System, process and apparatus for determining linac isocenter

Abstract

To provide a system for determining the linac isocenter.SOLUTION: A system includes apparatus and processes. In one embodiment, this is done by determining axes of rotation for a collimator, a gantry and a couch. In another embodiment, only determining an axis of rotation 5 for the collimator is required. The system and apparatus enable the tracking of the translation-rotation of mechanical components attached to the LINAC to compute the axis of rotation of the gantry, collimator and couch. Based on data collected regarding these axes, the LINAC isocenter is determined. The main apparatus utilized in the system includes a single emitter module, a signal receiver module, and a positioning module. The system also includes an isocenter target module and a gravity module to determine a gravity vector for a signal receiver.SELECTED DRAWING: Figure 4

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of non-provisional application Ser. No. 16,934,586, filed July 21, 2020, and claims priority to U.S. Provisional Patent Applications Nos. 62,986,957, filed March 9, 2020, and 63,033,328, filed June 2, 2020, both of which are incorporated by reference herein in their entirety for all purposes. [Technical Field]

[0002] A system, process, device, apparatus, and method for tracking the translational rotation of mechanical components to determine the isocenter for a medical linear accelerator (LINAC) by calculating the rotational axis of the gantry, collimator, and couch. [Background technology]

[0003] Mechanical rotation Radiation therapy is a type of cancer treatment that uses beams of intense high-energy radiation to kill cancer cells.

[0004] During treatment, a medical linear accelerator (LINAC) delivers a beam of radiation to a precise point within the patient.

[0005] One of the key factors in treatment accuracy is the geometric accuracy of the linac mechanical rotation. Each linac has three types of rotation that it must rotate around a known point in space to ensure the most accurate treatment possible. The three rotations are described below. 1. Gantry rotation. The gantry [1] rotates around the gantry rotation axis [2]. The gantry can rotate 360 degrees around the patient on the treatment couch [3]. 2. Collimator rotation. The collimator [4] rotates around the collimator axis [5]. The collimator can rotate 360 degrees. 3. Couch rotation. The couch [3] rotates around the couch axis [6]. The couch [3] is connected to a rotating disk that controls the couch rotation. The couch can typically rotate 180 degrees.

[0006] Mechanical and Radiation Isocenters The mechanical isocenter [8] is defined as the intersection of the gantry rotation axis [2], the collimator rotation axis [5], and the couch rotation axis [6].

[0007] The radiation isocenter is the point in space where the radiation beams intersect when the gantry, collimator, or couch rotates.

[0008] The accuracy of patient treatment depends heavily on the proper determination of the radiation isocenter point in space. The radiation isocenter is an important concept in radiation therapy: if the patient is positioned so that the tumor is located at the isocenter, the radiation will be fixed to the tumor through the rotation of the gantry, collimator, or couch. If the isocenter is incorrectly defined or the tumor is not properly positioned at the isocenter, high doses of radiation will be delivered to areas other than the tumor, resulting in unwanted and harmful side effects.

[0009] Mechanical Error (Walkout) Ideally, each rotating subsystem (gantry, collimator, and couch) would rotate through a perfect circular orbit in space, creating a fixed, immovable, and precise axis of rotation for each rotating subsystem. This ideal scenario is unlikely to be realized, and each rotation may have some mechanical error that effectively smears the radiation beam. Some of the causes of non-concentric rotation can be non-circular rotating bearings, the effect of gravity when components are rotating, and mechanical instability of the moving subsystem. The magnitude of this non-concentricity needs to be measured to estimate its impact on the accuracy of radiation treatment.

[0010] Shaft non-concentricity Ideally, all three axes (gantry, collimator, and couch) intersect in space. Often these three axes are separated, which requires that an isocenter location be selected that minimizes radiation delivery errors across all three rotational axes.

[0011] direction of gravity Many of the components of a linac are oriented with reference to the direction of gravity. For example, the gantry is oriented with its axis of rotation parallel to the horizontal plane of the Earth, and the treatment couch is oriented with its axis of rotation parallel to the vertical plane of the Earth (perpendicular to gravity). Traditionally, instruments such as a plumb line or spirit level are used.

[0012] Treatment Room Laser The linac treatment room contains three sets of orthogonal lasers that converge at the isocenter from the ceiling to the left, right, and above the patient. The patient has a small, permanent point tattoo placed on the patient's skin at the expected point of incidence of each laser. The treatment room lasers are then used to align them with the patient's tattoos and set up the patient for each treatment. Therefore, it is important for treatment accuracy that the lasers are properly focused at the machine's mechanical isocenter. Summary of the Invention

[0013] A system is disclosed that includes a process and apparatus for tracking the translational rotation of mechanical components attached to a linac to calculate the rotation axes of the gantry, collimator, and couch. All other systems use radiation to determine the radiation isocenter, for example, by acquiring radiographic images through radiopaque markers or by exposing film to a narrow radiation beam as the linac components rotate. By calculating the collimator rotation axis and using this as an ideal surrogate for the radiation beam, the present system and method can locate the radiation isocenter without using radiation. This is more accurate than current techniques that use radiation alone, because it can eliminate radiation steering errors that can typically complicate results.

[0014] The disclosed system tracks the translational rotation of mechanical components attached to the linac to calculate the rotational axes of the gantry, collimator, and couch. The device and system measure the rotation of each of these three linac components and accurately determine each of these axes from the rotational measurements. The axes are represented in 3D space by skew lines, which are then used to calculate the optimal linac isocenter.

[0015] The disclosed system provides real-time tracking of the linac's mechanical motion, which is currently not possible with current state-of-the-art equipment and procedures. For each of the three rotational axes, the disclosed system displays the calculated rotation and observed tracking position during rotation in 3D and 2D via software. This allows the user to gain a highly intuitive understanding of how the linac behaves. The system calculates the axis "walkout" for each rotational axis. This walkout is defined by the maximum deviation from perfect concentric rotation. The system can also measure the direction of gravity so that all of the axis determinations described above are within a coordinate system aligned with Earth's gravity. The system can also align its internal coordinate system with the plane of gantry rotation, eliminating the need for perfect alignment of the signal receiver or signal emitter with the gantry.

