Apparatus and method for calibrating and controlling collimator leaves

Abstract

A computer-implemented method for calibrating a multi-leaf collimator of a radiotherapy device. The multi-leaf collimator includes a plurality of leaves, each leaf including an imaging marker, wherein the radiotherapy device includes an imaging device configured to image the leaves. The method includes: receiving, from the imaging device, an image of the multi-leaf collimator in a calibration position, wherein, in the calibration position, the tips of the leaves abut an edge of a rigid calibration block, the edge having a known calibration profile; for each leaf, calculating a small offset of the marker relative to a reference point based on the calibration profile and the positioning of the marker in the image; and outputting a calibration value based on the calculated small offset, wherein at least one leaf of the multi-leaf collimator is controlled based on the calibration value.

Description

Technical Field

[0001] The present disclosure generally relates to multi-leaf collimators of radiotherapy devices. More specifically, the present disclosure relates to devices and methods for calibrating and controlling the movement of the leaves of a multi-leaf collimator. Background Art

[0002] Radiotherapy equipment involves the generation of an ionizing radiation beam, which is typically an x-ray or an electron beam or other subatomic particles. This is directed towards the cancerous region of a patient and has an adverse effect on the tumor cells, thereby alleviating the patient's symptoms. The beam is defined such that the radiation dose is maximized in the tumor cells and minimized in the patient's healthy cells, as this improves the treatment efficiency and reduces the side effects suffered by the patient.

[0003] In radiotherapy equipment, a beam limiting device such as a "Multi-Leaf Collimator" (MLC) can be used to define the beam. This is a multi-leaf collimator composed of a large number of slender and thin leaves arranged side by side in a matrix. The leaves are typically made of a material with a high atomic number (usually tungsten) such that they are substantially opaque to radiation.

[0004] Each leaf can be longitudinally moved such that its tip or leading edge can extend into or retract from the radiation beam. All the leaves can be retracted to allow the radiation beam to pass through, or all the leaves can be extended to completely block the radiation beam. Alternatively, some leaves can be retracted and some leaves can be extended to define any desired shape within the operating limits. The array of leaf tips can thus be positioned to define the variable edge of the collimator. A multi-leaf collimator typically consists of two groups of such arrays (i.e., leaf groups), each leaf group projecting into the radiation beam from opposite sides of the collimator. Thus, the variable edges provided by the two leaf groups collimate the radiation beam into a selected cross-sectional shape, typically the shape of the target tumor volume to be irradiated. That is, the two leaf groups combine to provide a variable-shaped aperture for shaping the radiation beam.

[0005] Precisely controlling the beam shape is important, and thus techniques for calibrating the positions of the collimator leaves have been developed. Summary of the Invention

[0006] Aspects and features of the present invention are described in the appended claims.

[0007] Devices and methods for precisely measuring minute offsets of collimator leaves are disclosed herein. Specific examples of the present disclosure can precisely determine the positions of the collimator leaves, thereby providing more precise positioning of the leaves during radiotherapy to shape the radiation beam. Brief Description of the Drawings

[0008] The following describes specific embodiments by way of example only in conjunction with the accompanying drawings, wherein:

[0009] Figure 1 shows a radiotherapy device;

[0010] Figure 2A shows a top view of a leaf array of a multi - leaf collimator;

[0011] Figure 2B is a side view of a leaf of the multi - leaf collimator;

[0012] Figure 3 is a flowchart of a leaf imaging method according to an aspect of the present disclosure;

[0013] Figure 4A is a cross - sectional view of two leaf groups in a calibration position;

[0014] Figure 4B is a top view of two leaf groups in a calibration position;

[0015] Figure 5 is a flowchart of a method for calculating a small offset;

[0016] Figure 6A is a cross - sectional view of two leaf groups in a calibration position;

[0017] Figure 6B is a top view of two leaf groups in a calibration position;

[0018] Figure 7 is a flowchart of a method for verifying a small offset;

[0019] Figure 8 is a computer - implemented method for calibrating a multi - leaf collimator;

[0020] Figure 9 is a top view of two leaf groups in a calibration position;

[0021] Figure 10A shows a calibration block having a castle - like structure according to an embodiment;

[0022] Figure 10B shows a calibration block having a castle - like structure according to another embodiment. Detailed Description

[0023] Considering the importance of precisely controlling the beam shape of a radiotherapy device, techniques for calibrating the positions of collimator leaves have been developed.

[0024] For example, some radiation-based calibration techniques utilize x-ray film or point dosimeters to confirm that the leaves form the desired radiation beam shape. However, such techniques can be time-consuming and often provide a poor indication of the actual beam geometry. Other calibration techniques involve using a laser beam and an optical detector to determine when the MLC leaves have reached a defined calibration position. However, such techniques may not provide an accurate indication of the leaf position for all leaf shape configurations. Further calibration techniques involve imaging optical markers on the leaves with a camera and using the positions of the detected optical markers to determine the leaf positions. However, the lens of the camera can distort the image of the marker, meaning that additional calibration steps may be required to provide an accurate determination of the leaf position.

[0025] In addition, since the optical markers are manually placed on the collimator leaves, the distance between the marker and the leaf tip (a distance referred to as the "tiny offset") is different for each leaf. Existing MLCs cannot simply measure the tiny offset with a camera because the leaves are not visible to the camera. For these reasons, existing collimator devices may require computationally intensive and time-consuming calibration steps to ensure that the collimator leaves are correctly positioned during radiotherapy.

[0026] The present disclosure provides devices and methods for generating an accurate measurement of the tiny offset, enabling the true position of the leaves to be determined without adding excessive calibration time to the machine setup process. As a result, the leaves can be more precisely positioned during radiotherapy, enabling the desired beam geometry to be achieved. In known systems, many components with strict tolerances are required to obtain satisfactory calibration accuracy. Due to the high precision and strict tolerances, the production cost of many components increases significantly.

[0027] There is a desire to provide a method for calibrating a multi-leaf collimator that addresses the above problems.

[0028] Figure 1 is a view of an exemplary radiotherapy device 100. The radiotherapy device 100 is, for example, a Linear Accelerator (LINAC) or a combination of Magnetic Resonance Imaging (MRI) and a linear accelerator.

