Functional safety for a radiation treatment system using a single surface camera

Abstract

Disclosed is a computer-implemented method of determining an error in positional tracking by a tracking camera device. The disclosed method encompasses generating a tracking image of the gantry of a radiation treatment system with an imaging device such as laser scanner or structured light camera at a current rotational angle of the gantry which is known in a tracking reference system due to control data used for controlling the gantry position or from measuring the rotational angle with sensors installed in the radiation treatment system. A model of the gantry in a known angle in the tracking reference system is matched to the image of the gantry, leading to a matching function. The matching function is considered to represent a difference angle between the known angle the angle which the gantry is considered to have according to the tracking image. If the difference angle does not indicate a rotational angle of the gantry which complies with the current angle, an error in tracking the gantry is considered to be present.

Description

[0001] FUNCTIONAL SAFETY FOR A RADIATION TREATMENT SYSTEM USING A SINGLE SURFACE CAMERA

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to computer-implemented methods of determining an error in positional tracking by a tracking camera device and of determining control data for controlling a radiation treatment system comprising a treatment beam emission device, a corresponding computer program, a computer-readable storage medium storing such a program and a computer executing the program, as well as a medical system comprising an electronic data storage device and the aforementioned computer.

[0004] TECHNICAL BACKGROUND

[0005] Functional safety is the part of the overall safety of a system or piece of equipment that relies on automatic protection operating correctly in response to its inputs or failure in a predictable manner (fail-safe). In the context of surface-guided radiotherapy systems automated protection is provided by the tracking system which is configured to observe and thereby track the patient’s position relative to the treatment beam. It therefore is desirable to have safety functions to identify systematic errors or hardware failures associated with the hardware of the tracking system which might go undetected otherwise and thus increase quality and safety of the treatment.

[0006] To ensure that the tracking sensor, i.e. a camera configured to image the surface of the patient’s body, performs correctly and the system thus does not rely on false data input regular plausibility checks can be applied during the treatment process. This is usually achieved by introducing a redundancy of sensors observing the patient and issuing a warning if the detection results received from the sensors do not agree. In this way, problems of one camera sensor acquiring a distorted three-dimensional image due to thermal stress or a dislocated camera due to unintended mechanical stress or collision, which both could invalidate the calibration, be detected and avoided.

[0007] Known products use three 3D sensors and make sure that always at least two of the three sensors can track the patient at the same time and thus can check for an agreement of at least two sensors. This leads to an increase in required hardware. Other radiotherapy systems use the x-ray system to check on a single 3D camera. This leads to an increase in imaging dose applied to the patient. The redundancy of sensors used by both aforementioned solutions leads to an increase in production costs.

[0008] The present invention has the object of providing efficient means for monitoring the calibration of a radiotherapy tracking system.

[0009] The present invention can be used for tracking procedures e.g. in connection with a system for image-guided and surface-guided radiotherapy such as ExacTrac Dynamic®, a product of Brainlab AG.

[0010] Aspects of the present invention, examples and exemplary steps and their embodiments are disclosed in the following. Different exemplary features of the invention can be combined in accordance with the invention wherever technically expedient and feasible.

[0011] EXEMPLARY SHORT DESCRIPTION OF THE INVENTION

[0012] In the following, a short description of the specific features of the present invention is given which shall not be understood to limit the invention only to the features or a combination of the features described in this section.

[0013] The disclosed method according to the first aspect encompasses generating a tracking image of the gantry of a radiation treatment system with an imaging device such as laser scanner or structured light camera at a current rotational angle of the gantry which is known in a tracking reference system due to control data used for controlling the gantry position or from measuring the rotational angle with sensors installed in the radiation treatment system. A model of the gantry in a known angle in the tracking reference system is matched to the image of the gantry, leading to a matching function. The matching function is considered to represent a difference angle between the known angle the angle which the gantry is considered to have according to the tracking image. If the difference angle does not indicate a rotational angle of the gantry which complies with the current angle, an error in tracking the gantry is considered to be present.

[0014] GENERAL DESCRIPTION OF THE INVENTION

[0015] In this section, a description of the general features of the present invention is given for example by referring to possible embodiments of the invention.

[0016] In general, the invention reaches the aforementioned object by providing, in a first aspect, a computer-implemented method of determining an error in positional tracking by a tracking camera device. The method according to the first aspect is for example a medical method. The method according to the first aspect comprises executing, on at least one processor of at least one computer (for example at least one computer being part of a radiation treatment system), the following exemplary steps which are executed by the at least one processor.

[0017] In a (for example first) exemplary step of the method according to the first aspect, object tracking data is acquired which describes a digital representation of a tracked object. The tracked object is for example a moving or movable object. For example, the tracked object is at least a part of radiation treatment system, for example at least a part of a treatment beam emission device, for example an irradiation unit such as a gantry of a radiation treatment system. The digital representation is for example a digital image or a digital point cloud generated using the output of a camera device, for example a digital imaging or scanning device used to image or scan, respectively, the tracked object to effect the tracking. As used in the present disclosure, tracking the tracked object means tracking the position of the tracked object, i.e. determining the position of the tracked object at at least one point in time, for example along a plurality of points in time. The tracking therefore is a positional tracking. For example, the camera device is a scanner for generating a three-dimensional image of a scanned surface, for example a structured light camera or a time-of-flight camera or a laser scanner. For example, the point cloud describes points on a surface of the tracked object. Furthermore, the object tracking data describes a position of the digital representation in a current movement state of the tracked object and in a tracking reference system. For example, the object tracking data has been generated based on imaging the tracked object with the tracking camera device, for example from a digital image of the tracked object.

