A radiotherapy bed deformation measurement device and method

Abstract

The present invention belongs to the field of radiotherapy technology, and specifically relates to a radiotherapy treatment bed deformation measurement device and method, the device includes a camera, a marking line a and an image processing device, the marking line a is set at the bottom of the treatment bed plate a, the camera is placed at a certain height below the treatment bed plate a and deviates from the vertical plane where the marking line a is located at a certain distance, and the camera and the image processing device are connected. The present invention serves as a basis for dynamically adjusting the posture of the treatment bed, reducing the impact of the treatment bed deformation on the treatment. The measurement of the present invention can be carried out in real time during the positioning process. When the positioning error is adjusted by tilting and other methods, due to the existence of additional inclination angles, the indirect measurement method will produce additional uncertainty, but the present invention will not be affected, and can more accurately perform dynamic compensation of the bed position, thereby improving the accuracy of treatment.

Description

Technical Field

[0001] The invention belongs to the technical field of radiotherapy, and in particular relates to a radiotherapy bed deformation measurement device and method. Background Art

[0002] Precision radiotherapy is an important means of tumor treatment. During the treatment process, positioning accuracy is a very important technical indicator. Positioning requires moving the patient's tumor determined by medical images such as CT to the vicinity of the center of the accelerator by moving the treatment bed. Therefore, the position accuracy determined by the treatment bed becomes the key to the problem. In addition to being affected by the motion control accuracy, the position accuracy of the treatment bed is also affected by its own deformation.

[0003] There are two solutions to the position error caused by the deformation of the treatment bed: one is to control the deformation through structural strength; the other is to compensate for the deformation through a motion control system.

[0004] There are two solutions to increase the strength of the treatment bed to reduce deformation: one is to increase the thickness of the bed board, and the other is to transfer the pressure on the bed board to other supporting structures as quickly as possible through a complex supporting structure. Increasing the thickness of the bed board will inevitably increase the absorption of the radiation dose by the bed board, reducing the efficiency of radiation use. Therefore, this solution usually cannot completely solve the deformation problem. Other solutions in the prior art that increase the supporting structure will encounter problems with the cost and control difficulty caused by the complex structure. At the same time, due to the increase in the motion mechanism, new problems and safety risks such as motion synchronization and collision will be introduced.

[0005] The deformation compensation method generally assumes that the weight on the bed board has a certain distribution characteristic, and compensates for the total weight of the treatment bed, or the deformation of a certain point on the treatment bed. However, patients have different body shapes and different positions on the treatment bed. Therefore, even if the patients have the same weight, the deformation of the bed board is not exactly the same. Therefore, this compensation method will inevitably have certain errors.

[0006] Compensation for the deformation of the treatment bed can also be achieved through image guidance, but this method usually requires X-ray imaging, and the patient must receive a certain radiation dose; in addition, the positioning process is relatively complicated, which prolongs the total treatment time. Therefore, it is more suitable for the first treatment and key treatment nodes, but it is not a position compensation method suitable for every treatment.

[0007] Tumors are usually three-dimensional structures with irregular shapes. The deformation of the bed board not only causes the center position to shift, but also causes a certain degree of rotation. At present, the compensation for bed deformation either does not compensate for rotation, and the three-dimensional treatment bed cannot achieve angle compensation, or only compensates for the pitch angle at a fixed position on the bed, and generally does not compensate for left and right rolling.

[0008] Therefore, it is necessary to provide a radiotherapy treatment bed deformation measurement device and method to solve the deficiencies in the prior art. Summary of the invention

[0009] The purpose of the present invention is to provide a radiotherapy treatment bed deformation measurement device and method, which can serve as a basis for dynamically adjusting the posture of the treatment bed and reduce the influence of the treatment bed deformation on the treatment.

[0010] The technical solution to achieve the purpose of the present invention is:

[0011] A radiotherapy treatment bed deformation measuring device comprises a camera, a marking line a and an image processing device. The marking line a is arranged at the bottom of the treatment bed plate a. The camera is placed at a certain height below the treatment bed plate a and deviates from the vertical plane where the marking line a is located by a certain distance. The camera and the image processing device are connected.

[0012] The marking line a is arranged on the bottom of the treatment bed plate a by engraving or laser surface projection.

