Method and device for calibrating ionization chamber type beta applicator monitor

Abstract

The invention relates to a calibration method and device for an ionization chamber type beta applicator monitor. A balance cover is arranged on an ionization chamber main body in the beta applicator monitor; during calibration of a 90Sr-90Y beta standard radiation field, the ionization chamber main body is not provided with the balance cover; when a 60Co gamma standard radiation field is calibrated, a balance cover is mounted on the ionization chamber main body, a beam axis of a ray is aligned with the center of the ionization chamber main body, and the thickness of the balance cover is not smaller than the maximum penetration distance of the ray in a material corresponding to the balance cover; alternately applying positive and negative polarity high voltage to the ionization chamber main body, ionizing working gas in the ionization chamber main body by rays to generate ionization current, and measuring the ionization current through an electrometer; based on the ionization current, a calibration factor is obtained. According to the ionization chamber, the technical effect that the ionization chamber main body accurately monitors the high-dose-rate beta rays emitted by the beta applicator is achieved.

Description

Technical Field

[0001] This invention relates to the field of ionization chamber calibration technology, and in particular to a calibration method and apparatus for an ionization chamber type β patch monitor. Background Technology

[0002] Beta rays are a type of weak penetrating radiation, widely present in various fields such as nuclear industry, radiation medicine, and the radioactive isotope industry. Beta nuclide applicators are surface sources with different shapes and areas, sealed with beta radioactive nuclides of a certain activity and energy, used as radiation sources for topical therapy; they are simply called beta applicators. Clinically, beta radioactive nuclides used to treat skin diseases mainly include... 32 P, 90 Sr- 90 Y, 32 The half-life of P is 14.26 days, and the maximum energy of β rays is 1.7 MeV. 90 The half-life of Sr is 28.8 years. 90 The half-life of gamma rays is 64 hours, and the maximum energy of beta rays is 2.2 MeV. To ensure treatment effectiveness and prevent acute radiation damage to the patient's skin, it is essential to accurately measure the surface absorbed dose rate of the beta patch to correctly estimate the skin dose received by the patient. Therefore, a beta patch monitor is required to accurately monitor the surface absorbed dose rate of the beta patch.

[0003] An extrapolation ionization chamber is a flat-plate ionization chamber with variable electrode spacing. In principle, it is the optimal device for measuring the surface absorbed dose rate of beta patch applicators, and also the absolute measurement device, thus forming an ionization chamber-type beta patch monitor. However, the maximum absorbed dose rate provided by common beta standard radiation fields does not exceed 400 mGy / h, while the surface absorbed dose rate of beta patches used in hospitals is generally on the order of 10 Gy / h. Neither domestic nor international beta standard radiation fields can provide such a high absorbed dose rate, therefore, the high dose rate measurement points required for calibrating the ionization chamber cannot be covered.

[0004] In related technologies, the surface absorbed dose rate of medical beta patch is generally on the order of 10 Gy / h in actual use, while the highest absorbed dose rate provided by the beta standard radiation field does not exceed 400 mGy / h.

[0005] The above problems urgently need to be addressed. Summary of the Invention

[0006] This invention discloses a calibration method and apparatus for an ionization chamber type β-adhesive monitor, aiming to solve the technical problems existing in the prior art.

[0007] The present invention adopts the following technical solution: On one hand, the present invention provides a calibration method for an ionization chamber type β-adhesive patch monitor, comprising: setting a balance cover on the ionization chamber body within the β-adhesive patch monitor, wherein the balance cover is made of polymethyl methacrylate or polystyrene; 90 Sr- 90 During Yβ standard radiation field calibration, no balance cover is installed on the main body of the ionization chamber; 60 During calibration of the Coγ standard radiation field, a balancing cover is installed on the ionization chamber body to provide secondary electron balancing conditions. The ionization chamber body is placed on the beam axis of the radiation beam, and the balancing cover is located on the side of the ionization chamber body facing the radiation beam. The beam axis of the radiation beam is aligned with the center of the ionization chamber body. The thickness of the balancing cover is not less than the maximum penetration distance of secondary electrons in the material of the corresponding balancing cover. Alternating positive and negative high voltages are applied to the ionization chamber body, and the radiation beam ionizes the working gas inside the ionization chamber body, generating an ionization current. This ionization current is measured by an electrometer. Based on this ionization current, a calibration factor is obtained.

