Whole center dose verification method based on no-wash film EBT3

Abstract

The invention discloses a full center dose verification method based on a no-wash film EBT3, and belongs to the technical field of radiation measurement, and the method specifically comprises the following steps: continuously collecting an irradiated radiation chromatography film, and synchronously obtaining gray data and a scanning device driving voltage sequence; establishing a response function model between the driving voltage and the gray response according to the driving voltage value at each acquisition moment and the mean value of the corresponding gray data; determining a target voltage in advance, determining a correction coefficient corresponding to each driving voltage value based on the target voltage and the response function model, correcting a preset dose-gray curve graph according to the correction coefficient, obtaining the gray data of the current film and the corresponding driving voltage, and correcting the gray value point by point by using the correction coefficient, and based on the corrected dose-gray curve, converting into a dose value, and finally generating a dose distribution diagram. According to the invention, through real-time monitoring and dynamic correction of scanning voltage fluctuation, the accuracy of dose measurement is significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of radiation measurement, in particular to a full central dose verification method based on EBT3 no-wash film. BACKGROUND

[0002] In a Chinese patent with the patent publication number CN118131294A, a gamma radiation irradiation dose measurement method based on machine vision is disclosed. In the scheme, the relationship between the irradiation intensity received by the camera and the irradiation noise caused by the camera image gamma rays is analyzed by numerical statistical method, and the irradiation intensity is obtained, so as to infer the radiation dose, which embodies the technical idea of using image features to deduce the dose.

[0003] At the same time, the no-wash radiochromic film (such as EBT3) gradually becomes an important tool for dose verification due to its high spatial resolution, direct digitization characteristics and fast analysis advantages. It can accurately reflect the influence of multi-leaf collimator (MLC) dynamic intensity modulation, ray scattering and tissue non-uniformity by directly scanning the two-dimensional dose distribution after irradiation. When using radiochromic film for dose measurement, net optical density (netOD) calibration is needed to eliminate systematic bias introduced by scanner hardware characteristics and scanning environment factors, but this method is based on the assumption that the light source intensity is completely consistent when scanning the background and exposing the film. When the light source intensity changes dynamically, the error cannot be effectively compensated.

[0004] In addition, the reference film calibration method, spatial non-uniformity interpolation correction method and other methods also have their own limitations. For example, the reference film calibration method requires the preparation of high-precision reference film, which is complex to operate and has high cost; the spatial non-uniformity interpolation correction method requires a high distribution and quantity of calibration points, and its application is limited in complex scenarios. Therefore, there is an urgent need for a technical solution that can effectively compensate for the brightness dynamic change of the scanning instrument and improve the digital dose verification accuracy of the radiochromic film. SUMMARY

[0005] The purpose of the present application is to provide a full central dose verification method based on EBT3 no-wash film, which solves the following technical problems: There is an urgent need for a technical solution that can effectively compensate for the brightness dynamic change of the scanning instrument and improve the digital dose verification accuracy of the radiochromic film.

[0006] The purpose of the present application can be achieved by the following technical solution: A full central dose verification method based on EBT3 no-wash film, comprising the following steps: S1, continuously collecting the same irradiated radiochromic film to obtain the gray scale data sequence of each collection and the corresponding scanning device driving voltage sequence; S2, establishing a response function model between the driving voltage and the gray response according to the driving voltage value of each acquisition time and the mean value of the corresponding gray data; S3, determining a target voltage in advance, and determining a correction coefficient corresponding to each driving voltage value based on the target voltage and the response function model; S4, correcting a preset dose-gray curve graph according to the correction coefficient, to obtain a corrected dose-gray curve graph; S5, acquiring gray data of a current radiochromic film and driving voltage at the time of acquisition, and determining a gray correction coefficient corresponding to the driving voltage, for any data point in the gray graph, multiplying the gray data of the data point by the gray correction coefficient to obtain corrected gray data; S6, substituting the corrected gray data into the corrected dose-gray curve to obtain the dose value at the data point, and collecting the dose values at all data points to generate a final dose distribution graph.

[0007] As a further scheme of the present application: in S4, the specific acquisition process of the preset dose-gray curve graph is: S11, labeling information and dose information on multiple target radiochromic films; S12, irradiating multiple target radiochromic films based on the dose information of each target radiochromic film; S13, scanning the target radiochromic film after irradiation and acquiring the driving voltage of the scanning device to obtain the corresponding gray data under the driving voltage; S14, calculating the mean value of the gray data, pairing the corresponding dose information with the calculated mean value of the gray data to generate a discrete data point set, and establishing a dose-gray curve graph based on the discrete data point set.

[0008] As a further scheme of the present application: in S3, the specific determination process of the target voltage is: A plurality of film groups with different predetermined dose levels are acquired, the film groups are scanned at several different voltages respectively, and the corresponding optical density values of each film are measured, a curve of optical density value changing with voltage is generated according to each predetermined dose level and the corresponding optical density value, the change rate of optical density value in different voltage intervals is calculated, the voltage interval in which the change rate of optical density value tends to be the smallest is identified, and the mean value of the voltage interval is selected as the target voltage.

