System, process, and apparatus for determining the isocenter of a linac

Abstract

To provide a system to determine an isocenter of a LINAC.SOLUTION: One embodiment does this by determining the axis 5 of rotation for a collimator, a gantry, and a couch. In another embodiment, only determining the axis of rotation of a collimator is required. A system and apparatus enable tracking of translation-rotation of mechanical components attached to a LINAC to compute the axis of rotation of the gantry, the collimator, and the couch. Based on data collected related to these axes, a LINAC isocenter is determined. A primary apparatus utilized in the system includes a signal 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 relative to the signal receiver.SELECTED DRAWING: Figure 4

Description

Cross - reference to related applications

[0001] This application is a divisional continuation of non - provisional application No. 16,934,586, filed on Jul. 21, 2020, and claims priority to U.S. Provisional Patent Application No. 62986957, filed on Mar. 9, 2020, and No. 63033328, filed on Jun. 2, 2020, which are hereby incorporated by reference in their entirety for all purposes.

Technical Field

[0002] A system, process, device, apparatus, and method for tracking the translational and rotational movements of mechanical components for determining an isocenter for a medical linear accelerator (LINAC) by calculating the rotation axes of a gantry, collimator, and couch.

Background Art

[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 radiation beam is directed from a medical linear accelerator (LINAC) to an accurate point within the patient.

[0005] One of the important elements of treatment accuracy is the geometric accuracy of the LINAC's mechanical rotation. Each LINAC has three types of rotations that need to rotate about known points in space to ensure the most accurate treatment possible. The three rotations are described below. 1. Gantry rotation. The gantry [1] rotates about 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 about the collimator axis [5]. The collimator can rotate 360 degrees. 3. Rotation of the couch. The couch [3] rotates about the couch axis [6]. The couch [3] is connected to a rotating disk that controls the rotation of the couch. The couch can typically rotate 180 degrees.

[0006] Mechanical Isocenter and Radiation Isocenter 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 largely on the proper determination of the radiation isocenter point in space. The radiation isocenter is an important concept in radiation therapy: when the patient is positioned so that the tumor is located at the isocenter, the radiation will be fixed on the tumor through the rotation of the gantry, collimator, or couch. If the isocenter is inaccurately defined or the tumor is not correctly positioned at the isocenter and high doses of radiation are delivered outside the tumor, it will result in unwanted harmful side effects.

[0009] Mechanical Error (Walkout) Ideally, each rotating subsystem (gantry, collimator, and couch) rotates through a perfect circular orbit in space and creates an exact fixed and immovable rotation axis for each rotating subsystem. This ideal scenario is almost never achieved, and each rotation may have some mechanical error that effectively blurs the radiation beam. Some of the causes of non-concentric rotation can be non-circular rotation bearings, the influence of gravity when components are rotating, and mechanical instability of the moving subsystems. It is necessary to measure the magnitude of this non-concentricity in order to estimate its impact on the accuracy of radiation therapy.

[0010] Non-Concentricity of the Axis Ideally, all three axes (gantry, collimator, and couch) intersect within space. In many cases these three axes are separated, which requires that an isocenter location be selected that minimizes radiation exposure errors across all three axes of rotation.

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

[0012] Treatment room laser A linac treatment room includes three sets of orthogonal lasers that converge on the isocenter from the left, right, and upper ceiling of the patient. Small, persistent point tattoos are placed at the predicted point of incidence of each laser on the patient's skin. The treatment room lasers are then used to align them with the patient's tattoos to set up the patient for each treatment. Therefore, it is important for the accuracy of treatment that the lasers be properly focused on the mechanical isocenter of the machine. 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 gantry, collimator, and couch rotation axes. All other systems use radiation to determine the radiation isocenter, for example, by acquiring a radiation transmission image through a radiation-opaque marker or by exposing a film to a narrow radiation beam when 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 only radiation, as it can remove radiation steering errors that can typically complicate the results.

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

[0015] The disclosed system provides real-time tracking of the mechanical motion of a linac. This is currently not possible with current state-of-the-art devices and procedures. For each of the three rotational axes, the disclosed system shows the calculated rotation and observed tracking position during rotation in 3D and 2D via software. This allows the user to very intuitively understand how the linac behaves. The system calculates an "out-of-walk" for each axis of rotation. This out-of-walk 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 determination described above is within a coordinate system aligned with the Earth's gravity. The system can also align its internal coordinate system with the plane of rotation of the gantry. This eliminates the need to perfectly align the signal receiver or signal transmitter with the gantry.

[0016] A signal transmitting module having tracking markers is attached to the linac collimator, and the tracking markers are monitored by a signal receiving module as the gantry or collimator rotates. As shown in the drawings, the signal transmitting module is a camera pod that uses a stereo camera and visible light to determine the real-time position and orientation of the rotating components of the (linac). However, the position and orientation of the linac components can be determined equally efficiently using infrared imaging or triangulation of a ranging system including RF ranging, laser ranging, lidar, or sonar, or other similar techniques. The signal transmitter functions 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 having a calibrated stereo camera. The camera pod is disposed on a treatment couch in proximity to the signal transmitting module. The positioning module shown in the drawings is also attached to the couch and is mechanically interconnected to the camera pod such that the relative position of the target body of the positioning module is in a reproducible location relative to the camera pod. However, the positioning module need not be attached to the couch. The camera pod defines a coordinate system in space within which the rotational movement of the linac components can be measured, recorded, and analyzed to calculate the mechanical axis of rotation of the linac.