[0029] The radiotherapy device 100 includes a gantry 102 that supports a radiation head 104 and a detection panel 106. The radiation head 104 and the detection panel 106 are mounted on the gantry 102 opposite each other, and the axis of rotation of the gantry 102 is located between them. The radiation head 104 is configured to generate a radiation beam 122 according to a treatment plan to deliver a radiation dose to a patient 124 supported by a couch 110. The gantry 102 is configured to rotate the radiation head 104 and the detection panel 106 around the couch 110 to provide the patient 124 with a variety of different doses of radiation according to the treatment plan.

[0030] The radiation head 104 includes a collimator for collimating the radiation beam 122. The collimator described in conjunction with other figures below is a multi-leaf collimator. The radiation head 104 also includes an imaging device for imaging the positioning of the leaves of the multi-leaf collimator.

[0031] In some embodiments, the device 100 includes an imaging device, such as being configured as an MR-LINAC device. The exemplary device 100 utilizes MR images, CT images, and / or pseudo-CT images to monitor and control the radiation delivered by the radiation head 104.

[0032] The radiotherapy device 100 includes a controller 140, which is programmed to control the radiation head 104, the detection panel 106, the couch 110, the imaging device, and the gantry. The controller 140 can perform functions or operations such as, for example, treatment planning, treatment execution, image acquisition, image processing, motion tracking, motion management, and / or other tasks involved in the radiotherapy process. The hardware components of the controller 140 can include one or more computers (e.g., general-purpose computers, workstations, servers, terminals, portable / mobile devices, etc.); processors (e.g., Central Processing Unit (CPU), Graphics Processing Unit (GPU), microprocessor, Digital Signal Processor (DSP), Field Programmable Gate Array (FPGA), dedicated or specially designed processors, etc.); memory / storage devices, such as memory 142 (e.g., Read-Only Memory (ROM), Random Access Memory (RAM), flash memory, hard disk drive, optical disc, Solid-State Drive (SSD), etc.); input devices (e.g., keyboard, mouse, touch screen, model, button, knob, trackball, lever, handle, joystick, etc.); output devices (e.g., display, printer, speaker, vibration device, etc.); circuits; Printed Circuit Board (PCB); or other suitable hardware. The software components of the controller 140 can include operating system software, application software, etc.

[0033] The controller 140 is programmed to control the features of the device 100 in accordance with a radiotherapy treatment plan for irradiating a target tissue of a patient. The treatment plan includes information about a specific dose to be applied to the target tissue, as well as other parameters such as beam angles, dose histogram-volume information, the number of radiation beams to be used during treatment, the dose per beam, etc. The controller 140 is programmed to control various components of the device 100, such as the gantry 102, the radiation head 104, the detection panel 106, and the couch 110, in accordance with a predetermined treatment plan.

[0034] Figure 2A is a top view of an exemplary leaf array of the MLC 200, Figure 2B is a side view of an exemplary leaf 202.

[0035] The MLC 200 includes a plurality of elongated leaves 202, 204 that are oriented perpendicular to the axis of the beam 122, which travels in the direction into the page in the top view of the MLC 200 in Figure 2A . During a radiotherapy treatment, the leaves of the MLC 200 are controlled to assume different positions to selectively block some or all of the radiation beam 122, thereby altering the shape of the beam reaching the patient.

[0036] The MLC 200 includes two leaf groups 210, 220, each of which can be individually extended into and withdrawn from the path of the radiation beam 122 such that their respective tips 206 shape the cross-section of the beam by blocking portions of the beam. The term "tip" can refer to the functional end of the leaf 202 along its longitudinal axis for the purpose of forming a shaped window for the radiation beam 122. The term "tip" does not necessarily refer to the end point of the leaf 202 relative to its longitudinal axis (i.e., the point on the leaf 202 closest to the center of the MLC 200), although in some embodiments it can refer to the end point of the leaf 202 relative to its longitudinal axis. In some embodiments, the MLC 200 includes a set of motors, each of which is configured to move a corresponding one of the leaves. The movement of each leaf by the motors is controlled by the controller 140. For example, the controller 140 controls the placement of the leaf tips 206 via the motors, for example, in accordance with a predetermined treatment plan, to shape the radiation beam 122 for irradiating the target tissue 300. In some embodiments, the leaves 202, 204 are configured to extend into the path of the radiation beam 122 to a position beyond the midpoint between the leaf groups 210, 220, thereby allowing the leaves 202, 204 to close completely together.

[0037] The radiation head 104 also includes an imaging device, such as a camera, that is configured to observe the collimator leaves 202, 204. The leaves 202, 204 may be invisible to the camera; thus, the leaves 202, 204 include imaging markers, such as ruby or fluorescent markers, mounted thereon that are visible to the camera.

[0038] In an embodiment where each of the leaves 202, 204 includes a ruby as an imaging marker, the ruby is configured to fluoresce in the dark red / near-infrared light band (e.g., 695 nm) when irradiated with light having a wavelength in the green light band at 525 nm or in the violet / near-ultraviolet light band at 410 nm. The camera uses the light emitted by the ruby to generate image data of the leaves 202, 204. The controller 140 uses the image data to determine the position of the leaves and controls the movement of the leaves into or out of the path of the radiation beam 122 to shape the radiation beam (e.g., according to a predetermined treatment plan).

[0039] The leaves 202, 204 are made of a radiation-impermeable material such as tungsten, for example, and are arranged side by side relative to each other in two opposing groups 210, 220; thus, the area below the leaves 202, 204 is not irradiated. Each leaf faces a corresponding leaf in the other leaf group; two opposing leaves form a leaf pair 225. Each leaf is thin in its lateral (y) direction to provide high resolution and limit the size of the tissue area that is unnecessarily irradiated. Each leaf is also deep in the (z) direction to provide effective radiation absorption.

[0040] The MLC has a centerline midway between the groups of opposing leaves. That is, the centerline is equidistant between the first leaf group 210 and the second leaf group 220. The camera is centered on the centerline of the MLC. For example, the MLC has four reference markers, such as rubies, mounted above the MLC and symmetrically positioned with respect to the centerline. The optomechanical workflow and alignment align the camera and the lens (image center) with these rubies. The block is fixed at the mechanical / beam center of the MLC because all calibration and distortion calculations are made from the center / image center of the camera lens that coincides with the beam center. Thus, the image of the MLC from the camera is centered on the centerline.