[0009] As a further scheme of the present application: in S3, the acquisition process of the correction coefficient is: The first gray mean theoretical value corresponding to the target voltage is determined based on a response function model, the second gray mean theoretical value is obtained by the response function model for each driving voltage value, and the first gray mean theoretical value and the second gray mean theoretical value are subjected to ratio operation, so as to obtain the gray correction coefficient corresponding to each voltage value.

[0010] As a further scheme of the present application, the specific process of correcting the preset dose-gray curve is as follows in S4: For each dose-gray data point of the preset dose-gray curve, the gray value of the data point is multiplied by the gray correction coefficient corresponding to the voltage value at the acquisition time of the data point, to obtain the corrected gray data; the dose value is paired with the corrected gray data point to generate a corrected dose-gray curve.

[0011] As a further scheme of the present application, if there are multiple voltage intervals corresponding to the same and minimum optical density value change rate, the mean voltage of each interval is taken as the test voltage, and the multiple radiocolorimetric films after irradiation are scanned under each test voltage, the standard deviation of the optical density value corresponding to each test voltage is calculated, and the test voltage with the minimum standard deviation is selected as the target voltage.

[0012] As a further scheme of the present application, S6 further includes obtaining a verification plan dose distribution map, and performing image registration based on the final dose map and the verification plan dose distribution map to obtain a dose passing value, and if the dose passing value is greater than or equal to the preset passing value threshold, the dose is determined to be qualified.

[0013] As a further scheme of the present application, the specific calculation process of the dose passing value is as follows: The feature points in the dose map and the plan dose distribution map are extracted, the feature points include field boundary points, dose extreme points and anatomical structure identification points; the spatial transformation parameters including translation, rotation angle, scaling ratio and shear factor are calculated according to the corresponding relationship of the feature points; the coordinate transformation is performed on the dose map based on the spatial transformation parameters, so that the dose map and the plan dose distribution map are in the same coordinate system. For all pixel points in the dose map, the dose value corresponding to each pixel point is identified, for pixel point i, the planned dose value at the same position in the planned dose distribution map is obtained, the difference between the planned dose value and the dose value of pixel point i is calculated to obtain the dose difference value D, the spatial distance d of pixel point i to the isodose line closest to its dose value in the planned dose distribution map is calculated, and the error value of the pixel point i is calculated based on the spatial distance d and the dose difference value D, so as to obtain the error value corresponding to all pixel points, the pixel points with error values less than the preset error threshold are marked as qualified pixel points, and the ratio of the qualified pixel points to the total pixel points in the dose map is calculated as the dose passing value.

[0014] The beneficial effects of the present application are: 1) The present application can determine the voltage interval with relatively stable light source intensity by obtaining film groups with different predetermined dose levels, scanning at several different voltages and generating a curve of optical density versus voltage, calculating the rate of change of optical density value in different voltage intervals, identifying the voltage interval with the minimum rate of change of optical density value and selecting the mean value as the target voltage, so that the scanning is carried out at the target voltage, thereby reducing the influence of light source intensity fluctuation on subsequent dose measurement from the source, breaking the dependence of traditional methods on the complete consistency of light source intensity when scanning the background and exposing the film, and improving the stability of dose measurement.

[0015] 2) Based on the determined target voltage and the generated gray scale mean value versus voltage response function model, the gray scale correction coefficient corresponding to each point voltage value is determined, and the pixel gray scale value of the current gray scale image is corrected. This operation can track the dynamic changes of light source intensity in the scanning process in real time, accurately compensate the deviation of pixel gray scale value caused by light source intensity fluctuation through the correction coefficient, so that the corrected gray scale value can more truly reflect the actual irradiation of the radiochromic film, solve the problem that the error cannot be effectively compensated when the light source intensity changes dynamically in the traditional method, and provide protection for the accurate conversion of subsequent dose map.

[0016] 3) The present application eliminates the influence of light source intensity fluctuation by determining the target voltage and correcting the actual obtained dose value, without the need to prepare high-precision reference films as in the reference film calibration method, avoiding the problems of complex operation and high cost, and overcoming the limitation of high requirement for the distribution and number of calibration points in spatial non-uniformity interpolation correction. This method simplifies the whole central dose verification process, improves the efficiency and reliability of dose verification, and makes it better adapt to the strict requirements of complex technologies such as intensity modulated radiotherapy on dose verification accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0017] The present application will be further described below with reference to the accompanying drawings.

