Wide range air ionization chamber based on microporous fr4 and flash-rt monitoring method thereof

Abstract

This invention discloses a wide-range air ionization chamber based on microporous FR4 and its FLASH-RT monitoring method, which relates to the field of dose monitoring technology. The microporous FR4 substrate of this invention ensures the uniformity of electrode spacing, significantly expanding the effective area of ​​the detector. The microporous array, acting as a transport channel for electrons and ions, effectively shortens the ion collection distance and suppresses ion recombination effects at ultra-high dose rates. Two double-sided aluminum-plated Mylar conductive films are closely attached to both sides of the substrate, forming multiple parallel micro-ionization chamber units together with the microporous array, enabling spatial sampling detection and avoiding large-area signal saturation. Combining a signal partitioning method based on the difference in electron and ion drift velocities and a dose rate adaptive integration strategy, the detector can integrate the entire signal at conventional dose rates and integrate only the positive ion region at ultra-high FLASH dose rates, effectively solving the signal nonlinearity problem caused by ion recombination effects in traditional ionization chambers at ultra-high dose rates.

Description

Technical Field

[0001] This invention relates to the field of dose monitoring technology, and in particular to a wide-range air ionization chamber based on microporous FR4 and its FLASH-RT monitoring method. Background Technology

[0002] Radiotherapy is one of the main treatments for malignant tumors, and its quality is closely related to patient prognosis. In radiotherapy, dose monitoring is a crucial step in ensuring treatment accuracy and safety. Traditional dose monitoring equipment mainly consists of parallel-plate ionization chambers or finger-shaped ionization chambers, which work by measuring the ionization charge generated by radiation in the air to assess the dose.

[0003] In recent years, ultra-high dose rate radiotherapy (UHDR-RT), also known as flash radiotherapy, has become a research hotspot in the field of radiotherapy due to its unique biological effects. Flash radiotherapy has shown the potential to protect normal tissues while maintaining tumor control in various preclinical models. However, the dose rate of flash radiotherapy is as high as 40 Gy / s to several hundred Gy / s, far exceeding the dose rate range of 0.01-10 Gy / min of conventional radiotherapy.

[0004] Traditional dose detection devices have significant limitations under ultra-high dose rate conditions. Studies by Petersson et al. revealed that conventional ionization chambers under Flash conditions can lead to a 30%-40% dose underestimation due to ion recombination effects, severely impacting treatment quality assurance. Although various detectors are available on the market, such as CVD diamond detectors and scintillation fiber array dosimeters, they are either expensive or only applicable to specific dose rate ranges, failing to simultaneously meet the needs of both conventional and Flash radiotherapy.

[0005] The ionization chamber operates on the principle of electron-ion pairs generated by the interaction of ionizing radiation with gas molecules. When radiation passes through the filling gas, it causes primary ionization along its trajectory, forming electron-ion pairs. Under the influence of an applied electric field, negatively charged carriers (electrons) rapidly move towards the anode, while positive ions drift slowly towards the cathode. The electron migration velocity is approximately 10⁶–10⁷ cm / s, while the positive ion migration velocity is only 10³–10⁴ cm / s. This significant difference leads to the bicomponent nature of the signal formation. The electron signal manifests as a rapid pulse with a response time on the order of nanoseconds to microseconds; while the ion signal is a slow, continuous current with a response time on the order of milliseconds. At conventional dose rates, both signals can be collected completely; however, under ultra-high dose rate conditions, the slow drift of positive ions leads to charge accumulation and recombination effects, affecting measurement accuracy. Summary of the Invention

[0006] The purpose of this invention is to provide a wide-range air ionization chamber based on microporous FR4 and its FLASH-RT monitoring method, so as to improve the technical problem that existing detectors cannot be simultaneously compatible with conventional and ultra-high dose rate (FLASH) radiotherapy monitoring, especially the signal saturation and measurement inaccuracy caused by ion recombination effect at ultra-high dose rates.

[0007] To achieve the above-mentioned objectives, the embodiments of the present invention provide the following technical solutions:

[0008] A wide-range air ionization chamber based on microporous FR4 includes:

[0009] Microporous FR4 substrates are used to provide equally spaced electrode support structures and serve as transport channels for electrons and ions.

[0010] The first double-sided aluminum-coated Mylar conductive film and the second double-sided aluminum-coated Mylar conductive film have the same structure and are both used as positive and negative electrodes of the ionization chamber to collect ionized charges.

[0011] The detector housing provides mechanical support and a radiation entrance window;

[0012] The microporous FR4 substrate, the first double-sided aluminum-plated Mylar conductive film, and the second double-sided aluminum-plated Mylar conductive film are all placed inside the detector housing.

[0013] The surface of the microporous FR4 substrate is provided with a uniformly distributed array of through-holes; the first double-sided aluminum-plated Mylar conductive film and the second double-sided aluminum-plated Mylar conductive film are respectively attached to and cover the two sides of the microporous FR4 substrate, serving as the positive and negative electrodes of the ionization chamber, and together with the microporous FR4 substrate, they form a multi-parallel micro-ionization chamber unit array.

[0014] Both the first double-sided aluminum-coated Mylar conductive film and the second double-sided aluminum-coated Mylar conductive film are connected to an external measurement circuit via electrode leads.