[0041] As can be seen from Figure 2B it is visible that Figure 2BA side view of an exemplary leaf 202 is shown. The leaf includes a body 240 made of a radiopaque material such as tungsten, for example. The leaf 202 also includes an imaging marker 242 (such as ruby) located near the leaf tip 206. The imaging marker 242 of each leaf is manually placed at a predetermined distance from the leaf tip 206. For example, the imaging marker 242 can be placed such that its center is approximately 4.5 millimeters from the leaf tip 206. However, because each imaging marker is manually placed, the small offset 244 between the center of the imaging marker 242 and the leaf tip 206 can be different for each leaf. The camera cannot measure the small offset 244 by imaging the position of the leaf tip 206 because the leaf 202 is invisible to the camera except for the imaging marker 242. Therefore, a technique is needed to determine the small offset, that is, the exact distance from the center of the imaging marker 242 to the leaf tip 206, so that the exact position of the leaf tip 206 can be accurately determined based on the image from the camera showing the marker 242.

[0042] The leaves of the MLC 200 can have the same shape and size; for example, for all the leaves of the MLC 200, the leaf length, the length of the drive coupler, and the length of the body can be constant. However, because each marker 242 is manually and individually placed, the small offset 244 can vary from leaf to leaf.

[0043] Calibrate the MLC

[0044] Figure 3 An exemplary calibration method 300 for a multi-leaf collimator (such as the MLC 200) is shown, in which the small offset is quantified and used to determine the position of the leaf tip based on the detected position of the collimator leaf marker.

[0045] 300A is a method for obtaining a calibration image from which the small offset value of the leaf can be calculated. 300B is a method for obtaining a verification image from which the small offset value can be verified.

[0046] The steps in the dashed lines are performed by a computer program on a processor (such as a computer program on the processor in the controller 140). The method performed by the computer program is shown in more detail in Figure 8 The steps in the dashed lines do not necessarily need to be performed in the order shown in Figure 3 For example, the processing of the images can be performed after two images (the calibration image and the verification image) have been obtained.

[0047] Obtain a calibration image

[0048] 300A is a method for obtaining a calibration image of the leaves of a multi-leaf collimator. The calibration image can be used to calculate the value of the minute offset of the leaves. That is, the calibration image can be used to determine the distance between the leaf marker 242 and the leaf tip 206 for each leaf of the MLC 200.

[0049] In step 310, a calibration block is inserted between two leaf groups. Figure 4A An embodiment of the calibration block 410 is shown in. The calibration block is mounted between the first leaf group and the second leaf group. A technician or a controller inserts the calibration block 410 between the first leaf group (e.g., leaf group 210) and the second leaf group (e.g., leaf group 220).

[0050] The calibration block is inserted between the first leaf group and the second leaf groups (210 and 220). In Figure 4A and Figure 4B 's embodiment, the calibration block 410 is elongated and mounted such that the longitudinal centerline of the calibration block 410 is parallel to the centerline of the MLC.

[0051] To mount the calibration block in a fixed position, several techniques can be used. Mounting blocks can be used. Alternatively, the collimator leaves can be used to mount the calibration block.

[0052] The collimator is composed of two attenuation leaves, which can move perpendicular to the MLC leaves. These two attenuation leaves form the upper and lower boundary edges of the beam. The aperture leaves can be used to hold the calibration block in the desired orientation. The calibration block is inserted between the leaf groups of the MLC. The aperture leaves extend inward perpendicular to the travel direction of the MLC leaves to abut the ends of the calibration block and hold it in the correct orientation.

[0053] Alternatively, the outer leaves of the MLC can fully extend above the ends of the calibration block and hold the calibration block between them.

[0054] The calibration block 410 is made of a rigid material. In Figure 4A and Figure 4B 's embodiment, the calibration block has a uniform thickness. In this aspect, the calibration block has a thickness of approximately 10 mm. In other aspects, the calibration block has a thickness, for example, between 9 mm and 11 mm or between 8 mm and 12 mm.

[0055] In step 320, the controller 140 advances the leaves of the first leaf group and the second leaf group toward the centerline. The controller 140 moves the leaves by actuating the leaf motors, including advancing and retracting the leaves. The controller 140 moves the leaves until the tips of the leaves abut the calibration block. That is, the leaves of the two groups are advanced until the tips of the leaves contact the calibration block 410.

[0056] The calibration block is rigid, meaning it does not deform when in contact with the leaves of the MLC. Thus, the tips of the leaves are aligned in a line along the edge of the calibration block. In Figure 4A and Figure 4B 's embodiment, the calibration block 410 has a uniform thickness (the thickness in the direction parallel to the leaf movement direction), and the longitudinal axis is parallel to the centerline of the MLC. Thus, the tips of the leaves in each group are aligned on a straight line parallel to the centerline of the MLC.

[0057] When the tips of the leaves each abut the calibration block 410, the leaves of the MLC are in the calibration position.

[0058] In step 330, an image of the MLC in the calibration position is taken. A camera is used to image the MLC. The image of the MLC in the calibration position is referred to herein as the calibration image. The calibration image is sent to a processor, such as the processor of the controller 140.

[0059] Figure 4B A top view of the MLC in the calibration position is shown. The leaves in the two leaf groups abut the calibration block 410, which means that in each pair of leaves, the tips of the leaves are separated by a distance equal to the thickness of the calibration block 410.

[0060] The leaf markers 242 are visible in the calibration image. Since the markers on each leaf are positioned at approximately the same distance from the leaf tip, the markers 242 of each leaf group are also approximately located on a line equivalent to the edge of the calibration block in the calibration position. In Figure 4A and Figure 4B 's embodiment, the edge of the calibration block is a straight line, so the markers in the calibration image are approximately straight lines. The calibration block 410 is not visible in the image. Additionally, the leaves 204 are not visible in the image.

[0061] Since the markers 242 are visible to the camera and are visible in the calibration image, two approximate straight lines of the markers are visible in the calibration image, even though the leaves of the MLC are not visible.

[0062] In step 340, the calibration image is processed by the processor 140 and used to calculate the value of the micro - offset. Details of processing the calibration image to calculate the micro - offset are given in Figure 5 . The micro - offset is the offset of the marker relative to a reference positioning. If calculating the absolute micro - offset, the reference positioning is the tip of the leaf, or if calculating the relative micro - offset, the reference positioning is the reference marker of the leaf in the leaf group. This will be discussed in more detail below.

[0063] The micro - offset can be calculated as the distance from the centroid of each marker.

[0064] Calculate a minute offset

[0065] Figure 5 shows a computer-implemented method that is performed in a processor that calculates a minute offset value for each leaf in a calibration image (such as the calibration image obtained in 300A).

