CN111408073A - Method and system for calculating radiation radiation plane detector dose - Google Patents

Abstract

The invention discloses a method and a matching system for calculating the dose of a radiotherapy ray plane detector. Its contents include: calibrating the parameters of the depth deviation model of the measurement plane; receiving a three-dimensional patient external beam treatment plan from the radiotherapy treatment planning system (TPS) and measuring the depth position of the plane; according to the treatment head angle of each field and the depth of the measurement plane The deviation model calculates the depth deviation of the measurement plane of the field; calculates the dose distribution on the measurement plane after the depth position is shifted according to the treatment plan and the depth deviation of each field; The distributions are superimposed to produce a calibrated detector measuring the dose on the plane.

Description

Method and system for calculating radiation radiation plane detector dose

technical field

The invention relates to a method for calculating the dose of a radiation detector, in particular to a method and a system for calculating the dose of a radiotherapy ray plane detector.

Background technique

Contemporary radiotherapy techniques, such as conformal intensity-modulated radiotherapy (IMRT) and volumetric intensity-modulated radiotherapy (VMAT), require the control of the radiotherapy equipment to irradiate the patient's body containing the tumor or cancer from different angles in a complex manner, in order to achieve the best possible Improve the efficiency and safety of the treatment while reducing the damage to the surrounding human tissue. This makes radiation therapy planning increasingly complex and the importance of plan validation increasing.

When planning verification of a patient's radiotherapy plan, it is necessary to execute the corresponding verification plan on a specific water model, and use a radiotherapy radiation detector to obtain the radiation dose absorbed at the designated position. The expected absorbed dose to the detector can also be calculated using the radiotherapy device model and the radiotherapy plan. The accuracy of dose calculations for radiotherapy planning can generally be determined by comparing the above two measured and calculated doses. The principle of a planar detector is to use a detector array to measure the dose distribution on a specified plane. Each pixel detector in the array can be an ionization chamber (eg, MatriXX) or a semiconductor detector (eg, MapCHECK).

In clinical use, the researchers found that the measurement results of the planar detector were dependent on the angle of incidence of the beam. When the beam is directed perpendicular to the detector, the detector dose measurements are in good agreement with the model calculations. When the angle between the direction of the treatment head and the vertical direction increases, especially when it is close to 90 degrees, the deviation between the dose measurement value of the detector and the calculated value of the model can be very large, even close to 11%. Some researchers have tried to correct this bias by introducing a "correction field" in a phenomenological way. However, the resulting "correction field" exhibits sensitivity to changes in the incident angle at certain angles, and cannot be explicitly expressed as a function of equipment parameters and planning parameters. Therefore, planar detectors are often used for dose verification of 0-degree angle fields in actual clinical quality control work. In compound field verification (that is, each field is not rotated to 0 degrees, but is located at the original position set in the plan), physicists generally choose a non-planar detector with a special design (for example: ArcCHECK), so that In the design, the influence of the field angle on the plane detector is eliminated, but the cost is relatively expensive; or the high-precision film without angle dependence is selected for measurement, but the calibration and scanning process of the film are quite complicated and tedious.

At present, as a dose verification tool for radiotherapy planning, the planar detector lacks a method to correct the calculated dose of non-vertically incident rays on the detector to conform to the measured value of the detector based on its own structural characteristics. Such a method is helpful for composite field verification using planar detectors in planned verification work, reducing costs and improving quality control work efficiency compared to ArcCHECK and film.

SUMMARY OF THE INVENTION

This part is used to briefly introduce the content of the present invention, and for a detailed description, please refer to "Detailed Description of Embodiments". The contents here are not intended to limit the key elements, important features and claims of the present invention.

Based on the necessity of the dose calculation method of the radiotherapy ray plane detector mentioned above, the present invention proposes a method for calculating the dose of the radiotherapy ray plane detector based on the structural characteristics of the detector itself and considering the angle-dependent characteristics of each pixel detector. And the system makes it possible to use the plane detector for composite field verification in the plan verification work, thereby reducing the cost and improving the quality control work efficiency.

