An image-guided based proton therapy system

Abstract

This application provides an image-guided proton radiotherapy system, comprising: a carrier system for carrying a calibration object; an imaging system for imaging the calibration object; and an irradiation system including a collimation component and a beam detector. The collimation component receives protons emitted from an external proton source and outputs a proton beam, and is adjustable in multiple degrees of freedom. The beam detector receives the proton beam output by the collimation component to form a beam image. A control and processing system is configured to: control the carrier system to move according to the position information of the object image and the position information of the imaging center axis of the imaging system so that the center of the object image is located on the imaging center axis; repeatedly perform the following registration operation until a preset termination condition is met so that the center of the calibration object projected on the beam detector coincides with the center of the beam image, thereby achieving registration between the imaging center axis and the beam center axis; and control the collimation component to move according to the position information of the projection and the position information of the beam image on the beam detector.

Description

Technical Field

[0001] This application relates to the field of biomedical imaging and radiotherapy equipment technology, and more specifically, to an image-guided proton radiotherapy system. Background Technology

[0002] Small animal radiotherapy platforms are crucial experimental tools for studying tumor radiobiology, mechanisms of damage to normal tissues, fractionated irradiation effects, spatially fractionated irradiation effects, and the relative biological effects of protons. Compared to clinical human radiotherapy, small animal experiments are characterized by smaller target areas, smaller irradiation fields, stringent geometric tolerances, and high requirements for experimental repeatability. Therefore, higher demands are placed on the imaging accuracy, beam positioning accuracy, mechanical execution accuracy, and consistency of the treatment plan. Existing small animal irradiation platforms, when applied to proton irradiation scenarios, generally suffer from the technical challenge of achieving a stable and unified match between imaging coordinates, beam irradiation coordinates, and mechanical execution coordinates. Summary of the Invention

[0003] In view of this, this application provides an image-guided proton radiotherapy system, comprising:

[0004] The carrier system, used to carry the calibration object, is configured to adjust the position of the calibration object;

[0005] An imaging system includes a radiation source and a radiation detector disposed opposite to each other on both sides of a carrying system in a first direction. The radiation source is used to emit radiation toward the calibration object, and the radiation detector is used to receive the radiation to form an object image of the calibration object.

[0006] The irradiation system includes a collimation component and a beam detector disposed opposite to each other on both sides of the carrier system in a second direction. The collimation component is used to receive protons emitted by an external proton source and output a proton beam, and can be adjusted in multiple degrees of freedom. The beam detector is used to receive the proton beam output by the collimation component to form a beam image of the proton beam. The second direction intersects with the first direction.

[0007] The control and processing system is configured as follows:

[0008] Based on the position information of the object image and the position information of the imaging center axis of the imaging system, the object carrying system is controlled to move so that the center of the object image is located on the imaging center axis.

[0009] Repeat the following registration operation until the preset termination condition is met, so that the center of the object being calibrated projects onto the beam detector coincides with the center of the beam image, thereby achieving registration between the imaging central axis and the proton beam central axis:

[0010] The collimation assembly is moved based on the position information of the object being calibrated projected onto the beam detector and the position information of the beam image on the beam detector.

[0011] According to an embodiment of this application, the collimation assembly includes: a collimator displacement stage, and a plurality of collimators with different apertures disposed on the collimator displacement stage; the control and processing system is further configured to: sequentially switch collimators with different apertures to the proton beam path, and control the movement of the collimator displacement stage according to the beam image of the proton beam output by each collimator, so as to perform phased registration between the imaging center axis and the beam center axis.

[0012] According to embodiments of this application, a plurality of collimators with different apertures include at least a first collimator and a second collimator, wherein the aperture of the first collimator is larger than the aperture of the second collimator; the control and processing system is configured to: switch the first collimator to the proton beam path, and control the collimator displacement stage to move according to the beam image of the proton beam output by the first collimator, so as to perform initial registration between the imaging center axis and the beam center axis; after the initial registration is completed, switch the second collimator to the proton beam path, and control the collimator displacement stage to move according to the beam image of the proton beam output by the second collimator, so as to perform secondary registration between the imaging center axis and the beam center axis.

[0013] According to an embodiment of this application, the beam detector is configured to move in the vertical direction; the control and processing system is further configured to: control the beam detector to move upward so that the beam detector is located on the proton beam path when the imaging center axis and the beam center axis are registered; and control the beam detector to move downward so that the beam detector leaves the proton beam path when the imaging center axis and the beam center axis are registered and the object to be irradiated is irradiated.

[0014] According to an embodiment of this application, the control and processing system is further configured to: control the beam detector to acquire the proton beam output by the collimation component to form a beam image; generate control commands for the collimator displacement stage based on the deviation between the position information of the beam image and the position information of the calibration object projected on the beam detector; and control the collimator displacement stage to move according to the control commands so that the center of the beam image coincides with the center of the projection.

[0015] According to embodiments of this application, the preset termination condition includes at least one of the following conditions:

[0016] The registration operation is repeated a preset number of times; the deviation of each registration operation is less than a preset deviation threshold; in the continuously acquired beam images, the drift of the center of each beam image relative to the center of the projection meets a preset drift threshold; the maximum difference between the deviations of each registration operation is less than a second deviation threshold; and the beam spot shape of the beam image meets a preset quality index.

[0017] According to an embodiment of this application, the system further includes: a treatment planning system, used to determine an irradiation scheme for the object to be irradiated based on a proton source model at the exit of the collimation component, a material distribution model of the object to be irradiated, and parameters of the collimation component; wherein the proton source model includes the following parameters: transverse beam size, angular divergence, position-direction correlation term, average energy, energy broadening, and the number of incident particles per unit monitoring quantity.

[0018] According to an embodiment of this application, the treatment planning system is further configured to: fit the spatial distribution of the proton beam to a two-dimensional Gaussian distribution on a selected phase space reference plane to determine the transverse beam spot size of the proton beam; use the angular divergence and position-direction correlation terms at the phase space reference plane as transverse transmission characteristic parameters, the average energy and energy broadening of the proton beam as energy characteristic parameters, and the number of incident particles corresponding to a unit monitoring quantity as a dose calibration parameter, and combine them to form a proton source model.