[0015] In the aforementioned process, this invention solves the core technical challenges faced by existing detectors in unified dose monitoring for both FLASH and conventional radiotherapy through a combination structure of a microporous FR4 substrate and a first / second double-sided aluminized Mylar conductive film. Firstly, the microporous FR4 substrate, as a high-precision insulating support material, utilizes its through-hole array to provide an effective transport channel for electrons and ions. Furthermore, the substrate's thickness precisely controls the electrode spacing on both sides, increasing the effective detector area and overcoming the measurement errors caused by uneven time spacing in large-area applications of traditional parallel-plate ionization chambers, thus meeting the large-area requirements for online monitoring of accelerator output. Secondly, the double-sided aluminized Mylar conductive film, as an ultra-thin electrode (25 micrometers), is closely attached to both sides of the substrate, forming multiple parallel micro-ionization chamber units together with the microporous array. This significantly shortens the ion collection distance, effectively suppressing ion recombination effects and signal saturation problems at ultra-high dose rates, while maintaining an ionization chamber operating mode without electron multiplication, ensuring linear response of the detector across the entire dose rate range from 0.01 Gy / min to 250 Gy / s. Finally, the detector housing provides stable mechanical support and a radiation incident window, ensuring structural reliability in different application scenarios. The wide-range air ionization chamber can achieve full-spectrum dose monitoring from conventional radiotherapy to FLASH radiotherapy, combining the advantages of high precision, wide range, and large area, while also being low in cost and simple in structure, making it easy to promote and apply in clinical practice.

[0016] Furthermore, the microporous FR4 substrate uses an insulating support material with a thickness of 200 micrometers; the microporous FR4 substrate is divided into an internal perforated area and an outer non-perforated area; the outer non-perforated area is the PCB frame;

[0017] The micro-hole array located in the internal perforated area has a pore size of 100 micrometers, a spacing of 200 micrometers between adjacent microholes, and is uniformly distributed on the surface of the micro-hole FR4 substrate.

[0018] In the above process, this invention employs a 200-micrometer-thick microporous FR4 substrate, achieving micrometer-level precision in electrode spacing. This overcomes the technical bottleneck of traditional parallel-plate ionization chambers, where uniformity in spacing is difficult to guarantee due to increased area. The microporous FR4 substrate is divided into an internal perforated area and an external non-perforated area. The micropore array provides directional transport channels for electrons and ions, shortening the ion collection distance to suppress recombination effects at ultra-high dose rates. Simultaneously, the external solid frame (PCB frame) provides reliable fixed support for the ultra-thin Mylar film, ensuring tight electrode adhesion and structural stability. The micropore array in this invention achieves spatial sampling detection while maintaining sensitive volume, distributing large-area signals into multiple parallel micro-ionization chamber units, effectively avoiding signal saturation.

[0019] Furthermore, the electrode leads are electrically connected to the aluminum layer on the surface of the first double-sided aluminum-plated Mylar conductive film or the second double-sided aluminum-plated Mylar conductive film, for leading out the ionization signal to the external measurement circuit.

[0020] Furthermore, the thickness of the first double-sided aluminum-coated Mylar conductive film is 25 micrometers, and it is fixed to the PCB frame with epoxy adhesive; the first double-sided aluminum-coated Mylar conductive film and the second double-sided aluminum-coated Mylar conductive film are tightly attached to both sides of the microporous FR4 substrate with a tension of 20-25 N / m, and are connected to the external measurement circuit through corresponding electrode leads to form a micro-ionization chamber array structure as electrodes.

[0021] In the above process, the present invention ensures a reliable electrical connection between the electrode leads and the aluminum layer on the surface of the double-sided aluminum-plated Mylar conductive film, ensuring that the ionization signal is stably led out to the external measurement circuit, thus solving the problems of poor contact and noise interference during signal transmission. The ultra-thin Mylar film with a thickness of 25 micrometers is used as the substrate, and the 100-nanometer aluminum layer on its surface serves as the electrode, ensuring good conductivity while minimizing radiation attenuation, so that radiation reaches the sensitive volume without damage. In addition, the Mylar film is precisely fixed to the PCB frame with epoxy adhesive and tightly attached to both sides of the substrate with a suitable tension of 20-25 N / m. This ensures a tight fit between the film and the substrate, and that the electrode spacing in each micro-hole unit is strictly determined by the thickness (200 micrometers) of the micro-hole FR4 substrate. It also avoids excessive tension causing film damage or insufficient tension causing electrode loosening, thereby ensuring the uniformity of the electric field distribution and long-term working stability within the micro-hole array. This electrode fixing and connection scheme, combined with the high-precision structure of the microporous FR4 substrate, jointly constructs a mechanically reliable and electrically stable micro-ionization chamber array. This enables the detector to achieve a large area while ensuring the consistency of response of each microporous unit, effectively suppressing ion recombination and signal saturation, and ultimately achieving accurate dose monitoring across the entire dose rate range.

[0022] Furthermore, the detector housing is provided with ray windows on the incident and exit surfaces to ensure that the rays pass through without attenuation or reflection.

[0023] In the above process, the detector housing is provided with X-ray windows on the incident and exit surfaces to ensure that the X-rays pass through without attenuation or reflection. On the one hand, the incident window allows the radiation beam to enter the sensitive volume of the microporous FR4 substrate with minimal energy loss, ensuring the accuracy of the measurement results. On the other hand, the exit window avoids secondary scattering or reflection of the X-rays inside the detector, reducing background noise interference and improving the signal-to-noise ratio. At the same time, the X-ray window and the overall encapsulation structure of the detector housing together provide stable mechanical support and environmental protection for the internal microporous FR4 substrate and the first and second double-sided aluminum-plated Mylar conductive films, ensuring the reliability and repeatability of the detector in long-term use.

[0024] A FLASH-RT monitoring method for a wide-range air ionization chamber based on microporous FR4 includes:

[0025] A wide-range air ionization chamber was placed in the radiation beam irradiation area, with the ray direction perpendicular to the plane of the microporous FR4 substrate, to determine the dose rate characteristics of the radiation beam irradiation area.

