Method and system for dosimetry using scanning ion beam irradiated radiographic film

Abstract

This invention relates to a method and system for dosimetry measurement of radiochromic film under scanning ion beam irradiation, comprising: dividing the radiochromic film into a calibration area and a dose measurement area; irradiating the calibration area with beam spots of different dose-area product gradients; and irradiating the irradiation field to be measured in the dose measurement area; simultaneously digitizing the calibration area and the dose measurement area of ​​the radiochromic film to obtain the film color change index distribution in the calibration area and the film color change distribution in the dose measurement area; and constructing f based on the functional relationship between dose and film color change degree and the beam spot dose distribution function. ′ (d ′ (x,y)); adjust f ′ (d ′ The parameters of (x,y)), the distribution of film color change index and f ′ (d ′ The method minimizes the difference between (x, y) values; calculates the functional relationship between dose and film color change degree and the beam spot dose distribution function to obtain the film dose calibration curve; and obtains the dose distribution in the film dose measurement area. This addresses the differences in film dose calibration curves between batches and within batches of radiochromic films, as well as the need for long-term light-protected storage after irradiation before digitization.

Description

Technical Field

[0001] This invention relates to a method and system for measuring the dose of radiation-chromatic film under scanning ion beam irradiation, belonging to the field of radiation dose measurement technology. Background Technology

[0002] In ion beam irradiation science and technology research, industrial and clinical medical applications, dose distribution measurements of the ion beam's radiation field are frequently required to ensure irradiation accuracy. Dose distribution measurements generally require two-dimensional dose detectors. Two-dimensional dose detectors come in various types, including two-dimensional ionization chamber matrices based on multiple ionization chambers, which can be further divided into semiconductor and air ionization chamber types; there are also detectors based on the emission of light from irradiated materials, such as thermoluminescent thin films and scintillator detectors; and there are detectors based on the radiochromic properties of chemical materials, such as developing radiographic films and non-developing radiochromic films, and gel dosimeter films.

[0003] Radiochromic film is a type of radiation dosimeter based on organic molecules. Since the size of organic polymer molecules is on the order of micrometers, theoretically, the spatial resolution of dose measurement using radiochromic film is also on the order of micrometers. Therefore, radiochromic film can be used in dose measurement scenarios where high spatial resolution is required. Furthermore, radiochromic film is minimally affected by the dose rate (<10). 6 (Gy / s), which can be used for dosage measurement and planning verification of Flash therapy technology.

[0004] While radiochromic film offers many advantages, its dose measurement requires strict operating procedures to ensure accuracy. To improve dose measurement resolution, radiochromic film needs to be digitized using a specialized transmission scanner to output a 48-bit color positive film. When measuring dose using radiochromic film, the film must first be dose-calibrated. This involves creating a quantitative index of the degree of color change after exposure to radiation, corresponding to the radiation dose. This curve is called the film dose response curve or calibration curve. When measuring the dose distribution using the film, the radiation dose distribution is then calculated based on the quantitative index of the film's color change and the film dose calibration curve. Therefore, the accuracy of the dose calibration curve is crucial in film dose measurement. Due to differences in the purity of raw materials or processing techniques between different batches of film, their dose responses vary. Therefore, dose calibration of each batch of film is necessary when performing dose measurements using different batches. The conventional film dosimetry calibration method involves taking one sheet of film from a batch, dividing it into several small sections, irradiating each section with a known dose in a uniform radiation field, and then digitizing the film after it has fully discolored (usually after irradiation, it is stored in the dark for about 24 hours). Finally, film analysis tools are used to establish a one-to-one correspondence curve between the quantitative index of the film's discoloration degree and the dose. Long-term storage of film or different exposure histories can lead to differences in the film's dose response. Therefore, even when using dose calibration curves from the same batch of film, a significant difference between the date the calibration curve was obtained and the date of dose measurement can result in non-negligible measurement errors over time. Thus, the conventional film dosimetry method is affected by batch-specific response differences related to film storage time, exposure environment, and other factors. To improve dose measurement accuracy, the frequency of obtaining film calibration curves can be increased; however, this increases both workload and film usage costs. Furthermore, the conventional film calibration method uses a uniform irradiation field, irradiating each section according to the dose gradient, resulting in a long irradiation time required for film dose response calibration. Finally, when using film for dose measurement, it is crucial to pay attention to the interval between film calibration and digitization, i.e., the time required for light-protected storage after film irradiation. To ensure measurement accuracy, the light-protected storage time for dose measurement film after irradiation is generally required to be consistent with that for calibration film. In actual measurements, strictly controlling the consistency of light-protected storage time is difficult to achieve. Therefore, to reduce measurement errors caused by inconsistent film discoloration after irradiation, it is generally required that the film be stored in the dark for 24 hours after irradiation to allow for sufficient discoloration before digitization using a scanner. Thus, the procedure for measuring radiation dose using film is complex and time-consuming. The non-immediacy of waiting for the film to fully discolor after irradiation before digitization for subsequent dose analysis is the biggest limiting factor for using radiation-chromatic films for dose verification in daily treatment plans. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a method and system for measuring the dose of radiochromic film under scanning ion beam irradiation. This method solves the problems encountered in traditional methods of using radiochromic film, such as differences in film dose calibration curves between batches and within batches, as well as the untimely nature of digitization due to the need for long-term light-protected storage after irradiation.

