Device for fast cone-beam tomography and extended SAD imaging in radiation therapy

Abstract

A cone-beam computed tomography (CBCT) system employs a large area detector and a cone-beam radiation source to allow acquisition of projection images at approximately 180 degrees plus a fan angle, thereby providing a complete data set for CBCT reconstruction to generate an image volume with a field of view (FOV) of at least about 20 centimeters.

Description

Technical Field

[0001] The present disclosure relates generally to radiation imaging and therapy. In particular, various embodiments of a cone-beam computed tomography (CBCT) system including a large or very large image detector and a radiotherapy machine including the CBCT system are described. Background Art

[0002] Cone-beam computed tomography is known and has proven to be an invaluable tool for many clinical applications. When performing CBCT, a cone-beam radiation source and an image detector rotate around an object to acquire multiple projection images. Computer software reconstructs the acquired projection images to generate tomographic images, which can be displayed or visualized in two-dimensional (2D) image slices or three-dimensional (3D) image volumes of the object.

[0003] Image artifacts and distortions in the reconstructed images are common in CBCT. Some of the most severe image artifacts in CBCT are caused by patient motion or motion of internal anatomical structures. Such motion may occur randomly in time and at different anatomical locations. Some motion is periodic, some is sporadic, and some is just a slow drift. One way to overcome motion artifacts is to acquire projection images quickly so that potential motion during acquisition can be minimized. This approach is popular in diagnostic CT. However, due to the system design of radiotherapy machines, such as heavy gantries, rotational constraints, and collision avoidance, fast scanning as used in diagnostic CT has not yet been implemented on radiotherapy machines.

[0004] There are instances where the target volume cannot be placed in the isocenter of the radiotherapy machine, and when the target volume is placed offset from the isocenter, the standard detector may be too small to cover the target volume. One approach is to move the detector laterally out during treatment to image the target volume. This approach may help for treatments that utilize a stationary gantry. For treatments that utilize a rotating gantry (such as in volumetric modulated arc therapy (VMAT), ), intensity modulated radiation therapy (IMRT), stereotactic radiosurgery (SRS), stereotactic body radiation therapy (SBRT), etc.), the lateral offset method may leave the target volume invisible or untrackable for certain gantry angles.

[0005] Therefore, there is a general need for improved CBCT technology. It would be desirable to provide a CBCT system for radiation therapy that allows for rapid data acquisition to reduce image artifacts. It would also be desirable to provide a CBCT system for radiation therapy that allows for monitoring or tracking of deviations in target volume positioning from the isocenter of a radiation therapy machine at all gantry angles. Summary of the Invention

[0006] An exemplary cone-beam computed tomography (CBCT) system is provided. The CBCT system includes a source operable to generate a cone beam of radiation, and an area detector operable to acquire projection images of an object while the object is irradiated by the cone beam of radiation. The source is rotatable about an axis, and the area detector is rotatable synchronously with the source. The area detector and the source are configured to enable acquisition of multiple projection images at approximately 180 degrees plus a fan angle of the cone beam to provide a complete data set for CBCT reconstruction to generate an image volume having a field of view (FOV) of at least approximately 20 centimeters.

[0007] An example radiation therapy system is provided. The radiation therapy system includes a first source rotatable about an axis and operable to generate radiation suitable for treatment; a second source operable to generate radiation suitable for imaging; and an area detector operable to acquire an image of the subject while the subject is irradiated with radiation from the second source. The area detector and the second source are synchronously rotatable and configured to acquire an image of the subject at any angle of the first source, including a reference volume located at least approximately 10 centimeters from the axis.

[0008] An example system is provided. The system includes a source operable to generate a cone beam of radiation, and an area detector disposed opposite the source, the area detector operable to acquire a projected image of an object when irradiated by the cone beam of radiation. The area detector includes a planar plate imager having an active detection area having a first dimension ranging from 54 cm to 105 cm and a second dimension ranging from 43 cm to 86 cm.