[0026] Based on the dose rate characteristics of the radiation beam irradiation area, the operating saturation voltage of the wide-range air ionization chamber is set.

[0027] The raw electrical signal output from the wide-range air ionization chamber, which operates stably at the working saturation voltage, is acquired.

[0028] Based on the difference in drift velocities between electrons and positive ions in a wide-range air ionization chamber, a time threshold for the signal waveform is set to divide the original electrical signal into an electron response region and a positive ion drift region.

[0029] Based on the current dose rate, select the electronic response region and / or positive ion drift region and perform dose calculation to generate FLASH-RT dose monitoring results.

[0030] Furthermore, if the current dose rate is the conventional dose rate, the electrical signals of the electronic response region and the positive ion drift region are integrated as a whole, the corresponding integrated charge is calculated and converted, and FLASH-RT dose monitoring results are generated.

[0031] If the current dose rate is an ultra-high dose rate, the electrical signal in the positive ion drift region is integrated, the corresponding integrated charge is calculated and converted to generate FLASH-RT dose monitoring results.

[0032] Furthermore, if the current dose rate is an ultra-high dose rate, the formula for generating the FLASH-RT dose monitoring results is:

[0033] ;

[0034] in, This indicates the integration operation. This indicates the FLASH-RT dose monitoring results. Indicates the calibration factor. The electrical signal representing the positive ion drift region.

[0035] Furthermore, the working dose rate range of the wide-range air ionization chamber is [0.01 Gy / min, 250 Gy / s].

[0036] In the above process, this invention first determines the radiation field dose rate characteristics and sets the corresponding saturation operating voltage to ensure that the detector always operates in a stable state with the highest charge collection efficiency; by utilizing the inherent difference between electron and positive ion drift velocities to set a time threshold, the original signal is divided into an electron response region and a positive ion drift region, achieving physical separation of the contributions of the two types of charge carriers; based on this, different signal integration strategies are selected according to the current dose rate—integrating the entire signal at a conventional dose rate to fully utilize the signal-to-noise ratio advantage, and integrating only the positive ion region at ultra-high dose rates to avoid the electron signal saturation region, thereby achieving accurate measurement of the entire dose rate range from conventional radiotherapy to FLASH radiotherapy on the same detector, effectively solving the signal nonlinearity problem caused by ion recombination effect in traditional ionization chambers at ultra-high dose rates, while maintaining high-precision measurement capabilities at conventional dose rates. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a structural diagram of the wide-range air ionization chamber in Embodiment 1 of the present invention;

[0039] Figure 2 This is a flowchart of the method in Embodiment 1 of the present invention;

[0040] Figure 3(a) is a signal response curve of the wide-range air ionization chamber in Embodiment 3 of the present invention under a conventional accelerator test environment;

[0041] Figure 3(b) is a signal response curve of the wide-range air ionization chamber in the ultra-high dose rate environment in Embodiment 3 of the present invention;

[0042] Figure 4(a) is a linear curve of conventional dose for wide-range air ionization chamber in different accelerator settings in Embodiment 4 of the present invention;

[0043] Figure 4(b) is a linear fitting residual diagram of the wide-range air ionization chamber and the accelerator output dose in Embodiment 4 of the present invention;

[0044] Figure 4(c) is a linear relationship between the wide-range air ionization chamber and the conventional dose of PTW Farmer 30013 in Example 4 of the present invention;

[0045] Figure 4(d) is a linear fitting residual plot of the wide-range air ionization chamber and PTW Farmer 30013 in Embodiment 4 of the present invention;

[0046] Figure 5(a) is a dose linearity graph between the wide-range air ionization chamber and the preset dose in an ultra-high dose rate environment in Embodiment 5 of the present invention;

[0047] Figure 5(b) is a linear fitting residual diagram between the wide-range air ionization chamber and the preset dose in an ultra-high dose rate environment in Embodiment 5 of the present invention;

[0048] Figure 5(c) is a dose linearity graph of the wide-range air ionization chamber and the EBT3 film in Example 5 of the present invention;

[0049] Figure 5(d) is a linear fitting residual diagram between the wide-range air ionization chamber and the EBT3 thin film in Example 5 of the present invention;

[0050] The components include: 1. Microporous FR4 substrate; 2. First double-sided aluminum-plated Mylar conductive film; 3. Second double-sided aluminum-plated Mylar conductive film; 4. Detector housing; and 5. Electrode leads. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0052] Please see Figure 1 This embodiment provides a wide-range air ionization chamber based on microporous FR4, comprising:

[0053] Microporous FR4 substrate 1 is used to provide an equally spaced electrode support structure and serve as a transport channel for electrons and ions;

[0054] While traditional ultra-narrow pitch parallel-plate ionization chambers can achieve high-precision measurements, their area is limited (e.g., the collecting electrode radius is only 5mm). The fundamental reason is that under current technological conditions, it is difficult to guarantee micron-level spacing uniformity on large-area thin plates, and spacing errors directly lead to inaccurate dose measurements. Therefore, to address this problem, this invention introduces an FR4 microporous plate as the core supporting component. Utilizing its mature PCB manufacturing process, the thickness can be precisely controlled within tolerances, ensuring that the electrode spacing accuracy is entirely determined by the processing precision of the FR4 microporous plate, thus overcoming the contradiction between area and accuracy inherent in traditional structures. Based on this, a through-hole micro-aperture array is set up, providing directional transport channels for electrons and ions, shortening the collection distance to suppress recombination effects, and avoiding the process complexity introduced by adding a conductive layer to the substrate surface.

