, the ultrafast proton bunch distribution system 30 utilizes the ultrafast low-level technology of the low-level system to independently control the horizontal and vertical intensities by independently adjusting the pulsed microwave power corresponding to different polarization directions, switches the beam distribution angle according to the requirements of proton CT, and guides the proton beam current to a coil unit 41 of the downstream treatment gantry 40 from different azimuth angles and elevation angles. The beam distribution angle switching frequency of the ultrafast proton bunch distribution system 30 (i.e., the frequency at which its low-level system switches the power level) is at least 1 kilohertz. Therefore, the proton beam current distribution for at least 100 scanning layers can be completed within 100 milliseconds. The energy points of the proton bunches within each scanning layer are the same, and the beam distribution angles are consistent; the maintenance time of the corresponding beam distribution angle is at least 10 microseconds (the same energy point may correspond to 1-2 scanning layers of the scanned object). According to the energy and prescription requirements of different scanning layers, the distribution system quickly completes the switching and preparation of the beam distribution angle (azimuth angle and elevation angle). The overall time of the entire switching, preparation, and beam current distribution (i.e., the working repetition period) is at most 1 millisecond.

[0045] The principle of the ultrafast proton bunch scanning system 50 is also based on the deflection cavity technology with variable polarization directions. It includes 2 sets of acceleration structures, each set of acceleration structures corresponding to a polarization direction, including a power source system, and a radio frequency deflection structure and a low-level system connected to the power source system. Among them, the low-level system is connected to the power source system through a cable; the power source system is configured to provide pulsed microwave power; the radio frequency deflection structure generates two independent and orthogonal microwave electromagnetic fields through the pulsed microwave power of the 2 sets of power source systems, and provides two independent and orthogonal transverse deflection forces (i.e., kick forces) to the proton beam current through the microwave electromagnetic fields; the low-level system is configured to independently control the power level of the pulsed microwave power of its corresponding power source system. The ultrafast proton bunch scanning system 50 is configured to deflect the proton beam current by a three-dimensional scanning angle under the action of two independent and orthogonal transverse deflection forces (i.e., the deflection forces in the X and Y directions), so that different proton beam currents are uniformly and orderly emitted to different transverse positions of the object to be scanned at different three-dimensional scanning angles over time.

[0046] The ultrafast proton bunch scanning system 50 macroscopically performs scanning in a manner of continuous and rapid energy switching in the transverse position.

[0047] Such as Figure 4The working principle of the ultrafast proton bunch scanning system 50 and the scanning path diagram of the transverse position are shown. The ultrafast proton bunch scanning system can independently control the scanning directions in the X and Y directions. Starting from the X-direction scanning as the starting point, after scanning to the end point in the X direction, the Y-direction scanning proceeds one step further, and then the X direction scans reversely to the end point again, scanning alternately in turn to complete the single-layer scanning. The time for single-layer scanning of the object to be scanned is at most 10 microseconds, and the maintenance time of the beam splitting angle is at least 10 microseconds.

[0048] The scanning process of continuous and rapid energy switching at the transverse position is realized by the low-level control technology with a sub-microsecond-level response speed. Each set of acceleration structures is connected to the low-level system through the power source system, so as to be independently driven by the power source and independently controlled by the low-level system. The rapid energy switching ensures that after the proton CT at a certain position is completed, the proton energy during proton CT scanning can be quickly switched to the proton energy required for proton therapy to perform proton therapy at the same position. Among them, the proton CT energy is 350 MeV, and the treatment energy point is 70 - 235 MeV.

[0049] The number of the ultrafast proton bunch scanning systems 50 is equal to the number of the coil units 41 of the treatment gantry 40, and they are evenly distributed and fixed downstream of the coil unit 41.

[0050] Next, based on three different treatment gantries, the computer tomography device of the proton beam and its imaging mode according to three embodiments of the present invention will be specifically described. The present invention proposes three corresponding different imaging modes based on three different treatment gantries.