[0016] A signal-emitting module having tracking markers is attached to the linac collimator, and the tracking markers are monitored by the signal-receiving module as the gantry or collimator rotates. As shown in the drawings, the signal-emitting module is a camera pod that uses stereo cameras and visible light to determine the real-time position and orientation of the (linac) rotating components. However, the position and orientation of the linac components can be equally effectively determined using infrared imaging or by triangulation of ranging systems including RF ranging, laser ranging, lidar, or sonar, or other similar techniques. The signal emitter acts as an extension of the collimator, and by tracking its position and orientation in space, the real-time position and orientation of the linac gantry and / or collimator can be derived.

[0017] The signal-receiving module shown in the drawings is a camera pod with a calibrated stereoscopic camera. The camera pod is positioned on the treatment couch in close proximity to the signal-emitting module. The positioning module shown in the drawings is also mounted on the couch and mechanically interconnected to the camera pod such that the relative position of the target body of the positioning module is a repeatable location with respect to the camera pod. However, the positioning module does not need to be mounted on the couch. The camera pod defines a coordinate system in space in which the rotational motion of the linac components can be measured, recorded, and analyzed to calculate the mechanical rotation axis of the linac.

[0018] The intersection of all mechanical axes (collectively referred to as the linac mechanical isocenter) is determined with great precision via software in the camera pod coordinate system. The system then enables precise physical identification of this mechanical isocenter location in space by an isocenter target module that can be placed under real-time optical tracking and guidance. This target module provides a real-world target for the mathematically determined isocenter. This physical target versus isocenter is extremely useful in many situations throughout the linac installation and its routine quality assurance procedures.

[0019] Since the collimator rotation axis would theoretically be at the center of the radiation beam if the radiation beam were perfectly calibrated, this system allows the radiation isocenter to be identified by calculating the collimator rotation axis for several different gantry angles. The radiation isocenter is then the intersection of these axes.

[0020] The system also incorporates a plumb line that can be measured with the stereo camera pod, allowing detection of the Earth's vertical (gravity) within the camera pod's coordinate system. Corrections can be made to align the camera pod's coordinate system with the Earth's vertical, providing a high level of utility during linac installation, maintenance, and routine quality assurance. [Brief explanation of the drawings]

[0021] [Figure 1] Depicts the gantry [1] rotation, the gantry rotation axis [2], and the treatment couch [3]. [Figure 2] Depicts the rotation of the collimator [4] around the collimator rotation axis [5]. [Figure 3] Describes the rotation of the couch [3] around the couch rotation axis [6]. [Figure 4] The isocenter [8] is depicted as the intersection of the gantry rotation axis [3] and the collimator and couch rotation axis [5]. [Figure 5] Depicts a collimator mount

[11] , a signal emitting module

[12] attached to the collimator mount

[11] , and a signal receiving module / camera pod

[10] . [Figure 6] Depicts the signal-emitting module

[12] connected to the collimator [4] via the collimator mount

[11] . The signal-receiving module / camera pod

[10] is shown in a suitable position for attachment to the positioning module

[22] attached to the patient's treatment couch. [Figure 7] It depicts a signal transmission module

[12] connected to the collimator mount

[11] via a bayonet mechanism (40) on both the collimator mount

[11] and the signal transmission module

[12] . [Figure 8] 1 depicts a side view of the signal emitting module

[12] showing the spherical emitter

[14] . [Figure 9] Depicts the camera pod showing the left camera

[17] , right camera

[18] , and mechanical interface

[20] to the positioning module

[22] . [Figure 10] Depicts the positioning module

[22] , which mechanically connects the two components, the isocenter target module

[21] and the camera pod

[10] . Locating pins

[23] and

[24] on the positioning module ensure a robust and repeatable mechanical interface. [Figure 11]This figure depicts the isocenter target module

[21] fixed within the positioning module

[22] . The camera pod monitors the signal emitter

[25] of the isocenter target module

[22] to accurately position the target body

[26] at the isocenter. [Figure 12] This figure depicts an isocenter target module

[21] positioned directly below the gantry [1] within the radiation field. A camera pod

[10] is positioned on the couch to track the position / orientation of the isocenter target module

[21] . [Figure 13] The components of the positioning module

[22] are depicted: the positioning module Z adjustment knob

[27] , the positioning module X adjustment knob

[28] , the mechanical interface between the positioning module and the camera pod

[23] , the positioning module Y adjustment knob

[29] , the clamping knob

[60] , the couch clamp

[30] , and the mechanical interface between the positioning module and the isocenter target module

[24] . [Figure 14] The components of the isocenter target module

[21] are depicted in rear view: signal generator

[25] , target body

[26] , backplate

[34] , and extension neck

[33] . [Figure 15] The components of the isocenter target module

[21] are depicted in front view: the signal generator for the isocenter target module

[25] , the target body of the isocenter target module

[26] , the backplate of the isocenter target module

[34] , the extension neck of the isocenter target module

[33] , and the aiming line on the isocenter target module

[35] . [Figure 16] 1 depicts a cross-sectional view of the isocenter target module showing the radiopaque marker

[36] aligned with the external aiming line

[35] etched into the target body

[26] . [Figure 17] Depicts the gravity detection module

[37] attached to the collimator mount

[11] using bayonet connections

[39] and

[38] . [Figure 18] This figure depicts the Gravity Detection Module (Gravity Module)

[37] in a typical use configuration connected to the collimator mount

[11] . The isocenter target module

[21] has been removed from the positioning module

[22] to avoid collision with the Gravity Module

[37] . The camera pod

[10] is positioned on the couch top [3] to monitor the Gravity Module

[37] . [Figure 19] 1 depicts the gravity detection module showing the pendulum wire