[0019] According to an embodiment of this application, the control and processing system is further configured to: when using a range shifter, determine the exit plane of the range shifter as a phase space reference plane; and when not using a range shifter, determine the exit plane of the collimation assembly as a phase space reference plane.

[0020] According to an embodiment of this application, the system further includes: a platform body for carrying the payload system, imaging system, and irradiation system, and is configured as a movable structure; and a positioning system disposed on the platform body for positioning the platform body according to preset marks in the treatment space so that the proton beam path is within a preset beam axis calibration range.

[0021] According to embodiments of this application, an imaging system is used to acquire an image of the calibration object. Based on the position information of the object image and the position information of the imaging central axis, the movement of the carrier system is controlled so that the center of the calibration object is located on the imaging central axis. Then, a beam detector is used to acquire an image of the proton beam. Based on the projection position information of the calibration object on the beam detector and the position information of the beam image, the movement of the collimation component is controlled so that the projection center coincides with the center of the beam image. Through the above registration method, the imaging central axis of the imaging system and the beam central axis of the proton beam are precisely registered, thereby establishing a unified reference between the imaging coordinates, beam irradiation coordinates, and mechanical execution coordinates. This effectively solves the problem in the prior art where the planned isocenter is inconsistent with the actual irradiation position due to the inconsistency of coordinate systems. Attached Figure Description

[0022] The above and other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0023] Figure 1A top view of a proton radiotherapy system according to an embodiment of this application is shown schematically.

[0024] Figure 2 The illustration shows a perspective view of the proton radiotherapy system in the embodiment of this application from a first-view perspective.

[0025] Figure 3 The diagram illustrates a perspective view of the proton therapy system in an embodiment of this application from a second perspective.

[0026] Figure 4 The illustration shows a perspective view of the proton radiotherapy system in the embodiments of this application from a third-person perspective.

[0027] Figure 5 The flowchart illustrating a proton radiotherapy system performing proton radiotherapy according to an embodiment of this application is shown schematically.

[0028] Figure label:

[0029] 1. Carrying system; 11. Carrying platform; 12. Adjustment module; 2. Imaging system; 21. X-ray source; 22. X-ray detector; 3. Irradiation system; 31. Collimation assembly; 311. Collimator; 312. Collimator displacement stage; 32. Beam detector; 33. Window; 4. Platform body; 5. Positioning system; 6. Electric lifting mechanism. Detailed Implementation

[0030] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of this application. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of this application for ease of explanation. However, it will be apparent that one or more embodiments may be implemented without these specific details. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this application.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0032] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0033] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0034] Small animal radiotherapy platforms are important experimental tools for studying tumor radiobiology, mechanisms of damage to normal tissues, fractionated irradiation effects, spatially fractionated irradiation effects, and the relative biological effects of protons. Compared with clinical human radiotherapy, small animal experiments are characterized by smaller target areas, smaller irradiation fields, stricter geometric tolerances, and higher repeatability requirements. Therefore, they place higher demands on the system's imaging accuracy, beam positioning accuracy, mechanical execution accuracy, and consistency of treatment planning.

[0035] Existing small animal irradiation platforms primarily use X-ray sources, which present the following problems in proton irradiation scenarios for small animals:

[0036] First, it is difficult to stably unify the imaging coordinates, beam irradiation coordinates, and mechanical execution coordinates. X-ray imaging systems have independent geometric centers, proton beams have their own beam centerlines, and animal displacement stages and collimator displacement stages correspond to mechanical coordinates. If a unified benchmark is lacking, it can easily lead to inconsistencies between the planned isocenter and the actual irradiation position.

[0037] Second, the relationship between the proton beam center axis and the imaging center axis is not fixed when the mobile platform is used in different experimental scenarios. After the platform is moved, reinstalled, or the proton conditions are changed, the original beam axis relationship usually cannot be directly used and needs to be recalibrated. For irradiation fields at the millimeter level or even smaller, this problem will directly affect the irradiation accuracy.

[0038] Third, existing solutions mostly rely on offline quality assurance (QA), manual adjustments, or semi-automatic processing, lacking an automatic closed-loop calibration mechanism based on beam images. Especially under small aperture collimation conditions, the key is not whether there is a beam, but whether the beam center accurately falls on the planned illumination axis.

[0039] Fourth, existing treatment planning systems (TPS) often focus on image processing and dose calculation, with insufficient coupling between them and hardware execution. The conversion of planning results into collimator position, animal platform position, rotation angle, and step-by-step irradiation sequence still requires significant manual intervention, which is detrimental to accuracy control and repeatability of experiments.

[0040] Based on this, this application provides an image-guided proton radiotherapy system that uses the X-ray imaging coordinate system as a unified reference. Through laser coarse positioning, real-time beam imaging, and automatic correction by the collimator displacement stage, it achieves automatic calibration of the proton beam central axis and the imaging central axis. On this basis, the TPS outputs planning parameters, calibration targets, and execution parameters, and the control and processing system controls the hardware to complete cone-beam computed tomography (CBCT)-guided positioning and stepwise proton irradiation, which can at least solve some of the above-mentioned technical problems.

[0041] The following is combined Figures 1-4 The image-guided proton radiotherapy system of this embodiment will be further described.

[0042] like Figures 1-4 As shown, the image-guided proton radiotherapy system of this embodiment includes a carrier system 1, an imaging system 2, an irradiation system 3, and a control and processing system (not shown in the figure).

[0043] The carrier system 1, used to carry the calibration object, is configured to adjust the position of the calibration object.

[0044] The calibration object is a standard phantom used for calibrating a proton therapy system, such as a specialized phantom containing multiple high-precision metal spheres (BB spheres), the three-dimensional spatial coordinates of the centers of each sphere having been precisely measured and are known values. In some embodiments, the carrier system 1 is also used to carry the object to be irradiated, such as a small animal.

[0045] The loading system 1 may include a loading platform 11 and an adjustment module 12 for adjusting the spatial position of the loading platform 11. The adjustment module 12 is capable of adjusting the position of the loading platform 11 in multiple degrees of freedom, such as translation in the X-axis, Y-axis, and Z-axis directions and rotation about each axis.