[0006] To achieve the above objectives, the present invention proposes the following technical solution: a method for measuring the dose of radiochromic film under scanning ion beam irradiation, comprising the following steps: dividing the radiochromic film into a calibration area and a dose measurement area; irradiating the calibration area with beam spots of different dose-area product (DAP) gradients; irradiating the dose measurement area with the irradiation field to be measured; simultaneously digitizing the calibration area and the dose measurement area of ​​the radiochromic film to obtain the film color change index distribution f1(x,y) of the calibration area and the film color change distribution f2(x,y) of the dose measurement area; defining the functional relationship f′(d) between dose and the degree of film color change and the beam spot dose distribution function d. Based on f′(d) and d′(x,y), construct the functional relationship of f′(d′(x,y)). By adjusting the parameters of f′(d′(x,y)), minimize the difference between the film discoloration index distribution f1(x,y) and f′(d′(x,y)). Calculate the functional relationship f′(d) between dose and film discoloration degree and the beam spot dose distribution function d′(x,y) based on the finally obtained f′(d′(x,y)) to obtain the film dose calibration curve. Based on the film dose calibration curve and the film discoloration distribution f2(x,y) in the film dose measurement area, obtain the dose distribution in the film dose measurement area.

[0007] Furthermore, the method for simultaneously digitizing the scale area and dose measurement area of ​​the radiochromic film includes: simultaneously generating a digital image of the film by scanning the scale area and the film dose measurement area with a film scanner; correcting lateral artifacts on the digital image of the film; extracting the pixel values ​​of the red, green, and blue channels of the scale area; or converting the digital image of the film into optical density values ​​or net optical density values ​​to obtain the film color change index distribution f1(x,y);

[0008] Extract the pixel values ​​of the red, green, and blue channels in the film dosimetry area, or convert the digitized image of the film into optical density values ​​or net optical density values ​​to obtain the film color change distribution f2(x,y).

[0009] Furthermore, based on the finally obtained f′(d′(x,y)), the beam spot dose distribution function d′(x,y) is calculated. The film discoloration index distribution f1(x,y) in the scale area corresponds one-to-one with the beam spot dose distribution function d′(x,y). The film discoloration index distribution f1(x,y) is fitted with the beam spot dose distribution function d′(x,y) to obtain the film dose scale curve. The film discoloration distribution f2(x,y) in the film dose measurement area is input into the film dose scale curve to obtain the dose distribution in the film dose measurement area.

[0010] Furthermore, by using the beam spot of multiple dose-area product DAP gradients, it is possible to obtain dose and film color change index distribution f1(x,y) data points of different ranges. The dose and film color change index distribution f1(x,y) data points of different ranges are then incorporated into the film dose calibration curve for fitting.

[0011] Furthermore, based on the finally obtained f′(d′(x,y)), the functional relationship between dose and film discoloration degree f′(d) is calculated. The inverse function of the functional relationship between dose and film discoloration degree f′(d) is obtained to obtain the film dose calibration curve. The film discoloration distribution f2(x,y) of the film dose measurement area is input into the film dose calibration curve to obtain the dose distribution of the film dose measurement area.

[0012] Furthermore, the beam spot dose distribution function d′(x,y) is an elliptic Gaussian distribution or a multi-elliptic Gaussian distribution.

[0013] Furthermore, the formula for calculating the difference between the film color change index distributions f1(x,y) and f′(d′(x,y)) is as follows:

[0014] min∑(f1(x,y)-f′(d′(x,y))) 2 .

[0015] Furthermore, the scanning ion beam irradiation uses X-direction scanning magnets and Y-direction scanning magnets to guide the deflection of the ion pencil beam in the X and Y directions, respectively, so that the ion pencil beam irradiates the coordinate point on the isocenter plane. The formula for calculating the dose-area product (DAP) is as follows:

[0016] DAP = N / k = D·Δx·Δy

[0017] Where Δx and Δy are the distances between adjacent scan points in the X and Y directions, respectively, N is the monitoring ionization chamber count irradiated at each scan point, D is the absolute dose measured at the isocenter, and k is the proportionality coefficient between DAP and N.