[0013] The camera obtains the images of the undeformed marking line a and the bent marking line b on the treatment bed board b after deformation due to force. The image processing device calculates the descent data of the treatment bed board a in the treatment center area by comparing the images of the marking line a and the marking line b.

[0014] The laser lamp bracket is installed and fixed just below the treatment bed plate a, and the laser lamp is fixed at the other end of the laser lamp bracket. The laser lamp outputs a vertical laser plane, which irradiates the bottom side of the treatment bed plate a to form a marking line a on the lower surface of the treatment bed plate a.

[0015] The pan-tilt bracket is installed near the supporting structure of the treatment bed board a, one end of the pan-tilt bracket is connected to the treatment bed board a, and the other end is fixedly connected to the camera. The camera moves with the treatment bed board a, and the collected image is not affected by the position of the treatment bed board a.

[0016] The laser light uses infrared light, and the camera lens uses a filter with the same wavelength as the laser light to remove interference from ambient light.

[0017] A method for measuring a radiotherapy bed deformation measuring device, the method comprising the following steps:

[0018] Step 1: Calibrate parameters to obtain the correspondence between the pixel points in the image captured by the camera and the position in the real space;

[0019] Step 2: Measure the vertical deformation of a single point;

[0020] Step 3: Measure the inclination of the treatment bed board a.

[0021] The step 1 comprises the following steps:

[0022] Step 1.1 Place a calibration object of known size at a specific position on the marked line a on the lower surface of the treatment bed board a:

[0023] Step 1.2: Use a camera to capture images of the marking line a and the calibration object;

[0024] Step 1.3 determines the relationship between the camera pixel coordinates and the spatial position according to the number of pixels of the calibration object in the calibration image.

[0025] The step 1.1 includes:

[0026] Step 1.1.1 Prepare a calibration object, the height h of which is greater than the maximum deformation of the treatment bed plate a, and the surface photographed by the camera is covered with black and white grids;

[0027] Step 1.1.2 Place the calibration object. Install the calibration object on the bottom of the treatment bed board a, and make the long side of the side with black and white alternating grids overlap on the marking line a;

[0028] Step 1.1.3 Check the deformation of the treatment bed board a and adjust the treatment bed board a to a level level.

[0029] The step 1.3 includes:

[0030] Step 1.3.1 Use computer software to identify the pixel coordinates of each grid intersection in the calibration object image;

[0031] Step 1.3.2 calculates the correspondence between the pixel coordinates of the intersection point and the actual space coordinates, and stores them in the lookup table.

[0032] The step 2 comprises the following sub-steps:

[0033] Step 2.1 When the patient is on the treatment bed board a, use a camera to aim at the marking line a and take an image;

[0034] Step 2.2: Calculate the deformation of the treatment bed board a according to the deformation of the marking line a in the measurement image;

[0035] Step 2.2.1 In the image, identify the pixel coordinates corresponding to the marker line a at the treatment location of interest;

[0036] Step 2.2.2: Find the coordinate value of the reference pixel closest to the coordinate of the pixel to be measured in the lookup table obtained in step 1.3.2;

[0037] Step 2.2.3 calculates the position of the pixel to be measured in the real space through interpolation, thereby obtaining the deformation of the treatment bed board a.

[0038] The step 3 comprises the following steps:

[0039] Step 3.1: Measure the vertical deformation at two locations on the treatment bed board a;

[0040] Step 3.2: Calculate the inclination of the line connecting the two positions.

[0041] The method for measuring the pitch inclination in step 3.2 is: respectively measure the deformation of two points with a known interval of Δy on the marking line a along the Y direction of the long side of the bed, calculate the difference between the deformations and record it as Δz, then the pitch inclination angle of the treatment bed board a at this point is:

[0042]

[0043] The method for measuring the roll tilt in step 3.2 is as follows: two marking lines are set at the bottom of the treatment bed plate a along the Y direction of the long side of the bed, and the distance between the two marking lines is d. The vertical deformation data of the treatment bed plate a on the two marking lines are measured respectively, and are recorded as Δz1 and Δz2 respectively. Then the roll tilt angle is:

[0044]

[0045] The calibration object is an object with more than one known size.

