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WO2019056134A1 - Systèmes et procédés permettant de corriger un désalignement induit par un mouvement de portique et de lit pendant un traitement par rayonnement basé sur un arc - Google Patents

Systèmes et procédés permettant de corriger un désalignement induit par un mouvement de portique et de lit pendant un traitement par rayonnement basé sur un arc Download PDF

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Publication number
WO2019056134A1
WO2019056134A1 PCT/CA2018/051208 CA2018051208W WO2019056134A1 WO 2019056134 A1 WO2019056134 A1 WO 2019056134A1 CA 2018051208 W CA2018051208 W CA 2018051208W WO 2019056134 A1 WO2019056134 A1 WO 2019056134A1
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Prior art keywords
treatment
couch
gantry
radiation
radiation treatment
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English (en)
Inventor
Alasdair SYME
David Parsons
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Dalhousie University
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Dalhousie University
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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N5/1042—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy with spatial modulation of the radiation beam within the treatment head
    • A61N5/1045—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy with spatial modulation of the radiation beam within the treatment head using a multi-leaf collimator, e.g. for intensity modulated radiation therapy or IMRT
    • A61N5/1047—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy with spatial modulation of the radiation beam within the treatment head using a multi-leaf collimator, e.g. for intensity modulated radiation therapy or IMRT with movement of the radiation head during application of radiation, e.g. for intensity modulated arc therapy or IMAT
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N5/1048—Monitoring, verifying, controlling systems and methods
    • A61N5/1064—Monitoring, verifying, controlling systems and methods for adjusting radiation treatment in response to monitoring
    • A61N5/1069—Target adjustment, e.g. moving the patient support
    • A61N5/107—Target adjustment, e.g. moving the patient support in real time, i.e. during treatment
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B90/00—Instruments, implements or accessories specially adapted for surgery or diagnosis and not covered by any of the groups A61B1/00 - A61B50/00, e.g. for luxation treatment or for protecting wound edges
    • A61B90/39—Markers, e.g. radio-opaque or breast lesions markers
    • A61B2090/3966—Radiopaque markers visible in an X-ray image
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/04—Positioning of patients; Tiltable beds or the like
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/52—Devices using data or image processing specially adapted for radiation diagnosis
    • A61B6/5211—Devices using data or image processing specially adapted for radiation diagnosis involving processing of medical diagnostic data
    • A61B6/5223—Devices using data or image processing specially adapted for radiation diagnosis involving processing of medical diagnostic data generating planar views from image data, e.g. extracting a coronal view from a 3D image
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N5/1048—Monitoring, verifying, controlling systems and methods
    • A61N5/1049—Monitoring, verifying, controlling systems and methods for verifying the position of the patient with respect to the radiation beam
    • A61N2005/1054—Monitoring, verifying, controlling systems and methods for verifying the position of the patient with respect to the radiation beam using a portal imaging system

Definitions

  • High precision radiotherapy and radiosurgery such as stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) is a rapidly growing component of the workload of a modern radiation oncology clinic.
  • SRS stereotactic radiosurgery
  • SBRT stereotactic body radiation therapy
  • MLCs multileaf collimators
  • cone-based treatments may confer some dosimetric advantages.
  • Spatial offsets are determined at a plurality of calibration control points alone one or more arcs associated with a treatment plan, and the spatial offsets are processed to determine couch position (and optionally orientation) corrections for correcting the misalignments when executing the treatment plan.
  • the treatment plan may employ a virtual isocenter, such that the position of the couch is varied, and corrected, during treatment.
  • the present methods may be employed to achieve alignment for treatment plans involving small imaging fields that are defined by reduced number of multileaf collimator leaves, such as a single leaf pair.
  • a couch- position-corrected virtual isocenter-based treatment arc may be employed to enable clinical radiation treatment with small projected field sizes defined by one or more multileaf collimator defined fields.
  • a method of controlling a radiation treatment system to compensate for positional errors associated with couch rotation and gantry rotation comprising a couch, a gantry, and a multileaf collimator, the method comprising:
  • each calibration control point having a respective gantry angle and a respective couch angle, wherein the plurality of calibration control points reside along one or more treatment arcs prescribed by a treatment plan, and detecting a portal image at each calibration control point;
  • a method of controlling a radiation treatment system to compensate for positional errors associated with couch rotation and gantry rotation comprising a couch, a gantry, and a multileaf collimator
  • the method comprising: prior to a treatment phase, rotating the gantry and the couch to position the gantry and the couch according to a plurality of calibration control points, each calibration control point having a respective gantry angle and a respective couch angle, wherein the plurality of calibration control points reside along one or more treatment arcs prescribed by a treatment plan, wherein the one or more treatment arcs employ a virtual isocenter to dynamically position a subject during treatment, such that the subject resides closer to an exit aperture of the radiation treatment system than a true isocenter of the radiation treatment system during treatment, and such that a projected field defined by the multileaf collimator is magnified at the virtual isocenter relative to the true isocenter of the radiation treatment system, and detecting a portal image at each calibration control point;
  • a method of calibrating a radiation treatment system to compensate for positional errors associated with couch rotation and gantry rotation comprising a couch, a gantry, and a multileaf collimator, the method comprising, prior to a treatment phase:
  • each calibration control point having a respective gantry angle and a respective couch angle, wherein the plurality of calibration control points reside along one or more treatment arcs prescribed by a treatment plan, and detecting a portal image at each calibration control point;
  • a radiation treatment system comprising:
  • a gantry configured to rotate about a rotation axis
  • an X-ray source and a detector wherein the X-ray source and the detector are supported in an opposing configuration by the gantry, such that the X-ray source and the detector are rotatable by the gantry about the rotation axis, wherein the X-ray source is configured to emit a treatment radiation beam and a portal imaging beam;
  • a multileaf collimator comprising a plurality of leaves, wherein positions of the leaves are controllable for generating dynamically defined radiation fields;
  • a couch positioned adjacent the gantry, wherein a position of the couch is controllable in three-dimensions;
  • control and processing circuitry operatively coupled to the gantry, the X-ray source, the couch, and the multileaf collimator, the control and processing circuitry comprising a processor and a memory, wherein the processor is configured to execute instructions stored in the memory for performing the steps of:
  • each calibration control point having a respective gantry angle and a respective couch angle, wherein the plurality of calibration control points reside along one or more treatment arcs prescribed by a treatment plan, and detecting a portal image at each calibration control point;
  • a radiation treatment system comprising:
  • a gantry configured to rotate about a rotation axis
  • an X-ray source and a detector wherein the X-ray source and the detector are supported in an opposing configuration by the gantry, such that the X-ray source and the detector are rotatable by the gantry about the rotation axis, wherein the X-ray source is configured to emit a treatment radiation beam and a portal imaging beam;
  • a multileaf collimator comprising a plurality of leaves, wherein positions of the leaves are controllable for generating dynamically defined radiation fields;
  • a couch positioned adjacent the gantry, wherein a position of the couch is controllable in three-dimensions;
  • control and processing circuitry operatively coupled to the gantry, the X-ray source, the couch, and the multileaf collimator, the control and processing circuitry comprising a processor and a memory, wherein the processor is configured to execute instructions stored in the memory for performing the steps of:
  • each calibration control point having a respective gantry angle and a respective couch angle, wherein the plurality of calibration control points reside along one or more treatment arcs prescribed by a treatment plan, and detecting a portal image at each calibration control point;
