WO2010145711A1

WO2010145711A1 - System and method for positioning a patient

Info

Publication number: WO2010145711A1
Application number: PCT/EP2009/057645
Authority: WO
Inventors: Timothy Holmes; Chuck Lindley
Original assignee: IBA Dosimetry GmbH
Current assignee: IBA Dosimetry GmbH
Priority date: 2009-06-19
Filing date: 2009-06-19
Publication date: 2010-12-23
Anticipated expiration: 2011-12-19

Abstract

System (1) for positioning a patient relative to patient couch (2) and to a radiation treatment and/or imaging device, particularly to a linac and/or in the context of tomotherapy, comprising: A movable patient couch (2) with first position sensing means (4) for acquiring data related to the spatial position of a patient in relation to the patient couch (2), with the patient and the patient couch (2) having allocated separated frames of reference; a computing device for evaluating the data acquired by the first position sensing means (4), the computing device being adapted to derive information for positioning the patient with respect to the patient couch (2) from the data and to define an integrated single patient-and-couch-system frame of reference from the former separated frames of reference of the patient and the patient couch; and the computing device for evaluating further data acquired by the first position sensing means (4) and/or by second position sensing means (4a), the further data being related to the spatial position of the patient-and-couch system relative to the radiation treatment and/or imaging device and the computing device adapted to derive information for positioning the patient-and-couch-system frame of reference relative to a frame of reference of the radiation treatment and/or imaging device from the further data so that the planned treatment and/or imaging can be performed.

Description

Description System and method for positioning a patient

Technical field [0001] The invention relates to the field of radiation treatment and/or imaging. More particularly, it relates to a system and method for positioning a patient relative to a patient couch and to a radiation treatment and/or imaging device, particularly to a linac and/or in the context of tomotherapy.

Description of related art [0002] Radiation treatment and/or imaging devices are used in the treatment of tumors or the like and/or for imaging structures in the body of a patient. Tumors are treated with high energy radiation. Frequently, linear particle accelerators (linacs) are used. They are devices for the acceleration of subatomic particles and are used to generate X-rays for imaging and treatment, for example in the context of tomotherapy. Tomotherapy is a method for radiation therapy whereby the delivery of radiation is performed slice by slice. It is a form of an intensity modulated radiation therapy (IMRT).

[0003] In order to determine the pattern for the delivery of the radiation, computer implemented applications are used. In this way, an optimization of the radiation delivery and, in the phase of treatment planning, a simulation of the treatment are achieved. The radiation dose and placement of the radiation dose must be accurately controlled not only to ensure that the tumor receives the prescribed dose to allow its erradication, but also to ensure that the damage to surrounding non-tumorous tissue is minimized. Not only in the field of radiation treatment, but also in imaging it is important that the radiation is applied to the correct parts of the body of the patient with the correct dose.

[0004] Therefore, a central aspect is the correct alignment of the patient relative to the radiation treatment and/or imaging equipment. Systems which are currently used for positioning the patient align the patient to the linac. After the couch on which the patient is placed is once put in its position, it is completely neglected as static and fixed to the linac reference frame. There are no solutions for cases in which the couch cannot be ignored, but has to be actively accounted for due to various reasons.

Discussion of the prior art

[0005] From document WO 2009/01 1643 A1 , a patient monitoring arrangement at radiation machines is known. A patient is positioned on a couch in connection with a radiation gantry. A 2D or 3D pattern is projected onto the patient and detected by detectors on a first and a second side of the gantry.

The detectors are fixed with respect to the room reference frame.

[0006] Document WO 02/09588 A1 refers to radiation treatment planning localization and treatment position verification with respect to the coordinate space of an imaging system and a therapy device. There are also position sensing means for sensing the position of an ultrasound probe so that localization ultrasound images can be acquired which are referenced in the coordinate space of the diagnostic imaging system.

[0007] Document WO 2006/138643 A2 aims at facilitating and verifying proper target alignment for radiation delivery by the use of a trackable body and a trackable body detector. From document US 2004/026031 1 A1 , a non-invasive retention device for radiotherapy treatment is known. A lesion detected in imaging is first localised spatially relative to a reference frame connected to the imaging device. The radiotherapy equipment itself has its own reference frame. Besides, there is an arch with locating means for a pedestal to be placed on a radiotherapy table.

[0008] None of these documents of the prior art contains a technical teaching with respect to the alignment of a patient relative to the radiation treatment and/or imaging equipment explicitly taking into account a patient couch. [0009] Therefore, it is an object of the present invention to provide a system and method for positioning a patient relative to a patient couch and to a radiation treatment and/or imaging device, particularly to a linac and/or in the context of tomotherapy, which is improved in this regard.

Summary of the invention

[0010] The present invention is related to a system for positioning a patient relative to a patient couch and to a radiation treatment and/or imaging device and to a corresponding method as described in the claims.

Brief description of the drawings

[0011] Fig. 1 is a perspective drawing of a part of a system for positioning a patient relative to patient couch and to a radiation treatment and/or imaging device according to the invention with a radiation detector embedded in the patient couch.

[0012] Fig. 2 shows a side view and a top view of the part of the system according to fig. 1.

[0013] Fig. 3 shows a side view and a top view of another part of a system for positioning a patient relative to patient couch and to a radiation treatment and/or imaging device according to the invention including a primary and a secondary couchtop.

[0014] Fig. 4 is a view of a treatment room with a system and for using a method according to the invention with an in-room computing device and a data connection to an operator's console.