[44] , compartment for dampening fluid

[46] , high contrast background

[47] , and fluid discharge port

[48] . [Figure 20] Cross-section of the gravity detection module depicting the pendulum wire

[44] , pendulum ball

[45] , compartment for damping fluid

[46] , fluid discharge port

[48] , and mounting location for the pendulum string

[49] . [Figure 21] It depicts a signal emission module

[12] with individual signal emitters

[14] , calculated emitter centers

[51] and calculated emitter positions / orientations

[52] . [Figure 22] 1 depicts six example images captured by the camera pod

[10] as the signal-emitting module

[12] rotates while connected to the collimator mount

[11] . [Figure 23] 23 depicts the signal emitting position / orientation calculated from the position of the signal emitting module shown in FIG. 22. [Figure 24] We depict the discovered oscillator vector head

[52] and the optimized fit of this vector head

[52] . The normal to the optimized fit yields the rotation axis [2]. [Figure 25] 1 is an example of a linac isocenter based on the rotational axes of the gantry, collimator, and couch. [Figure 26] 10 is an example of a position offset vector. [Figure 27] 10 is an example of a walk-out radius determined from a bounding sphere for every point of closest approach. [Figure 28] Depiction of the gravity vector

[59] determined by the intersection of

[57] and

[58] : Left camera image during gravity image determination

[53] , Right camera image during gravity image determination

[54] , Pendulum wire as seen from the left camera

[55] , Pendulum wire as seen from the right camera

[56] , Projection plane of the left pendulum wire from the left camera focus

[57] , Projection plane of the right pendulum wire from the left camera focus

[58] . [Figure 29] An example of a multi-rotation axis center (MARC) dataset is depicted. The MARC dataset captures the signal emitter position for a series of collimator rotation measurements taken under different fixed gantry angles. In this example, nine measurements were collimated. For each measurement (e.g., items

[61] ,

[62] , and

[63] ), the collimator is fully rotated while the gantry is in a fixed position. The center of rotation

[64] and axis of rotation

[65] are calculated for each collimator rotation. [Figure 30] A two-dimensional orthogonal view of the example MARC dataset is depicted in Figure 29. For each collimator rotation, the center of rotation

[64] and the rotation axis

[65] are shown. A point in space can be calculated that represents the center of a sphere

[66] whose smallest radius encompasses all the rotation axes. The center of this sphere is the radiation isocenter, and the radius of this sphere represents the radiation isocenter error. DETAILED DESCRIPTION OF THE INVENTION

[0022] Parts List 1. Gantry. The main component of the linac that rotates around the patient as radiation is delivered during radiation therapy. 2. Gantry rotation axis. A mathematical construct that represents the axis around which the gantry rotates. 3. Patient treatment couch: Supports the patient during treatment. 4. Collimator. The end of the gantry closest to the patient. The collimator contains jaws that collimate the radiation beam. The collimator can rotate about its own axis to orient the jaws relative to the treatment area on the patient. 5. Collimator rotation axis. A mathematical construct that represents the axis around which the collimator rotates. 6. Couch rotation axis. A mathematical construct that represents the axis around which the couch rotates. 7. Not in use. 8. Mechanical isocenter. The intersection of the axes of the gantry, collimator, and couch. 9. Not in use. 10. Signal receiving module (camera pod), which acquires stereoscopic images and sends them to a computer for processing. 11. Collimator mount: Mechanically connects the signal transmission module and gravity module to the linac collimator. 12. A signal-emitting module, mechanically connected to the collimator, that emits signals during the rotation of the gantry, collimator, or couch. These signals are processed by a computer to determine the mechanical axis of rotation of the gantry, collimator, or couch. 13. Not in use. 14. Signal Emitters. Individual signal emitters of the signal-emitting module. They may be spherical or of any other symmetrical or asymmetrical shape. They may emit optical light, infrared light, radio frequency waves, or any signal that can be used to determine the module's position and orientation. 15. Not in use. 16. Not in use. 17. Left camera. 18. Right camera. 19. Not in use. 20. Mechanical Interface. Provides a mechanical connection point between the signal receiver and the positioning module. 21. Isocenter target module, which contains a signal emitter that is precisely positioned relative to the radiopaque marker. The emitter is tracked by a signal receiver so that the radiopaque marker can be placed with high accuracy at the found isocenter. 22. Positioning module, which allows for precise manual adjustment of the location of the isocenter target module in space. 23. Mechanical interface between positioning module and camera signal detector. Ensures that the mechanical connection between the isocenter target module and the signal receiver will be easily reproduced. 24. Mechanical interface between the positioning module and the isocenter target module. Ensures that the mechanical connection between the isocenter target module and the signal receiver will be easily reproduced. 25. Signal Emitters for Isocenter Target Modules. Individual signal emitters for the isocenter target modules. These can emit optical, infrared, radio frequency, or any signal that can be used to determine the position and orientation of the signal emitting module. 26. The target body of the isocenter target module. It encapsulates a radiopaque marker (typically a sphere made of a high density metal such as tungsten). It includes a crosshair on its outer surface that is aligned with the sphere. 27. Z adjustment knob on the positioning module. Provides manual adjustment of the radiopaque marker in the Z direction. 28. Positioning module X adjustment knob. Provides manual adjustment of the radiopaque marker in the X direction. 29. Y adjustment knob on the positioning module. Provides manual adjustment of the radiopaque marker in the Y direction. 30. Couch clamp. Connects the positioning module to the couch. 31. Not in use. 32. Not in use. 33. Extension neck of isocenter target module. 34. Isocenter target module backplate. 35. Aiming lines on the target body of the isocenter target module, providing a visual indication of the location of radiopaque markers embedded within the target body. 36. Radiopaque spherical target. The spherical target is used to verify that the radiation is properly focused at the found isocenter. The process of focusing the radiation is not described here; the present invention is only concerned with positioning the target at the correct location. 37. Gravity detection module. Enables detection of the direction of gravity. 38. Plug-in mounting mechanism for collimator mount. 39. Gravity module bayonet mounting mechanism. 40.SEP bayonet mounting mechanism. 41. Not in use. 42. Not in use. 43. Not in use. 44. Pendulum wire of gravity module. Used as an indicator of the direction of gravity. Image processing techniques calculate the wire direction. 45. Gravity module pendulum ball. Ensures the pendulum wire is taut and aligned with Earth's gravitational field. 46. Compartment for damping fluid in the gravity module. It is filled with a viscous fluid (water) to damp the oscillations of the pendulum wire. 47. High contrast background for pendulum wire. 48.Fluid discharge port. 49. Mounting location for pendulum string. 50. Calculated Center of Transmitters. The three-dimensional location of the center of each transmitter, calculated through image processing techniques. The computer determines this location by combining the found centers of the transmitters in each of the left and right images and then triangulating these positions into three dimensions. 51. The discovered center of each individual transmitter. 52. Head of the calculated oscillator vector. 53. Left camera image during determination of the gravity image. This is a representation of the image sensor of the left camera. 54. Right camera image during determination of the gravity image. This is a representation of the image sensor of the left camera. 55. Pendulum wire as seen by the left camera