  • a radiation treatment system comprising:
  • a gantry configured to rotate about a rotation axis
  • an X-ray source and a detector wherein the X-ray source and the detector are supported in an opposing configuration by the gantry, such that the X-ray source and the detector are rotatable by the gantry about the rotation axis, wherein the X-ray source is configured to emit a treatment radiation beam and a portal imaging beam;
  • a multileaf collimator comprising a plurality of leaves, wherein positions of the leaves are controllable for generating dynamically defined radiation fields;
  • a couch positioned adjacent the gantry, wherein a position of the couch is controllable in three-dimensions;
  • control and processing circuitry operatively coupled to the gantry, the X-ray source, the couch, and the multileaf collimator, the control and processing circuitry comprising a processor and a memory, wherein the processor is configured to execute instructions stored in the memory for performing the steps of:
  • each calibration control point having a respective gantry angle and a respective couch angle
  • the plurality of calibration control points reside along one or more treatment arcs prescribed by a treatment plan, and detecting a portal image at each calibration control point
  • the one or more treatment arcs employ a virtual isocenter to dynamically position a subject during treatment, such that the subject resides closer to an exit aperture of the radiation treatment system than a true isocenter of the radiation treatment system during treatment, and such that a projected field defined by the multileaf collimator is magnified at the virtual isocenter relative to the true isocenter of the radiation treatment system;
  • a megavoltage radiation treatment system adapted for pre-clinical studies, the megavoltage radiation treatment system comprising:
  • a gantry configured to rotate about a rotation axis
  • a megavoltage X-ray source and a detector wherein the megavoltage X-ray source and the detector are supported in an opposing configuration by the gantry, such that the megavoltage X-ray source and the detector are rotatable by the gantry about the rotation axis, wherein the megavoltage X-ray source is configured to emit a treatment radiation beam and a portal imaging beam;
  • a multileaf collimator comprising a plurality of leaves, wherein positions of the leaves are controllable for generating dynamically defined radiation fields;
  • a couch positioned adjacent the gantry, wherein a position of the couch is controllable in three-dimensions;
  • control and processing circuitry operatively coupled to the gantry, the X-ray source, the couch, and the multileaf collimator, the control and processing circuitry comprising a processor and a memory, wherein the processor is configured to execute instructions stored in the memory for performing the steps of:
  • each calibration control point having a respective gantry angle and a respective couch angle
  • the plurality of calibration control points reside along one or more treatment arcs prescribed by a treatment plan, and detecting a portal image at each calibration control point
  • the one or more treatment arcs employ a virtual isocenter to dynamically position a subject during treatment, such that the subject resides closer to an exit aperture of the radiation treatment system than a true isocenter of the radiation treatment system during treatment, and such that a projected field defined by the multileaf collimator is magnified at the virtual isocenter relative to the true isocenter of the radiation treatment system;
  • FIG. 1 schematically illustrates an example radiation treatment system adapted for correcting misalignment induced by gantry motion and couch motion during radiation treatment.
  • FIG. 2A is a flow chart illustrating an example method of detecting spatial offsets along one or more arcs of a treatment plan, processing the spatial offsets to determine couch position corrections, and employing the couch position corrections when executing the treatment plan.
  • FIG. 2B is a flow chart illustrating an example method of performing verification of couch position corrections prior to treatment.
  • FIG. 2C is a flow chart illustrating an example method of performing verification of couch position corrections during execution of a treatment plan.
  • FIG. 3A is a photograph of an example radiation treatment system adapted for the detection of spatial offsets at a plurality of calibration control points using portal imaging of a calibration phantom.
  • FIG. 3B is another photograph of the example system shown in FIG.
  • FIG. 3C schematically illustrates relative motion of various components of an example radiation treatment system during the execution of a treatment plan having a virtual isocenter, showing motion of the radiation source, detector and subject/object being irradiated.
  • FIG. 3D is a table presenting two different coordinate scales of the relative axes of motion used for virtual isocenter.
  • FIGS. 4A-4C plot couch translations for couch rotations of 135°, 180° and 225°, respectively, for a source-to-axis distance (SAD) of 77 cm.
  • SAD source-to-axis distance
  • FIGS. 5A-5D show raw (FIGS. 5A and 5C) and convolved (FIGS. 5B and 5D) projections from the initialization (FIGS. 5A and 5B) and verification (FIGS. 5C and 5D) imaging arc, where the crosshair is centered with respect to the centroid of the MLC field.
  • FIGS. 6A-6D plot dose distributions from Monte Carlo simulations (heat map) and film (contours) for various single MLC leaf separation settings.
  • FIG. 7 plots the results from Monte Carlo dose calculations, showing simulated dose crossline profiles of various MLC leaf separation ranging from 0.2 to 3.0 mm.
  • FIGS. 8A-8C plot the magnitude of couch lateral, vertical and longitudinal corrections for couch rotations of 135°, 180° and 225°,
  • FIGS. 9A-9D plot relative dose distributions for non-coplanar acquisitions, with (FIG. 9B) and without (FIG. 9A) corrections for a 1 mm leaf separation. For comparison, corrected results for 0.2 mm (FIG. 9C, abutting) and 3 mm (FIG. 9D) leaf separations are also shown.
  • FIG. 10 plots measured crossline profiles for non-coplanar and coplanar dose distributions using a 1 mm MLC leaf separation, with and without image corrections.
  • FIGS. 11A-11 D plot the volume (FIG. 1 1 A) and effective radius (FIG. 1 1 B) receiving a percentage of the maximum dose for a coplanar and non- coplanar acquisition, while FIGS. 1 1 C and 1 1 D illustrate the dose fall off characteristics of the system.
  • FIGS. 12A and 12B plots the volume (FIG. 12A) and effective radius (FIG. 12B) receiving a percentage of the maximum dose for a 0.2 mm
  • FIGS. 13A-13F illustrate example embodiments in which a plurality of subfields are employed to treat multiple targets within a patient.
  • exemplary means “serving as an example, instance, or illustration,” and should not be construed as preferred or advantageous over other configurations disclosed herein.
  • the terms “about” and “approximately” are meant to cover variations that may exist in the upper and lower limits of the ranges of values, such as variations in properties, parameters, and dimensions. Unless otherwise specified, the terms “about” and “approximately” mean plus or minus 25 percent or less.
  • any specified range or group is as a shorthand way of referring to every member of a range or group individually, as well as each and every possible sub-range or sub - group encompassed therein and similarly with respect to any sub-ranges or sub-groups therein. Unless otherwise specified, the present disclosure relates to and explicitly incorporates each and every specific member and
  • the term "on the order of”, when used in conjunction with a quantity or parameter, refers to a range spanning approximately one tenth to ten times the stated quantity or parameter.
  • arc-based treatment that involves both the rotation of the gantry and the translation and/or rotation of the couch.
  • the treatment of small tumors in the brain can be realized with several arcs, each of which involves a unique couch rotation (i.e. a fixed couch rotation angle for a given arc) and a prescribed angular range through which the gantry rotates for each arc.
  • couch rotation i.e. a fixed couch rotation angle for a given arc
  • angular range through which the gantry rotates for each arc.
  • the inclusion of multiple couch angles ensure that the total delivered dose is non-coplanar which has benefits with respect to rendering the high-dose component of the dose distribution more compact relative to a coplanar dose distribution.
  • the radiation field in each arc can be designed to remain conformal to the shape of the target throughout the arc (dynamic conformal arc - DCA) or the shape of the aperture can be modulated throughout the arc to further help tailor the dose distribution to adhere to a pre-defined set of dose constraints (volumetric modulated arc therapy - VMAT).
  • dynamic conformal arc - DCA dynamic conformal arc - DCA
  • shape of the aperture can be modulated throughout the arc to further help tailor the dose distribution to adhere to a pre-defined set of dose constraints
  • volumetric modulated arc therapy - VMAT volumetric modulated arc therapy - VMAT
  • the resulting gantry- angle-dependent couch position corrections and couch-angle dependent couch position corrections are separately generated via interpolation and employed during treatment to correct for misalignment.