[0015] Fig. 5 shows a view of an alternative setup of a treatment room with a system and for using a method according to the invention with an on-board computing device integrated into the treatment unit control system. [0016] Fig. 6 shows diagrams of an accumulated radiation dose at a detector and of a displacement vector displayed at an operator's treatment console during a treatment delivery.

[0017] Fig. 7 shows the three reference frames playing a role in the positioning process according to the invention.

[0018] Fig. 8 shows the alignment of the patient reference frame and the couch reference frame according to the invention.

[0019] Fig. 9 is related to the alignment of the patient-couch-system reference frame to the reference frame of the radiation treatment and/or imaging device.

[0020] Fig. 10 illustrates intra-fraction motion monitoring according to the invention.

Detailed description of the invention

[0021] The present invention is directed to a system for positioning a patient relative to a patient couch and to a radiation treatment and/or imaging device, particularly to a linac and/or in the context of tomotherapy, comprising:

- A movable patient couch with first position sensing means for acquiring data related to the spatial position of a patient in relation to the patient couch, with the patient and the patient couch having allocated separated frames of reference,

- a computing device for evaluating the data acquired by the first position sensing means, the computing device being adapted to derive information for positioning the patient with respect to the patient couch from the data and to define an integrated single patient-and-couch- system frame of reference from the formerly separated frames of reference of the patient and the patient couch, and - the computing device for evaluating further data acquired by the first position sensing means and/or by second position sensing means, the further data being related to the spatial position of the patient-and-couch system relative to the radiation treatment and/or imaging device and the computing system being adapted to derive information for positioning the patient-and-couch-system frame of reference relative to a frame of reference of the radiation treatment and/or imaging device from the further data so that the planned treatment and/or imaging can be performed.

[0022] The system according to the invention comprises a patient couch which is, in contrast to known systems, neither static nor fixed to a reference frame of a radiation treatment and/or imaging device such as a linac, but is movable, in particular with respect to the treatment and/or imaging device, instead. The patient couch includes or has first position sensing means, especially fixed to, attached to and/or integrated into the couch. The first position sensing means are designed to obtain data in order to allow alignment of the patient relative to the patient couch. In the course of this first positioning process, a single integrated patient-and-couch-system reference frame is created from the former two separated reference frames of the patient and the couch, respectively.

[0023] The combination of the two frames of reference to form a new single frame of reference is achieved by use of the computing device, which is also a part of the inventive system and does the computing work. The computing device receives the position-related data collected by the first position sensing means via a data connection, evaluates them and computes localization data of the patient and/or values of parameters for positioning the patient as desired or required for the a treatment or imaging process to be performed.

[0024] Specifically, localization is the process of reducing the error between a set of point coordinates measured by the first-position sensing means and a corresponding reference set of point coordinates derived from the CT representation of the patient used for treatment planning. The reference points (X₀, y₀, z₀) are defined in the patient coordinate system (PRF), whereas the set of point coordinates measured by the first-position sensing means (x, y, z) are defined in the couch reference system (CRF). The points may represent the patient's surface; a localization frame rigidly attached to the patient; internal anatomical points; or implanted markers/transponders. The coordinate systems are aligned by translating and rotating (yaw) the secondary couchtop on the primary couchtop to minimize an error metric. For example, one might choose to simply minimize the absolute deviation along each coordinate axis within a small acceptable error tolerance:

|x - XoI < δx; |y - y_o| < δy; |z - z_o| < δz.

[0025] Advantageously, the computing device also controls the mechanisms by which the actual (re)positioning of the patient is achieved as moving a secondary couchtop with respect to a primary couchtop. After the positioning of the patient is done, the patient and the couch form a united patient-couch system, which constitutes the basis for further computing steps performed by the computing device. The computing device can be a single, stand-alone computer or it can be formed by several computers connected in a network such as an in-room computer in a treatment room having a data connection to an operator's console outside the treatment room or as an onboard computer of a treatment unit such as a linac having a data connection to an operator's console in a second room.

[0026] In the next step, the first and/or second position sensing means of the positioning system, which are in contact with the computing device, are used for gathering (further or a second set of) data for the computing device allowing the positioning of the patient-and-couch-system frame of reference relative to the frame of reference of the radiation treatment and/or imaging device so that the planned treatment and/or imaging can finally be performed. Of course, the first and second position sensing means, respectively, have to be adapted for measuring these further data, which includes being placed in an appropriate position for gathering these data.

[0027] Preferably, the movable patient couch includes an integrated and/or embedded sensor system for radiation, particularly a plurality of radiation detectors, which are preferably arranged in an array and/or a linear format, and/or an embedded sensor system for radiation relative to which the patient is to be positioned and/or which is sandwiched between two layers of the patient couch, particularly between two carbon fiber sections, and/or which is a sensor system for data quality assurance and/or for planning and/or treatment and/or radiation verification, especially in real-time, and/or which is, particularly relative to the patient, positioned via megavoltage computed tomography.

[0028] So the radiation treatment and/or imaging patient couch preferably provides means for inserting a radiation detector into the body of the couch and also for removing it again. The embedded sensor or detector system may be sandwiched between two carbon fiber layers or the like. A preferred embodiment is one in which there is no direct pressure applied to the radiation detection system. For example, there can be bars keeping the two layers sandwiching the detector at a distance, or there can be a drawer-like structure or the like for the sensor system. The radiation detection system may be used for measuring the radiation transmitted through the couchtop during treatment delivery, for example. Then, the radiation dose measured via the detector is compared to a pre-calculated dose to verify the radiation delivery. In general, the radiation detection system may be intended to be used to verify a complex radiotherapy treatment plan prior to its application to a patient and/or to verify a patient treatment delivery either in real-time or following treatment completion.