[0051] As Figures 5 - 6 shown, the present invention proposes three corresponding different imaging modes based on three different treatment gantries 40, namely, the traditional rotating treatment gantry, the rotatable superconducting coil treatment gantry, and the static superconducting coil treatment gantry. Among them, the rotatable superconducting coil treatment gantry and the static superconducting coil treatment gantry are both superconducting coil treatment gantries. The treatment gantry 40 can have a magnet unit that can rotate to switch positions (i.e., the traditional rotating treatment gantry), or multiple coil units arranged in rotational symmetry and capable of rotating around the axis of symmetry within a small range to switch positions (i.e., the rotatable superconducting coil treatment gantry), or multiple stationary symmetrically arranged coil units (i.e., the static superconducting coil treatment gantry).

[0052] The computer tomography device of the proton beam and its imaging method under the imaging mode based on the traditional rotating treatment gantry in Embodiment 1.

[0053] In this embodiment, since the treatment gantry 40 is a traditional rotating treatment gantry, therefore, the treatment gantry 40 can be composed of a magnet unit that can rotate to switch positions. The traditional treatment gantry realizes the irradiation of the object to be scanned at multiple angles by the rotation of a single magnet unit.

[0054] Since the traditional treatment gantry only has one magnet unit, and the traditional treatment gantry realizes the irradiation of proton beam currents in different directions by the rotation of the magnet, therefore, it only needs one proton CT system 60 that matches the magnet unit to rotate together with the treatment gantry 40 to realize proton irradiation. The difference between the proton CT system 60 and the proton CT system 60 in the first embodiment is only that: both position detectors 61 and 62 are aligned with the exits of the proton beam currents of the corresponding magnet units. The position detectors 61 and 62 of each proton CT system 60 are located inside the magnet unit; the remaining energy detector 63 is located outside the magnet unit.

[0055] Based on the computer tomography device of the proton beam implemented by the above-mentioned computer tomography device of the proton beam based on the traditional rotating treatment gantry, the imaging method of the computer tomography device of the proton beam, the imaging mode of which is implemented based on the traditional rotating treatment gantry (i.e., the first imaging mode), includes:

[0056] Step S0": Provide the above-mentioned computer tomography device of the proton beam;

[0057] Step S1": Start the S-band high-gradient proton acceleration structure 20 to fix the proton energy for irradiation in the proton beam current at 350 MeV;

[0058] Step S2": Place the object to be scanned in the treatment gantry 40, rotate the treatment gantry 40 within 180°, scan the object to be scanned based on multiple angles, and simultaneously collect the information of the proton CT system 60;

[0059] Among them, each rotation angle of the treatment gantry 40 is a scanning angle.

[0060] In this embodiment, the rotation angles of the treatment gantry 40 within 180° are evenly distributed. Thus, the treatment gantry 40 performs multiple uniform angle scans on the object to be scanned within 180°.

[0061] In addition, in other embodiments, in order to improve the proton CT imaging speed, in step S2, the rotation angles of the treatment gantry 40 within 180° are uniform incomplete angles, that is, incomplete projection angles are selected for irradiation, such as 60 limited angles within 180°.

[0062] Step S3": Perform image reconstruction according to the collected information to obtain a proton CT image;

[0063] Among them, there are mainly two methods for image reconstruction: the iterative method and the filtered backprojection method.

[0064] This imaging mode takes a relatively long time, and the entire imaging process usually takes several minutes to complete.

[0065] Step S4”: After the image reconstruction is completed, turn off the S-band high-gradient proton acceleration structure 20, transform the proton energy of the proton beam into 70 MeV - 235 MeV, and perform proton therapy according to the proton CT image.

[0066] Embodiment 2: A computed tomography device for proton beams and an imaging method thereof in an imaging mode based on a rotatable superconducting coil therapy gantry.

[0067] In this embodiment, the therapy gantry 40 is a rotatable superconducting coil therapy gantry, which is composed of multiple groups of identical coil units 41, and the coil units 41 are all superconducting coil units. For the structure of multiple groups of superconducting coil units, refer to the patent document “Superconducting dose rate proton therapy device and scanning method based on linear accelerator” with the application number 202110007637.3.