[0018] This invention also discloses a radiation-chromatic film dose measurement system under scanning ion beam irradiation, used to implement the radiation-chromatic film dose measurement method under scanning ion beam irradiation as described in any of the above claims. The system includes: a scanning ion beam irradiation device, an isocenter plane, a film scanner, a data processing module, and an output module. The scanning ion beam irradiation device is used to generate an ion pencil beam; the isocenter plane is used to place the radiation-chromatic film and irradiate it with the ion pencil beam; the film scanner is used to digitize the radiation-chromatic film to generate a digital image; the data processing module is used to process the digital image to generate a film colorimetric index distribution f1(x,y) in the scale area and a film colorimetric distribution f2(x,y) in the film dose measurement area, obtaining a film dose scale curve, and obtaining the dose distribution in the film dose measurement area based on the film dose scale curve and the film colorimetric distribution f2(x,y) in the film dose measurement area; the output module is used to visualize the dose distribution in the film dose measurement area.

[0019] Furthermore, the scanning ion beam irradiation device includes: an X-direction scanning magnet, a Y-direction scanning magnet, and an online monitoring ionization chamber; the X-direction scanning magnet is used to guide the deflection of the ion pencil beam in the X direction; the Y-direction scanning magnet is used to guide the deflection of the ion pencil beam in the Y direction; and the online monitoring ionization chamber is used to control and record the ionization chamber count at the coordinate point position irradiated on the isocentric plane.

[0020] The present invention has the following advantages due to the adoption of the above technical solutions:

[0021] 1. Since the present invention uses pencil-shaped beam spot irradiation for film dose calibration instead of uniform irradiation in the traditional calibration method, the total dose of dose calibration irradiation can be greatly reduced, thereby greatly shortening the calibration irradiation time.

[0022] 2. Using a pen-shaped beam pattern for dosage calibration can save on film usage, as the dosage of film can be calibrated in a small area of ​​the film.

[0023] 3. Traditional calibration methods obtain discrete data points of dose and corresponding film color change index, and then use discrete points to fit to obtain a dose calibration curve. However, in the method of this invention, multiple dose-area product gradient beams can be used for calibration. The dose distribution of the beam is continuous, so theoretically, countless dose and color change index data points can be obtained to fit the dose calibration curve, thereby obtaining a higher precision calibration curve.

[0024] 4. Because the film area required for film calibration is small, calibration and dosage measurement can be performed on the same film, thus avoiding the errors caused by dosage calibration and dosage measurement on different films in traditional methods.

[0025] 5. Dosage calibration and measurement are performed on the same film, and the calibration exposure time is very short, which is equivalent to simultaneous dosing calibration and measurement. Therefore, there is no need to wait for the film to fully change color before digitizing it, solving the timeliness problem in film measurement.

[0026] 6. The distribution parameters of beam spot dose obtained in this invention are part of the quality control of the scanning ion beam irradiation device, thus sharing some of the workload for the quality control of the irradiation device. Attached Figure Description

[0027] Figure 1 This is a flowchart of a method for measuring the dose of radiochromic film under scanning ion beam irradiation in one embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of a radiochromic film irradiated by an isocentric plane in one embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of the dose-area product (DAP) measured at the isocenter plane in one embodiment of the present invention;

[0030] Figure 4 This is a schematic diagram of a radiation-sensitive film dose measurement system under scanning ion beam irradiation in one embodiment of the present invention;

[0031] Figure 5 This is a schematic diagram of a scanning ion beam irradiation device in one embodiment of the present invention.

[0032] 1-Scale area; 2-Dose measurement area; 3-Absolute dose ionization chamber; 4-Signal line; 5-Scanning ion beam irradiation device; 51-Ion pencil beam; 52-X-direction scanning magnet; 53-Y-direction scanning magnet; 54-Online monitoring ionization chamber; 6-Isocentric plane; 7-Film scanner; 8-Data processing module; 9-Output module. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention has been described in detail through specific embodiments. However, it should be understood that the specific embodiments are provided only for a better understanding of the present invention and should not be construed as limiting the present invention. In the description of the present invention, it should be understood that the terminology used is for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0034] The color-changing principle of radiochromic film is that organic diacetylene molecules break their chemical bonds and recombine under the influence of radiation to form a poly(diacetylene) dye polymer. This polymer, adhering to the plastic film, reduces the film's light transmittance. For the same type of radiation, the higher the dose irradiated onto the film, the lower the film's light transmittance, macroscopically manifested as a darkening and color change in the film. Therefore, the radiochromic property can be used to measure radiation dose and its distribution.

[0035] To fully leverage the advantages of radiochromic film and address the issues of batch-to-batch and intra-batch differences in film dose calibration curves, as well as the timeliness of digitization due to prolonged light-protected storage after irradiation, this invention provides a method and system for measuring the dose of radiochromic film under scanning ion beam irradiation. By utilizing the characteristics of the scanning ion beam and the radiochromic film, it achieves dose calibration and dose distribution measurement on the same film, thus avoiding the inaccuracy caused by differences in dose calibration curves between and within film batches. Furthermore, because dose calibration and dose distribution measurements are performed within a short time, the consistency of the calibration and measurement time of the film's color change after irradiation is ensured. The film can be digitized at any time after irradiation, and the dose measurement results can then be analyzed and processed. This invention improves the accuracy and timeliness of film dose measurement. The technical solution of this invention is described in detail below through embodiments.