[0018] In a (for example second) exemplary step of the method according to the first aspect, current movement state data is acquired which describes the current movement state of the tracked object. The current movement state is defined for example as a rotational phase, i.e. a rotational angle, of the tracked object which is associated with the position of the digital representation of the tracked object in the tracking reference system described by the object tracking data. For example, the current movement state is defined as a gantry angle of the aforementioned radiation treatment system. The current movement state data is for example acquired from control data used for controlling the radiation treatment system or acquired from at least one signal or signals acquired by at least one sensor included in the radiation treatment system which is configured to determine the current movement state, for example the rotational phase, of the irradiation unit.

[0019] In a (for example third) exemplary step of the method according to the first aspect, object model data is acquired which describes a digital model of the tracked object (for example of an outer surface of the tracked object) and a position of the model in a known movement state and in the tracking reference system. The digital model of the tracked object is or has been acquired from constructional data of the tracked object or by recording (for example imaging) movement (for example the same type of movement as the movement causing the current movement state and the predetermined movement state and the known movement state such as rotational movement of an irradiation unit of a radiation treatment system) to generate comparative images describing the tracked object in the known movement state which may serve as the digital model or a basis for generating the digital model, for example by extracting a reference point cloud describing points on the surface of the tracked object from the comparative images and using the reference point cloud as the digital model. The known movement state is defined for example as a rotational phase, i.e. a rotational angle, of the model of the tracked object in the tracking reference system. For example, the known movement state is defined as a gantry angle of the aforementioned radiation treatment system. For example, the model of the tracked object is defined as a point cloud, for example a point cloud describing points on a surface of the tracked object, specifically, the model of the tracked object. The surface of the tracked object described by point cloud described by the object tracking data is at least partly the same surface as the surface described by the point cloud described by the object model data.

[0020] In a (for example fourth) exemplary step of the method according to the first aspect, tracking error data is determined based on the object tracking data and the current movement state data and the object model data. The tracking error data describes whether there exists an error in acquiring the object tracking data. The error is for example an offset between the position of the object described by the object tracking data and the calibration of the camera used for generating the object tracking data. Such an offset may be due to for example thermal expansion of the camera or due to unintentionally changing the position of the camera in the tracking reference system, for example due to mechanical collision with the camera. For example, the known movement state is a predetermined movement state, which has for example been fixedly defined before execution of the method according to the first aspect. The predetermined movement state is defined for example as a rotational phase, i.e. a rotational angle, of the model of the tracked object in the tracking reference system. For example, the current movement state and the predetermined movement state are different movement states. If the known movement state is the predetermined movement state, the position of the model in the known movement state is determined for example by determining a mapping (for example, a transformation such as a positional transformation) between the position of the model in the predetermined movement state and the position of the tracked object in the current movement state as it is described by the object tracking data. Specifically, the digital representation of the tracked object described by the object tracking data is matched with the digital model to determine a matching function between the digital model in the known movement state and the tracked object as it is shown in the digital representation. The output of such matching is a matching function which can be embodied by a transformation (for example, positional transformation) and which indicates a difference between the known movement state and the movement state of the tracked object derivable from the digital representation, for example a difference angle between the rotational angle of the gantry shown in the digital representation and the rotational angle defined by the known movement state. Such a transformation can be determined by applying a fusion algorithm such as an elastic fusion to the position of the model in the predetermined movement state and the position of the tracked object, for example to the surface geometry defined by the model and the surface geometry of the tracked object defined by the digital representation of the tracked object described by the object tracking data. To this end, the surface geometry of the tracked object can be extracted from a digital image constituting the digital representation for example by applying a segmentation algorithm, or the digital representation is or can be generated by applying a three-dimensional scanning method for generating a three- dimensional data set describing the surface geometry. If the matching function corresponds to a determination of the movement state, for example corresponds to the movement state, of the tracked object determined from the object tracking data which deviates from the current movement state described by the current movement state data, the method determines the tracking error data to describes that a tracking error is present.

[0021] For example, the tracking error data can be or is determined by determining a difference in movement states (for example a difference in the rotational phase, for example the rotational angle) corresponding to the aforementioned mapping. On the basis of this difference, the error in acquiring the object tracking data can be or is determined if this difference deviates from a difference between the predetermined moving state and the current movement state as it is described by the current movement state data. For example, the known movement state is the current movement state. If the known movement state is the current movement state, the position of the model in the known movement state is determined for example by transforming the position of the model in a predetermined movement state into the position of the model in the current movement state, for example by rotating the model in the tracking reference system so that it attains the current movement state. Then, a difference between the position of the model in the current movement state and the position of the tracked object described by the object tracking data is determined, for example as a mean distance between points of the respective point clouds (for example by applying an iterative closest point [ICP] algorithm).

[0022] In an example of the method according to the first aspect, positional difference data is determined which describes a difference between the position of the tracked object described by the object tracking data and the position of the model described by the object model data. This approach can be used for both the case of the known movement state being the current movement state and the case of the known movement state being the current movement state. The positional difference data is determined based on the object tracking data and the current movement state data and the object model data, and the tracking error data is determined based on the positional difference data. For example, the digital representation of the tracked object is a point cloud, called object point cloud, describing points on the surface of the tracked object, and wherein the model of the tracked object is a point cloud, called model point cloud, describing points at least on the surface of the tracked object. For example, the positional difference data (specifically, the difference between the position of the tracked object described by the object tracking data and the position of the model described by the object model data) is determined by determining a distance (for example a mean distance such as a root-mean-square distance or mean Euclidean distance) between points of the object point cloud and points, for example corresponding points, of the model point cloud, for example by applying an iterative closest point algorithm or a particle filter or Monte-Carlo optimization to the point clouds.