[17] . This is the pendulum wire as seen by the camera (projected onto the image sensor). 56. Pendulum wire as seen from the right camera

[18] . This is the pendulum wire as seen by the camera (projected onto the imaging sensor). 57. Plane of projection of the left pendulum wire. This is a mathematical construction. The focus of the pendulum wire and the left camera

[17] on the image sensor creates a plane. 58. Projection plane of the right pendulum wire. This is a mathematical construction. The focus of the pendulum wire and the left camera

[17] on the image sensor creates a plane. 59. Gravity vector determination. Calculated from the intersection of the previously calculated plane

[57] with the plane

[58] . 60. Clamping knob. Used to secure the positioning module to the couch top. 61. Data set of signal emitter positions acquired as the collimator rotated through a full 360 degree rotation while the gantry was in a fixed angular position of approximately -40 degrees. 62. Data set of signal emitter positions acquired as the collimator rotates through a full 360 degree rotation while the gantry is in a fixed angular position of approximately 0 degrees. 63. Data set of signal emitter positions acquired as the collimator rotates through a full 360 degree rotation while the gantry is in a fixed angular position of approximately +40 degrees. 64. Calculated center of rotation for a dataset

[63] acquired when the gantry was positioned at +40. 65. Calculated rotation axis for a dataset

[63] acquired when the gantry was positioned at +40. 66. MARC sphere calculated from the data shown in Figure 29. The MARC sphere is defined as the sphere with the smallest possible radius while still satisfying the requirement that every axis of rotation involves at least one point on the sphere. The center of the MARC sphere is the radiation isocenter, and the radius of the sphere represents the radiation isocenter error.

[0023] The major assemblies / components of the disclosed system are as follows: Signal Transmitting Module The signal-emitting module shown in Figure 8 contains spherical markers

[14] in a fixed orientation. These spherical markers reflect or emit light at a frequency detectable by the detector (Figure 6) in the camera pod

[10] . The signal-emitting module is rigidly attached to the linac collimator via the collimator mounting mechanism (item

[11] in Figure 6). Once attached, it rotates with the gantry and collimator and acts as a trackable physical extension to them.

[0024] Signal Receiving Module / Camera Pod The camera pod

[10] (see Figure 9) contains cameras housed in a rigid outer body with known, fixed orientations relative to each other. The camera pod acquires time-synchronized images and transmits them to a computer / processor for analysis. Using stereoscopic image processing techniques, the discovered locations of objects in each image can be used to determine the location and orientation of the objects in real space.

[0025] The camera pod is positioned on the couch with a direct line of sight to the attached signal-emitting module (Figure 6). This orientation allows a full view of the signal-emitting module during gantry rotation (see Figure 1), collimator rotation (see Figure 2), and couch rotation (see Figure 3).

[0026] Positioning Module As shown in Figure 10, the positioning module

[22] is located in front of the couch. The positioning module

[22] , camera pod

[10] , and isocenter target module

[21] are mechanically interfaced when mounted on the couch, which fixes their relative positions with respect to each other. It is not necessary for the positioning module to be mounted on the couch; for example, a tripod or a ceiling or floor mounting bracket could be used just as effectively.

[0027] The positioning module

[22] provides a means for adjusting the position of the isocenter target module

[21] relative to the camera pod

[10] . It includes three manual adjustment knobs (items

[27] ,

[28] , and

[29] in Figure 13) that individually adjust the isocenter target module in three Cartesian directions.

[0028] Isocenter Target Module The purpose of the isocenter target module

[21] is to place a physical target at either the discovered isocenter location or the collimator rotation axis, thereby creating a real-world reference to a location that previously existed only mathematically within the computer / processor's software coordinate system. Once placed at the collimator rotation axis, an x-ray image of the linac-generated radiation beam passing through the target can be used to steer the linac's radiation to the center of the spherical target (resulting in the linac's radiation beam and collimator rotation axis being aligned). A similar process can be used when placing a target at the radiation isocenter. In this case, an x-ray image of the linac radiation passing through the target as the gantry, collimator, and couch rotate will be an independent check on the calculated radiation isocenter location and size. Similarly, a crosshair on the target body can then be used to adjust the treatment room patient setup laser to align with the discovered isocenter. The isocenter target module (

[21] in Figure 11) is placed on the positioning module

[22] . It contains a spherical transmitter marker

[25] at a fixed, known location. The transmitter is visible to the camera pod and is used to determine its position and orientation within the camera pod's coordinate system. The spherical transmitter location is precisely fixed to the module relative to a radiopaque target (typically a high-density metal sphere) contained within the target body

[26] .

[0029] The target body

[26] is shown in cross section on Figure 16 and includes an embedded radiopaque spherical target

[36] aligned with an external sighting line

[35] on its outer surface. The target body is shown as a rectangular rod with sighting lines on all or some of its sides. Other shapes can be used, such as a cylindrical tubular shape with sighting lines spaced 90 degree apart around the circumference of the tubular body.