[0036] Example 1:

[0037] Traditional film calibration methods involve irradiating discrete films with different doses to obtain the relationship between different degrees of color change f and dose d, i.e., the dose calibration curve d(f). The principle of this embodiment is consistent with the traditional method, also requiring the establishment of a relationship between f and d. However, this embodiment uses the correspondence between a continuous dose distribution d(x,y) and a color change distribution f(x,y) on a plane to establish the d(f) curve. More specifically, it uses the dose distribution d(x,y) of one or more ion pencil beam spots and the film color change f(x,y) to construct the film dose calibration curve, which is then used for film dose measurement.

[0038] This embodiment discloses a method for measuring the dose of radiation-chromatic film under scanning ion beam irradiation, such as... Figure 1 As shown, it includes the following steps:

[0039] S1 divides the radiochromic film into a calibration zone 1 and a dose measurement zone 2. Beams with different dose-area product (DAP) gradients are irradiated in calibration zone 1, while the target irradiation field is irradiated in dose measurement zone 2. Figure 2 As shown.

[0040] First, it is necessary to accurately measure the conversion relationship between the irradiation count N and the dose-area product DAP in the online measurement ionization chamber of the scanning ion beam device.

[0041] The scanning ion beam irradiation, guided by scanning magnets in the X and Y directions, deflects the ion pencil beam 51 in the X and Y directions respectively, causing the ion pencil beam 51 to irradiate the coordinate point on the isocenter plane 6. This coordinate point is called the "scanning point". The ion pencil beam irradiating the isocenter plane 6 yields... Figure 3 The uniform irradiation field shown is formed by a pencil beam irradiating six regularly arranged scanning points on an isocentric plane. Each scanning point is irradiated by the same number of ionization chambers.

[0042] The formula for calculating the dose-area product (DAP) of the irradiated field is:

[0043] DAP = N / k = D·Δx·Δy

[0044] Where Δx and Δy are the distances between adjacent scan points in the X and Y directions, respectively, N is the monitoring ionization chamber count irradiated at each scan point, D is the absolute dose measured at the isocenter, and k is the proportionality coefficient between DAP and N. Figure 3 An absolute dose ionization chamber 3 is placed at the center of a uniform irradiation field. The dose ionization chamber is connected to an absolute dosimeter via a signal line 4 for absolute dose measurement.

[0045] To perform dose response calibration and dose measurement on the same radiochromic film, the film needs to be divided into dose calibration area 1 and dose measurement area 2, such as... Figure 2 As shown. The film dose scale area 1 and dose measurement area 2 can be cut apart or left uncut. If cut apart, the two areas need to be irradiated twice at the isocenter plane 6; if left uncut, the film can be placed on a mobile irradiation platform for sectional irradiation. Positioning points are marked on the film with a marker pen, i.e. Figure 3 The black dots in the image are used to obtain the film origin information in the analysis software. The size of the scale area 1 and the dose measurement area 2 can be determined according to the actual size of the pencil beam spot and the size of the irradiation field to be measured. To improve the accuracy of the film dose calibration, multiple monitoring ionization chamber counting gradients, i.e., multiple DAP gradient beam spots, can be irradiated.

[0046] S2 simultaneously digitizes the scale area 1 and dose measurement area 2 of the radiochromic film to obtain the film color change index distribution f1(x,y) of scale area 1 and the film color change distribution f2(x,y) of dose measurement area 2.

[0047] The method for simultaneously digitizing the scale area 1 and the dose measurement area 2 of the radiochromic film includes: simultaneously generating a digital image of the film by passing the scale area 1 and the film dose measurement area 2 through the film scanner 7; performing lateral artifact correction on the digital image of the film; extracting the pixel values ​​of the red, green, and blue channels of the scale area 1, or converting the digital image of the film into optical density values ​​or net optical density values ​​to obtain the film color change index distribution f1(x,y); extracting the pixel values ​​of the red, green, and blue channels of the film dose measurement area 2, or converting the digital image of the film into optical density values ​​or net optical density values ​​to obtain the film color change distribution f2(x,y).

[0048] S3 defines the functional relationship between dose and film chromatic aberration f′(d) and the beam spot dose distribution function d′(x,y). Based on f′(d) and d′(x,y), the functional relationship of f′(d′(x,y)) is constructed.

