Modulated radiation beam alignment for medical linear accelerators.

Abstract

To provide systems and methods for delivering a radiation beam using a linear accelerator (LINAC).SOLUTION: Optimal beam alignment parameters are determined and stored for respective N gantry angles. The beam alignment parameters may adjust current supplied to one or more bending magnets of a LINAC and, thus, change an angle and direction of a radiation beam. An optimal beam alignment parameter for a gantry angle may be determined by adjusting the beam alignment parameter until the center of a radiation field of the radiation beam in a radiation transmission image is at the center of a shadow of a radiation opaque marker, which may be placed at a radiation isocenter. The beam alignment parameters stored for the N gantry angles may be used to adjust beam steering current as a gantry is rotated through any arbitrary gantry angle.SELECTED DRAWING: Figure 5

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001]

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 070,456, filed August 26, 2020, which is incorporated herein by reference in its entirety. [Technical Field]

[0002]

[0002] Technical field to which the invention pertains

[0003] The present invention relates generally to radiation therapy, in which a medical linear accelerator (LINAC) delivers a beam of radiation to a precise point within a patient. [Background technology]

[0003]

[0004] Background Considerations

[0005] 1.1 Mechanical rotation

[0006] Radiation therapy is a type of cancer treatment that uses a beam of intense, high-energy radiation to kill cancer cells. During treatment, as shown in Figures 1 and 2, a gantry 102 of a medical linear accelerator (LINAC) 100 delivers a radiation beam 104 to a precise point (not shown) within a patient supported on a couch 106. During treatment, the gantry 102 of the LINAC 100 rotates to different gantry angles, including, for example, 0 degrees and 180 degrees, as shown in Figures 1 and 2, respectively. The geometric precision of the LINAC mechanical rotation affects the precision of the treatment.

[0004]

[0007] 1.2 Radiation Isocenter

[0008] The radiation isocenter is the point in space where the radiation beams intersect as the gantry rotates. Proper determination of the radiation isocenter point in space can improve the accuracy of patient treatment. If the patient is positioned so that the tumor is located at the radiation isocenter, the radiation beams will be fixed to the tumor through the gantry. If the radiation isocenter is imprecisely defined and / or the tumor is not precisely positioned at the isocenter, high doses of radiation may be delivered to areas other than the tumor, resulting in unwanted and harmful side effects.

[0005]

[0009] 1.3 Gantry rotation mechanical error

[0010] As the gantry 102 of the LINAC 100 rotates, the gantry 102 tends to translate due to its own weight. In many cases, the gantry 102 tends to translate in and out of the ideal gantry plane of rotation. The amount and direction of this translation depends on the gantry angle and the LINAC mechanical design. An example of translation is shown in FIG. 3, which provides a side view of the LINAC 100 showing the gantry 102 at a 0-degree angle and an overlaid view of the gantry 102 at a 180-degree angle. The axes of the radiation beam 104 from the gantry 102 at both the 0-degree and 180-degree angles are shown as dashed lines. The separation between the two axes of the radiation beam 104 is due to the sag of the LINAC gantry, which causes the gantry 102 to translate forward or backward as it rotates. Typically, there is not much that can be done to reduce these mechanical errors, and they are currently accepted as inaccuracies in patient treatment. Summary of the Invention

[0006]

[0011] Embodiments of the present invention may use modulated beam alignment to correct for gantry errors. In some embodiments, a linear accelerator (LINAC) may modulate the beam electromagnetic current at each gantry position to compensate for mechanical errors in the gantry by redirecting the beam so that the central axis of the beam points to the same location in space at all gantry angles.

[0007]

[0012] One aspect of the present invention may provide a method that includes generating a radiation beam using one or more bending magnets and collimators of a linear accelerator (LINAC). The method may include using the LINAC to position a gantry at a first gantry angle. The method may include acquiring, with the gantry positioned at the first gantry angle, a first radiographic image that shows the radiation field of the radiation beam after passing a radiopaque marker. The method may include using the first radiographic image to determine a center of the radiation field of the radiation beam and a center of a shadow of the radiopaque marker in the radiation field of the radiation beam. The method may include using the LINAC to determine that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker. The method may include, if it is determined that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker, adjusting the radiation beam by adjusting beam alignment parameters until it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, and repeating the radiographic image acquisition step and the center determination step using the adjusted radiation beam and a gantry positioned at the first gantry angle, wherein adjusting the beam alignment parameters adjusts currents supplied by the LINAC to one or more bending magnets. If it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, the method may include, if it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, storing the adjusted beam alignment parameters, using the LINAC, as optimal beam alignment parameters for the first gantry angle. The method may include, when the gantry of the LINAC rotates to the first gantry angle, adjusting currents supplied by the LINAC to the one or more bending magnets using the adjusted beam alignment parameters stored as optimal beam alignment parameters for the first gantry angle.

[0008]

[0013] In some aspects, the method may further include positioning a radiopaque marker. In some aspects, the method may further include positioning the radiopaque marker at a radiation isocenter, which may be a point in space where radiation beams generated by the LINAC intersect as the gantry of the LINAC rotates. In some aspects, the method may further include determining the radiation isocenter.

[0009]

[0014] In some embodiments, the method may further include generating a first radiographic image using an electrophoretic display device (EPID) based on the radiation received by the EPID. In some embodiments, the radiopaque marker may be a spherical radiopaque marker. In some embodiments, the radiation field of the radiation beam may be a square radiation beam.

[0010]

[0015] In some embodiments, determining using the LINAC that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker can include determining a distance between the center of the radiation field of the radiation beam and the center of the shadow of the radiopaque marker and determining that the distance is greater than a distance tolerance threshold. In some embodiments, determining using the LINAC that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker can include determining a distance between the center of the radiation field of the adjusted radiation beam and the center of the shadow of the radiopaque marker and determining that the distance is less than a distance tolerance threshold.

[0011]

[0016] In some aspects, the adjusted beam alignment parameters may be stored in a lookup table as the optimal beam alignment parameters for the first gantry angle.