[0030] Gravity Detection Module The gravity module

[37] (Fig. 18) connects to the collimator mount

[11] in the same manner and location as the signal-emitting module so that it can also be imaged by the camera pod

[10] . As can be seen in Fig. 19, it contains a plumb wire

[44] visible to the camera pod through an opening in its outer housing. The plumb wire is kept taut by a weight at its end (

[45] in Fig. 20), and a liquid container surrounding the weight damps its vibrations (see cross-section in Fig. 20).

[0031] Determining the radiation isocenter (without considering the couch) 1. The signal transmission module

[12] is attached to the collimator [4] of a medical linear accelerator (LINAC) gantry via a collimator mount

[11] as shown in Figure 6. The signal receiver

[10] is placed on the linac couch [3] at a position to acquire a stereoscopic image of the signal transmission module

[12] . 2. The gantry is fixed at a given position (e.g., at 0 degrees downwards) and the collimator ([4] in Figure 2) rotates mechanically while the signal receiver

[10] acquires the image pair as the signal emitter module

[12] rotates. For good results, the maximum rotation allowed by the linac is preferred, but partial rotation can also be used if full rotation is not possible. 3. A software registration process is used to calculate the orientation and location of the signal-emitting module (shown as

[52] in Figure 21) for each image pair acquired above. After each acquisition, a left and right image pair is sent from the signal receiver

[10] to a computer, and the location and orientation of the signal-emitting module is determined in three dimensions. To accomplish this, image processing techniques locate the center of each individual emitter (see

[51] in Figure 21) in each image. Stereo image processing techniques then calculate the three-dimensional coordinates of each individual signal emitter from its location in the left and right images. The group of three-dimensional positions of all individual signal emitters are then registered with the expected individual emitter locations to calculate the module's location and orientation. 4. The gantry is then incremented either clockwise or counterclockwise (e.g., 30 degrees from the previous position). With the gantry fixed in the new position, the collimator ([4] in Figure 2) is again rotated through its mechanical rotation while the signal receiver

[10] captures an image of the signal emitting module

[12] . 5. This process continues until collimator rotations at multiple fixed gantry angles are obtained. A minimum of two fixed gantry angles is recommended. 6. For each gantry position, the rotation axes for all signal emitter positions are calculated. 7. The isocenter is then determined as the point in space that minimizes the maximum distance from the isocenter to all calculated axes.

[0032] Determining the radiation isocenter (without considering the couch) 1. Follow the process described above for determining the radiation isocenter without the use of a couch, except for the additional step that the couch rotation axis is measured. 2. The couch rotation axis is combined with all collimator rotation axes. The isocenter is then determined as the point in space that minimizes the maximum distance from the isocenter to all calculated axes.

[0033] Determining the mechanical isocenter 1. The mechanical isocenter is set at the intersection of the axes determined for the gantry and collimator. The axis of rotation for the couch may also be determined and included. Since these three axes rarely intersect exactly, the mechanical isocenter is set at the location that minimizes the maximum distance to any of the calculated axes. Other techniques, such as differential weighting of each axis' contribution to the isocenter, may also be used.

[0034] Determining the gantry rotation axis 1. The signal transmission module

[12] is attached to the linac collimator [4] via a collimator mount

[11] as shown in Figure 6. The signal receiver

[10] is placed on the linac couch [3] in a position to acquire a stereoscopic image of the signal transmission module

[12] as the gantry rotates. While maximum rotation is preferred for good results, partial rotation can also be used if full rotation is not possible. 2. The gantry ([1] in Figure 1) rotates through its mechanical rotation while the signal receiver

[10] captures images of the signal-emitting module

[12] at regular time intervals. An example of five acquisitions over a 360 degree rotation is shown in Figure 22. 3. After each acquisition, a pair of left and right images is sent from the signal receiver

[10] to a computer to determine the location and orientation of the signal-emitting module in three dimensions. To accomplish this, image processing techniques locate the center of each individual emitter (see

[51] in Figure 21) in each image. Stereo image processing techniques then calculate the three-dimensional coordinates of each individual signal emitter from its location in the left and right images. 4. The signal-emitting module locations (see Figure 24) from all data acquisitions are then fitted to a three-dimensional circular path, whose central axis represents the gantry rotation axis ([2] in Figure 1).

[0035] Determining the collimator rotation axis 1. The system is configured as described for determining the gantry rotation axis. 2. Follow the same steps as described for determining the gantry rotation axis, except instead of rotating the gantry, the collimator ([4] in Figure 2) rotates. Maximum rotation is preferred for good results, but partial rotation can be used if full rotation is not possible. 3. Determine the collimator rotation axis ([5] in Figure 2) following the same image processing and data analysis steps as described in determining the gantry rotation axis.

[0036] Determining the couch rotation axis 1. The system is configured as described for determining the gantry rotation axis. 2. Follow the same steps as described for determining the gantry rotation axis, except instead of rotating the gantry, the couch ([3] in Figure 3) rotates. Maximum rotation is preferred for optimal results, but partial rotation can be used if full rotation is not possible. 3. Determine the couch rotation axis ([6] in Figure 3) following the same image processing and data analysis steps as described in determining the gantry rotation axis.