[0018] The intersection of all mechanical axes (collectively referred to as the linac mechanical isocenter) is determined with very high precision via software within the camera pod coordinate system. The system then enables the accurate physical identification of this mechanical isocenter position 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 to the mathematically determined isocenter. This physical target-to-isocenter is extremely useful in many situations throughout the installation of the linac and its prescribed quality assurance procedures.

[0019] If the radiation beam is perfectly calibrated, the collimator axis of rotation will, in theory, be the center of the radiation beam, and this system enables the identification of the radiation isocenter by calculating the collimator axis of rotation for multiple 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 by the stereo camera pod. This enables the detection of the vertical direction (gravity) of the earth within the coordinate system of the camera pod. A correction can be made to align the coordinate system of the camera pod to the vertical direction of the earth, providing a high level of utility during the installation, management, and prescribed quality compensation of the linac.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

[11] , the signal transmission module

[12] attached to the collimator mount

[11] , and the signal reception module / camera pod

[10] are depicted.

Figure 6

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

[11] is depicted. The signal reception module / camera pod

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

[22] attached to the patient's treatment couch.

Figure 7

[12] connected to the collimator mount

[11] via the plug-in mechanism (40) present in both the collimator mount

[11] and the signal transmission module

[12] is depicted.

Figure 8

[12] showing the spherical transmitter

[14] is depicted.

Figure 9

[17] , the right camera

[18] , and the mechanical interface

[20] to the positioning module

[22] is depicted.

Figure 10

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

[21] and the camera pod

[10] , is depicted. The positioning pins

[23] and

[24] on the positioning module ensure a robust and reproducible mechanical interface.

Figure 11

[21] fixed within the positioning module

[22] . The camera pod monitors the signal transmitter

[25] of the isocenter target module

[22] in order to accurately position the target body

[26] at the isocenter.

Figure 12

[21] placed directly below the gantry [1] within the radiation field. The camera pod

[10] is placed on the couch and tracks the position / orientation of the isocenter target module

[21] .

Figure 13

[22] : Z adjustment knob

[27] of the positioning module, X adjustment knob

[28] of the positioning module, mechanical interface

[23] between the positioning module and the camera pod, Y adjustment knob

[29] of the positioning module, tightening knob

[60] , couch clamp

[30] , and mechanical interface

[24] between the positioning module and the isocenter target module.

Figure 14

[21] : Signal transmitter

[25] , target body

[26] , backplate

[34] , and extension neck

[33] , are depicted in a rear view.

Figure 15

[21] : Signal transmitter

[25] for the isocenter target module, target body

[26] of the isocenter target module, backplate

[34] of the isocenter target module, extension neck

[33] of the isocenter target module, aiming line

[35] on the isocenter target module, are depicted in a front view.

Figure 16

[36] aligned with the external aiming line

[35] etched on the target body

[26] .

Figure 17

[37] attached to the collimator mount

[11] using plug-in connections

[39] and

[38] .

Figure 18

[37] of a typical usage configuration connected to a collimator mount

[11] . The isocenter target module

[21] is removed from the positioning module

[22] so as not to collide with the gravity module

[37] . The camera pod

[10] is arranged on the couch top surface [3] to monitor the gravity module

[37] .

Figure 19

[44] , a compartment

[46] for a dampening fluid, a high contrast background

[47] , and a fluid discharge port

[48] .

Figure 20

[44] , a pendulum ball

[45] , a compartment

[46] for a dampening fluid, a fluid discharge port

[48] , and a mounting location

[49] for a pendulum string.

Figure 21

[12] having individual signal transmitters

[14] , a calculated transmitter center

[51] , and a calculated transmitter position / orientation

[52] .

Figure 22

[10] when the signal transmission module

[12] rotates while connected to the collimator mount

[11] .

Figure 23

Figure 24

[52] and the optimized fit

[52] of this vector head. The normal to the optimized fit gives rise to the axis of rotation [2].

Figure 25

Figure 26

Figure 27

Figure 28

[59] determined by the intersection of

[57] and

[58] : the left camera image

[53] during gravitational image determination, the right camera image

[54] during gravitational image determination, the pendulum wire seen from the left camera

[55] , the pendulum wire seen from the right camera

[56] , the projection plane

[57] of the left pendulum wire from the left camera focus, and the projection plane

[58] of the right pendulum wire from the left camera focus.

Figure 29

[61] ,

[62] , and

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

[64] and the axis of rotation

[65] are calculated for each rotation of the collimator.

Figure 30

[64] and the axis of rotation

[65] are shown for each rotation of the collimator. A point in space representing the center