[0023] In an example of the method according to the first aspect, acquiring position difference threshold data describing a predetermined threshold, for example a predetermined value such as a predetermined threshold value, for the difference between the position of the tracked object, for example the position of the tracked object described by the object tracking data, and the position of the model, for example the position of the model described by the object model data. The tracking error data is or can be determined for example based on the position difference threshold data. For example, the tracking error data is determined based on comparing the difference between the position of the tracked object and the position of the model to the predetermined threshold. For example, the tracking error data describes that there exists an error in acquiring the object tracking data (for example in imaging the tracked object with the tracking camera device) if it is determined that the difference between the position of the tracked object and the position of the model has a predetermined relationship to the predetermined threshold, for example is different from, for example greater than, the predetermined threshold.

[0024] In an example of the method according to the first aspect, the current movement state and the known movement state and the predetermined movement state, are defined by one, for example only (i.e. exactly) one, degree of freedom of the tracked object, for example a rotational degree of freedom of the tracked object (such as a rotational angle, for example a gantry angle), for example by different values of the degree of freedom of the tracked object.

[0025] In a second aspect, the invention reaches the aforementioned object by providing a computer-implemented method of determining control data for controlling a radiation treatment system comprising a treatment beam emission device. The method according to the second aspect is for example a medical method. The method according to the second aspect comprises executing, on at least one processor of at least one computer (for example at least one computer being part of a radiation treatment system), the following exemplary steps which are executed by the at least one processor.

[0026] In a (for example first) exemplary step of the method according to the second aspect, the method according to the first aspect is executed.

[0027] In a (for example first) exemplary step of the method according to the second aspect, control data is determined based on the tracking error data. The control data describes at least one control signal for controlling the treatment beam emission device.

[0028] In an example, the method according to the second aspect comprises a step of controlling the treatment beam emission device by executing the control signal. In an example, the method according to the second aspect comprises determining whether the tracking error data describes that there exists an error in acquiring the object tracking data, for example in imaging the tracked object with the tracking camera device. The control signal then for example constitutes information for causing prohibition, for example interruption or not starting, of emission of a treatment beam by the treatment beam emission device if it is determined that the tracking error data describes that there exists an error in acquiring the object tracking data.

[0029] In an example, the method according to the second aspect comprises determining whether the tracking error data describes that there exists an error in acquiring the object tracking data. The control signal then for example constitutes information for causing emission of a treatment beam by the treatment beam emission device if it is determined that the tracking error data does not describe that there exists an error in acquiring the object tracking data or describes that there does not exist an error in acquiring the object tracking data.

[0030] In a third aspect, the invention is directed to a computer program comprising instructions which, when the program is executed by at least one computer, causes the at least one computer to carry out method according to the first aspect. The invention may alternatively or additionally relate to a (physical, for example electrical, for example technically generated) signal wave, for example a digital signal wave, such as an electromagnetic carrier wave carrying information which represents the program, for example the aforementioned program, which for example comprises code means which are adapted to perform any or all of the steps of the method according to the first aspect. The signal wave is in one example a data carrier signal carrying the aforementioned computer program. A computer program stored on a disc is a data file, and when the file is read out and transmitted it becomes a data stream for example in the form of a (physical, for example electrical, for example technically generated) signal. The signal can be implemented as the signal wave, for example as the electromagnetic carrier wave which is described herein. For example, the signal, for example the signal wave is constituted to be transmitted via a computer network, for example LAN, WLAN, WAN, mobile network, for example the internet. For example, the signal, for example the signal wave, is constituted to be transmitted by optic or acoustic data transmission. The invention according to the second aspect therefore may alternatively or additionally relate to a data stream representative of the aforementioned program, i.e. comprising the program.

[0031] In a fourth aspect, the invention is directed to a computer-readable storage medium on which the program according to the second aspect is stored. The program storage medium is for example non-transitory.

[0032] In a fifth aspect, the invention is directed to at least one computer (for example, a computer), comprising at least one processor (for example, a processor), wherein the program according to the third aspect is executed by the processor or the processor is configured to execute the program according to the third aspect, or wherein the at least one computer comprises the computer-readable storage medium according to the fourth aspect.

[0033] In a sixth aspect, the invention is directed to a radiation treatment system, comprising: a) the computer according to the fifth aspect; b) an electronic data storage device storing the object model data; and c) a treatment beam emission device for emitting a treatment beam; d) a camera tracking device for tracking the position of the treatment beam emission device by generating at least one electronic signal corresponding to the object tracking data, wherein the at least one computer is operably coupled to

[0034] - the electronic data storage device for acquiring, from the data storage device, the object model data, and

[0035] - the treatment beam emission device for acquiring, from the treatment beam emission device, at least one electronic signal corresponding to the current movement state data; and

[0036] - the camera tracking device for acquiring, from the camera tracking device, the at least one electronic signal corresponding to the object tracking data.

[0037] In an example of the system according to the fifth aspect, the computer program comprises instructions which, when the program is executed by the computer, cause the computer to carry out the method according to the second aspect, and the computer is operably coupled to the treatment beam emission device for issuing, to the treatment beam emission device, the least one control signal for controlling the treatment beam emission device.

