Non-interception type detector for measuring beam position and cross section of proton / heavy ion radiotherapy equipment

Abstract

The invention discloses a non-interception type detector for measuring the beam position and the cross section of proton / heavy ion radiotherapy equipment, and belongs to the technical field of nuclear medicine and electronics crossing. Secondary particles (electrons or ions) obtained after ionization reaction of high-energy protons / heavy ions and residual gas molecules are used as signals, the signals are amplified to reconstruct the original position and cross section distribution of a beam, and the detector is a completely non-interception type detector and can be used as long-term online measurement equipment. According to the invention, the structure of the detector is systematically designed and optimized aiming at the position and section measurement of an extremely weak beam in proton / heavy ion radiotherapy equipment, a test is carried out on an experimental platform, a clear signal image can be obtained, the structure is compact, the performance is good, the work is stable and reliable, and the cost is low. The method is of great significance to debugging, operation and maintenance of proton / heavy ion radiotherapy equipment.

Description

Technical Field

[0001] The present invention belongs to the cross - technical field of nuclear medicine and electronics, and more specifically, relates to a non - intercepting detector for measuring the beam position and cross - section of a proton / heavy - ion radiotherapy equipment. Background Art

[0002] Proton / heavy - ion radiotherapy is one of the most precise cancer treatment technologies at present. It utilizes the unique Bragg peak effect of proton / heavy - ion beams to concentrate the radiation dose in the tumor area, causing little harm to the surrounding healthy tissues, thus achieving the "fixed - point blasting" of tumor tissues. The proton / heavy - ion radiotherapy equipment delivers the high - energy particle beam generated by the accelerator to the patient's lesion through the beam transmission line, which is a very complex high - end medical device. To ensure the smooth commissioning and normal operation of the device, detectors are usually arranged at different positions on the beam transmission line to monitor the beam position and cross - section distribution. Currently, the most commonly used position and cross - section detectors on the beam transmission line of such devices are gas ionization chambers. When measuring, the beam will pass through multiple vacuum membranes and electrode membranes in sequence, which has a certain impact on the downstream transmission of the beam. Therefore, this type of detector generally needs to be inserted into the beam pipe through a driving structure only when measurement is required, and needs to be pulled out after measurement. It is not suitable as a long - term online measurement device and cannot perform multi - point simultaneous measurement.

[0003] Traditional non - intercepting detectors are based on the principle of electromagnetic induction. The electromagnetic signals carried by the charged particle beam are coupled out through the detector, and the relevant information of the beam is restored after algorithm analysis. According to clinical requirements, the beam intensity in proton / heavy - ion radiotherapy equipment is generally in the nano - ampere or pico - ampere level. At such a low beam intensity, the electromagnetic signal of the beam is extremely weak and cannot be effectively coupled. Therefore, non - intercepting measurement in proton / heavy - ion radiotherapy equipment is generally considered infeasible. Summary of the Invention

[0004] In view of the above - mentioned defects or improvement requirements of the prior art, the present invention provides a non - intercepting detector for measuring the beam position and cross - section of a proton / heavy - ion radiotherapy equipment, thereby solving the technical problem that the beam will pass through multiple vacuum membranes and electrode membranes in sequence during measurement in the existing detector, which has a certain impact on the downstream transmission of the beam.

[0005] To achieve the above object, according to one aspect of the present invention, there is provided a non - intercepting detector for measuring the beam position and cross - section of a proton / heavy - ion radiotherapy equipment. The detector is arranged on a vacuum chamber connected to the beam transmission pipe of the radiotherapy equipment. The detector includes: a guiding electric - field module, a signal amplification module, a fluorescent target, and an optical read - out system;

[0006] The guiding electric field module is used to make the secondary charged particles generated by the ionization reaction of protons / heavy ions in the beam transmission pipeline with the residual air molecules in the vacuum chamber move to the signal amplification module;

[0007] The signal amplification module is used to amplify the secondary charged particle signal and output it to the fluorescent target;

[0008] The fluorescent target is used to collect the amplified secondary charged particle signal and interact with it to form a luminescent image;

[0009] The optical readout system is arranged outside the vacuum chamber and includes a camera and a host computer. The camera is used to capture the luminescent image of the fluorescent target and transmit the luminescent image information to the host computer; the host computer is used to obtain and process the luminescent image information and finally display the position and cross-sectional distribution information of the original beam.