[0029] An embedded radiation detection system according to the invention may consist of a single radiation detector but also of a plurality of radiation detectors arranged in a linear or array format. The detectors can be detectors of the ionization cavity-type or solid state-type detectors (using diodes, amorphous silicon and so on) that are embedded into the couchtop. Preferably, a corresponding signal electronics module is located near the foot of the couch and can be easily removed for servicing and replacement. Signals are transmitted from the module via wire or wirelessly to the computing device running a dosimetry software which can be located at the treatment and/or imaging unit operator's workstation.

[0030] According to the invention, simple post-treatment verification of the applied radiation can be performed by comparing a dose measured at the detector with a dose computed by a treatment planning system. The treatment planning system may be integrated in the computing device of the positioning system which is also used for the localization tasks, or it may be a separated system implemented on a separate computer. The detector can be used as a real-time monitor of radiation delivery. For this purpose, a treatment planning system can be built to export the dose delivered to the detector as a function of treatment time, for example in the context of 4D treatment planning systems. More complex verification methods can be realized that include reconstructing 3D dose estimates using the embedded detector combined with an entrance fluence detector and appropriate software. Preferably, the radiation measurements will be exportable to an electronic medical record via the computing device of the system or a separate computing system.

[0031] According to the invention, the first position sensing means for acquiring data related to the spatial position of a patient on the patient couch can be integrated in the patient couch and/or have a fixed position with respect to, at least a part of, the patient couch and/or include one or more couch-based cameras and/or optical means, particularly means using visible light and/or infrared light and/or laser light, and/or electromagnetic means and/or pressure sensing means and/or are also used for an intra-fraction motion detection during treatment and/or imaging.

[0032] The spatial position sensing system is intended to be used to at first verify the correct position of the patient with respect to the couch (and, as the case may be, to an embedded detector system) and later on possibly to verify the position of the patient-couch-system in relation to the treatment and/or imaging device geometry as specified by a radiation treatment plan, for example. They can, in certain embodiments in combination with second position sensing means for example fixed to a treatment device, be used to detect movement of the patient on the treatment couch regardless of the type of the treatment delivery, whether static or dynamic, and to detect movement of the treatment and/or imaging device such as a treatment unit gantry and/or of the couch when the treatment is dynamic.

[0033] The spatial position sensing can be done by optical means including infrared and/or electromagnetic means and/or pressure sensing means. Combinations of position sensing means of different types can be used. The first and/or second positioning means can be used to set the correct geometry of the patient-couch-system to the treatment and/or imaging device such as a gantry prior to initiating a treatment delivery or for a treatment completion following a treatment interruption, and/or to detect patient movement on the couchtop during treatment delivery and/or to detect incorrect positioning of the couchtop and/or a gantry during a dynamic treatment, and/or to provide information to allow the treatment to be interrupted manually by the operator or automatically by a treatment and/or imaging device's safety interlock system. Therefore, depending on the circumstances of the treatment and/or imaging and/or of the data to be collected during the treatment and/or imaging process, the patient reference frame and the couch reference frame will still be regarded as the united system created during the first positioning process or as individual systems again.

[0034] In order to integrate the first position sensing means in the couch, the couch is designed for allowing the introduction of a position sensing technology onto it. Preferably, the couchtop is designed for immobilization and positioning systems like thermoplastic shells and/or masks and/or evacuated bean bags to be fixed to its surface via standard arrangements, pins, holes, rails and/or slots. In addition, such immobilization and positioning systems may include robotically controlled positioning devices that are directed by the spatial positioning system of the invention and/or are a part of it. An example would be a motorized head positioning device that corrects small movements in real-time during delivery of radiation by using negative feedback from the position sensing means. In addition, the couchtop according to the invention can have geometrical markings and labeling of pins, holes, slots and/or rails on its surface to assist the operator in correctly positioning the patient and the immobilization and positioning devices on the couchtop.

[0035] Preferably, the spatial position data measured by the first or, optionally in addition or alternatively, by second position sensing means, are exportable to an electronic medical record. The position data can also be used in a dose computation model for reconstructing an estimate of delivered dose that includes the effect of intra-fraction motion. For example, the signals produced by the positionining means may be used for the control of a robotic positioner to correct for small errors during treatment delivery.

[0036] According to the invention, the patient couch may include a primary couchtop attached to a couch pedestal, particularly a primary couchtop including integrated the first position sensing means and/or an integrated and/or embedded sensor system for radiation, and at least one secondary couchtop floating and/or gliding on the primary couchtop for positioning the patient with respect to the primary couchtop.

[0037] It is to be preferred that the primary couchtop is attached to a couch pedestal whose motion is controlled by a computing device of the treatment and/or imaging device such as a linac. The computing device of the positioning system according to the invention is preferably, at least with respect to the hardware components, a part of the computing device of the treatment and/or imaging device so that there is one single computer system controlling the treatment and/or imaging process and the positioning pocess. With advantage, a radiation detector such as an array detector is embedded in the primary couchtop. First position sensing means such as a camera system are attached to the primary couchtop and used for patient localization and, optionally, later on for intra-fraction motion detection.

[0038] The secondary couchtop preferably "floats" on the primary couchtop (is movable relative to the primary couchtop) so that the patient can be localized with respect to the primary couchtop and therewith to the embedded radiation detector. Once the patient is localized to the primary couchtop or the radiation detector, the secondary couchtop is secured to the primary couchtop. In this way, a single patient-couch-system is formed.