[0038] For example, the disclosed methods are not methods for treatment of the human or animal body by surgery or therapy. For example, the invention does not involve or in particular comprise or encompass an invasive step which would represent a substantial physical interference with the body requiring professional medical expertise to be carried out and entailing a substantial health risk even when carried out with the required professional care and expertise. For example, the disclosed methods do not necessitate irradiation of the human or animal body with treatment radiation, for example ionizing treatment radiation. Rather, the disclosed methods are directed to steps of data processing.

[0039] DEFINITIONS

[0040] In this section, definitions for specific terminology used in this disclosure are offered which also form part of the present disclosure.

[0041] The method in accordance with the invention is for example a computer-implemented method. For example, all the steps or merely some of the steps (i.e. less than the total number of steps) of the method in accordance with the invention can be executed by a computer (for example, at least one computer). An embodiment of the computer implemented method is a use of the computer for performing a data processing method. An embodiment of the computer implemented method is a method concerning the operation of the computer such that the computer is operated to perform one, more or all steps of the method.

[0042] The computer for example comprises at least one processor and for example at least one memory in order to (technically) process the data, for example electronically and / or optically. The processor being for example made of a substance or composition which is a semiconductor, for example at least partly n- and / or p-doped semiconductor, for example at least one of II-, III-, IV-, V-, Vl-sem iconductor material, for example (doped) silicon and / or gallium arsenide. The calculating or determining steps described are for example performed by a computer. Determining steps or calculating steps are for example steps of determining data within the framework of the technical method, for example within the framework of a program. A computer is for example any kind of data processing device, for example electronic data processing device. A computer can be a device which is generally thought of as such, for example desktop PCs, notebooks, netbooks, etc., but can also be any programmable apparatus, such as for example a mobile phone or an embedded processor. A computer can for example comprise a system (network) of "sub-computers", wherein each sub-computer represents a computer in its own right. The term "computer" includes a cloud computer, for example a cloud server. The term computer includes a server resource. The term "cloud computer" includes a cloud computer system which for example comprises a system of at least one cloud computer and for example a plurality of operatively interconnected cloud computers such as a server farm. Such a cloud computer is preferably connected to a wide area network such as the world wide web (WWW) and located in a so-called cloud of computers which are all connected to the world wide web. Such an infrastructure is used for "cloud computing", which describes computation, software, data access and storage services which do not require the end user to know the physical location and / or configuration of the computer delivering a specific service. For example, the term "cloud" is used in this respect as a metaphor for the Internet (world wide web). For example, the cloud provides computing infrastructure as a service (laaS). The cloud computer can function as a virtual host for an operating system and / or data processing application which is used to execute the method of the invention. The cloud computer is for example an elastic compute cloud (EC2) as provided by Amazon Web Services™. A computer for example comprises interfaces in order to receive or output data and / or perform an analogue-to-digital conversion. The data are for example data which represent physical properties and / or which are generated from technical signals. The technical signals are for example generated by means of (technical) detection devices (such as for example devices for detecting marker devices) and / or (technical) analytical devices (such as for example devices for performing (medical) imaging methods), wherein the technical signals are for example electrical or optical signals. The technical signals for example represent the data received or outputted by the computer. The computer is preferably operatively coupled to a display device which allows information outputted by the computer to be displayed, for example to a user. One example of a display device is a virtual reality device or an augmented reality device (also referred to as virtual reality glasses or augmented reality glasses) which can be used as "goggles" for navigating. A specific example of such augmented reality glasses is Google Glass (a trademark of Google, Inc.). An augmented reality device or a virtual reality device can be used both to input information into the computer by user interaction and to display information outputted by the computer. Another example of a display device would be a standard computer monitor comprising for example a liquid crystal display operatively coupled to the computer for receiving display control data from the computer for generating signals used to display image information content on the display device. A specific embodiment of such a computer monitor is a digital lightbox. An example of such a digital lightbox is Buzz®, a product of Brainlab AG. The monitor may also be the monitor of a portable, for example handheld, device such as a smart phone or personal digital assistant or digital media player.

[0043] The invention also relates to a computer program comprising instructions which, when on the program is executed by a computer, cause the computer to carry out the method or methods, for example, the steps of the method or methods, described herein and / or to a computer-readable storage medium (for example, a non-transitory computer- readable storage medium) on which the program is stored and / or to a computer comprising said program storage medium and / or to a (physical, for example electrical, for example technically generated) signal wave, for example a digital signal wave, such as an electromagnetic carrier wave carrying information which represents the program, for example the aforementioned program, which for example comprises code means which are adapted to perform any or all of the method steps described herein. The signal wave is in one example a data carrier signal carrying the aforementioned computer program. The invention also relates to a computer comprising at least one processor and / or the aforementioned computer-readable storage medium and for example a memory, wherein the program is executed by the processor.

