A method for correcting the angle of a portal imaging device

Abstract

The present invention discloses a method for correcting the deflection angle of a portal imaging device. The method first opens a radiation source with a certain size of the portal imaging device, irradiates the portal imaging device at different positions, and collects the grayscale images formed; based on the collected grayscale images, the grayscale value sequence along the X and Y directions through the center point, the physical specification data of the portal imaging device, and the calibration information of the fluence and grayscale are used to calculate the offset angle correction parameters of the portal imaging device in the X and Y directions at different angles; when the portal imaging device is used to collect images, the deflection angle correction parameters of the imaging device position are interpolated to obtain the correction parameters of the current position and perform deflection angle correction on the grayscale image. The present invention can perform efficient and accurate deflection angle correction on the portal imaging device, and provide accurate images for subsequent radiation source reconstruction, positioning and placement, etc.

Description

Technical Field

[0001] The invention relates to a correction method for a portal imaging device, and in particular to an angle correction method for a portal imaging device applied to fields such as radiotherapy or industrial nondestructive testing. Background Art

[0002] The portal imaging device generates grayscale images when receiving radiation exposure. Based on the grayscale images, the radiation source and medium can be reconstructed and analyzed. It has been widely used in the fields of radiotherapy dose monitoring, radiotherapy positioning, industrial non-destructive testing, and medical image reconstruction. Due to the influence of gravity, the portal imaging device will produce a certain angle deflection at different spatial positions, resulting in a certain grayscale value deviation in the generated grayscale image. The grayscale image needs to be corrected for the deflection angle in order to provide accurate input information for the reconstruction of the radiation source and medium. Therefore, the study of the deflection angle correction method of the portal imaging device is of great significance to radiotherapy monitoring, industrial testing, radiotherapy positioning, and medical image reconstruction.

[0003] At present, the deflection angle correction of the portal imaging device generally adopts the marking point method. The marking points are used to obtain the correction parameters of the deflection angle of the portal imaging device at different positions. This method requires pasting marking points at fixed positions of the accelerator's portal field. This makes the accuracy of the deflection angle correction parameters directly related to the accuracy of pasting the marking points. Therefore, it is greatly affected by human interference and the accuracy is still difficult to control. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method for correcting the angle of a portal imaging device with higher precision.

[0005] Technical solution: The method for calibrating the angle of a portal imaging device with high accuracy of the present invention comprises the following steps:

[0006] (1) Open a radiation source to a certain size of the field, irradiate from different angles using the field imaging device, and collect the resulting grayscale image;

[0007] (2) Smoothing the grayscale image acquired in step (1) to obtain a smoothed grayscale image, and mapping the grayscale image into a fluence map according to a calibration relationship between grayscale and fluence;

[0008] (3) obtaining a sequence of pixel values ​​along the X and Y directions passing through the center point of the grayscale image in the portal according to the acquired grayscale image and the parameters of the portal imaging device;

[0009] (4) calculating the deflection angles of the portal imaging device in the X and Y directions according to the pixel value sequences along the X and Y directions passing through the center point of the grayscale image obtained in step (3);

[0010] (5) When using a portal imaging device to collect images, the deflection angle obtained in step (4) is interpolated according to the position of the imaging device to obtain the deflection angle of each position and perform deflection angle correction on the grayscale image.

[0011] The parameters that affect the device include resolution, physical size of pixels and size of the portal image.

[0012] Step (4) comprises the following steps:

[0013] (41) The distance between the grayscale image collected at the i-th position in the X direction and the center point coordinates is calculated as follows:

[0014] d mid，i =s*i

[0015] Where s is the physical size of the pixel of the portal imaging device;

[0016] (42) According to the inverse square relationship between the injection amount and the distance, the deflection angle of the i position point in the Y direction is calculated;

[0017] (43) Calculate the deflection angle of i position points in the X direction according to the method described in steps (41)-(42);

[0018] (44) calculating the θ values ​​of the remaining pixel points selected in the X direction and calculating their average value to obtain the deflection angle of the portal imaging device in the Y direction;

[0019] (45) Calculate the θ values ​​of the remaining pixel points selected in the Y direction and calculate their average value to obtain the deflection angle of the portal imaging device in the X direction.