[0018] Figure 1This is a flow chart of a method for verifying total central nervous system dose based on the wash-free film EBT3 according to the present invention. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0020] See also Figure 1 As shown, the present invention is a full central dose verification method based on the wash-free film EBT3, comprising the following steps: S1, continuously collecting data from the same irradiated radiochromatographic film to obtain a grayscale data sequence and a corresponding scanning device driving voltage sequence for each collection; S2, establishing a response function model between the driving voltage and the grayscale response according to the driving voltage value at each acquisition moment and the mean value of the corresponding grayscale data; S3, predetermining a target voltage, and determining a correction coefficient corresponding to each driving voltage value based on the target voltage and the response function model; S4, correcting the preset dose-grayscale curve according to the correction coefficient to obtain a corrected dose-grayscale curve; S5, obtaining the grayscale data of the current radiochromatographic film and the driving voltage during acquisition, and determining a grayscale correction coefficient corresponding to the driving voltage. For any data point in the grayscale image, multiplying the grayscale data of the data point by the grayscale correction coefficient to obtain corrected grayscale data; S6, substituting the corrected grayscale data into the correction dose-grayscale curve to obtain the dose value at the data point, and collecting the dose values ​​at all data points to generate a final dose distribution map.

[0021] 1) The present invention obtains film sets with different predetermined dose levels, scans them at several different voltages, generates curves showing the optical density changing with voltage, calculates the rate of change of optical density values ​​within different voltage intervals, identifies the voltage interval where the rate of change of optical density values ​​tends to be minimum, and selects its mean as the target voltage. This allows the determination of a voltage interval in which the light source intensity is relatively stable, allowing scanning to be performed at this target voltage. This reduces the impact of light source intensity fluctuations on subsequent dose measurements from the source, breaks the traditional method's reliance on the light source intensity being completely consistent when scanning the background and exposing the film, and improves the stability of dose measurement.

[0022] 2) Based on the determined target voltage and the generated grayscale mean voltage response function model, the grayscale correction coefficient corresponding to each voltage point is determined, and the pixel grayscale values ​​of the current grayscale image are corrected. This operation can track the dynamic changes in light source intensity during the scanning process in real time. The correction coefficient accurately compensates for the pixel grayscale value deviation caused by light source intensity fluctuations, so that the corrected grayscale value can more accurately reflect the actual irradiation of the radiation chromatography film. This solves the problem of traditional methods that cannot effectively compensate for errors caused by dynamic changes in light source intensity, and provides a guarantee for the accurate conversion of subsequent dose maps.

[0023] 3) This method eliminates the effects of light source intensity fluctuations by determining a target voltage and correcting the actual dose value. This eliminates the need for high-precision reference film preparation, as required by reference film calibration methods. This avoids the complex and costly operation and overcomes the limitations of spatial non-uniformity interpolation correction, which requires a high number and distribution of calibration points. This method simplifies the full-center dose verification process, improving its efficiency and reliability, making it more adaptable to the stringent dose verification accuracy requirements of complex techniques such as intensity-modulated radiotherapy.

[0024] In a preferred embodiment of the present invention, in S4, the specific process of obtaining the preset dose-grayscale curve diagram is as follows: S11, annotating label information and dose information for multiple target radiochromatographic films; S12, irradiating a plurality of target radiation chromatographic films based on the dose information of each target radiation chromatographic film; S13, scanning the irradiated target radiation chromatographic film and simultaneously acquiring a driving voltage of a scanning device to obtain grayscale data corresponding to the driving voltage; S14, calculating the mean of the grayscale data, pairing the corresponding dose information with the calculated mean of the grayscale data, generating a discrete data point set, and establishing a dose-grayscale curve based on the discrete data point set.

[0025] First, multiple target radiation chromatography films are uniquely identified and dose-labeled, for example, by using a marker pen to clearly write the number on the edge of each film and record its preset absorbed dose value. This step ensures that each film has a distinguishable identity and clear dose attribution, laying the foundation for the subsequent establishment of an accurate dose-grayscale correspondence; then, based on the dose information marked on each film, it is accurately irradiated through a radiation source (such as a medical linear accelerator), and the radiation beam parameters are controlled so that the actual absorbed dose value of each film is consistent with the preset value, thereby ensuring that the film response truly reflects the expected dose level; after irradiation is completed, each processed radiation chromatography film is scanned using a film digitizer under certain scanning conditions, and the scan is simultaneously monitored and recorded. The driving voltage of the device light source is used to obtain the overall grayscale response data of the film under this voltage. In this step, the physical response of the film is converted into a quantifiable digital signal using a scanning device, and the working status during scanning is recorded to eliminate errors introduced by fluctuations in external factors. For the grayscale data obtained from scanning each film, the overall grayscale average value is calculated after eliminating invalid and edge areas. The calculated grayscale average value is paired with the preset dose value corresponding to the film to form the original data point. After collecting the paired data of all films, the fitting method is used to establish the corresponding curve between dose and grayscale value. Characterizing the overall response level by the grayscale mean can reduce the interference of local non-uniformity, and data fitting can reveal the inherent law between dose and grayscale, providing a conversion basis for subsequent actual measurements.