[0046] The beneficial technical effects of the present invention are:

[0047] (1) The present invention can accurately measure the deformation of the bed board and provide accurate information for the treatment system for position correction and compensation, thereby achieving precise radiotherapy;

[0048] (2) For the same treatment accuracy requirement, compared with the solution of increasing the thickness of the bed plate, the present invention reduces the absorption of the bed plate to the dose, improves the treatment efficiency, thereby shortening the treatment time and reducing unnecessary loss of accelerator components;

[0049] (3) Compared with the method of adding an additional support structure to the bed board, the structure of the present invention is simpler, especially for systems with difficult structural constraints, such as when it is inconvenient to make a major upgrade to the structure of the bed in a series of products, and when the accuracy requirements are increased, the method and device of the present invention make fewer changes to the original system, turning the impossible into possible. In addition, the simplified structure has a lower cost. In particular, because cameras are developing rapidly with consumer products such as mobile phones, the cost and measurement accuracy advantages of the present invention will continue to increase over time;

[0050] (4) The present invention directly measures the error caused by deformation. Compared with the method of using weighing or measuring the deformation of a fixed point on the bed and then calculating the deformation of the treatment position, the present invention can directly measure the deformation of any point on the bed, and the data is more accurate and reliable. In particular, when the patient has a special body shape, or when other equipment needs to be placed on the treatment bed in addition to the patient, or when the accelerator treatment system is being maintained or repaired, it is necessary to add special tooling equipment and other loads with a large weight distribution different from that of the person to the bed board. The advantage of direct measurement is more obvious.

[0051] (5) The present invention adopts a direct measurement method, which is completely independent of the stability of the calculation parameters compared to the method of calculating the position error. For example, the stiffness of the bed varies with factors such as temperature, humidity, and fatigue during use, which will not have any impact on the method of the present invention;

[0052] (6) In addition to measuring the sinking caused by bed deformation, the present invention can also obtain information on the pitch and roll direction of the bed board by measuring multiple points in the treatment area. Compared with the single sinking measurement method, it provides more information, so that better compensation can be performed. Therefore, from the perspective of the entire system, the positioning accuracy is higher, so the treatment of patients is more accurate;

[0053] (7) The measurement of the present invention can be performed in real time during the positioning process. When the positioning error is adjusted by tilting or other methods, additional uncertainty will be generated by the indirect measurement method due to the existence of additional tilt angles. However, the present invention will not be affected and can more accurately perform dynamic compensation for the bed position, thereby improving the accuracy of treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 An assembly diagram of a radiotherapy bed deformation measuring device provided by the present invention;

[0055] Figure 2 Schematic diagram of an embodiment of a radiotherapy bed deformation measurement device provided by the present invention

[0056] Figure 3 A schematic diagram of a calibration object on a radiotherapy bed deformation measurement device provided by the present invention;

[0057] Figure 4 A schematic diagram of a method for calculating the pitch angle of a radiotherapy treatment bed deformation provided by the present invention;

[0058] Figure 5 A schematic diagram of a method for calculating the deformation and rolling angle of a radiotherapy treatment bed provided by the present invention;

[0059] In the figure: 101-treatment bed base; 102-camera; 103-treatment bed board a; 104-marking line a; 105-treatment bed board b; 106-marking line b; 107-image processing device; 501-laser plane; 502-laser light; 503-laser light bracket; 504-pan-tilt bracket; 601-calibration object; 602-black and white alternating grid. DETAILED DESCRIPTION

[0060] In order to make those skilled in the art better understand the present invention, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the embodiments described below are only a part of the embodiments of the present invention, not all. Based on the embodiments recorded in the present invention, all other embodiments obtained by those skilled in the art without paying creative work are within the scope of protection of the present invention.

[0061] like Figure 1 As shown, a radiotherapy bed deformation measuring device provided by the present invention includes a camera 102, a marking line a104 and an image processing device 107. The camera 102 and the image processing device 107 are connected.

[0062] The marking line a104 is set at the bottom of the treatment bed plate a103, and the setting method is engraving or projecting through a laser surface.

[0063] The camera 102 is placed at a certain height ΔZ below the treatment bed plate a103 and at a certain distance ΔX away from the vertical plane where the marking line a104 is located.

[0064] When there is no weight on the treatment bed plate a103, the camera 102 is used to obtain an image of the undeformed marking line a104 and its vicinity.

[0065] The camera 102 obtains the image of the bent marking line b106 on the treatment bed plate b105 that is deformed due to the force, and the image processing device 107 compares it with the undeformed marking line a104 to calculate the descending data of the treatment bed plate a103 in the treatment center area.