[0020] In step (42), the deflection angle of i position points in the Y direction is calculated as follows:

[0021]

[0022] in Among them l i is the distance from the source to point i, l mid is the distance from the source to the center of the portal imaging device, flux mid is the fluence at the center of the portal imaging device, flux i is the injection volume at point i.

[0023] The interpolation method used in step (5) is linear interpolation.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: accurate deflection angle correction parameters can be obtained without adding marking points, reducing human interference in the correction process, and is more applicable than the traditional marking point method. It can perform efficient and accurate deflection angle correction on the portal imaging device, providing accurate images for subsequent radiation source reconstruction, positioning and placement, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0027] like Figure 1 As shown, the portal imaging device angle correction method of the present invention comprises the following steps:

[0028] (1) Open a radiation source to a certain size of the field, irradiate from different angles using the field imaging device, and collect the resulting grayscale image;

[0029] (2) Smoothing the grayscale image acquired in step (1) to obtain a smoothed grayscale image, and mapping the grayscale image into a fluence map according to a calibration relationship between grayscale and fluence;

[0030] (3) obtaining a sequence of pixel values ​​along the X and Y directions passing through the center point of the grayscale image in the portal according to the acquired grayscale image and the parameters of the portal imaging device;

[0031] (4) calculating the deflection angles of the portal imaging device in the X and Y directions according to the pixel value sequences along the X and Y directions passing through the center point of the grayscale image obtained in step (3);

[0032] (5) When using a portal imaging device to collect images, the deflection angle obtained in step (4) is interpolated according to the position of the imaging device to obtain the deflection angle of each position and perform deflection angle correction on the grayscale image.

[0033] The parameters that affect the device include resolution, physical size of pixels and size of the portal image.

[0034] Step (4) comprises the following steps:

[0035] (41) The distance between the grayscale image collected at the i-th position in the X direction and the center point coordinates is calculated as follows:

[0036] d mid,i =s*i

[0037] Where s is the physical size of the pixel of the portal imaging device;

[0038] The grayscale distribution of the center point and the i-th position is g mid , g i ;

[0039] (42) According to the inverse square relationship between the injection amount and the distance, the deflection angle of the i position point in the Y direction is calculated;

[0040] (43) Calculate the deflection angle of i position points in the X direction according to the method described in steps (41)-(42);

[0041] (44) calculating the θ values ​​of the remaining pixel points selected in the X direction and calculating their average value to obtain the deflection angle of the portal imaging device in the Y direction;

[0042] (45) Calculate the θ values ​​of the remaining pixel points selected in the Y direction and calculate their average value to obtain the deflection angle of the portal imaging device in the X direction.

[0043] In step (42), the deflection angle of i position points in the Y direction is calculated as follows:

[0044]

[0045] in Among them l i is the distance from the source to point i, l mid is the distance from the source to the center of the portal imaging device.

[0046] The specific steps of embodiment 1 of the present invention are as follows:

[0047] (1) The source-to-isocenter distance (SSD) was set to 100 cm, and the source-to-port imaging device distance (SID) was set to 160 cm. The accelerator had a rotation range of 360 degrees, so every 5 degrees was divided into one angle, forming a total of 72 angles. The accelerator opened a 10 cm × 10 cm field to irradiate each angle, with an irradiation intensity of 50 MU. No medium was placed between the source and the portal imaging device, and the grayscale image generated on the portal imaging device was collected.

[0048] (2) Smooth the collected grayscale image to obtain a smoothed grayscale image, and map the grayscale image into a flux map epid .