[0046] For example, the adjustment module 12 may include a translation stage and a rotation stage, which can adjust the position and angle of the object to be irradiated during the imaging and irradiation process, so that CBCT imaging and irradiation adopt the same positioning posture.

[0047] Specifically, after imaging is completed, the carrier system 1 adjusts the object to be irradiated to a preset initial irradiation angle; if the irradiation angle needs to be changed during irradiation, it is achieved by rotating the displacement stage. The carrier system 1 can also convert the positioning correction amount output by the TPS and the position and angle parameters of each irradiation sub-step into mechanical execution actions.

[0048] Imaging system 2 includes a radiation source 21 and a radiation detector 22 disposed opposite to each other on both sides of the object-carrying system 1 in a first direction. The radiation source 21 is used to emit radiation toward the calibration object, and the radiation detector 22 is used to receive the radiation to form an object image of the calibration object. Imaging system 2 is used to acquire two-dimensional or three-dimensional images of the calibration object or the object to be irradiated.

[0049] The first direction can be, for example, a horizontal direction. The radiation source 21 and radiation detector 22 are positioned opposite each other on either side of the transport system 1 in the first direction; for example, the radiation source 21 can be located on the left side of the transport system 1, and the radiation detector 22 can be located on the right side of the transport system 1. The radiation source 21 can be an X-ray tube, and the radiation detector 22 can be a flat panel detector.

[0050] In some embodiments, the imaging center axis in the imaging system 2 coordinate system can be calibrated by imaging a standard phantom. The proton radiotherapy system in this application uses this imaging system 2 coordinate system as the coordinate reference.

[0051] In one implementation, the imaging system 2 can employ a cone-beam computed tomography (CBCT) architecture. The X-ray source 21 generates a cone-beam X-ray beam that penetrates the BB sphere phantom placed on the payload system 1 and is received by a flat-panel detector opposite it. The control and processing system controls the rotation of the payload stage 11 to acquire object images from multiple angles. A three-dimensional CT image of the standard phantom is generated using an image reconstruction algorithm, and image processing techniques are used to extract the center coordinates of each BB sphere in the CT image. Then, combined with the known spatial coordinates of the BB spheres, the position of the imaging central axis is obtained through geometric calculations.

[0052] The irradiation system 3 includes a collimation component 31 and a beam detector 32 disposed opposite to each other on both sides of the carrier system 1 in a second direction. The collimation component 31 is used to receive protons emitted by an external proton source and output a proton beam, and can be adjusted in multiple degrees of freedom. The beam detector 32 is used to receive the proton beam output by the collimation component 31 to form a beam image of the proton beam. The second direction intersects with the first direction. The beam image is a two-dimensional intensity distribution map of the proton beam on the plane of the beam detector 32.

[0053] The irradiation system 3 is used to receive protons emitted by an external proton source and output a proton beam to irradiate the calibration object or the object to be irradiated.

[0054] like Figure 3 As shown, the irradiation system 3 includes a collimation component 31 and a beam detector 32, as well as a window 33. This window 33 is used to dock with an external proton source to receive protons emitted by the external proton source. After the protons enter through the window 33, they pass through an air gap into the collimation component 31. The collimator 311 of the collimation component 31 shapes the protons into a specific shape and size before outputting them.

[0055] The second direction can be a horizontal direction that forms an angle with the first direction. For example, the first direction can be perpendicular to the second direction to avoid spatial interference between the imaging system 2 and the illumination system 3.

[0056] In some embodiments, the collimation assembly 31 is disposed on the transmission path of the proton beam and includes a collimator displacement stage 312 and a plurality of collimators 311 with different apertures mounted thereon. Exemplarily, the collimators with different apertures may include a primary collimator, a secondary collimator, and a micro-aperture collimator. The primary and secondary collimators are used to progressively constrain the proton beam range; the micro-aperture collimator is disposed at the final collimation position to form a small field of illumination. The aperture of the micro-aperture collimator may include 1 mm, 3 mm, 5 mm, and 8 mm. Different apertures determine the cross-sectional size and beam intensity of the output proton beam.

[0057] The collimator displacement stage 312 can be adjusted in multiple degrees of freedom (such as translation along the X and Y axes and rotation around the Z axis) to change the output direction and position of the proton beam. For example, the collimator displacement stage 312 is a two-dimensional translational structure, used both for lateral fine-tuning after the collimator assembly 31 is installed and for automatically correcting the position of the collimator assembly 31 based on beam center deviation during beam axis calibration. During calibration, initial calibration can be completed first with a large-aperture collimator, and then a micro-aperture collimator actually used in treatment can be used for verification and secondary fine-tuning.

[0058] The beam detector 32 can be a high-resolution scintillator detector, which generates fluorescence when the proton beam hits the scintillator, and the beam image is captured by a high-sensitivity CCD sensor or CMOS camera.

[0059] In some embodiments, the beam detector 32 is configured to move vertically. Specifically, the beam detector 32 is mounted on an electrically driven lifting mechanism 6 and moves up and down via the mechanism. The beam detector 32 may include the following operating states: automatic calibration state (i.e., when the imaging center axis and the beam center axis are registered): the beam detector 32 rises to the proton beam path, continuously acquires beam images, and feeds back beam center and beam spot parameters; real-time verification state: it rises briefly before formal irradiation or before subfield execution to determine whether the current beam meets the tolerance requirements; exit state (i.e., when the imaging center axis and the beam center axis are registered and the object to be irradiated is irradiated): the beam detector 32 descends to the outside of the irradiation field to avoid blocking the formal irradiation beam.

[0060] It should be noted that the rise or fall of the beam detector 32 is controlled by the control and processing system. Specifically, the control and processing system is also configured to: control the beam detector 32 to move upward when the imaging center axis and the beam center axis are registered, so that the beam detector 32 is located on the proton beam path; and control the beam detector 32 to move downward when the imaging center axis and the beam center axis are registered and the object to be irradiated is irradiated, so that the beam detector 32 leaves the proton beam path.

[0061] The control and processing system is configured to: control the movement of the carrier system 1 based on the position information of the object image and the position information of the imaging center axis of the imaging system 2, so that the center of the object image is located on the imaging center axis; repeatedly perform the following registration operation until a preset termination condition is met, so that the center of the calibration object projected on the beam detector coincides with the center of the beam image, so as to achieve the registration of the imaging center axis and the beam center axis of the proton beam; and control the movement of the collimation component 31 based on the position information of the calibration object projected on the beam detector 32 and the position information of the beam image on the beam detector 32.