[0068] Specifically, as Figure 5 shown, the rotatable superconducting coil therapy gantry is composed of multiple identical coil units arranged in rotational symmetry and capable of rotating within a small range around the axis of symmetry to switch positions. For example, 24 superconducting coils are evenly distributed in the azimuthal direction with an interval of 15 degrees. In order to accelerate the imaging speed of proton CT, the entire rotatable superconducting coil therapy gantry is not completely fixed and can perform multiple small-angle rotations within a small range. For example, within an 8-degree range, there are 5 transformation angles, and each angle interval is 2 degrees, so as to achieve multiple non-uniform angle scans of the object to be scanned. This shortens to a certain extent the time that the patient needs to hold their breath during the proton CT process and reduces the influence caused by organ movement during this process.

[0069] The magnetic field distribution of the coil unit 41 is specially designed. Without changing the magnetic field intensity, it is set to receive proton beam currents at multiple different energy points emitted at the same azimuth angle and different pitch angles of the beam distribution angle to the therapy gantry 40, and deflect multiple beam orbits to guide proton beam currents at multiple different energy points, so that the proton beam currents converge at the same beam orbit at the outlet of the coil unit or magnet unit, and then are transmitted to the downstream ultra-fast proton bunch scanning system 50.

[0070] Compared with the coil units of the traditional therapy gantry, the coil units of the superconducting coil therapy gantry (such as the rotatable superconducting coil therapy gantry) have greatly reduced weight, and it can utilize the upstream ultra-fast proton bunch distribution system 30 to realize the switching of proton beam currents in the pitch angle and azimuth angle according to different requirements of proton imaging and proton therapy.

[0071] Since in this embodiment, the treatment gantry 40 is composed of multiple groups of identical coil units 41, and the proton beam realizes proton irradiation through the coil units 41 in the treatment gantry 40. Therefore, the treatment gantry 40 needs to be provided with independent proton CT systems 60 having the same number as the superconducting coils to respectively match each coil unit 41, that is, each coil unit 41 is connected to a proton CT system 60, and each proton CT system 60 can independently process the data of this coil unit 41, greatly accelerating the imaging speed of the proton CT and being able to quickly track the proton information in each direction; or it is also feasible to use a rotatable proton CT system 60 while ensuring the rotation speed of the treatment gantry 40, which can reduce costs.

[0072] Each proton CT system 60 is composed of two major parts, including two position detectors 61, 62 and a residual energy detector 63.

[0073] As Figure 7 shown, both of the two position detectors 61, 62 are aligned with the exits of the proton beams of the corresponding coil units 41; and the two position detectors 61, 62 include a first position detector 61 disposed in front of the installation position of the object to be scanned and a second position detector 62 disposed behind the installation position of the object to be scanned, so as to independently detect the positions where each proton in the proton beam enters and exits the object to be scanned through the first position detector 61 and the second position detector 62. Both the first position detector 61 and the second position detector 62 are composed of two direction detectors (i.e., an x-direction detector and a y-direction detector), so they can detect the two-dimensional position of the proton.

[0074] The residual energy detector 63 is located behind the second position detector 62, and is set to measure the residual energy of the protons in the proton beam. Thus, the residual energy detector 63 can measure the energy loss of the protons passing through the object to be scanned, so as to perform image reconstruction.

[0075] The position detectors 61, 62 of each proton CT system 60 are located inside its corresponding coil unit 41 and are fixed to the inside of the entire treatment gantry 40 (i.e., the side close to the axis of symmetry of the treatment gantry 40) through a support structure, and the residual energy detector 63 is located outside its corresponding coil unit 41 and is fixed to the outside of the entire treatment gantry 40 through a support structure. Thus, the proton CT position detector is located inside the superconducting coil gantry, that is, in the innermost circle closest to the irradiated object, so as to ensure that the detected positions are where the protons enter and exit the object to be scanned without being interfered by other devices; the residual energy detector is located outside (i.e., the side far from the axis of symmetry of the treatment gantry 40), so that the outgoing proton beam can be absorbed while detecting the residual energy.

[0076] In this embodiment, the resolution requirement of the position detector is within 1 mm, and the readout rate of the proton CT system 60 reaches 1 MHz.