[0037] Positioning of target marker on rotation axis 1. Once the axis of rotation (of either the gantry, collimator, or couch) is determined, a target marker can be placed at any point along this axis (this is useful for the collimator axis when adjusting the direction of the radiation beam, collectively called "steering"). 2. Without interfering with the camera pod

[10] from the setup used to determine the isocenter (this ensures the same coordinate system), the isocenter target module

[21] is placed on the positioning module as shown in Figure 11. 3. The isocenter target module consists of a set of signal emitters (

[25] in Figure 11) precisely positioned relative to radiopaque spherical markers

[36] embedded within the target body

[26] . 4. The signal receiver

[10] is configured to capture images of the signal emitter

[25] of the isocenter target module. These images are sent to a computer to determine the location of the isocenter target module in three dimensions through the same image processing techniques used to determine the gantry axis. Again, in summary, these images are analyzed to find the center of each individual emitter (see

[51] in Figure 21) in three-dimensional coordinates. The position and orientation of the isocenter target module in space are then determined, and these found locations are registered with the expected locations of the individual emitter locations. This registration process is used to determine the signal emitter orientation and location for each acquisition. 5. For each image pair acquisition, the found location of the isocenter target module's radiopaque spherical marker is compared to the axis of the object, and the software instructs the user on how to shift the isocenter target module in three dimensions to align this marker with the axis. Figure 13 shows the X-dial

[28] , Y-dial

[29] , and Z-dial

[27] that can be used to perform these shifts. The software provides real-time feedback to guide the user through this process.

[0038] Positioning of target markers at isocenter 1. Once the mechanical or radiological isocenter is determined, a target marker can be placed at that isocenter (this is useful because tests must be performed to ensure that the radiation is properly focused towards the radiological isocenter). 2. Without interfering with the camera pod

[10] from the setup used to determine the isocenter (this ensures the same coordinate system), the isocenter target module

[21] is placed on the positioning module as shown in Figure 11. 3. The isocenter target module consists of a set of signal emitters (

[25] in Figure 11) precisely positioned relative to radiopaque spherical markers

[36] embedded within the target body

[26] . 4. The signal receiver

[10] is configured to capture images of the signal emitter

[25] of the isocenter target module. These images are sent to a computer to determine the location of the isocenter target module in three dimensions through the same image processing techniques used to determine the gantry axis. Again, in summary, these images are analyzed to find the center of each individual emitter (see

[51] in Figure 21) in three-dimensional coordinates. The position and orientation of the isocenter target module in space are then determined, and these found locations are registered with the expected locations of the individual emitter locations. This registration process is used to determine the signal emitter orientation and location for each acquisition. 5. For each image pair acquisition, the discovered location of the radiopaque spherical marker on the isocenter target module is compared to the discovered isocenter, and the software instructs the user on how to shift the isocenter target module in three dimensions to align the two positions. Figure 13 shows the X-dial

[28] , Y-dial

[29] , and Z-dial

[27] that can be used to accomplish these shifts. The software provides real-time feedback to guide the user through this process.

[0039] Determining Collimator Axis Walkout 1. The signal transmission module

[12] is attached to the linac collimator [4] via a collimator mount

[11] as shown in Figure 6. The signal receiver

[10] is placed on the linac couch [3] in a position to acquire a stereoscopic image of the signal transmission module

[12] as the collimator rotates. While maximum rotation is preferred for good results, partial rotation can also be used if full rotation is not possible. 2. The collimator ([1] in Figure 1) rotates through its mechanical rotation while the signal receiver

[10] captures images of the signal emitting module

[12] at regular time intervals. 3. After each acquisition, a left and right image pair is sent from the signal receiver

[10] to a computer to determine the location and orientation of the signal-emitting module in three dimensions. To achieve this, image processing techniques locate the center of each individual emitter (see

[51] in Figure 21) in each image. Stereo image processing techniques then calculate the three-dimensional coordinates of each individual signal emitter from its location in the left and right images. 4. The signal-emitting module locations from all data acquisitions are then fitted to a three-dimensional circular path. This fitted circular path represents the ideal path that the emitter would have followed if the collimator rotation were "ideal", i.e., if there were no errors or deviations in its mechanical rotation. 5. For each measured signal-emitting module position, the vector between the position and the closest point on the fitted circular path represents the error in that position. The set of all error vectors represents the walkout for that axis.

[0040] Deciding on a couch axis walkout 1. The system is configured as described for determining collimator axis walkout. 2. Follow the same steps as described for determining the collimator axis walk-out, except instead of rotating the collimator, the couch ([3] in Figure 3) is rotated. Maximum rotation is preferred for optimal results, but partial rotation can be used if full rotation is not possible. 3. Determine couch axis walkout following the same image processing and data analysis steps described in determining collimator axis walkout.

[0041] Room Laser Adjustment 1. The target body

[26] of the isocenter target module contains radiopaque spherical markers

[36] embedded in a position that is aligned orthogonally with the four sets of aiming lines

[35] marked on the outer surface (see cross section in Figure 16). 2. The aiming line on the outside of the target body allows the room laser to be adjusted to precisely align with the radiopaque sphere (which is invisible) located inside. 3. Once the radiopaque sphere

[36] is aligned with the discovered isocenter (described in the step above), the left, right, and top room lasers are manually adjusted to focus on the aiming lines located to the left, right, and top of their target body (

[26] in Figure 11).

[0042] Determining the direction of gravity 1. Instead of using a typical spirit level to align the gantry level with the Earth's gravitational field, a gravity module

[37] shown in Figure 17 can be connected to the linac via a collimator mount

[11] . 2. The gravity module, shown in cross section in Figure 20, includes a pendulum ball

[45] suspended by a flexible wire

[44] . The pendulum ball is surrounded by a viscous liquid (typically water) contained in a container

[46] . This liquid quickly damps the ball's oscillations (without the damping liquid, the time it takes for the pendulum to stop oscillating would be extremely long). 3. The signal receiving module acquires image pairs of the gravity module and uses signal processing techniques to determine the orientation in space of the pendulum wire, which correlates to the direction of the gravity vector. 4. Figure 28 shows a diagrammatic illustration of the mathematical process used: the pendulum wire

[44] is detected in the left image

[53] and the right image

[56] acquired by the camera pod. 5. The pendulum wireline is mathematically projected from the camera's focal point to create a left plane

[55] and a right plane

[58] . 6. The intersection of the two planes is calculated and represents the direction of the gravity vector

[59] .