The present invention provides a method for calculating the plane dose of a radiotherapy ray plane detector. The method includes the following steps:

Step 1: Calibrate the parameters of the depth deviation model of the measurement plane;

Step 2: Receive a three-dimensional patient external beam treatment plan and measure the plane depth position from the radiation therapy treatment planning system (TPS);

Step 3: Calculate the depth deviation of the measurement plane of the field according to the treatment head angle of each field and the depth deviation model of the measurement plane;

Step 4: Calculate the dose distribution on the measurement plane after the depth position shift is calculated according to the treatment plan and the depth deviation of each field;

Step 5: Superimpose the dose distributions of each field on the offset measurement plane to generate the calibrated dose on the detector measurement plane.

In some embodiments, the depth deviation model can adopt the formula:

Among them, Δd is the position depth deviation, θ is the angle of the treatment head of the field, a and b are the semi-major axis length and the semi-minor axis length of the semi-major axis length of the semi-ellipse model of the effective measurement point trajectory of the detector pixel probe.

In some embodiments, the step 1 includes at least the following steps:

Step 1.1: Rotate the square field formed by the collimator by several angles around the isocenter;

Step 1.2: irradiate a fixed number of ray doses at each angle;

Step 1.3: Measure the plane dose distribution of each angle in the isocenter plane with the detector to be calibrated;

Step 1.4: Calculate the dose distribution of each angle field in the isocenter plane;

Step 1.5: Calculate the translation deviation Δx between the calculated dose distribution and the measured dose distribution in the isocenter plane of each angle field;

Step 1.6: Calculate the optimal fitting parameters a and b with the following formulas;

Among them, Δx is the translational deviation between the calculated dose distribution and the measured dose distribution, θ is the angle of the treatment head of the portal, and a and b are the half-short of the semi-major axis length of the semi-ellipse model of the effective measurement point trajectory of the detector pixel probe. Shaft length; the optimization goal is to minimize the mean square mean of the difference between the translation deviation Δx between the calculated dose distribution and the measured dose distribution in the isocenter plane of each angle field and the difference between the translation deviation obtained by the calculation formula in this step .

In some embodiments, the rays include but are not limited to: photon rays, electron rays, proton rays and heavy ion rays.

In some embodiments, the planar detectors include but are not limited to: ionization chamber matrix detectors and semiconductor matrix detectors.

In some embodiments, the radiotherapy dose calculation methods include but are not limited to: look-up table interpolation method, convolution stacking method and Monte Carlo method.

The present invention provides a system for calculating the plane dose of the radiotherapy ray plane detector with computer codes stored in a non-volatile storage medium, which can be used to calculate the plane dose of the radiotherapy ray plane detector. The system includes the following parts:

A detector calibration module is responsible for calibrating the parameters of the trajectory model of the effective measurement points of the pixel probe; a plane dose calculation module is responsible for receiving the patient external beam treatment plan from the radiation therapy treatment planning system (TPS) and measuring the plane depth position; The treatment head angle of the field and the depth deviation model of the measurement plane are used to calculate the depth deviation of the measurement plane of the field; the dose distribution on the measurement plane after the depth position shift is calculated according to the treatment plan and the depth deviation of each field; The dose distributions at the offset measurement planes of the portals are superimposed to generate the dose at the calibrated detector measurement plane. Wherein, data communication is performed between the detector calibration module and the plane dose calculation module through a data bus or a data network.

In some embodiments, the depth deviation model can adopt the formula:

Among them, Δd is the position depth deviation, θ is the angle of the treatment head of the field, a and b are the semi-major axis length and the semi-minor axis length of the semi-major axis length of the semi-ellipse model of the effective measurement point trajectory of the detector pixel probe.

In some embodiments, the step of calibrating the parameters of the trajectory model of the effective measurement point of the pixel probe includes at least the following steps:

Step 2.1: Rotate the square field formed by the collimator several angles around the isocenter;

Step 2.2: irradiate a fixed number of ray doses at each angle;

Step 2.3: Measure the plane dose distribution of each angle in the isocenter plane with the detector to be calibrated;

Step 2.4: Calculate the dose distribution of each angle field in the isocenter plane;

Step 2.5: Calculate the translation deviation Δx between the calculated dose distribution and the measured dose distribution in the isocenter plane of each angle field;

Step 2.6: Calculate the optimal fitting parameters a and b with the following formulas;

Among them, Δx is the translational deviation between the calculated dose distribution and the measured dose distribution, θ is the angle of the treatment head of the portal, and a and b are the half-short of the semi-major axis length of the semi-ellipse model of the effective measurement point trajectory of the detector pixel probe. Shaft length; the optimization goal is to minimize the mean square mean of the difference between the translation deviation Δx between the calculated dose distribution and the measured dose distribution in the isocenter plane of each angle field and the difference between the translation deviation obtained by the calculation formula in this step .