  • various example embodiments of the present disclosure provide systems and methods for correcting for misalignment induced by gantry motion and couch motion during arc-based radiation treatment via the detection of spatial offsets along one or more arcs of a treatment plan, and the processing of the spatial offsets for the determination of couch position corrections (in one, two or three-dimensions, and optionally one or more angular corrections) along the one or more arcs for correcting the misalignment during the execution of the treatment plan.
  • Filiberti method involves the determination of spatial offsets at various combinations of gantry and couch angles during a calibration phase that is performed prior to selecting a specific treatment plan
  • various example embodiments of the present disclosure involve the detection of misalignment spatial offsets along one or more treatment arcs that are associated with a treatment plan, and the subsequent processing of the spatial offsets to determine suitable couch position corrections for correcting the misalignments during treatment.
  • the treatment plan may be subject-specific (i.e. unique to a specific patient or subject), or the treatment plan may be employed for more than one patient or subject.
  • the detection of misalignment, in the form of spatial offsets, along the one or more arcs of a treatment plan, and the subsequent determination of couch position corrections along the one or more treatment arcs defined by the treatment plan, may provide several benefits over the Filiberti method in which the spatial offsets were determined for various gantry and couch angles that are not pre-selected to lie on the treatment plan arc(s).
  • One potential advantage of the present example methods that involve the detection and use of treatment-plan-specific couch position correction offsets is that the spatial offsets can be detected at a higher angular resolution than according to the Filiberti methods. In other words, the present methods enable the
  • the couch position corrections can be updated more frequently due to the shortened time frame required to sample spatial offsets along the one or more treatment arcs than the time required to sample a wide range of angle combinations as per the Filiberti method.
  • the couch position corrections may be measured each time a treatment is to be performed, thereby providing couch position corrections that are likely to be more accurate than those based on the processing of calibration data that was previously measured.
  • the present treatment- arc-specific methods also permit both the detection of misalignment-induced spatial offsets and the calculation of corresponding couch position corrections immediately prior to treatment, with the subject positioned on the treatment couch.
  • example methods are based on the comparison of DDR images and portal images of the subject, collected along the one or more treatment arcs, in order to determine treatment-plan-specific spatial offsets and corresponding treatment-plan-specific couch position corrections.
  • the spatial offsets can be determined with the patient positioned on the treatment couch using image registration methods, where the net dose delivered to the patient during the calibration phase is lower than the dose that would be delivered to a patient when sampling a broader phase space of gantry and couch angles according to the Filiberti method.
  • the determination of patient-specific couch offsets immediately prior to treatment and with the patient on the couch overcomes these limitations since, by definition, the measured offsets correspond to locations (points) that are part of one or more of the treatment arcs, and they correspond to the patient weight and the weight distribution along the couch.
  • the couch position corrections may be employed to maintain the positional accuracy of a virtual isocenter during execution of a treatment plan.
  • Treatment plans that employ a virtual isocenter involve changes in gantry angle, couch angle, and changes in the couch position (vertical, longitudinal and lateral) that are employed to maintain the positioning of the target at the virtual isocenter at different gantry and couch angles along the one or more treatment arcs, such that the target is maintained along the central axis of the treatment beam with a constant distance to the x-ray source.
  • such an example embodiment may be useful in adapting a clinical megavoltage radiation therapy system to deliver small field size beams for pre-clinical or clinical applications.
  • couch position corrections can be beneficially employed to maintain positional accuracy of the treatment beam relative to the virtual isocenter, especially with fields having an effective radius in the range of 5 to 10 mm that are highly sensitive to misalignment.
  • the example radiation treatment system includes a rotatable gantry 1 10, which supports a radiation source (e.g. a linear accelerator; not shown, e.g. housed within the gantry), such that a radiation beam 1 15 (e.g. an x-ray beam) is emitted and directed through a multileaf collimator 100.
  • the beam modulation device 105 includes a multileaf collimator 100 and at least a set of jaws (e.g. a four-jaw set, not shown).
  • the multileaf collimator 100 includes a set of movable leaves for selectively altering a spatial profile of the radiation beam.
  • the gantry 1 10 is rotatable for varying a beam angle of the radiation beam relative to the subject, and the multileaf collimator 100 may be rotatable relative to a beam axis of the radiation beam 1 15, for rotating the axis of the leaves relative to the subject.
  • the gantry 100 may, for example, be a ring gantry having a central aperture, or, for example take other geometric forms such as a C-type or robotic arm gantry.
  • the gantry 1 10 and the couch 120 may be rotatable such that their respective rotation axes intersect at an isocenter of the radiation treatment system.
  • the subject is positioned on a treatment couch 120 that is rotatable about at least one axis, and positionable (translatable) in three dimensions.
  • the subject is a patient or an animal, such as a small animal (e.g. a mouse) for performing pre-clinical studies.
  • a sample may be treated by the radiation beam, such as a tissue construct, cell construct, cell scaffold, tissue scaffold, in-vitro tissue sample, or other in-vitro or tissue engineered sample.
  • the radiation source includes a linear accelerator (LINAC).
  • the LINAC may be a megavoltage (MV) system for generating MV radiation.
  • the radiation beam 1 15 is a photon beam generated by the interaction of electrons with a target, while in another example implementation, the treatment beam 1 15 may be an electron beam.
  • Examples of different types of treatments that can be performed according to the present example embodiments, or variations thereof, include, but are not limited to, intensity modulated radiation therapy (I MRT), intensity modulated arc therapy (I MAT), volumetric modulated arc therapy (VMAT), tomotherapy, dynamic conformal arc therapy (DCA), modulated electron arc therapy and variations thereof.
  • I MRT intensity modulated radiation therapy
  • I MAT intensity modulated arc therapy
  • VMAT volumetric modulated arc therapy
  • DCA dynamic conformal arc therapy
  • modulated electron arc therapy and variations thereof.
  • the gantry 1 10 may also support (e.g. via a support arm or a robotic assembly) an imaging device 130 for acquiring portal images that are generated via the detection of radiation emitted by the radiation source.
  • portal images may be acquired with low-dose radiation, with a dose sufficiently small to avoid therapeutic effect, while providing sufficient fluence for image guidance.
  • the imaging device 130 may be, for example, a 2D digital x-ray imaging detector.
  • Portal images collected via the imaging device 130 may be employed for initial patient positioning, for example, via comparison and registration to images generated based on volumetric image data acquired prior to the therapeutic treatment session (e.g. DRR images generated from computed tomography (CT) image data).
  • CT computed tomography
  • the rotation of the gantry 1 10 and the couch 120, and (and optionally the rotation) of the multileaf collimator 100 are controlled by one or more controllers, which are shown by way of example as the controller 280 in FIG. 1 .
  • the controller 280 may include motor controllers for controlling the operation of the motors that drive the rotation of the gantry 1 10, the couch 120, and the collimator leaves (and jaws).
  • the controller 280 (or another controller) also controls the three-dimensional position of the couch, enabling the dynamic positioning of the couch 120 during radiation treatment.
  • the controller 280 may also control the operation of the radiation source.
  • the controller may also control the orientation of the treatment couch 120 according to one or more angles.
  • the couch may be positionable in three dimensions, and rotatable in one or more dimensions (e.g. the couch may be controllable in four, five or six spatial and angular dimensions).
  • the radiation treatment system may include encoders for detecting the position and/or orientation of the gantry 1 10 and the couch 120.
  • the controller 280 is operatively coupled to control and processing hardware 200.
  • the controller 280 may optionally be directly integrated into a control and processing device 270, or may be provided as an external device.