[0012]

[0017] In some aspects, the method may further include using the LINAC to position the gantry at a second gantry angle. In some aspects, the method may further include acquiring, with the gantry positioned at the second gantry angle, a second radiographic image showing the radiation field of the radiation beam after passing through the radiopaque marker. In some aspects, the method may further include using the second radiographic image to determine a center of the radiation field of the radiation beam and a center of the shadow of the radiopaque marker in the radiation field of the radiation beam, and determining, using the LINAC, that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker. In some aspects, if it is determined that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker, the method may further include adjusting the radiation beam by adjusting beam alignment parameters until it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, and repeating the radiographic image acquiring step and the center determining step using the adjusted radiation beam and the gantry positioned at the second gantry angle. In some aspects, adjusting the beam alignment parameters may include adjusting currents supplied by the LINAC to one or more bending magnets. In some aspects, the method may further include, when it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, storing the adjusted beam alignment parameters, using the LINAC, as optimal beam alignment parameters for the second gantry angle. In some aspects, the method may further include, when the gantry of the LINAC rotates to the second gantry angle, adjusting currents supplied by the LINAC to the one or more bending magnets using the adjusted beam alignment parameters stored as optimal beam alignment parameters for the second gantry angle.

[0013]

[0018] In some aspects, the method may further include, for each of the N gantry angles, using a LINAC to position the gantry at a gantry angle among the N gantry angles, determining optimal beam alignment parameters for the gantry angle among the N gantry angles, where the optimal beam alignment parameters adjust currents supplied by the LINAC to one or more bending magnets such that a center of a radiation field of the radiation beam is at a center of the radiopaque marker when the gantry is at the gantry angle among the N gantry angles, and storing the optimal beam alignment parameters for the gantry angle among the N gantry angles. In some aspects, the method may further include adjusting currents supplied by the LINAC to the one or more bending magnets during a rotation of the gantry using the N optimal beam alignment parameters stored for the N gantry angles. In some aspects, the method may further include using a LINAC to determine an equation for determining the beam alignment parameters based on the N optimal beam alignment parameters stored for the N gantry angles, and using the LINAC to adjust, as the gantry rotates, a current supplied by the LINAC to one or more bending magnets based on the equation. In some aspects, the LINAC may use parametric curve fitting or interpolation to determine the equation.

[0014]

[0019] In some aspects, the method may further include using the LINAC to position the collimator at at least a first collimator angle and a second collimator angle. In some aspects, the first radiographic image may be acquired with the gantry positioned at the first gantry angle and the collimator positioned at the first collimator angle. In some aspects, the second collimator angle is different from the first collimator angle. In some aspects, the method may further include acquiring an additional radiographic image showing the radiation field of the radiation beam after passing through the radiopaque marker with the gantry positioned at the first gantry angle and the collimator positioned at the second collimator angle. In some aspects, the first radiographic image and the additional radiographic image may be used to determine a center of the radiation field of the radiation beam. In some aspects, the LINAC may determine the center of the radiation field of the radiation beam by averaging the center of the radiation field in the first radiographic image and the center of the radiation field in the additional radiographic image.

[0015]

[0020] Another aspect of the present invention may provide a linear accelerator (LINAC) including a gantry, one or more bending magnets, a collimator, and a controller. The controller may be configured to cause the LINAC to generate a radiation beam using the one or more bending magnets and the collimator. The controller may be configured to cause the LINAC to position the gantry at a first gantry angle. The controller may be configured to cause the LINAC, with the gantry positioned at the first gantry angle, to acquire a first radiographic image showing a radiation field of the radiation beam after passing a radiopaque marker. The controller may be configured to cause the LINAC to determine, using the first radiographic image, a center of the radiation field of the radiation beam and a center of a shadow of the radiopaque marker in the radiation field of the radiation beam. The controller may be configured to cause the LINAC to determine that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker. The controller may be configured to, if it is determined that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker, cause the LINAC to adjust the radiation beam by adjusting beam alignment parameters until it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, and to repeat the radiographic image acquisition step and the center determination step using the adjusted radiation beam and a gantry positioned at the first gantry angle, where adjusting the beam alignment parameters may adjust currents supplied to one or more bending magnets. The controller may be configured to, if it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, cause the LINAC to store the adjusted beam alignment parameters as optimal beam alignment parameters for the first gantry angle.The controller may be configured to cause the LINAC, when the gantry of the LINAC rotates to a first gantry angle, to adjust the current supplied by the LINAC to one or more bending magnets using the adjusted beam alignment parameters stored as optimal beam alignment parameters for the first gantry angle.

[0016]

[0021] Yet another aspect of the present invention may provide a method that includes generating a radiation beam using one or more bending magnets and collimators of a gantry of a linear accelerator (LINAC). The method may include rotating the gantry to each of N gantry angles. At each of the N gantry angles, the method may include adjusting currents supplied by the LINAC to the one or more bending magnets using beam alignment parameters stored for the gantry angles, where the beam alignment parameters stored for the N gantry angles compensate for mechanical rotation errors of the gantry.

[0017]

[0022] Yet another aspect of the invention may provide a linear accelerator (LINAC) including a gantry and a controller. The gantry may include one or more bending magnets and a collimator. The controller may be configured to generate a radiation beam using the one or more bending magnets and collimators of the gantry. The controller may be configured to rotate the gantry to each of N gantry angles. At each of the N gantry angles, the controller may be configured to adjust current supplied by the LINAC to the one or more bending magnets using beam alignment parameters stored for the gantry angles, where the beam alignment parameters stored for the N gantry angles compensate for mechanical rotation errors of the gantry.

[0018]

[0023] A further aspect of the invention may provide a computer program comprising instructions for adapting a linear accelerator (LINAC) to perform any of the methods described above. A further aspect of the invention may provide a carrier comprising the computer program, the carrier being one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium.

[0019]

[0024] Yet another aspect of the present invention may provide a linear accelerator (LINAC) including a processing circuit and a memory, the memory may include instructions executable by the processing circuit whereby the LINAC operates to perform any of the methods described above.