In some embodiments, the rays include but are not limited to: photon rays, electron rays, proton rays and heavy ion rays.

In some embodiments, the planar detectors include but are not limited to: ionization chamber matrix detectors and semiconductor matrix detectors.

In some embodiments, the radiotherapy dose calculation methods include but are not limited to: look-up table interpolation method, convolution stacking method and Monte Carlo method.

Description of drawings

The following schematic diagrams are used to describe the present invention more clearly in conjunction with the more detailed specific embodiments, rather than to limit the claims of the present invention.

FIG. 1 is a flow chart of the method for calculating the plane dose of the radiotherapy radiation plane detector according to the present invention.

FIG. 2 is a sub-flow diagram of the present invention for calibrating the parameters of the depth deviation model of the measurement plane.

FIG. 3 is a schematic diagram of a system according to an embodiment of the present invention.

FIG. 4 is a schematic diagram of the arrangement of the phantom and the planar detector when measuring the dose distribution in one embodiment of the present invention.

Figure 5 is a schematic diagram of the dependence of the plane detector on the angle of incidence of the radiation beam described by the depth deviation model of the present invention.

Figure 6 is a schematic diagram of the difference between the equivalent measured planar dose distribution and the measured planar dose distribution in one embodiment of the present invention.

FIG. 7 is a schematic diagram of the derivation of formulas 1, 2, 3, and 4 in an embodiment of the present invention.

Detailed ways

Below in conjunction with the accompanying drawings, a set of terms is used to describe the preferred embodiments of the present invention in detail, so as to facilitate those skilled in the art to understand the advantages and features of the present invention, so as to define the protection scope of the present invention more clearly.

The innovative concept encompassed by the present invention has various embodiments. Therefore, the detailed description of the preferred embodiments should not be used as the boundary of the claims of the present invention with respect to the innovative concept, but the description herein should be used to help those skilled in the art to understand the innovative concept contained in the present invention. . In addition, the size and relative size of the layers and parts of the objects in the schematic will be appropriately deformed to avoid overlapping.

Here, the description objects of a paragraph of description will be indicated in the schematic diagram in the form of reference numbers. However, in the schematic diagrams of the embodiments of the present invention, not all components are numbered. The reasons include: 1) the public information in the related field will not be described in detail here; 2) the parts that overlap with the context will not be described in detail.

In describing the present invention herein, "comprising" will be used to refer to objects encompassed by the present invention. Such citations are non-exhaustive if not expressly stated in the context, indicating that parts of the information are omitted from the description, and such omissions are not believed to affect the understanding of the methods of the invention by those skilled in the art.

The detailed description here will use some vocabulary with precedence to facilitate the listing of the objects that need to be described. These words should not be regarded as limitations on the composition and structure of the method of the present invention, but should only be regarded as temporarily added marks for the convenience of distinguishing the described content, and changing the order of the described content. The exchange of the two phrases "first item" and "second item" will not affect the description of the innovative concept of the present invention herein. Similarly, when the words "and/or" are used herein to connect a group of statements, no limitation is imposed on the sequential combination of the objects of the statements. Arbitrarily changing the order in which these objects are stated is acceptable.

Unless explicitly stated herein to give unique definitions to designated terms, the terms used in the detailed description are consistent with the usage of those skilled in the art to which this invention belongs. Furthermore, the description herein will use some commonly used vocabulary to describe the invention. If the reader finds that the ideal definition of these words, or the usage habits in informal situations, is inconsistent with the context, unless a clear definition is given, it should be considered that the use of these everyday words here has been based on The explanations in various general dictionaries have made adjustments to these words in line with the usage habits in the field.