[0066] Some embodiments of the methods disclosed herein can be used to calculate relative minute offsets, which are discussed in the section titled "Relative Minute Offsets" below. Other embodiments, such as Figure 5 the embodiment shown in, calculate the absolute minute offset for each leaf.

[0067] In step 510, the processor receives a calibration image from the camera. In step 520, the processor identifies the positioning of the edges of the calibration block in the image. Since, in the calibration position, the tip of the leaf abuts the calibration block 410, the positioning of the edges of the calibration block 410 in the calibration image corresponds to the positioning of the tips of the leaves in the calibration image.

[0068] There are several ways to identify the positioning of the edges of the calibration block. In an embodiment where the block has a uniform thickness and is mounted on the centerline of the MLC along its longitudinal axis, the following method can be used to identify the edges of the calibration block in the image.

[0069] The processor first identifies the centerline of the MLC. As described above, the camera is centered on the centerline of the MLC, so the image is centered on the centerline of the MLC. Since the calibration block 410 is centered on the centerline, the thickness of the calibration block can be used to identify the positioning of each edge of the calibration block in the image.

[0070] That is, half of the thickness 420 of the calibration block 410 is located on either side of the centerline 230. If the center of the image is taken as x = 0, the positioning of the edges of the calibration block is located at the lines and at.

[0071] This line is also the lateral positioning of the tips of the MLC leaves.

[0072] In other embodiments, different techniques can be used to identify the edges of the block.

[0073] In one embodiment, the block is inserted such that its longitudinal axis is aligned with an alignment line that is offset from the centerline by a known distance. Since the image is centered on the centerline, the known distance can be used to locate the alignment line in the image. Once the alignment line is located in the image, the thickness of the block is used to determine the positioning of the edges of the block using a method similar to that in step 520 above.

[0074] In other embodiments, the calibration block is inserted such that its edges are at known predetermined positions. The predetermined positions are known, so they can be identified in the image.

[0075] In embodiments where the blocks do not have a uniform thickness (detailed below in the "Non-uniform thickness" section), the thickness of the blocks and the known profile of the edges can be used to identify the edges of the blocks relative to the alignment line in the image.

[0076] In some embodiments, the blocks can be placed by a technician into a predefined profile. The positioning of this profile is known and identified in the image.

[0077] Alignment marks can be marked on the MLC to assist the technician in inserting the calibration blocks into the correct position.

[0078] In step 530, the processor 140 obtains the imaging marker positions. That is, the processor determines the positioning of the leaf markers 242 in the calibration image for each leaf. The obtained imaging marker positions include the imaging marker position coordinates for the imaging markers of each leaf.

[0079] In step 540, the processor calculates a fine offset 244 for each leaf in the group. The fine offset is the lateral difference between the marker position identified in the image and the reference positioning. In Figure 5 the embodiments, the fine offset is an absolute fine offset, i.e., the distance between the positioned leaf tip (which coincides with the positioned edge of the calibration block) and the marker position identified in the image. In other embodiments, the fine offset is a relative fine offset, as explained later in the specification.

[0080] The processor calculates the leaf position coordinates corresponding to the positions of the tips 206 of the collimator leaves, which can include the x and y coordinates of each leaf tip 206. For a given leaf at a given location, the value of the fine offset can be subtracted from the value of the imaging marker x coordinate to determine the value of the leaf position x coordinate. In this way, the fine offset can be corrected and the x coordinate of the leaf tip can be identified. For a given leaf at a given position, the value of the leaf position y coordinate can be equal to the value of the imaging marker y coordinate. Since the fine offset only distorts the calculation of the leaf position along the x-axis, the y coordinate of the leaf does not require correction for the fine offset.

[0081] In step 350, the leaves of the MLC are retracted away from the centerline such that the leaf tips no longer abut the calibration blocks. Once the leaves have been retracted, the calibration blocks 410 can be removed from the MLC. The calibration blocks can be removed by hand by a technician, or in a radiotherapy device there can be an actuator to insert and remove these blocks.

[0082] Obtain a verification image

[0083] 300B is a method for obtaining a verification image of the leaves of a multi-leaf collimator. The verification image can be used to verify the values of the minute offsets of the leaves that have been calculated by the processor in step 340. The verification of the minute offset values is to confirm that each of the minute offset values is accurate enough to fall within the threshold of the device.

[0084] Optionally, the verification image can also be used to verify lens distortion. As described above, the lens of the camera can distort the image of the markers. The degree of this distortion is different for each lens and may change whenever the camera is adjusted; therefore, the distortion correction techniques developed for one camera may not be applicable to other cameras or to the camera under discussion after repair. The amount of distortion varies with the lens and thus varies across the image. The lens distortion is calculated using other known techniques and stored in the processor.

[0085] In step 360, a verification block is inserted between two leaf groups. Figure 6A The verification block 610 is shown in. The verification block is installed between the first leaf group and the second leaf group in a manner similar to the installation of the calibration block. A technician or the controller inserts the verification block 610 between the first leaf group (e.g., leaf group 210) and the second leaf group (e.g., leaf group 220).

[0086] In Figure 6A and Figure 6B In the embodiments, the verification block 610 is elongated and installed such that the longitudinal centerline of the verification block 610 is parallel to the centerline of the MLC.

[0087] The verification block 610 can be installed as discussed above regarding the installation of the calibration block. That is, the aperture leaf or the outermost leaf of the MLC can be used to install the verification block and hold it in a known orientation.

[0088] Similar to the calibration block 410, the verification block 610 is made of a rigid material. The verification block also has a known thickness. The verification block 610 has a thickness 620 that is different from the thickness 420 of the calibration block.

[0089] In some embodiments, the thickness of the verification block 610 is greater than the thickness of the calibration block 410. This provides the advantage of allowing the calculation of more accurate minute offset values as explained below.

[0090] In Figure 6A and Figure 6B In the embodiments, the verification block has a constant thickness of approximately 50 mm. In other respects, the calibration block has a thickness, for example, between 9 mm and 11 mm or between 8 mm and 12 mm.

[0091] At step 370, the controller 140 advances the leaves of the first and second leaf groups towards the centerline. The controller 140 moves the leaves until the tips of the leaves abut the verification block 610. That is, the leaves of the two groups are advanced until the tips of the leaves contact the verification block 610.