  • the control and processing hardware 200 may include a processor 210, a memory 215, a system bus 205, one or more input/output devices 220, and a plurality of optional additional devices such as communications interface 235, display 225, external storage 230, and data acquisition interface 240.
  • the display 225 may be employed to provide a user interface for displaying aspects of the volumetric modulated arc therapy plan and/or for providing input to control the operation of the system.
  • the display may be directly integrated into a control and processing device 270 (for example, as an embedded display), or may be provided as an external device (for example, an external monitor).
  • executable instructions represented as couch position module 290 are processed by control and processing hardware 200 to identify suitable couch position corrections associated with a trajectory prescribed by a treatment plan (e.g. during a calibration phase, prior to radiation treatment of a subject).
  • the control and processing hardware 200 may include, for example, and execute instructions for performing one or more of the methods illustrated in FIGS. 2A-2C, or other methods described herein, or variants thereof.
  • Such executable instructions may be stored, for example, in the memory 215 and/or other internal storage.
  • the control and processing hardware 200 may include executable instructions for performing radiation therapy according to a treatment plan, as represented by treatment plan module 295, where the treatment plan module incorporates couch position corrections generated by the couch position correction module 290.
  • the control and processing hardware 200 may be configured to receive planning data from an external arc therapy planning system.
  • the treatment plan module 295 may send signals to the controller 280 in order to coordinate and automate the positioning of the gantry 1 10, the couch 120 (according to both the treatment plan and couch position corrections), and the multileaf collimator 100 in order to deliver the treatment beam with treatment fields having a size, shape, and direction as prescribed by a treatment plan.
  • the motion of the gantry 1 10 and the couch 120 may be coordinated in order to maintain the subject at a dynamic virtual isocenter that is closer to an exit aperture of the multileaf collimator than the system isocenter.
  • the methods described herein can be partially implemented via hardware logic in processor 210 and partially using the instructions stored in memory 215. Some embodiments may be implemented using processor 210 without additional instructions stored in memory 215. Some embodiments are implemented using the instructions stored in memory 215 for execution by one or more microprocessors. Thus, the disclosure is not limited to a specific configuration of hardware and/or software.
  • control and processing hardware 200 may be provided as an external component that is interfaced to a processing device.
  • bus 205 is depicted as a single connection between all of the components, it will be appreciated that the bus 205 may represent one or more circuits, devices or communication channels which link two or more of the components.
  • the bus 305 may include a motherboard.
  • the control and processing hardware 200 may include many more or less components than those shown.
  • Some aspects of the present disclosure can be embodied, at least in part, in software, which, when executed on a computing system, transforms an otherwise generic computing system into a specialty-purpose computing system that is capable of performing the methods disclosed herein, or variations thereof. That is, the techniques can be carried out in a computer system or other data processing system in response to its processor, such as a microprocessor, executing sequences of instructions contained in a memory, such as ROM, volatile RAM, non-volatile memory, cache, magnetic and optical disks, or a remote storage device. Further, the instructions can be downloaded into a computing device over a data network in a form of compiled and linked version.
  • the logic to perform the processes as discussed above could be implemented in additional computer and/or machine readable media, such as discrete hardware components as large- scale integrated circuits (LSI's), application-specific integrated circuits (ASIC's), or firmware such as electrically erasable programmable read-only memory (EEPROM's) and field-programmable gate arrays (FPGAs).
  • LSI large- scale integrated circuits
  • ASIC application-specific integrated circuits
  • firmware such as electrically erasable programmable read-only memory (EEPROM's) and field-programmable gate arrays (FPGAs).
  • a computer readable storage medium can be used to store software and data which when executed by a data processing system causes the system to perform various methods.
  • the executable software and data may be stored in various places including for example ROM, volatile RAM, nonvolatile memory and/or cache. Portions of this software and/or data may be stored in any one of these storage devices.
  • the phrases “computer readable material” and “computer readable storage medium” refers to all computer-readable media, except for a transitory propagating signal per se.
  • FIG. 2A an example method is shown for controlling a radiation treatment system to compensate for positional errors associated with couch rotation and gantry rotation.
  • the method involves a set of steps performed during a calibration phase, shown at steps 300-310, and a step that is subsequently performed during a treatment phase, shown at step 315.
  • step 300 spatial offsets are measured at a plurality of calibration control points along one or more arcs that are prescribed by a treatment plan.
  • these calibration control points involve combinations of gantry angles and couch angles (and vertical, longitudinal, lateral translations when the treatment plan involves a virtual isocenter, as described below) that lie along the one or more arcs prescribed by the treatment plan.
  • the calibration control points are therefore treatment-plan- specific, in contrast to a generic set of control points spanning a broader three-dimensional region through which the one or more arcs pass.
  • a portal image is detected at each calibration control point, providing a beam-eye-view image based on a calibration radiation field defined by the multileaf collimator.
  • the portal images are processed to determine, for each calibration control point, a respective spatial offset associated with
  • a set of spatial offsets are thus obtained which characterize the positional errors of the radiation treatment system along the one or more treatment arcs.
  • the spatial offsets associated with the plurality of calibration control points are then processed to determine couch position corrections suitable for correcting the positional errors along the one or more treatment arcs associated with the treatment plan.
  • These couch position errors which are specific to the treatment plan, may then be employed during the treatment phase, as shown at step 315, to control a position of the couch according to the couch position corrections.
  • the couch position corrections may be applied at one or more treatment control points of the treatment plan, prior to delivery of the treatment beam.
  • the couch position corrections may be applied as the gantry angle and couch angle are changed during continuous beam delivery.
  • the calibration control points that are employed for the detection of portal images along the one or more arcs of the treatment plan may be arranged such that at least one calibration control point overlaps with a respective treatment control point of the treatment plan (e.g. a treatment control point of an IMRT treatment plan).
  • a treatment control point may refer to a system configuration (e.g. gantry and couch angle, MLC arrangement, and optionally collimator angle and couch lateral, longitudinal and vertical position) in which a specified amount of monitor units (dose) is to be delivered.
  • a calibration control point refers to a combination of couch angle and gantry angle (and optionally couch lateral, longitudinal and vertical position) along one or more arcs defined by a treatment plan. As explained below, calibration control point need not overlap with a treatment control point.
  • any or all of the calibration control points can be selected to correspond to respective treatment control points. This may be performed, for example, by selecting smaller number of calibration control points than treatment control points, such that only a subset of the treatment control points have associated calibration control points, or by selecting an equal number of calibration control points and treatment control points.
  • one or more of the calibration control points may lie on a trajectory associated with the treatment plan, but not co-incident with a corresponding treatment control point.
  • the treatment plan may employ a continuous radiation modality without well- defined treatment points, and in such cases, the calibration control points are selected to lie along the one or more arcs associated with the treatment plan.
  • the spatial offsets measured at the calibration control points, as per step 305 in FIG. 2A, may be interpolated to estimate spatial offsets at additional locations along the one or more arcs of the treatment plan.
  • the couch position corrections may be interpolated to estimate couch position corrections at additional locations along the one or more arcs of the treatment plan.
  • the spatial offsets may be determined in steps 300 and 305 via portal imaging of a phantom, where the phantom is secured to the treatment couch prior to treatment.
  • a phantom containing a radiopaque marker such as a BB (e.g. a lead bead)
  • BB e.g. a lead bead
  • a series of portal images may then be obtained at calibration control points corresponding to different combinations of gantry angle and couch angle along one or more arcs associated with the treatment plan, with the multileaf collimator leaves defining a calibration field sufficiently large to image the phantom at the different calibration control points.
  • the portal images may be processed to determine spatial offsets between the imaged marker and the perimeter of the calibration field.