[0044] Within the framework of the invention, computer program elements can be embodied by hardware and / or software (this includes firmware, resident software, micro-code, etc.). Within the framework of the invention, computer program elements can take the form of a computer program product which can be embodied by a computer-usable, for example computer-readable data storage medium comprising computer-usable, for example computer-readable program instructions, "code" or a "computer program" embodied in said data storage medium for use on or in connection with the instructionexecuting system. Such a system can be a computer; a computer can be a data processing device comprising means for executing the computer program elements and / or the program in accordance with the invention, for example a data processing device comprising a digital processor (central processing unit or CPU) which executes the computer program elements, and optionally a volatile memory (for example a random access memory or RAM) for storing data used for and / or produced by executing the computer program elements. Within the framework of the present invention, a computer-usable, for example computer-readable data storage medium can be any data storage medium which can include, store, communicate, propagate or transport the program for use on or in connection with the instruction-executing system, apparatus or device. The computer-usable, for example computer-readable data storage medium can for example be, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared or semiconductor system, apparatus or device or a medium of propagation such as for example the Internet. The computer-usable or computer-readable data storage medium could even for example be paper or another suitable medium onto which the program is printed, since the program could be electronically captured, for example by optically scanning the paper or other suitable medium, and then compiled, interpreted or otherwise processed in a suitable manner. The data storage medium is preferably a non-volatile data storage medium. The computer program product and any software and / or hardware described here form the various means for performing the functions of the invention in the example embodiments. The computer and / or data processing device can for example include a guidance information device which includes means for outputting guidance information. The guidance information can be outputted, for example to a user, visually by a visual indicating means (for example, a monitor and / or a lamp) and / or acoustically by an acoustic indicating means (for example, a loudspeaker and / or a digital speech output device) and / or tactilely by a tactile indicating means (for example, a vibrating element or a vibration element incorporated into an instrument). For the purpose of this document, a computer is a technical computer which for example comprises technical, for example tangible components, for example mechanical and / or electronic components. Any device mentioned as such in this document is a technical and for example tangible device. The expression "acquiring data" for example encompasses (within the framework of a computer implemented method) the scenario in which the data are determined by the computer implemented method or program. Determining data for example encompasses measuring physical quantities and transforming the measured values into data, for example digital data, and / or computing (and e.g. outputting) the data by means of a computer and for example within the framework of the method in accordance with the invention. A step of “determining” as described herein for example comprises or consists of issuing a command to perform the determination described herein. For example, the step comprises or consists of issuing a command to cause a computer, for example a remote computer, for example a remote server, for example in the cloud, to perform the determination. Alternatively or additionally, a step of “determination” as described herein for example comprises or consists of receiving the data resulting from the determination described herein, for example receiving the resulting data from the remote computer, for example from that remote computer which has been caused to perform the determination. The meaning of "acquiring data" also for example encompasses the scenario in which the data are received or retrieved by (e.g. input to) the computer implemented method or program, for example from another program, a previous method step or a data storage medium, for example for further processing by the computer implemented method or program. Generation of the data to be acquired may but need not be part of the method in accordance with the invention. The expression "acquiring data" can therefore also for example mean waiting to receive data and / or receiving the data. The received data can for example be inputted via an interface. The expression "acquiring data" can also mean that the computer implemented method or program performs steps in order to (actively) receive or retrieve the data from a data source, for instance a data storage medium (such as for example a ROM, RAM, database, hard drive, etc.), or via the interface (for instance, from another computer or a network). The data acquired by the disclosed method or device, respectively, may be acquired from a database located in a data storage device which is operably to a computer for data transfer between the database and the computer, for example from the database to the computer. The computer acquires the data for use as an input for steps of determining data. The determined data can be output again to the same or another database to be stored for later use. The database or database used for implementing the disclosed method can be located on network data storage device or a network server (for example, a cloud data storage device or a cloud server) or a local data storage device (such as a mass storage device operably connected to at least one computer executing the disclosed method). The data can be made "ready for use" by performing an additional step before the acquiring step. In accordance with this additional step, the data are generated in order to be acquired. The data are for example detected or captured (for example by an analytical device). Alternatively or additionally, the data are inputted in accordance with the additional step, for instance via interfaces. The data generated can for example be inputted (for instance into the computer). In accordance with the additional step (which precedes the acquiring step), the data can also be provided by performing the additional step of storing the data in a data storage medium (such as for example a ROM, RAM, CD and / or hard drive), such that they are ready for use within the framework of the method or program in accordance with the invention. The step of "acquiring data" can therefore also involve commanding a device to obtain and / or provide the data to be acquired. In particular, the acquiring step does not involve an invasive step which would represent a substantial physical interference with the body, requiring professional medical expertise to be carried out and entailing a substantial health risk even when carried out with the required professional care and expertise. In particular, the step of acquiring data, for example determining data, does not involve a surgical step and in particular does not involve a step of treating a human or animal body using surgery or therapy. In order to distinguish the different data used by the present method, the data are denoted (i.e. referred to) as "XY data" and the like and are defined in terms of the information which they describe, which is then preferably referred to as "XY information" and the like.

[0045] It is the function of a marker to be detected by a marker detection device (for example, a camera or an ultrasound receiver or analytical devices such as CT or MRI devices) in such a way that its spatial position (i.e. its spatial location and / or alignment) can be ascertained. The detection device is for example part of a navigation system. The markers can be active markers. An active marker can for example emit electromagnetic radiation and / or waves which can be in the infrared, visible and / or ultraviolet spectral range. A marker can also however be passive, i.e. can for example reflect electromagnetic radiation in the infrared, visible and / or ultraviolet spectral range or can block X-ray radiation. To this end, the marker can be provided with a surface which has corresponding reflective properties or can be made of metal in order to block the X-ray radiation. It is also possible for a marker to reflect and / or emit electromagnetic radiation and / or waves in the radio frequency range or at ultrasound wavelengths. A marker preferably has a spherical and / or spheroid shape and can therefore be referred to as a marker sphere; markers can however also exhibit a cornered, for example cubic, shape.