"Radiation therapy" or "radiotherapy" refers to the use of a directional radiation therapy device to deliver a "radiation beam" of high-energy particles to an area of a patient's body occupied by cancer cells or tumors in order to create a certain amount of radiation absorption in the area doses, to directly damage the DNA of cells in that area, or indirectly by generating charged particles within the cells. Cells repair DNA damage, and when repair capacity is insufficient to restore DNA damage, cells stop dividing or die. But the process also causes damage to healthy cells in vital organs and anatomical structures surrounding the area. Therefore, one of the important parts of the radiation therapy planning process is to make accurate segmentation based on high-precision medical images, so as to ensure the avoidance of vital organs when planning radiation therapy, minimize the absorption meter formed in healthy tissue, and completely cover the whole target area in order to reduce the probability of recurrence.

"Radiation therapy planning" or "radiation therapy planning" is a step in the radiation therapy process that is designed by a group of professionals, including: radiation oncologists, radiation therapists, medical physicists, and medical dosimetrists A plan for a tumor patient to undergo external radiation therapy; the resulting treatment plan is called a "radiotherapy plan." Usually, the medical image of the patient needs to be processed to obtain a "segment", and then a radiation therapy plan is designed accordingly. "Segmentation" here refers to using a set of regions of interest to describe the correspondence between pixels in medical images and target regions, vital organs, and other human anatomical structures in the human body.

"Treatment Planning System" (Treatment Planning System, TPS) generally refers to computer software that can be used to rapidly assist in the design of radiation treatment plans. In this article, it specifically refers to a full-process radiation therapy planning system software developed by our company to help doctors design and evaluate radiation therapy plans.

"Dose verification of radiotherapy plan" refers to operating radiotherapy equipment to perform radiotherapy on the phantom according to the radiotherapy plan and simultaneously measuring the absorbed dose at the designated measurement point by using the dose measuring device; comparing the absorbed dose distribution thus measured with the expected dose proposed by the radiotherapy plan The distribution is compared, and the degree of agreement between the planned expected value of the dose at the measurement point and the actual measured value is calculated according to a certain standard (for example: 3%/3mm). Statistical results can be used to describe how well a radiotherapy device fits a model of that device.

An "ionization chamber" is a gas detector that detects ionizing radiation. When the detector is exposed to radiation, the radiation interacts with molecules in the gas, creating ion pairs consisting of an electron and a positive ion. These ions diffuse freely to the surrounding area. During diffusion, electrons and positive ions can recombine to form neutral molecules. However, if a DC polarizing voltage is applied to the collector and high-voltage electrodes that constitute the gas detector to form an electric field, then electrons and positive ions will be pulled to the positive and negative poles, respectively, and collected to form an electrical signal. In the field of radiotherapy, ionization chambers are used to measure the absorbed dose of radiation at a specified point.

"Planar detectors" can be used to measure the absorbed dose of radiation therapy radiation on a specified plane during the validation of radiation therapy plans, and are generally composed of two-dimensional detector lattices, including but not limited to: ionization chamber matrix detectors and semiconductor matrix detectors.

"Ion Chamber Matrix Detector"

A planar detector consisting of a two-dimensional ionization chamber lattice. Commonly used ion chamber matrix detector brands include: I’mRTMatriXX (IBA Dosimetry, Germany).

The embodiments of the present invention are mainly used to correct the measurement results according to the depth deviation model when using the plane detector to measure the radiation beam, so as to obtain accurate plane dose measurement data. In some embodiments, the software and hardware designed and manufactured according to the present invention can also be used to help doctors more effectively complete the quality verification of radiotherapy plans. In some embodiments, the present invention is used as part of a radiation therapy planning system (TPS) to process planar dose data and eliminate planar detectors due to their dependence on radiation beam incidence angles during radiation therapy planning quality verification. The deviation brought by the measurement data, so that the quality verification of the radiotherapy plan can be completed more accurately.

FIG. 1 is a flowchart 100 of the method for calculating the plane dose of the radiation therapy radiation plane detector according to the present invention. The figure illustrates the steps for calibrating the survey plane measurement data using the depth deviation model. The specific implementation steps include:

Begin at step 101.

At step 102, the parameters of the depth deviation model of the measurement plane are calibrated using the reference data.

At step 103, a three-dimensional patient external beam treatment plan is received from a radiation therapy treatment planning system (TPS) and a measured plane depth position.

In step 104, the depth deviation of the measurement plane of each field is calculated according to the angle of the treatment handpiece of each field and the depth deviation model of the measurement plane.