  • the location of the marker and the MLC field edge may be automatically detected, for example using a method such as a maximum convolution approach.
  • the maximum convolution approach may be implemented using a convolution kernel with the central pixels set to negative one and surrounded by a one-pixel border with a positive value such that the total value of the kernel is zero.
  • the result is zero for objects larger than the marker, maximum values for objects with the same size and shape.
  • the resulting convolved projection may be thresholded and binarized.
  • the centroid of the marker and MLC field edge may then be calculated, and the two-dimensional spatial offsets can be extracted as the differences between the two centroids, for example, according to the following equations:
  • BB X , BB y , MLC X and MLC y are the x-y coordinate of the marker and MLC field centroid, respectively.
  • the spatial offsets can then be processed in order to calculate the associated couch translations as follows (in the non- rotated couch frame):
  • couch position corrections can be determined, for other points associated with the treatment plan, via methods such as, interpolation, extrapolation, and parametric fitting.
  • the preceding method involving the use of a calibration phantom may be beneficially employed, for example, in the case of subjects, such as small animals or tissue samples/constructs/scaffolds, that do not apply a significant perturbation to the treatment couch due to their light weight.
  • the method may also be beneficial for performing quality assurance of the radiation planning system in order to verify the alignment of the system for a specific treatment plan.
  • additional misalignments may be caused by the weight of the patient when the patient is placed on the treatment couch, and these additional misalignments may not be compensated by couch position corrections that are determined using a phantom.
  • Such limitations may be overcome by performing calibration with the patient or subject supported on the couch, and detecting portal images of the patient rather than portal images of a calibration phantom.
  • portal imaging of the patent may be performed, resulting in portal images of skeletal features of the patient. These portal images may then be spatially registered to DRR images that are respectively generated for each for each calibration control point.
  • a DRR image may be derived from a 3-dimensional, volumetric image data set (e.g. a CT data set) by creating a simulated projection radiograph based on the attenuation information presented in the CT voxel data.
  • the orientation of the view through the patient anatomy is determined by the arbitrary source-detector configuration.
  • the resultant DRR provides the "correct" patient position information to which the portal image acquired at the calibration control point will be compared.
  • Numerous image registration algorithms are available to determine the positioning error of the portal image, and non-limiting examples include: mutual information, normalized mutual information and principal axis transformation.
  • the objective of the image registration algorithm is to adjust the position of the portal image relative to the DRR in order to maximize the similarity of the image information when the two images are superimposed. The offsets required to maximize this similarity are then translated into couch position adjustments using methods described herein.
  • portal images of the subject may be obtained using low doses suitable for imaging.
  • the portal imaging dose can be selected to be less than a pre-selected dose threshold. It may also be beneficial to employ a different beam energy and/or target for performing portal imaging than during therapeutic treatment.
  • portal imaging can be employed using a low-Z target, and optionally with an imaging beam with a nominal stated energy that is less than the nominal stated energy of the treatment beam (e.g. 2.5 MV for the imaging beam versus 6 MV for the treatment beam).
  • misalignments may additionally or alternatively be corrected via the determination and application of couch orientation corrections.
  • the three rotations may be employed as alternative or additional degrees of freedom for applying treatment couch based corrections to compensate for misalignment.
  • image registration algorithms can be adapted to include rotations when comparing a portal image to a DRR.
  • the portal images that are employed to determine spatial offsets are obtained at a plurality of calibration control points such that the system is at rest during portal image acquisition.
  • it may be useful to acquire portal images while one or more components of the system e.g. the couch and/or gantry
  • the rotational and/or translational velocities of various movable system components can change substantially for different types of treatments (different treatment plans), or possibly even during execution of a single treatment plan, and as a result, mechanical stability (or similarity, or reproducibility) may vary, resulting in dynamic misalignment errors.
  • some treatment plans may prescribe the continuous motion of one or more system components during the during the delivery of radiation (continuous delivery), such as continuous rotation of the gantry, and/or, continuous rotation and/or translation of the treatment couch, and/or, continuous translation and/or rotation of the multileaf collimator leaves.
  • continuous delivery such as continuous rotation of the gantry, and/or, continuous rotation and/or translation of the treatment couch, and/or, continuous translation and/or rotation of the multileaf collimator leaves.
  • portal images associated with one or more calibration control points may be acquired during motion of one or more system components.
  • at least one portal image is acquired during motion of one or more system components, where the speed of the one or more system components is controlled, during acquisition of the portal image (translational and/or angular speed), according to a speed that is prescribed by the treatment plan at the corresponding location along the treatment arc.
  • a verification scan can be performed prior to employing the couch position corrections to correct for misalignments during treatment.
  • the verification scan may be implemented by positioning the gantry and the couch at one or more verification control points along the one or more arcs of the treatment plan.
  • steps 320 to 335 may be performed to verify the suitability of the couch position corrections.
  • couch position corrections are determined (e.g. via interpolation if the verification control point is not coincident with calibration control point) and employed to reposition the couch in order to correct for misalignment.
  • a verification portal image is acquired, and the verification portal image is processed in step 335 to determine a residual spatial offset that may persist after having applied the couch position corrections in step 325.
  • the detected residual spatial offset may be compared to pre-determined verification criteria in order to determine whether or not the residual spatial offset is acceptable. The process may be repeated at one or more additional verification control points, as indicated by 345.
  • the verification portal image may be taken of a phantom, from which the residual spatial offsets may be
  • the portal images may be taken of patient anatomy with the patient positioned on the couch, where the residual spatial offsets are determined using image registration with DRR images, as explained above.
  • step 350 with the radiation treatment system configured such that the gantry and couch angles correspond to a given intra-treatment control point along the one or more arcs of a treatment plan, and prior to performing treatment with a radiation beam at the intra-treatment control point, couch position corrections (having been determined according to one of the example methods described herein, or variations thereof) are applied to correct for misalignment.
  • a verification portal image is obtained in step 355, where the verification portal image includes patient anatomy.
  • Image registration is performed between the verification portal image and a DRR image in step 360 in order to detect a residual spatial offset that may be present at the intra-treatment control point.
  • the detected residual spatial offset may be compared to predetermined verification criteria in order to determine whether or not the residual spatial offset is acceptable, as determined at step 370.
  • the treatment may be permitted to proceed, and steps 350 to 370 may be repeated at one or more intra-treatment control points.
  • one or more actions may be performed that interrupt the treatment process.
  • the treatment may be interrupted and a misalignment alert may be communicated to a system operator (e.g. an audible and/or visible alert or alarm).
  • the residual spatial offsets may be processed to determine supplemental couch position corrections that are suitable for correcting the residual positional error, and the supplemental couch position corrections may be employed to reposition the couch prior to application of the treatment beam.
  • This process may be repeated at one or more intra-treatment control points, and in one example implementation, the process may be repeated at all control points associated with a treatment plan.
  • the preceding methods may be adapted to a treatment plan involving gantry and couch motion to preserve alignment of the treatment beam with a virtual isocenter that is spatially offset from a true isocenter of the system.
  • FIG. 3C illustrates an example of gantry and couch motion about a virtual isocenter. The figure shows an example initial configuration in which a subject is to be treated with a radiation field at a virtual isocenter 450 that is spatially offset from the true isocenter 455 of the system. As the gantry 1 10 rotates the LINAC, the subject is moved in an arc 460 that preserves the spatial alignment of the subject relative to the treatment beam. For example, for the configuration shown in FIG. 3C, the relative positioning of the subject and the treatment beam is preserved by positioning the couch according the following equations:
  • Lat flj 0 Lat iso + r sin ⁇ cos ⁇ ,
  • ⁇ is the gantry angle (-4 ⁇ ⁇ 364, in Varian coordinates)
  • Lat iso , Vrt iso are the initial longitudinal, lateral and vertical couch positions when the target is placed at the true machine isocenter, and ⁇ is the couch angle.