[0092] The verification block is rigid, meaning it does not deform when contacting the leaves of the MLC. When the tips of the leaves each abut the verification block 610, the MLC is in the verification position. In Figure 6A and Figure 6B 's embodiments, the verification block 610 has a uniform thickness (thickness in the direction parallel to the leaf movement direction), and the longitudinal axis is parallel to the centerline of the MLC. Thus, the tips of the leaves in each group are aligned on a straight line parallel to the centerline of the MLC.

[0093] At step 380, an image of the MLC in the verification position is taken. A camera is used to image the MLC. The image of the MLC in the verification position is referred to herein as the verification image. The verification image is sent to a processor, such as the processor of the controller 140.

[0094] Figure 6B A top view of the MLC in the verification position is shown. The leaves in the two leaf groups abut the verification block, which means that in each leaf pair, the tips of the leaves are separated by a distance equal to the thickness of the verification block 610.

[0095] The leaf markers 242 are visible in the verification image. Since the markers on each leaf are positioned at a substantially the same distance from the leaf tip, in embodiments where the verification block has a uniform thickness, the markers 242 of each leaf group in the verification position are also substantially positioned on a straight line. The verification block 610 is not visible in the image. Additionally, the leaves 204 are not visible in the image.

[0096] Since the markers 242 are visible to the camera and are visible in the verification image, two approximate straight lines of the markers are visible in the verification image, even though the leaves of the MLC are not visible.

[0097] At step 390, the verification image is processed by the processor 140 and used to verify the value of the minute offset calculated in step 340. Details of processing the verification image to verify the minute offset are given below in Figure 7 '.

[0098] In the above description, separate calibration and verification blocks were described. In another embodiment, a single tool can be used as both the calibration block and the verification block. When inserted in a first orientation (e.g., at step 310), the block serves as the calibration block and presents a first profile for the leaf to abut in the calibration position. The tool is then removed and rotated. It is re-inserted in a second orientation (e.g., at step 360) to serve as the verification block. In the second orientation, the block provides a second profile for the leaf to abut in the calibration position. In this way, a single tool is provided to perform the functions of both the calibration block and the verification block.

[0099] Verify the minute offset

[0100] Figure 7 A computer-implemented method is shown that is performed in a processor that validates the minute offset values of each leaf in a verification image (e.g., the verification image obtained at 300B).

[0101] In step 710, the processor receives the verification image from the camera. In step 720, the processor identifies the positioning of the edges of the verification block in the image. In the verification position, the tip of the leaf abuts the verification block 610, and the positioning of the edges of the verification block 610 in the verification image corresponds to the positioning of the tip of the leaf in the verification image.

[0102] Any technique can be used to identify the edges of the verification block, such as those described above in step 520 for identifying the edges of the calibration block.

[0103] In an embodiment where the block has a known uniform thickness and is centered on the centerline of the MLC, the following steps can be used.

[0104] Half of the thickness 620 of the verification block 610 lies on either side of the centerline 230. If the center of the image is taken as x = 0, the positioning of the edges of the verification block lies on the lines and at.

[0105] This line is also the lateral positioning of the tip of the MLC leaf. As described above regarding step 520, other methods can be used.

[0106] In one embodiment, the verification block is inserted such that its longitudinal axis is aligned with an alignment line that is offset from the centerline by a known distance. Since the image is centered on the centerline, the known distance can be used to locate the alignment line in the image. Once the alignment line is located in the image, the thickness of the verification block is used to determine the positioning of the edges of the block using a method similar to that in step 720 above.

[0107] In other embodiments, the verification block is inserted such that its edges are at known predetermined positions. The predetermined positions are known and can thus be identified in the image.

[0108] In embodiments where the verification block does not have a uniform thickness (detailed below in the "Non-uniform thickness" section), the thickness of the block and the known profile of the edges can be used to identify the edges of the block relative to the alignment line in the image.

[0109] In some embodiments, the block can be placed by a technician into a predefined profile. The positioning of the profile is known and identified in the image.

[0110] Alignment marks can be marked on the MLC to assist the technician in inserting the verification block into the correct position.

[0111] In step 730, the processor 140 calculates the expected positioning of each mark in the verification image. The expected positioning is the positioning where the mark would be if the calculated distortion and the minute offset are correct.

[0112] For each leaf, the total displacement of the mark is calculated by adding the calculated minute offset to the calculated edge of the verification block in the image, thereby calculating the expected positioning.

[0113] The distortion value is also considered. Known techniques are used to calculate the distortion, and if both the minute offset and the calculated distortion are correct, the calculated distortion is used to determine the position in the image where the mark is expected to be.

[0114] In step 740, for each leaf, the actual positioning of the mark in the image is located and compared with the expected positioning of the mark. If the actual positioning of the mark coincides with the expected positioning, the distance between the two is zero, and the image confirms the calculated minute offset and the calculated distortion.

[0115] If the actual positioning of the mark does not coincide with the expected positioning of the mark, the processor determines the distance between the actual positioning and the expected positioning.

[0116] In step 750, the distance between the actual positioning and the expected positioning of the mark in the image is compared with a threshold. The threshold is predetermined and stored in a memory associated with the processor. The threshold can be input by the technician or can be determined during manufacturing. If the distance is less than the threshold, the calculated minute offset value and the distortion are determined to be acceptable and within the tolerance of the machine. The minute offset and the distortion are determined to be valid (step 70).

[0117] If the distance between the positioning of the mark in the image and the expected positioning of the mark is greater than the threshold, the calculated minute offset and the distortion are not within the acceptable tolerance. The minute offset and the distortion are determined not to be valid (step 770).

[0118] Steps 720 to 760 / 770 are performed for each leaf using the calculated minute offsets of the respective leaf and the image localization of the leaf markers of that leaf. It is possible that the calculated minute offsets or some of the leaves of the MLC are determined to be valid, while the calculated minute offsets for the remaining leaves of the MLC are determined to be not valid.

[0119] Once verified, the value of the minute offset for each leaf is output. This value can be saved to the memory 142 of the device. The minute offset of each leaf is stored in the memory and can be used in future radiotherapy procedures. That is, once the minute offsets are calculated and saved, there is no need to calibrate the MLC before each use of the radiotherapy device. Once the MLC is calibrated by calculating the minute offsets, these values can be saved in the device and used during future use of the MLC.

[0120] In radiotherapy, minute offsets are used to accurately calculate the positions of the tips of the leaves of the multi-leaf collimator. Based on the detected positions of the collimator leaf markers, minute offsets are used to determine the positions of the leaf tips. The positions of the leaf tips must be known during the treatment process in order to know the shape of the radiation beam and thus the radiation dose delivered to the patient.