[0062] An object image refers to a two-dimensional or three-dimensional image formed by imaging system 2 (such as cone-beam CT) after scanning a calibration object (such as a BB spherical phantom). The positional information of the object image refers to the coordinates of the center of the calibration object (e.g., the geometric center of the BB spherical phantom or the center of a specific BB sphere) in the imaging system 2 coordinate system defined by imaging system 2.

[0063] The imaging center axis is a virtual spatial straight line determined by the calibration of imaging system 2. It is typically defined as a straight line originating from the focal point of X-ray source 21, passing perpendicularly through the center of the detector, and passing through the center of rotation. The positional information of the imaging center axis refers to the spatial equation or key point coordinates of this axis in the imaging system 2 coordinate system defined by the imaging system 2 itself. In this imaging system 2 coordinate system, the imaging center axis is usually defined as the Z-axis, and its intersection with the detector plane is defined as the origin (0, 0, 0) of the imaging system 2 coordinate system.

[0064] Projection refers to the shadow or image formed on the plane of beam detector 32 after a calibration object (such as a BB spherical model) is illuminated by an external light source (such as a proton beam). The positional information of the projection refers to the coordinates of the geometric center of the projection in the physical coordinate system of beam detector 32.

[0065] A beam image is a two-dimensional intensity distribution map formed by the direct acquisition of a proton beam by the beam detector 32, reflecting the spatial distribution of the proton beam on the detector plane. The positional information of the beam image refers to the coordinates of the beam center (i.e., the centroid of the proton beam intensity distribution) in the coordinate system of the beam detector 32.

[0066] Registration refers to the process of aligning two spatial references from different sources (i.e., the imaging center axis defined by imaging system 2 and the actual propagation axis of the proton beam) to coincide with each other. After registration, the target location (such as the tumor center) presented by imaging system 2 is spatially consistent with the location where the proton beam actually hits.

[0067] According to an embodiment of this application, the above-mentioned proton radiotherapy system further includes: a platform body 4, which is used to support the carrier system 1, the imaging system 2, and the irradiation system 3, and is constructed as a movable structure.

[0068] In some embodiments, the platform body 4 may be equipped with multiple casters at its bottom to facilitate movement between different experimental scenarios. The platform body 4 is also equipped with a lifting adjustment assembly (e.g., an electric push rod or a screw jack) to adjust the level of the platform body 4 after reaching the predetermined working position, ensuring that its platform surface is level. Furthermore, the platform body 4 is provided with multiple positioning reference points (e.g., positioning pin holes or optical markers) for precise positioning in conjunction with an external positioning system 5.

[0069] With the movable platform body 4, each time the platform body 4 is moved to a new position, it does not rely on a fixed installation relationship, but re-establishes the consistency relationship between the beam center axis and the imaging center axis through automatic closed-loop calibration.

[0070] According to an embodiment of this application, an image of the calibration object is acquired using an imaging system 2. Based on the position information of the object image and the position information of the imaging central axis, the object-carrying system 1 is moved to ensure that the center of the calibration object is located on the imaging central axis. Then, an image of the proton beam is acquired using a beam detector 32. Based on the projection position information of the calibration object on the beam detector 32 and the position information of the beam image, the collimation component 31 is moved to ensure that the projection center coincides with the center of the beam image. Through the above registration method, the imaging central axis of the imaging system 2 is precisely registered with the beam central axis of the proton beam, thereby establishing a unified reference between the imaging coordinates, beam irradiation coordinates, and mechanical execution coordinates. This effectively solves the problem in the prior art where the planned isocenter and the actual irradiation position are inconsistent due to the inconsistency of coordinate systems.

[0071] like Figure 1 As shown, according to an embodiment of this application, the proton radiotherapy system described above may further include a positioning system 5, disposed on the platform body 4, for positioning the platform body 4 according to preset marks in the treatment space, so that the proton beam path is within a preset beam axis calibration range. Exemplarily, the positioning system may include two sets of laser emitters.

[0072] The proton beam path refers to the spatial trajectory of protons emitted from an external proton source, after transmission, shaping, and collimation, to finally reach the calibration object or the object to be irradiated. In a proton radiotherapy system, the proton beam path can be described as an ideal straight line starting from the proton source exit, passing sequentially through window 33, air gap, and collimation assembly 31 (including primary collimator, secondary collimator, and micropore collimator), and finally reaching the calibration object or the object to be irradiated on the carrier system 1.

[0073] The beam axis calibration range refers to the spatial area within which the beam detector 32 can effectively acquire images of the proton beam. Specifically, the limitations are as follows: In the horizontal direction, the center of the proton beam should fall within the effective imaging area of ​​the beam detector 32, such as within ±10mm around the detector center; in the vertical direction, the height of the proton beam should match the sensitive detection area of ​​the beam detector 32. In the angular dimension, the incident direction of the proton beam should be substantially perpendicular to the plane of the beam detector 32, and the incident angle deviation should be controlled within a preset tolerance range, for example, not exceeding ±2°.

[0074] In some embodiments, multiple marker points (e.g., crosshairs, reflective patches, or laser targets) are pre-set on the walls, floor, or fixed supports of the treatment space. The positioning system 5 may include a laser positioning module and / or a visual positioning module. The laser positioning module emits crosshairs to align the positioning reference point on the platform body 4 with the pre-set marker points in the treatment space, thereby achieving coarse positioning of the platform body 4. A level (e.g., an electronic level) is used to detect the horizontal state of the platform body 4 and adjusts it to a horizontal position by controlling the lifting adjustment components.

[0075] In one implementation, the positioning system 5 is configured as follows: First, the platform body 4 is moved to a preset working area in the treatment space using casters; second, the positioning reference point on the platform body 4 is aligned with a preset marker point in the treatment space using a laser positioning module; then, the levelness of the platform body 4 is detected by a level instrument, and the lifting adjustment component is driven to adjust it until the platform surface of the platform body 4 is level; finally, the casters are locked to fix the platform body 4 in this working position. After the above coarse positioning is completed, the transmission path of the proton beam is limited to the working range of the subsequent beam axis calibration system, thus providing the prerequisite for subsequent fine calibration operations.