[0026] Unique identification and dose labeling can effectively distinguish different films and clearly define their target doses, avoiding confusion and misoperation, and providing a basis for subsequent data correlation. Precise irradiation based on the labeled dose ensures that the dose received by each film is accurately known, establishing a true and reliable correspondence between film response and dose. Synchronously recording the drive voltage during scanning helps monitor and compensate for the instability of the scanning system itself, improving data consistency and repeatability. Calculating the overall grayscale mean and performing data fitting can effectively reduce the impact of random errors and local variations on the results, thereby establishing a stable and accurate dose-grayscale conversion curve. This method ultimately provides a key quantitative conversion foundation for the entire verification scheme, making it possible to reverse-infer dose distribution from grayscale data, significantly improving the accuracy and reliability of dose verification, and providing a solid guarantee for the comprehensive evaluation of the execution quality of radiotherapy plans.

[0027] In another preferred embodiment of the present invention, in step S3, the specific process of determining the target voltage is as follows: The film set with different predetermined dose levels is scanned at different voltages to obtain the corresponding optical density values of the films, a curve of the optical density values changing with the voltage is generated according to the predetermined dose levels and the corresponding optical density values, the change rate of the optical density values in different voltage intervals is calculated, the voltage interval in which the change rate tends to be minimum is identified, and the average value in the voltage interval is selected as the target voltage.

[0028] In actual operation, first, five radiochromic films with different predetermined dose levels are obtained to form a film set, for example, labeled as A, B, C, D, and E, and the corresponding predetermined dose levels are 5 Gy, 10 Gy, 15 Gy, 20 Gy, and 25 Gy, respectively. Then, the film set is scanned at different voltages, for example, four different voltage values of 15 W, 20 W, 25 W, and 30 W are selected. During each scanning, the film set is placed in the scanner to ensure consistency of the scanning environment, and then the corresponding optical density values of each film at each voltage are measured by using professional optical density measurement software or equipment, for example, the optical density of film A at 15 W is recorded as OD1, the optical density at 20 W is recorded as OD2, and so on. Subsequently, a curve of the optical density values changing with the voltage is generated by using drawing software according to the predetermined dose levels and the corresponding optical density values at different voltages, for example, the voltage is taken as the horizontal coordinate and the optical density value is taken as the vertical coordinate, and the curves for films A to E are drawn. Then, the change rate of the optical density values in different voltage intervals is calculated by using a mathematical calculation method, for example, the voltage range is divided into intervals of 15-20 W, 20-25 W, and 25-30 W, the slope of the optical density value changing with the voltage in each interval is calculated as the change rate, and then the voltage interval in which the change rate tends to be minimum is identified. Assuming that it is found through calculation that the change rate of the optical density of each curve in the interval of 20-25 W is minimum, finally, the average value in the voltage interval is selected as the target voltage.

[0029] Because different voltages can affect the stability of the light source of the scanner, and then cause fluctuations in the measurement of the optical density values of the films. By obtaining the optical density values of the films at different dose levels at multiple voltages and drawing curves, the trend of the change of the optical density values with the voltage can be directly observed, and the interval in which the change rate is minimum is found by calculating the change rates in different voltage intervals, which means that in this voltage interval, the light source intensity is relatively stable, and the optical density value is less affected by the voltage fluctuations. Selecting the average value in this interval as the target voltage can make the subsequent scanning operation be performed under the condition of high light source stability, thereby reducing the optical density measurement error caused by the fluctuation of the light source intensity, laying a reliable foundation for the subsequent establishment of the dose-gray scale curve graph based on the target voltage and the correction of the gray scale image, and ensuring that the final radiochromic film dose graph can accurately reflect the actual irradiation dose, realizing the accurate verification of the whole central dose, and guaranteeing the accuracy and reliability of the implementation of the radiotherapy plan.

[0030] In another preferred case of the embodiment, in the S3, the process of obtaining the correction coefficient is: The first gray mean theoretical value corresponding to the target voltage is determined based on the response function model, the second gray mean theoretical value is obtained for each measured voltage point through the response function model, and the first gray mean theoretical value and the second gray mean theoretical value are subjected to ratio operation, so as to obtain the gray correction coefficient corresponding to each voltage value.

[0031] Because in the scanning process, the voltage of the light source can fluctuate, the gray value of the collected gray image is affected. By determining the correction coefficient based on the response function model, the gray mean value under the actual collection voltage can be converted into the theoretical gray mean value under the target voltage, so as to compensate for the influence of the light source voltage fluctuation on the gray value. Thus, the error caused by the light source intensity fluctuation is eliminated, the corrected gray image can more accurately reflect the actual received irradiation dose of the radiochromic film, and thus the conversion of the gray image into a dose map is more accurate, and the reliability of the dose verification result can be ensured, thereby providing strong support for the correct implementation of the radiotherapy plan.