[0010] Further preferably, the detector uses the residual gas molecules in the beam transmission vacuum chamber as the medium. The high-energy proton / heavy ion beam interacts with the residual gas molecules to generate ionization reaction, generating secondary charged particles. The charged particles move to the signal amplifier (microchannel plate) under the action of the guiding electric field perpendicular to the beam propagation direction.

[0011] Preferably, the guiding electric field mechanism includes an upper plate, a lower plate and multiple groups of compensating plates; the multiple groups of compensating plates are arranged between the upper plate and the lower plate; the widths and spacings of the compensating plates in the multiple groups of compensating plates are equal, and the multiple groups of compensating plates are used to provide a uniform electric field during the movement of secondary charged particles.

[0012] Further preferably, to ensure the uniformity of the guiding electric field, multiple groups of compensating plates are arranged between the upper plate and the lower plate (or the left plate and the right plate) for voltage division. The widths and spacings of the compensating plates are equal and are powered by a series connection of equal-value resistors.

[0013] Further preferably, to better shield the influence of stray electric fields, the upper plate and the lower plate (or the left plate and the right plate) are set with a high voltage symmetric to the ground potential. When the potential of one side plate is 3 kV, the other side is -3 kV.

[0014] Further preferably, the present invention uses the positively charged ions in the secondary particles as signal particles for collection and amplification, which can avoid the need to additionally configure a magnetic field to constrain their orbits when using an electron collection scheme, and is more conducive to realizing a compact structure.

[0015] Further preferably, when the signal ions pass through the negative potential plate and reach the entrance of the microchannel plate under the action of the guiding electric field, due to the local opening of the plate and the potential difference between the plate and the entrance of the microchannel plate, local electric field distortion occurs. The electric field distortion can be reduced by adjusting the potential of the microchannel plate entrance to achieve high-fidelity measurement.

[0016] Preferably, the signal amplification module is composed of multiple stacked microchannel plates, and signal multiplication channels are arranged in an array on the microchannel plates. The microchannel plates are used to amplify the secondary particle signals, so as to achieve a high signal-to-noise ratio under extremely weak current intensities.

[0017] Preferably, the microchannel plate includes a microchannel plate entrance and a microchannel plate exit. When secondary charged particles bombard the microchannel plate entrance, an electron shower will be generated at the microchannel plate exit, thereby realizing signal amplification.

[0018] Preferably, the number of the microchannel plates is set according to the required signal amplification factor.

[0019] Preferably, the microchannel plates are located on the upper and lower sides or the left and right sides of the beam transmission direction, without any obstruction to the beam, so as to achieve completely non-interceptive measurement.

[0020] Further preferably, multiple sets of compensating plates are used for voltage division to ensure the uniformity of the guiding electric field. At the same time, the potential of the microchannel plate entrance electrode is optimized so that the transverse distribution of the secondary particles when reaching the entrance is as close as possible to the original beam distribution, thereby realizing high-precision measurement of the beam position and cross-section.

[0021] Preferably, the fluorescent target is arranged on the surface of the microchannel plate and integrated with the microchannel plate into an integral structure.

[0022] Further preferably, the exposure duration of the camera can be adjusted according to the on-site use effect, generally in the millisecond to second order of magnitude, and it can also be connected to the timing system of the proton / heavy ion radiotherapy equipment for trigger control.

[0023] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the following beneficial effects can be obtained:

[0024] 1. The non-interceptive detector proposed by the present invention for measuring the beam position and cross-section of a proton / heavy ion radiotherapy equipment uses the residual gas molecules in the beam transmission vacuum pipeline as the medium, takes the secondary particles after the ionization reaction of high-energy protons / heavy ions and residual gas molecules as signals, amplifies and processes them, and then reconstructs the original beam position and cross-section distribution. This detector is a completely non-interceptive detector and will not affect the downstream transmission of the beam, and can be used as a long-term online measurement device.

[0025] 2. The non-intercepting detector proposed by the present invention for measuring the beam position and cross-section of proton / heavy ion radiotherapy equipment can be arranged at different positions on the beam transmission line to simultaneously measure the beam state at multiple points.