[66] of a sphere that encloses all the axes of rotation with the minimum radius can be calculated. 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 a linac that rotates around the patient when irradiating radiation during radiotherapy. 2. Gantry rotation axis. A mathematical structure representing 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 includes a jaw that collimates the radiation beam. The collimator can rotate about its own axis to direct the jaw towards the treatment site of the patient. 5. Collimator Rotation Axis. A mathematical structure representing the axis about which the collimator rotates. 6. Couch Rotation Axis. A mathematical structure representing the axis about which the couch rotates. 7. Not Used. 8. Mechanical Isocenter. The intersection of the axes of the gantry, collimator, and couch. 9. Not Used. 10. Signal Receiving Module (Camera Pod). Acquires stereoscopic images and transmits those images to a computer for processing. 11. Collimator Mount. Mechanically connects the signal transmitting module and the gravity module to the linear accelerator collimator. 12. Signal Transmitting Module. Is mechanically connected to the collimator and emits signals during the rotation of the gantry, collimator, or couch. These signals are processed by a computer to determine the mechanical rotation axes of the gantry, collimator, or couch. 13. Not Used. 14. Signal Transmitter. Individual signal transmitters of the signal transmitting module. These may be spherical or may have any other symmetric or asymmetric shape. They can emit optical light, infrared light, radio frequency waves, or any signal that can be used to determine the position and orientation of the module. 15. Not Used. 16. Not Used. 17. Left Camera. 18. Right Camera. 19. Not Used. 20. Mechanical Interface. Provides a mechanical connection point between the signal receiver and the positioning module. 21. Isocenter Target Module. Includes signal transmitters accurately positioned relative to radiation - opaque markers. The transmitters are tracked by the signal receiver so that the radiation - opaque markers can be positioned with high precision at the discovered isocenter. 22. Positioning Module. Enables precise manual adjustment of the location of the isocenter target module in space. 23. The mechanical interface between the positioning module and the camera signal detector. Ensure that the mechanical connection between the isocenter target module and the signal receiver can be easily reproduced. 24. The mechanical interface between the positioning module and the isocenter target module. Ensure that the mechanical connection between the isocenter target module and the signal receiver can be easily reproduced. 25. A signal transmitter for the isocenter target module. Individual signal transmitters of the isocenter target module. These can emit any signal that can be used to determine the position and orientation of the signal transmission module, such as optical light, infrared, radio frequency. 26. The target body of the isocenter target module. Encapsulates a radiation-impermeable marker (typically a sphere made of a high-density metal such as tungsten). It includes a sight line on the outer surface aligned with the sphere. 27. The Z-adjustment knob of the positioning module. Provides manual adjustment in the Z direction of the radiation-impermeable marker. 28. The X-adjustment knob of the positioning module. Provides manual adjustment in the X direction of the radiation-impermeable marker. 29. The Y-adjustment knob of the positioning module. Provides manual adjustment in the Y direction of the radiation-impermeable marker. 30. A couch clamp. Connects the positioning module to the couch. 31. Not in use. 32. Not in use. 33. The extension neck of the isocenter target module. 34. The backplate of the isocenter target module. 35. The sight line on the target body of the isocenter target module. Provides a visual indication of the location of the radiation-impermeable marker embedded within the target body. 36. A radiopaque spherical target. The spherical target is used to ensure that radiation is properly focused on the discovered isocenter. The process of focusing the radiation is not described herein. The present invention is only concerned with positioning the target in the correct location. 37. A gravity detection module. Enables detection of the direction of gravity. 38. A plug-in mounting mechanism for the collimator mount. 39. A plug-in mounting mechanism for the gravity module. 40. A plug-in mounting mechanism for the SEP. 41. Not used. 42. Not used. 43. Not used. 44. The pendulum wire of the gravity module. Used as an indication of the direction of gravity. Image processing techniques calculate the wire direction. 45. The pendulum ball of the gravity module. Ensures that the pendulum wire is taut and aligned with the Earth's gravitational field. 46. A compartment for the damping fluid of the gravity module. Filled with a viscous fluid (water) to damp the vibration of the pendulum wire. 47. A high-contrast background for the pendulum wire. 48. A fluid release port. 49. A mounting location for the pendulum string. 50. The calculated center of the transmitter. The three-dimensional location of the center of an individual transmitter, calculated through image processing techniques. The computer determines this location by combining the discovered centers of the transmitter 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. The head of the calculated transmitter vector. 53. The left camera image during gravity image determination. This is a depiction of the image sensor of the left camera. 54. The right camera image during gravity image determination. This is a depiction of the image sensor of the left camera. 55. The pendulum wire as seen from the left camera

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

[18] . This is the pendulum wire as seen from the camera (projected onto the imaging sensor). 57. The projection plane of the left pendulum wire. This is a mathematical structure. The pendulum wire on the image sensor and the focal point of the left camera

[17] create a plane. 58. The projection plane of the right pendulum wire. This is a mathematical structure. The pendulum wire on the image sensor and the focal point of the left camera

[17] create a plane. 59. Gravity vector determination. Calculated from the intersection of the previously calculated planes

[57] and

[58] . 60. Tightening knob. Used to fasten the positioning module to the upper surface of the couch. 61. A dataset of the positions of the acquired signal transmitters when the collimator rotates through a full 360 - degree rotation while the gantry is at a fixed angle position of approximately - 40 degrees. 62. A dataset of the positions of the acquired signal transmitters when the collimator rotates through a full 360 - degree rotation while the gantry is at a fixed angle position of approximately 0 degrees. 63. A dataset of the positions of the acquired signal transmitters when the collimator rotates through a full 360 - degree rotation while the gantry is at a fixed angle position of approximately + 40 degrees. 64. The calculated center of rotation of the dataset

[63] acquired when the gantry is at + 40. 65. The calculated axis of rotation of the dataset

[63] acquired when the gantry is at + 40. 66. The 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 meeting the requirement that any axis of rotation is involved in at least one point of 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 main assemblies / components of the disclosed system are as follows: Signal transmission module The signal emitting module shown in Figure 8 includes spherical markers

[14] in a fixed direction. These spherical markers reflect or emit light at a frequency detectable by the detector of the camera pod

[10] (Figure 6). The signal emitting module is rigidly attached to the linac via a collimator mounting mechanism (item

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

[0024] Signal reception module / Camera pod The camera pod

[10] (see Figure 9) includes cameras housed in a rigid outer body in a fixed orientation known to each other. The camera pod acquires time-synchronized images and transmits those images to a computer / processor for analysis. Using stereoscopic imaging processing techniques, the location and orientation of an object in real space can be determined from the discovered locations of the objects in each image.

[0025] The camera pod is positioned where it can directly view the attached signal emitting module (Figure 6) on the couch. This orientation allows the signal emitting module to be fully visible during the rotation of the gantry (see Figure 1), the rotation of the collimator (see Figure 2), and the rotation of the couch (see Figure 3).