[0076] According to embodiments of this application, by setting a movable platform body 4 and a positioning system 5 for initial positioning of the platform body 4, the entire proton radiotherapy system can be flexibly transferred between different experimental scenarios, and the proton beam path can be quickly limited to a preset beam axis calibration range after each positioning. This effectively solves the problem of uncertain beam axis relationships caused by the transfer, reinstallation, or change of proton conditions of the movable platform, providing a reliable prerequisite for subsequent automatic closed-loop fine calibration based on beam images. This significantly improves the system's environmental adaptability and calibration efficiency, and is beneficial for achieving sub-millimeter-level irradiation accuracy.

[0077] According to an embodiment of this application, the control and processing system is further configured to: control the collimation component 31 to move so that the center of the projection coincides with the center of the beam image based on the position information of the calibration object projected on the beam detector 32 and the position information of the beam image on the beam detector 32; control the beam detector 32 to acquire the proton beam output by the collimation component 31 to form a beam image; generate a control command for the collimator displacement stage 312 based on the deviation between the position information of the beam image and the position information of the calibration object projected on the beam detector 32; and control the collimator displacement stage 312 to move so that the center of the beam image coincides with the center of the projection based on the control command.

[0078] The position information of the projection is the coordinate value of the geometric center of the projection in the beam detector 32 coordinate system. This projection center represents the target position that the proton beam should hit, that is, the target projection position of beam registration.

[0079] For example, a BB spherical phantom is placed on the carrier system 1, and the center of the BB spherical phantom has been calibrated to be located on the imaging central axis by the imaging system 2. Based on the geometric projection relationship, the theoretical projection position of the phantom center on the beam detector 32 plane is pre-calculated. For example, after calculation, the physical coordinates of the projection center are (102.40mm, 204.80mm), corresponding to the detector pixel coordinates (512, 512). This position is the target projection position for subsequent registration.

[0080] Deviation is the spatial difference between the actual measured beam image center and the target projection center, usually represented by a two-dimensional vector (Δx, Δy). This deviation reflects the offset between the actual propagation centerline of the proton beam and the ideal target position, and is the core input parameter of closed-loop feedback control.

[0081] According to an embodiment of this application, since the collimation assembly 31 may include multiple collimators 311 with different apertures, the control and processing system is further configured to: sequentially switch the collimators 311 with different apertures to the proton beam path, and control the collimator displacement stage 312 to move according to the beam image of the proton beam output by each collimator 311, so as to perform phased registration between the imaging center axis and the beam center axis.

[0082] Staged registration refers to breaking down the registration process between the imaging center axis and the proton beam's beam center axis into multiple sequential stages. Each stage uses a collimator 311 with a different aperture to complete an alignment task with varying degrees of precision. Typically, the first stage uses a larger aperture collimator 311 for rapid coarse calibration, while subsequent stages use smaller aperture collimators 311 for fine verification and adjustment.

[0083] In some embodiments, the collimators 311 with different apertures include at least a first collimator and a second collimator, where the aperture of the first collimator is larger than that of the second collimator. In this case, the staged registration can include two stages: In the first stage, the first collimator is used, and it is switched to the proton beam path. Based on the beam image of the proton beam output by the first collimator, the collimator displacement stage 312 is controlled to move to perform initial registration between the imaging center axis and the beam center axis, reducing the deviation between the center of the beam image and the center of the projection to less than 0.5 mm. In the second stage, the second collimator is used. After the initial registration is completed, the second collimator is switched to the proton beam path, and based on the beam image of the proton beam output by the second collimator, the collimator displacement stage 312 is controlled to move to perform secondary registration between the imaging center axis and the beam center axis, further reducing the deviation between the center of the beam image and the center of the projection to less than 0.05 mm.

[0084] The technical solution of this application balances calibration efficiency and registration accuracy through a phased registration strategy. At the same time, it uses the same microporous collimator as the actual treatment for verification registration, ensuring a high degree of consistency between the registration results and the actual irradiation conditions. This provides key technical support for high precision, high efficiency and high automation of proton radiotherapy in small animals.

[0085] According to the embodiments of this application, the deviation of each registration operation is less than a preset deviation threshold; in the continuously acquired beam images, the drift of the center of each beam image relative to the center of the projection satisfies a preset drift threshold; the maximum difference between the deviations of each registration operation is less than a second deviation threshold; and the beam spot shape of the beam image satisfies a preset quality index.

[0086] The registration operation refers to the complete closed-loop control process executed by the control and processing system, which includes "acquiring beam images, calculating deviations, and driving the collimator displacement stage 312 for correction." At different stages such as initial registration and verification registration, the system can iteratively execute the registration operation multiple times, gradually converging to the target accuracy.

[0087] For example, in the initial registration stage, the deviation measured in the first registration operation is (+0.12mm, -0.10mm), the deviation measured in the second registration operation after correction is (+0.05mm, -0.04mm), and the deviation measured in the third registration operation is (+0.02mm, -0.01mm). Each of the above measurement-correction cycles constitutes one registration operation.

[0088] The preset number of operations is the minimum number of operations required before registration is completed and can be preset as needed to avoid accidental success on a single attempt and to ensure the stability and reliability of the registration results.

[0089] The preset deviation threshold is the maximum deviation value between the beam center and the target projection center, which is set in advance. The specific value can be set according to actual needs.

[0090] The method for determining whether the deviation of each registration operation is less than a preset deviation threshold includes: during the execution of a preset number of registration operations, after each registration operation, the current deviation (i.e., the distance between the beam center and the target projection center) is calculated, and this deviation is compared with the preset deviation threshold. If the deviation of each registration operation is less than the preset deviation threshold, then this condition is met.

[0091] Drift refers to the magnitude of the change in position of the beam center over time in a continuously acquired beam image sequence. Drift reflects the dynamic stability of the proton beam. The preset drift threshold refers to the maximum allowable drift magnitude, which is usually measured by the displacement of the beam center between adjacent frames (inter-frame jitter) or the standard deviation of the beam center in consecutive frames.