In step 105, the dose distribution on the measurement plane after the depth position shift is calculated according to the treatment plan and the depth deviation of each field.

In step 106, the dose distributions of each field on the shifted measurement plane are superimposed to generate the calibrated dose on the detector measurement plane.

End at step 107 .

In some embodiments, when calibrating the parameters of the depth deviation model of the measurement plane in step 102, the depth deviation in the depth deviation model can be expressed as Equation 1.

FIG. 2 is a sub-flow chart 200 of the present invention for calibrating the parameters of the depth deviation model of the measurement plane, which is used to illustrate that in step 102 of the flow chart 100 of the method for calculating the plane dose of the radiation radiation plane detector in FIG. 1, the depth deviation is calibrated A necessary step in the process of the parameters of the model. Necessary steps include:

Begin at step 201 .

At step 202, the collimator is set to a square field for modulating the radiation beam, and several angles of incidence are selected for the field around the isocenter.

In step 203, the radiation dose of a fixed number of machines is irradiated at each angle.

In step 204, when the accelerator irradiates the radiation dose specified in step 203 with the field and angle in step 202, the plane dose distribution of each angle is measured on the isocenter plane with the detector to be calibrated.

In step 205, a dose calculation function of a radiotherapy planning system is used to calculate the plane dose distribution of the isocenter plane based on the field and angle specified in step 202 and the number of machine hops specified in step 203.

In step 206, the translational deviation Δx between the calculated dose distribution and the measured dose distribution in the isocenter plane of each angular field is calculated.

In step 207, based on formula 2, the fitting parameters a and b are optimized with respect to the depth deviation model; the optimization goal is to minimize the translation deviation Δx between the calculated dose distribution and the measured dose distribution in the isocenter plane of each angle field and this Calculate the mean squared mean of the difference between the translation deviations obtained by the formula in the step.

End at step 208 .

In some embodiments, the field set in step 202 may be a rectangular field, for example, a field of 4 cm×10 cm. The angle selected in step 202 may be a set of equally spaced angles, for example: 0°, ±40°, ±80°, ±120°, ±160°. The planar detectors that can be calibrated in step 204 include but are not limited to: ionization chamber matrix detectors and semiconductor matrix detectors.

FIG. 3 is a schematic diagram of a system according to an embodiment of the present invention. In this system, the plane detector dose data processing system 303 takes the data generated by the plane detector 301 and the radiation therapy planning system (TPS) 302 as input and saves it to a storage device, and the user manipulates the system through the user interface 305, provides Enter and view processing results. The three devices exchange data over the local area network 314 . The components of the planar detector dose data processing system 303 are connected to each other through an internal bus 321 . The system manipulates storage device 306 under the control of processor 304 to read or save files, build processing engine 307 in memory, respond to operations from user interface 305 or display processing results on user interface 305 . Specific steps include:

Based on the same set of plans for calibration, the user uses the plane detector 301 to acquire a set of measurement data 315 of the dose distribution on the measurement plane, and the radiation therapy planning system (TPS) 302 to acquire a set of dose distributions on the same measurement plane. Calculate data 316 . The planar detector dose data processing system 303 acquires the measurement data 315 and the calculation data 316 to form a calibration data set 310 and saves it on the storage device 306 . The model parameter calibration module 313 reads the calibration data set 310 from the storage device 306 as input, optimizes and fits the parameters of the depth deviation model, and saves the optimized parameters as output to the model setting file 309 .

After calibration of the model parameters is complete, the user may use the planar detector dose data processing system 303 to process a set of dose distribution data 317 for calculation of a set of measured planar dose distribution data 320 and display on the user interface 305 . Specific steps include:

Planar detector dose data processing system 303 obtains a radiation therapy plan from radiation therapy planning system (TPS) 302, which plan includes dose distribution data 317 on a measurement plane. This data is stored on storage device 306 as dose distribution dataset 308 . The depth bias calculation module 312 loads a calibrated depth bias model through the input model settings file 309 . The dose distribution dataset 308 will be input to the dose calculation module and the corrected measured plane dose distribution 320 is calculated from the deviation depth deviation 319 generated by the depth deviation model calculation. The measurement plane dose distribution 320 is passed to the user interface 305 as a dose distribution corresponding to the user specified measurement plane depth value 318 and displayed.