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

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

[22] , the camera pod

[10] , and the isocenter target module

[21] are mechanically interfaced and connected when attached to the couch, which fixes their relative positions with respect to each other. It is not essential for the positioning module to be attached to the couch. For example, a tripod or a mounting bracket to the ceiling or floor can be used equally efficiently.

[0027] The positioning module

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

[21] relative to the camera pod

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

[27] ,

[28] , and

[29] in FIG. 13) for individually adjusting 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 software coordinate system of the computer / processor. When placed on the collimator rotation axis, the x-ray image of the radiation beam generated by the linac passing through the target can be used to steer the linac's radiation to the center of the spherical target (as a result, the linac's radiation beam and the collimator rotation axis are aligned). A similar process can be used when placing the target at the radiation isocenter. In this case, the x-ray image of the linac radiation passing through the target as the gantry, collimator, and couch rotate will be an individual check of the calculated radiation isocenter position and size. Then, similarly, the aiming line on the target body can also be used to adjust the treatment room patient setup laser to be aligned with the discovered isocenter. The isocenter target module (

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

[22] . It includes a spherical transmitting marker

[25] at a fixed known position. The transmitter can be seen by 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 radiation-opaque target (usually a high-density metal sphere) contained within the target body

[26] .

[0029] The target body

[26] is shown in cross-section in FIG. 16 and includes an implanted radiopaque spherical target

[36] aligned with an external aiming line

[35] on the outer surface. The target body is shown as a rectangular rod having aiming lines on all sides or some sides. For example, other shapes such as a cylindrical tube shape having aiming lines at 90-degree intervals around a tubular body can be used.

[0030] Gravity detection module The gravity module

[37] (FIG. 18) is also connected to the collimator mount

[11] in the same manner and location as the signal transmitting module so as to be imageable by the camera pod

[10] . As can be seen from FIG. 19, it includes a plumb wire

[44] that the camera pod can see through an opening in its outer housing. The plumb wire remains pinned taut by a weight (

[45] in FIG. 20) at its end, and a container of liquid surrounding the weight damps its vibration (see cross-sectional view in FIG. 20).

[0031] Determination of radiation isocenter (without considering the couch) 1. The signal transmitting module

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

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

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

[12] . 2. While the signal receiver

[10] acquires its image pair while the signal transmitting module

[12] rotates, the gantry is fixed at a given position (e.g., 0 degrees downward), and the collimator ([4] in FIG. 2) rotates mechanically. For proper results, the maximum rotation allowed by the linac is preferred, but partial rotation can also be used if full rotation is not possible. 3. For each image pair obtained above, a software registration process is used to calculate the orientation and location of the signal transmitting module (shown as

[52] in FIG. 21). Each time an acquisition is made, the left and right image pairs are sent from the signal receiver

[10] to the computer, and the location and orientation of the signal transmitting module are determined in three dimensions. To achieve this, image processing techniques locate the center of each individual transmitter (see

[51] in FIG. 21) in each image. Then, stereoscopic image processing techniques calculate the three-dimensional coordinates of each individual signal transmitter from its location in the left and right images. Then, a group of the three-dimensional positions of all the individual signal transmitters is registered against the expected individual transmitter locations to calculate the location and direction of the module. 4. Next, the gantry is incremented either clockwise or counterclockwise (e.g., 30 degrees from the previous position). While the gantry is fixed in the new position and the signal receiver

[10] captures an image of the signal transmitting module

[12] , the collimator ( [4] in FIG. 2) rotates again through its mechanical rotation. 5. This process continues until the rotation of the collimator is acquired at a plurality of fixed gantry angles. At least two fixed gantry angles are recommended. 6. For each gantry position, the axis of rotation for all the signal transmitters is calculated. 7. Then, the isocenter is determined as the point in space that minimizes the maximum distance to all the axes calculated from the isocenter.

[0032] Determination of radiation isocenter (without considering the couch) 1. Except for the additional step of measuring the couch rotation axis, follow the process described above to determine the radiation isocenter without using the couch. 2. The couch rotation axis is combined with all the collimator rotation axes. Then, the isocenter is determined as the point in space that minimizes the maximum distance to all the axes calculated from the isocenter.

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

[0034] Determination of gantry rotation axis 1. The signal transmitting module

[12] is attached to the linear accelerator collimator [4] via the collimator mount

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

[10] is placed on the linear accelerator couch [3] at a position to acquire a stereoscopic image of the signal transmitting module

[12] while the gantry is rotating. Maximum rotation is preferred for proper results, but partial rotation may also be used if full rotation is not possible. 2. While the signal receiver

[10] captures images of the signal transmitting module

[12] at regular time intervals, the gantry ([1] in FIG. 1) rotates through its mechanical rotation. An example of acquiring 5 times over a 360-degree rotation is shown in FIG. 22. 3. Each time an acquisition is made, a pair of left and right images is sent from the signal receiver

[10] to the computer, and the location and orientation of the signal transmitting module are determined in three dimensions. To achieve this, image processing techniques locate the center of each individual transmitter (see

[51] in FIG. 21) in each image. Then, stereoscopic image processing techniques calculate the three-dimensional coordinates of each individual signal transmitter from its location in the left and right images. 4. Then, the location of the signal transmitting module from all data acquisitions (see FIG. 24) is fitted to a three-dimensional circular path, and its central axis represents the gantry rotation axis ([2] in FIG. 1).

[0035] Determination of collimator rotation axis 1. The system is configured as described for the determination of the gantry rotation axis. 2. Follow the same steps as described for determining the gantry rotation axis, except that the collimator ([4] in Figure 2) rotates instead of the gantry. Maximum rotation is preferred for proper results, but partial rotation may also 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 for determining the gantry rotation axis.