[0092] For continuously acquired beam images, the method for determining whether the drift of the beam image center relative to the projection center meets a preset drift threshold includes: continuously acquiring multiple frames of beam images at a high frame rate during any registration operation; calculating the offset of the beam center relative to the target projection center in each frame; determining the magnitude of the offset change over time (e.g., standard deviation, maximum inter-frame displacement); and comparing it with the preset drift threshold. If the offset is less than the preset drift threshold, the drift is considered to meet the requirement.

[0093] The maximum difference between the deviations of each registration operation (also known as repeatability deviation) refers to the maximum difference between the deviation values ​​measured in multiple registration operations. The second deviation threshold refers to the maximum allowable repeatability deviation value.

[0094] A method for determining whether the maximum difference between the deviations of each registration operation is less than a second deviation threshold can include: comparing the deviations measured in each registration operation within a preset number of operations, determining the maximum and minimum values, and calculating the difference. If this difference is less than the preset second deviation threshold, it indicates that the multiple registration results have good consistency and the repeatability requirement is met. For example, the deviations measured in three registration operations are 0.04mm, 0.05mm, and 0.06mm, respectively. The maximum difference between the deviations is 0.06 - 0.04 = 0.02mm. If the second deviation threshold is set to 0.03mm, then 0.02mm is less than 0.03mm, and the repeatability requirement is met.

[0095] The beam spot shape refers to the shape characteristics of the two-dimensional intensity distribution formed by the proton beam on the beam detector plane 32, which typically includes ellipticity, symmetry, tailing degree, and edge sharpness. Preset quality indicators refer to the quantitative judgment criteria set by the system for the beam spot shape, such as ellipticity less than 1.2, no significant tailing, and goodness of fit (R²) greater than 0.95.

[0096] The method for determining whether the beam spot shape of a conditional beam image meets the preset quality indicators includes: in any registration operation, performing beam spot shape analysis on the acquired beam image, including calculating ellipticity, analyzing tailing, and calculating the goodness of fit with a Gaussian distribution, and comparing each indicator with the preset quality indicators. For example, in the third registration operation, a two-dimensional Gaussian fit is performed on the acquired beam image. The fitting results are as follows: the half-width at half-maximum (WHM) in the X direction is 1.18 mm, the WHM in the Y direction is 1.10 mm, the ellipticity (major axis / minor axis) is 1.073, which is less than the preset 1.2; the fitting residual analysis shows no significant tailing, the energy proportion in the outer periphery (beyond the 3σ radius) is 2.8%, which is less than the preset 5%; the goodness of fit R² is 0.987, which is greater than the preset 0.95. All of the above indicators meet the preset quality indicators, and condition four is satisfied.

[0097] The technical solution of this application, through the above-mentioned multi-dimensional and multi-condition comprehensive judgment, can comprehensively evaluate the quality of the registration results and ensure that the system meets the stringent requirements of proton radiotherapy in terms of positional accuracy, dynamic stability, repeatability consistency and beam quality, thereby providing a reliable guarantee for subsequent precise irradiation.

[0098] According to embodiments of this application, it further includes: a treatment planning system for determining an irradiation scheme for the object to be irradiated based on a proton source model at the exit of the collimation component 31, a material distribution model of the object to be irradiated, and parameters of the collimation component 31.

[0099] The Treatment Planning System (TPS) is a dedicated system adapted to the hardware structure and execution process of a proton radiotherapy system, used to directly control all hardware except for the proton beam output. Specifically, the TPS may include the following modules: image import and processing module, material density mapping module, proton source model module, and dose calculation module.

[0100] The image import and processing module is used to import two-dimensional projection data and reconstruct CBCT images, or to import existing reference plan images. In this module, the target area, organs at risk, and regions of interest are delineated in the imaging system's coordinate system 2, and the current CBCT image can be registered with the reference plan image.

[0101] The material density mapping module is used by TPS to establish a mapping relationship between material and density based on the image's Henle unit (HU value). This mapping relationship can be obtained by scanning a standard phantom with known material density, and a piecewise linear fitting method is used to establish it according to the different types of biological tissue materials, thereby forming a three-dimensional physical model of the animal for subsequent Monte Carlo transport calculations.

[0102] The proton source model includes the following parameters: transverse beam size, angular divergence, position-direction correlation term, average energy, energy broadening, and the number of incident particles per unit of surveillance quantity.

[0103] In TPS, proton source modeling employs an equivalent source surface parameterization method, executed by the control and processing system. Specifically, this includes: fitting a two-dimensional Gaussian distribution to the spatial distribution of the proton beam on a selected phase space reference plane to determine the transverse beam size; using angular divergence and position-direction correlation terms at the phase space reference plane as transverse transport characteristic parameters, the average energy and energy broadening of the proton beam as energy characteristic parameters, and the number of incident particles per unit monitoring quantity as dose calibration parameters, combining these to form the proton source model. For example, Courant-Snyder theory can be used to describe beam propagation.

[0104] Specifically, when using a range shifter, the exit plane of the range shifter is determined as the phase space reference plane; when not using a range shifter, the exit plane of the collimation assembly 31 is determined as the phase space reference plane.

[0105] The angular divergence and position-direction correlation terms can be determined by controlling the focusing element in the collimation assembly 31 to focus the proton beam at at least two different intensities; using the beam detector 32, acquiring the transverse beam spot size of the proton beam downstream of the phase space reference plane at each focusing intensity; and fitting the beam optical transfer matrix based on the at least two focusing intensities and the corresponding transverse beam spot size to deduce the angular divergence and position-direction correlation terms at the phase space reference plane.

[0106] The average energy and energy broadening can be determined by controlling the output of the proton beam from the irradiation system 3 to irradiate the water phantom set on the carrier system 1; measuring the dose distribution at different depths in the water phantom to generate a percentage depth dose curve; determining the average energy based on the actual range in the percentage depth dose curve; and determining the energy broadening based on the full width at half maximum (FWHM) of the Bragg peak in the percentage depth dose curve.

[0107] The number of incident particles corresponding to a unit monitoring quantity can be determined in the following way: a reference detector is set on the carrier system 1 and placed in the path of the proton beam; the irradiation system 3 is controlled to output a proton beam with a preset monitoring quantity value; the response signal measured by the reference detector is acquired, and the total number of incident particles corresponding to this irradiation is calculated based on the response signal; the total number of incident particles is divided by the preset monitoring quantity value to obtain the number of incident particles corresponding to a unit monitoring quantity.