[0020]

[0025] A further aspect of the present invention may provide a linear accelerator (LINAC) adapted for any of the methods described above.

[0021]

[0026] Yet another aspect of the present invention may provide any combination of the aspects described above.

[0022]

[0027] Further variations encompassed within the systems and methods are described below in the detailed description of the invention.

[0023]

[0028] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate various non-limiting embodiments of the present invention, in which like reference numbers indicate identical or functionally similar elements. [Brief explanation of the drawings]

[0024] [Figure 1]

[0029] FIG. 1 illustrates a medical linear accelerator (LINAC) gantry rotated to a gantry angle of 0 degrees to deliver a radiation beam. [Figure 2]

[0030] FIG. 2 illustrates the gantry of a LINAC rotated through a gantry angle of 180 degrees and delivering a radiation beam. [Figure 3]

[0031] FIG. 3 illustrates the translation of a radiation beam generated by a gantry of a LINAC between when the gantry is at a 0 degree angle and when the gantry is at a 180 degree angle. [Figure 4]

[0032] FIG. 4 is a cross-sectional view of a gantry of a LINAC and a radiation beam emitted by the LINAC, according to some embodiments. [Figure 5]

[0033] FIG. 5 is a side view of a LINAC showing the gantry at angles of 0 and 180 degrees, in which beam steering is used to compensate for mechanical inaccuracies in the rotation of the gantry, according to some embodiments. [Figure 6]

[0034] FIG. 6 illustrates a marker assembly, according to some embodiments. [Figure 7]

[0035] FIG. 7 illustrates a setup for acquiring transmission images to determine whether a radiation beam is aligned, according to some embodiments. [Figure 8]

[0036] FIG. 8 illustrates an unprocessed radiographic image, according to some embodiments. [Figure 9]

[0037] FIG. 9 illustrates a processed radiographic image according to some embodiments. [Figure 10]

[0038] FIG. 10 illustrates the difference between the location of the center of a radiopaque marker and the location of the center of a radiation field, according to some embodiments. [Figure 11]

[0039] FIG. 11 illustrates a process according to some embodiments. [Figure 12]

[0040] FIG. 12 illustrates a controller for a LINAC, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0025] [Parts List]

[0041] 100-Linear accelerator (LINAC)100

[0042] 102-Gantry

[0043] 104-Radiation Beam

[0044] 106-Couch

[0045] 402-Waveguide

[0046] 404 - One or more bending magnets

[0047] 406-Radiation beam in one or more bending magnets

[0048] 408 - The angle at which the radiation beam is directed onto the target

[0049] 410-Collimator

[0050] 412-Central beam axis

[0051] 414-Upper beam edge

[0052] 416-Lower beam edge

[0053] 600-Marker Assembly

[0054] 602-Radiopaque Marker

[0055] 604-Stem

[0056] 606-base

[0057] 902-Radiation Field Boundary

[0058] 904-Marker Boundary

[0059] 1200-LINAC controller

[0060] 1202-Processing circuit (PC)

[0061] 1208-Local Storage Unit

[0062] 1210-Network

[0063] 1241-Computer Program Products (CPP)

[0064] 1242-Computer Readable Medium (CRM)

[0065] 1243-Computer Program (CP)

[0066] 1244-Computer Readable Instructions (CRI)

[0067] 1248-Steering Current Generator

[0068] 1250-Gantrirotator

[0069] 1252-Collimator Rotator

[0070] 1254-Radiation Beam Generator

[0071] 1255 - One or more processors (P)

[0072] 1265-Transmitter (Tx)

[0073] 1267-Receiver (Rx) 1267

[0074] 1268 - Network Interface

[0075] 2.1 Radiation Beam Alignment

[0026]

[0076] FIG. 4 illustrates a cross-sectional view of a gantry 102 of a linear accelerator (LINAC) 100 and a radiation beam 104 emitted by the LINAC 100, according to some embodiments. In some embodiments, as shown in FIG. 4, the radiation beam 104 may include a central beam axis 412, an upper beam edge 414, and a lower beam edge 416. In some embodiments, as shown in FIG. 4, the radiation beam 104 may be created in the LINAC 100 by accelerating electrons in a waveguide 402 and bending these electrons downward through an exit window. In some embodiments, the electrons may be bent (e.g., downward) using one or more bending magnets 404 (e.g., one or more electromagnets). In some embodiments, the one or more bending magnets 404 may allow for changing the angle 408 at which the electron beam 104 is directed onto the target, which also changes the direction the radiation beam 104 faces when it exits a collimator 410 of the LINAC 100. In some aspects, these changes may effectively change the direction of the beam 102 as it travels through the patient during treatment. In some aspects, the magnitude of the radiation beam angle may be controlled by adjusting the current through one or more bending magnets 404. Reference numeral 406 represents the radiation beam within the one or more bending magnets 404.

[0027]

[0077] 2.2 Gantry Error Correction Using Modulated Beam Alignment

[0078] In some embodiments, the LINAC 100 (e.g., a controller of the LINAC) may modulate the beam electromagnet current at each position of the gantry 102 to compensate for any mechanical errors in the gantry 102 that redirect the radiation beam 104 so that the central beam axis 412 points to the same location in space at each gantry angle. FIG. 5 provides a side view of the LINAC 100 showing the gantry 102 at a 0-degree angle with the gantry 102 at a 180-degree angle superimposed. As shown in FIG. 5, when beam steering is used to compensate for mechanical inaccuracies (e.g., mechanical shifts) related to the rotation of the gantry 102, the central beam axis of the radiation beam 104 emitted by the gantry 102 at a 0-degree angle can be converged with the central beam axis of the radiation beam 104 emitted by the gantry 102 at a 180-degree angle. In some embodiments, the radiation beam 102 can converge because the deflection magnet currents for gantry angles of 0 and 180 degrees are selected to align the radiation beam 104 in a direction that forces the radiation beam 104 to converge at a single fixed location in space.