[0036] Determination of 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 that the couch ([3] in Figure 3) rotates instead of the gantry. Maximum rotation is preferred for proper results, but partial rotation may also 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 for determining the gantry rotation axis.

[0037] Positioning of target markers on the rotation axis 1. Once the rotation axis (of either the gantry, collimator, or couch) is determined, a target marker can be placed at any point along this axis (which is useful for the collimator axis when adjusting the direction of the radiation beam, collectively referred to as "steering"). 2. The isocenter target module

[21] is placed on the positioning module as shown in Figure 11, without obstructing the camera pod

[10] from the setup used to determine the isocenter (thereby ensuring the same coordinate system). 3. The isocenter target module consists of a set of signal emitters (

[25] in Figure 11) that are precisely positioned relative to the radiation-impermeable spherical marker

[36] embedded within the target body

[26] . 4. The signal receiver

[10] is set to capture an image of the signal transmitter

[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. To recap here, these images are analyzed to find the center of each individual transmitter (see

[51] in Figure 21) in three-dimensional coordinates. Next, the position and orientation of the isocenter target module in space are determined, and these found locations are registered against the expected locations of the individual transmitter locations. This registration process is used to determine the orientation and location of the signal transmitter for each acquisition. 5. For each image pair acquisition, the found location of the radiation-opaque spherical marker of the isocenter target module is compared to the axis of the subject, 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 during this process.

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

[10] from the setup used to determine the isocenter (thus ensuring 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 is composed of a set of signal transmitters (

[25] in Fig. 11) that are accurately positioned relative to the radiation-opaque spherical marker

[36] embedded within the target body

[26] . 4. The signal receiver

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

[25] of the isocenter target module. These images are sent to a computer to determine the three-dimensional location of the isocenter target module through the same image processing techniques used to determine the gantry axis. To recap here, these images are analyzed to find the center of each individual transmitter (see

[51] in Fig. 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 relative to the expected locations of the individual transmitter locations. This registration process is used to determine the orientation and location of the signal transmitters for each acquisition. 5. For each image pair acquisition, the found location of the radiation-opaque spherical marker of the isocenter target module is compared to the found isocenter, and the software instructs the user on how to shift the isocenter target module three-dimensionally to align the two positions. Fig. 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 during this process.

[0039] Determination of collimator axis walkout 1. The signal transmission module

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

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

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

[12] while the collimator is rotating. Maximum rotation is preferred for proper results, but partial rotation can also be used if full rotation is not possible. 2. While the signal receiver

[10] captures an image of the signal transmission module

[12] at regular time intervals, the collimator ([1] in FIG. 1) rotates through its mechanical rotation. 3. Upon each acquisition, a pair of left and right images is sent from the signal receiver

[10] to a computer, and the location and orientation of the signal transmission module are determined in three dimensions. To achieve this, the image processing technique locates the center of each individual transmitter (see

[51] in FIG. 21) in each image. Then, the stereoscopic image processing technique calculates the three-dimensional coordinates of each individual signal transmitter from its location in the left and right images. 4. Then, the location of the signal transmission module from all data acquisitions is fitted to a three-dimensional circular path. This fitted circular path represents the ideal path that the transmitter would have followed if the rotation of the collimator had been "ideal", i.e., without any error or deviation in its mechanical rotation. 5. For each measured location of the signal transmission module, the vector between the location and the shortest point on the fitted circular path represents the error at that location. The set of all error vectors represents the walkout of its axis.

[0040] Determination of couch axis walkout 1. The system is configured as described for the determination of the collimator axis walkout. 2. Follow the same steps as described for the determination of the collimator axis walkout, except that the couch ([3] in FIG. 3) rotates instead of the collimator. A maximum rotation is preferred for proper results, but a partial rotation may also be used if a full rotation is not possible. 3. Determine the couch axis walkout following the same image processing and data analysis steps as described in the determination of the collimator axis walkout.

[0041] Adjustment of room laser 1. The target body

[26] of the isocenter target module includes a radiopaque spherical marker

[36] embedded at a position orthogonal and aligned with four sets of aiming lines

[35] marked on the outer surface (see the cross-sectional view of Fig. 16). 2. The room laser can be adjusted by the aiming lines on the outside of the target body to be exactly aligned with the radiopaque sphere (which is not visible) located inside. 3. When the radiopaque sphere

[36] is aligned with the isocenter where it is found (as described in the above step), the left, right, and upper room lasers are manually adjusted to converge on the aiming lines located on the left, right, and upper sides of their target bodies (

[26] in Fig. 11).

[0042] Determination of gravity direction 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 Fig. 17 can be connected to the linac via a collimator mount

[11] . 2. The gravity module shown in cross-section in Fig. 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 vibration of the ball (if there is no damping liquid, the time it takes for the pendulum to stop vibrating would be extremely long). 3. The signal receiving module acquires an image pair of the gravity module and uses signal processing techniques to determine the direction of the pendulum wire in space, which correlates with the direction of the gravity vector. 4. Fig. 28 shows a graphical illustration of the mathematical process used: The pendulum wire

[44] is detected in the left image

[53] and right image

[56] acquired by the camera pod. 5. The pendulum wire line is mathematically projected from the focus of the camera to create the left plane

[55] and right plane

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

[59] .