[0049] (3) Confirm and select the two line segment pixels in the X and Y directions of the grayscale image:

[0050] (31) The current field size is 10 cm 2 , the distance from the source to the isocenter is 100cm, the distance from the source to the center of the portal imaging device is 160cm, and the size of the portal imaging device is Due to the influence of angle deflection, the effective field of the portal imaging device is relative to E beamsize The inward shrinkage is 2 cm, and the calculation is

[0051] Effective field E of the portal imaging device beamsizev =14cm;

[0052] (32) The pixel size of the portal imaging device is 0.04 cm, and 350 pixels are selected on the two line segments in the X direction and the Y direction passing through the geometric center point of the grayscale image.

[0053] (4) Calculation of the angle of the portal imaging device:

[0054] (41) Calculate the distance d between the grayscale image collected at the i-th position in the X direction and the center point coordinates mid，i =s*i, s is the physical size of the pixel of the portal imaging device, and the grayscale distribution of the center point and the i-th position is gmi d , gi; According to step (2), the corresponding point flux can be obtained mid 、flux i According to the inverse square relationship between the injection amount and the distance, the deflection angle of the i position point in the Y direction can be calculated as:

[0055]

[0056] in l i is the distance from the source to point i, l mid is the distance from the source to the center of the portal imaging device;

[0057] (42) By calculating the θ values ​​of the remaining pixel points selected in the X direction and calculating their average value, the deflection angle of the portal imaging device in the Y direction can be obtained.

[0058] (43) Similarly, by calculating the θ values ​​of the remaining pixel points selected in the Y direction and calculating their average value, the deflection angle of the portal imaging device in the X direction can be obtained.

[0059] (5) Portal imaging device deflection angle correction:

[0060] When the portal imaging device is used to collect images, the deflection angle obtained in step (3) is interpolated according to the position of the imaging device to obtain the deflection angle of the current position and the deflection angle of the grayscale image is corrected.

Claims

1. A method for calibrating the angle of a portal imaging device, characterized in that: The following steps are involved: (1) Open the radiation source to irradiate the radiation field, irradiate the radiation field imaging device from different angles, and collect the grayscale image formed; (2) Smoothing the grayscale image acquired in step (1) to obtain a smoothed grayscale image, and mapping the grayscale image into a fluence map according to a calibration relationship between grayscale and fluence; (3) obtaining a sequence of pixel values ​​along the X and Y directions passing through the center point of the grayscale image in the portal according to the acquired grayscale image and the parameters of the portal imaging device; (4) calculating the deflection angles of the portal imaging device in the X and Y directions according to the pixel value sequences along the X and Y directions passing through the center point of the grayscale image obtained in step (3); (5) When the portal imaging device is used to collect images, the deflection angle obtained in step (4) is interpolated according to the position of the imaging device to obtain the deflection angle of each position and the deflection angle of the grayscale image is corrected. The parameters of the portal imaging device include resolution, physical size of pixel points and portal image size. The step (4) comprises the following steps: (41) The distance between the grayscale image collected at the i-th position in the X direction and the center point coordinates is calculated as follows: d mid，i =s*i Where s is the physical size of the pixel of the portal imaging device; (42) According to the inverse square relationship between the injection amount and the distance, the deflection angle of the i position point in the Y direction is calculated; (43) Calculate the deflection angle of i position points in the X direction according to the method described in steps (41)-(42); (44) calculating the θ values ​​of the remaining pixel points selected in the X direction and calculating their average value to obtain the deflection angle of the portal imaging device in the Y direction; (45) Calculate the θ values ​​of the remaining pixel points selected in the Y direction and calculate their average value to obtain the deflection angle of the portal imaging device in the X direction, In the step (42), the deflection angle of i position points in the Y direction is calculated as follows: in Among them l i is the distance from the source to point i, l mid is the distance from the source to the center of the portal imaging device, flux mid is the fluence at the center of the portal imaging device, flux i is the injection volume at point i.

2. The portal imaging device angle correction method according to claim 1, characterized in that: In step (5), the deflection angle is linearly interpolated.

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