[0121] During the treatment process, the leaves are controlled by a controller to produce the desired beam shape. The leaves are imaged by a camera so that the positions of the leaves can be checked against the treatment plan, i.e., to ensure that the leaves are in the expected positions and to define the beam according to the treatment plan. The leaves themselves may not be visible in the image. In some examples, the leaves may be partially visible. The leaf markers 242 are visible in the image. For each leaf, the absolute position of the leaf tip is calculated using the localization of the leaf marker 242 in the image and the corresponding minute offset of that leaf.

[0122] Once the absolute positions of the leaf tips are known, this is used to determine the collimation provided by the leaves during the treatment. The MLC is controlled using the minute offsets based on the calculated positions of the leaf tips. For example, if it is determined from an image of the MLC during the treatment that a leaf tip needs to extend or retract from the beam to align with the treatment plan, the controller controls the leaf as needed.

[0123] These blocks can be inserted by hand by a technician or an operator. There may be markings on the MLC such that the operator can align the center of the calibration / verification block with the center line of the MLC.

[0124] Alternatively, the blocks can be included in an adapter that fits onto an attachment ring for the MLC. The blocks can be moved to the appropriate positions by an actuating device rather than by hand. As described below, the actuating device can include a diaphragm in the radiation head.

[0125] Computer-implemented method

[0126] Method 800 is a method executed by a processor. In some embodiments, the steps of method 800 are executed by the same processor in a radiotherapy device, such as the processor in controller 140. Alternatively, one or more steps of method 600 may be executed by a separate processor.

[0127] Alternatively, the method may be executed at a location remote from the radiotherapy device (e.g., at a central server that receives images via a network).

[0128] In step 810, the processor receives a calibration image of the MLC from a camera. The calibration image may be obtained using the steps in 300A. The calibration image may be obtained at any time. For example, method 800 may start as soon as a technician obtains the calibration image. Alternatively, the calibration image may have been obtained some time ago.

[0129] At 820, the processor calculates the minute offset of each leaf. This may be done using the positioning of the markers 242 in the image and the known contour of the calibration block. The method in Figure 5 may be used to calculate the minute offset. The minute offset may be stored in a memory.

[0130] In step 830, the processor receives a verification image of the MLC from the camera. The verification image may be obtained using the steps in 300B. The verification image may be obtained at any time. For example, the verification image may have been obtained before the calibration image.

[0131] At 840, the processor determines from the verification image whether the minute offset calculated in step 820 is valid. This is achieved by comparing the expected positioning of the markers in the image with the positioning of the marker image, which is calculated using the contour of the verification block and the calculated minute offset. If the difference between the two is below a threshold, the calculated minute offset is valid. The method in Figure 7 may be used to calculate the expected positioning.

[0132] If it is determined that the calculated minute offset is valid, the minute offset is output in step 850, e.g., sent to the processor of the radiotherapy device or stored in a memory. The memory may be a memory located at the radiotherapy device, such as memory 142, or may be stored at a remote location. The calculated minute offset for each of the plurality of leaves is output as a calibration value.

[0133] In step 870, the calibration value is used to control the leaves of the MLC. This step is optional and not necessary in the method of calibrating the MLC.

[0134] If it is determined in step 840 that the minute offset is not valid, the processor provides feedback that the minute offset has been determined to be not valid. This feedback can be a message to the operator via the user interface. Alternatively, the feedback can be a message prompting re-analysis of the calibration image to recalculate the minute offset of the leaf.

[0135] Step 840 can also include including the lens distortion value when calculating the expected positioning of the markers in the image. The lens distortion value is calculated using other known techniques and stored in the processor. If the positioning of the markers in the verification image is within the threshold of the expected positioning, it is determined that both the minute offset and the lens distortion are valid. If the positioning of the markers in the verification image is not within the threshold of the expected positioning, the calculated minute offset or lens distortion value or both are not valid.

[0136] Non-uniform thickness

[0137] In Figure 4A 、 Figure 4B 、 Figure 6A and Figure 6B In the embodiments of, the calibration block and the verification block each have a uniform thickness. When the calibration / verification block has a uniform thickness, at the calibration / verification position, the tips of the leaves are aligned in a straight line. In this way, the relative offset of the leaf markers is known. That is, the position of each leaf marker relative to the other markers for the leaves to be in a straight line is known. Thus, during the diagnosis and treatment, the relative offset of the markers in the image can be used to determine the relative offset of the tips of the leaves. Therefore, the shape formed by the edges of the leaf group is known.

[0138] Obviously, a calibration block with any known thickness can be used to calculate the minute offset. That is, the calibration block does not need to have a uniform thickness.

[0139] For example, a calibration block with a stepped thickness as shown in, for example, Figure 9 can be used. The calibration block has a first thickness T1 and a second thickness T2. When the leaf is in the calibration position, the shape formed by the edges of the leaf group is known. This shape is the shape of the edge of the block. Instead of a straight line, as in the examples of Figure 4A and Figure 4B , the tips of the leaves in a group form a stepped edge.

[0140] In the same way as in the above example, the positioning of the leaf marker 242 in the calibration image can be used to obtain the value of the minute offset of the marker.

[0141] The same is true for the verification block - any shape can be used where the relative positions of the leaf tips are known. This allows calculation of the minute offset of the leaf markers.

[0142] The "profile" of the edge of the calibration / verification block is referred to herein. This profile is the shape of the edge of the block adjacent to the leaf tip. For a block of uniform thickness (e.g., Figure 4A and Figure 4B the calibration block in Figure 6A and Figure 6B the verification block in), the profile of each edge is a straight line. Figure 9 The profile of each edge of the calibration block shown in

[0143] is a stepped shape. In some embodiments, the calibration block and / or verification block may have a castellated structure. A castellated structure is a recess in the profile of the block, shaped to accommodate one or more MLC leaves adjacent to the inner edge of the protrusion. Alternatively, the castellated structure may be a protrusion extending from the edge of the block, shaped such that one or more MLC leaves are adjacent to the protrusion. Figure 10A A block 910 is shown having a pair of opposing castellated structures 902, 904 at each end of the block. The "block" 910 may be a calibration block or a verification block. In use, when the leaves are positioned adjacent to the edge of the block, the end leaves of each leaf group fit into the castellated structure and are adjacent to the edge of the castellated structure. In this way, the block can self-position correctly between the leaf groups. The castellated structure is shaped such that it accommodates the leaves and negligible longitudinal movement is possible, such that the castellated structure ensures correct longitudinal positioning of the calibration block in the field.