[0039] It is possible, that the system according to the invention includes several (different) secondary couchtops, for example couchtops designed for different body sites which can be chosen depending on the treatment to be performed. A further advantage of using a secondary couchtop is the possibility that the setup of the patient can be done off-line outside a treatment room. After the setup is completed, the patient on the secondary couchtop can be moved into the treatment room on a stretcher with rails to slide the device onto the patient couch. This advantageously leads to a better resource utilization by freeing the linac or another treatment or imaging device to perform treatments or other tasks in the meantime.

[0040] According to the invention, the origin of the frame of reference of the patient can be located at a patient setup point, particularly inside an internal target where the radiation to be applied will be concentrated, and/or the origin of the frame of reference of the patient couch can be assumed to be at the center of an integrated and/or embedded sensor system for radiation and/or the single patient-and-couch-system frame of reference can be defined within an acceptable setup error.

[0041] The origin of the patient reference system (abbreviated PRF) is preferably located at the patient setup point, typically inside the internal target where the radiation dose to be applied will be concentrated. [0042] The origin of the couch reference system (CRF) can be assumed to be at the center of the field-of-view of an embedded radiation detector. First position sensing means such as a camera and additional sensors can be fixed to the primary couchtop at the foot of the couch. The patient can be aligned to the embedded detector using the camera by matching the patient's surface to a surface generated from a treatment plan. The goal is to align the patient reference frame to the couch reference frame within an acceptable setup error ε_1;

[0043] Once this condition is achieved, then the secondary couchtop can be secured to the primary couchtop. A common patient-and- couch-system frame of reference is formed. An acceptable setup error may be an error of <2mm (e.g., half the width of a detector). Of course, the acceptable setup error may vary depending on the geometry and components of the system and the planned treatment or imaging process.

[0044] The patient-and-couch system is preferably movable relative to the isocenter and/or origin of the frame of reference of the radiation treatment and/or imaging device, particularly a linac, in order to position the patient-and- couch system relative to the frame of reference of the radiation treatment and/or imaging device.

[0045] The patient can be localized to the linac or another treatment and/or imaging device by moving the integrated patient-and-couch system. Preferably, the linac's or device's isocenter is the origin of the linac or device reference system (in the following abbreviated as LRF). The localization or positioning can be done using radiographic localization methods on the basis of computed tomography (CT) or using implanted fiducials. Alternatively, optical surface matching using a camera (forming a part of the first position sensing means or of second position sensing means) can be used when the radiation dose from daily radiographic localization is unwarranted (e.g., in breast treatments). The goal is to align the patient reference system (which has before been aligned to form a common patient-and-couch reference system with the former separated couch reference system) to the linac or device reference system within an acceptable setup error ε₂:

|LRF - PRF| < ε₂.

[0046] To name non-limiting examples, the acceptable error may range from 0.5-1 mm for intracranial stereotactic radio surgery (SRS) to 1 -3 mm for other body sites.

[0047] In the context of the invention, there can be a treatment plan according to which the patient-and-couch-system frame of reference is positioned relative to the frame of reference of the radiation treatment and/or imaging device and/or the system of the invention may include second position sensing means as a target inside the patient and/or radiographic targeting methods, particularly CT imaging and/or imaging means integrated in and/or imaging means of the radiation treatment and/or imaging device.

[0048] For example, the target inside the patient can be localized to a linac isocenter per the treatment plan and by moving the patient-couch system relative the linac isocenter. This localization can be performed by either a couch-based camera or other first position sensing means or by radiographic targeting methods such as on-board CT imaging or other second position sensing means or by evaluating data of first and second position sensing means in combination.

[0049] The first and/or second position sensing means and/or the computing device can be designed for treating the patient as a rigid static object when positioned with respect to the patient couch and for treating him as a dynamic object during treatment and/or imaging and/or for treating the couch as static or dynamic, particularly with respect to a planned motion and/or a realtime corrective motion, during treatment and/or imaging. [0050] When the patient is treated, first position sensing means as a couch-based camera and/or second position sensing means can be used for intra-fraction motion detection during the treatment. For example, in terms of the patient reference frame (PRF), the patient can be treated as a rigid static object when he is being localized first. During the treatment or imaging procedure the patient can then be treated as a dynamic object and monitored for intra-fraction motion. Once the patient-linac localization is achieved, the radiotherapy procedure can commence. The patient reference frame can then be assumed to be dynamic and represented as a function of time, PRF(t). The objective is then to maintain the patient (and/or a target related to the patient) within an acceptable motion tolerance Δ,

|LRF - PRF(t)| < Δ.

[0051] To mention examples, this tolerance might range from 0.5- 1 mm for stereotactic radio surgery (SRS) to 1 -3 mm for routine intensity- modulated radiation therapy (IMRT). If the patient or target, respectively, moves beyond a distance Δ, the treatment is preferably interrupted until the patient (the target) is moved back within the distance Δ of the isocenter. The displacement signal can be used for gating a treatment beam.

[0052] A comparable approach can be used for the patient couch reference frame (CRF). Depending on the type of treatment and/or imaging device, the couch can be either static or dynamic during treatment. One example where a static couch might be appropriate is radiotherapy using a conventional linac, which is typically performed with a fixed couch position for both localization imaging and treatment delivery.

[0053] The second possibility is that the couch is dynamic and moves during treatment or radiation delivery. Couch motion during treatment can be divided into two cases, namely planned motion and real-time corrective motion. [0054] The case of a planned motion can be represented by helical tomotherapy where the couch moves at constant velocity into the gantry bore. But this case can also be generalized to a conventional linac for example as a means of extending the length of a treatment volume beyond a multileaf collimator's 40 cm field-of-view limit. In general, a planned motion can be monitored by a treatment and/or imaging device's, for example a linac's, control and safety interlock system. In this case, a further camera or first position sensing means can be used to monitor this planned motion, but are not necessarily needed.