[0046] The present invention relates to the field of controlling a treatment beam. The treatment beam treats body parts which are to be treated and which are referred to in the following as "treatment body parts". These body parts are for example parts of a patient's body, i.e. anatomical body parts.

[0047] The present invention relates to the field of medicine and for example to the use of beams, such as radiation beams, to treat parts of a patient's body, which are therefore also referred to as treatment beams. A treatment beam treats body parts which are to be treated and which are referred to in the following as "treatment body parts". These body parts are for example parts of a patient's body, i.e. anatomical body parts. Ionising radiation is for example used for the purpose of treatment. For example, the treatment beam comprises or consists of ionising radiation. The ionising radiation comprises or consists of particles (for example, sub-atomic particles or ions) or electromagnetic waves which are energetic enough to detach electrons from atoms or molecules and so ionise them. Examples of such ionising radiation include X-rays, high-energy particles (high-energy particle beams) and / or ionising radiation emitted from a radioactive element. The treatment radiation, for example the treatment beam, is for example used in radiation therapy or radiotherapy, such as in the field of oncology. For treating cancer in particular, parts of the body comprising a pathological structure or tissue such as a tumour are treated using ionising radiation. The tumour is then an example of a treatment body part.

[0048] The treatment beam is preferably controlled such that it passes through the treatment body part. However, the treatment beam can have a negative effect on body parts outside the treatment body part. These body parts are referred to here as "outside body parts". Generally, a treatment beam has to pass through outside body parts in order to reach and so pass through the treatment body part. Reference is also made in this respect to the following web pages: http: / / www.elekta.com / healthcare_us_elekta_vmat.php and http: / / www.varian.com / us / oncology / treatments / treatment_techniques / rapidarc.

[0049] Mapping describes a transformation (for example, linear transformation) of an element (for example, a pixel or voxel), for example the position of an element, of a first data set in a first coordinate system to an element (for example, a pixel or voxel), for example the position of an element, of a second data set in a second coordinate system (which may have a basis which is different from the basis of the first coordinate system). In one embodiment, the mapping is determined by comparing (for example, matching) the color values (for example grey values) of the respective elements by means of an elastic or rigid fusion algorithm. The mapping is embodied for example by a transformation matrix (such as a matrix defining an affine transformation).

[0050] Image fusion can be elastic image fusion or rigid image fusion. In the case of rigid image fusion, the relative position between the pixels of a 2D image and / or voxels of a 3D image is fixed, while in the case of elastic image fusion, the relative positions are allowed to change.

[0051] In this application, the term "image morphing" is also used as an alternative to the term "elastic image fusion", but with the same meaning.

[0052] Elastic fusion transformations (for example, elastic image fusion transformations) are for example designed to enable a seamless transition from one dataset (for example a first dataset such as for example a first image) to another dataset (for example a second dataset such as for example a second image). The transformation is for example designed such that one of the first and second datasets (images) is deformed, for example in such a way that corresponding structures (for example, corresponding image elements) are arranged at the same position as in the other of the first and second images. The deformed (transformed) image which is transformed from one of the first and second images is for example as similar as possible to the other of the first and second images. Preferably, (numerical) optimisation algorithms are applied in order to find the transformation which results in an optimum degree of similarity. The degree of similarity is preferably measured by way of a measure of similarity (also referred to in the following as a "similarity measure"). The parameters of the optimisation algorithm are for example vectors of a deformation field. These vectors are determined by the optimisation algorithm in such a way as to result in an optimum degree of similarity. Thus, the optimum degree of similarity represents a condition, for example a constraint, for the optimisation algorithm. The bases of the vectors lie for example at voxel positions of one of the first and second images which is to be transformed, and the tips of the vectors lie at the corresponding voxel positions in the transformed image. A plurality of these vectors is preferably provided, for instance more than twenty or a hundred or a thousand or ten thousand, etc. Preferably, there are (other) constraints on the transformation (deformation), for example in order to avoid pathological deformations (for instance, all the voxels being shifted to the same position by the transformation). These constraints include for example the constraint that the transformation is regular, which for example means that a Jacobian determinant calculated from a matrix of the deformation field (for example, the vector field) is larger than zero, and also the constraint that the transformed (deformed) image is not self-intersecting and for example that the transformed (deformed) image does not comprise faults and / or ruptures. The constraints include for example the constraint that if a regular grid is transformed simultaneously with the image and in a corresponding manner, the grid is not allowed to interfold at any of its locations. The optimising problem is for example solved iteratively, for example by means of an optimisation algorithm which is for example a first-order optimisation algorithm, such as a gradient descent algorithm. Other examples of optimisation algorithms include optimisation algorithms which do not use derivations, such as the downhill simplex algorithm, or algorithms which use higher-order derivatives such as Newton-like algorithms. The optimisation algorithm preferably performs a local optimisation. If there is a plurality of local optima, global algorithms such as simulated annealing or generic algorithms can be used. In the case of linear optimisation problems, the simplex method can for instance be used.

[0053] In the steps of the optimisation algorithms, the voxels are for example shifted by a magnitude in a direction such that the degree of similarity is increased. This magnitude is preferably less than a predefined limit, for instance less than one tenth or one hundredth or one thousandth of the diameter of the image, and for example about equal to or less than the distance between neighbouring voxels. Large deformations can be implemented, for example due to a high number of (iteration) steps.