[0055] The first double-sided aluminum-coated Mylar conductive film 2 and the second double-sided aluminum-coated Mylar conductive film 3 have the same structure and are used as positive and negative electrodes of the ionization chamber to collect ionized charges.

[0056] Detector housing 4, used to provide mechanical support and X-ray entrance window;

[0057] The microporous FR4 substrate 1, the first double-sided aluminum-plated Mylar conductive film 2 and the second double-sided aluminum-plated Mylar conductive film 3 are all placed inside the detector housing 4.

[0058] Through precision CNC drilling, a uniformly distributed array of through-holes is formed on the surface of the microporous FR4 substrate 1; the first double-sided aluminum-plated Mylar conductive film 2 and the second double-sided aluminum-plated Mylar conductive film 3 are respectively attached to and cover the two sides of the microporous FR4 substrate 1, serving as the positive and negative electrodes of the ionization chamber, and together with the microporous FR4 substrate 1, they form a multi-parallel micro-ionization chamber unit array.

[0059] Both the first double-sided aluminum-coated Mylar conductive film 2 and the second double-sided aluminum-coated Mylar conductive film 3 are connected to an external measurement circuit via electrode leads 5.

[0060] The micro-hole FR4 substrate 1 is made of an insulating support material and has a thickness of 200 micrometers; the micro-hole FR4 substrate 1 is divided into an internal perforated area and an outer non-perforated area; the outer non-perforated area is a PCB frame;

[0061] The micro-hole array located in the internal perforated area has a pore size of 100 micrometers, a spacing of 200 micrometers between adjacent microholes, and is uniformly distributed on the surface of the micro-hole FR4 substrate 1. In practice, the thickness of the micro-hole FR4 substrate 1 ranges from 200±5 micrometers, the pore size of the micro-hole array ranges from 100±5 micrometers, and the spacing between adjacent microholes ranges from 200±5 micrometers.

[0062] In addition, after the micro-hole array processing is completed, the micro-hole FR4 substrate (1) needs to be surface treated to remove burrs from the hole walls and substrate surface to ensure hole diameter accuracy and surface smoothness; then it is cleaned so that the substrate body does not contain any conductive layer and is used only as an insulating support structure.

[0063] The electrode lead 5 forms an electrical connection with the aluminum layer on the surface of the first double-sided aluminum-plated Mylar conductive film 2 or the second double-sided aluminum-plated Mylar conductive film 3, and is used to lead the ionization signal to an external measurement circuit.

[0064] The first double-sided aluminum-coated Mylar conductive film 2 has a thickness of 25 micrometers and is fixed to the PCB frame with epoxy adhesive. The first double-sided aluminum-coated Mylar conductive film 2 and the second double-sided aluminum-coated Mylar conductive film 3 are tightly attached to both sides of the microporous FR4 substrate 1 with a tension of 20-25 N / m, and are connected to the external measurement circuit through the corresponding electrode leads 5 to form a micro-ionization chamber array structure as electrodes.

[0065] The detector housing 4 has ray windows on the incident and exit surfaces to ensure that the rays pass through without attenuation or reflection.

[0066] Compared to existing ultra-thin parallel plate ionization chambers (such as the detector described in "Development of an ultra-thin parallel plate ionization chamber for dosimetry in FLASH radiotherapy"), the wide-range air ionization chamber of this embodiment has the following advantages:

[0067] Firstly, regarding structural scalability, existing ultra-thin parallel plate ionization chambers (such as the detector described in "Development of anultra-thin parallel plate ionization chamber for dosimetry in FLASH radiotherapy," DOI: 10.1002 / mp.15668) are limited by manufacturing processes, with an electrode spacing of only 270 micrometers. However, the effective area cannot be increased significantly, with a collection electrode diameter of only 1 cm. This is mainly because traditional parallel plate structures struggle to maintain micrometer-level spacing uniformity under large-area conditions, and spacing errors directly affect dose measurement accuracy. This embodiment uses a microporous FR4 substrate as the core support element. Utilizing current mature PCB manufacturing processes, its thickness uniformity error can be controlled within 2%, allowing the electrode spacing accuracy to be entirely determined by the FR4 manufacturing precision. This overcomes the contradiction between area and accuracy, enabling the detector's effective area to be expanded to over 5 cm × 5 cm, and allowing for flexible adjustment based on application requirements—a large-area version is suitable for online monitoring of accelerator output, while a small-area version is suitable for quality control absolute dose measurement, realizing a transformation from a single-purpose to a multi-purpose application.

[0068] Secondly, in terms of structural design, existing ultrathin parallel plate ionization chambers still follow the basic structure of traditional ionization chambers. Their innovation mainly lies in their ability to measure FLASH dose, rather than in the innovation of the structure itself. In contrast, this embodiment innovatively endows the microporous FR4 substrate with dual functions: it serves as both an insulating support material to precisely control the electrode spacing and a transport channel for electrons and ions. This design is unprecedented in the field of dose monitoring. Compared with microporous detectors such as GEMs or THGEMs, this invention deliberately avoids setting a conductive layer on the hole wall and does not pursue electron avalanche amplification. Instead, it purely utilizes the microporous structure to achieve equidistant support and charge transport. The usage method and structural design are fundamentally different, and there is no precedent for using GEMs for absolute dose measurement.