[0008] Optionally, the thickness of the balancing cover is not less than the maximum penetration distance of the secondary electrons in the material of the corresponding balancing cover. The method for obtaining the maximum penetration distance includes: obtaining the photon energy corresponding to the ray; calculating the maximum energy of the secondary electron based on the photon energy; and calculating the maximum penetration distance of the secondary electron based on the maximum energy using interpolation.

[0009] Optionally, based on the photon energy, the maximum energy of the secondary electron is calculated as follows: in, The maximum energy of the secondary electron. This represents the photon energy corresponding to high dose rate gamma rays.

[0010] Optionally, based on the maximum energy, the maximum penetration distance of the secondary electron is calculated using interpolation, as follows: in, E represents the maximum penetration distance, and E represents the maximum energy of the secondary electron. The energy in the table of approximate range data for continuously slowed-down materials corresponding to the balance cap that is closest to E and less than E; The energy in the table of approximate range data for continuously slowed-down materials corresponding to the balance cap that is closest to E and greater than E; for Corresponding range; for The corresponding range.

[0011] Optionally, the alternating application of positive and negative high voltages to the ionization chamber body, wherein the radiation ionizes the working gas within the ionization chamber body to generate an ionization current, and the ionization current is measured by an electrometer, includes: alternatingly applying positive and negative high voltages to the high-voltage electrode of the ionization chamber body, and acquiring the positive and negative high-voltage currents based on the electrometer, wherein the positive high-voltage current... The negative high-voltage current is used to indicate the current within the ionization chamber body measured under conditions of applied positive high voltage. Used to indicate the current within the ionization chamber body measured under conditions of applied negative high voltage; ionization current. The calculation is as follows: in, It is the ionization current. It is a positive high voltage current. It is a negative high voltage current.

[0012] Optionally, obtaining the calibration factor based on the ionization current includes: obtaining the conventional true value of the absorbed dose rate corresponding to the standard radiation field; determining the ambient atmospheric pressure and ambient temperature under the measurement environment conditions; determining the corrected ionization current based on the ambient atmospheric pressure, ambient temperature, and ionization current; and determining the calibration factor based on the ratio of the conventional true value of the absorbed dose rate corresponding to the standard radiation field and the corrected ionization current.

[0013] Optionally, determining the calibration factor based on the ratio of the conventional true value of the absorbed dose rate corresponding to the standard radiation field and the corrected ionization current includes: the calibration factor is calculated as follows: Wherein, N is the calibration factor, which is the true value of the absorbed dose rate / the corrected ionization current; This is the conventional true value of the absorbed dose rate corresponding to the standard radiation field; It is the ionization current; Standard atmospheric pressure; Atmospheric pressure; It is 293.15K; The ambient temperature.

[0014] According to another aspect of the present invention, a calibration device for an ionization chamber type β-adhesive patch monitor is also provided, comprising: a balance cover, detachably connected to the ionization chamber body within the β-adhesive patch monitor and located on the side of the ionization chamber body facing γ-ray emission; an electrometer connected to the ionization chamber body, the electrometer being used to measure the ionization current generated within the ionization chamber body; the balance cover is made of polymethyl methacrylate or polystyrene.

[0015] Optionally, the balance cover is in the shape of a cover body, including a circular flat plate and an annular side plate. The annular side plate is disposed on the outer periphery of the circular flat plate, and the height of the annular side plate is greater than the thickness of the circular flat plate. Multiple vent holes are provided on the annular side plate.

[0016] Optionally, the thickness of the circular plate is not less than the maximum penetration distance of the secondary electrons corresponding to the ray.