  • the preceding example embodiments may be adapted for a treatment plan having a virtual isocenter by controlling the couch position as prescribed by the virtual isocenter based treatment plan, as further modified based on couch position corrections determined from spatial offsets that are calculated at various calibration control points along the one or more arcs of the treatment plan.
  • the calibration control points not only involve different gantry and couch angles, but also different couch positions, as per the positional constraints required to preserve the alignment of the virtual isocenter.
  • a virtual isocenter may be employed to achieve an improvement in the spatial profile and/or dose level associated with a treatment beam .
  • the projected leaf size at virtual isocenter will be smaller than the projected leaf size at the true isocenter of the system, thereby enabling a higher spatial resolution of the projected field, and a smaller minimum field size (e.g. as defined by a single pair of MLC leaves).
  • the smaller distance from the source to the virtual isocenter relative to the true machine isocenter also results in an increased dose rate, which can be utilized to provide treatment with a decreased treatment time.
  • a virtual isocenter based treatment plan may be configured to employ a small field size, such as a field size having a characteristic dimension (e.g. a width, radius, or other measure of transverse beam size) that is less than 5 mm , less than 4 mm, less than 3mm, less than 2 mm , or less than 1 .5 mm, where the characteristic dimension is determined according to a 50% isodose level.
  • a characteristic dimension e.g. a width, radius, or other measure of transverse beam size
  • This may be achieved, for example, using a so called "high-definition" multileaf collimator, or a multileaf collimator having at least a subset of leaves with a width less than 3 mm.
  • the multileaf collimator may be configured to produce a projected field based on the separation of a single pair of leaves.
  • the separation between a single pair of leaves may be between 0.5 mm and 1.5 mm.
  • the field size may have a characteristic dimension larger than 5 mm.
  • a field size may be between 5 mm and 10 mm, between 5 mm and 20 mm, between 5 mm and 30 mm, between 5 mm and 40 mm, and between 5 mm and 40 mm.
  • misalignments can have a much stronger impact on the spatial accuracy of the field. Indeed, while a large field projected to the system isocenter may be capable of tolerating misalignments of approximately 1 mm, very small fields projected to a virtual isocenter, having a characteristic dimension on the mm scale, can be very sensitive to such misalignments. Accordingly, the aforementioned methods of determining and employed treatment arc specific couch position corrections may be beneficially employed for treatment plans having a small projected field at a virtual isocenter.
  • a small target irradiation field may be achieved by defining the field by a single pair of opposed MLC leaves. Such a field may be collimated with the smallest allowable jaw-defined field, with the remaining MLC pairs junctioned under the jaws. In other words, such a field may use the smallest allowable jaw-defined field that does not occlude the MLC-defined field in order to minimize interleaf leakage. The remaining MLC pairs may be junction under the jaws.
  • the planar dose distribution of such a configuration is characterized as a function of MLC leaf gap, demonstrating that a small field with an effective radius of approximately 1 mm (based on 50% isodose) is achievable when a high- definition MLC is employed.
  • the compactness (magnification) of the field was enhanced using a shortened virtual isocenter in the treatment aperture, where the virtual isocenter was maintained by implementing dynamic couch motions.
  • Pre-treatment imaging as described above, was employed to detect and correct for couch position errors arising from imperfections in the circular trajectories of the couch/collimator/gantry.
  • the ability to treat very small lesions is a requirement of modern preclinical irradiation platforms such as the X-RAD family of products (Precision X-ray, North Branford, USA), the small-animal radiation research platform (SARRP) that was developed at Johns Hopkins University, among others.
  • Pre-clinical studies can be used to investigate the effectiveness of new treatment approaches and may be able to improve the efficiency with which such novel techniques are translated into human patients.
  • small animal irradiation systems should be able to deliver advanced techniques such as non-coplanar arc therapies.
  • the SARRP is capable of producing collimated beams as small as 0.5 mm in diameter.
  • the irradiated volume can have a FWHM as small as 1 .07 mm.
  • the latest X-RAD products are capable of producing beams of 1 mm diameter. Both systems come with image guidance capabilities.
  • treatment-arc-specific couch position corrections for a treatment plan having a virtual isocenter and a small projected field may be employed to adapt a clinical, megavoltage radiation treatment system for pre-clinical studies, avoiding the need for a separate pre-clinical system.
  • the Examples below demonstrate how such adaptations can produce narrow MV treatment beams having a characteristic dimension (e.g. a radius) of less than 2 mm.
  • Such example embodiments provide several potential advantages over conventional pre-clinical practice that requires a dedicated and separate kV pre-clinical radiation treatment system. Firstly, such pre-clinical irradiators are costly and potentially not available to investigators with interests in in-vivo irradiation studies in small animals.
  • these irradiators make use of kilovoltage x-ray beams with known differences in biological effectiveness relative to megavoltage beams used for clinical treatments.
  • the present example embodiments have the potential to offer a re-purposed tool - namely a MV clinical radiation treatment system adapted to employ a small MLC-defined field at a virtual isocenter with corrections to couch misalignment, in order to perform studies without the requirement for additional significant capital outlay.
  • the pre-clinical subject may be a subject such as, but not limited to, a small animal, a tissue construct, cell construct, cell scaffold, tissue scaffold, in-vitro tissue sample, or other in-vitro or tissue engineered sample.
  • the subject may be secured or supported on a holder that is mechanically supported relative to the couch.
  • the holder may be supported at a location that extends beyond an end of the couch, in order to facilitate a reduced spatial separation between the virtual isocenter and the exit aperture of the collimator.
  • the holder may be
  • the example embodiments described herein may be adapted for use with clinical treatment plans involving a virtual isocenter. It may be advantageous to adapt such dual- motion implementations to bring the patient as closer to the exit window of the accelerator (e.g. as close as safely possible) in order to realize the benefits of a decreased projected leaf size at virtual isocenter and increased dose rate (which can result in decreased treatment times) primarily driven by inverse square gains.
  • the present inventors therefore set out to adapt a clinical megavoltage radiation treatment system to achieve small target irradiation using an MLC-defined field.
  • the present example embodiments may also be applied to virtual-isocenter-based treatment plans that prescribe dual and simultaneous motion of the couch and gantry. Indeed, treatment plans in which both the couch and the gantry are in simultaneous motion are expected to soon be a clinical reality.
  • the treatment field may be defined based on a plurality of separate subfields.
  • multiple subfields may be employed during a treatment plan to treat a plurality of lesions within a patient.
  • metastases range from a 1 mm in diameter (potentially even smaller, but hard to visualize and treat) up to several cm in diameter.
  • the consequences of such size variations typically manifest as differences in the total dose used to treat the target. Small targets can be treated with higher doses because treatment of the target will result in a small volume of normal brain receiving a high dose.
  • FIGS. 13A-13F An example of such an embodiment is illustrated in FIGS. 13A-13F.
  • the insert on the lower right of the figure shows a patient residing on a treatment couch with the gantry rotated to given first angle.
  • the inset at the top left of the figure shows a plurality of subfields defined by the leaves of the MLC.
  • the horizontal lines are representative of the individual leaf positions in the MLC.
  • the vertical line extending from Y2 to Y1 represents the abutment of two opposed leaves (it is continuous because the abutting leaves are located at the same y-coordinate).
  • the leaves that do not abut are the ones that are actively collimating a target structure.
  • X1 , X2, Y1 and Y2 are labels for the independent jaws that are used to provide rectangular collimator to the field denoted by the square box surrounding the subfields.