[0069] Finally, regarding application performance, existing gas detectors generally suffer from signal saturation issues at ultra-high FLASH dose rates—the output curve bends downwards and the maximum output fails to reach the expected linear value. This invention effectively shortens the ion collection distance and suppresses ion recombination effects through a micropore array structure. Combined with a signal partitioning method based on the difference in electron and ion drift velocities and a dose rate adaptive integration strategy, it achieves precise linear response across the entire range from conventional dose rates (0.01 Gy / min) to FLASH dose rates (250 Gy / s). It also boasts advantages such as large area coverage, low cost, and simple structure, providing a practical dose monitoring solution for the clinical translation of FLASH radiotherapy.

[0070] like Figure 2As shown, a FLASH-RT (FLASH radiotherapy) monitoring method based on a wide-range air ionization chamber using microporous FR4 includes:

[0071] S1. Place the wide-range air ionization chamber in the radiation beam irradiation area, making the ray direction perpendicular to the plane of the microporous FR4 substrate 1, and determine the dose rate characteristics of the radiation beam irradiation area; the working dose rate range of the wide-range air ionization chamber is [0.01 Gy / min, 250 Gy / s].

[0072] S2. Set the working saturation voltage of the wide-range air ionization chamber according to the dose rate characteristics of the radiation beam irradiation area;

[0073] Specifically, by measuring the charge collection amount of the wide-range air ionization chamber at different operating voltages and plotting voltage-response curves (i.e., plateau characteristic curves), the saturation range of the wide-range air ionization chamber under specific dose rate conditions is determined. At conventional dose rates (e.g., 600 MU / min), the stable operating plateau region of THGEM-ADIC is approximately -350V to -700V; at ultra-high dose rates (e.g., 250 Gy / s), the plateau region shortens to -200V to -400V. Therefore, based on the dose rate characteristics of the actual radiation environment, the operating voltage is set to the midpoint of the corresponding plateau region (e.g., -500V for conventional dose rates and -300V for ultra-high dose rates) to ensure that the wide-range air ionization chamber operates in a charge collection saturation state, avoiding signal loss caused by ion recombination and preventing nonlinear responses caused by entering the gas amplification region.

[0074] S3. Acquire the raw electrical signal output from the wide-range air ionization chamber that is operating stably at the working saturation voltage;

[0075] S4. Based on the difference in drift velocity between electrons and positive ions in the wide-range air ionization chamber, a time threshold for the signal waveform is set to divide the original electrical signal into an electron response region and a positive ion drift region.

[0076] Specifically, based on the significant difference in drift velocities between electrons and positive ions in an electric field (electron velocity is approximately 10⁻⁶), 6 -10 7 cm / s, the velocity of positive ions is approximately 10³-10 4(The velocities of electrons and positive ions differ by approximately three orders of magnitude, at cm / s), the raw current signal waveform output from the wide-range air ionization chamber is acquired. At a conventional dose rate, the signal corresponding to each radiation pulse exhibits a two-component characteristic: a sharp pulse (electron response region) formed by rapid electron collection within the initial hundreds of nanoseconds to microseconds, followed by a trailing current (positive ion drift region) formed by the slow drift of positive ions within the subsequent few milliseconds. Based on the electrode spacing (200 micrometers) and electron drift velocity of the medium-wide-range air ionization chamber, the signal waveform time threshold required for complete electron collection can be calculated, for example, using the formula:

[0077] ;

[0078] Calculate the time threshold of the signal waveform .in, Indicates the electrode spacing of the wide-range air ionization chamber. This indicates the electron drift velocity.

[0079] In actual data processing, the waveform of the acquired raw electrical signal is analyzed in the time domain using CERN ROOT software to determine the position of the time threshold on the waveform: the signal integration region before the threshold corresponds to the electronic response region, and the signal integration region after the threshold corresponds to the positive ion drift region.

[0080] S5. Based on the current dose rate, select the electronic response region and / or the positive ion drift region and perform dose calculation to generate FLASH-RT dose monitoring results.

[0081] Specifically, when the wide-range air ionization chamber operates in a conventional accelerator testing environment, its radiation is output in pulses with long pulse intervals (typically on the order of milliseconds), much longer than the time required for complete collection of electrons and ions in the detector. Each radiation pulse generates a complete and independent signal waveform, and the detector can synchronously complete the collection of electrons and ions after each pulse ends. This phenomenon stems from the following physical mechanism: when the radiation passes through the microporous sensitive area of ​​the wide-range air ionization chamber, it interacts with air molecules to generate a large number of electron-ion pairs; under the influence of an applied electric field, the electrons move at approximately 10⁻⁶ ppm. 6 -10 7 They drift rapidly toward the positive electrode at a speed of cm / s, and are collected within hundreds of nanoseconds to microseconds to form a sharp electronic response region. The positive ions move at a speed of approximately 10³-10 4The positive ions slowly drift towards the negative electrode at a velocity of cm / s, and are collected within milliseconds, forming a trailing positive ion drift region. Because the pulse interval is sufficiently long, the positive ions have ample time to completely migrate out of the sensitive region before the next pulse arrives, preventing space charge accumulation. Therefore, the electrons and ions generated by each pulse can be completely collected by the electrodes, the detector operates in the saturation region, and the ion recombination effect is negligible. At this point, the signals from the electron response region and the positive ion drift region are integrated as a whole. The total charge obtained is proportional to the total number of ions generated during the initial ionization, i.e., proportional to the radiation dose. Therefore, if the current dose rate is a conventional dose rate, the electrical signals from the electron response region and the positive ion drift region are integrated as a whole, the corresponding integrated charge is calculated and converted, and the FLASH-RT dose monitoring result is generated.