[0017] The technical solution adopted in this invention can achieve at least one of the following beneficial effects: In this embodiment of the invention, a balancing cover is provided on the ionization chamber body within the β-applier monitor, wherein the balancing cover is made of polymethyl methacrylate or polystyrene. 90 Sr- 90 During Yβ standard radiation field calibration, no balance cover is installed on the main body of the ionization chamber; 60 During calibration using the Coγ standard radiation field, a balance cover is installed on the ionization chamber to provide secondary electron balance conditions. The ionization chamber is placed on the beam axis of the γ-rays, with the balance cover located on the side of the ionization chamber facing the γ-ray emission. The beam axis of the γ-rays is aligned with the center of the ionization chamber. The thickness of the balance cover is not less than the maximum penetration distance of secondary electrons of the γ-rays in the corresponding material of the balance cover. Alternating positive and negative high voltages are applied to the ionization chamber, causing the γ-rays to ionize the working gas inside the chamber, generating an ionization current. This ionization current is measured using an electrometer. Based on this ionization current, a calibration factor is obtained. This method effectively solves the technical problem that the surface absorbed dose rate of medical β-adhesive patches is generally on the order of 10 Gy / h in practical use, while the highest absorbed dose rate provided by the β standard radiation field does not exceed 400 mGy / h, which cannot cover the high dose rate measurement points required for ionization chamber calibration. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, forming part of the present invention. The illustrative embodiments of the present invention and their descriptions explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings: Figure 1 This is a flowchart of a calibration method for an ionization chamber type β-adhesive monitor according to Embodiment 1 of the present invention; Figure 2 This is a calibration flowchart of dose rate segmentation in the calibration method of an ionization chamber type β patch monitor in Embodiment 1 of the present invention; Figure 3 This is a diagram showing the position of the balance cover of the calibration device for the ionization chamber type β patch monitor in Embodiment 2 of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. In the description of this invention, it should be noted that the term "or" is generally used to include the meaning of "and / or," unless otherwise expressly indicated.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or a magnetic connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Furthermore, in the description of this application, the terms "first," "second," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance. In the description of this invention, "a plurality of" means at least two, such as two, three, or more, unless otherwise explicitly specified.

[0021] Obviously, the described embodiments are only some, not all, of the embodiments of the present 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.

[0022] 90 Sr- 90 The absorbed dose rate range provided by the Yβ standard radiation field is limited. To calibrate the ionization chamber body under high dose rate (high dose rate gamma rays) conditions, [the following method is used]. 60 The relative inherent error of the ionization chamber body at various calibration points within a high measurement range was measured using a Co γ-ray standard radiation field. To ensure the ionization chamber body reaches secondary electron equilibrium with the measured γ-rays, a sufficiently thick layer of tissue-equivalent material needs to be added to the entrance window of the ionization chamber body. Considering the difference in response of the ionization chamber body to the two types of radiation, the ionization chamber body needs to be... 60 The response to Co γ radiation is normalized to the response to 90 Sr- 90 The response to standard β radiation is converted using the same dose rate point of the ionization chamber body in both radiation fields as the common point of convergence.

[0023] First, to facilitate understanding of the embodiments of the present invention, some terms or nouns involved in the present invention will be explained below: A beta patch is a surface source with different shapes and areas, which is made by sealing a beta radionuclide with a certain activity and energy in a certain way, and then using it as a radiation source for patch therapy.

[0024] Surface absorbed dose rate is the amount of ionizing radiation energy absorbed per unit mass of material per unit time (e.g., per second, per minute, or per hour) at the surface of an irradiated material (or within a thin layer of the surface closest to the radiation source).

[0025] To address the problems existing in related technologies, this application provides a calibration method and apparatus for an ionization chamber type β-adhesive patch monitor.