[0108] The dose calculation module is used for dose calculation in TPS, employing a GPU-based fast Monte Carlo algorithm. In the Monte Carlo simulation, the explicit modeling scope covers all actual transport objects behind the reference plane, including air gaps, collimators at various stages, and the phantom. After particles are generated by the proton source model, they pass through collimators at various stages and air, finally reaching the phantom for transport and energy deposition calculations. The output includes the three-dimensional dose distribution, LETd (linear energy transfer dose), and uncertainty parameters within the phantom.

[0109] According to embodiments of this application, the control and processing system may include an automatic calibration control module and an execution control module.

[0110] The automatic calibration control module is used to receive continuous frame images from the irradiation system 3, automatically extract the beam center, calculate its deviation from the target projection position, and automatically control the two-dimensional collimator displacement stage 312 to make corrections according to preset rules. At the same time, it completes drift analysis, over-limit judgment, alarm and prohibition of irradiation control.

[0111] The execution control module is used to translate the plan into hardware actions. Its output includes: the isocenter position of the plan, the irradiation direction, and the sequence of sub-steps; the aperture of the micro-collimator and the target position of the collimator displacement stage 312; the translation and rotation corrections for the animal displacement stage and the rotary displacement stage; and automatic calibration parameters such as the target projection position, deviation tolerance, number of consecutive acquisition frames, number of repeated measurements, stability judgment conditions, and abnormal beam stop conditions. The TPS directly controls each actuator based on these parameters to complete automatic calibration, positioning, verification, and step-by-step irradiation.

[0112] In the embodiments of this application, the TPS is no longer just planning and calculation software, but the control core of the entire execution chain. In addition to image processing and dose calculation, it is also responsible for issuing calibration targets, tolerances, number of repetitions, beam stopping conditions, and execution parameters for each irradiation sub-step, and, in conjunction with the control and processing system, controls the hardware to complete automatic calibration, positioning, and step-by-step irradiation.

[0113] The proton radiotherapy system described in this application is applicable to different proton beam emission conditions. The differences between different conditions are mainly handled by calling different source model parameters, while the imaging, automatic calibration, and execution links within the system remain unchanged, demonstrating good adaptability.

[0114] The following combination Figure 5 The working principle of the proton radiotherapy system according to the embodiments of this application will be explained.

[0115] The proton radiotherapy system of this application embodiment includes the following operations S510 to S580 when performing proton radiotherapy.

[0116] When operating S510, the imaging coordinate system is established or invoked using the control and processing system: the imaging coordinate system is established by calibrating the phantom using a BB sphere (spherical reference mark) and determining the imaging central axis. If the geometric relationship of imaging system 2 has not changed, the existing imaging coordinate system can be directly invoked without recalibrating for each experiment. The geometric relationship of imaging system 2 includes the spatial position and attitude constraints between the various core components constituting imaging system 2 (mainly X-ray source 21 and detector), as well as their transformation relationships with the system's center point and the animal coordinate system.

[0117] During the operation of S520, the positioning system is used for coarse positioning of the platform and proton beam: the laser positioning module is activated, and the platform body 4 is initially aligned using the geometric relationship with the preset markers in the treatment room and the level. The platform is leveled by using the lifting platform, and the position and orientation of the platform are adjusted by using the casters, so that the platform enters the preset alignment state and the proton beam path enters the preset calibration range.

[0118] In operation of S530, automatic beam axis calibration is performed using the control and processing system: First, the electrically operated lifting beam detector 32 is raised to the calibration position, placing it on the proton beam path behind the platform 11. Then, the BB sphere calibration phantom is placed on the platform 11, and the platform 11 is moved to align the center of the BB sphere with the imaging center axis, determining the target projection position of the imaging center axis on the plane of the beam detector 32 (i.e., the projection position of the BB sphere on the plane of the beam detector 32). Subsequently, the proton beam is emitted, preferably using a large-aperture collimator for initial calibration. The beam detector 32 continuously acquires beam images, automatically extracting the beam center position, beam spot size, and beam spot shape, and calculating the deviation between the beam image and the target projection position. The control and processing system automatically drives the two-dimensional collimator displacement stage 312 to perform translational correction based on the deviation, gradually bringing the beam center closer to the target projection position. The beam axis calibration is judged to be complete only when all of the following conditions are met: the beam center deviation in each cycle is less than the preset threshold; the beam drift in consecutive frames meets the stability requirements; the mutual deviation between repeated cycles meets the repeatability requirements; and the beam spot shape meets the preset quality requirements. If the above conditions are not met, automatic correction continues; if the number of corrections exceeds the upper limit or the deviation continues to exceed the limit, an alarm is triggered and the formal irradiation procedure is prohibited. After the initial calibration is completed, the micropore collimator used in actual treatment can be replaced, and a second verification is performed through the beam detector 32, with secondary fine-tuning if necessary. After the final calibration is passed, the beam detector 32 automatically descends to the irradiation field.

[0119] In operation of S540, the animal is loaded using the carrier system, and CBCT imaging is performed using the imaging system: the small animal is fixed on the carrier platform 11, and two-dimensional CBCT projection data is acquired. After imaging is completed, the small animal is controlled to return to the preset initial irradiation angle.

[0120] When operating the S550, image reconstruction and delineation are performed using the treatment planning system: 2D projection data is imported into the TPS to reconstruct CBCT images. In online planning mode, target areas and organs at risk can be delineated based on the current CBCT images, and treatment planning calculations can be performed.

[0121] When using the reference plan registration mode, the current CBCT image can be registered with the existing reference plan image to obtain the spatial deviation between the target area and the plan isocenter, thereby calculating the positioning correction amount.

[0122] When operating the S560, the treatment planning system is used for planning: the target center, prescription dose, field angle and field weight are set or called through TPS, and the three-dimensional dose distribution is obtained through Monte Carlo calculation.