[0049] In this embodiment, the functional relationship between dosage and film discoloration degree is: f′(d)=a·D+b·D c ,

[0050] In this embodiment, parameters a, b, and c are unknowns. The functional relationship between dosage and film discoloration is merely illustrative and not the only option. Specific functional relationships can be determined using empirical formulas or data fitting methods, and are not limited to the content disclosed in this embodiment.

[0051] The beam spot dose distribution function d′(x,y) can be an elliptic Gaussian distribution or a multi-elliptic Gaussian distribution. For example, if a single-fold elliptic Gaussian distribution function is used to characterize the beam spot dose distribution, then...

[0052]

[0053] in,

[0054] Considering the actual dose distribution of a certain spot in scale region 1 as d(x,y), then:

[0055] DAP=∫∫d(x,y)dxdy

[0056] DAP is the dose-area product. Since the dose distribution of the ion pencil beam spot 51 exhibits a Gaussian-like distribution, it can be approximated by one or more two-dimensional elliptic Gaussian functions. Furthermore, the dose-area product DAP is known. Therefore, if the parameters of the distribution function can be determined, the dose distribution d′(x,y) of the beam spot can be obtained through calculation.

[0057] d′(x,y)=DAP∑ i w i G i(x,y|x 0,i ,y 0,i ,σ X,i ,σ Y,i ,θ i )

[0058] Where G(·) is a two-dimensional elliptic Gaussian function, and ∫∫∑ i w i G i (x,y|x 0,i ,y 0,i ,σ X,i ,σ Y,i ,θ i dxdy=1.

[0059] The relationship between the degree of film discoloration and the dose, f(d), which is the inverse function of the dose calibration curve d(f), can be described by a parameterized fitting formula. Therefore, the degree of discoloration of the 1st beam spot in the calibration area can be calculated using the function f′(d′(x,y)). Since the parameters a, b, and c in the functional relationship between dose and film discoloration f′(d) are unknown, f′(d′(x,y)) also has unknown parameters. The parameters in f′(d′(x,y)) will be adjusted in the next step.

[0060] S4 minimizes the difference between the film color change index distribution f1(x,y) and f′(d′(x,y)) by adjusting the parameters of f′(d′(x,y)).

[0061] The film discoloration index distribution f1(x,y) represents the discoloration degree distribution of the actual calibrated film beam spot. When the parameters of the assumed d′(x,y) distribution function and the function parameters of f(d) are consistent with the actual parameters, the difference between the calculated f′(d′(x,y)) and the actually measured film discoloration index distribution f1(x,y) will be minimized. Therefore, an iterative optimization method can be used to find the optimal dose distribution function parameters and film calibration curve parameters that minimize the difference between f′(d′(x,y)) and f(x,y), i.e.

[0062] min∑(f1(x,y)-f′(d′(x,y))) 2 .

[0063] Although the degree of color change of the pixel values ​​in the R, G, and B channels of radiochromic film does not vary with dose, each channel has its own dose response curve f. X (d),X∈{R,G,B}, but for a certain spot, the distribution parameters of d′(x,y) obtained by optimizing the color change distribution information of different channel pixel values ​​should be consistent.

[0064] S5 calculates the functional relationship between dose and film discoloration degree f′(d) and the beam spot dose distribution function d′(x,y) based on the finally obtained f′(d′(x,y)), and obtains the film dose calibration curve;

[0065] Based on the finally obtained f′(d′(x,y)), the beam spot dose distribution function d′(x,y) is calculated. The film discoloration index distribution f1(x,y) of scale area 1 corresponds one-to-one with the beam spot dose distribution function d′(x,y). The film dose calibration curve is obtained by fitting the film discoloration index distribution f1(x,y) with the beam spot dose distribution function d′(x,y). By obtaining beam spots with multiple dose area products (DAP gradients), dose and film discoloration index distribution f1(x,y) data points of different ranges can be obtained. These data points are then incorporated into the film dose calibration curve for fitting. By repeatedly obtaining scale beam spots with multiple DAP gradients and performing film dose calibration curve d(f), a film dose response calibration curve with a wider dose range and higher accuracy can be obtained.

[0066] Based on the finally obtained f′(d′(x,y)), calculate the functional relationship f′(d) between dose and film discoloration. Find the inverse function of the functional relationship f′(d) between dose and film discoloration to obtain the film dose calibration curve. Input the film discoloration distribution f2(x,y) of film dose measurement area 2 into the film dose calibration curve to obtain the dose distribution of film dose measurement area 2.

[0067] S6 obtains the dose distribution of film dose measurement area 2 based on the film dose calibration curve and the film color change distribution f2(x,y) of film dose measurement area 2.

[0068] Example 2:

[0069] Based on the same inventive concept, this embodiment further illustrates the solution of the present invention through a specific example. The method for measuring the dose of radiation-chromatic film under scanning ion beam irradiation in this embodiment includes the following steps:

[0070] S1 divides the radiochromic film into a scale area 1 and a dose measurement area 2. The scale area 1 is irradiated with beams of different dose area product (DAP) gradients, and the dose measurement area 2 is irradiated with the field to be tested.

