Phantom body and method for aligning and checking the coordinate systems of image-guided and surface-guided radiation therapy systems

Abstract

The invention relates to a phantom body for aligning and checking the coordinate systems of image-guided and surface-guided radiation therapy systems, comprising a main part which has the shape of a truncated pyramid, wherein the main part has a flat lower face, a flat upper face at a distance therefrom, and four flat lateral faces which connect the lower face and the upper face; each of the lateral faces extends towards the upper face at an angle to the lower face of the main part; and at least one first angle between a first lateral face and the lower face differs from a second angle between a second lateral face and the lower face. The main part has a plurality of optical markers which can be detected by means of an optical detection device, and the main part additionally has a plurality of radiation-opaque balls which are arranged asymmetrically within the main part and which can be detected by means of a kilovolt imaging device (kV imaging device) and / or a megavolt imaging device (MV imaging device).

Description

[0001] - 1 - January 13, 2026

[0002] Phantom bodies and methods for aligning and verifying the coordinate systems of image-guided and surface-guided radiotherapy systems

[0003] DESCRIPTION

[0004] The invention relates to a phantom body and a method for aligning and verifying the coordinate systems of systems for image-guided and surface-guided beam therapy.

[0005] In the field of radiation therapy, imaging methods such as computed tomography are used for diagnosis and treatment planning. Laser projection supports the reproducible positioning and alignment of the patient during imaging.

[0006] Radiotherapy machines frequently employ techniques such as cone beam CT (cone-beam computed tomography) or planar kV / MV (kilovolt / megavolt) imaging to ensure reproducible patient positioning and to verify the patient's position during treatment. Image-guided radiotherapy (IGRT) compares the image data acquired during treatment planning with the image data generated by the radiotherapy machine.

[0007] In recent years, surface-guided radiotherapy (SGRT) has gained considerable importance. This involves the use of optical imaging devices such as 2D or 3D camera systems, time-of-flight (ToF) cameras, LiDAR (Light Detection and Ranging), or light sectioning to generate a 3D surface of the patient and compare it with the 3D model created during treatment planning.

[0008] Compared to IGRT, SGRT offers the advantage that the measurement can be performed more frequently, as the patient is not exposed to any additional radiation dose.

[0009] The various systems used for radiotherapy each have their own coordinate system. To define a position simultaneously for all systems, see zu-2 - January 13, 2026.

[0010] To achieve this, the transformations between the different coordinate systems must be determined during system setup. These transformations are essential for the accuracy of the irradiation and therefore must be regularly checked as part of quality assurance (QA).

[0011] The invention is based on the objective of providing a methodology and a suitable phantom body for determining and testing the transformations between the coordinate systems.

[0012] The invention is solved by the subject matter described in the independent claims. Advantageous embodiments are specified in the dependent claims.

[0013] For determining the transformation between the coordinate systems of the treatment device (treatment coordinate system) and the SGRT system, a cube-shaped phantom (also called phantom body) is currently often used, which is usually made of plastic and contains several radiopaque spheres made of materials that create good contrast to the base body when imaging the phantom with suitable radiation (for example, X-rays).

[0014] Cross-sectional images are taken of this phantom using a CT (computed tomography) device, from which the surface of the phantom and the surfaces of the sphere contained in the phantom are extracted.

[0015] The transformation between coordinate systems describes the mathematical conversion of points or vectors from a source coordinate system to a target coordinate system. This process typically includes translations (displacements along the coordinate axes), rotations (rotations about the axes), and optionally scaling (enlargement or reduction). For the calibration processes described here according to the invention, usually only one translation and one rotation are considered. The other systems use the same units. The position of a point is described by coordinate vectors that are adjusted using transformation matrices. A typical transformation consists of a rotation matrix that specifies the orientation of the target coordinate system relative to the source coordinate system, and a translation vector that specifies the displacement. 3 - January 13, 2026

[0016] describes. If the coordinate systems have different scales or distortions, a scaling matrix is ​​also used.

[0017] The invention is based on the finding that, due to the cube's shape, the two end faces of the cube, whose normals run parallel to the table's direction of travel on the CT scanner, are not captured by the CT scanner. Typically, one slice is taken in front of the surface to be scanned and another behind it. A common solution to this problem is to rotate the cube on the table so that, during the CT scan, the normals of all end faces are not parallel to the table's direction of travel.

[0018] The phantom is placed on the treatment table and positioned as precisely as possible at the isocenter (origin of the coordinate system) of the treatment unit, for example, using an alignment laser. Imaging is then performed using cone beam CT (3D). Alternatively, imaging can be performed using kV or MV planar (2D), typically acquiring multiple images from different angles (gantry angles). This is followed by 6DOF localization (from treatment unit to phantom). For this, one or more volumes are defined in the CT images, and grayscale values ​​within these volumes are compared between CT and CBCT (kV imaging). The surface areas of the phantom's base and the spheres contained within it, extracted from the CT slices, can be used as additional information to validate the calculated localization.Alternatively, instead of CT slices, an artificially generated 3D model of the surface can be used for registration. Comparing the surfaces can be an alternative to comparing the grayscale values ​​of the voxels.

[0019] It is known from the prior art to capture the 3D surface of the phantom using the optical acquisition device of the SGRT system. The 3D surface thus captured is then compared with the 3D surface extracted from the CT images. A second 6DOF localization (SGRT system to phantom) is determined from the comparison of the two surfaces.

[0020] ,.. / 4-4 - January 13, 2026

[0021] A 6DOF positional describes the position (translation) and orientation (rotation) of an object in 3D space using six degrees of freedom: three axes for the orientation (X, Y, Z) and three axes for the rotation (roll, pitch, yaw). It enables a precise and complete description of the position and movement of a body in three-dimensional space.

[0022] As has been recognized, a phantom in the form of a cube has the disadvantage that its surface has symmetries and therefore a unique 6DOF location cannot be determined.

[0023] The two 6DOF coordinates determined in this way can then be used to transform measured values ​​from the coordinate system of the irradiation device to the SGRT system or vice versa.