[0028]

[0079] 2.3 Creating an Aligned Beam

[0080] 6 illustrates an example of a marker assembly 600 according to some embodiments. In some embodiments, as shown in FIG. 6, the marker assembly 600 can include a spherical, high-density marker 602 (e.g., made of tungsten), a low-density stem 604 (e.g., made of plastic), and a base 606 for positioning. In some embodiments, the marker 602 can be a radiopaque marker.

[0029]

[0081] In some embodiments, radiation beam 104 may be aligned when the target at which radiation beam 104 is aimed is positioned within the center of the radiation field. FIG. 7 illustrates a setup for acquiring a transmission image (e.g., an X-ray transmission image) to determine whether radiation beam 104 is aligned, according to some embodiments. In some embodiments, as shown in FIG. 7, a marker 602 may be positioned at the target location. In some embodiments, an electrophoretic display device (EPID) 702 may be used to generate a radiographic image of the radiation received by EPID 702. In some embodiments, the radiographic image may be used to determine whether radiation beam 104 is aligned by determining whether the center of the radiation field of radiation beam 104 and the center of marker 602 coincide.

[0030]

[0082] 8 illustrates an example of an unprocessed radiographic image generated by EPID 702, according to some embodiments. In some embodiments, the radiographic image may be an X-ray image. In some embodiments, the dark square region may be created by a square radiation field, and the lighter circular inner shape may be created by the shadow of a radiopaque marker 602 positioned within the radiation field. In some embodiments, as shown in FIG. 8, in the radiographic image, the boundary of the radiation field and the circle created by marker 602 may be clearly visible.

[0031]

[0083] In some embodiments, the LINAC 100 (e.g., a controller of the LINAC 100) can use automatic image processing techniques to determine the boundary of the radiation field and the circle created by the markers 602. In some embodiments, as shown in FIG. 9, the LINAC 100 can detect a boundary 902 of the radiation field and a boundary 904 of the markers 602. In some embodiments, the LINAC 100 (e.g., a controller of the LINAC 100) can calculate the center of the radiation field and the center of the circle using the boundary 902 of the radiation field and the boundary 904 of the circle created by the markers 602. In some embodiments, the LINAC 100 can use the calculated center of the radiation field and the center of the circle to determine a marker error vector. In some embodiments, as shown in FIG. 10, the marker error vector can be the difference between the location of the center of the marker and the location of the center of the radiation field. In some embodiments, if the marker error has a non-zero magnitude, the LINAC beam alignment can be adjusted (e.g., by adjusting the current through one or more bending magnets 404) to move the position of the marker 602 relative to the radiation field until the marker 602 is located in the center of the radiation field where the magnitude of the marker error is minimized.

[0032]

[0084] 2.4 Determination of gantry-dependent beam alignment currents

[0085] FIG. 11 illustrates a process 1100 for determining a gantry-dependent beam alignment current according to some aspects. In some aspects, one or more of the steps of process 1100 may be performed by LINAC 100 (e.g., a controller of LINAC 100). In some aspects, process 1100 may create a look-up table (LUT) with N gantry angle positions as LUT inputs and a beam steering current for that gantry angle as the LUT output. In some aspects, process 1100 may include applying a beam steering current versus a gantry angle when the gantry is at the gantry angle. In some aspects, process 1100 may additionally or alternatively include using a parametric fit at the N measured gantry angles to derive an equation for determining the beam steering current for any gantry angle.

[0033]

[0086] In some aspects, process 1100 may include step 1102 of positioning a radiopaque marker 602 (e.g., a spherical marker). In some aspects, marker 602 may be positioned at a radiation isocenter. In some aspects, the radiation isocenter may be a point in space where radiation beams 104 intersect as gantry 102 of LINAC 100 rotates. In some aspects, marker 602 may be positioned at the radiation isocenter using a room laser, a mechanical front pointer, and / or a mechanical crosshair. In some aspects, the radiation isocenter may be determined and / or marker 602 may be positioned at the determined radiation isocenter in the manner described in U.S. Patent Application No. 16 / 934,586, filed July 21, 2020, and / or U.S. Patent Application No. 16 / 999,693, filed August 21, 2020, both of which are incorporated by reference in their entireties.

[0034]

[0087] In some aspects, the process 1100 may include a step 1104 in which the LINAC 100 generates the radiation beam 104. In some aspects, the LINAC may generate the radiation beam 104 using one or more bending magnets 404 and a collimator 410.

[0035]

[0088] In some aspects, the process 1100 may include a step 1106 in which the LINAC 100 positions the gantry 102 at a first gantry angle.

[0036]

[0089] In some embodiments, the process 1100 may include a step 1106 in which the LINAC 100 positions the collimator 410 at a first collimator angle (eg, 0 degrees).

[0037]

[0090] In some aspects, process 1100 may include step 1108 in which LINAC 100 acquires a radiographic image showing the radiation field of radiation beam 104 after passing through radiopaque marker 602. In some aspects, electrophoretic display device (EPID) 702 may generate the radiographic image based on the radiation received by EPID 702. In some aspects, radiation beam 102 generated using collimator 410 of LINAC 100 may have a square cross-section, and the radiation field may be a square radiation field. In some alternative aspects, radiation beam 102 generated using collimator 410 of LINAC may have a circular cross-section, and the radiation field may be a circular radiation field.

[0038]

[0091] In some aspects, process 1100 may include step 1110 in which LINAC 100 uses the radiographic image to determine the center of the radiation field and the center of the shadow in the radiation field created by radiopaque marker 602. In some aspects, LINAC 100 may use image processing techniques to determine the center of the radiation field in the radiographic image and the center of the shadow in the radiation field in the radiographic image.