Thus, the user can use the planar detector dose data processing system 303 to process the dose distribution data 317 contained in the radiation therapy plan, and output a calculated dose distribution 320 that can be compared with the actual measured dose. .

FIG. 4 is a schematic diagram of the arrangement of the phantom and the planar detector when measuring the dose distribution of normal incidence in one embodiment of the present invention. Among them, the upper layer of solid water 402, the plane detector 403 and the lower layer of solid water 404 are stacked horizontally. The distance from the light source 401 to the upper surface of the upper solid water 402 is represented as SSD. The distance from the light source 401 to the upper surface of the planar detector 403 is denoted as SSmD. The distance from the light source 401 to the measurement plane 406 is denoted SMeaD. The thickness of the upper layer of solid water 402 is denoted as Dwu, and the thickness of the lower layer of solid water 404 is denoted as Dw1. The distance between the detector upper surface 405 and the measurement plane 406 is denoted Dmea.

Figure 5 is a schematic diagram of the dependence of the plane detector on the angle of incidence of the radiation beam described by the depth deviation model of the present invention. The flat detector consists of a group of detector units arranged in a two-dimensional lattice. Each unit can be divided into two parts in structure: the absorption material 501, the pixel chamber 506; the lower surface of the absorption material 501 is in contact with the upper surface of the pixel chamber 506, and the contact surface is a part of the measurement plane 503; the default measurement point 502 is located at The geometric center of the contact part. In actual use, the incident angle of the beam can be divided into two cases: the beam 1 507 incident from the side of the absorbing material 501 of the measurement plane 503, the beam 2 508 incident from the side of the pixel chamber 506 of the measurement plane 503 . The equivalent measurement plane 504 is offset from the measurement plane 503 to the pixel chamber 506 side by a depth value due to the angular dependence of the plane detector with respect to the beam when measuring the radiation beam dose. For beam one 507, its transmitted portion enters pixel chamber 506. The intersection of the transmitted light passing through the measurement point 502 and the equivalent measurement plane 504 is regarded as the equivalent measurement point 505 of the beam one 507 . For beam two 508 , its reflected portion enters pixel chamber 506 . The intersection of the reflected light passing through the measurement point 502 and the equivalent measurement plane 504 is regarded as the equivalent measurement point 505 of the beam two 508 . As the angle of incidence changes, the equivalent measurement points 505 form a trajectory 509 consisting of half an ellipse. The semi-major and semi-minor axes of the ellipse are a and b, respectively. Thus, the offset Δd of the measurement plane and the horizontal offset Δx of the measured dose can be represented by Equation 1 and Equation 2, respectively. The derivation of these formulas is illustrated by FIG. 7 . Therefore, the method proposed in the present invention can be used to calibrate the parameters of the depth deviation model according to the reference dose distribution data, and use the equivalent measurement point 505 of each detector unit of the planar detector to deviate from the measurement point 502 according to the calibrated depth deviation model. to adjust the dose distribution on the dose plane.

6 is a schematic diagram of the difference between the uncorrected calculated dose distribution and the measured dose distribution on the measurement plane in one embodiment of the present invention, including: a comparison 601 between the measured value and the calculated value when the incident angle is 40°, and the incident angle is 80° When the incident angle is 120°, the measured value is compared with the calculated value 603, and when the incident angle is 160°, the measured value is compared with the calculated value 604. The translational deviation between each uncorrected calculated dose distribution and the measured dose distribution can be used to optimally calibrate the parameters of the field depth deviation model, that is, the semi-major axis and semi-major axis of the half-ellipse 509 of the trajectory 509 composed of the equivalent measurement points 505 . The minor axes are a and b, respectively.