[0026] 3. The non-intercepting detector proposed by the present invention for measuring the beam position and cross-section of proton / heavy ion radiotherapy equipment does not require a driving mechanism, and there is no risk of failure of the driving mechanism due to the on-site radiation environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic structural diagram of the non-intercepting detector proposed by the present invention for measuring the beam position and cross-section of proton / heavy ion radiotherapy equipment;

[0028] Figure 2 are the internal and external physical diagrams of the non-intercepting detector in the embodiment of the present invention;

[0029] Figure 3 is the electrical structure diagram of the non-intercepting detector in the embodiment of the present invention;

[0030] Figure 4 is the electric field distribution diagram inside the non-intercepting detector in the embodiment of the present invention;

[0031] Figure 5 are the beam images and processing results measured by the non-intercepting detector in the embodiment of the present invention on the experimental platform. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] As Figure 1 and Figure 2 shown, the present invention proposes a non-intercepting detector for measuring the beam position and cross-section of proton / heavy ion radiotherapy equipment. First, a special vacuum chamber is designed at the position where the detector needs to be arranged, and the vacuum chamber is connected to the beam transmission pipeline through a flange. A three-dimensional adjustment base is designed at the bottom of the vacuum chamber, and the detector body can be inserted from the upper side, left side or right side of the vacuum chamber (relative to the beam advancing direction). The detector body includes a guiding electric field module, a signal amplification module, a fluorescent target and an optical readout system.

[0034] As Figure 3As shown, the guiding electric field module is composed of an upper electrode plate, a lower electrode plate, and 7 sets of compensating electrode plates. In the positive charge ion collection mode, the potentials of the upper and lower electrode plates are set to positive and negative potentials symmetric with respect to the ground potential. Secondary charged particles move to the side of the negative potential electrode plate under the action of the guiding electric field and are collected by the signal amplification module (MCP, microchannel plate). The compensating electrode plates are powered in series through voltage-dividing resistors to provide a uniform electric field during the movement of ions. The same set of compensating electrode plates on the opposite side are connected by copper bars, and both the compensating electrode plates and the copper bars are installed in the grooves of the insulating backplane.

[0035] As a preferred embodiment of the present invention, the material of the compensating electrode plate is 316 stainless steel, and the material of the insulating backplane is G10 resin.

[0036] Furthermore, the entire detector needs to provide 5 independent high-voltage power supply interfaces to apply high-voltage potentials to the upper electrode plate, the lower electrode plate, the microchannel plate inlet, the microchannel plate outlet, and the fluorescent target respectively.

[0037] Furthermore, the distribution of the guiding electric field in the detector has a significant impact on the movement trajectory of secondary charged particles and is also the core factor affecting the measurement accuracy of the detector. As Figure 4 shown, for the positive charge ion collection mode, the signal amplification module is located on the side of the negative potential electrode plate. Due to the local opening of the electrode plate and the potential difference between the electrode plate and the entrance of the signal amplification module, local electric field distortion occurs. The electric field distortion can be reduced by adjusting the potential of the signal amplification module entrance, that is, having a more uniform electric field equipotential line, so that the position where the secondary charged particles reach the entrance of the signal amplification module is as close as possible to the position of its initial ionization, thereby achieving high-fidelity measurement.

[0038] Specifically, the signal amplification module uses a microchannel plate, which is integrated with an array of signal multiplication channels. When secondary charged particles bombard the channel entrance, an electron shower will be generated at the exit to achieve signal amplification. In order to obtain a high signal gain, a double-layer cascade is adopted, and the gain intensity can reach 10 7 orders of magnitude.

[0039] Furthermore, in the present invention, the fluorescent target and the double-layer microchannel plate are integrated into one body, and insulation is completed using ceramic washers. The fluorescent target uses a special target material to emit fluorescence after receiving electron bombardment, thereby obtaining the profile information of the electron reaction.

[0040] Specifically, the surface of the fluorescent target is covered with two layers of materials: one layer close to the exit electrode of the signal amplification module is an absorption layer for absorbing bombarding electrons; the other layer is a deposition layer for avoiding the fluorescence reflection of the fluorescent target material and improving the luminous efficiency.