[0032] In another preferred case of the embodiment, in the S4, the specific process of correcting the preset dose-gray curve is: For each dose-gray data point of the preset dose-gray curve, the gray value of the data point is multiplied by the gray correction coefficient corresponding to the voltage value at the collection time of the data point, to obtain the corrected gray data; the dose value is paired with the corrected gray data point, to generate a corrected dose-gray curve.

[0033] First, an original dose-gray curve generated by pre-experimental calibration is obtained, and the curve is composed of a series of discrete dose values and corresponding gray value data points; for each data point in the curve, the driving voltage value of the scanning device light source at the scanning time corresponding to the gray value of the data point is queried, and then the gray correction coefficient corresponding to the voltage value is obtained according to the established voltage-gray response relationship model; for example, the driving voltage at the collection time of a data point is 5.0V, and the correction coefficient at the voltage is 1.05, which is obtained by querying; the original gray value is multiplied by the coefficient to obtain the corrected gray value; the above operation is performed on all data points on the original curve, that is, the gray value is recalibrated one by one; finally, each dose value is paired with the corrected new gray value to form a new data point set, and a corrected dose-gray curve subjected to system error compensation is generated based on the new data point set.

[0034] The reason for performing point-by-point voltage-driven grayscale correction on the preset curve is that during the establishment of the original dose-grayscale relationship, the driving voltage of the scanner light source may fluctuate, causing the recorded grayscale value to be interfered with by non-dose factors and unable to fully and truly reflect the physical correspondence between dose and film response; by tracing the acquisition voltage of each grayscale data point and correcting it using a correction coefficient that reflects the voltage-grayscale dependence, the error caused by the instability of the scanning system itself can be effectively eliminated, so that the corrected curve can more accurately reflect the essential law between dose and grayscale; this approach improves the reliability and accuracy of the dose-grayscale conversion relationship, reduces systematic errors from the source of the data source, and provides a more reliable mathematical model basis for the subsequent conversion of the grayscale data of the film to be tested into dose distribution, thereby ensuring the repeatability and accuracy of the full-center dose verification results, and ultimately supporting the effectiveness and safety verification of the radiotherapy plan at the execution level.

[0035] In another preferred situation of this embodiment, if there are multiple voltage intervals corresponding to the same optical density value change rate and all are minimum values, the average value of the voltage in each interval is used as the test voltage, and multiple irradiated radiation chromatography films are scanned at each test voltage, and the standard deviation of the optical density value corresponding to each test voltage is calculated, and the test voltage with the smallest standard deviation is selected as the target voltage.

[0036] If there are multiple voltage intervals with the same optical density value change rate and all of them are minimum values, the midpoint voltage values ​​of these voltage intervals are first calculated as candidate test voltages. For example, when the change rates of the 15-20V and 25-30V intervals are the same and the lowest, two test voltages of 17.5V and 27.5V are calculated respectively; then, at each test voltage, multiple radiochromatographic films irradiated with the same known dose are used to perform repeated scanning measurements to obtain multiple sets of optical density readings. Then, the multiple optical density values ​​measured by all films at each test voltage are statistically analyzed to calculate their standard deviations. The size of the standard deviation reflects the degree of discreteness of multiple measurement results at this voltage; finally, the test voltage with the smallest standard deviation is selected as the final target voltage. For example, if the standard deviation value is smaller at 17.5V, it is determined to be the target voltage.

[0037] The reason for introducing repeated scanning and calculating the standard deviation for secondary screening when the same rate of change cannot be distinguished is that the rate of change of optical density value can only measure the sensitivity of voltage fluctuation to reading, but cannot directly reflect the repeatability and stability of the measurement itself under the voltage. By actually repeating the scanning under the candidate voltage and calculating the standard deviation of the optical density value, it can be objectively evaluated which voltage condition the output of the scanning system is the most stable and least affected by random errors. Selecting the voltage with the smallest standard deviation as the target voltage means that all subsequent scanning and measurement will be carried out under the most stable and lowest noise condition of the system, which maximally reduces the random fluctuations introduced by the measurement instrument itself from the source, provides essential stability guarantee for the subsequent accurate establishment of dose-gray scale curve and accurate dose conversion of the measured film, and finally ensures the high reliability and consistency of the full central dose verification result, meeting the strict requirements of radiation therapy for dose precision control.

[0038] In another preferred case of the embodiment, the S6 further includes obtaining a verification plan dose distribution map, and performing image registration based on the final dose map and the verification plan dose distribution map to obtain a dose passing value. If the dose passing value is greater than or equal to the preset passing value threshold, it is determined that the dose is qualified.