据此，P点的坐标值可以表示为半长轴、半短轴的长度，原点到点P的线段的长度，以及两个线段与横轴701的夹角等变量的函数：FIG. 7 is a schematic diagram of the derivation of formulas 1, 2, 3, and 4 in an embodiment of the present invention. The figure shows the relationship between the variables used in the formula. In the figure, the horizontal axis 701 and the vertical axis 702 are perpendicular and intersect at the origin. An ellipse 710, the long axis is placed along the horizontal axis, the short axis is placed along the vertical axis, the semi-major axis is a, the semi-minor axis is b, and the geometric center is located at the origin. Taking the origin as the center of the circle and the major and minor axes of the ellipse as the diameters, draw the circumscribed circle 711 and the inscribed circle 709 of the ellipse, respectively. Point P 703 is a point on the ellipse with coordinates (x, y). The abscissa of the projection 705 of the point on the horizontal axis is (x, 0), and the ordinate of the projection 706 of the point on the vertical axis is (0, y). There is a point Q on the circumscribed circle 711 , and the straight line passing through Q and P is perpendicular to the horizontal axis 701 . The line segment from the origin to the point P, the length is r, the angle with the horizontal axis is φ, and the angle with the vertical axis is θ. The line segment from the origin to the point Q, the angle with the horizontal axis is

Accordingly, the coordinate value of point P can be expressed as a function of variables such as the length of the semi-major axis and the semi-minor axis, the length of the line segment from the origin to the point P, and the angle between the two line segments and the horizontal axis 701:

则可以将原点到P点的距离r表示为半长轴a、半短轴b和夹角φ的函数：Eliminate in this formula

Then the distance r from the origin to point P can be expressed as a function of the semi-major axis a, the semi-minor axis b and the included angle φ:

From this, the coordinates of point P can be expressed as:

Since θ+φ=π/2, replacing φ with θ gives:

5, the origin is the measurement point 502 on the measurement plane 503, the angle of incidence of beam one 507 is from point P 703 to the origin, the angle of incidence is θ and is acute. According to the depth deviation model, the equivalent measurement point 505 will have a depth-direction offset Δd and a horizontal offset Δx from the origin along the incident direction of the beam one 507 to obtain one of the equivalent measurement points 505 . When the incident angle is θ and an obtuse angle, that is, the beam two 508, according to the depth deviation model, the equivalent measurement point 505 will be opposite to the incident direction of the beam two 508, and the depth direction offset Δd and the horizontal offset will occur from the origin. Shift Δx to get another of the equivalent measurement points 505 . Then, according to Equation 8, in conjunction with FIG. 5 and FIG. 7, for the case of beam one 507 and beam two 508, the offset Δd and horizontal offset Δx of the equivalent measurement point 505 relative to the measurement point 502 in the depth direction It can be expressed as:

and

Although the specific embodiments of the present invention are described herein around specific embodiments, those skilled in the art should understand that: without violating and deviating from the innovative concepts and methods proposed by the present invention, the embodiments can be replaced by etc. Different embodiments can be obtained by modifying effective components or other methods to obtain different embodiments that can be used in the same situation, or according to the specific use environment, requirements, available materials, the composition of the processing object or the requirements for the work flow, through the implementation of The example is modified to work the same in these cases. Such modifications made without departing from or deviating from the innovative concepts and methods proposed by the present invention also fall within the scope of the claims of the present invention.

Claims (12)

1. a method for calculating radiation radiation plane detector dose, is characterized in that: comprise the following steps: Step 1: Calibrate the parameters of the depth deviation model of the measurement plane; Step 2: Receive a three-dimensional patient external beam treatment plan and measure the plane depth position from the radiation therapy treatment planning system (TPS); Step 3: Calculate the depth deviation of the measurement plane of the field according to the treatment head angle of each field and the depth deviation model of the measurement plane; Step 4: Calculate the dose distribution on the measurement plane after the depth position shift is calculated according to the accelerator treatment head model, the treatment plan and the depth deviation of each field; Step 5: Superimpose the dose distributions of each field on the offset measurement plane to generate the calibrated dose on the detector measurement plane. 2. a kind of method for calculating radiation therapy radiation plane detector dose according to claim 1, is characterized in that: described depth deviation model can adopt formula:

Among them, Δd is the position depth deviation, θ is the angle of the treatment head of the field, a and b are the semi-major axis length and the semi-minor axis length of the semi-major axis length of the semi-ellipse model of the effective measurement point trajectory of the detector pixel probe. 3. The method for calculating the dose of a radiotherapy ray plane detector according to claim 1, wherein said step 1 at least comprises the following steps: Step 3.1: Rotate the square field formed by the collimator by several angles around the isocenter; Step 3.2: irradiate a fixed number of machine hops at each angle with a ray dose; Step 3.3: Measure the plane dose distribution of each angle in the isocenter plane with the detector to be calibrated; Step 3.4: Calculate the dose distribution of each angle field in the isocenter plane; Step 3.5: Calculate the translational deviation Δx between the calculated dose distribution and the measured dose distribution in the isocenter plane of each angle field; Step 3.6: Calculate the optimal fitting parameters a and b with the following formulas;