[0077] Based on the computer tomography device for proton beams of the rotatable superconducting coil treatment gantry described above, the imaging method of the computer tomography device for proton beams implemented thereby, the imaging mode of which is implemented based on the rotatable superconducting coil treatment gantry (i.e., the second imaging mode), includes:

[0078] Step S0: Provide the computer tomography device for proton beams described above;

[0079] Step S1: Start the S-band high-gradient proton acceleration structure 20 to fix the proton energy for irradiation in the proton beam current at 350 MeV;

[0080] Step S2: Place the object to be scanned into the treatment gantry 40, perform an ultrafast proton beam current scan projection on the object to be scanned within 180°, and collect the information of the proton CT system 60;

[0081] Among them, the fixed position of each coil is a scanning angle. In this embodiment, the treatment gantry 40 has 12 coil units 41 within 180°, and the information of the proton CT system 60 includes the information of the object to be measured at 12 large angles.

[0082] The proton imaging system 60 is composed of position detectors 61, 62 and a residual energy detector 63. Therefore, the information of the proton CT system 60 includes the positions where each proton in the proton beam current enters and exits the object to be scanned, and the residual energy of the protons in the proton beam current.

[0083] Step S3: After completing an ultrafast proton beam current scan projection, rotate the rotatable superconducting coil treatment gantry within the rotation range of the superconducting coil treatment gantry so that the superconducting coil rotates simultaneously, repeat the ultrafast proton beam current scan projection, and collect the corresponding information of the proton CT system 60; among them, the rotatable angles of each coil unit of the rotatable superconducting coil treatment gantry are distributed in a plurality of small non-uniform angles, so that the imaging angles obtained by rotation are distributed in a plurality of non-uniform angles;

[0084] In this embodiment, since the rotatable superconducting coil treatment gantry is composed of 24 uniformly distributed superconducting coil units, the included angle between two adjacent coil units 41 is 15 degrees. Therefore, the rotation range in which the coil unit 41 can rotate is 0-15 degrees, and the interval between each small angle position where the coil unit 41 can rotate and be fixed is set at 2 degrees.

[0085] Step S4: Use the information collected in Step S3 to correct the information collected in Step S2, implement proton CT image reconstruction based on non-uniform angular projections, and obtain a proton CT image, thereby accelerating the proton CT imaging speed.

[0086] That is to say, after obtaining multiple non-uniform angular projection information, high-precision proton CT image reconstruction is achieved based on the non-uniform incomplete projection angle algorithm, accelerating the proton CT imaging speed.

[0087] Step S5: After the proton CT image reconstruction is completed, turn off the S-band high-gradient proton acceleration structure 20, change the proton energy of the proton beam to 70 MeV - 235 MeV, and perform proton therapy based on the proton CT image.

[0088] Embodiment 3: A computed tomography device for a proton beam and an imaging method thereof in an imaging mode based on a static superconducting coil therapy gantry.

[0089] In this embodiment, the specific structure of the computed tomography device for a proton beam is the same as that of the computed tomography device for a proton beam in Embodiment 2, and the difference is only that the coil unit is not a plurality of coil units that can rotate around the symmetry axis in a small range to switch positions, but a plurality of stationary symmetrically arranged coil units.

[0090] The number, arrangement method, and specific structure of the proton CT system 60 are the same as those of the proton CT system 60 in Embodiment 2.

[0091] Based on the computed tomography device for a proton beam described above based on a static superconducting coil therapy gantry, the imaging method of the computed tomography device for a proton beam is implemented. Its imaging mode is based on a static superconducting coil therapy gantry (i.e., the third imaging mode), and it includes:

[0092] Step S0': Provide the computed tomography device for a proton beam described above and perform proton CT calibration;

[0093] The proton CT calibration is completed before proton imaging. The specific steps are as follows: 1. Place the calibration model between the front and rear position detectors; 2. Increase the proton beam energy to 350 MeV and irradiate the calibration model once; 3. According to the detection information, obtain the correspondence between the proton water equivalent path length (i.e., the path length that the proton passes through in water, Water Equivalent PathLength, WEPL) and the remaining proton energy, that is, the energy loss corresponding to the length that the proton passes through, for proton CT image reconstruction.