[0071] A uniform irradiation field is formed using a sufficiently large, regularly distributed scan point, with each scan point irradiating the same number of counts in the monitoring ionization chamber. The absolute dose value D at the center of the field is measured. The spacing between scan points is related to the beam size of the ion pencil beam, typically 2 / 3 of the beam width at half maximum (WHM). The scan field size generally needs to exceed 4 cm; generally, a larger scan field yields more accurate DAP and monitoring ionization chamber counts. For example, if the scan field size is set to 100 mm × 100 mm, and the scan point spacing is 2 mm, then the scan field consists of 51 × 51 regularly distributed scan points. If each scan point irradiates 1000 counts (MU) in the monitoring ionization chamber, and the average value of multiple dose ionization chamber measurements is 0.57 Gy, then the area product DAP is: 0.57 Gy × 2 mm × 2 mm / 1000 MU = 2.28 × 10⁻⁶. - 3 Gy·mm 2 / MU. In ion beam spot scanning radiotherapy techniques, this relationship typically remains relatively stable.

[0072] Before irradiation, a film can be divided into a calibration area 1 and a dose measurement area 2. These two areas can be cut to form two separate films, which are then irradiated separately. When the film is large enough, it can be divided into two calibration areas 1, with one area serving as background radiation and not irradiated. Different beam doses for monitoring ionization chamber counts are then irradiated into calibration area 1, for example, irradiating 3 × 10⁻⁶ beams into this area. 5 6×10 5 9×10 5 1.2×10 6 The four beams of the MU can also irradiate four identical beams of the MU. Irradiation of 6x10 5 The beam spot of MU corresponds to a DAP of 2.28 × 10⁻⁶. -3 Gy·mm 2 / MU×6×10 5 MU = 1368 Gy·mm 2 Irradiation of dose measurement area 2 can be performed according to the irradiation parameters of the field to be tested. When scale area 1 and dose measurement area 2 are not separated, the irradiation method is the same, but the irradiation parameters of the two need to be integrated in the irradiation control system to achieve continuous irradiation.

[0073] S2 simultaneously digitizes the radiation-induced color change scale area 1 and the dose measurement area 2 to obtain the film color change index distribution f1(x,y) of scale area 1 and the film color change distribution f2(x,y) of film dose measurement area 2.

[0074] The film is scanned into a digital image using a film scanner 7. When scanning pre-cut film, the scale area 1 and the dose measurement area 2 should be scanned together to ensure that they have the same color change time. Furthermore, attention must be paid to the orientation of the scale area 1 and dose measurement area 2 on the cut film; their orientation on the scanner panel should be consistent with the original film frame. Other settings are the same as those for traditional film digitization.

[0075] Lateral artifact correction for digitized film images follows the same method as conventional approaches. It can correct pixel values ​​(PV), optical density values ​​(OD), or net optical density values ​​(netOD) of digitized film images.

[0076] Establish a coordinate system in scale area 1. If the degree of color change of the film is represented by netOD, then the distribution of the degree of color change in scale area 1 can be represented by netOD(x,y). Similarly, PixelValue(x,y) or OD(x,y) can be obtained. For convenience, the netOD value will be used to represent the degree of color change of the film below.

[0077] S3 defines the functional relationship between dose and film chromatic aberration f′(d) and the beam spot dose distribution function d′(x,y). Based on f′(d) and d′(x,y), the functional relationship of f′(d′(x,y)) is constructed.

[0078] Define the functional relationship f′(d) between dose and film color change: In the film dose scale, the dose D received by the film corresponds one-to-one with netOD. Fit the two, assuming that D and netOD have netOD = a·D + b·D c The functional relationship between D and netOD is not unique and can be represented using other functional forms.

[0079] Define the beam spot dose distribution d′(x,y): Since the spatial distribution of the ion pencil beam 51 provided by the accelerator tends to a positive Gaussian distribution during transmission, an approximately two-dimensional Gaussian dose spot will be formed in the isocentric plane 6. To generalize the dose distribution of the pencil beam spot, it can be characterized using a single-fold elliptic Gaussian or multiple-fold elliptic Gaussian distribution function. For example, using a single-fold elliptic Gaussian distribution function to characterize the beam spot dose distribution, then...

[0080]

[0081] in,

[0082] Since the ionization chamber count for a given beam spot is known (i.e., the magnitude of DAP is known), applying an area integral to the dose distribution of that beam spot yields ∫∫d(x,y)=DAP, i.e.

[0083]

[0084] The netOD distribution of film can be predicted using the relationship between netOD and D, i.e.,

[0085] netOD′(x,y)=a·d′(x,y)+b·d′(x,y) c

[0086] Finally, the netOD distribution can be described as follows:

[0087] netOD′(x,y|x0,y0,σ X ,σ Y ,θ,a,b,c).