[0024] Another method for determining the transformation between the coordinate systems of the treatment device and the SGRT system (optical acquisition device) involves using a two-part phantom. The first part of the phantom consists of a cylinder equipped with numerous radiopaque spheres that provide good contrast to the cylinder material in radiation-penetrating imaging. The second part of the phantom consists of a planar plate with numerous optical markers on its surface. The two parts of the phantom can be mechanically connected, resulting in a known relative arrangement.

[0025] This two-part phantom is placed on the table of the treatment unit and roughly aligned with its isocenter. Several planar 2D images are acquired at kV or MV from various positions on the treatment unit. Using the first part of the phantom, an initial 6DOF localization (treatment unit to phantom) is calculated from these images.

[0026] Images are taken from the same position of the two-part phantom using the cameras of the SGRT system. The optical markers of the second part of the phantom are used to calculate a second 6DOF localization (SGRT system to phantom).

[0027] ...15-5-13 January 2026

[0028] These two 6DOF coordinate systems can be used to transform coordinates from the irradiation device's coordinate system to the SGRT coordinate system or vice versa.

[0029] It was recognized that the size of the two-part phantom and the associated handling difficulties proved to be disadvantages. Ensuring the planarity of the second part of the phantom could also pose a challenge.

[0030] Based on these findings, the invention comprises a phantom body for aligning and verifying the coordinate systems of image-guided and surface-guided radiotherapy systems, comprising a base body having the shape of a truncated pyramid, wherein the base body includes a flat underside and a flat top arranged at a distance therefrom, as well as four flat side surfaces connecting the underside and the top, wherein the side surfaces each extend at an angle to the underside of the base body towards the top, and wherein at least one first angle between a first side surface and the underside differs from a second angle between a second side surface and the underside, wherein the base body has several optical markers that can be detected by means of an optical detection device, and wherein the base body further comprises several radiation-opaque spheres.which are arranged asymmetrically within the base body and which can be detected using a kilovolt imaging device (kV imaging device) and / or a megavolt imaging device (MV imaging device).

[0031] Using the phantom body according to the invention, CT slice images of the phantom can result in a closed 3D surface. The surface of the phantom body preferably has no symmetries or symmetries that are irrelevant for imaging, so that unambiguous 6DOF localization is possible from the 3D surface using the imaging of the irradiation device and the SGRT system.

[0032] With regard to the specific geometry of the phantom body, a preferred embodiment provides that the underside and the top side are parallel to each other.

[0033] ...16-6-13 January 2026

[0034] The angles are designed to run. Furthermore, it is ensured that each of the four angles between the underside and the side surfaces differs from the others.

[0035] As explained, the phantom is designed to have asymmetrically arranged spheres within the volume of the base body. These spheres generate good contrast in CT imaging and imaging from the treatment machine, enabling unambiguous 6DOF localization via imaging from the treatment machine. The base body is preferably made of a solid material, with bores provided for the placement of the spheres. These bores can be sealed with plugs to ensure the base body material is as homogeneous as possible. Alternatively, the base body could be designed as a hollow body, with its lateral surfaces formed on four side walls that define the base body.

[0036] The radiation-opaque spheres, meaning those visible in imaging techniques that transmit radiation through the body, are made of materials such as metal or another high-density material. Alternatively, a material with a very low density, such as air, could be used. For the spheres to be visible in imaging techniques that transmit radiation through the body, they must be made of a material with a different density than the base material. Due to the high contrast of the spheres in the imaging technique, a precise 6DOF localization of the phantom within the imaging system of a radiation therapy device is possible.

[0037] In a preferred embodiment, three to eight radiation-opaque spheres are arranged within the base body. The use of five spheres is particularly preferred. One of the spheres is preferably located at the isocenter of the phantom body. The isocenter defines the origin of the phantom coordinate system. The remaining spheres are arranged asymmetrically within the phantom.

[0038] The base of the truncated pyramid is preferably made of a plastic material. The spheres are made of a material such as air, metal, or ceramic, which provides good contrast to the base in imaging while avoiding artifacts.

[0039] ,.. / 7- 7 - January 13, 2026

[0040] The optical markers, which can be detected on the surface of the phantom body using an optical detection device, enable a unique 6DOF localization of the phantom in the SGRT system.

[0041] Regarding the design of the optical markers, it is conceivable that they are arranged on at least one of the surfaces of the top or the four side surfaces, wherein it is particularly provided that the optical markers are arranged on at least two surfaces from the selection of top and four side surfaces and further preferably on each of the surfaces of the top and the four side surfaces.

[0042] It is conceivable that at least some of the optical markers are implemented as a print placed on the surface of the top or side surfaces, or by using a material that differs in color from the surface material.

[0043] When using a material that contrasts in color with the surface, it is ensured that the marker element is attached to the surface or integrally formed with the material of the body part forming the surface. For example, a recess may be provided in the base body at the position intended for the optical marker, into which the marker element is pressed and / or glued. The marker element may, for example, have a cylindrical surface shape. In this variant, the marker element is preferably flush with the surface of the recess.

[0044] To simplify 6DOF localization of the phantom body, a preferred embodiment provides for the asymmetrical distribution of optical markers. A symmetrical distribution is also conceivable. To enable unambiguous 6DOF localization, at least one optical marker contains additional information for resolving the symmetry, which can be read by an optical detection device. This information allows, for example, the determination of the marker's position relative to the base body. Such special markers are also called coded targets.

[0045] An asymmetric arrangement of the optical markers or radiation-opaque spheres can be understood to mean that the optical markers or spheres are each internally

[0046] ,.. / 8- 8 - January 13, 2026

[0047] are arranged in different movement and / or rotation positions with respect to the three spatial axes of a coordinate system located in the isocenter of the phantom body.

[0048] To simplify manual alignment of the phantom body, the base body may be provided with several laser line markings (20) for aligning the isocenter of the phantom body with respect to a treatment device or with respect to an optical detection device, wherein the laser line markings are preferably arranged on at least two surfaces from the selection of top surface and four side surfaces and more preferably on each of the surfaces of the top surface and the four side surfaces.