[0082] When a wide-range air ionization chamber operates in an ultra-high dose rate environment, its radiation is output in the form of macropulses with extremely narrow pulse widths (nanosecond to microsecond levels). This results in an extremely high instantaneous dose rate, causing a massive number of electron-ion pairs to be generated in the detector's sensitive volume (air within the micropore) within a very short time. At this point, the signal waveform exhibits characteristics significantly different from those of conventional dose rates: electrons drift at very high speeds (approximately 10⁻⁶ ppm). 6 -10 7 The positive ion velocity is 10 cm / s, which can still be rapidly collected during a single macropulse to form a sharp electronic response region; however, the positive ion drift velocity is slow (approximately 10³-10 cm / s). 4 (cm / s) Positive ions can only move a very small distance during the pulse duration, failing to completely escape the sensitive region before the next pulse arrives, resulting in a "tailing" phenomenon where positive ions accumulate pulse by pulse. The core physical mechanism of this phenomenon lies in the space charge effect. A large number of positive ions that fail to escape in time accumulate in the sensitive region, forming a positive space charge cloud, distorting the local electric field distribution and producing two effects: first, weakening the electric field strength for subsequent pulse electron drift, leading to incomplete electron collection; second, increasing the probability of electron-ion recombination. This causes the signal in the electron response region to exhibit saturation and nonlinear characteristics, and direct integration over the electron region will introduce significant errors. However, despite the interference with electron collection, the total amount of positive ions produced is still proportional to the initial logarithm of ionization, and although the positive ions drift slowly, they will eventually be completely collected by the electrodes. By setting an appropriate signal waveform time threshold (a theoretical time threshold calculated based on the difference in electron and ion drift velocities), the fast electron components affected by space charge are filtered out, and the complete positive ion drift region signal is retained for integration. The resulting integrated charge accurately reflects the initial total ionization, thus characterizing the radiation dose. Therefore, if the current dose rate is an ultra-high dose rate, the electrical signal in the positive ion drift region is integrated, the corresponding integrated charge is calculated and converted, and the FLASH-RT dose monitoring result is generated. If the current dose rate is an ultra-high dose rate, the formula for generating the FLASH-RT dose monitoring result is:

[0083] ;

[0084] in, This indicates the integration operation. This indicates the FLASH-RT dose monitoring results. Indicates the calibration factor. The electrical signal representing the positive ion drift region.

[0085] In summary, the microporous FR4 substrate of this invention ensures the uniformity of electrode spacing, significantly expanding the effective area of ​​the detector. The microporous array, acting as a transport channel for electrons and ions, effectively shortens the ion collection distance and suppresses ion recombination effects at ultra-high dose rates. Two double-sided aluminum-plated Mylar conductive films are closely attached to both sides of the substrate, forming multiple parallel micro-ionization chamber units together with the microporous array, enabling spatial sampling detection and avoiding large-area signal saturation. Combining the signal partitioning method based on the difference in electron and ion drift velocities and the dose rate adaptive integration strategy, the detector can integrate the entire signal at conventional dose rates and integrate only the positive ion region at ultra-high FLASH dose rates, effectively solving the signal nonlinearity problem caused by ion recombination effects in traditional ionization chambers at ultra-high dose rates.

[0086] Example 2:

[0087] This embodiment is based on Embodiment 1. The specific process of constructing the wide-range air ionization chamber in this embodiment is as follows:

[0088] First, the first double-sided aluminum-coated Mylar conductive film 2 and the second double-sided aluminum-coated Mylar conductive film 3, each with a thickness of 25 micrometers, are fixed to the PCB frame (i.e., the non-perforated area around the microporous FR4 substrate) using epoxy adhesive, with the tension controlled within the range of 20-25 N / m to ensure that it is flat and taut. Then, the fixed first double-sided aluminum-coated Mylar conductive film 2 and the second double-sided aluminum-coated Mylar conductive film 3 are tightly attached to both sides of the microporous FR4 substrate 1 prepared in Example 1, and a special clamp is used to apply pressure to fix them, ensuring that the film and the substrate surface are tightly adhered, uniform, and free of air bubbles.

[0089] After fixing the first double-sided aluminum-coated Mylar conductive film 2 and the second double-sided aluminum-coated Mylar conductive film 3, the signal lead (electrode lead 5) is connected to the aluminum layer of the first double-sided aluminum-coated Mylar conductive film 2 or the second double-sided aluminum-coated Mylar conductive film 3 by conductive adhesive or miniature metal clips to form a reliable electrical connection for leading out the ionization signal to the external measurement circuit.

[0090] The assembled micro-aperture FR4-Mylar assembly was mounted on the designed aluminum bracket, and its position was adjusted so that the detector plane was perpendicular to the direction of the incident rays, ensuring that the rays passed through the micro-aperture array in a direction perpendicular to the substrate plane.

[0091] Finally, X-ray windows are set on the incident and exit surfaces of the detector housing 4, respectively. The window material is a thin film with extremely low X-ray attenuation, to ensure that the X-rays pass through the sensitive volume without attenuation or reflection.

[0092] In this embodiment, a microporous FR4 substrate 1 is used as an insulating support, and combined with two double-sided aluminum-coated Mylar films to form a micro-ionization chamber array structure. Each micropore on the microporous FR4 substrate 1, together with the first and second double-sided aluminum-coated Mylar conductive films 2 and 3 on both sides, constitutes an independent micro-ionization chamber. The aluminum layers of the first and second double-sided aluminum-coated Mylar conductive films 2 and 3 on both sides serve as electrodes to form a uniform electric field. Multiple micropore units are arranged in parallel to achieve spatial sampling and detection of incident radiation.

[0093] Example 3:

[0094] This embodiment is based on Embodiment 1. The plateau characteristic curve of a gas detector is an important indicator for evaluating the stability of the detector's performance, describing the count rate variation characteristics of the detector under different operating voltages. A complete plateau characteristic curve typically includes a low-voltage region (recombination region), a plateau region (operating region), and an amplification region (gain > 1).