[0039]

[0092] In some embodiments, process 1100 may include step 1112, in which LINAC 100 determines whether the center of the radiation field of radiation beam 104 is at the center of radiopaque marker 602 (e.g., within a given tolerance). In some embodiments, determining whether the center of the radiation field of radiation beam 104 is at the center of radiopaque marker 602 may include (i) determining a distance between a determined center of the radiation field in the radiographic image and a determined center of a shadow in the radiation field in the radiographic image, and (ii) determining whether the determined distance is less than a distance tolerance threshold. In some embodiments, the distance tolerance threshold may depend on the type of treatment being performed. In some embodiments, the distance tolerance threshold may be a distance in the range of 0.1 mm to 0.5 mm, for example and not by way of limitation.

[0040]

[0093] In some aspects, if it is determined that the center of the radiation field of radiation beam 104 is not at the center of radiopaque marker 602, process 1100 may proceed from step 1112 to beam alignment adjustment step 1114. In some aspects, beam alignment adjustment step 1114 may include adjusting beam alignment parameters of LINAC 100 to change the direction of the beam. In some aspects, adjusting beam alignment parameters of LINAC 100 may include adjusting current supplied to one or more bending magnets 404. In some aspects, process 1100 may proceed from step 1114 to step 1108 to repeat radiographic image acquisition step 1108, center determination step 1110, and center alignment determination step 1112 with radiation beam 104 adjusted for the adjusted beam alignment parameters.

[0041]

[0094] In some aspects, if it is determined that the center of the radiation field of radiation beam 104 is at the center of radiopaque marker 602, process 1100 proceeds from step 1112 to step 1116, where LINAC 100 stores the beam alignment parameters used when it was determined in step 1112 that the center of the radiation field of radiation beam 104 is at the center of radiopaque marker 602 as the optimal beam alignment parameters for the first gantry angle. In some aspects, the optimal beam alignment parameters for the first gantry angle may be stored in a look-up table (LUT).

[0042]

[0095] In some aspects, process 1100 may include step 1118, in which LINAC 100 determines (e.g., in the LUT) whether any gantry angles remain for which optimal beam alignment parameters have not been determined. In some aspects, if any gantry angles remain, process 1100 may proceed from step 1118 to step 1120, in which LINAC 100 positions gantry 102 at a second (or subsequent) gantry angle. In some aspects, process 1100 may proceed from step 1120 to step 1106. In some aspects, process 1110 may repeat steps 1106, 1108, 1110, 1112, 1114, 1116, and 1118 until there are no more gantry angles for which optimal beam alignment parameters have not been determined. In some aspects, LINAC 100 may determine optimal beam alignment parameters for each of the N gantry angles. In some embodiments, N gantry angles may be equal to the number of gantry angles at which the LINAC 100 can position the gantry 102 (e.g., for a LINAC 100 that can position the gantry 102 at 360 gantry angles, N may be equal to 360, and for a LINAC 100 that can position the gantry 102 at 720 gantry angles, N may be equal to 720). In some alternative embodiments, N gantry angles may be less than the number of gantry angles at which the LINAC 100 can position the gantry 102 (e.g., for a LINAC 100 that can position the gantry 102 at 360 gantry angles, N may be equal to 4, 8, 16, 45, 90, or 180, and for a LINAC 100 that can position the gantry 102 at 720 gantry angles, N may be equal to 4, 8, 16, 45, 90, or 180).

[0043]

[0096] In some aspects, if no gantry angles remain, process 1100 may proceed from step 1118 to step 1122, where LINAC 100 automatically adjusts the beam alignment parameters for each gantry angle based on stored optimal beam alignment parameters (e.g., during a radiation therapy treatment). In some aspects, for a gantry angle that is not one of the N gantry angles for which optimal beam alignment parameters have been determined using radiographic images, LINAC 100 may calculate optimal beam alignment parameters for the gantry angle using one or more of the optimal beam alignment parameters for one or more of the N gantry angles proximate to the gantry angle (e.g., optimal beam alignment parameters for two of the N gantry angles adjacent to the gantry angle) (e.g., using a mathematical process such as, for example and without limitation, averaging or linear or polynomial interpolation). In some embodiments (e.g., in some embodiments where the N gantry angles for which optimal beam alignment parameters have not been determined are fewer than the number of gantry angles at which the LINAC 100 can position the gantry 102), the process 1100 may include the LINAC 100 using the N stored optimal beam alignment parameters for the N measured gantry angles to determine a formula for determining the beam alignment parameter (e.g., beam steering current) for any gantry angle at which the LINAC 100 can position the gantry 102, and using this formula to adjust the beam alignment parameter as the gantry angle changes. In some embodiments, the LINAC 100 may use a mathematical process, such as, by way of example and not limitation, parametric curve fitting or interpolation to determine the formula.

[0044]

[0097] 2.5 Variations for poorly calibrated collimators

[0098] In some aspects, the collimation system of LINAC 100, which defines the radiation field of radiation beam 104, may be poorly calibrated. If the collimation system is poorly calibrated, rotating collimator 410 180 degrees will result in a different field of view location. In some aspects, process 1100 may account for poor calibration of the collimation system by capturing two or more radiographic images for each measured beam alignment parameter. In some aspects, the two or more radiographic images may have different collimator angles (e.g., collimator angles 180 degrees apart). In some aspects, the radiation field center determined in step 1110 may be the average of the radiation field centers found at two or more collimator angles (e.g., 0 degrees and 180 degrees). In some aspects, if collimator 410 is well calibrated, the two or more radiation field centers will be the same, and the average between the two or more radiation field centers will be the same as the radiation field center if only one radiographic image were acquired.