[0026] Example 1 This embodiment provides a calibration method for an ionization chamber type β-adhesive patch monitor, such as... Figure 1 As shown, Figure 1 This is a flowchart of a calibration method for an ionization chamber type β-adhesive patch monitor according to Embodiment 1 of the present invention. The method includes: Step S102: A balance cover is installed on the ionization chamber body inside the β-apply monitor, wherein the balance cover is made of polymethyl methacrylate or polystyrene. Optional, such as Figure 2 As shown, Figure 2 This is a calibration flowchart of dose rate segmentation in the calibration method of an ionization chamber type β patch monitor according to Embodiment 1 of the present invention. The β patch's radiation is segmented according to dose rate range, dividing the entire dose rate range into two segments: a low range and a high range. Within the low range, the ionization chamber type β patch monitor is placed in a β-ray absorbed dose standard device. 90 Sr- 90 Calibration was performed in the gamma radiation field (low dose rate range). In the high dose rate range, the ionization chamber type beta patch monitor was placed... 60 The Co γ standard radiation field (high range dose rate range) was calibrated.

[0027] Specifically, the ionization chamber can measure the entire dose rate range from 10 mGy / h to 20 Gy / h, with the lower range being... 90 Sr- 90 The calibration point range that the Yβ standard radiation field can encompass is determined by the maximum absorbed dose rate of the ionization chamber type β patch monitor, which is approximately 300 mGy / h. Therefore, the low range is set to 10 mGy / h to 300 mGy / h, and the remaining dose rate range of 0.3 Gy / h to 20 Gy / h constitutes the high range. 60 Co γ standard radiation field provided.

[0028] Optionally, the balancing cover should be made of a tissue-equivalent material, such as polymethyl methacrylate (PMMA) or polystyrene. Two vents are provided on the side of the balancing cover to prevent damage to the entrance window membrane in front of the ionization chamber body due to air pressure changes during installation. The balancing cover not only provides secondary electronic equilibration conditions during calibration but also protects the entrance window membrane. The main body of the balancing cover is a circular flat plate, with two 2 mm diameter vents machined on its side (annular side plate) for balancing internal air pressure. The balancing cover assembly is tightly connected to the top of the ionization chamber body and has a detachable design.

[0029] In some preferred embodiments, the thickness of the balancing cap is not less than the maximum penetration distance of the secondary electrons in the material of the corresponding balancing cap. The method for obtaining the maximum penetration distance includes: obtaining the photon energy corresponding to the ray; calculating the maximum energy of the secondary electrons based on the photon energy; and calculating the maximum penetration distance of the secondary electrons by interpolation based on the maximum energy.

[0030] Optionally, in order to make the ionization chamber in 60 To satisfy the secondary electron equilibrium condition, the thickness of the equilibrium cap must be no less than the maximum range of the secondary electrons in its material. 60 The gamma photon energies emitted by Co range from a minimum of 1.17 MeV to a maximum of 1.33 MeV. The maximum energy of the secondary electron (Compton recoil electron) is determined based on the photon energy. Under these conditions, the maximum penetration distance of the secondary electron is then determined. It should be noted that the thickness of the balancing cover must be greater than or equal to the maximum penetration distance to ensure that the ionization chamber achieves a secondary electron equilibrium state for the measured high-dose-rate gamma rays.

[0031] In some preferred embodiments, the maximum energy of the secondary electron is calculated based on the photon energy, as follows: in, The maximum energy of the secondary electron. This represents the photon energy corresponding to high dose rate gamma rays.

[0032] Optionally, when the photon energy is at most 1.33 MeV, the maximum energy of the secondary electron (Compton recoil electron) is: / =1.116.

[0033] In some preferred embodiments, the maximum penetration distance of the secondary electron is calculated by interpolation based on the maximum energy, as follows: in, E represents the maximum penetration distance, and E represents the maximum energy of the secondary electron. The energy in the table of approximate range data for continuously slowed-down materials corresponding to the balance cap that is closest to E and less than E; The energy in the table of approximate range data for continuously slowed-down materials corresponding to the balance cap that is closest to E and greater than E; for Corresponding range; for The corresponding range.