[0049] In addition to marking the isocenter with laser lines, it can also be provided to mark a sphere located outside the isocenter on the surface of the side faces using a crosshair or similar device. The markings are preferably implemented as orthogonal projections with respect to the underside of the base body, so that a laser beam parallel to the plane of the underside and perpendicular to the horizontal, and directed at the marking, is precisely aimed at the center of the corresponding sphere inside.

[0050] To achieve high accuracy in the calculated transformation, the phantom is designed to be manufactured with high precision. Furthermore, one design incorporates a support platform on which the phantom can be precisely positioned, while being secured against unintentional slippage. Despite the high accuracy requirements, the phantom is easy to use.

[0051] To support precise positioning of the phantom, particular consideration is given to the fact that the base body has a bearing device on the underside, by means of which a positioning secured against slipping, in particular a 3-point positioning, can be produced on a support platform in at least one predefined orientation relative to the support platform.

[0052] To ensure good handling of the phantom body, the base body has two recessed grips on the underside for transporting the phantom body.

[0053] ...19-9-13 January 2026

[0054] According to the invention, a system also consists of a phantom body according to one of the previously described embodiments and a support platform for storing the phantom body, wherein the support platform is set up and designed to hold the phantom body in predefined orientations different from the support platform.

[0055] The platform, on which the phantom can be positioned at defined locations, allows for defined translations and / or rotations relative to the phantom's isocenter. This serves as a basis for evaluating the quality of the transformation between coordinate systems determined using the phantom. Additionally, each system can be tested independently. This includes 6DOF positioning of the IGRT system and 6D OF positioning of the SGRT system.

[0056] In a preferred embodiment of the carrier platform, it is considered that the carrier platform has an upper body and a lower body, wherein the upper body has a first bearing device which is designed to be complementary to the bearing device of the phantom body, such that when the bearing device of the phantom body interacts with the first bearing device of the upper body, a bearing secured against slipping, in particular a 3-point bearing, of the phantom body on the upper body can be produced.

[0057] The upper body, also called the rotating plate, is positioned between the phantom body and the lower body, also called the base plate. The upper body's bearing mechanism can consist of several recesses or protrusions. Similarly, the phantom body's bearing mechanism can consist of complementary protrusions or recesses, such that the protrusions of the phantom body fit precisely and without play into the recesses of the upper body (or vice versa). The protrusions can be made, for example, using glass beads. Other bearing configurations are also conceivable.

[0058] Furthermore, it is envisaged that the upper body has a second bearing device, which is designed to be complementary to a bearing device of the lower body, such that when the bearing device of the lower body interacts with the second bearing device

[0059] ... / 10- 10 - January 13, 2026

[0060] The upper body can be mounted on the lower body in a way that prevents slippage, in particular a 3-point mounting. This allows the upper body to be positioned in various ways relative to the lower body. The phantom body can remain in a position relative to the upper body. As already described for the first mounting device for the upper body, the second mounting device for the upper body and the mounting device for the lower body can be designed in the form of bulges and depressions. Preferably, the lower body contains a plurality of systematically distributed bulges or depressions to allow for a multitude of different positions of the upper body relative to the lower body.

[0061] Using a 3-point recording, defined translations and / or rotations of the upper body relative to the lower body, and thus also of the phantom body relative to the lower body of the support platform, can be easily performed. These translations or rotations are performed relative to the isocenter or the origin of the phantom coordinate system.

[0062] The invention is based on the idea that, together with the phantom, a first workflow, or a first calibration process, should enable the calculation of the transformation between the coordinate systems of the radiation therapy device and the SGRT system. Here, a first 6DOF localization should be calculated using previously generated CT images and CBCT imaging (3D) at the radiation therapy device. Alternatively, virtual CT images should be able to be used instead of CT images. A second 6DOF localization should be calculated in the SGRT system using the optical markers of the phantom and the 2D camera images.

[0063] A second workflow, or calibration process, will use the phantom to calculate the transformation between the coordinate systems of the radiation therapy device and the SGRT system. This involves acquiring multiple planar kV or MV (2D) images at the radiation therapy device with varying gantry angles. From the multitude of planar images and the extracted positions of the spheres contained within the volume, an initial 6DOF localization will be calculated. Using the phantom's optical markers and the 2D camera images from the SGRT system, a second 6DOF localization will then be determined.

[0064] ... / ll- 11 - January 13, 2026

[0065] According to the invention, a method for aligning and verifying the coordinate systems of systems for image-guided and surface-guided radiotherapy using a kV imaging device and / or an MV imaging device of a radiotherapy device, an optical detection device for optically detecting a patient to be treated with the radiotherapy device and a phantom body according to one of the embodiments described above, or a system according to one of the embodiments described above, is therefore also provided.with the steps: Performing a first calibration process and / or a second calibration process to determine the transformation between a coordinate system of the kV imaging device and a coordinate system of the optical acquisition device and / or to determine the transformation between a coordinate system of an MV imaging device and a coordinate system of the optical acquisition device.

[0066] The kV imaging system is a device used to create CBCT (cone-beam computed tomography) images. It preferably produces 3D cross-sectional images of the phantom. Typically, the radiation source for MV imaging and the radiation source for kV imaging are positioned at a 90-degree angle to each other.

[0067] The radiation from the MV imaging device is typically the same type of radiation used for patient treatment. For imaging, the device is adjusted so that the radiation penetrates the phantom body and is detected by a sensor located on the opposite side of the phantom body from the radiation source. The MV sensor is also known as an EP ID (Electronic Portal Imaging Device). It is an imaging system used in radiotherapy to verify the patient's precise position and the alignment of the radiation field.

[0068] As part of the initial calibration process, a first 6DOF localization will be calculated using initially provided CT images and CBCT imaging (3D; kV imaging) on ​​the treatment device. The CT images can be acquired on an external CT scanner or generated virtually using digital 3D data of the phantom model. A second 6DOF localization will be performed in the SGRT system (optical).