[0045]

[0099] 12 is a block diagram of a controller 1200 of the LINAC 100, according to some embodiments. As shown in FIG. 12, the controller 1200 includes a processing circuit (PC) 1202, which may include one or more processors (P) 1255 (e.g., one or more general-purpose microprocessors and / or one or more other processors, such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), etc.), where these processors may be co-located in a single housing or a single data center, or may be geographically distributed (i.e., the system may be a distributed computing device), and the controller 1200 may communicate with other nodes connected to a network 1210 (e.g., an Internet Protocol (IP) network) to which a network interface 1268 is connected. The PC 1202 may comprise a network interface 1268 comprising a transmitter (Tx) 1265 and a receiver (Rx) 1267 for enabling transmission of data to and reception of data from other nodes, a steering current generator 1248 configured to provide beam steering currents for one or more bending magnets 404, a gantryrotator 1250, a collimator rotator 1252 configured to rotate the collimator 410, a radiation beam generator 1254 configured to generate an electron beam in the waveguide 402, and a local storage unit (a.k.a. "data storage system") 1208, which may include one or more non-volatile storage devices and / or one or more volatile storage devices. In aspects in which the PC 1202 comprises a programmable processor, a computer program product (CPP) 1241 may be provided. In some aspects, the CPP 1241 may include a computer readable medium (CRM) 1242 that stores a computer program (CP) 1243 comprising computer readable instructions (CRI) 1244. In some embodiments, CRM 1242 may be a non-transitory computer-readable medium, such as a magnetic medium (e.g., a hard disk), an optical medium, or a memory device (e.g., a random access memory, a flash memory).In some aspects, the CRI 1244 of the computer program 1243, when executed by the PC 1202, may be configured such that the CRI causes the LINAC 100 to perform the steps described herein (e.g., one or more steps described herein with reference to the flowcharts herein). In other aspects, the controller 1200 may be configured to perform the steps described herein without the need for code. That is, for example, the PC 1202 may consist solely of one or more ASICs. Thus, features of aspects described herein may be implemented in hardware and / or software.

[0046]

[0100] While various embodiments have been described herein, it should be understood that they are presented by way of example only, and not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof may be encompassed by the present disclosure unless otherwise expressly indicated herein or clearly contradicted in content.

[0047]

[0101] Additionally, while the processes described above and illustrated in the figures are shown as a series of steps, this is done for illustrative purposes only, and it is therefore contemplated that some steps may be added, some steps may be omitted, the order of steps may be rearranged, and some steps may be performed simultaneously.

[0048]

[0102] Although preferred embodiments have been described that serve to illustrate various concepts, structures, and techniques that are the subject of this patent, it will be apparent to those skilled in the art that other embodiments incorporating these concepts, structures, and techniques may be used. Accordingly, it is asserted that the scope of this patent should not be limited to the described embodiments, but rather should be limited only by the spirit and scope of the following claims. The following is a summary of the claims as originally filed: [1] Generating a radiation beam using one or more bending magnets and collimators of a linear accelerator (LINAC); positioning a gantry at a first gantry angle using the LINAC; acquiring, with the gantry positioned at the first gantry angle, a first radiographic image indicative of a radiation field of the radiation beam after passing a radiopaque marker; using the first radiographic image to determine a center of the radiation field of the radiation beam and a center of a shadow of the radiopaque marker in the radiation field of the radiation beam; determining, using the LINAC, that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker; if it is determined that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker, adjusting the radiation beam by adjusting beam alignment parameters until it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, and repeating the steps of acquiring the first radiographic image using the adjusted radiation beam and the gantry positioned at the first gantry angle and determining the center, wherein adjusting the beam alignment parameters comprises adjusting a current supplied by the LINAC to the one or more bending magnets; if it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, using the LINAC, storing the adjusted beam alignment parameters as optimal beam alignment parameters for the first gantry angle; adjusting currents supplied by the LINAC to the one or more bending magnets when a gantry of the LINAC rotates to the first gantry angle using the adjusted beam alignment parameters stored as the optimal beam alignment parameters for the first gantry angle; A method for providing the above. [2] The method of [1], further comprising positioning the radiopaque marker. [3] The method of [1], further comprising positioning the radiopaque marker at a radiation isocenter, the radiation isocenter being a point in space where the radiation beams generated by the LINAC intersect when a gantry of the LINAC rotates. [4] The method of [3], further comprising determining the radiation isocenter. [5] The method of [1], further comprising using an electrophoretic display device (EPID) to generate the first radiographic image based on radiation received by the EPID. [6] The method according to [1], wherein the radiopaque marker is a spherical radiopaque marker. [7] The method according to [1], wherein the radiation field of the radiation beam is a square radiation beam. [8] Using the LINAC to determine that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker may include: determining a distance between a center of a radiation field of the radiation beam and a center of a shadow of the radiopaque marker; determining that the distance is greater than a distance tolerance threshold; The method according to [1], comprising: [9] Using the LINAC to determine that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker includes: determining a distance between a center of a radiation field of the adjusted radiation beam and a center of a shadow of the radiopaque marker; determining that the distance is less than a distance tolerance threshold; The method according to [1], comprising:

[10] The method according to [1], wherein the adjusted beam alignment parameters are stored in a look-up table as optimal beam alignment parameters for the first gantry angle.

[11] using the LINAC to position the gantry at a second gantry angle; acquiring, with the gantry positioned at the second gantry angle, a second radiographic image indicative of the radiation field of the radiation beam after passing the radiopaque marker; using the second radiographic image to determine a center of a radiation field of the radiation beam and a center of a shadow of the radiopaque marker in the radiation field of the radiation beam; determining, using the LINAC, that a center of a radiation field of the radiation beam is not at a center of a shadow of the radiopaque marker; if it is determined that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker, adjusting the radiation beam by adjusting beam alignment parameters until it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, and repeating the steps of acquiring the second radiographic image using the adjusted radiation beam and the gantry positioned at the second gantry angle and determining the center, wherein adjusting the beam alignment parameters comprises adjusting a current supplied by the LINAC to the one or more bending magnets; if it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, using the LINAC to store the adjusted beam alignment parameters as optimal beam alignment parameters for the second gantry angle; adjusting currents supplied by the LINAC to the one or more bending magnets when the gantry of the LINAC rotates to the second gantry angle using the adjusted beam alignment parameters stored as the optimal beam alignment parameters for the second gantry angle; The method according to [1], further comprising:

[12] For each of the N gantry angles, positioning the gantry at one of the N gantry angles using the LINAC; determining optimal beam alignment parameters for the gantry angles among the N gantry angles, wherein the optimal beam alignment parameters adjust current supplied by the LINAC to the one or more bending magnets such that a center of a radiation field of the radiation beam is at a center of the radiopaque marker when the gantry is at the gantry angle among the N gantry angles; storing the optimal beam alignment parameters for the gantry angles among the N gantry angles; The method according to [1], further comprising:

[13] The method of

[12] , further comprising adjusting the current supplied by the LINAC to the one or more bending magnets during rotation of the gantry using the N optimal beam alignment parameters stored for the N gantry angles.