[0034] Optionally, the maximum energy E of the Compton recoil electron generated by a 1.33 MeV γ photon after a Compton collision (θ=0°) is 1.116 MeV. Table 1 shows the data on the continuously moderated approximate range (CSDA range) of electrons in PMMA material from the NIST database. When the maximum energy of the electron is 1.116 MeV, the required PMMA thickness in front of the ionization chamber entrance window is calculated to be at least 4.33 mm using interpolation. Finally, a 5 mm thick PMMA plate is selected to fabricate the balancing cover. That is, the dimensions of the balancing cover are: a thickness of 5 mm and a central diameter of 70 mm (not less than the diameter of the ionization chamber collector electrode).

[0035] The specific relationship between secondary electron range and photon energy in PMMA materials is shown in the table below: Table 1. Relationship between secondary electron range and photon energy in PMMA materials.

[0036] Based on the data given in Table 1, the maximum energy of the γ-photon, 1.33 MeV, can be calculated. This energy just meets the tissue equivalent material thickness required for the secondary electron equilibrium condition. That is, the thickness of the equilibrium cap is at least 0.432757 cm, which is rounded to 5 mm.

[0037] Specifically, given the existence of two electron energy data points, the calculation is as follows: Where E is 1.116, E1 is 1.00, E2 is 1.25, d1 is 0.378, and d2 is 0.496, we get d = L(E) = 0.432757.

[0038] Step S104, in 90 Sr- 90 During Yβ standard radiation field calibration, no balance cover is installed on the main body of the ionization chamber; 60When calibrating the Coγ standard radiation field, a balance cover is installed on the ionization chamber body to provide secondary electron balance conditions. The ionization chamber body is placed on the beam axis of the radiation, the balance cover is located on the side of the ionization chamber body facing the radiation emission, the beam axis of the radiation is aligned with the center of the ionization chamber body, and the thickness of the balance cover is not less than the maximum penetration distance of the secondary electrons in the material of the corresponding balance cover. Optionally, the calibration method includes two scenarios during operation: 90 Sr- 90 During gamma radiation field calibration, the ionization chamber body does not need to be covered with a balancing cover, otherwise it will block low-energy beta rays; 60 When calibrating the Co γ standard radiation field, the ionization chamber must be covered with a balancing cover to achieve a secondary electron equilibrium state.

[0039] Place the entrance window of the ionization chamber body at the calibration point, and ensure that the axis of the X-ray beam is perpendicular to the ionization chamber body and aligned with the center.

[0040] Step S106: Apply positive and negative high voltage alternately to the main body of the ionization chamber. The X-rays ionize the working gas inside the main body of the ionization chamber to generate an ionization current, which is measured by an electrometer. Optionally, a measurement method to eliminate polarity effects can be adopted. Specifically, positive and negative high voltages are alternately applied to the high-voltage electrodes of the ionization chamber body, thereby eliminating measurement deviations caused by different electrode polarities. The current measured by the ionization chamber body under positive high voltage is the positive high-voltage current. The current measured under negative high voltage is the negative high voltage current. The ionization current is determined based on the positive and negative high voltage currents.

[0041] Specifically, the ionization chamber body generates a measurable electrical signal by ionizing the working gas with X-rays. The ionization chamber body consists of plate electrodes (anode and cathode), which form an electric field when a DC voltage is applied. The interior of the ionization chamber body is filled with an inert gas (such as argon or nitrogen) or air as the ionization medium.

[0042] When radiation (such as beta rays and gamma rays) enters the sensitive volume of the ionization chamber, it ionizes the working gas molecules, producing ionization pairs (positive ions and electrons). Under the influence of an electric field, the positive ions move towards the cathode, and the electrons move towards the anode, forming a weak ionization current. The absorbed dose rate is calculated by measuring this current.