Among them, Δx is the translational deviation between the calculated dose distribution and the measured dose distribution, θ is the angle of the treatment head of the portal, and a and b are the half-short of the semi-major axis length of the semi-ellipse model of the effective measurement point trajectory of the detector pixel probe. Shaft length; the optimization goal is to minimize the mean square mean of the difference between the translation deviation Δx between the calculated dose distribution and the measured dose distribution in the isocenter plane of each angle field and the difference between the translation deviation obtained by the calculation formula in this step . 4. The method of claim 1, wherein the radiation includes but is not limited to: photon rays, electron rays, proton rays and heavy ion rays. 5 . The method of claim 1 , wherein the planar detector includes but is not limited to: an ionization chamber matrix detector and a semiconductor matrix detector. 6 . 6. The method for calculating the radiation dose of a radiotherapy ray plane detector according to claim 1, wherein the radiation dose calculation method includes but is not limited to: look-up table interpolation method, convolution stacking method and Monte Carlo method Law. 7. A system having computer code stored in a non-volatile storage medium that can be used to calculate the dose of a radiation radiation plane detector comprising the following parts: A detector calibration module is responsible for calibrating the parameters of the trajectory model of the effective measurement points of the pixel probe; a plane dose calculation module is responsible for receiving the patient external beam treatment plan from the radiation therapy treatment planning system (TPS) and measuring the plane depth position; The treatment head angle of the field and the depth deviation model of the measurement plane are used to calculate the depth deviation of the measurement plane of the field; according to the accelerator treatment head model, the treatment plan and the depth deviation of each field, the depth position deviation is calculated on the measurement plane. The dose distribution of each field on the offset measurement plane is superimposed to generate the dose on the calibrated detector measurement plane. Wherein, data communication is performed between the detector calibration module and the plane dose calculation module through a data bus or a data network. 8. The system for calculating the dose of radiation therapy radiation plane detector according to claim 7, wherein the depth deviation model can adopt the formula:

Among them, Δd is the position depth deviation, θ is the angle of the treatment head of the field, a and b are the semi-major axis length and the semi-minor axis length of the semi-major axis length of the semi-ellipse model of the effective measurement point trajectory of the detector pixel probe. 9. A system for calculating the dose of radiation therapy radiation plane detector according to claim 7, wherein the step of calibrating the parameters of the trajectory model of the effective measurement point of the pixel probe at least comprises the following steps: Step 9.1: Rotate the square field formed by the collimator by several angles around the isocenter; Step 9.2: irradiate a fixed number of machine hops at each angle with a ray dose; Step 9.3: Measure the plane dose distribution at each angle in the isocenter plane with the detector to be calibrated; Step 9.4: Calculate the dose distribution of each angle field in the isocenter plane; Step 9.5: Calculate the translational deviation Δx between the calculated dose distribution and the measured dose distribution in the isocenter plane of each angle field; Step 9.6: Calculate the optimal fitting parameters a and b with the following formulas;

Among them, Δx is the translational deviation between the calculated dose distribution and the measured dose distribution, θ is the angle of the treatment head of the portal, and a and b are the half-short of the semi-major axis length of the semi-ellipse model of the effective measurement point trajectory of the detector pixel probe. Shaft length; the optimization goal is to minimize the mean square mean of the difference between the translation deviation Δx between the calculated dose distribution and the measured dose distribution in the isocenter plane of each angle field and the difference between the translation deviation obtained by the calculation formula in this step . 10 . The system for calculating the dose of a radiotherapy radiation plane detector according to claim 7 , wherein the radiation includes but is not limited to: photon radiation, electron radiation, proton radiation and heavy ion radiation. 11 . 11. The system of claim 7, wherein the plane detectors include but are not limited to: ionization chamber matrix detectors and semiconductor matrix detectors. 12. The system for calculating the radiation dose of a radiation radiation plane detector according to claim 7, wherein the radiation radiation dose calculation method includes but is not limited to: look-up table interpolation method, convolution stacking method and Monte Carlo method Law.

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