[14] using the LINAC to determine a formula for determining beam alignment parameters based on the stored N optimal beam alignment parameters for the N gantry angles; using the LINAC to adjust the current supplied by the LINAC to the one or more bending magnets based on the formula as the gantry rotates; The method according to

[12] , further comprising:

[15] The method of

[14] , wherein the LINAC uses parametric curve fitting or interpolation to determine the equation.

[16] using the LINAC to position the collimator at at least a first collimator angle and a second collimator angle, wherein the first radiographic image is acquired with the gantry positioned at the first gantry angle and the collimator positioned at the first collimator angle, and the second collimator angle is different from the first collimator angle; acquiring an additional radiographic image showing the radiation field of the radiation beam after passing through the radiopaque marker with the gantry positioned at the first gantry angle and the collimator positioned at the second collimator angle; Further provided with the first radiographic image and the additional radiographic image are used to determine a center of a radiation field of the radiation beam. [1] The method described in [1].

[17] The method described in

[16] , wherein the LINAC determines the center of the radiation field of the radiation beam by averaging the center of the radiation field in the first radiographic image and the center of the radiation field in the additional radiographic image.

[18] A linear accelerator (LINAC), The gantry and one or more bending magnets; A collimator; Controller and wherein the controller generating a radiation beam using the one or more bending magnets and the collimator; positioning the gantry at a first gantry angle; acquiring, with the gantry positioned at the first gantry angle, a first radiographic image indicative of a radiation field of the radiation beam after passing a radiopaque marker; determining a center of a radiation field of the radiation beam and a center of a shadow of the radiopaque marker in the radiation field of the radiation beam using the first radiographic image; determining that a center of a radiation field of the radiation beam is not at a center of a shadow of the radiopaque marker; if it is determined that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker, adjusting the radiation beam by adjusting beam alignment parameters until it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, and repeating the steps of acquiring the first radiographic image using the adjusted radiation beam and the gantry positioned at the first gantry angle and determining the center, wherein adjusting the beam alignment parameters is adjusting current supplied to the one or more bending magnets; if it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, storing the adjusted beam alignment parameters as optimal beam alignment parameters for the first gantry angle; adjusting currents supplied by the LINAC to the one or more bending magnets when a gantry of the LINAC rotates to the first gantry angle using the adjusted beam alignment parameters stored as the optimal beam alignment parameters for the first gantry angle; The LINAC is configured to perform the above.

[19] generating a radiation beam using one or more bending magnets and collimators of a gantry of a linear accelerator (LINAC); rotating the gantry to each of N gantry angles; at each of the N gantry angles, adjusting current supplied by the LINAC to the one or more bending magnets using beam alignment parameters stored for the gantry angle, wherein the beam alignment parameters stored for the N gantry angles compensate for mechanical rotation errors of the gantry. A method comprising:

[20] A linear accelerator (LINAC), a gantry including one or more bending magnets and a collimator; Controller and wherein the controller generating a radiation beam using the one or more bending magnets and the collimator of the gantry; rotating the gantry to each of N gantry angles; at each of the N gantry angles, adjusting current supplied by the LINAC to the one or more bending magnets using beam alignment parameters stored for the gantry angle, wherein the beam alignment parameters stored for the N gantry angles compensate for mechanical rotation errors of the gantry. A LINAC is configured to perform

Claims

1. generating a radiation beam using one or more bending magnets and collimators of a linear accelerator (LINAC); positioning a gantry at a first gantry angle using the LINAC; acquiring, with the gantry positioned at the first gantry angle, a first radiographic image indicative of a radiation field of the radiation beam after passing a radiopaque marker; using the first radiographic image to determine a center of the radiation field of the radiation beam and a center of a shadow of the radiopaque marker in the radiation field of the radiation beam; determining that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker; if it is determined that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker, adjusting the radiation beam by adjusting beam alignment parameters until it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, and repeating the steps of acquiring the first radiographic image using the adjusted radiation beam and the gantry positioned at the first gantry angle and determining the center, wherein adjusting the beam alignment parameters is adjusting a current supplied by the LINAC to the one or more bending magnets; if it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, storing the adjusted beam alignment parameters as optimal beam alignment parameters for the first gantry angle; adjusting the current supplied by the LINAC to the one or more bending magnets when the gantry of the LINAC rotates to the first gantry angle using the adjusted beam alignment parameters stored as the optimal beam alignment parameters for the first gantry angle; A method for providing the above.

2. The method of claim 1 , further comprising positioning the radiopaque marker.

3. 10. The method of claim 1, further comprising positioning the radiopaque marker at a radiation isocenter, the radiation isocenter being a point in space where radiation beams generated by the LINAC intersect as the gantry of the LINAC rotates.

4. The method of claim 3 further comprising determining the radiation isocenter.

5. The method of claim 1 , further comprising using an electrophoretic display device (EPID) to generate the first radiographic image based on radiation received by the EPID.

6. The method of claim 1 , wherein the radiopaque marker is a spherical radiopaque marker.

7. The method of claim 1 , wherein the radiation field of the radiation beam is a square radiation beam.

8. Determining that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker comprises: determining a distance between a center of the radiation field of the radiation beam and a center of the shadow of the radiopaque marker; determining that the distance is greater than a distance tolerance threshold; The method of claim 1 , comprising:

9. Determining that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker comprises: determining a distance between a center of the radiation field of the adjusted radiation beam and a center of the shadow of the radiopaque marker; determining that the distance is less than a distance tolerance threshold; The method of claim 1 , comprising:

10. The method of claim 1 , wherein the adjusted beam alignment parameters are stored in a look-up table as the optimal beam alignment parameters for the first gantry angle.