[0039] First, feature points with clear physical or geometric meaning are extracted from the two images, such as the corner points of the field, the center points of high or low dose values, etc. The spatial correspondence between the two images is established through these stable and identifiable features. Then, according to the correspondence of these feature points, a set of transformation parameters is calculated using a spatial transformation algorithm. The parameters usually include translation distance, rotation angle, scaling ratio, etc. The coordinates of each pixel point in the final dose map are mathematically transformed using this set of parameters, so that they are completely aligned in space with the plan dose distribution map, thereby eliminating the position, angle and scale differences between the images caused by physical factors such as patient positioning and scanning placement, providing a unified spatial reference for subsequent accurate dose comparison. After registration is completed, the planned dose value of each pixel point in the dose map is read at the corresponding position in the plan dose distribution map, the dose difference between them is calculated, and the spatial distance of the pixel point dose value from the nearest isodose line in the plan map is calculated. The dose deviation and spatial distance deviation are combined to form a comprehensive error index. The comprehensive error of all pixel points in the image is calculated, and the pixel points with an error lower than the preset tolerance threshold are determined as qualified points. The final dose passing value is the proportion of qualified pixel points to total pixel points. If the proportion is greater than or equal to the preset passing threshold, it is determined that the dose verification is qualified.

[0040] The reason is that in the actual clinical environment, there is inevitably a small spatial displacement, rotation or scaling between the actual dose distribution measured by radiochromic film and the planned dose distribution calculated by the treatment planning system. If these geometric mismatches are not corrected, they will directly lead to serious misjudgment when comparing doses. Image registration by extracting stable features can accurately eliminate these geometric deviations and ensure that each pixel point is compared at the same anatomical location, which is the primary prerequisite for accurate dose verification. The use of a comprehensive error index combining dose deviation and spatial distance for pass rate calculation is because a single dose difference is sometimes insufficient to fully reflect the clinical acceptability of the dose distribution. For example, in the high dose gradient area, even a small spatial shift can result in a large dose difference. The comprehensive criterion can more scientifically and clinically evaluate the accuracy of dose execution.

[0041] In another preferred case of the embodiment, the specific calculation process of the dose pass value is as follows: Extracting feature points in the dose map and the planned dose distribution, the feature points including field boundary points, dose extreme points and anatomical structure identification points; calculating spatial transformation parameters according to the correspondence of the feature points, the spatial transformation parameters including translation, rotation angle, scaling ratio and shear factor; performing coordinate transformation on the dose map based on the spatial transformation parameters, so that the dose map and the planned dose distribution are in the same coordinate system; For all pixel points in the dose map, identifying the dose value corresponding to each pixel point, for pixel point i, obtaining the planned dose value at the same position in the planned dose distribution, calculating the dose difference value D between the planned dose value and the dose value of pixel point i; calculating the spatial distance d of pixel point i to the isodose line closest to its dose value in the planned dose distribution, calculating the error value of pixel point i based on the spatial distance d and the dose difference value D, thereby obtaining the error values corresponding to all pixel points, marking the pixel points with error values less than the preset error threshold as qualified pixel points, and calculating the ratio of qualified pixel points to total pixel points in the dose map as the dose pass value.

[0042] The specific calculation process of the dose pass value is as follows: ; Wherein, Hi is the error value corresponding to the i-th pixel point, Delta D is the preset dose tolerance, Delta d is the preset spatial distance tolerance, Di is the dose difference value D corresponding to the i-th pixel point, and di is the spatial difference value d corresponding to the i-th pixel point.

[0043] In actual operation, first, the dose map and the planned dose distribution map are processed by means of an image processing software (such as MATLAB), the profile of the radiation field region in the dose map is identified by an edge detection algorithm (such as Canny operator), so as to extract the field boundary points, for example, the edge inflection point of the skull base field in the dose map; the highest and lowest dose points are determined by traversing the image pixel value, and the dose extreme points are extracted, such as the lowest dose point of the spinal cord region and the highest dose point of the tumor target region; according to the preset anatomical structure template, anatomical structure marker points such as cervical vertebrae, brain ventricles and the like are marked in the image as anatomical structure marker points. Then, according to the deformation degree of the two images, a transformation model is selected, if there is only linear transformation such as translation, rotation and scaling between the images, an affine transformation model is adopted, if there is nonlinear deformation, an elastic transformation model is selected, taking the affine transformation model as an example, the corresponding relationship between the feature points is calculated by the least square method, and the spatial transformation parameters are solved, for example, the translation amount is (5 pixels, -3 pixels), the rotation angle is 5 degrees, the scaling ratio is 1.02, and the shear factor is 0.01. Finally, the solved spatial transformation parameters are applied to the dose map, and the coordinates of each pixel point in the dose map are calculated, such as the original coordinates of a pixel (x, y), and the new coordinates (x', y') are obtained after translation, rotation, scaling and shearing, so that the dose map and the planned dose distribution map are in the same coordinate system, the image registration is completed, for example, the position of the spinal cord in the dose map is accurately overlapped with the position of the spinal cord in the planning map.