[0095] When a wide-range air ionization chamber is in operation, selecting the appropriate operating voltage has a decisive impact on its performance and measurement accuracy. In this embodiment, a conventional accelerator testing environment and an ultra-high dose rate environment are selected as the operating environments for the wide-range air ionization. In this embodiment, the parameters for the conventional accelerator testing environment are as follows: in the Elekta accelerator (6MV, 600-1200MU / min) testing environment, compared with the standard PTW Farmer ionization chamber, the dose linearity is better than 97%, the repeatability is better than 1%, and the long-term stability drift is less than 2% within 3 months. The parameters for the Flash radiotherapy environment (ultra-high dose rate environment) are as follows: in the Flash radiotherapy prototype machine (6MV, 40-250Gy / s) testing environment.

[0096] As shown in Figure 3(a), this wide-range air ionization chamber has a stable operating platform of approximately 400V within the range of -350V to -700V. When the voltage drops below -350V, the detector begins to exhibit significant positron-ion recombination, leading to a decrease in signal amplitude. Therefore, in traditional accelerator dose measurement applications, the optimal operating voltage for the wide-range air ionization chamber is determined to be -450V, located in the center of the plateau region, providing the best signal stability and reproducibility.

[0097] As shown in Figure 3(b), under the same total dose output conditions, the stable plateau region of this wide-range air ionization chamber shrinks to between -200V and -400V, with a width of approximately 200V. This further verifies that the composite effect of this wide-range air ionization chamber is more pronounced under high dose rate conditions, correspondingly narrowing the operating voltage window. Considering the special requirements under ultra-high dose rate conditions, the Flash-RT operating voltage of this wide-range air ionization chamber was ultimately determined to be -300V, balancing signal stability and ionization efficiency. In Figures 3(a) and 3(b), charge-conts represents the charge reading, and Voltage represents the operating bias voltage.

[0098] In summary, at conventional dose rates, the ion pair density is low, and the internal electric field distribution of the wide-range air ionization chamber is uniform (consistent with the applied voltage). Avalanche amplification requires the global electric field to exceed the avalanche threshold of the gas (approximately 10⁻⁶). 6 The voltage required is V / m, thus necessitating a higher applied voltage. In Flash-RT, the dense cloud of space charge distorts the electric field distribution: positive ions near the cathode and electrons near the anode superimpose, forming a "localized field enhancement region" around the anode. Even at lower applied voltages, the combined electric field in this localized region can exceed the avalanche threshold, triggering weak avalanche multiplication (entering the finite-proportion region), manifesting as "early amplification." To prevent exacerbating this localized, non-uniform "early amplification," high applied voltages should be avoided. Higher voltages distort the localized electric field, forcing the ionization chamber into the finite-proportion region and impairing the linear dose response required for Flash-RT dosing measurements.

[0099] Example 4:

[0100] This embodiment is based on Embodiment 2. In the routine accelerator condition test, this embodiment uses the clinical gold standard PTW Farmer 30013 ionization chamber as the reference detector to compare the output linearity of PTW Farmer 30013 with that of THGEM-ADIC (wide-range air ionization chamber).

[0101] The tests were conducted in the unflattened filter (FFF) mode of the Elekta Axesse accelerator, with a dose rate of 1400 MU / min (0.233 Gy / s) and total output doses of 1 Gy, 10 Gy, 20 Gy, 40 Gy, 70 Gy, and 100 Gy.

[0102] As shown in Figure 4(a), within the dose range of 0~80Gy, the output of THGEM-ADIC increases linearly with the set dose, exhibiting good dose response characteristics. Further analysis using least squares linear fitting shows that THGEM-ADIC exhibits excellent linearity in response to conventional accelerator beam doses. As shown in Figure 4(b), the fitting residuals at each measurement point are controlled within 3%, fully meeting the accuracy requirements for linearity in clinical dose measurement.

[0103] The THGEM-ADIC was compared with a reference detector. As shown in Figure 4(c), under conventional accelerator conditions, the signal responses of the two detectors showed a highly consistent trend with dose changes, indicating that the THGEM-ADIC has dose measurement performance comparable to the reference detector. As shown in Figure 4(d), signal deviation analysis between the two detectors confirmed that the response of the THGEM-ADIC remained in good agreement with the reference detector across the entire measurement range. This result demonstrates that the THGEM-ADIC can reliably perform absolute dose measurement tasks in conventional radiotherapy settings.

[0104] In summary, under normal dose rate conditions, the real-time response characteristics of THGEM-ADIC to each radiation pulse remain constant—the amplitude of the single-pulse signal is proportional to the single-pulse dose, while the amplitude of the inherent noise remains stable. Therefore, the signal-to-noise ratio (SNR) of single-pulse measurements remains unchanged.

[0105] Example 5:

[0106] This embodiment is based on Example 2. The EBT3 thin-film dosimeter was selected as a reference.

[0107] As shown in Figure 5(a), the response relationship between the output signal and the preset dose of THGEM-ADIC (wide-range air ionization chamber) under an ultra-high dose rate of 250 Gy / s is plotted, indicating that the output of THGEM-ADIC shows a good linear growth trend with the increase of dose.

[0108] As shown in Figure 5(b), linear fitting analysis reveals that the output linearity of THGEM-ADIC in the FLASH environment remains above 99%, and the fitting residuals are controlled within a reasonable range. Although slightly lower than that under traditional dose rate conditions, it still exhibits excellent high dose rate adaptability.