[0069] ,.. / 12- 12 - 13 January 2026

[0070] The detection device calculates the phantom's optical markers using the 2D camera images.

[0071] According to a specific embodiment, the first calibration process therefore comprises the following steps: placing the phantom body on a table of the irradiation device and aligning the phantom body with the coordinate system of the irradiation device; acquiring images of the phantom body using the kV imaging device and generating 3D image data of the phantom body; determining an initial 6DOF localization of the phantom body in the coordinate system of the kV imaging device using CT image data of the phantom body and CBCT image data of the phantom body, wherein the CT image data are acquired using a physical computed tomography device or derived from a digital 3D model of the phantom body; acquiring 2D images of the phantom body using the optical acquisition device;Determining a second 6DOF localization of the phantom body in the coordinate system of the optical acquisition device using the 2D images and a digital 3D model of the optical markers of the phantom body in the coordinate system of the phantom body; determining the transformation between the coordinate system of the kV imaging device and the coordinate system of the optical acquisition device using the first 6DOF localization and the second 6DOF localization.

[0072] The initial 6DOF localization is achieved by comparing CT and kV images. This typically involves comparing grayscale values ​​within a specific volume (which, for example, contains the spheres). This volume can also include the surface of the phantom. Usually, the volume is defined to contain only the spheres.

[0073] The acquisition of CT image data using a physical computed tomography scanner includes, in particular, the following steps: placing the phantom body on a table of a computed tomography (CT) scanner; aligning the phantom body with the CT scanner's coordinate system; and acquiring CT images of the phantom. Alternatively, the CT image data can be generated virtually, i.e., digitally, using 3D data of the phantom body. This 3D data can, for example, be contained in a CAD (computer-aided design) model of the phantom body.

[0074] ,.. / 13- 13 - January 13, 2026

[0075] Aligning the phantom body with the coordinate system of the radiation therapy device (i.e., the coordinate system of the MV radiation system intended for the patient's irradiation) involves aligning the isocenter of the phantom body with the isocenter of the radiation therapy device. The fundamental goal is to align both the IGRT system (kV and MV imaging) and the SGRT system (optical imaging) with the isocenter of the MV radiation. The manufacturer of the radiation therapy device (Linac system; Linear Accelerator System) aligns the IGRT system with the MV radiation center using specially designed phantom bodies.

[0076] The same MV radiation source is typically used for both MV irradiation intended for patient treatment and MV imaging. However, the sensor, i.e., the receiver for the MV radiation, may have a slight misalignment relative to the MV source. Therefore, two coordinate systems are used (MV imaging and MV irradiation), which must be aligned with each other.

[0077] Using the phantom body according to the invention, the SGRT system (optical image acquisition) is aligned with the MV irradiation center. It is assumed that the IGRT system is already optimally aligned with the MV irradiation center.

[0078] To align the phantom body with the coordinate system of the irradiation device, alignment lasers of the irradiation device are typically used. These alignment lasers are usually line lasers, preferably cross-line lasers, aligned such that the laser line intersects the MV irradiation center of the irradiation device. The alignment lasers are typically arranged so that they are directed towards the irradiation center from different directions, and the intersection of the laser lines marks the irradiation center. The phantom body according to the invention preferably has laser line markings that are used for laser-assisted alignment of the phantom body. The phantom body is moved along all spatial axes until the laser lines of the alignment lasers coincide exactly with the laser line markings of the phantom body.For fine-tuning the phantom body, the table of the treatment device can, for example, be height- and / or laterally adjustable by motor and / or manual means.

[0079] ,.. / 1413. January 2026

[0080] During the second calibration process, several planar kV or MV images (2D) with different gantry angles will be acquired at the irradiation device. From the multitude of planar images and the extracted positions of the spheres contained within the volume, an initial 6DOF localization will be calculated. Using the optical markers of the phantom and the 2D camera images from the SGRT system, a second 6DOF localization will be determined.

[0081] According to a specific embodiment, the second calibration process therefore comprises the following steps: placing the phantom body on a table of the irradiation device and aligning the phantom body with the coordinate system of the irradiation device; acquiring several planar 2D kilovolt images (kV images) of the phantom body using the kV imaging device and / or several 2D megavolt images (MV images) of the phantom body using the MV imaging device of the irradiation device from different rotational angles relative to the phantom body; determining a first 6DOF localization of the phantom body in the coordinate system of the kV imaging device using the kV images and a digital 3D model of the radiation-opaque spheres in the coordinate system of the phantom body;and / or determining a second 6DOF localization of the phantom body in the coordinate system of the MV imaging device of the irradiation unit using the MV images and a digital 3D model of the radiation-opaque spheres in the coordinate system of the phantom body; acquiring 2D images of the phantom body using the optical acquisition device; determining a further 6DOF localization of the phantom body in the coordinate system of the optical acquisition device using the 2D images and a digital 3D model of the optical markers of the phantom body in the coordinate system of the phantom body; determining the transformation between the coordinate system of the kV imaging device and the optical acquisition device based on the first 6DOF localization of the phantom body in the coordinate system of the kV imaging device and the further 6DOF localization of the phantom body in the coordinate system of the optical acquisition device;and / or determining the transformation between the coordinate system of the MV imaging device and the coordinate system of the optical detection device using the second 6DOF localization of the phantom body in the coordinate system of the MV imaging device and the further;

[0082] ,.. / 15- 15 - January 13, 2026

[0083] 6DOF positioning of the phantom body in the coordinate system of the optical detection device.

[0084] As already explained in the first calibration process, the alignment of the phantom body to the coordinate system of the irradiation device can be carried out using laser lines that project the coordinate origin of the irradiation device.