[0044] Because the dose map and the planned dose distribution map may have spatial position deviation due to factors such as scanning angle and patient positioning, by extracting representative feature points such as the field boundary points, the dose extreme points and the anatomical structure marker points, the spatial correspondence of the two images can be accurately captured, the spatial transformation parameters are calculated by using the affine transformation model or the elastic transformation model, and the coordinate transformation is performed, so that the spatial differences such as translation, rotation, scaling and shearing between the images can be eliminated, and the two images are in the same coordinate system. The advantage of this is to ensure that when the subsequent dose pass value is calculated, the actual dose distribution and the planned dose distribution can be accurately compared on the same spatial scale, to avoid the dose deviation misjudgment caused by spatial misalignment, to realize the high-precision spatial alignment of the dose map and the planned dose distribution map, to lay a foundation for accurately calculating the dose pass value and judging whether the dose is qualified, and for the final purpose of the scheme, to ensure the accuracy of the whole central dose verification, to make the comparison between the dose distribution in the radiotherapy plan and the actual execution more reliable, and to provide strong support for the precise radiotherapy of tumors.

[0045] In actual operation, first find the center pixel point of the dose map, such as by calculating the middle position of the number of rows and columns of the image to determine the point, and establish a rectangular coordinate system with the point as the origin, the horizontal axis and the vertical axis corresponding to the horizontal and vertical directions of the image. Then, for each pixel point in the gray-scale image, generate its corresponding coordinates (x, y) according to the established coordinate system, for example, a certain pixel point is located at the 10th position to the right of the origin and the 5th position above, and its coordinates are (10, 5), and identify the dose value corresponding to the pixel point from the previously generated radiochromic film dose map, such as the dose value of the pixel point is 20Gy. Next, set the dose tolerance DeltaD and the spatial distance tolerance Deltad according to the requirements of clinical radiotherapy, such as setting the corresponding reasonable tolerance range according to the conventional standard. For each pixel i (xi, yi), find the nearest isodose line in the planned dose distribution map, calculate the spatial distance d of the pixel to the isodose line, such as calculating the distance to be 1.5 unit lengths through the geometric distance formula. Then, based on the distance d and the set tolerance, calculate the error value of each pixel point, such as comparing the size of the distance d and the spatial distance tolerance Deltad, and combining the dose value and the difference of the planned dose. If the error value is less than the preset threshold, mark the pixel point as a qualified pixel point, such as the distance d of a certain pixel point is less than the spatial distance tolerance and the dose difference is also within the dose tolerance, which is marked as qualified. Finally, count the number of all qualified pixel points in the dose map, calculate the ratio of the number of qualified pixel points to the total number of pixel points, and mark this ratio as the deviation value, such as the qualified pixel points are 900 and the total pixel points are 1000, the ratio is 0.9.

[0046] The center pixel point of the dose map is taken as the origin of the rectangular coordinate system, which can provide a unified spatial reference basis for the dose map and the planned dose distribution map, and facilitate subsequent comparison and analysis of the spatial position and dose value of each pixel point. The coordinates of all pixel points are generated and the corresponding dose values are identified in order to realize fine and quantitative evaluation of the dose distribution. The dose tolerance and spatial distance tolerance are set in order to determine the standard for judging whether the dose is qualified and to ensure that the evaluation has rules to follow. The distance from the pixel point to the nearest isodose line is calculated and the error value is calculated based on this, which can comprehensively evaluate the dose accuracy of each pixel point from the two dimensions of spatial position and dose deviation. The pixel points with error values less than the preset threshold are marked as qualified and the proportion is counted, which can intuitively reflect the degree of conformity between the actual dose distribution and the planned dose distribution in a quantitative way. The advantage of this is that the accuracy of the actual dose execution in the whole central dose verification can be objectively and comprehensively evaluated, and a quantitative basis is provided for judging whether the radiotherapy plan is accurately implemented. The purpose is to obtain reliable dose passing values through a series of rigorous calculation and statistical steps, so as to determine whether the dose is qualified. It can ensure that the results of the whole central dose verification are accurate and reliable, and provide important protection for the precise irradiation of the tumor target area and the effective protection of the normal tissue in the process of radiotherapy, and help to achieve the goal of precise radiotherapy.

[0047] The above describes one embodiment of the present application in detail, but the content described is only the preferred embodiment of the present application and cannot be considered to limit the implementation range of the present application. Any equivalent changes and improvements made according to the scope of the present application should still belong to the patent coverage range of the present application.