[0094] Step S1': Start the S-band high-gradient proton acceleration structure 20 to fix the proton energy for irradiation in the proton beam at 350 MeV;

[0095] Step S2': Place the object to be scanned into the treatment gantry 40, perform an ultrafast proton beam scanning projection on the object to be scanned within 180°, and collect the information of the proton CT system 60;

[0096] Among them, the fixed position of each coil is a scanning angle. In this embodiment, the treatment gantry 40 has 12 coil units 41 within 180°, and the information of the proton CT system 60 includes the information of the object to be measured at 12 large angles.

[0097] The proton imaging system 60 is composed of position detectors 61, 62 and the residual energy detector 63. Therefore, the information of the proton CT system 60 includes the positions where each proton in the proton beam enters and exits the object to be scanned, and the residual energy of the protons in the proton beam.

[0098] Step S3': Use the RSP distribution image of photon CT as the prior image, and perform iterative image reconstruction using the information collected in Step S2 to obtain the final three-dimensional RSP distribution image as the proton CT image. Thus, high-precision proton CT imaging is achieved.

[0099] Among them, iterative image reconstruction means that the image reconstruction uses the iterative method. Thus, only 12-angle scans are required, reducing the scanning angle and accelerating the imaging speed, providing a feasible technical solution for realizing proton therapy technology based on real-time image guidance.

[0100] Step S4': After the iterative image reconstruction is completed, turn off the S-band high-gradient proton acceleration structure 20, change the proton energy of the proton beam to 70 MeV - 235 MeV, and perform proton therapy according to the proton CT image.

[0101] In the iterative image reconstruction of the proton image, based on a static superconducting coil treatment gantry, using the RSP distribution image of photon CT as the prior image can calibrate the range error of RSP, realize real-time image guidance, so as to meet the requirements of the ultrafast and ultra-high dose rate of proton flash therapy (FLASH). Thus, it provides a feasible solution for realizing clinically significant proton CT and proton therapy technology based on real-time image guidance.

[0102] The three different imaging modes proposed in this patent are based on different gantries, where the proton CT system is integrated with the gantry. The first is the imaging mode based on the traditional gantry, which can be upgraded according to the existing proton therapy gantry to reduce the image guidance error and achieve real-time lateral image guidance. The second is the imaging mode based on a rotatable superconducting coil gantry. By rotating the coil within a certain small angle range, proton irradiation is performed on the object to be scanned, accelerating the proton CT imaging speed. The third is the proton imaging mode based on a static superconducting coil gantry. Combined with photon CT, the RSP distribution image of photon CT is used as a prior image, and image reconstruction is performed through proton scans at a small number of angles to achieve proton CT localization, improve image quality, and thus achieve real-time image guidance. The third imaging mode shortens the proton CT imaging time, improves the imaging speed, for example, it can be completed within 1 s, and at the same time, it can reduce the influence of human respiratory movement on lesion localization, improve image resolution, and meet the requirements of proton flash therapy (FLASH).

[0103] In summary, the increase in the proton energy of the computer tomography device based on proton beam in the present invention is achieved by an S-band high-gradient linear accelerator, realizing high-energy proton CT imaging.

[0104] In addition, the present invention proposes imaging methods under three different proton CT imaging modes. The corresponding proton detection platforms are the same, both consisting of a position detector and a residual energy detector. The first gantry type is based on a traditional rotating gantry, and the first imaging mode is proposed based on this gantry. This imaging mode uses a fixed-energy proton beam, similar to the existing photon CT scanning method, and performs proton CT imaging on the object to be scanned through irradiations at multiple uniform angles within 180°, which can directly solve the error problem generated during the photon CT conversion process. The second gantry type is based on a superconducting coil gantry, and two imaging modes are proposed based on this gantry: the second imaging mode is based on a rotatable superconducting coil gantry. The gantry consists of multiple identical superconducting coils, and the gantry can rotate at a small angle multiple times within a certain small range, using a fixed-energy proton beam to achieve an imaging mode based on multiple non-uniform angles. Since the rotation angle is smaller, the proton CT imaging speed can be improved; the third imaging mode is based on a static superconducting coil gantry. The superconducting coil unit is fixed, that is, the proton beam scanning angle is fixed. Using the RSP distribution image of photon CT as a prior image, fixed-energy ultra-fast proton beam scanning projection is performed under the condition of a small number of scanning angles, achieving high-precision proton CT imaging and obtaining three-dimensional RSP distribution information. At the same time, the projection time of this scheme is very short, enabling fast proton imaging, providing a feasible solution for realizing clinically significant proton CT and proton therapy technology based on real-time image guidance.