[0123] During operation of S570, the control and processing system executes irradiation based on the three-dimensional dose distribution. The control and processing system outputs and distributes the following parameters based on the planned results: the planned isocenter position, collimator configuration parameters, translation and rotation corrections for the platform 11, and the position, angle, and execution sequence of each irradiation sub-step. Subsequently, the control and processing system sequentially controls the platform 11 and the rotary displacement stage to move to the corresponding positions and angles according to the predetermined sequence of each irradiation sub-step. When the current position meets the execution conditions, proton beam emission for the current sub-step is triggered. After the sub-step is completed, the beam is stopped, and the system switches to the next position and angle until all irradiation sub-steps are completed.

[0124] It should be noted that under the conditions of micro-aperture collimator and multi-field step-by-step irradiation, before formal irradiation or before the execution of subfields, the beam detector 32 is used to determine whether the current beam meets the tolerance requirements. This method of combining automatic calibration with implementation verification helps to maintain the consistency between the beam center and the planned irradiation axis, which is suitable for carrying out high-precision small animal proton radiotherapy experiments.

[0125] When operating the S580, the treatment planning system is used for recording and verification: imaging data, automatic beam calibration results, TPS parameters, collimator configuration, animal stage corrections, and execution records of each irradiation sub-step are all saved throughout the process. If necessary, real-time beam imaging sequences, beam center trajectories, and verification results can also be saved for traceability and quality control.

[0126] The embodiments of this application have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of this application. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. This application does not depart from its scope, and those skilled in the art can make various substitutions and modifications, all of which should fall within the scope of this application.

Claims

1. An image-guided proton radiotherapy system, comprising: A carrier system for carrying a calibration object is configured to adjust the position of the calibration object; An imaging system includes a radiation source and a radiation detector disposed opposite to each other on both sides of the object-carrying system in a first direction. The radiation source is used to emit radiation toward the calibration object, and the radiation detector is used to receive the radiation to form an object image of the calibration object. The irradiation system includes a collimation component and a beam detector disposed opposite to each other on both sides of the object carrier system in a second direction. The collimation component is used to receive protons emitted by an external proton source and output a proton beam, and can be adjusted in multiple degrees of freedom. The beam detector is used to receive the proton beam output by the collimation component to form a beam image of the proton beam. The second direction intersects with the first direction. The control and processing system is configured as follows: Based on the position information of the object image and the position information of the imaging center axis of the imaging system, the object carrying system is controlled to move so that the center of the object image is located on the imaging center axis; Repeat the following registration operation until a preset termination condition is met, so that the center of the projection of the calibration object onto the beam detector coincides with the center of the beam image, thereby achieving registration of the imaging central axis with the beam central axis of the proton beam: The collimation assembly is controlled to move based on the position information of the calibration object projected on the beam detector and the position information of the beam image on the beam detector.

2. The system according to claim 1, wherein, The collimation assembly includes: a collimator displacement stage, and a plurality of collimators with different apertures disposed on the collimator displacement stage; The control and processing system is also configured to: Collimators with different apertures are sequentially switched to the proton beam path, and the collimator displacement stage is controlled to move according to the proton beam image output by each collimator, so as to perform phased registration between the imaging center axis and the beam center axis.

3. The system of claim 2, wherein, The plurality of collimators with different apertures include at least a first collimator and a second collimator, wherein the aperture of the first collimator is larger than the aperture of the second collimator; The control and processing system is configured as follows: The first collimator is switched to the proton beam path, and the collimator displacement stage is controlled to move according to the proton beam image output by the first collimator, so as to perform initial registration between the imaging center axis and the beam center axis. After the initial registration is completed, the second collimator is switched to the proton beam path, and the collimator displacement stage is controlled to move according to the proton beam image output by the second collimator, so as to perform secondary registration between the imaging center axis and the beam center axis.

4. The system according to claim 1, wherein, The beam detector is configured to move in the vertical direction; The control and processing system is also configured to: With the imaging center axis and the beam center axis registered, the beam detector is controlled to move upward so that the beam detector is located on the proton beam path; After the imaging center axis and the beam center axis are aligned, when the object to be irradiated is being irradiated, the beam detector is controlled to move downward so that the beam detector leaves the proton beam path.

5. The system according to claim 2, wherein, The control and processing system is also configured to: The beam detector is controlled to acquire the proton beam output by the collimation component to form the beam image; Based on the deviation between the position information of the beam image and the position information of the calibration object projected on the beam detector, control commands are generated for the collimator displacement stage. The collimator displacement stage is moved according to the control command so that the center of the beam image coincides with the center of the projection.

6. The system according to claim 5, wherein, The preset termination condition includes at least one of the following: The registration operation is repeated a preset number of times; The deviation of each of the registration operations is less than a preset deviation threshold; In the continuously acquired beam images, the drift of the center of each beam image relative to the center of the projection satisfies a preset drift threshold. The maximum difference between the deviations of each of the registration operations is less than the second deviation threshold; The beam spot shape of the beam image meets the preset quality index.

7. The system according to claim 1, further comprising: A treatment planning system is used to determine an irradiation scheme for the object to be irradiated based on the proton source model at the beam exit of the collimation component, the material distribution model of the object to be irradiated, and the parameters of the collimation component. The proton source model includes the following parameters: transverse beam size, angular divergence, position-direction correlation term, average energy, energy broadening, and the number of incident particles per unit of surveillance quantity.

8. The system according to claim 7, wherein, The treatment planning system is also configured to: On the selected phase space reference plane, the spatial distribution of the proton beam is fitted with a two-dimensional Gaussian distribution to determine the transverse beam spot size of the proton beam. The angular divergence and position-direction correlation at the phase space reference plane are used as lateral transport characteristic parameters, the average energy and energy broadening of the proton beam are used as energy characteristic parameters, and the number of incident particles per unit monitoring quantity is used as dose calibration parameters. These are combined to form the proton source model.

9. The system according to claim 8, wherein the control and processing system is further configured to: When using a range shifter, the exit plane of the range shifter is defined as the phase space reference plane; Without using a range shifter, the beam exit plane of the collimation assembly is determined as the phase space reference plane.

10. The system according to any one of claims 1 to 9, further comprising: The platform body, used to support the cargo system, the imaging system, and the irradiation system, is constructed as a movable structure. A positioning system, installed on the platform body, is used to position the platform body according to preset marks in the treatment space so that the proton beam path is within the preset beam axis calibration range.

Images