[0085] The irradiation device typically has a sensor for each of the kV and MV imaging units to detect the radiation. To derive a 6DOF pose from the acquired kV or MV images, the kV or MV source, along with the opposing sensors, is positioned in various rotational positions around the phantom body. For this purpose, the MV radiation source, and preferably also the kV radiation source, is mounted on a swivel arm that can pivot around the treatment table of the irradiation device. The rotational position of the swivel arm supporting the MV radiation source is also referred to as the gantry angle. For the generation of 3D data, kV or MV images are typically acquired from at least two different gantry angles. Preferably, images are acquired from four different angles (for example, each at an angular interval of 90°).For kV imaging (CBCT), images are preferably acquired from a multitude of different angles and processed to create a 3D slice model. When acquiring images from two or four different angles (as in the second workflow), several 2D images are obtained. The pose of the scanned object (for example, the phantom body) is then determined from the multitude of 2D images.

[0086] A third workflow, utilizing the phantom and platform, aims to enable an end-to-end (E2E) test. This test will involve CT imaging of the phantom or, alternatively, the use of virtually generated CT data. Following treatment planning, the phantom, along with the platform, should be aligned at the isocenter of the treatment unit using the SGRT system. Defined translations and / or rotations can then be performed using the platform to verify the SGRT system's measurements. The same tests should also be possible using CBCT imaging directly at the treatment unit.

[0087] ,.. / 16- 16 - January 13, 2026

[0088] According to a specified embodiment, the method further includes the step of performing an end-to-end test (E2E test) to verify a previously performed calibration process, wherein the E2E test comprises the following steps: providing CT image data of the phantom body, wherein this CT image data is derived from a previously or subsequently performed computed tomography scan using a physical computed tomography device or is generated by derivation from a digital 3D model of the phantom body; placing the phantom body and a support platform designed and configured for supporting the phantom body on a table of the irradiation device and aligning the phantom body with the coordinate system of the irradiation device; performing a validation process comprising the following steps: capturing a 3D surface of the phantom body using the optical capture device;Determining an initial 6DOF localization of the phantom body using the 3D surface acquired by the optical acquisition device, comparing the 3D surface with a 3D surface generated from the CT image data; determining a deviation between a target value, representing a change in the position of the phantom body relative to the isocenter of the irradiation device as defined by the position of the phantom body on the carrier platform, and an actual value, representing the position of the phantom body using the previously determined initial 6DOF localization and applying the transformation determined in a previously performed calibration process between the coordinate system of the optical acquisition device and the coordinate system of the irradiation device.

[0089] In this end-to-end (E2E) test, the phantom is aligned on the table with the coordinate origin of the irradiation device. The phantom can then be moved to different positions using the platform. At each position, a 3D surface can be created using the SGRT system, and the 6DOF position can be calculated from this. This can then be compared with the expected value.

[0090] At the same positions, a CBCT scan can then be acquired and a 6DOF localization calculated. This can be compared with the expected value. In a further development, the validation process is therefore intended to include the following steps: determining a second 6DOF localization of the phantom body.

[0091] ,.. / 17- 17 - January 13, 2026

[0092] using CBCT image data of the phantom body obtained by the kV imaging device, comparing the CBCT image data with the CT image data; and detecting a deviation between a target value representing a change in position of the phantom body relative to the isocenter of the irradiation device defined by the position of the phantom body on the carrier platform and an actual value representing the position of the phantom body using the previously determined second 6DOF localization.

[0093] To provide multiple comparative values, the following steps are planned after an initial validation process: the phantom body is moved to at least one new position on the carrier platform, and the validation process is repeated for each new position. This validation process, followed by moving the phantom body, can be repeated multiple times.

[0094] The invention will be explained in more detail below with the aid of figures. The figures show:

[0095] Fig. 1 shows a schematic representation of a phantom body according to the invention in an isometric view from an oblique angle above,

[0096] Fig. 2 is a schematic representation of the phantom body according to the invention from Fig. 1 in an isometric view from a low angle,

[0097] Fig. 3 is a schematic representation of the phantom body according to the invention from Fig. 1 in isometric view with transparency to illustrate the internal structure.

[0098] Fig. 4 is a schematic representation of a system according to the invention consisting of a phantom body according to the invention and a support platform carrying the phantom body in an isometric view from an oblique angle above,

[0099] Fig. 5 is a schematic representation of the lower body of the support platform from Fig. 4 in an isometric view from a slant above,

[0100] Fig. 6 is a schematic representation of the upper body of the support platform from Fig. 4 in an isometric view from a low angle.

[0101] ,.. / 1813. January 2026

[0102] Fig. 7 is a schematic representation of the upper body of the support platform from Fig. 4 in an isometric view from a top oblique angle.

[0103] Fig. 8 shows a schematic representation of a computed tomography device for generating CT data of a phantom body according to the invention in an isometric view from an oblique angle above, and

[0104] Fig. 9 shows a schematic representation of an irradiation device for radiotherapy treatment of a patient with a phantom body according to the invention placed on the table of the irradiation device.

[0105] Figures 1 to 3 show a phantom 10 or a phantom body 10 according to the invention. Figure 1 shows that the phantom body 10 has a base shaped as a rectangular truncated pyramid. In this perspective of Figure 1, two side surfaces 16 can be seen, extending from a bottom surface 14 upwards to a top surface 12. The top surface 12 is aligned parallel to the bottom surface 14. The area of ​​the top surface 12 is smaller than the area of ​​the bottom surface 14. As indicated by an angle W in Figure 3, the side surfaces 16 each extend at an angle, here each less than 90°, to the bottom surface 14.

[0106] Optical markers 18 are arranged on the side surfaces 16 and the top surface 12, which can be detected by an optical detection device. The optical markers 18 are color-coded and differ from the surrounding areas of the surfaces. In the example shown, the optical markers 18 are circular. The optical markers 18 can be printed on or, for example, embedded as separate elements in the surface of the side surfaces 16 or the top surface 12. It is also conceivable that the optical markers are etched, laser-etched, or applied to the surfaces in some other way. As can be seen, the optical markers are distributed asymmetrically on the surfaces.