[0043] Overview of software 1. Initialize the coordinate system correlated with the real-world coordinates of the signal transmission module. 2. Display the location of the signal transmission module in real time (in both 3D view and 2D projection). 3. Present the position and orientation of the signal transmission module when rotation is being recorded. 4. Calculate the direction of gravity within the previously initialized coordinate system. 5. Calculate the rotation axis (gantry, collimator, or couch). 6. Present the position of the calculated axis in 3D view and 2D projection. 7. Calculate the linac mechanical or radiation isocenter based on the calculated rotation axis. 8. Present the linac isocenter in 3D and 2D views. 9. Create a report for presenting the linac rotation axis and linac isocenter. 10. Store the previous dataset to enable post-processing and data review. 11. Use 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 the signal transmission module to the collimator, attaching the signal reception module at a location where the signal transmission module can be seen, determining the rotation axis of the gantry by rotating the gantry while the signal reception module receives signals from the signal transmission module during the rotation of the gantry, determining the rotation axis of the collimator by rotating the collimator while the signal reception module receives signals from the signal transmission module during the rotation of the collimator, and determining the linac mechanical isocenter by processing the received signals regarding the rotation axes of the gantry and collimator.

[0045] The rotation axis of the couch can be determined by attaching the signal receiving module to the couch and rotating the couch while the signal receiving module is in a state of receiving a signal from the signal transmitting module. Next, the linear accelerator mechanical isocenter can be determined by processing the signals received for the gantry, collimator, and the rotation axis of the couch.

[0046] In one embodiment for the linear accelerator mechanical and radiation isocenter determination process, the signal transmitting module emits an optical signal and the signal receiving module receives the optical signal. However, as described, other signal sources can be utilized by other similar techniques such as, for example, infrared imaging, or triangulation of a ranging system including RF ranging, laser ranging, lidar, or sonar, or using a laser beam.

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

[0048] The linear accelerator 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 linear accelerator isocenter. The isocenter target module includes at least one target marker. The isocenter target module can include a radiation-impermeable marker inside the target body and can include a sight line outside the target body. Thereby, the laser can be adjusted by focusing it on the linear accelerator isocenter.

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

[0050] The linear accelerator mechanical isocenter determination process may include using a processor to collect data and utilize software to process that data.

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

[0052] In another embodiment, a signal receiving module is fixed to the collimator, and the signal transmitting module is attached to the couch. The signal receiving module can be attached at any location where the signal transmitter can be seen.

[0053] In another embodiment, the linear accelerator radiation isocenter determination process includes attaching a signal transmitting module to the collimator, attaching a signal receiving module at a location where the signal transmitting module can be seen, rotating the collimator while the gantry is positioned at a first angle while the signal receiver captures the position and orientation of the signal transmitting module, rotating the collimator while the gantry is positioned at a second angle while the signal receiver captures the position and orientation of the signal transmitting module, determining the calculated three-dimensional collimator rotation axis while the gantry is positioned at the first angle and while the gantry is positioned at the second angle, and determining the linear accelerator radiation isocenter using the calculated collimator rotation axis while the gantry is positioned at the first angle and the calculated collimator rotation axis while the gantry is positioned at the second angle.

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

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

[0056] Attaching a signal transmission module to a collimator, attaching a signal reception module at a location where the signal transmission module has a clear line of sight, and determining the rotation axis of the gantry by rotating the gantry while the signal reception module receives a signal from the signal transmission module during rotation of the gantry, a linear accelerator gantry rotation axis determination process is disclosed.

[0057] Attaching a signal transmission module to a collimator, attaching a signal reception module at a location where the signal transmission module has a clear line of sight, and determining the rotation axis of the collimator by rotating the collimator while the signal reception module receives a signal from the signal transmission module during rotation of the collimator, a linear accelerator collimator rotation axis determination process is disclosed.

[0058] Attaching a signal transmission module to a collimator, attaching a signal reception module at a location where the signal transmission module has a clear line of sight, and determining the rotation axis of the collimator by rotating the couch while the signal reception module receives a signal from the signal transmission module during rotation of the gantry, a linear accelerator couch rotation axis determination process is disclosed.

[0059] Attaching a signal transmission module to a collimator, attaching a signal reception module at a location where the signal transmission module has a clear line of sight, determining the path through the space of the signal transmitter during rotation of the collimator by analyzing the signal receiver data acquired during rotation, fitting the calculated position of the signal transmitter to a three-dimensional circle in space, and calculating the error vector between each position and the shortest point to the fitted three-dimensional circle, a process for determining a collimator axis walkout determination process is disclosed.

[0060] Attaching a signal transmitting module to a collimator, attaching a signal receiving module to a location visible to the signal transmitting module, determining a path through the space of the signal transmitter during rotation of the couch by analyzing the signal receiver data acquired during rotation, fitting the calculated position of the signal transmitter to a three-dimensional circle in space, and calculating an error vector between each position and the shortest point to the fitted three-dimensional circle. A process for determining a couch axis walkout is also disclosed.