[0054] The determined elastic fusion transformation can for example be used to determine a degree of similarity (or similarity measure, see above) between the first and second datasets (first and second images). To this end, the deviation between the elastic fusion transformation and an identity transformation is determined. The degree of deviation can for instance be calculated by determining the difference between the determinant of the elastic fusion transformation and the identity transformation. The higher the deviation, the lower the similarity, hence the degree of deviation can be used to determine a measure of similarity.

[0055] A measure of similarity can for example be determined on the basis of a determined correlation between the first and second datasets.

[0056] BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In the following, the invention is described with reference to the appended figures which give background explanations and represent specific embodiments of the invention. The scope of the invention is however not limited to the specific features disclosed in the context of the figures, wherein

[0058] Fig. 1 illustrates the basic steps of the method according to the first aspect;

[0059] Fig. 2 shows an embodiment of the present invention, specifically the method according to the first aspect;

[0060] Fig. 3 illustrates a conventional approach to functional safety of patient tracking;

[0061] Fig. 4 illustrates the approach to functional safety of patient tracking provided by the method according to the first aspect; and

[0062] Fig. 5 is a schematic illustration of the system according to the sixth aspect. DESCRIPTION OF EMBODIMENTS

[0063] Fig. 1 illustrates the basic steps of the method according to the first aspect, in which step S11 encompasses acquisition of the object tracking data, step S12 encompasses acquisition of the current movement state data and subsequent step S13 encompasses acquisition of the object model data. The acquired data sets serve as a basis for determining, in step S14, the tracking error data.

[0064] Fig. 2 illustrates an embodiment of the present invention that includes all essential features of the invention. In this embodiment, the entire data processing which is part of the method according to the first aspect is performed by a computer 2. Reference sign 1 denotes the input of data acquired by the method according to the first aspect into the computer 2 and reference sign 3 denotes the output of data determined by the method according to the first aspect.

[0065] Fig. 3 shows a conventional approach of comparing an image of the gantry 9 taken in the current position of the gantry to a recorded reference 11 (an image or a model) of the gantry in the same (current) position. Reference sign 10 denotes the patient couch. Any deviation of the imaging geometry of the tracking camera from the calibration of the tracking camera can be determined from a deviation between the image of the gantry and the recorded reference.

[0066] Fig. 4 shows the present invention in which an image in which the image of the gantry 9 can show the gantry in a rotated position 9’ at a gantry angle of significantly more than 0°. The digital model 12 of the gantry can be fitted to the image of the gantry in the rotated position 9’ by considering the current gantry angle 14 as the current movement state and the known gantry angle 15 being the known movement state to determine any possible deviation between an angle resulting from fitting the digital model 12 to the image of the gantry in the rotated position 9’ from the current gantry angle received from the control unit of the radiation treatment system, irrespective of whether the known gantry angle is the same as the current gantry angle. The result of determining any possible deviation is the indication 16 of a tracking error being present or not. Fig. 5 is a schematic illustration of the medical system such as a radiation treatment system 4 according to the sixth aspect. The system is in its entirety identified by reference sign 4 and comprises a computer 5, a camera tracking device 8, a (for example non-transitory) electronic data storage device 6 for storing at least the patient data and a treatment beam emission device 7. The components of the medical system 4 have the functionalities and properties explained above with regard to the sixth aspect of this disclosure.

[0067] The present invention achieves functional safety using a single 3D tracking sensor, i.e. a single tracking camera device.

[0068] The present invention validates the output of the sensors by comparing portions of the image which are considered to be background with assumptions based on the knowledge about the general setup of a treatment room and clinical processes:

[0069] 1 . The sensor is calibrated to the linac (linear accelerator) coordinate system which serves as a tracking reference system.

[0070] 2. The calibration of the sensor is checked each time just before a new patient arrives.

[0071] 3. Part of the linac can be seen in the background of the data received by the sensor because a. the patient couch is not at treatment position and therefore does not clutter the field of view completely (the couch typically is in a low position, comfortable for the patient to get on the couch); and b. the linac is not perfectly at zero degrees but in an angle very close to 0° (about 0° ± 1 °).

[0072] Based on these assumptions, the present invention registers a model of the linac, in particular the gantry of the linac (e.g. a CAD model with coordinates defined in the linac coordinate system and including knowledge about the degree of freedom of the gantry angle), against (i.e. with) the point cloud is received from the 3D tracking sensor, acquired at a point in time when the gantry has moved along a known rotational trajectory. A full 6D pose of the gantry relative to the camera can be generated. The pose can be compared against data known from isocentre calibration.

[0073] The only angle that is not clear for comparison yet is the gantry angle (which is commonly close to zero between patient treatments). This angle however is read from the gantry software interface and used for the comparison.

[0074] If the pose is equivalent to the expected pose, the check is considered to be successful. If the poses are not equivalent, the check is considered not to be successful so that errors of a slightly distorted point cloud due to thermal stress or a dislocated camera to mechanical stress can be excluded.

[0075] Instead of loading a CAD model, the ground truth reference data for the geometry of the linac could also - for example in an initial setup procedure - be retrieved by: the surface camera observing specific gantry movement(s) and generating comparative images describing known gantry positions which may serve as a digital model or generating a digital model of the tracked object. the camera surface at every possible gantry angle showing the linac is stored and used as a reference, with approval by a user.