[0088] S4 minimizes the difference between the film color change index distribution f1(x,y) and f′(d′(x,y)) by adjusting the parameters of f′(d′(x,y)).

[0089] The actual netOD(x,y) distribution of the 1-beam spot in the scale region was obtained from experimental measurements, and therefore the following formula can be iteratively optimized.

[0090] min∑(netOD(x,y)-netOD′(x,y|x0,y0,σ X ,σ Y ,θ,a,b,c)) 2

[0091] Determine the beam spot shape parameters (x0, y0, σ) X ,σ Y By determining the parameters (a, b, c) of the D-netOD relationship function, the absolute dose distribution of the beam spot and the explicit D-netOD relationship can be obtained. Since the digitized film is a color digital image, one or more channels of R, G, and B can be used to optimize the above formula. For a given beam spot, its shape distribution parameters should be consistent, thereby constraining the convergence direction of the optimization algorithm.

[0092] S5 calculates the functional relationship between dose and film discoloration degree f′(d) and the beam spot dose distribution function d′(x,y) based on the finally obtained f′(d′(x,y)), and obtains the film dose calibration curve.

[0093] The absolute dose distribution, i.e., the dose distribution of the beam spot d′(x,y|x0,y0,σ), can be obtained using the parameters of the beam spot dose distribution function. X ,σY The netOD distribution of the graduated film, netOD(x,y), is related to the absolute dose distribution of the beam spot, d′(x,y|x0,y0,σ). X ,σ Y By establishing a one-to-one correspondence between dose and netOD, a large number of dose and corresponding netOD data points can be obtained. Fitting these data points together yields the film dose calibration curve D(netOD). If multiple DAP gradient calibration spots are available, dose and netOD data points in different ranges can be obtained. Incorporating these data points into the film dose calibration curve fitting can further improve the accuracy of the calibration curve.

[0094] The relationship between D and netOD, i.e., netOD(D), can also be obtained through optimization. Taking the inverse function of netOD(D) yields the relationship between D and netOD. This method can also be used to obtain the dose calibration curve when only one beam spot is used for dose calibration.

[0095] S6 obtains the dose distribution of film dose measurement area 2 based on the film dose calibration curve and the film color change distribution f2(x,y) of film dose measurement area 2.

[0096] Example 3:

[0097] Based on the same inventive concept, this embodiment discloses a dosimetry system for radiochromic film under scanning ion beam irradiation, used to implement the dosimetry method for radiochromic film under scanning ion beam irradiation as described in any of the above embodiments. Figure 4 As shown, it includes: a scanning ion beam irradiation device 5, an isocentric plane 6, a film scanner 7, a data processing module 8, and an output module 9.

[0098] Scanning ion beam irradiation device 5, used to generate ion pencil beam 51; scanning ion beam irradiation device 5, such as Figure 5 As shown, it includes: an X-direction scanning magnet 52, a Y-direction scanning magnet 53, and an online monitoring ionization chamber 54;

[0099] X-direction scanning magnet 52 is used to guide the deflection of ion pen beam 51 in the X direction;

[0100] Y-direction scanning magnet 53 is used to guide the deflection of ion pen beam 51 in the Y direction;

[0101] The online monitoring ionization chamber 54 is used to monitor the dose of the ion pen beam 51 in real time.

[0102] The central plane 6 is used to place the radiochromic film and to allow the ion pen beam 51 to irradiate the radiochromic film.

[0103] Film scanner 7 is used to digitize radiochromic film and generate digital images of the film.

[0104] The data processing module 8 is used to process the digital image, generate the film color change index distribution f1(x,y) of the scale area 1 and the film color change distribution f2(x,y) of the film dose measurement area 2, obtain the film dose scale curve, and obtain the dose distribution of the film dose measurement area 2 based on the film dose scale curve and the film color change distribution f2(x,y) of the film dose measurement area 2.

[0105] Output module 9 is used to visualize the dose distribution in film dose measurement area 2.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific embodiments of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention. The above content is only a specific embodiment of this application, but the protection scope of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be covered within the protection scope of this application. Therefore, the protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A method for measuring the dose of radiation-chromatic film under scanning ion beam irradiation, characterized in that, Includes the following steps: The radiochromic film is divided into a scale area and a dose measurement area. Different doses are irradiated into the product of the areas in the scale area. DAP A gradient beam spot irradiates the test field in the dose measurement region; The scale area and dose measurement area of ​​the radiation-chromatic film are digitized simultaneously to obtain the distribution of film color change indexes in the scale area. Film discoloration distribution in the film dosimetry area ; Define the functional relationship between dosage and the degree of film discoloration. and beam spot dose distribution function ,according to and , build The functional relationship; By adjusting The parameters determine the distribution of film color change indices in the graduated area. and Minimize the difference; According to the final obtained Calculate the functional relationship between dosage and film discoloration. and beam spot dose distribution function Obtain the film dosage calibration curve; Based on the film dosing calibration curve and the film discoloration distribution in the film dosing measurement area... To obtain the dose distribution in the film dosimetry area; According to the final obtained Calculate the beam spot dose distribution function The distribution of film color change indicators in the scale area With beam spot dose distribution function One-to-one correspondence, and the distribution of the film color change indexes With beam spot dose distribution function The film dosing calibration curve is obtained by fitting the film dosing measurement area, and the film discoloration distribution is obtained by fitting the film dosing calibration curve. Input the film dose calibration curve to obtain the dose distribution in the film dose measurement area.