[0107] In addition to the optical markers 18, the side surfaces 16 and the top surface 12 are provided with laser line markings 20 and 26, respectively. The laser line markings 20 and 26 are each designed in the form of a crosshair, with the laser lines 20 positioned at the edges of the phantom body 10. The laser line markings 20 mark the isocenter 24, i.e., the origin of the coordinate system.

[0108] ,.. / 19- 19 - January 13, 2026

[0109] Phantom body. The laser line marking 20 is arranged on the side surfaces 16 such that a line laser aligned parallel and a line laser aligned perpendicular to the underside 14 and the topside 12, respectively, and directed towards the laser marking 20 of the side surfaces 16, would each hit the isocenter 24. Similarly, two line lasers aligned perpendicular to the topside 12, each directed towards the laser marking 20 of the topside 12, would each hit the isocenter 24.

[0110] If these line lasers are arranged such that they intersect at the isocenter of an irradiation device or at the isocenter of the megavolt irradiation unit (MV irradiation unit) of the irradiation device, i.e., at the coordinate origin of the irradiation device, the phantom body 10 can be aligned with the coordinate system of the irradiation device by aligning these line lasers with the laser line marker 20. In doing so, the isocenter 24 is positioned at the isocenter of the irradiation device.

[0111] The laser line marker 26, analogous to the laser line marker 20, marks the center point of a radiation-opaque sphere 22 placed inside the phantom body 10. As clearly shown in the transparent representation of the phantom body 10 in Fig. 3, spheres 22 are arranged inside the phantom body 10. These spheres 22 are made of a material whose density differs from that of the material immediately surrounding them. Thus, these radiation-opaque spheres 22 are clearly visible and detectable in images from imaging that penetrates the phantom body 10 with radiation.

[0112] One of the radiation-opaque spheres 22 is precisely positioned at the isocenter 24 of the phantom body 10. Four other spheres 22 are asymmetrically distributed within the volume of the phantom body 10. The spheres 22 can be made of, for example, metal or ceramic. Alternatively, the spheres 22 themselves can be designed as cavities within a base body of the phantom body 10 made of solid material.

[0113] The positions of the optical markers 18, the spheres 22, top / bottom 12, 14, the side surfaces 16 and the receptacles or recesses for the bearing device 28 (for

[0114] ,.. / 2013. January 2026

[0115] The positions of the three points (e.g., 3-point bearings) relative to each other are exactly known and available, for example, as a digital 3D model.

[0116] On the underside 14 of the phantom body 10, a bearing device 28 is visible, formed here by means of indentations or recesses incorporated into the underside 14. This bearing device 28 serves to support the phantom body 10 on a designated support platform 32 (see Fig. 4). In the present example, the bearing device 28 is formed by means of three recesses which can interact with complementary protrusions or guide elements on a support platform 32 to create a secure, slip-resistant bearing. As shown, exactly three bearing elements 28 can be provided to enable a 3-point bearing. It is understood that, in addition to indentations or recesses, protrusions or the use of other additional guide elements are also conceivable for creating a bearing.For example, it is conceivable to use guide elements in the form of spheres made of glass, ceramic, metal, or the like, which fit precisely and without play into recesses 28 on the underside 14 of the phantom body 10. Similarly, corresponding recesses can be provided on a support platform into which the guide elements can be inserted without play. This enables precise mounting of the phantom body 10 on a support platform.

[0117] Furthermore, on the underside 14 of the phantom body there are two grip recesses 30, by means of which the phantom body 10 can be conveniently transported and handled by hand.

[0118] Figure 4 shows a system according to the invention consisting of a phantom body 10 and a support platform 32. The phantom body 10 is shown transparently in Figure 4. The phantom body 10 is mounted on an upper body 34 of the support platform 32. The upper body 34, also shown transparently in Figure 4, is mounted on a lower body 36 of the support platform 32.

[0119] Figures 5 to 7 show the lower body 36 and the upper body 34 of the support platform from Fig. 4 in more detail. Figures 4 and 5 show that the lower body 36 has a bearing arrangement 38 consisting of a plurality of recesses or protrusions. The upper body 34 also has a first bearing arrangement 44 on its upper surface 42 and on its

[0120] ,.. / 2113. January 2026

[0121] Underside 40 features a second bearing assembly 46. Analogous to the explanations regarding the bearing assembly 28 of the phantom body 10, the bearing assemblies 38, 44, and 46 of the upper body 34 and the lower body 34 can each be designed as recesses into which a guide element, such as a ball or the like, can be inserted precisely and without play. In the example shown, the bearing assembly 28 of the phantom body 10 and the first and second bearing assemblies 44, 46 of the upper body 34 of the support platform 32 are each designed with three recesses. The bearing assemblies 10 can be designed such that the phantom body 10 can be mounted on the upper body 34 in a single position or in different positions. For example, it can be provided that three different predefined rotational positions can be achieved with a three-point mounting.In the example shown, the lower body 36 has a bearing device 38 with a plurality of recesses that are designed to complement the recesses of the bearing device 46 on the underside 40 of the upper body 34. The recesses are arranged such that the upper body 34 can be mounted on the lower body 36 in various predetermined rotational and / or translational positions.

[0122] As can be seen in Figures 5 to 7, the upper body 34 and lower body 36 of the support platform 32 are approximately plate-shaped in the example shown. The lower body 36 has an approximately square base shape. The upper body 34 has an approximately circular shape with three projections 48 on its outer circumference, in the area of ​​which the recesses of the second bearing device 46 are arranged on the underside 40.

[0123] Upper body 34 and lower body 36 can be made of plastic, CFRP (carbon fiber reinforced plastic), aluminum or another dimensionally stable material.

[0124] Figure 8 shows a computed tomography (CT) scanner 50, which can be used to generate CT image data of a phantom body 10. In the example shown in Figure 7, a phantom body 10 is placed on the table 56 of the CT scanner 50. In this case, the phantom body 10 is arranged on the table 56 without a support platform 32. It is also conceivable to place the phantom body 10 on the table 56 together with a support platform 32. Alignment lasers 54 can be used to align the phantom body 10 on the table 56, with the phantom body 10 being positioned so that the lasers 54 are aligned with the laser marking 20 of the phantom body 10. This establishes the isocenter 24 of the phantom body.