Claims

1. A method for verifying the total central nervous system dose based on the wash-free film EBT3, characterized in that: The following steps are involved: S1, continuously collecting data from the same irradiated radiochromatographic film to obtain a grayscale data sequence and a corresponding scanning device driving voltage sequence for each collection; S2, establishing a response function model between the driving voltage and the grayscale response according to the driving voltage value at each acquisition moment and the mean value of the corresponding grayscale data; S3, predetermining a target voltage, and determining a correction coefficient corresponding to each driving voltage value based on the target voltage and the response function model; S4, correcting the preset dose-grayscale curve according to the correction coefficient to obtain a corrected dose-grayscale curve; S5, obtaining the grayscale data of the current radiochromatographic film and the driving voltage during acquisition, and determining a grayscale correction coefficient corresponding to the driving voltage. For any data point in the grayscale image, multiplying the grayscale data of the data point by the grayscale correction coefficient to obtain corrected grayscale data; S6, substituting the corrected grayscale data into the correction dose-grayscale curve to obtain the dose value at the data point, and collecting the dose values ​​at all data points to generate a final dose distribution map.

2. A method for verifying total central nervous system dose based on EBT3 film according to claim 1, characterized in that: In S4, the specific process of obtaining the preset dose-grayscale curve is as follows: S11, annotating label information and dose information for multiple target radiochromatographic films; S12, irradiating a plurality of target radiation chromatographic films based on the dose information of each target radiation chromatographic film; S13, scanning the irradiated target radiation chromatographic film and simultaneously acquiring a driving voltage of a scanning device to obtain grayscale data corresponding to the driving voltage; S14, calculating the mean of the grayscale data, pairing the corresponding dose information with the calculated mean of the grayscale data, generating a discrete data point set, and establishing a dose-grayscale curve based on the discrete data point set.

3. A method for verifying total central nervous system dose based on EBT3 film according to claim 2, characterized in that: In S3, the specific process of determining the target voltage is as follows: Obtain a set of multiple films with different predetermined dose levels, scan the film set separately at several different voltages and measure the optical density value corresponding to each film, generate a curve of optical density value versus voltage based on each predetermined dose level and its corresponding optical density value, calculate the rate of change of optical density values ​​in different voltage intervals, identify the voltage interval where the rate of change of optical density value tends to be minimum, and select the mean value of this voltage interval as the target voltage.

4. A method for verifying total central nervous system dose based on EBT3 film according to claim 3, characterized in that: In S3, the process of obtaining the correction coefficient is as follows: Based on the response function model, the first grayscale mean theoretical value corresponding to the target voltage is determined, and the second grayscale mean theoretical value is obtained for each driving voltage value through the response function model. The first grayscale mean theoretical value and the second grayscale mean theoretical value are ratio-operated to obtain the grayscale correction coefficient corresponding to each voltage value.

5. The method for verifying the total central nervous system dose based on the EBT3 film according to claim 2, characterized in that: In S4, the specific process of correcting the preset dose-grayscale curve is as follows: For each dose-grayscale data point of the preset dose-grayscale curve, multiply its grayscale value by the grayscale correction coefficient corresponding to the voltage value at the acquisition moment of the data point to obtain corrected grayscale data; The dose values ​​were paired with their corrected grayscale data points to generate a corrected dose-grayscale curve.

6. A method for verifying total central nervous system dose based on EBT3 film according to claim 3, characterized in that: If there are multiple voltage intervals with the same optical density value change rate and all of them are minimum values, then the voltage mean of each interval is used as the test voltage. Scan multiple irradiated radiochromatographic films at each test voltage, calculate the standard deviation of the optical density value corresponding to each test voltage, and select the test voltage with the smallest standard deviation as the target voltage.

7. The method for verifying the total central nervous system dose based on the EBT3 film according to claim 1, characterized in that: The S6 also includes obtaining a verification plan dose distribution map, and performing image registration based on the final dose map and the verification plan dose distribution map to obtain a dose pass value. If the dose pass value is greater than or equal to the preset pass value threshold, the dose is determined to be qualified.

8. A method for verifying total central nervous system dose based on EBT3 film according to claim 7, characterized in that: The specific calculation process of the dose passing value is: Extracting characteristic points from the dose map and the planned dose distribution map, the characteristic points including field boundary points, dose extreme points, and anatomical structure identification points; calculating spatial transformation parameters based on the correspondence between the characteristic points, the spatial transformation parameters including translation, rotation angle, scaling ratio, and shear factor; performing coordinate transformation on the dose map based on the spatial transformation parameters so that the dose map and the planned dose distribution map are in the same coordinate system; For all pixels in the dose map, identify the dose value corresponding to each pixel. For pixel i, obtain the planned dose value at the same position in the planned dose distribution map. Calculate the difference between the planned dose value and the dose value of pixel i to obtain the dose difference D. Calculate the spatial distance d between pixel point i and the isodose line closest to its dose value in the planned dose distribution map, calculate the error value of pixel point i based on the spatial distance d and the dose difference D, and thus obtain the error values ​​corresponding to all pixel points. Pixel points with error values ​​less than the preset error threshold are marked as qualified pixel points, and the ratio of qualified pixels to total pixels in the dose map is counted, and the ratio is used as the dose passing value.

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