[0043] In some preferred embodiments, alternating positive and negative high voltages are applied to the ionization chamber body. The radiation ionizes the working gas within the ionization chamber body, generating an ionization current. This ionization current is measured using an electrometer. The process includes: alternating positive and negative high voltages at the high-voltage electrode of the ionization chamber body; and acquiring the positive and negative high-voltage currents using an electrometer. The positive high-voltage current... Used to indicate the current within the ionization chamber body measured under positive high voltage conditions; negative high voltage current. Used to indicate the current inside the ionization chamber body measured under conditions of applied negative high voltage; Ionization current The calculation is as follows: in, It is the ionization current. It is a positive high voltage current. It is a negative high voltage current.

[0044] Step S108: Obtain the calibration factor based on the ionization current; In some preferred embodiments, obtaining a calibration factor based on the ionization current includes: obtaining the conventional true value of the absorbed dose rate corresponding to the standard radiation field; determining the ambient atmospheric pressure and ambient temperature under the measurement environment conditions; determining the corrected ionization current based on the ambient atmospheric pressure, ambient temperature, and ionization current; and determining the calibration factor based on the ratio of the conventional true value of the absorbed dose rate corresponding to the standard radiation field and the corrected ionization current.

[0045] Optionally, a calibration factor can be calculated using a conversion formula. To ensure the accuracy of the measurement results, corrections need to be made based on ambient temperature and air pressure to obtain a more accurate calibration factor. Specifically, the conventional true value of the absorbed dose rate corresponding to the standard radiation field is obtained, where the standard radiation field refers to the corresponding... 90 Sr- 90 Yβ standard radiation field and 60 Co γ standard radiation field.

[0046] Optionally, based on the current ambient temperature and atmospheric pressure, accurate measurement results can be obtained during the experiment, thus yielding a more accurate calibration factor.

[0047] In some preferred embodiments, a calibration factor is determined based on the ratio of the conventional true value of the absorbed dose rate corresponding to the standard radiation field and the corrected ionization current, including: The calibration factor is calculated as follows: Where N is the calibration factor, which is the true value of the absorbed dose rate / the corrected ionization current; This is the conventional true value of the absorbed dose rate corresponding to the standard radiation field; It is the ionization current; Standard atmospheric pressure; Atmospheric pressure; It is 293.15K; The ambient temperature.

[0048] Optionally, based on a calibration factor, the β-applied device monitor measures and calibrates the surface absorbed dose rate of the β-applied device. Based on the above method, measurements of high-dose-rate radiation and low-dose-rate radiation were performed, and the results are shown in Table 2 below: Among them, the first four points in Table 2 are 90 Sr- 90 Yβ standard radiation field (low range dose rate range) measurement, remaining points are in 60 The Co γ standard radiation field (high dose rate range) measurement ultimately yielded a calibration factor N, which is the absorbed dose rate / current conversion coefficient of 1.534 × 10⁻⁶. 10 Gy·h -1 / A, within the range of absorbed dose rates from 10 mGy / h to 30 Gy / h, the relative inherent error of the ionization chamber body at each calibration point does not exceed ±2%.

[0049] Through the above steps S102 to S10, the technical problem that the surface absorbed dose rate of medical β patch is generally on the order of 10 Gy / h in actual use, while the highest absorbed dose rate provided by the β standard radiation field does not exceed 400 mGy / h, cannot cover the high dose rate measurement points required for calibrating the ionization chamber is solved.

[0050] Example 2 According to embodiments of the present invention, a calibration device embodiment for an ionization chamber type β-adhesive patch monitor is also provided, such as... Figure 3 As shown, Figure 3 This is a diagram showing the position of the balance cover of the calibration device for the ionization chamber type β patch monitor in Embodiment 2 of the present invention.

[0051] The device includes: a balance cover, which is detachably connected to the ionization chamber body inside the β-applier monitor and is located on the side of the ionization chamber body facing the γ-ray emission, wherein the working gas in the ionization chamber is ionized by γ-rays to obtain an ionization current; an electrometer, which is connected to the ionization chamber body and is used to acquire the ionization current in the ionization chamber body; the balance cover is made of polymethyl methacrylate or polystyrene.