  • the circle with the white dot in the centre represents the location of the central axis of the beam from the beam's eye view.
  • the central axis does not need to be the centre of the field aperture because the linear accelerator is capable of producing asymmetric fields using the 4 independent jaws.
  • FIGS. 13A-13F demonstrate how the relative positions of multiple targets vary with respect to the central axis of the beam when the gantry rotates about its axis, where each sub-figure (A through F) corresponds to a different gantry angle.
  • each sub-figure (A through F) corresponds to a different gantry angle.
  • the positions of the MLC leaves that are used to collimate the beam to treat a given target will need to move in synchrony with the given target.
  • the separately defined treatment fields rotate about the virtual isocenter as the gantry and couch are positioned at different angles along the one or more arcs of the treatment plan.
  • the pairs of leaves within the MLC that are used to collimate the beam to a given target may become variable.
  • this motion of the beam's eye view results in dynamic changes to the specific pairs of opposed leaves that are used to collimate the beam to the target.
  • Dynamic conformal arc treatment can be employed dynamically reposition the MLC leaves to ensure that they conformally fit the outer boundary of the target (in the beam's eye view) as the gantry rotates around the patient.
  • the specific location of a given target within the beam's eye view can be calculated based on its position relative to the virtual isocenter and the required leaves and their collimating positions can subsequently be determined.
  • the preceding example systems and methods for correcting for misalignments induced by changes in gantry and couch motion during arc-based radiation treatment may implemented for such a case in order to improve the conformal accuracy of multiple subfields when a treatment plan involving a virtual isocenter is employed.
  • the width of the MLC leaves near the center of the field is 2.5 mm when projected to the machine's mechanical isocenter of 100 cm (source to axis distance - SAD). This projected leaf size is reduced when using a shortened virtual isocenter but may still require the use of 15 - 20 leaves if at least one target is large (e.g. 4 cm diameter).
  • dynamic conformal arc treatment can be employed dynamically reposition the MLC leaves to ensure that they conformally fit the outer boundary of the target (in the beam's eye view) as the gantry rotates around the patient.
  • the use of a virtual isocenter confers the advantages of reducing the projected leaf width at the virtual isocenter (relative to the leaf width at the machine's mechanical isocenter) which may permit more conformal fitting of the MLC leaves to the target shape.
  • the reduced source to target distance associated with the use of a virtual isocenter will also result in an increase in the dose rate at the target (relative to positioning the target at the mechanical isocenter distance) which could reduce treatment times. Reduced treatment times are
  • the aforementioned systems and methods may be employed for the (e.g. experimental) treatment of multiple targets in multiple animals in applications in which a virtual isocenter is employed for field size reduction (and/or increased dose).
  • the multiple animals (subjects) may be mounted or otherwise supported in close proximity to enable the simultaneous treatment thereof using the definition of multiple subfields via the MLC.
  • two or more animals may be simultaneously treated during a common treatment plan (e.g. treatment arc), where each animal includes at least one target.
  • a common treatment plan e.g. treatment arc
  • each animal of the two or more animals includes a single target, while in another example implementation, at least one animal of the two or more animals includes multiple targets.
  • one or more subfields may have a small characteristic dimension (e.g. less than 20 mm, less than 10 mm, less than 5 mm, less than 4 mm, less than 2mm, or less than 1 .5 mm, as per a 50% isodose measure).
  • Such small subfields may be defined by different subsets of leaves of a the multileaf collimator.
  • a set of narrow beams may be generated based on gaps formed between different pairs of leaves. Interleaf leakage may be reduced or minimized by dynamically controlling jaws of the radiotherapy system, such that a jaw-defined field is sufficiently large to accommodate the projected subfields.
  • the treatment plan may be calculated using a Monte Carlo method in order to provide improved spatial accuracy.
  • Other example methods of performing dose calculations during treatment planning include, but are not limited to, convolution- superposition-type dose calculation algorithms and numerical solving of radiation transport equations such as the Boltzmann transport equations.
  • the present example pertains to the measurement and simulation of the dose profile at the isocenter of a radiation treatment system where only a single leaf pair of a multileaf collimator is employed to define the field.
  • the planar dose distribution for a treatment aperture defined by a single opposed leaf pair of the NDS120HD MLC was measured using gafchromic film (EBT3, Ashland Specialty Ingredients, Bridgewater, NJ) and compared to Monte Carlo simulations using EGSnrc.
  • Leaf gaps ranging from an abutting leaf pair (0.2 mm separation at isocentre) to a 3.0 mm opening at isocentre were studied.
  • All other MLC leaves were positioned behind the 1x1 cm 2 jaw-defined field. Distributions were measured using a sheet of gafchromic film positioned between two 30x30x5 cm 3 blocks of solid water at a source-to-surface distance (SSD) of 75 cm. Immediately after irradiation, the film was enclosed in a sealed envelope and twelve hours were allotted for film processing time. Films were scanned with a EPSON EXPRESSION 10000 XL, with a resolution of 300 dpi, and 48 bit colour-depth. Seven pre-scans were performed to ensure uniform heating of the bulb within the scanner; and films were scanned at the same spatial location on the scanner bed.
  • Absolute dosimetry was calculated with a triple-channel film dosimetry algorithm outlined in Mayer et al (R. R. Mayer, Y. Chen, R.I . Miller, and J. Mcdonough, "Enhanced dosimetry procedures and assessment for EBT2 radiochromic film,” Med. Phys. 39(4), 2147-55 (2012)).
  • the measured dose distributions were compared to Monte Carlo simulation of the physical setup.
  • the treatment head of the TrueBeam STx platform was simulated using previously validated phase space files for a 6 MV photon beam generated in VirtuaLinac (Varian Medical Systems, Inc., Palo Alto, CA).
  • the phase space was located 73 cm above isocentre and was validated as accurate to within better than 2% compared to measured depth dose and off-axis profiles.
  • This served as the input for a BEAMnrc model (D.W. Rogers, B.A. Faddegon, G.X. Ding, CM. Ma, J. We, and T.R. Mackie, "BEAM: a Monte Carlo code to simulate radiotherapy treatment units," Med. Phys.
  • FIGS. 6A-6D show Monte Carlo and film dose distributions for four
  • FIG. 7 shows corresponding Monte Carlo crossline profiles (i.e. in leaf motion direction) for MLC leaf separations ranging from 0.2 to 3 mm (at isocentre).
  • a 1 mm leaf separation provides the most compact dose distribution with lowest peripheral dose.
  • the peripheral dose distribution increases with minimal effect on the dose full width at half maximum (FWHM), likely due to an increase in the relative intensity of radiation transmitted through the rounded leaf ends. Above 1 mm, the FWHM increases with gap width and converges with the 1 mm peripheral dose.
  • couch position corrections were determined, via portal imaging of a phantom, for a treatment plan involving a virtual isocenter.
  • the phantom was formed by 3D printing two 8.0 cm diameter spheres using polylactic acid (PLA).
  • PLA polylactic acid
  • the spheres were printed in two halves.
  • a divot was machined into both halves to allow a 2.0 mm ball bearing (BB) to be inserted between them.
  • BB 2.0 mm ball bearing
  • FIGS. 3A and 3B show the phantom sphere 400, supported by the plastic extension are 405, extending beyond the couch 120. This configuration permitted either sphere to be reproducibly attached to the arm using two set pins 410 and two screws 415.
  • the sphere was initially positioned at the true machine isocenter (i.e. 100 cm SAD) using the room lasers and kV-kV alignment.
  • couch positions were calculated as:
  • ⁇ is the gantry angle (-4 ⁇ ⁇ 364, in Varian coordinates)
  • Lat iso Lat iso
  • Vrt iso the initial longitudinal, lateral and vertical couch positions
  • ⁇ is the couch angle.