[0105] The proton beam-based computed tomography device of the present invention is integrated into a new superconducting proton flash therapy device at the same time, which can shorten the imaging time of proton CT, accelerate the imaging speed of proton CT, such as completing it within 1 s, realize the function of real-time image guidance of proton CT in the whole proton therapy, and provide a feasible technical solution for the future proton flash (FLASH) technology.

[0106] One of the imaging methods of the present invention also innovatively proposes to use the RSP distribution based on photon CT as a prior image, and perform secondary depth imaging with a small number of proton irradiation angles. After secondary iteration, high-precision CT image reconstruction is achieved, the RSP accuracy is significantly improved, the imaging time of proton CT is greatly shortened, the error caused by respiratory motion is reduced, and the real-time image-guided proton therapy technology is realized, which also provides a feasible technical solution for future proton flash (FLASH).

[0107] The above are only the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Various changes can be made to the above examples of the present invention. That is, all simple, equivalent changes and modifications made according to the claims and the content of the specification of the present invention application fall within the scope of the claims of the present invention patent. The content not described in detail in the present invention is all conventional technical content.

Claims

1. A computed tomography device for a proton beam, characterized in that, It includes an accelerator, an S-band high-gradient proton acceleration structure, an ultrafast proton bunch distribution system, a treatment gantry, an ultrafast proton bunch scanning system arranged successively along the direction of the proton beam, and a proton CT system installed on the treatment gantry; The accelerator is set to emit a proton beam with a proton energy of 70 MeV - 235 MeV; the S-band high-gradient proton acceleration structure is set to be switchable between an on state and an off state, and when in the on state, it raises the proton energy of the proton beam to 350 MeV; The accelerator is a cyclotron or a synchrotron, and a bunching structure is provided between the accelerator and the S-band high-gradient proton acceleration structure; or the accelerator is a linear accelerator, and the proton beam it emits directly passes through the S-band high-gradient proton acceleration structure; The ultrafast proton bunch distribution system is set to emit proton beams at different energy points to the coil units at the same position of the treatment gantry with the same azimuth angle and different elevation angle beam distribution angles, so that the proton beams converge on the same beam orbit at the outlet of the downstream treatment gantry; the ultrafast proton bunch distribution system is also set to emit proton beams to the coil units at different positions of the treatment gantry with different azimuth angle beam distribution angles; The S-band high-gradient proton acceleration structure is an S-band high-gradient proton linear accelerator.

2. The computed tomography device for a proton beam according to claim 1, characterized in that, The treatment gantry has a plurality of coil units arranged in rotational symmetry and capable of rotating within a small range around the axis of symmetry to switch positions, or a plurality of stationary symmetrically arranged coil units.

3. The computed tomography device for a proton beam according to claim 2, characterized in that, Each proton CT system corresponds to a coil unit, and it includes two position detectors and a residual energy detector; both position detectors are aligned with the outlet of the proton beam of the corresponding coil unit; and the two position detectors include a first position detector arranged in front of the installation position of the object to be scanned and a second position detector arranged behind the installation position of the object to be scanned, and the residual energy detector is located behind the second position detector.

4. The computed tomography device for a proton beam according to claim 3, characterized in that, The position detectors of each proton CT system are located inside its corresponding coil unit and are fixed to the inside of the entire treatment gantry through a support structure; the residual energy detector is located outside its corresponding coil unit and is fixed to the outside of the entire treatment gantry through a support structure.

5. The computed tomography device for a proton beam according to claim 1, characterized in that, The treatment gantry has a magnet unit that can rotate to switch positions; the number of proton CT systems is 1, and it includes two position detectors and a residual energy detector; both position detectors are aligned with the outlet of the proton beam of the corresponding magnet unit; and the two position detectors include a first position detector arranged in front of the installation position of the object to be scanned and a second position detector arranged behind the installation position of the object to be scanned, and the residual energy detector is located behind the second position detector; the position detectors of the proton CT system are located inside the magnet unit; the residual energy detector is located outside the magnet unit.

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