[0061] While having described preferred embodiments that function to illustrate various concepts, structures, and techniques that are the subject of the present 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 patent scope should not be limited to the described embodiments, but should be limited only by the principles and scope of the following claims. Hereinafter, the matters described in the claims of the original application are appended as they are. [1] A process for determining the mechanical isocenter of a linac, comprising: attaching a signal transmission module to a collimator; attaching a signal reception module to a location where the signal transmission module is visible; determining the rotation axis of the gantry by rotating the gantry while the signal reception module acquires the position of the signal transmission module; determining the rotation axis of the collimator by rotating the collimator while the signal reception module acquires the position of the signal transmission module during rotation of the collimator; determining the mechanical isocenter of the linac by processing the position of the signal transmission module during rotation of the collimator and rotation of the gantry. A process for determining the mechanical isocenter of a linac comprising the above steps. [2] The process for determining the mechanical isocenter of a linac according to [1], further comprising: the signal reception module is attached to a couch, determining the rotation axis of the couch by rotating the couch while the signal reception module acquires the position of the signal transmission module during rotation of the couch, and determining the mechanical isocenter of the linac by processing the position of the signal transmission module with respect to the rotation axes of the gantry, the collimator, and the couch. [3] The signal transmission module emits an optical signal, and the signal reception module receives the optical signal, for the linear accelerator mechanical isocenter determination process according to [1]. [4] The signal transmission module includes at least one marker that reflects or emits light at a specific frequency optimized for the signal reception module, for the linear accelerator mechanical isocenter determination process according to [3]. [5] The signal reception module is a camera pod, for the linear accelerator mechanical isocenter determination process according to [4]. [6] The camera pod is composed of at least two cameras capable of acquiring time-synchronized images for computer analysis, for the linear accelerator mechanical isocenter determination process according to [5]. [7] Further comprising attaching an isocenter target module to a positioning module and positioning the isocenter target module at the mechanical isocenter of the linear accelerator using at least one transmitter marker on the isocenter target module, for the linear accelerator mechanical isocenter determination process according to [1]. [8] The isocenter target module includes a radiation-opaque marker inside the target body, for the linear accelerator mechanical isocenter determination process according to [7]. [9] The isocenter target module includes a sight line outside the target body, for the linear accelerator mechanical isocenter determination process according to [8].

[10] The positioning module includes control for X position, Y position, and Z position, for the linear accelerator mechanical isocenter determination process according to [9].

[11] Further comprising using a processor to collect data and process the data using software, for the linear accelerator mechanical isocenter determination process according to [1].

[12] A process for determining the radiation isocenter of a linear accelerator, attaching a signal transmission module to a collimator, attaching a signal reception module at a location visible to the signal transmission module, rotating the collimator while the gantry is arranged at a first angle while the signal reception module acquires the position of the signal transmission module, Determining the calculated collimator rotation axis from the position of the signal transmission module obtained with the gantry arranged at the first angle; Rotating the collimator while the gantry is arranged at a second angle while the signal reception module captures the position of the signal transmission module; Determining the calculated collimator rotation axis from the position of the signal transmission module obtained with the gantry arranged at the second angle; Determining the linear accelerator radiation isocenter using the calculated collimator rotation axis with the gantry arranged at the first angle and the calculated collimator rotation axis with the gantry arranged at the second angle; A process for determining the radiation isocenter of a linear accelerator comprising the above.

[13] The process for determining the radiation isocenter of a linear accelerator according to

[12] , further comprising rotating the collimator while the gantry is arranged at at least one additional angle while the signal reception module captures the position of the signal transmission module.

[14] The process for determining the radiation isocenter of a linear accelerator according to

[12] , wherein the signal transmission module emits an optical signal and the signal reception module receives the optical signal.

[15] The process for determining the radiation isocenter of a linear accelerator according to

[12] , wherein the signal reception module is attached to a couch.

[16] The process for determining the radiation isocenter of a linear accelerator according to

[12] , further comprising rotating the couch and determining the linear accelerator radiation isocenter using the calculated collimator and the couch axis.

[17] A process for determining the rotation axis of a linear accelerator gantry, comprising: Attaching a signal transmission module to a collimator; Attaching a signal reception module at a location where the signal transmission module can be seen; Determining the rotation axis of the gantry by rotating the gantry while the signal reception module acquires the position of the signal transmission module A process for determining the rotation axis of a linear accelerator gantry comprising the above.

[18] A process for determining the rotation axis of a linear accelerator collimator, comprising: Attaching a signal transmission module to a collimator; Attaching a signal reception module at a location where the signal transmission module can be seen; Determining the rotation axis of the collimator by rotating the collimator while the signal receiving module acquires the position of the signal transmitting module A collimator rotation axis determination process for a linac comprising the above.

[19] A couch rotation axis determination process for a linac, comprising: Attaching a signal transmitting module to the collimator; Attaching a signal receiving module at a location where the signal transmitting module can be seen; Determining the rotation axis of the collimator by rotating the couch while the signal receiving module acquires the position of the signal transmitting module A couch rotation axis determination process for a linac comprising the above.

[20] A gravity vector determination process, comprising: Attaching a gravity module to the collimator; Attaching a camera pod at a location where the gravity module can be seen; Acquiring an image of the location of the gravity module using the camera pod to determine the direction of the gravity vector with respect to the internal coordinate system of the camera pod A gravity vector determination process comprising the above.

[21] A collimator axis walkout determination process, comprising: Attaching a signal transmitting module to the collimator; Attaching a signal receiving module at a location where the signal transmitting module can be seen; Determining the path through the space of the signal transmitting module during rotation of the collimator by analyzing the position of the signal transmitting module; Fitting the calculated position of the signal transmitting module to a three-dimensional circle in space; Calculating the error vector between each position and the shortest point to the fitted three-dimensional circle A collimator axis walkout determination process comprising the above.

[22] A couch axis walkout determination process, comprising: Attaching a signal transmitting module to the collimator; Attaching a signal receiving module at a location where the signal transmitting module can be seen; Determining the path through the space of the signal transmitting module during rotation of the couch by analyzing the position of the signal transmitting module; Fitting the calculated position of the signal transmitting module to a three-dimensional circle in space; Calculating the error vector between each position and the shortest point to the fitted three-dimensional circle A couch axis walkout determination process comprising the above.