[0066] When the deformation measuring device is used, an embodiment such as Figure 2As shown: directly below the treatment bed plate a103, the laser lamp 502 is fixed by the laser lamp bracket 503. The other end of the laser lamp bracket 503 is fixed near the support structure of the treatment bed plate a103 to ensure that the position of the laser lamp 502 does not change with the deformation of the treatment bed plate a103. The laser lamp 502 outputs a laser plane 501 in the vertical direction. The laser plane 501 irradiates the bottom side of the treatment bed plate a103, forming a marking line a104 on the lower surface of the treatment bed plate a103. In order to avoid the thickness of the marking line a104 being affected by the change in the distance between the marking line a104 and the laser lamp 502, the laser lamp 502 is fixed on the treatment bed plate a103 and moves with it, and at the same time, it also avoids additional errors caused by the vertical movement axis of the treatment bed plate a103 not being parallel to the laser plane 501.

[0067] A pan-tilt bracket 504 is installed near the supporting structure of the treatment bed board a103. One end of the pan-tilt bracket 504 is connected to the treatment bed board a103, and the other end is fixedly connected to the camera 102. The camera 102 moves with the treatment bed board a103, so the collected image is not affected by the position of the treatment bed board a103.

[0068] In order to fully utilize the resolution of the camera 102, the pan / tilt bracket 504 is used to accurately control the direction of the camera 102, so that the camera 102 only acquires the image of the marking line a104 near the area of ​​interest for treatment.

[0069] In order to prevent ambient light from interfering with the video signal, the wavelength of the laser light 502 takes full account of the ambient light and uses infrared light that is not present in the treatment environment. The lens of the camera 102 uses a filter with the same wavelength as the laser light 502 to remove interference from ambient light.

[0070] The present invention also provides a method for measuring the deformation of a radiotherapy bed, the method comprising the following steps:

[0071] Step 1: parameter calibration, obtaining the correspondence between the pixel points in the image captured by the camera 102 and the positions in the real space;

[0072] The purpose of parameter calibration is to obtain the correspondence between the pixel points in the image captured by the camera 102 and the position in the real space, such as the size ratio and the coefficient of the offset, so that in the subsequent measurement process, the displacement in the actual space can be calculated by the number of pixels offset by the marking line a104 in the picture.

[0073] The parameter calibration process only needs to be performed once and does not need to be repeated before each measurement.

[0074] Step 1.1 Place a calibration reference object of known size at a specific position on the marking line a104 on the lower surface of the treatment bed a103:

[0075] Step 1.1.1 Prepare the calibration material:

[0076] The calibration object has at least one known dimension, which is used to calibrate the dimension in the image. For example, a sheet or strip with a clear thickness, or a test block with a grid drawn on it, or a vertical surface with a coordinate paper attached. Figure 3 The calibration object 601 shown is used for the calibration process. The calibration object 601 is made of metal, and each adjacent surface is perpendicular to each other. The height h of the calibration object is greater than the maximum deformation that the treatment bed plate a103 may produce, and the surface photographed by the camera 102 is covered with black and white grids 602.

[0077] Step 1.1.2 Place the calibration object:

[0078] Place the calibration object 601 against the bottom surface of the treatment bed board a103, and make the long side of the side with the black and white alternating grid 602 overlap on the marking line a104.

[0079] One vertex of the calibration object 601 is placed at a position of a known coordinate point on the treatment couch a103, such as the projection position of the isocenter on the treatment couch a103, and fixed.

[0080] Step 1.1.3 Adjust the treatment bed board a103 to a level level:

[0081] If it is a six-dimensional bed, set the bed's pitch angle to zero. If it is a three-dimensional bed, proceed directly to the following steps.

[0082] Step 1.1.4 Check the deformation of the treatment bed board a103:

[0083] Use a laser level to check whether the surface of the treatment bed board a103 is completely horizontal. If any unevenness is found, it means that the treatment bed board a103 has undergone a significant deformation due to the weight of the calibration object. Appropriate support and adjustment should be used to restore the treatment bed board a103 to a completely horizontal state.