[0055] As for the case of a real-time corrective motion, work is underway at several research centers to use the couchtop to compensate for tumor motion during the treatment procedure (see for example: "Real-time intra- fraction-motion tracking using the treatment couch: a feasibility study", Warren D. D'Souza et al., 2005 Phys. Med. Biol. 50, 4021 -4033). It is intended as an alternative to gated treatment delivery methods.

[0056] In summary, there are three reference frames playing a role in the context of the positioning system according to the invention. A couch- mounted camera or other first position sensing means are used to align the reference frame of the patient (PRF) to the reference frame of the couch (CRF). The formerly two independent systems are then locked together to form a single integrated system. The camera and/or other first position sensing means can then be used to align the integrated PRF/CRF-system to the reference frame of the treatment and/or imaging device (such as a linac with a limac reference frame, LRF) as an alternative to radiographic localization or using further second position sensing means. The camera can then be used to monitor the PRF (as a single system again and/or as the integrated PRF/CRF-system) for motion during treatment delivery. As known software models of commercial camera systems are designed to measure displacement of only two reference frames, the system and processes according to the invention are compatible with these existing types of software models since only two reference frames are considered at each alignment step. [0057] Apart from that, the invention also concerns a method for positioning a patient relative to a movable patient couch and to a radiation treatment and/or imaging device, particularly to a linac and/or in the context of tomotherapy, especially with a system as described in the preceding, comprising the steps of :

- By use of a movable patient couch with first position sensing means acquire data related to the spatial position of a patient in relation to the patient couch, with the patient and the patient couch having allocated separated frames of reference,

- by use of a computing device evaluate the data acquired by the first position sensing means, the computing device deriving information for positioning the patient with respect to the patient couch from the data and defining an integrated single patient-and-couch-system frame of reference from the former separated frames of reference of the patient and the patient couch, and

- by use of the computing device evaluate further data acquired by the first position sensing means and/or by second position sensing means, the further data being related to the spatial position of the patient-and-couch system relative to the radiation treatment and/or imaging device and the computing device deriving information for positioning the patient-and- couch-system frame of reference relative to the frame of reference of the radiation treatment and/or imaging device from the further data so that the planned treatment and/or imaging can be performed.

[0058] It is to be noted that the method according to the invention is solely a method for positioning a patient in a certain manner, but not in any kind a method for treatment of the human or animal body by surgery or therapy nor a diagnostic method practised on the human or animal body. The treatment or diagnosis itself is not an object of the present invention. The localization and positioning according to the invention, which according to the basic embodiment of the invention takes part before a treatment and/or imaging even starts, is based on the gathering and evaluation of physical data and as such has no medical implications.

[0059] In the context of the present invention, a patient couch can be used which includes an integrated and/or embedded sensor system for radiation, particularly a plurality of radiation detectors, which are preferably arranged in an array and/or a linear format, and/or an embedded sensor system for radiation relative to which the patient is to be positioned and/or which is sandwiched between two layers of the patient couch, particularly between two carbon fiber sections, and/or which is a sensor system for data quality assurance and/or for planning and/or treatment and/or radiation verification, especially in real-time, and/or which is, particularly relative to the patient, positioned via megavoltage computed tomography.

[0060] The data related to the spatial position of a patient on the couch can be acquired by first position sensing means which are integrated in the patient couch and/or have a fixed position with respect to, at least a part of, the patient couch and/or include one or more couch-based cameras and/or optical means, particularly by means using visible light and/or infrared light and/or laser light, and/or by electromagnetic means and/or pressure sensing means and/or by means which are also used for an intra-fraction motion detection during treatment and/or imaging.

[0061] According to the invention, a patient couch can be used which includes a primary couchtop attached to a couch pedestal, particularly a primary couchtop including integrated the first position sensing means and/or an integrated and/or embedded sensor system for radiation, and at least one secondary couchtop floating and/or gliding on the primary couchtop for positioning the patient with respect to the primary couchtop with the secondary couchtop being secured to the primary couchtop after positioning the patient.

[0062] The origin of the frame of reference of the patient can be located at the patient setup point, particularly inside an internal target where the radiation to be applied will be concentrated, and/or the origin of the frame of reference of the patient couch can be assumed to be at the center of an integrated and/or embedded sensor system for radiation and/or the single patient-and-couch-system frame of reference can be defined within an acceptable setup error and/or the patient-and-couch-system frame of reference can be positioned relative to the frame of reference of the radiation treatment and/or imaging device by moving the patient-and-couch system relative to the isocenter and/or origin of the frame of reference of the radiation treatment and/or imaging device, particularly a linac, and/or the patient-and-couch frame of reference can be positioned relative to the frame of reference of the radiation treatment and/or imaging device within an acceptable setup error.

[0063] In the context of the invention, the patient-and-couch frame of reference can be positioned relative to the frame of reference of the radiation treatment and/or imaging device according to a treatment plan and/or by using a target inside the patient and/or by using radiographic targeting methods, particularly CT imaging and/or imaging means integrated in and/or of the radiation treatment and/or imaging device as second position sensing means

[0064] The patient can be treated as a rigid static object when positioned with respect to the patient couch and can be treated as a dynamic object during treatment and/or imaging and/or the couch can be treated as static or dynamic, particularly with respect to a planned motion and/or a realtime corrective motion, during treatment and/or imaging.

[0065] In the following description of the figures, for reasons of simplicity, parts which, at least basically, are comparable in the different figures will be referred to by the same reference numerals.