[0052] Optionally, the ionization chamber includes an ionization chamber body and an ionization chamber rear shell. The ionization chamber rear shell protects the ionization chamber body. A balance cover is disposed on the ionization chamber body and located on the side away from the ionization chamber rear shell. The balance cover is connected to the end of the ionization chamber near the high dose rate gamma ray emission.

[0053] In some preferred embodiments, the balance cover is in the shape of a cover body, including a circular flat plate and an annular side plate. The annular side plate is disposed on the outer periphery of the circular flat plate, and the height of the annular side plate is greater than the thickness of the circular flat plate. Multiple vent holes are provided on the annular side plate.

[0054] In some preferred embodiments, the thickness of the circular plate is not less than the maximum penetration distance of secondary electrons corresponding to high dose rate gamma rays.

[0055] The aforementioned device ensures accurate measurement of the ionization chamber body across its entire measurement range, thereby improving measurement accuracy and reliability. The removable balance cover protects the entrance window membrane on the front of the ionization chamber body, extending its service life. The introduction of temperature and pressure correction factors enhances measurement consistency and stability, optimizing measurement operation. The use of alternating positive and negative high-pressure methods eliminates polarity effects, further improving measurement accuracy.

[0056] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of calibrating an ionization chamber type beta applicator monitor, characterized by, The application relates to a calibration device for an ionization chamber type beta applicator monitor. A balance cover is arranged on the ionization chamber body in the beta applicator monitor, wherein the balance cover is made of polymethyl methacrylate or polystyrene material; exist 90 Sr- 90 During Yβ standard radiation field calibration, no balance cover is installed on the main body of the ionization chamber; 60 When calibrating the Coγ standard radiation field, a balance cover is installed on the ionization chamber body to provide secondary electron balance conditions. The ionization chamber body is placed on the beam axis of the radiation, the balance cover is located on the side of the ionization chamber body facing the radiation emission, the beam axis of the radiation is aligned with the center of the ionization chamber body, and the thickness of the balance cover is not less than the maximum penetration distance of the secondary electrons of the radiation in the material of the corresponding balance cover. A positive and negative high voltage is alternately applied to the ionization chamber body, the rays ionize the working gas in the ionization chamber body to generate an ionization current, and the ionization current is measured by an electrometer; Based on the ionization current, a calibration factor is obtained.

2. The method of calibrating a chamber-type beta applicator monitor according to claim 1, wherein, The thickness of the balance cover is not less than the maximum penetration distance of secondary electrons of the rays in the corresponding balance cover material, wherein the maximum penetration distance is obtained by: Obtaining the photon energy corresponding to the rays; Based on the photon energy, the maximum energy of the secondary electrons is calculated; Based on the maximum energy, the maximum penetration distance of the secondary electrons is calculated by interpolation.

3. The method of calibrating an ionization chamber type beta applicator monitor according to claim 2, characterized in that, The calculation of the maximum energy of the secondary electrons based on the photon energy is as follows: wherein is the maximum energy of the secondary electrons, is the photon energy corresponding to high dose rate gamma rays.

4. The method of calibrating a chamber-type beta applicator monitor according to claim 2, wherein, The calculation of the maximum penetration distance of the secondary electrons based on the maximum energy by interpolation is as follows: wherein, is the maximum penetration distance, E is the maximum energy of the secondary electrons; is the energy in the equilibrium cover corresponding material continuous slowing down approximation range data table that is closest to E and less than E; is the energy in the equilibrium cover corresponding material continuous slowing down approximation range data table that is closest to E and greater than E; is the range distance corresponding to E; is the range distance corresponding to E; is the range distance corresponding to E; is the range distance corresponding to E.