Claims

1. A mechanical isocenter determination process for a linear accelerator (LINAC), wherein the mechanical isocenter determination process comprises: Attaching a signal transmitting module to a collimator via a collimator mount, wherein the signal transmitting module is configured to emit an optical signal and functions as a point signal source in a three-dimensional space for the optical signal; Attaching a signal receiving module at a location visible to the signal transmitting module, wherein the signal receiving module is configured to receive the optical signal and includes at least two cameras; While the signal receiving module receives the optical signal emitted by the signal transmitting module and determines the position of the signal transmitting module indicating the position of the point signal source in the three-dimensional space during rotation of the gantry, determining the rotation axis of the gantry by rotating the gantry, wherein the collimator does not rotate while the gantry is rotating; With the gantry in a fixed position, while the signal receiving module receives the optical signal emitted by the signal transmitting module and determines the position of the signal transmitting module indicating the position of the point signal source in the three-dimensional space during rotation of the collimator, determining the rotation axis of the collimator by rotating the collimator; Determining the mechanical isocenter of the linear accelerator in the three-dimensional space using at least the determined rotation axis of the gantry and the determined rotation axis of the collimator; A mechanical isocenter determination process for a linear accelerator, comprising the above steps.

2. The signal receiving module is attached to a couch, and the mechanical isocenter determination process comprises: The signal receiving module further comprises determining the rotation axis of the couch by rotating the couch while receiving an optical signal emitted by the signal transmitting module and determining the position of the signal transmitting module indicating the position of the point signal source in the three-dimensional space during rotation of the couch. Determining the mechanical isocenter of the linear accelerator in the three-dimensional space uses the determined rotation axis of the gantry, the determined rotation axis of the collimator, and the determined rotation axis of the couch. The mechanical isocenter determination process of the linear accelerator according to claim 1, wherein the collimator and the gantry do not rotate while the couch is rotating.

3. The optical signal according to claim 1 is an optical signal of visible light, infrared, or radio frequency. The mechanical isocenter determination process of the linear accelerator.

4. The signal transmitting module according to claim 1 comprises at least one marker that reflects or emits light at a frequency detectable by the signal receiving module. The mechanical isocenter determination process of the linear accelerator.

5. The signal receiving module according to claim 1 is a camera pod. The mechanical isocenter determination process of the linear accelerator.

6. The at least two cameras according to claim 1 are capable of acquiring time-synchronized images for computer analysis. The mechanical isocenter determination process of the linear accelerator.

7. Attaching the isocenter target module to the positioning module, positioning the isocenter target module at the mechanical isocenter of the determined linear accelerator using at least one transmitting marker on the isocenter target module, using the signal receiving module to determine the position of the at least one transmitting marker in the three-dimensional space, and adjusting the position of the isocenter target module until the signal receiving module determines that the position of the at least one transmitting marker in the three-dimensional space is the mechanical isocenter of the linear accelerator. The mechanical isocenter determination process of the linear accelerator according to claim 1, further comprising.

8. The isocenter target module includes a radiation-opaque marker inside the target body. The mechanical isocenter determination process of the linear accelerator according to claim 7.

9. The isocenter target module includes a sight line outside the target body. The mechanical isocenter determination process of the linear accelerator according to claim 8.

10. The positioning module includes control for the X position, Y position, and Z position. The mechanical isocenter determination process of the linear accelerator according to claim 9.

11. Further comprising using a processor to collect data and process the data using software. The mechanical isocenter determination process of the linear accelerator according to claim 1.

12. Determining the mechanical isocenter of the linear accelerator in the three-dimensional space includes determining the intersection of the determined rotation axis of the gantry, the determined rotation axis of the collimator, and the determined rotation axis of the couch. The mechanical isocenter determination process of the linear accelerator according to claim 2.

13. The determined position of the mechanical isocenter of the linear accelerator is the position that minimizes the maximum value of the distance between the position and the determined rotation axis of the gantry, the distance between the position and the determined rotation axis of the collimator, and the distance between the position and the determined rotation axis of the couch. The mechanical isocenter determination process of the linear accelerator according to claim 2.

14. Determining the rotation axis of the gantry further comprises fitting the determined position of the signal transmission module indicating the position of the point signal source in the three-dimensional space during the rotation of the gantry to a three-dimensional circular path having a central axis representing the rotation axis of the gantry. Determining the rotation axis of the collimator further comprises fitting the determined position of the signal transmission module indicating the position of the point signal source in the three-dimensional space during the rotation of the collimator to a three-dimensional circular path having a central axis representing the rotation axis of the collimator. Determining the rotation axis of the couch further comprises fitting the determined position of the signal transmission module indicating the position of the point signal source in the three-dimensional space during the rotation of the couch to a three-dimensional circular path having a central axis representing the rotation axis of the couch. The mechanical isocenter determination process of the linear accelerator according to claim 2.

15. Determining the mechanical isocenter of the linear accelerator in the three-dimensional space comprises at least determining the intersection point between the determined rotation axis of the gantry and the determined rotation axis of the collimator. The mechanical isocenter determination process of the linear accelerator according to claim 1.

16. The determined position of the mechanical isocenter of the linear accelerator is the position that minimizes at least the maximum value of the distance between the position and the determined rotation axis of the gantry and the distance between the position and the determined rotation axis of the collimator. The mechanical isocenter determination process of the linear accelerator according to claim 1.

17. Determining the rotation axis of the gantry further comprises fitting the determined position of the signal transmission module indicating the position of the point signal source in the three-dimensional space during rotation of the gantry to a three-dimensional circular path having a central axis representing the rotation axis of the gantry. Determining the rotation axis of the collimator further comprises fitting the determined position of the signal transmission module indicating the position of the point signal source in the three-dimensional space during rotation of the collimator to a three-dimensional circular path having a central axis representing the rotation axis of the collimator. The mechanical isocenter determination process of the linear accelerator according to claim 1.

Images