[0066] Fig. 1 is a perspective drawing of a part of a system 1 for positioning a patient relative to patient couch 2 and to a radiation treatment and/or imaging device according to the invention with a radiation detector 3 embedded in the patient couch 2. In this embodiment, a positioning camera 4 which is attached to the patient couch 2 serves as first position sensing means. The camera 4 has a field-of-view region 5 where the patient is to be positioned on the patient couch 2 in the correct position with respect to the embedded radiation detector 3 as determined in a corresponding treatment plan. The computing device, which evaluates the data of the camera 4, is not shown in this representation.

[0067] Fig. 2 shows a side view and a top view of the part of the system 1 of fig. 1. For practical reasons, the camera 4 is mounted on the short end of the patient couch 2 which has the larger distance to the embedded radiation detector 3 (which will usually be the foot of the patient couch 2).

[0068] Fig. 3 shows a side view and a top view of a part of another system 6 for positioning a patient relative to patient couch 2 and to a radiation treatment and/or imaging device according to the invention including a primary couchtop 7 and a secondary couchtop 8. The patient couch 2 has an embedded radiation detector 3, which here is embedded in the primary couchtop 7. The primary couchtop is attached to a couch pedestal (not shown) whose motion is controlled by a computing device according to the invention belonging to a linac

(also not shown). The camera 4 as first position sensing means is attached to the primary couchtop 7 and used for patient localization and intra-fraction motion detection as well. Although in the figures there is only one camera 4, it lies within in the scope of the invention to use a system of several cameras and/or of additional sensors such as pressure sensors instead. The secondary couchtop 8 "floats" on the primary couchtop 7 so to make it possible to localize the patient to the embedded radiation detector 3 by moving the secondary couchtop 8.

[0069] Fig. 4 is a view of a treatment room 9 with a system and for using a method according to the invention. The treatment room 9 is equipped with an in-room computing device 10 and a data connection 1 1 to an operator's console 12 outside the treatment room 9 and receiving data from the in-room computing device 10. There is another data connection 1 1 via which the computing device 10 receives data related to the positioning process according to the invention as measured by the camera 4 and also data related to the treatment process to be performed after the first positioning is accomplished by the radiation treatment device 15. The patient couch 2 in fig. 4 consists of a couchtop 13 and a pedestal 14. Sensors on the couchtop 13 (as the first position sensing means in form of the camera 4) communicate with the computing device 10. The acquired data can be or is automatically displayed on the computing device 10 and, in this embodiment, also on the operator's treatment console 12. In the course of the treatment, the operator has the option of manually interrupting a treatment if the patient moves out of acceptable limits. In this example, there are also second position sensing means 4a attached to the radiation treatment device 15. The second position sensing means are connected via a data connection (not shown) to the computing device 10 and are adapted for acquiring data related to the spatial position of the patient-and-couch system relative to the radiation treatment device 15. Here, the further data acquired by the second position sensing means 4a are supplemental data to the data acquired by the camera 4.

[0070] Fig. 5 shows a view of an alternative setup of a treatment room 9 with a system and for using a method according to the invention with an on-board computing device 10 integrated into the control system of the radiation treatment device 15. In this embodiment, the patient couch 2, which again consists of a couchtop 13 and a pedestal 14, communicates with the on-board computing device 10. Again, the radiation detector 3 is embedded in the couchtop 13 and there is a camera 4 with a field-of-view region 5. The embodiment of fig. 5 faciliates the use of the position and motion detection system according to the invention for gated treatment delivery. It also allows the couchtop system to be interfaced to the radiation treatment device's safety interlock system for interrupting treatments when dose and displacement values exceed acceptable limits. The data connection 1 1 makes it possible to transfer the data of the computing device 10 to the operator's console 12 outside the treatment room 9.

[0071] Fig. 6 shows diagrams of an accumulated radiation dose at a detector and a displacement vector displayed at an operator's treatment console during a treatment delivery. The solid line data is an example from an uninterrupted treatment with a dose (D) and displacement vector (V) within chosen limits. Upper and lower range values beyond the allowed limits represent a treatment interrupted by the operator or an interlock system. The dashed line data show an example of an interrupted treatment where the interruption occurred at time T_int due to a displacement exceeding the upper displacement threshold limit, see dose D_int and displacement vector V_int.

[0072] Fig. 7 shows in an exemplary view the three reference frames playing a role in the positioning according to the invention for the case that the radiation treatment device is a linac. Firstly, there is the linac reference frame 18 (LRF) which is always static and fixed to the room geometry. The linac isocenter is the origin of this reference frame. Then there is the patient reference frame 19 (PRF). When the patient is being localized according to the basic embodiment of the present invention, the patient is treated as a rigid static object; during treatment the patient is treated as a dynamic object and monitored for intra-fraction motion. The third reference frame is the couch reference frame 20 (CRF). Depending on the type of treatment and/or imaging device, the couch is either static or dynamic during treatment. Radiotherapy using a conventional linac is typically performed with a fixed couch position (static couch) for both localization imaging and treatment delivery. Then there is the possibility that the couch moves during treatment delivery and is therefore a dynamic couch. As has already been pointed out before, couch motion during treatment can be divided into planned motion (as in the case of helical tomotherapy or for extending the length of a treatment volume of a linac) and real-time corrective motion. The case of real-time corrective motion implies concepts where the couchtop is used to compensate for tumor motion (patient motion, respectively) during the treatment procedure.