[0144] As will be appreciated, other arrangements of castellated structures on the calibration (or verification) block may be included. In another embodiment, the edge of the block is shaped such that each leaf pair is adjacent to a different castellated structure along at least a portion of the edge of the block. Figure 10B The block shown in

[0145] has a plurality of castellated structure "steps", 906 and 908. The leaves are adjacent to each castellated structure or step, creating a pattern that follows the shape of the castellated structures on the block. The block may be shaped such that the distance between the leaves adjacent to each side of the block varies to cover the entire field, or a larger portion of the entire field. This is useful for mapping non-linearity across the optical device. Figure 10BAs can be seen, the castle-like structure pattern 906 at the upper left corner of the block is different from the castle-like structure pattern 908 at the lower right corner of the block. That is to say, the outline of the block is asymmetric when rotated 180 degrees in the plane. Therefore, the block 910 can be inserted in different orientations to provide different outlines, and the outline provided in the first orientation is different from the outline provided in the second orientation. Using the block in two different orientations increases the field covered by the leaves at the calibration or verification position. This is useful for mapping the non-linearity of the optical device using a single block. Different orientations can be provided by rotating around one or more of the three axes (i.e., in-plane rotation, "horizontally" flipping, "vertically" flipping). In some examples, the block can have castle-like structures on all four sides and be asymmetric, such that each 90-degree in-plane rotation provides a different outline.

[0146] Using a block with a stepped castle-like structure and / or an asymmetric castle-like structure provides a single tool that can be used so that at the calibration and / or verification position, the distance between the leaves covers most of the field or the entire field. Alternatively, multiple tools can be used, each block having a different outline, to cover the entire range of the field.

[0147] In other embodiments, a block with a symmetric castle-like structure is provided. In Figure 10B it, the castle-like structure is adjacent continuous steps, and adjacent leaves are adjacent to adjacent steps. In other examples, the block can include separate castle-like structures of different depths, each castle-like structure having a width that can accommodate a single leaf or multiple leaves.

[0148] Therefore, a block for calibrating and / or verifying the leaf marking offset is also provided. The block can be used in the methods disclosed herein. In an embodiment, at least one side of the block has an outline including at least one castle-like structure. The side of the block can include an outline having a generally or substantially straight edge, and the outline has at least one castle-like structure. In this way, when the leaves of the leaf group are adjacent to the side, at least one leaf extends to a greater or lesser extent than the other leaves. Optionally, both opposite sides of the block include outlines having at least one castle-like structure. Each side can have an outline having a generally straight edge and at least one castle-like structure.

[0149] Optionally, the castle-like structure is shaped to accommodate a single leaf from the leaf group. The castle-like structure has substantially the same width as the leaf. In use (when the leaf extends to be adjacent to the side of the block), the single leaf extends to a greater extent than the other leaves in the leaf group. In this way, during use, the block can self-align between two leaf groups.

[0150] In some examples, the castle-shaped structure can accommodate multiple leaves of the MLC. For example, a castle-shaped structure configured to accommodate two MLC leaves will have a width that is substantially the same as (although slightly larger than) the width of two MLC leaves.

[0151] Optionally, both opposite sides of the block include two castle-shaped structures. The dimensions of each castle-shaped structure are adapted to accommodate a single leaf from a leaf group. The castle-shaped structures are positioned to accommodate the end leaves of each leaf group such that, in use, the end leaves of each leaf group extend to a greater extent than the other leaves in the leaf group. This provides an improved ability for the block to self-position between leaf groups.

[0152] Optionally, at least one side of the block includes a profile having multiple castle-shaped structures, each castle-shaped structure having a different depth. In this way, in use, the leaves abutting the castle-shaped structures extend to different extents. The dimensions of the castle-shaped structures can be set to accommodate one leaf or multiple leaves. In some embodiments, the block includes multiple stepped castle-shaped structures. By providing castle-shaped structures with different depths along the profile of the side of the block, in use, the leaves extend to multiple different extents to allow for non-linearity in the mapping optics.

[0153] Optionally, the castle-shaped structure is asymmetric such that the profile of the block is asymmetric under rotation. The block can be asymmetric when rotated about one or more of three axes (a first axis orthogonal to the plane of the block and any one of two axes mutually orthogonal to the first axis). Using an asymmetric block in two different orientations increases the field covered by the unused leaves, which is useful for mapping the non-linearity of the optics using a single block.

[0154] In other embodiments, a diaphragm in the radiation head can be used to correctly position the verification / calibration block. For beam shaping purposes, the radiation head includes a diaphragm located above or below the multi-leaf collimator, such as a field-defining diaphragm. These diaphragms can be controlled to extend into the beam to a greater or lesser extent. The diaphragm can be controlled to correctly position the calibration or verification block, which can include positioning or aligning the block between leaf groups.

[0155] Relative minute offset

[0156] Figure 5 and 7 The embodiments in disclose calculating the absolute minute offset of the leaves of the MLC and verifying the minute offset. The absolute minute offset is the distance between the leaf tip and the leaf marker of any given leaf. To calculate the absolute minute offset, the positioning and profile of the edge of the calibration block in the calibration image must be known. In the embodiments in Figure 5 this is determined using the thickness of the block.

[0157] As described above, an absolute minute offset can be used to determine the positioning of the tip of a given leaf based on the marker-based image and the calculated minute offset.

[0158] In some embodiments, a relative minute offset is calculated and / or verified. The relative minute offset is the minute offset (distance between the leaf marker and the leaf tip) of a particular leaf relative to the reference minute offset (distance between the leaf marker and the leaf tip) of a reference leaf in a leaf group of the MLC. The relative minute offset is used to determine the relative position of the tip of the leaf - i.e., the shape of the edge defined by the leaf tip - rather than the exact positioning of the tip of the leaf.

[0159] To calculate the relative minute offset and thus the shape defined by the leaf, the profile of the edge of the calibration block must be known. It is not necessary to know the exact positioning of the block, e.g., whether the block is centered on the centerline or off-center, in order to calculate the relative minute offset.

[0160] Advantages

[0161] Each feature of the leaf used for calibration needs to be machined to very strict tolerances. Machining to strict tolerances is time-consuming and expensive. Additionally, more components or features that need to be machined to strict tolerances may introduce more inaccuracies into the calibration measurements. Thus, it is desirable to provide a method for determining the minute offset of a leaf that does not require any additional parts or dimensions that must be machined to strict tolerances.