[0125] ...12213. January 2026

[0126] 10 is placed at the isocenter of CT 50. Alignment at CT 50 can be supported by a so-called indexing bar 52.

[0127] Figure 9 shows the use of the phantom body 10 on an irradiation device 58. In the state shown, the phantom body 10 is placed on the table 60 of the treatment device 58. Alignment lasers 62 can be used to align the isocenter 24 with the isocenter of the treatment device 58, with the phantom body 10 being positioned so that the lasers 62 are aligned with the laser marking 20 of the phantom body 10. For calibration processes, the phantom body 10 can be placed on the table 60 without a support platform 32. For the optional end-to-end (E2E) test, the phantom body 10 can be placed on the table 60 together with a support platform 32 (not shown).

[0128] Figure 9 schematically shows the optical detection device 66 used for the calibration processes. In this example, three separate camera devices are used to capture the patient to be treated or the phantom body 10 from different angles. Four or more camera devices can also be used. A kV imaging device 64, 72 is also shown. In the example setup shown, the radiation source 64 for the kV imaging device is arranged laterally to the table 60. The kV radiation emitted from the radiation source 64 is detected by a sensor 72 of the kV imaging device. The radiation source of the MV imaging device is arranged in the swivel arm 68. The MV radiation is detected by a sensor 70 located on the side of the table 60 opposite the radiation source of the MV imaging device.The MV images and kV images are generated by evaluating the radiation data recorded by sensors 70 and 72.

[0129] ,.. / 2323 - January 13, 2026

[0130] REFERENCE MARK LIST

[0131] 10 Phantom body 50 Computed tomography (CT) scanner 12 Top side 52 Indexing bar

[0132] 14 Underside 54 Alignment laser

[0133] 16 side surfaces 56 table of the CT

[0134] 18 opti see marker 58 irradiation device

[0135] 20 Laser line marking 60 Table of the irradiation device 22 Radiation-opaque spheres 62 Alignment lasers

[0136] 24 Isocenter 64 kV radiation source

[0137] 26 Ball marking 66 Optical detection device 28 Phantom body storage device 68 Swivel arm with MV radiation source 30 Recessed grips 70 Sensor for MV imaging (EPID) 32 Carrier platform 72 kV imaging sensor

[0138] 34 Upper body

[0139] 36 Lower body W Angle between side surface and underside of the phantom body 38 Bearing device of the lower body

[0140] 40 Underside of the upper body

[0141] 42 Upper body

[0142] 44 first storage facility of the

[0143] upper body

[0144] 46 second storage facility of the

[0145] upper body

[0146] 48 outriggers on the upper body

Claims

January 13, 2026 REQUIREMENTS 1. Phantom body (10) for aligning and verifying the coordinate systems of image-guided and surface-guided radiotherapy systems, comprising a basic body having the shape of a truncated pyramid, wherein the basic body comprises a flat bottom surface (14) and a flat top surface (12) spaced apart from it, as well as four flat side surfaces (16) connecting the bottom surface (14) and the top surface (16), wherein the side surfaces (16) each extend at an angle (W) to the underside (14) of the base body towards the top (12), and wherein at least one first angle (W) between a first side face (16) and the bottom surface (14) differs from a second angle (W) between a second side face (16) and the bottom surface (14), wherein the base body has several optical markers (18) which can be detected by means of an optical detection device, wherein the base body further comprises several radiation-opaque spheres (22) which are arranged asymmetrically within the base body and which can be detected by means of a kilovolt imaging device (kV imaging device) and / or a megavolt imaging device (MV imaging device).

2. Phantom body (10) according to claim 1, characterized in that the underside (14) and the top side (12) run parallel to each other.

3. Phantom body (10) according to one of claims 1 or 2, characterized in that each of the four angles (W) between the underside (14) and the side surfaces (16) differs from each other.

4. Phantom body (10) according to one of the preceding claims, characterized in that the optical markers (18) are arranged on at least one of the surfaces of the top (12) or of the four side surfaces (16), wherein it is particularly provided that the optical markers (18) are arranged on at least two surfaces. ...1213. January 2026 the selection of the top surface (12) and four side surfaces (16) and are further preferably arranged on each of the surfaces of the top surface (12) and the four side surfaces (16).

5. Phantom body (10) according to one of the preceding claims characterized in that at least some of the optical markers (18) are each designed as a print placed on the surface of the top (12) or the side surfaces (16) or each by using a material that differs in color from the material of the surface.

6. Phantom body (10) according to one of the preceding claims, characterized in that the optical markers (18) are asymmetrically distributed.

7. Phantom body (10) according to one of the preceding claims, characterized in that the base body has several laser line markings (20) for aligning an isocenter (24) of the phantom body (10) with respect to a treatment device or with respect to an optical detection device, wherein the laser line markings (20) are preferably arranged on at least two surfaces from the selection of top (12) and four side surfaces (16) and further preferably on each of the surfaces of the top (12) and the four side surfaces (16).

8. Phantom body (10) according to one of the preceding claims, characterized in that the base body has a bearing device (28) on the underside (14) by means of which a bearing secured against slipping, in particular a 3-point bearing, can be produced on a support platform (32) in at least one predefined orientation relative to the support platform (32).

9. Phantom body (10) according to one of the preceding claims, characterized in that the base body has two grip recesses (30) on the underside (14) for transporting the phantom body.

10. System comprising a phantom body (10) according to any one of claims 1 to 9 and a support platform (32) for supporting the phantom body (10), wherein the support platform (32) is configured and designed to hold the phantom body (10) in predefined orientations different from the support platform (32). January 13, 2026 11. System according to claim 10, characterized in that the support platform (32) has an upper body (34) and a lower body (36), wherein the upper body (34) has a first bearing device (44) which is designed to be complementary to the bearing device (28) of the phantom body (10), such that when the bearing device (28) of the phantom body (10) interacts with the first bearing device (44) of the upper body (34), a bearing secured against slipping, in particular a 3-point bearing, of the phantom body (10) on the upper body (34) can be produced.