[0073] Fig. 8 shows the alignment of the patient reference frame 19

(PRF) and the couch reference frame 20 (CRF) to form a single patient-and- couch-system frame of reference 21 according to the invention. The origin of the couch reference frame 20 is in this case assumed to be at the center of the field-of-view of a radiation detector system embedded in the couch. A camera is fixed to the primary couchtop at the foot of the couch. The patient is aligned to the embedded detector using the camera by matching the patient's surface to a surface generated from a treatment plan. The goal is then to align the patient reference frame 19 to the couch reference frame 20 within the acceptable setup error ε_u

as shown in fig. 8, and then to secure the secondary couchtop to the primary couchtop. An acceptable error may be an error in the range up to 1 or 2 mm.

[0074] Fig. 9 shows the alignment of the single patient-and-couch- system reference frame 21 to the reference frame of the radiation treatment and/or imaging device, here the linac reference frame 18. The patient is localized to the linac or another treatment and/or imaging device by moving the patient-and-couch system. The linac's or device's isocenter is the origin of the linac or device reference system 18 (LRF). The localization is done using radiographic localization methods (CT and/or implanted fiducials). Alternatively, optical surface matching using a camera can be used. The goal is to align the patient reference system 19 (which forms a common patient-and-couch-system reference frame 21 with the former couch reference system) to the linac or device reference frame 18 within the acceptable setup error ε₂,

|LRF - PRF| < ε₂.

[0075] Fig. 10 depicts the intra-fraction motion monitoring according to the invention. As soon as the patient-linac localization is achieved, the radiotherapy or radioimaging procedure can begin. The patient reference frame 19 can then be assumed to be dynamic and represented as a function of time, PRF(t). The patient and/or a target within the body or on the surface of the body of the patient is then kept within an acceptable motion tolerance Δ, |LRF - PRF(t)| < Δ.

The displacement vector 22 is measured as a function of time and compared to the acceptable error bound Δ indicated by the dashed circle 23 centered on the position (the origin) of the linac reference frame 18. If the patient (target) moves beyond a distance Δ, the treatment is preferably interrupted until the patient/ the target is moved back within Δ of the isocenter. The displacement signal can be used for gating the treatment beam.

List of reference numerals

1 (part of a) system for positioning a patient

2 patient couch

3 radiation detector

4 camera (first position sensing means)

4a second position sensing means

5 field-of-view region

6 (part of a) system for positioning a patient

7 primary couchtop

8 secondary couchtop

9 treatment room 10 in-room/on-board computing device

11 data connection

12 operator's console

13 couchtop 14 pedestal

15 radiation treatment device

16 accumulated radiation dose

17 displacement vector

18 linac reference frame 19 patient reference frame

20 couch reference frame

21 patient-and-couch-system frame of reference

22 displacement vector

23 dashed circle

Claims

page 1/6Claims

1. A system (1 , 6) for positioning a patient relative to a patient couch (2) and to a radiation treatment and/or imaging device (15), particularly to a linac and/or in the context of tomotherapy, comprising:

- A movable patient couch (2) with first position sensing means (4) for acquiring data related to the spatial position of a patient in relation to the patient couch (2), with the patient and the patient couch (2) having allocated separated frames of reference (19, 20), - a computing device (10) for evaluating the data acquired by the first position sensing means (4), the computing device (10) being adapted to derive information for positioning the patient with respect to the patient couch (2) from the data and to define an integrated single patient-and-couch-system frame of reference (21 ) from the former separated frames of reference (19, 20) of the patient and the patient couch, and

- the computing device (10) for evaluating further data acquired by the first position sensing means (4) and/or by second position sensing means (4a), the further data being related to the spatial position of the patient-and-couch system relative to the radiation treatment and/or imaging device (15) and the computing device (10) being adapted to derive information for positioning the patient-and-couch-system frame of reference (21 ) relative to a frame of reference (18) of the radiation treatment and/or imaging device from the further data so that the planned treatment and/or imaging can be performed.

2. The system (1 , 6) according to claim 1 characterized in that the movable patient couch (2) includes an integrated and/or embedded sensor system for radiation (3), particularly a plurality of radiation detectors (3), which are preferably arranged in an array and/or a linear format, and/or an embedded sensor system for radiation (3) relative to which the patient is to be positioned and/or which is sandwiched between two layers of the patient couch (2), particularly between two carbon fiber sections, and/or which is a sensor system (3) for data quality assurance and/or for planning and/or treatment and/or radiation verification, especially in realtime, and/or which is, particularly relative to the patient, positioned via megavoltage computed tomography.

3. The system (1 , 6) according to claim 1 or 2 characterized in that the first position sensing means (4) for acquiring data related to the spatial position of a patient on the patient couch (2) are integrated in the patient couch (2) and/or have a fixed position with respect to, at least a part of, the patient couch (2) and/or include one or more couch-based cameras (4) and/or optical means, particularly means using visible light and/or infrared light and/or laser light, and/or electromagnetic means and/or pressure sensing means and/or are also used for an intra-fraction motion detection during treatment and/or imaging.

4. The system (1 , 6) according to any of claims 1 to 3 characterized in that the patient couch (2) includes a primary couchtop (7) attached to a couch pedestal (14), particularly a primary couchtop (7) including integrated the first position sensing means (4) and/or an integrated and/or embedded sensor system for radiation (3), and at least one secondary couchtop (8) floating and/or gliding on the primary couchtop (7) for positioning the patient with respect to the primary couchtop (7).

5. The system (1 , 6) according to any of claims 1 to 4 characterized in that the origin of the frame of reference (19) of the patient is located at a patient setup point, particularly inside an internal target where the radiation to be applied will be concentrated, and/or that the origin of the frame of reference (20) of the patient couch is assumed to be at the center of an integrated and/or embedded sensor system for radiation (3) and/or that the single patient-and-couch-system frame of reference (21 ) is defined within an acceptable setup error. page 3/6

6. The system (1 , 6) according to any of claims 1 to 5 characterized in that the patient-and-couch system is movable relative to the isocenter and/or origin of the frame of reference (18) of the radiation treatment and/or imaging device, particularly a linac, in order to position the patient-and- couch system relative to the frame of reference (18) of the radiation treatment and/or imaging device.