[0041] For further explanation, the optical readout system consists of a camera and a host computer outside the vacuum chamber. A glass observation window needs to be welded on the vacuum chamber for image acquisition. A fixed-focus lens is selected according to the distance between the fluorescent target and the camera to ensure a good focusing effect. The resolution of the optical readout system is jointly determined by the lens field of view and the camera pixels, while the detector resolution is jointly determined by the optical readout system resolution and the single-channel aperture of the microchannel plate. In the example of the present invention, the single-channel aperture of the microchannel plate is 25 μm. Considering the arrangement gap between channels and the collection rate of the microchannel plate for secondary charged particles, the resolution of the microchannel plate is about three times the single-channel aperture, that is, 75 μm; the resolution of the optical readout system is 58 μm, and the detector resolution is about 95 μm.

[0042] The detector in the example of the present invention was tested on a proton beam experimental platform. The test conditions are compared with the performance parameters of proton radiotherapy equipment in the following table. It can be found that although the beam energy on the experimental platform is much lower than that of proton radiotherapy equipment, considering the beam current intensity and working pressure comprehensively, the initial ionization pairs at the lowest gain operating point are close for both, which indicates that the test results on the experimental platform can accurately reflect the working performance of proton radiotherapy equipment. The measurement results under extreme working conditions on the experimental platform are as Figure 5 shown. It can be found that the detector in the example of the present invention can still obtain clear images and be effectively processed under extreme working conditions. The measured beam position is 0.18 mm, and the beam root mean square size is 2.54 mm.

[0043] Parameter Experimental platform Radiotherapy equipment Beam energy 1.56 MeV 70 - 240 MeV Beam current intensity 5 nA - 1.1 mA 0.4 nA - 5 nA Working pressure 2.5E - 5 Pa 1.0E - 4 Pa Initial ionization pairs at the lowest gain operating point ~1000 ion - electron pairs ~1000 ion - electron pairs

[0044] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A non-interceptive detector for beam position and cross-section measurement of a proton / heavy ion radiotherapy equipment, the detector is arranged on a vacuum chamber connected to a beam transmission pipeline of the radiotherapy equipment, and is characterized in that, The detector includes: a guiding electric field module, a signal amplification module, a fluorescent target, and an optical readout system; The guiding electric field module is used to move the secondary charged particles generated by the ionization reaction of protons / heavy ions in the beam transmission pipeline with the residual air molecules in the vacuum chamber to the signal amplification module; The signal amplification module is used to amplify the secondary charged particle signal and output it to the fluorescent target; The fluorescent target is used to collect the amplified secondary charged particle signal and interact with it to form a luminescent image; the position and cross-sectional distribution information of the original beam is obtained by capturing and processing the luminescent image.

2. The non-interceptive detector for beam position and cross-section measurement of a proton / heavy ion radiotherapy equipment according to claim 1, characterized in that The guiding electric field mechanism includes an upper plate, a lower plate, and multiple sets of compensating plates; the multiple sets of compensating plates are arranged between the upper plate and the lower plate; the widths and spacings of the compensating plates in each set of compensating plates are equal, and the multiple sets of compensating plates are used to provide a uniform electric field during the movement of secondary charged particles.

3. The non-interceptive detector for beam position and cross-section measurement of a proton / heavy ion radiotherapy equipment according to claim 1, characterized in that, The signal amplification module is composed of multiple stacked microchannel plates.

4. The non-intercepting detector for beam position and cross-section measurement of a proton / heavy ion radiotherapy equipment according to claim 3, wherein The microchannel plate includes a microchannel plate inlet and a microchannel plate outlet. When secondary charged particles bombard the microchannel plate inlet, an electron shower will be generated at the microchannel plate outlet, thereby realizing signal amplification.

5. The non-intercepting detector for beam position and cross-section measurement of a proton / heavy ion radiotherapy equipment according to claim 3, characterized in that, The microchannel plate is located on the upper and lower sides or the left and right sides in the beam transmission direction.

6. The non-intercepting detector for beam position and cross-section measurement of a proton / heavy ion radiotherapy equipment according to claim 5, characterized in that, The fluorescent target is arranged on the surface of the microchannel plate and integrated with the microchannel plate into an integrated structure.

7. A non-interceptive detector for beam position and cross-section measurement of a proton / heavy ion radiotherapy equipment according to any one of claims 1-6, characterized in that, It further includes an optical readout system. The optical readout system is arranged outside the vacuum chamber and includes a camera and a host computer. The camera is used to capture the luminescent image of the fluorescent target and transmit the luminescent image information to the host computer; the host computer is used to obtain and process the luminescent image information and finally display the position and cross-sectional distribution information of the original beam.

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