12. System according to claim 11, characterized in that the upper body (34) has a second bearing device (46) which is designed to be complementary to a bearing device (38) of the lower body (36), such that when the bearing device (38) of the lower body (36) interacts with the second bearing device (46) of the upper body (34), a bearing secured against slipping, in particular a 3-point bearing, of the upper body (34) on the lower body (36) can be implemented.

13. Method for aligning and verifying the coordinate systems of image-guided and surface-guided radiotherapy systems using a kV imaging device and / or an MV imaging device of a radiotherapy device (58), an optical detection device (66) for optically detecting a patient to be treated with the radiotherapy device (58) and a phantom body (10) according to any one of claims 1 to 9 or a system according to any one of claims 10 to 12, comprising the steps: Performing a first calibration process and / or a second calibration process to determine the transformation between a coordinate system of the kV imaging device and a coordinate system of the optical detection device (66) and / or to determine the transformation between a coordinate system of an MV imaging device and a coordinate system of the optical detection device (66). ,.. / 413. January 2026 14. The method of claim 13, wherein the first calibration process comprises the following steps: Placing the phantom body (10) on a table (60) of the irradiation device (58) and aligning the phantom body (10) to the coordinate system of the irradiation device (58); Acquisition of images of the phantom body (10) using the kV imaging device and generation of 3D image data (CBCT) of the phantom body (io); Determining a first 6DOF localization of the phantom body (10) in the coordinate system of the kV imaging device using CT image data of the phantom body (10) and CBCT image data of the phantom body (10), wherein the CT image data are acquired using a physical computed tomography device (50) or derived from a digital 3D model of the phantom body (10); Acquisition of 2D images of the phantom body (10) using the optical detection device (66); Determining a second 6DOF location of the phantom body (10) in the coordinate system of the optical detection device (66) using the 2D images and a digital 3D model of the optical markers of the phantom body (10) in the coordinate system of the phantom body (10); Determining the transformation between the coordinate system of the kV imaging device and the coordinate system of the optical acquisition device (66) using the first 6DOF localization and the second 6DOF localization.

15. The method of claim 13, wherein the second calibration process comprises the following steps: Placing the phantom body (10) on a table (60) of the irradiation device (58) and aligning the phantom body (10) to the coordinate system of the irradiation device (58); Acquisition of multiple planar 2D kilovolt images (kV images) of the phantom body (10) using the kV imaging device (64, 72) and / or multiple 2D megavolt images (MV images) of the phantom body (10) using the MV imaging device (68, ...1513. January 2026 70) of the irradiation device (58) from different rotation angles (gantry angles) with respect to the phantom body (10); Determining a first 6DOF localization of the phantom body (10) in the coordinate system of the kV imaging device using the kV images and a digital 3D model of the radiation-opaque spheres (22) in the coordinate system of the phantom body (10); and / or Determining a second 6DOF localization of the phantom body (10) in the coordinate system of the MV imaging device of the irradiation device (58) using the MV images and a digital 3D model of the radiation-opaque spheres (22) in the coordinate system of the phantom body (10); Acquisition of 2D images of the phantom body (10) using the optical detection device (66); Determining a further 6DOF location of the phantom body (10) in the coordinate system of the optical detection device (66) using the 2D images and a digital 3D model of the optical markers of the phantom body (10) in the coordinate system of the phantom body (10); Determining the transformation between the coordinate system of the kV imaging device and the optical acquisition device (66) based on the first 6DOF localization of the phantom body (10) in the coordinate system of the kV imaging device and the further 6DOF localization of the phantom body (10) in the coordinate system of the optical acquisition device (66); and / or Determining the transformation between the coordinate system of the MV imaging device and the coordinate system of the optical detection device (66) using the second 6DOF localization of the phantom body (10) in the coordinate system of the MV imaging device and the further 6DOF localization of the phantom body (10) in the coordinate system of the optical detection device (10).

16. The method of claim 13, further comprising the step of: Performing an end-to-end (E2E) test to verify a previously performed calibration process, wherein the E2E test comprises the following steps: providing CT image data of the phantom body (10), wherein this CT image data is obtained from a previously or a repeat computed tomography scan using a ...1613. January 2026 physical computed tomography device (50) or are generated by derivation from a digital 3D model of the phantom body (10); Placing the phantom body (10) and a support platform (32) designed and equipped for the storage of the phantom body (10) on a table (60) of the irradiation device (58) and aligning the phantom body (10) to the coordinate system of the irradiation device (58); Conducting a validation process that includes the following steps: Capturing a 3D surface of the phantom body (10) using the optical capture device (66); Determining a first 6DOF localization of the phantom body (10) using the 3D surface acquired with the optical acquisition device, comparing the 3D surface with a 3D surface generated from the CT image data; Detecting a deviation between a target value, which represents a change in the position of the phantom body relative to the isocenter of the irradiation device as defined by the position of the phantom body on the carrier platform, and an actual value, which represents the position of the phantom body using the previously determined first 6DOF localization and applying the transformation determined in a previously performed calibration process between the coordinate system of the optical detection device and the coordinate system of the irradiation device.

17. The method of claim 16, wherein the validation process comprises the further steps: Determining a second 6DOF localization of the phantom body (10) using CBCT image data of the phantom body (10) acquired by the kV imaging device, comparing the CBCT image data with the CT image data; and Capturing a deviation between a target value, which represents a change in the position of the phantom body relative to the isocenter of the irradiation device as defined by the position of the phantom body on the carrier platform, and an actual value, which represents the position of the phantom body using the previously determined second 6DOF location. ,.. / 713. January 2026 18. Method according to one of claims 16 or 17, further comprising the step: After the validation process: Move the phantom body (10) on the carrier platform (32) to at least one new position and repeat the validation process for each new position.

Images