7. The system (1 , 6) according to claim 6 characterized in that there is a treatment plan according to which the patient-and-couch-system frame of reference (21 ) is positioned relative to the frame of reference (18) of the radiation treatment and/or imaging device and/or that the system (1 , 6) includes second position sensing means (4a) as a target inside the patient and/or radiographic targeting methods, particularly computed tomography imaging and/or imaging means integrated in and/or imaging means of the radiation treatment and/or imaging device (15).

8. The system (1 , 6) according to any of claims 1 to 7 characterized in that the first and/or second position sensing means (4, 4a) and/or the computing device (10) are designed for treating the patient as a rigid static object when positioned with respect to the patient couch (2) and for treating him as a dynamic object during treatment and/or imaging and/or for treating the patient couch (2) as static or dynamic, particularly with respect to a planned motion and/or a real-time corrective motion, during treatment and/or imaging.

9. A method for positioning a patient relative to a movable patient couch (2) and to a radiation treatment and/or imaging device (15), particularly to a linac and/or in the context of tomotherapy, especially with a system (1 , 6) according to any of the preceding claims, comprising the steps of: - By use of a movable patient couch (2) with first position sensing means (4) acquire data related to the spatial position of a patient in relation to the patient couch (2), with the patient and the patient couch (2) having allocated separated frames of reference (19, 20), page 4/6

- by use of a computing device (10) evaluate the data acquired by the first position sensing means (4), the computing device (10) deriving information for positioning the patient with respect to the patient couch (2) from the data and defining an integrated single patient-and-couch-system frame of reference (21 ) from the former separated frames of reference (19, 20) of the patient and the patient couch, and

- by use of the computing device (10) evaluate further data acquired by the first position sensing means (4) and/or by second position sensing means (4a), the further data being related to the spatial position of the patient-and-couch system relative to the radiation treatment and/or imaging device (15) and the computing device (10) deriving information for positioning the patient-and- couch-system frame of reference (21 ) relative to the frame of reference (18) of the radiation treatment and/or imaging device from the further data so that the planned treatment and/or imaging can be performed.

10. The method according to claim 9 characterized in that a patient couch (2) is used which includes an integrated and/or embedded sensor system for radiation (3), particularly a plurality of radiation detectors (3), which are preferably arranged in an array and/or a linear format, and/or an embedded sensor system for radiation (3) relative to which the patient is to be positioned and/or which is sandwiched between two layers of the patient couch (2), particularly between two carbon fiber sections, and/or which is a sensor system (3) for data quality assurance and/or for planning and/or treatment and/or radiation verification, especially in realtime, and/or which is, particularly relative to the patient, positioned via megavoltage computed tomography.

11. The method according to claim 9 or 10 characterized in that the data related to the spatial position of a patient on the patient couch (2) are acquired by first position sensing means (4) which are integrated in the page 5/6

patient couch (2) and/or have a fixed position with respect to, at least a part of, the patient couch (2) and/or include one or more couch-based cameras (4) and/or optical means, particularly by means using visible light and/or infrared light and/or laser light, and/or by electromagnetic means and/or pressure sensing means and/or by means which are also used for an intra-fraction motion detection during treatment and/or imaging.

12. The method according to any of claims 9 to 11 characterized in that a patient couch (2) is used which includes a primary couchtop (7) attached to a couch pedestal (14), particularly a primary couchtop (7) including integrated the first position sensing means (4) and/or an integrated and/or embedded sensor system for radiation (3), and at least one secondary couchtop (8) floating and/or gliding on the primary couchtop (7) for positioning the patient with respect to the primary couchtop (7) with the secondary couchtop (8) being secured to the primary couchtop

(7) after positioning the patient.

13. The method according to any of claims 9 to 12 characterized in that the origin of the frame of reference (19) of the patient is located at a patient setup point, particularly inside an internal target where the radiation to be applied will be concentrated, and/or that the origin of the frame of reference (20) of the patient couch (2) is assumed to be at the center of an integrated and/or embedded sensor system for radiation (3) and/or that the single patient-and-couch-system frame of reference (21 ) is defined within an acceptable setup error and/or that the patient-and- couch-system frame of reference (21 ) is positioned relative to the frame of reference (18) of the radiation treatment and/or imaging device by moving the patient-and-couch system relative to the isocenter and/or origin of the frame of reference (18) of the radiation treatment and/or imaging device, particularly a linac, and/or that the patient-and-couch- system frame of reference (21 ) is positioned relative to the frame of reference (18) of the radiation treatment and/or imaging device within an page 6/6

acceptable setup error.

14. The method according to claim 13 characterized in that the patient-and- couch-system frame of reference (21 ) is positioned relative to the frame of reference (18) of the radiation treatment and/or imaging device according to a treatment plan and/or by using a target inside the patient and/or by using radiographic targeting methods, particularly computed tomography imaging and/or imaging means integrated in and/or imaging means of the radiation treatment and/or imaging device (15) as second position sensing means (4a).

15. The method according to any of claims 9 to 14 characterized in that the patient is treated as a rigid static object when positioned with respect to the patient couch (2) and is treated as a dynamic object during treatment and/or imaging and/or that the patient couch (2) is treated as static or dynamic, particularly with respect to a planned motion and/or a real-time corrective motion, during treatment and/or imaging.