2. The method for measuring the dose of radiation-chromatic film under scanning ion beam irradiation as described in claim 1, characterized in that, The method for simultaneously digitizing the scale area and dose measurement area of ​​the radiochromic film includes: simultaneously generating digital images of the film using a film scanner by scanning the scale area and the film dose measurement area; performing lateral artifact correction on the digital images; extracting the pixel values ​​of the red, green, and blue channels of the scale area, or converting the corresponding digital images of the film into optical density values ​​or net optical density values, to obtain the distribution of the film's color-changing index. ; Pixel values ​​of the red, green, and blue channels in the film dosimetry area are extracted, or the corresponding digital images of the film are converted into optical density values ​​or net optical density values ​​to obtain the film color change distribution. .

3. The method for measuring the dose of radiation-chromatic film under scanning ion beam irradiation as described in claim 2, characterized in that, Through multiple dose-area products DAP Gradient beam patterns can achieve different ranges of dose distribution and film color distortion index distribution. Data points, which correlate different ranges of doses with the film's color change index distribution. The data points were also included in the film dosage scale curve for fitting.

4. The method for measuring the dose of radiation-chromatic film under scanning ion beam irradiation as described in claim 1, characterized in that, According to the final obtained Calculate the functional relationship between dosage and film discoloration. The functional relationship between the dosage and the degree of film discoloration Find the inverse function to obtain the film dosing calibration curve, and then determine the film discoloration distribution in the film dosing measurement area. Input the film dose calibration curve to obtain the dose distribution in the film dose measurement area.

5. The method for measuring the dose of radiation-chromatic film under scanning ion beam irradiation as described in any one of claims 1-4, characterized in that, The beam spot dose distribution function It is an elliptic Gaussian distribution or a multi-elliptic Gaussian distribution.

6. The method for measuring the dose of radiation-chromatic film under scanning ion beam irradiation as described in any one of claims 1-4, characterized in that, The distribution of film color change indicators in the scale area and The formula for calculating the difference is: 。 7. The method for measuring the dose of radiation-chromatic film under scanning ion beam irradiation as described in any one of claims 1-4, characterized in that, Scanning ion beam irradiation through Directional scanning magnet and Directional scanning magnets guide the ion pen beams in... direction and The deflection of direction causes the ion pencil beam to irradiate the coordinate point on the isocentric plane, the product of the dose and area. DAP The calculation formula is: in, , They are respectively direction and The spacing between adjacent scan points in the direction, N It is the monitoring ionization chamber count for each scan point irradiated. D The absolute dose is obtained by measuring at the isocenter. k It is the scaling factor between DAP and N.

8. A dosimetry system for radiation-chromatic film under scanning ion beam irradiation, characterized in that, A method for measuring the dose of radiochromic film under scanning ion beam irradiation as described in any one of claims 1-7, comprising: a scanning ion beam irradiation device, an isocentric plane, a film scanner, a data processing module, and an output module. The scanning ion beam irradiation device is used to generate an ion pencil beam; The isocentric plane is used to place the radiochromic film and to allow the ion pen beam to irradiate the radiochromic film. The film scanner is used to digitize the radiochromic film to generate a digital image of the film. The data processing module is used to process the digitized image and generate a film color change index distribution for the scale area. Film discoloration distribution in the film dosimetry area A film dosing calibration curve is obtained, and the film discoloration distribution in the film dosing measurement area is determined based on the film dosing calibration curve and the film discoloration distribution. To obtain the dose distribution in the film dosimetry area; The output module is used to visualize the dose distribution in the film dose measurement area.

9. The radiation-chromatic film dosimetry system under scanning ion beam irradiation as described in claim 8, characterized in that, The scanning ion beam irradiation device includes: X Directional scanning magnet, Y Directional scanning magnet and online monitoring ionization chamber; The X Directional scanning magnets are used to guide the ion pen beam in Directional deflection; The Y Directional scanning magnets are used to guide the ion pen beam in Directional deflection; The online monitoring ionization chamber is used to control and record the ionization chamber count at the coordinate point position irradiated on the isocentric plane.

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