[0109] The THGEM-ADIC and EBT3 thin-film dosimeters were compared, as shown in Figure 5(c), demonstrating their responses under ultra-high dose rate conditions. The EBT3 thin-film dosimeter, a commonly used reference dosimeter in FLASH radiotherapy, showed good consistency between its measurement results and the THGEM-ADIC output signal.

[0110] As shown in Figure 5(d), the response trends of THGEM-ADIC and the EBT3 thin-film dosimeter are in high agreement across the entire dose range. This result validates the reliability and accuracy of THGEM-ADIC in FLASH-RT (FLASH radiotherapy) applications.

[0111] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0112] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A wide range air ionization chamber based on microporous FR4, characterized in that, include: Microporous FR4 substrate (1) is used to provide an equally spaced electrode support structure and to serve as a transport channel for electrons and ions; The first double-sided aluminum-coated Mylar conductive film (2) and the second double-sided aluminum-coated Mylar conductive film (3) have the same structure and are used as positive and negative electrodes of the ionization chamber to collect ionized charges. The detector housing (4) provides mechanical support and a ray incident window; The microporous FR4 substrate (1), the first double-sided aluminum-plated Mylar conductive film (2) and the second double-sided aluminum-plated Mylar conductive film (3) are all placed inside the detector housing (4); The surface of the microporous FR4 substrate (1) is provided with a uniformly distributed array of through-holes; the first double-sided aluminum-plated Mylar conductive film (2) and the second double-sided aluminum-plated Mylar conductive film (3) are respectively attached to and covered on both sides of the microporous FR4 substrate (1) to serve as the positive and negative electrodes of the ionization chamber, and together with the microporous FR4 substrate (1) form a multi-parallel array of micro-ionization chamber units. Both the first double-sided aluminum-coated Mylar conductive film (2) and the second double-sided aluminum-coated Mylar conductive film (3) are connected to the external measurement circuit through electrode leads (5).

2. A wide range air ionization chamber based on microporous FR4 according to claim 1, characterized in that, The micro-hole FR4 substrate (1) is made of insulating support material and has a thickness of 200 micrometers; the micro-hole FR4 substrate (1) is divided into an internal perforated area and an outer non-perforated area; the outer non-perforated area is a PCB frame; The micro-hole array placed in the internal perforation area has a pore size of 100 micrometers, a spacing of 200 micrometers between adjacent micro-holes, and is uniformly distributed on the surface of the micro-hole FR4 substrate (1).

3. A wide range air ionization chamber based on microporous FR4 according to claim 1, characterized in that, The electrode lead (5) forms an electrical connection with the aluminum layer on the surface of the first double-sided aluminum-plated Mylar conductive film (2) or the second double-sided aluminum-plated Mylar conductive film (3), and is used to lead the ionization signal to the external measurement circuit.

4. A wide-range air ionization chamber based on microporous FR4 according to claim 2, characterized in that, The thickness of the first double-sided aluminum-plated Mylar conductive film (2) is 25 micrometers, and it is fixed on the PCB frame with epoxy adhesive. The first double-sided aluminum-plated Mylar conductive film (2) and the second double-sided aluminum-plated Mylar conductive film (3) are tightly attached to both sides of the microporous FR4 substrate (1) with a tension of 20-25 N / m, and are connected to the external measurement circuit through the corresponding electrode leads (5) to form a micro-ionization chamber array structure as electrodes.

5. A wide-range air ionization chamber based on microporous FR4 according to claim 1, characterized in that, The detector housing (4) has ray windows on the incident and exit surfaces to ensure that the rays pass through without attenuation or reflection.

6. A FLASH-RT monitoring method for a wide-range air ionization chamber based on microporous FR4, used to implement the wide-range air ionization chamber based on microporous FR4 as described in any one of claims 1 to 5, characterized in that, include: A wide-range air ionization chamber is placed in the radiation beam irradiation area, with the ray direction perpendicular to the plane of the microporous FR4 substrate (1), to determine the dose rate characteristics of the radiation beam irradiation area. Based on the dose rate characteristics of the radiation beam irradiation area, the operating saturation voltage of the wide-range air ionization chamber is set. The raw electrical signal output from the wide-range air ionization chamber, which operates stably at the working saturation voltage, is acquired. Based on the difference in drift velocities between electrons and positive ions in a wide-range air ionization chamber, a time threshold for the signal waveform is set to divide the original electrical signal into an electron response region and a positive ion drift region. Based on the current dose rate, select the electronic response region and / or positive ion drift region and perform dose calculation to generate FLASH-RT dose monitoring results.

7. A FLASH-RT monitoring method of a micro-porous FR4 based wide range air ionization chamber according to claim 6, characterized in that, If the current dose rate is the conventional dose rate, the electrical signals of the electronic response region and the positive ion drift region are integrated as a whole, the corresponding integrated charge is calculated and converted, and FLASH-RT dose monitoring results are generated. If the current dose rate is an ultra-high dose rate, the electrical signal in the positive ion drift region is integrated, the corresponding integrated charge is calculated and converted to generate FLASH-RT dose monitoring results.

8. A FLASH-RT monitoring method of a wide-range air ionization chamber based on microporous FR4 according to claim 7, characterized in that, If the current dose rate is an ultra-high dose rate, the formula for generating FLASH-RT dose monitoring results is: ； wherein, denotes an integration operation, denotes the FLASH-RT dose monitoring result, denotes a calibration factor, denotes the electrical signal of the positive ion drift region.

9. A FLASH-RT monitoring method for a wide-range air ionization chamber based on microporous FR4 according to claim 6, characterized in that, The working dose rate range of the wide-range air ionization chamber is [0.01 Gy / min, 250 Gy / s].

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