[0084] Step 1.2: Use the camera 102 to capture images of the marking line a104 and the calibration object 601;

[0085] Step 1.3 determines the relationship between the pixel coordinates of the camera 102 and the spatial position according to the number of pixels of the calibration object 601 in the calibration image;

[0086] The relationship between the pixel coordinates of the camera 102 and the spatial position can be selected in a variety of ways according to different calculation methods, such as calculating the relationship function between the image and the spatial position. In this embodiment, a lookup table is used as a relationship parameter bearing entity, including the following steps:

[0087] Step 1.3.1 Use computer software to identify the pixel coordinates of each grid intersection in the calibration object image;

[0088] Step 1.3.2 calculates the correspondence between the pixel coordinates of the intersection point and the actual space coordinates, and stores them in the lookup table. These pixels with known positions are called reference pixels.

[0089] Step 2: Single point vertical deformation measurement;

[0090] Step 2.1 When the patient is on the treatment couch a103, use the camera 102 to align with the marking line a104 to capture an image;

[0091] Step 2.2: Calculate the deformation of the treatment bed plate a103 according to the deformation of the marking line a104 in the measurement image;

[0092] Step 2.2.1: In the image, identify the pixel coordinates corresponding to the marker line a104 of the treatment location of interest;

[0093] Step 2.2.2: Find the coordinate value of the reference pixel closest to the coordinate of the pixel to be measured in the lookup table obtained in step 1.3.2;

[0094] Step 2.2.3 calculates the position of the pixel to be measured in the real space through interpolation, thereby obtaining the deformation of the treatment bed board a103.

[0095] Step 3: Measure the inclination of the treatment bed board a103

[0096] If the treatment system uses a treatment bed with more than three dimensions, this data can be used to correct the tilt. For treatment beds with less than three dimensions, or no need for angle correction, this step can be omitted. This step can be further refined:

[0097] Step 3.1: Measure the vertical deformation at two locations on the treatment bed board a103;

[0098] Step 3.2: Calculate the inclination of the line connecting the two positions.

[0099] The pitch tilt in the long side direction (Y direction) of the treatment bed and the roll tilt in the short side direction (X direction) of the treatment bed are of most concern, while the tilt in other directions can be decomposed into the tilt in these two directions. Therefore, the measurement of the tilt in these two directions is described in detail below:

[0100] like Figure 4 As shown, the pitch tilt measurement method is: measure the deformation of two points with a known spacing of Δy on the marking line a104 along the long side (Y) of the bed. Calculate the difference in deformation, recorded as Δz, and the pitch tilt angle of the treatment bed board a103 at this point is:

[0101]

[0102] like Figure 5 As shown in FIG. 1 , the method for measuring the rollover tilt is as follows: two marking lines are set at the bottom of the treatment bed plate a103 along the long side (Y) of the bed. The spacing between the marking lines is d, and the vertical deformation data of the treatment bed plate a103 on the two marking lines at the positions of interest for treatment are measured respectively, and are recorded as Δz1 and Δz2 respectively. Then the rollover tilt angle near the specified point is:

[0103]

[0104] The present invention is described in detail above with reference to the accompanying drawings and embodiments, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of ordinary technicians in the field without departing from the purpose of the present invention. The contents not described in detail in the present invention can adopt the existing technology.

Claims

1. A radiotherapy bed deformation measurement device, characterized in that: The device comprises a camera (102), a marking line a (104) and an image processing device (107); the marking line a (104) is arranged at the bottom of a treatment bed board a (103); the camera (102) is placed under the treatment bed board a (103) and deviates from the vertical plane where the marking line a (104) is located; the camera (102) and the image processing device (107) are connected: the marking line a (104) is arranged at the bottom of the treatment bed board a (103) by means of engraving or laser surface projection; The camera (102) acquires images of the undeformed marking line a (104) and the bent marking line b (106) on the treatment bed plate b (105) after deformation due to force, and the image processing device (107) calculates the descending data of the treatment bed plate a (103) in the treatment center area by comparing the images of the marking line a (104) and the marking line b (106); The laser lamp bracket (503) is fixedly installed directly below the treatment bed plate a (103), the laser lamp (502) is fixedly installed at the other end of the laser lamp bracket (503), the laser lamp (502) outputs a vertical laser plane (501), the laser plane (501) irradiates the bottom side of the treatment bed plate a (103), and forms a marking line a (104) on the lower surface of the treatment bed plate a (103); The pan-tilt bracket (504) is installed near the supporting structure of the treatment bed board a (103), one end of the pan-tilt bracket (504) is connected to the treatment bed board a (103), and the other end is fixedly connected to the camera (102), the camera (102) moves with the treatment bed board a (103), and the collected image is not affected by the position of the treatment bed board a (103); The laser light (502) uses infrared light, and the lens of the camera (102) uses a filter with the same wavelength as the laser light (502) to remove interference from ambient light.