11. positioning the gantry at a second gantry angle using the LINAC; acquiring, with the gantry positioned at the second gantry angle, a second radiographic image indicative of the radiation field of the radiation beam after passing the radiopaque marker; using the second radiographic image to determine a center of the radiation field of the radiation beam and a center of a shadow of the radiopaque marker in the radiation field of the radiation beam; determining that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker; if it is determined that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker, adjusting the radiation beam by adjusting beam alignment parameters until it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, and repeating the steps of acquiring the second radiographic image using the adjusted radiation beam and the gantry positioned at the second gantry angle and determining the center, wherein adjusting the beam alignment parameters comprises adjusting the current supplied by the LINAC to the one or more bending magnets; if it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, storing the adjusted beam alignment parameters as optimal beam alignment parameters for the second gantry angle; adjusting the current supplied by the LINAC to the one or more bending magnets when the gantry of the LINAC rotates to the second gantry angle using the adjusted beam alignment parameters stored as the optimal beam alignment parameters for the second gantry angle; The method of claim 1 further comprising:

12. For each of the N gantry angles, using the LINAC to position the gantry at a gantry angle among the N gantry angles; determining an optimal beam alignment parameter for the certain gantry angle among the N gantry angles, wherein the optimal beam alignment parameter adjusts the current supplied by the LINAC to the one or more bending magnets such that a center of the radiation field of the radiation beam is located at a center of the radiopaque marker when the gantry is at the certain gantry angle among the N gantry angles; storing the optimal beam alignment parameters for the one gantry angle among the N gantry angles; The method of claim 1 further comprising:

13. 13. The method of claim 12, further comprising adjusting the current supplied by the LINAC to the one or more bending magnets during a rotation of the gantry using the N optimal beam alignment parameters stored for the N gantry angles. determining a formula for determining beam alignment parameters based on the N optimal beam alignment parameters stored for the N gantry angles; using the LINAC to adjust the current supplied by the LINAC to the one or more bending magnets based on the formula as the gantry rotates; The method of claim 12 further comprising:

15. The method of claim 14 , wherein the LINAC uses parametric curve fitting or interpolation to determine the equation.

16. using the LINAC to position the collimator at at least a first collimator angle and a second collimator angle, wherein the first radiographic image is acquired with the gantry positioned at the first gantry angle and the collimator positioned at the first collimator angle, and the second collimator angle is different from the first collimator angle; acquiring an additional radiographic image showing the radiation field of the radiation beam after passing through the radiopaque marker with the gantry positioned at the first gantry angle and the collimator positioned at the second collimator angle; Further provided with the first radiographic image and the additional radiographic image are used to determine the center of the radiation field of the radiation beam. The method of claim 1.

17. The method described in claim 16, wherein the center of the radiation field of the radiation beam is determined by averaging the center of the radiation field in the first radiographic image and the center of the radiation field in the additional radiographic image.

18. A linear accelerator (LINAC), The gantry and one or more bending magnets; A collimator; Controller and wherein the controller generating a radiation beam using the one or more bending magnets and the collimator; positioning the gantry at a first gantry angle; acquiring, with the gantry positioned at the first gantry angle, a first radiographic image indicative of a radiation field of the radiation beam after passing a radiopaque marker; using the first radiographic image to determine a center of the radiation field of the radiation beam and a center of a shadow of the radiopaque marker in the radiation field of the radiation beam; determining that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker; if it is determined that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker, adjusting the radiation beam by adjusting beam alignment parameters until it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, and repeating the steps of acquiring the first radiographic image using the adjusted radiation beam and the gantry positioned at the first gantry angle and determining the center, wherein adjusting the beam alignment parameters is adjusting current supplied to the one or more bending magnets; if it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, storing the adjusted beam alignment parameters as optimal beam alignment parameters for the first gantry angle; adjusting the current supplied by the LINAC to the one or more bending magnets when the gantry of the LINAC rotates to the first gantry angle using the adjusted beam alignment parameters stored as the optimal beam alignment parameters for the first gantry angle; The LINAC is configured to cause the LINAC to perform the following:

19. The controller positioning the gantry at a second gantry angle; acquiring, with the gantry positioned at the second gantry angle, a second radiographic image indicative of the radiation field of the radiation beam after passing the radiopaque marker; using the second radiographic image to determine a center of the radiation field of the radiation beam and a center of a shadow of the radiopaque marker in the radiation field of the radiation beam; determining that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker; if it is determined that the center of the radiation field of the radiation beam is not at the center of the shadow of the radiopaque marker, adjusting the radiation beam by adjusting beam alignment parameters until it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, and repeating the steps of acquiring the second radiographic image using the adjusted radiation beam and the gantry positioned at the second gantry angle and determining the center, wherein adjusting the beam alignment parameters comprises adjusting the current supplied by the LINAC to the one or more bending magnets; if it is determined that the center of the radiation field of the adjusted radiation beam is at the center of the shadow of the radiopaque marker, storing the adjusted beam alignment parameters as optimal beam alignment parameters for the second gantry angle; when the gantry of the LINAC rotates to the second gantry angle, adjusting the current supplied by the LINAC to the one or more bending magnets using the adjusted beam alignment parameters stored as the optimal beam alignment parameters for the second gantry angle; 20. The LINAC of claim 18, further configured to cause the LINAC to:

20. The controller, for each of the N gantry angles, positioning the gantry at a gantry angle among the N gantry angles; determining an optimal beam alignment parameter for the certain gantry angle among the N gantry angles, wherein the optimal beam alignment parameter adjusts the current supplied by the LINAC to the one or more bending magnets such that a center of the radiation field of the radiation beam is located at a center of the radiopaque marker when the gantry is at the certain gantry angle among the N gantry angles; storing the optimal beam alignment parameters for the one gantry angle among the N gantry angles; 20. The LINAC of claim 18, further configured to cause the LINAC to:

Images