[0162] This limits the ultimately achievable calibration accuracy, increases cost, device complexity, and reliability. There are other errors and noises in known calibration techniques that affect calibration to a greater or lesser extent. For example, lens distortion affects different positions of the image by different amounts. It is beneficial to minimize these effects on leaf calibration. The current position sampling of the leaf affects the degree to which distortion affects leaf calibration.

[0163] The present method allows for the determination of the minute offset that does not rely on any additional components of the MLC that are machined to strict tolerances. The MLC components directly involved in the determination of the minute offset are the two components, namely the leaf marker and the leaf tip. Two blocks are required, each having a uniform known thickness. Uniform blocks that are not an integral part of the MLC are relatively easy to machine to an exact and uniform thickness.

[0164] The solution provided is simpler and more accurate than calculating the minute offset by including features with strict tolerances on each leaf of the MLC.

[0165] In addition, the calibration block is thinner than the verification block. The thickness of the selected calibration block is such that the leaf tips of the MLC are close to the centerline at the calibration position. The distortion effect of the lens is minimal at the center of the lens (i.e., the centerline of the MLC). Therefore, for the images used to calculate the minute offset, the influence of distortion is minimized, meaning that the minute offset can be calculated more precisely.

[0166] In the verification image, the leaf tips are away from the centerline, meaning that the distortion has a greater influence on the leaf tips and leaf markers in the verification image. This means that the verification image can be used to verify the combined effect of the calculated minute offset and the determined distortion.

[0167] The present invention provides a method for calculating the minute offset of the leaves of an MLC and verifying the calculated minute offset.

[0168] In one aspect, a method for calculating the minute offset as described above and shown in the drawings is provided, and in one aspect, a method for verifying the calculated minute offset as described above and shown in the drawings is provided. In one aspect, a method for calculating the minute offset and verifying the calculated minute offset is provided.

[0169] The features of the above various aspects can be combined in any suitable manner. It will be understood that the above description has only described specific embodiments by way of aspects, and many modifications and variations will be within the capabilities of those skilled in the art, and these modifications and variations are all intended to be covered by the scope of the appended claims.

Claims

1. A computer-implemented method for calibrating a multi-leaf collimator of a radiotherapy device, the multi-leaf collimator comprising a plurality of leaves, each leaf comprising an imaging marker, wherein, The radiotherapy device includes an imaging device configured to image the leaves, and the method includes: Receiving, from the imaging device, an image of the multi-leaf collimator in a calibration position, wherein, in the calibration position, the tip of the leaf abuts an edge of a rigid calibration block, and the edge has a known spatial calibration profile; For each leaf, calculating a small offset of the marker relative to a reference point based on the calibration profile and the positioning of the marker in the image; and Outputting a calibration value based on the calculated small offset, such that at least one leaf of the multi-leaf collimator can be controlled based on the calibration value.

2. The method according to claim 1, wherein, In the calibration position, the calibration block has a known positioning.

3. The method according to claim 2, wherein, Calculating the small offset includes calculating a small offset of the centroid of each marker from the tip of the corresponding leaf by the following steps: Identifying the positioning of the block in the image; Using the calibration profile to determine the positioning of the edge of the block in the image; Calculating an offset between the positioning of the marker in the image and the positioning of the edge of the block; And Designating the value as the small offset.

4. The method according to claim 1, further comprising: Receiving, from the imaging device, a verification image of the multi-leaf collimator in a verification position, wherein, in the verification position, the tip of the leaf abuts a rigid verification block having a known verification profile; Using the verification profile to determine the positioning of the tip of the leaf in the verification position; Calculating an expected marker positioning of each leaf marker based on the positioning of the tip of the leaf in the verification position and the calculated small offset; Comparing the marker positioning in the verification image with the expected marker positioning; and Based on the comparison, determining whether the calculated small offset is valid.

5. The method according to claim 3, further comprising: Receiving, from the imaging device, a verification image of the multi-leaf collimator in a verification position, wherein, in the verification position, the tip of the leaf abuts a rigid verification block having a known verification profile and a known positioning; Determining the positioning of the tip of the leaf in the verification image; Calculating an expected marker positioning of each leaf marker based on the positioning of the tip of the leaf in the verification image and the calculated small offset; Comparing the marker positioning in the verification image with the expected marker positioning; and Based on the comparison, determining whether the calculated small offset is valid.

6. The method according to claim 5, wherein Determining whether the calculated small offset is valid includes comparing the distance between the calculated positioning in the verification image and the marker positioning with a threshold; And If the distance is below the threshold, determining that the calculated offset is valid.

7. The method according to claim 4, 5 or 6, wherein The multi-leaf collimator includes two sets of opposing leaves that are opposite each other around a centerline; and In the calibration position, the calibration block is centered on the centerline; and in the verification position, the verification block is centered on the centerline.

8. The method according to any one of claims 4 to 6, wherein The calibration block has a uniform first thickness, and the verification block has a uniform second thickness, wherein the second thickness is greater than the first thickness.

9. The method according to any one of claims 4 to 6, wherein The calibration block has a uniform thickness of about 10 mm.

10. The method according to any one of claims 4 to 6, wherein, The calibration block has a uniform thickness greater than or equal to 50 mm.

11. The method according to any one of claims 5 to 6, wherein Calculating the expected marker positioning includes applying a calculated lens distortion factor.

12. The method according to claim 1, wherein The reference point is the imaging marker of a selected leaf among the plurality of leaves.

13. A computer-readable medium configured to execute the method according to any one of claims 1 to 12.

14. A radiotherapy device, comprising: A treatment radiation source configured to generate a treatment radiation beam; A multi-leaf collimator configured to define the radiation beam, the multi-leaf collimator including a plurality of individually movable leaves, each leaf including an imaging marker; An imaging device configured to image the leaves; and The computer-readable medium according to claim 13.

15. The radiotherapy device according to claim 14, further comprising a calibration block having an edge with a known calibration profile and a verification block having an edge with a known verification profile.

16. The radiotherapy device according to claim 15, wherein, At least one of the calibration block or the verification block includes a side surface having a profile that includes at least one toothed structure for receiving one or more leaves of the multi-leaf collimator.

17. The radiotherapy device according to claim 15 or 16, further comprising an actuating device configured to selectively move the calibration block and the verification block into an imaging position, wherein, In the imaging position, the corresponding block is located in the path of the leaves of the multi-leaf collimator.

Images