[0043] Software Overview 1. Initialize a coordinate system that is correlated with the real-world coordinates of the signal-emitting module; 2. Display the location of signal-emitting modules in real time (both in 3D view and 2D projection). 3. Presents the position and orientation of the signal-emitting module while recording rotation. 4. Calculate the direction of gravity in the previously initialized coordinate system. 5. Calculate the axis of rotation (gantry, collimator, or couch). 6. Present the calculated axis position in 3D view and 2D projection. 7. Calculates the linac mechanical or radiological isocenter based on the calculated rotation axis. 8. Presents the linac isocenter in 3D and 2D views. 9. Generates a report to show the linac rotation axis and linac isocenter. 10. Stores previous data sets to allow post-processing and data review. 11. Uses the walkout radius of each of the three axes to calculate the overall linac walkout radius.

[0044] The linac mechanical isocenter determination process includes attaching a signal-transmitting module to a collimator, attaching a signal-receiving module in a location where the signal-transmitting module is in line of sight, determining the rotation axis of the gantry by rotating the gantry with the signal-receiving module receiving signals from the signal-transmitting module while the gantry is rotating, determining the rotation axis of the collimator by rotating the collimator with the signal-receiving module receiving signals from the signal-transmitting module while the collimator is rotating, and determining the linac mechanical isocenter by processing the received signals about the rotation axes of the gantry and collimator.

[0045] The rotation axis of the couch can be determined by attaching a signal receiving module to the couch and rotating the couch with the signal receiving module receiving signals from the signal transmitting module during couch rotation. The linac mechanical isocenter can then be determined by processing the received signals for the rotation axis of the gantry, collimator, and couch.

[0046] In one embodiment for the linac mechanical and radiation isocenter determination process, the signal emitting module emits an optical signal and the signal receiving module receives the optical signal, however, as mentioned, other signal sources can be utilized, such as infrared imaging or by triangulation of ranging systems including RF ranging, laser ranging, lidar, or sonar, or other similar techniques such as using laser beams.

[0047] The signal emitting module comprises at least one marker that reflects or emits light at a specific frequency optimized for the signal receiver.

[0048] The linac isocenter determination process can include attaching an isocenter target module to the positioning module and positioning an isocenter target marker located on the isocenter target module at the linac isocenter. The isocenter target module includes at least one target marker. The isocenter target module can include a radiopaque marker inside the target body and a line of sight outside the target body, allowing the laser to be aligned by focusing on the linac isocenter.

[0049] In one embodiment, the positioning module includes a mechanism(s) for adjusting the X, Y, and Z positions, which may be controlled individually or a joystick-type mechanism may be used for all three.

[0050] The linac mechanical isocenter determination process may include utilizing a processor to collect data and process the data using software.

[0051] In one embodiment, a gravity module is attached to the collimator and a camera pod acquires images of the gravity module's location that will be used in determining the direction of the gravity vector.

[0052] In another embodiment, the signal receiving module is fixed to the collimator and the signal emitting module is attached to the couch. The signal receiving module can be attached to any location that has a line of sight to the signal emitter.

[0053] In another embodiment, the linac radiation isocenter determination process includes attaching a signal-transmitting module to a collimator, attaching a signal-receiving module in a location that has a line of sight to the signal-transmitting module, rotating the collimator with the gantry positioned at a first angle while the signal receiver captures the position and orientation of the signal-transmitting module, rotating the collimator with the gantry positioned at a second angle while the signal receiver captures the position and orientation of the signal-transmitting module, determining calculated three-dimensional collimator rotation axes with the gantry positioned at the first angle and with the gantry positioned at the second angle, and determining the linac radiation isocenter using the calculated collimator rotation axes with the gantry positioned at the first angle and the calculated collimator rotation axes with the gantry positioned at the second angle.

[0054] In another embodiment, the collimator is rotated with the gantry at least one additional angle.

[0055] The linac radiation isocenter determination process may include rotating the couch for inclusion in the radiation isocenter calculation.

[0056] A linac gantry rotation axis determination process is disclosed that includes mounting a signal-emitting module to a collimator, mounting a signal-receiving module in a location where the signal-emitting module has line-of-sight, and determining the rotation axis of the gantry by rotating the gantry with the signal-receiving module receiving a signal from the signal-emitting module during the gantry rotation.

[0057] A linac collimator rotation axis determination process is disclosed that includes mounting a signal-emitting module to a collimator, mounting a signal-receiving module in a location where the signal-emitting module is in line of sight, and determining the rotation axis of the collimator by rotating the collimator with the signal-receiving module receiving a signal from the signal-emitting module during a gantry rotation.

[0058] A linac couch rotation axis determination process is disclosed that includes mounting a signal-emitting module to a collimator, mounting a signal-receiving module in a location where the signal-emitting module has a line of sight to the signal-emitting module, and determining the rotation axis of the collimator by rotating the couch with the signal-receiving module receiving a signal from the signal-emitting module during a gantry rotation.

[0059] A process for determining a collimator axis walkout is disclosed that includes mounting a signal emitting module to a collimator, mounting a signal receiving module in a location that is line of sight to the signal emitting module, determining a path of the signal emitter through space during rotation of the collimator by analyzing signal receiver data acquired during the rotation, fitting the calculated signal emitter positions to a three-dimensional circle in space, and calculating an error vector between each position and the closest point to the fitted three-dimensional circle.

[0060] A process for determining couch axis walkout is also disclosed that includes mounting a signal emitting module to a collimator, mounting a signal receiving module in a location where the signal emitting module is in line of sight, determining the path of the signal emitter through space during couch rotation by analyzing signal receiver data acquired during rotation, fitting the calculated signal emitter positions to a three-dimensional circle in space, and calculating an error vector between each position and the closest point to the fitted three-dimensional circle.

[0061] While preferred embodiments have been described that serve to illustrate various concepts, structures, and techniques that are the subject of this invention, it will become more apparent to those skilled in the art that other embodiments incorporating these concepts, structures, and techniques may be used. Accordingly, the scope of this patent should not be limited to the described embodiments, but should be limited only by the principles and scope of the following claims.