  • the motions are illustrated in FIGS. 4A- 4C.
  • the couch angles were limited to -45°, 0° or 45°
  • FIG. 1 D is a table presenting a comparison of the clinical and Developer Mode coordinate scales.
  • the figure clearly demonstrates that when very small fields are to be treated, the deviations from ideal motion of system components such as the gantry, couch and MLCs must be taken in to account.
  • an initialization imaging arc was acquired in which the 2.5 MV beam was used to image the BB sphere at unit angle gantry increments.
  • the MLC was shaped into a diamond with the centre leaf pair opened to 1 .0 cm each and the three leaves on either side opened to 0.25, 0.5 and 0.75 cm, as shown in FIGS. 5A-5D.
  • the BB and field edge were automatically detected using a maximum convolution approach. This involved using a convolution kernel with the central pixels set to negative one and surrounded by a one- pixel border with a positive value such that the total value of the kernel is zero. When convolved with the projection, the result is zero for objects larger than the BB, maximum values for objects with the same size and shape. The resulting convolved projection was then thresholded and binarized. The centroid of the BB and MLC field edge was then calculated and the difference between the two taken
  • BB X , BB y , MLC X and MLC y are the x-y coordinate of the BB and MLC field centroid, respectively.
  • the necessary couch translations were then calculated in the non-rotated couch frame as
  • a verification imaging arc was then acquired to verify coincidence of the BB and MLC aperture centroid (FIGS. 5C and 5D).
  • a film dose distribution was acquired with a 1.0 mm single leaf gap using a 6 MVFFF beam, full gantry rotation and a couch angle of zero degrees. Additionally, in a subsequent acquisition two additional half gantry rotations with couch rotations of +45° were added in an attempt to reduce non-target dose of each arc and to increase the compactness of the high dose region.
  • FIGS. 8A-8C show the calculated corrections to couch motion as a function of gantry angle for couch angles of 135°, 180° and 225°.
  • the maximum magnitude of couch motion were 2.1 mm, 1.1 mm and 1 .9 mm for couch angles of 135°, 180° and 225°, respectively, while the maximum in any one direction for all three arcs was 1 .6 mm.
  • FIGS. 9A-9D shows relative dose distributions for non-coplanar acquisitions for an isocentre of 77 cm with and without corrections for the 1 mm leaf gap, and with corrections for the 0.2 mm and 3 mm gaps.
  • the effect of corrections with respect to dose compactness is readily apparent for the 1 mm gap films, as is the enhanced relative intensity of the low dose wash for the 0.2 mm gap.
  • FIG. 10 shows corresponding crossline dose profiles for coplanar and non-coplanar acquisitions using a 1 mm MLC leaf separation both with and without corrections.
  • the application of image corrections results in a more compact distribution. This is more significant for the non- coplanar acquisition, in which doses below approximately 75% of the maximum dose diverge from the corrected profile and add 1 .2 mm to the field width at the 30% dose level.
  • FIGS. 1 1 A-1 1 D present differences in the 3-dimensional dose volumes between a coplanar and non-coplanar acquisition for a 1 mm leaf gap.
  • the full gafchromic film stack was considered.
  • the maximum dose in the distribution was taken as an average of the 9 highest dose voxel elements (a 3x3 voxel array centred on the global maximum dose).
  • a data point in FIG. 1 1 A then corresponds to the total volume of space encompassed by the isodose level (x-axis) expressed as a percentage of the maximum dose.
  • the same data are shown in FIG. 1 1 B, but the spatial metric is presented as an effective radius for the dose cloud (this helps facilitate comparison with published results for other small animal irradiator systems). As shown in FIGS.
  • FIGS. 1 1 C and 1 1 D are intended to illustrate the dose fall off characteristics of the system. For example, if one intended to treat a target volume with a radius of 0.5 mm with the non- coplanar geometry, the target would be covered by the 90% isodose line (FIG. 1 1 B). The radial distance at which the dose would fall to 80%, 50% and 25% of the 90% prescription line would then be 0.8 mm, 1 mm and 1 .8 mm respectively (FIG. 1 1 D), or 0.3 mm, 0.5 mm and 1 .3 mm from the target edge respectively.
  • FIGS. 12A and 12B the volume receiving percentage of the maximum dose and effective radius (assuming a spherical distribution) is shown.
  • the data for the 1 mm gap are the same as those shown in FIGS. 1 1 A and 1 1 B (non-coplanar) and are included here for comparison with the dose volume data for the 0.2 mm gap and the 3 mm gap.
  • the 3 mm leaf separation produces isodose volumes that are larger than the 0.2 mm leaf gap.
  • a megavoltage photon beam is capable of producing a highly compact dose distribution.
  • a radiation field shaped by a single MLC leaf pair can effectively treat sub-millimeter sized targets with rapid dose fall off characteristics when dynamic couch motions are implemented to reduce the distance between the target and the MLC.

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  • Health & Medical Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Biomedical Technology (AREA)
  • Pathology (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Radiology & Medical Imaging (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
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Abstract

L'invention concerne des systèmes et des procédés pour corriger des désalignements induits par des changements de mouvement de portique et de lit pendant un traitement par rayonnement basé sur un arc. Des décalages spatiaux sont déterminés au niveau d'une pluralité de points de commande d'étalonnage le long d'un ou de plusieurs arcs associés à un plan de traitement, et les décalages spatiaux sont traités en vue de déterminer des corrections de position (et éventuellement d'orientation) de lit pour corriger les désalignements lors de l'exécution du plan de traitement. Le plan de traitement peut utiliser un isocentre virtuel, de sorte que la position du lit soit modifiée, et corrigée, pendant un traitement. Les présents procédés peuvent être utilisés en vue d'obtenir un alignement pour des plans de traitement impliquant de petits champs d'imagerie qui sont définis par un nombre réduit de lames de collimateur à lames multiples, telles qu'une paire de lames unique. Selon certains modes de réalisation, un arc de traitement basé sur un isocentre virtuel de position de lit corrigée peut être utilisé en vue de permettre un traitement par rayonnement clinique à l'aide de petites tailles de champ projetées, définies par un ou plusieurs champs définis par un collimateur à lames multiples.
PCT/CA2018/051208 2017-09-25 2018-09-25 Systèmes et procédés permettant de corriger un désalignement induit par un mouvement de portique et de lit pendant un traitement par rayonnement basé sur un arc Ceased WO2019056134A1 (fr)

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CN114206438A (zh) * 2019-06-20 2022-03-18 医科达有限公司 使用投影图像预测放射治疗控制点
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CN115190811A (zh) * 2020-01-31 2022-10-14 伊利克塔有限公司 用于校准和控制准直器叶的装置和方法
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CN116018181A (zh) * 2020-08-21 2023-04-25 上海联影医疗科技股份有限公司 用于动态多叶片准直器跟踪的系统和方法
JP2022174026A (ja) * 2021-05-10 2022-11-22 アクティナ・コーポレーション 医療用線形加速器のための放射線ビーム位置合わせ
WO2023006385A1 (fr) * 2021-07-26 2023-02-02 Koninklijke Philips N.V. Détermination d'un décalage de cadre de divan
CN114840933A (zh) * 2022-03-24 2022-08-02 上海新时达机器人有限公司 龙门偏角校准方法、装置及计算机可读存储介质
CN116726415A (zh) * 2023-08-14 2023-09-12 智维精准(北京)医疗科技有限公司 一种偏移补偿系统及直线加速器
CN116726415B (zh) * 2023-08-14 2023-10-20 智维精准(北京)医疗科技有限公司 一种偏移补偿系统及直线加速器

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