2. A measurement method for a radiotherapy bed deformation measurement device, applied to a radiotherapy bed deformation measurement device as claimed in claim 1, characterized in that: The method comprises the following steps: Step 1: calibrating parameters to obtain the corresponding relationship between the pixel points in the image captured by the camera (102) and the positions in the real space; Step 2: Measure the vertical deformation of a single point; Step 3: Measure the inclination of the treatment bed board a (103).

3. The measurement method of the radiotherapy bed deformation measurement device according to claim 2, characterized in that: The step 1 comprises the following steps: Step 1.1 Place a calibration object (601) of known size on the marking line a (104) on the lower surface of the treatment bed plate a (103): Step 1.2: Using a camera (102) to capture images of the marking line a (104) and the calibration object (601); Step 1.3 determines the relationship between the pixel coordinates of the camera (102) and the spatial position according to the number of pixels of the calibration object (601) in the calibration image.

4. The method for measuring the deformation of a radiotherapy bed according to claim 3, characterized in that: The step 1.1 includes: Step 1.1.1 prepare a calibration object (601), wherein the height h of the calibration object (601) is greater than the maximum deformation of the treatment bed plate a (103), and the surface photographed by the camera (102) is covered with black and white grids (602); Step 1.1.2: Place the calibration object (601). Install the calibration object (601) on the bottom surface of the treatment bed board a (103) so that the long side of the side with the black and white grid (602) overlaps the marking line a (104); Step 1.1.3 Check the deformation of the treatment bed board a (103) and adjust the treatment bed board a (103) to a level.

5. The method for measuring the deformation of a radiotherapy bed according to claim 4, characterized in that: The step 1.3 includes: Step 1.3.1 Use computer software to identify the pixel coordinates of each grid intersection in the calibration object image; Step 1.3.2 calculates the correspondence between the pixel coordinates of the intersection point and the actual space coordinates, and stores them in the lookup table.

6. The method for measuring the deformation of a radiotherapy bed according to claim 5, characterized in that: The step 2 comprises the following sub-steps: Step 2.1: When the patient is on the treatment bed board a (103), use the camera (102) to align with the marking line a (104) to capture an image; Step 2.2: Calculate the deformation amount of the treatment bed plate a (103) according to the deformation of the marking line a (104) in the measurement image; Step 2.2.1: in the image, identify the pixel coordinates corresponding to the marker line a (104) of the treatment location of interest; Step 2.2.2: Find the coordinate value of the reference pixel closest to the coordinate of the pixel to be measured in the lookup table obtained in step 1.3.2; Step 2.2.3 calculates the position of the pixel to be measured in the real space by interpolation, thereby obtaining the deformation of the treatment bed board a (103).

7. The method for measuring the deformation of a radiotherapy bed according to claim 6, characterized in that: The step 3 comprises the following steps: Step 3.1: Measure the vertical deformation at two locations on the treatment bed board a (103); Step 3.2: Calculate the inclination of the line connecting the two positions.

8. The measurement method of the radiotherapy bed deformation measurement device according to claim 7, characterized in that: The method for measuring the pitch tilt in step 3.2 is: respectively measure the deformation of two points with a known interval of Δy on the marking line a (104) along the Y direction of the long side of the bed, calculate the difference between the deformations and record it as Δz, then the pitch tilt angle of the treatment bed board a (103) at this point is:

9. The method for measuring the deformation of a radiotherapy bed according to claim 8, characterized in that: The method for measuring the roll tilt in step 3.2 is as follows: two marking lines are set at the bottom of the treatment bed plate a (103) along the Y direction of the long side of the bed, and the distance between the two marking lines is d. The vertical deformation data of the treatment bed plate a (103) on the two marking lines are measured respectively, and are recorded as Δz1 and Δz2 respectively. Then the roll tilt angle is:

10. The measurement method of the radiotherapy bed deformation measurement device according to claim 3, characterized in that: The calibration object (601) is an object with more than one known size.

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