Claims

1. A process for determining a mechanical isocenter of a linac, comprising: Attaching a signal transmission module to a collimator; mounting a signal receiving module in a location within line of sight of the signal emitting module; determining a rotation axis of the gantry by rotating the gantry while the signal-receiving module acquires the position of the signal-emitting module; determining a rotation axis of the collimator by rotating the collimator while the signal-receiving module acquires the position of the signal-emitting module during the rotation of the collimator; determining a mechanical isocenter of the linac by processing the position of a signal transmission module during rotation of the collimator and rotation of the gantry; A process for determining the mechanical isocenter of a linac comprising:

2. 2. The process of claim 1, further comprising: determining a rotation axis of the couch by rotating the couch while the signal receiving module is attached to the couch and the signal receiving module acquires the position of the signal transmitting module during the couch rotation; and determining a mechanical isocenter of the linac by processing the position of the signal transmitting module with respect to the rotation axis of the gantry, the collimator, and the couch.

3. The linac mechanical isocenter determination process of claim 1 , wherein the signal emitting module emits an optical signal and the signal receiving module receives the optical signal.

4. The linac mechanical isocenter determination process of claim 3 , wherein the signal-emitting module comprises at least one marker that reflects or emits light at a specific frequency optimized for the signal-receiving module.

5. The linac mechanical isocenter determination process of claim 4 , wherein the signal receiving module is a camera pod.

6. The linac mechanical isocenter determination process of claim 5 , wherein the camera pod is comprised of at least two cameras capable of acquiring time-synchronized images for computer analysis.

7. 2. The linac mechanical isocenter determination process of claim 1, further comprising: attaching an isocenter target module to a positioning module; and positioning the isocenter target module at the mechanical isocenter of the linac using at least one transmitter marker on the isocenter target module.

8. The linac mechanical isocenter determination process of claim 7 , wherein the isocenter target module includes a radiopaque marker inside a target body.

9. The linac mechanical isocenter determination process of claim 8 , wherein the isocenter target module includes a line of sight outside the target body.

10. The linac mechanical isocenter determination process of claim 9 , wherein the positioning module includes controls for X, Y, and Z positions.

11. 10. The linac mechanical isocenter determination process of claim 1, further comprising utilizing a processor to collect data and process said data using software.

12. A process for determining a radiation isocenter of a linac, comprising: Attaching a signal transmission module to a collimator; mounting a signal receiving module in a location within line of sight of the signal emitting module; rotating the collimator with the gantry positioned at a first angle while the signal-receiving module acquires the position of the signal-emitting module; determining a calculated collimator rotation axis from the position of the signal transmission module acquired with the gantry positioned at the first angle; rotating the collimator with the gantry positioned at a second angle while the signal-receiving module captures the position of the signal-emitting module; determining a calculated collimator rotation axis from the position of the signal transmission module acquired with the gantry positioned at the second angle; determining a linac radiation isocenter using the calculated collimator rotation axis with the gantry positioned at the first angle and the calculated collimator rotation axis with the gantry positioned at the second angle; A radiation isocenter determination process for a linac comprising:

13. 13. The linac radiation isocenter determination process of claim 12, further comprising rotating the collimator with the gantry positioned at at least one additional angle while the signal receiving module captures the position of the signal transmitting module.

14. The linac radiation isocenter determination process of claim 12 , wherein the signal emitting module emits an optical signal and the signal receiving module receives the optical signal.

15. The linac radiation isocenter determination process of claim 12 , wherein the signal receiving module is mounted on a couch.

16. 13. The linac radiation isocenter determination process of claim 12, further comprising: rotating a couch; and determining a linac radiation isocenter using the calculated collimator and couch axes.

17. A process for determining a gantry rotation axis of a linac, comprising: Attaching a signal transmission module to a collimator; mounting a signal receiving module in a location within line of sight of the signal emitting module; determining a rotation axis of the gantry by rotating the gantry while the signal-receiving module acquires the position of the signal-emitting module; A process for determining the rotation axis of a gantry of a linear accelerator.

18. A process for determining a collimator rotation axis of a linac, comprising: Attaching a signal transmission module to a collimator; mounting a signal receiving module in a location within line of sight of the signal emitting module; determining a rotation axis of the collimator by rotating the collimator while the signal-receiving module acquires the position of the signal-emitting module; A process for determining a collimator rotation axis of a linac comprising:

19. A process for determining a couch rotation axis of a linac, comprising: Attaching a signal transmission module to a collimator; mounting a signal receiving module in a location within line of sight of the signal emitting module; determining a rotation axis of the collimator by rotating the couch while the signal receiving module acquires the position of the signal emitting module; A process for determining a couch rotation axis of a linac comprising:

20. A gravity vector determination process comprising: attaching a gravity module to the collimator; mounting a camera pod at a location within line of sight of said gravity module; acquiring an image of the location of the gravity module using the camera pod to determine the direction of a gravity vector relative to an internal coordinate system of the camera pod; A gravity vector determination process comprising:

21. 1. A collimator axis walk-out determination process, comprising: Attaching a signal transmission module to a collimator; mounting a signal receiving module in a location within line of sight of the signal emitting module; determining a path through space of the signal-emitting module during rotation of the collimator by analyzing the position of the signal-emitting module; fitting the calculated positions of the signal emitting modules to a three-dimensional circle in space; calculating an error vector between each position and the closest point to the fitted three-dimensional circle; A collimator axis walkout determination process comprising:

22. 1. A couch axis walkout determination process, comprising: Attaching a signal transmission module to a collimator; mounting a signal receiving module in a location within line of sight of the signal emitting module; determining a path through space of the signal-emitting module during a rotation of the couch by analyzing the position of said signal-emitting module; fitting the calculated positions of the signal emitting modules to a three-dimensional circle in space; calculating an error vector between each position and the closest point to the fitted three-dimensional circle; A couch axis walkout decision process comprising:

Images