5. The method of calibrating an ionization chamber type beta applicator monitor according to claim 1, wherein, The positive and negative high voltage is alternately applied to the ionization chamber body, the rays ionize the working gas in the ionization chamber body to generate an ionization current, and the ionization current is measured by an electrometer; applying a high voltage of positive and negative polarity alternately to the high voltage pole of the ionization chamber body, obtaining a positive high voltage current and a negative high voltage current based on an electrometer, wherein the positive high voltage current for indicating a current in the ionization chamber body measured under the condition of applying a positive high voltage, the negative high voltage current for indicating a current in the ionization chamber body measured under the condition of applying a negative high voltage; Ionization current The calculation is as follows: wherein, is the ionization current, is the positive high voltage current, is the negative high voltage current.

6. The method of calibrating an ionization chamber type beta applicator monitor according to claim 1, wherein, Based on the ionization current, a calibration factor is obtained. Obtaining the standard radiation field corresponding to the absorbed dose rate true value; Determine the environmental atmospheric pressure and the environmental temperature in the measurement environment; Based on the environmental atmospheric pressure, the environmental temperature and the ionization current, a corrected ionization current is determined; Based on the ratio of the absorbed dose rate true value corresponding to the standard radiation field and the corrected ionization current, a calibration factor is determined.

7. The method of calibrating an ionization chamber type beta applicator monitor according to claim 6, characterized in that, The calibration factor is determined based on the ratio of the absorbed dose rate true value corresponding to the standard radiation field and the corrected ionization current, and the calibration factor is calculated as follows: The calibration factor is calculated as follows: N is a calibration factor, wherein the calibration factor is an absorbed dose rate agreed true value / corrected ionization current; is an absorbed dose rate agreed true value for a standard radiation field; is an ionization current; is a standard atmospheric pressure; is an ambient atmospheric pressure; is 293.15 K; is an ambient temperature.

8. A calibration device for an ionization chamber type beta applicator monitor, characterized by The application relates to a calibration device for an ionization chamber type beta applicator monitor. A balance cover is arranged on the ionization chamber body in the beta applicator monitor, wherein the balance cover is made of polymethyl methacrylate or polystyrene material; A positive and negative high voltage is alternately applied to the ionization chamber body, the rays ionize the working gas in the ionization chamber body to generate an ionization current, and the ionization current is measured by an electrometer; Based on the ionization current, a calibration factor is obtained. The thickness of the balance cover is not less than the maximum penetration distance of secondary electrons of the rays in the corresponding balance cover material, wherein the maximum penetration distance is obtained by: Obtaining the photon energy corresponding to the rays; Based on the photon energy, the maximum energy of the secondary electrons is calculated; Based on the maximum energy, the maximum penetration distance of the secondary electrons is calculated by interpolation. The calculation of the maximum energy of the secondary electrons based on the photon energy is as follows: The calculation of the maximum penetration distance of the secondary electrons based on the maximum energy by interpolation is as follows: The positive and negative high voltage is alternately applied to the ionization chamber body, the rays ionize the working gas in the ionization chamber body to generate an ionization current, and the ionization current is measured by an electrometer; Based on the ionization current, a calibration factor is obtained. Obtaining the standard radiation field corresponding to the absorbed dose rate true value; Determine the environmental atmospheric pressure and the environmental temperature in the measurement environment; Based on the environmental atmospheric pressure, the environmental temperature and the ionization current, a corrected ionization current is determined; Based on the ratio of the absorbed dose rate true value corresponding to the standard radiation field and the corrected ionization current, a calibration factor is determined. The calibration factor is determined based on the ratio of the absorbed dose rate true value corresponding to the standard radiation field and the corrected ionization current, and the calibration factor is calculated as follows: The calibration factor is calculated as follows: The application relates to a calibration device for an ionization chamber type beta applicator monitor. A balance cover is arranged on the ionization chamber body in the beta applicator monitor, wherein the balance cover is made of polymethyl methacrylate or polystyrene material; A positive and negative high voltage is alternately applied to the ionization chamber body, the rays ionize the working gas in the ionization chamber body to generate an ionization current, and the ionization current is measured by an electrometer; Based on the ionization current, a calibration factor is obtained.

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