Claims

CLAIMS1. A computer-implemented medical method of determining an error in positional tracking by a tracking camera device, the method comprising the following steps: a) object tracking data is acquired (S11 ) which describes a digital representation of a tracked object and a position of the digital representation in a current movement state and in a tracking reference system, wherein the object tracking data has been generated based on imaging the tracked object with the tracking camera device; b) current movement state data is acquired (S12) which describes the current movement state of the tracked object; c) object model data is acquired (S13) which describes a digital model of the object and a position of the model in a known movement state and in the tracking reference system; d) tracking error data is determined (S14) based on the object tracking data and the current movement state data and the object model data, wherein the tracking error data describes whether there exists an error in acquiring the object tracking data.

2. The method according to the preceding claim, comprising determining positional difference data describing a difference between the position of the tracked object described by the object tracking data and the position of the model described by the object model data, wherein the positional difference data is determined based on the object tracking data and the current movement state data and the object model data, wherein the tracking error data is determined based on the positional difference data.

3. The method according to the preceding claim, comprising acquiring position difference threshold data describing a predeterminedthreshold for the difference between the position of the tracked object and the position of the model, wherein the tracking error data is determined based on the position difference threshold data.

4. The method according to the preceding claim, wherein the tracking error data is determined based on comparing the difference between the position of the tracked object and the position of the model to the predetermined threshold.

5. The method according to any one of the two immediately preceding claims, wherein the tracking error data describes that there exists an error in acquiring the object tracking data if it is determined that the difference between the position of the tracked object and the position of the model has a predetermined relationship to the predetermined threshold, for example is different from, for example greater than, the predetermined threshold.

6. The method according to any one of the preceding claims, wherein the known movement state is a predetermined movement state.

7. The method according to any one of the preceding claims, wherein the known movement state is the current movement state.

8. The method according to the preceding claim, wherein the position of the model in the known movement state is determined by transforming the position of the model in a predetermined movement state into the position of the model in the current movement state.

9. The method according to any one of the predetermined claims, wherein the tracked object is at least a part of radiation treatment system, for example at least a part of a treatment beam emission device of a radiation treatment system.

10. The method according to any one of the preceding claims as far as dependent on claim 8, wherein the current movement state and the predetermined movement state are different movement states.11 . The method according to any one of the preceding claims, wherein the current movement state and the known movement state and, as far as the method depends on claim 8, the predetermined movement state, are defined by one degree of freedom of the tracked object, for example a rotational degree of freedom of the tracked object.

12. The method according to any one of the preceding claims as far as dependent on claim 9, wherein the current movement state and the known movement state and, as far as the method depends on claim 8, the predetermined movement state, are defined by a rotational angle of the tracked object.

13. The method according to any one of the preceding claims, wherein the tracking camera device is a scanner for generating a three-dimensional image of a scanned surface, for example a structured light camera or a time-of-flight camera or a laser scanner.

14. The method according to any one of the preceding claims, wherein the digital representation of the tracked object is a point cloud, called object point cloud, describing points on the surface of the tracked object, and wherein the model of the tracked object is a point cloud, called model point cloud, describing points at least on the surface of the tracked object.

15. The method according to the preceding claim as far as dependent on claim 2, wherein the positional difference data is determined by determining a distance between points of the object point cloud and points of the model point cloud.

16. A method of determining control data for controlling a radiation treatment system comprising a treatment beam emission device, the method comprising: a) executing the method according to any one of the preceding claims; b) determining, based on the tracking error data, control data describing at least one control signal for controlling the treatment beam emission device.

17. The method according to the preceding claim, comprising determining whether the tracking error data describes that there exists an error in acquiring the object tracking data, wherein the control signal constitutes information for causing prohibition, for example interruption or not starting, of emission of a treatment beam by the treatment beam emission device if it is determined that the tracking error data describes that there exists an error in acquiring the object tracking data.

18. The method according to any one of the two immediately preceding claims, comprising determining whether the tracking error data describes that there exists an error in acquiring the object tracking data, wherein the control signal constitutes information for causing emission of a treatment beam by the treatment beam emission device if it is determined that the tracking error data does not describe that there exists an error in acquiring the object tracking data or describes that there does not exist an error in acquiring the object tracking data.

19. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any one of the preceding claims.

20. A computer-readable storage medium on which the program according to the preceding claim is stored.21 . A computer comprising at least one processor, wherein the program according to claim 19 is executed by the processor.

22. A data carrier signal carrying the program according to claim 19.

23. A data stream comprising the program according to claim 19.

24. A radiation treatment system (4), comprising: a) the computer (5) according to claim 21 ; b) an electronic data storage device (6) storing the object model data; and c) a treatment beam emission device (7) for emitting a treatment beam; d) a camera tracking device (8) for tracking the position of the treatment beam emission device (7) by generating at least one electronic signal corresponding to the object tracking data, wherein the at least one computer is operably coupled to the electronic data storage device (6) for acquiring, from the data storage device (6), the object model data, and the treatment beam emission device (7) for acquiring, from the treatment beam emission device (7), at least one electronic signal corresponding to the current movement state data; and the camera tracking device (8) for acquiring, from the camera tracking device (8), at least one electronic signal corresponding to the object tracking data.

25. The system according to the preceding claim, wherein the computer program comprises instructions which, when the program is executed by the computer (5), cause the computer (5) to carry out the method according to any one of claims 16 to 18, and the computer (5) is operably coupled to the treatment beam emission device (7) for issuing, to the treatment beam emission device (7), the least one control signal for controlling the treatment beam emission device (8).

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