[0009] This Summary is provided to introduce selected embodiments in a simplified form and is not intended to identify key features or essential characteristics of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. Selected embodiments are presented to provide the reader with a brief overview of some possible forms the invention may take and are not intended to limit the scope of the invention. Other aspects and embodiments of the present disclosure are described in the Detailed Description. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] These and various other features and advantages of the present disclosure will be better understood from the following detailed description and appended claims read in conjunction with the accompanying drawings, in which:

[0011] Figure 1 An example radiation system according to an embodiment of the present disclosure is depicted.

[0012] Figure 2 The acquisition of projection images using a conventional CBCT system is illustrated.

[0013] Figure 3 Illustrated is the acquisition of projection images using an example CBCT system, according to an embodiment of the present disclosure.

[0014] Figure 4A A conventional radiotherapy machine equipped with a CBCT system comprising a detector centrally located on the beam axis is depicted.

[0015] Figure 4B A conventional radiotherapy machine equipped with a CBCT system having detectors that are laterally positioned offset from the beam axis is depicted.

[0016] Figures 5A-5D A radiation therapy machine equipped with a CBCT system according to an embodiment of the present disclosure is depicted. Figure 5A An extended source-to-axis distance (SAD) application is shown, wherein the CBCT system performs image acquisition while radiation for treatment is delivered at a 0 degree gantry angle; Figure 5B Image acquisition at a 50-degree gantry angle is shown; Figure 5C shows image acquisition at a 170 degree gantry angle; and Figure 5D Image acquisition at a 240 degree gantry angle is shown. DETAILED DESCRIPTION

[0017] refer to Figure 1-5D, describes a CBCT system and a radiation therapy machine including a CBCT system. In general, an example CBCT system includes a cone-beam radiation source and an area detector, the area detector operable to acquire projection images of a large object, or operable to acquire projection images encompassing a reference volume located away from the isocenter of the system. The area detector and cone-beam radiation source are capable of acquiring projection images at approximately 180 degrees plus a fan angle to provide a complete data set for CBCT reconstruction to generate an image volume having a field of view (FOV) of at least approximately 20 centimeters. Alternatively or additionally, the area detector and cone-beam radiation source are capable of acquiring projection images encompassing a reference volume located approximately 10 centimeters or more from the isocenter of the system at any gantry angle. As used herein, the term "gantry angle," which may be used interchangeably with the term "angle of the irradiation source," refers to the angle between a vertical line passing through the isocenter of the radiation system and a line passing through the isocenter and the radiation source.

[0018] In order to image large-scale objects (e.g., large anatomical structures in a patient), a conventional radiotherapy machine equipped with a CBCT system needs to rotate the detector and imaging source in a full rotation (360 degrees) to obtain the complete data set required for CBCT reconstruction. Figure 2 As shown in , in conventional imaging mode, the detector is offset with respect to the imaging source so that it can cover the complete anatomy in a full rotation. Figure 3 As shown in , according to an embodiment of the present disclosure, a large area detector and a cone beam imaging source are used to cover the entire anatomical structure that needs to be scanned. Since the area detector is large enough, half a rotation plus the beam fan angle should be sufficient to acquire a complete data set for CBCT reconstruction. This reduces the acquisition time by about half and therefore reduces the chance of patient and anatomical structure movement during image acquisition. As a result, image artifacts caused by patient or anatomical structure movement are minimized or significantly reduced. Any other optimizations such as faster rotation of the source and detector can further improve the imaging results. This optimization can bring the scan time into a range where breath holding techniques such as deep inspiration breath hold (DIBH) are possible. Applying the DIBH technique can further reduce patient motion and in some cases eliminate motion.

[0019] There are instances where the target volume is not placed at the isocenter of the radiation therapy machine. For stereotactic treatments such as SRS or SBRT, the radiation dose is delivered in high dose fractions. It is important to ensure that the patient's anatomy does not move during treatment. Motion of the target and organs at risk (OARs) is more likely to occur with the extended treatment times required for high dose treatments. Since the dose per fraction is significantly higher than in conventional treatments, any positional error of the target or organ is more serious. Therefore, it is important to monitor the target, organs at risk, and reference structures or surrogates such as the diaphragm during radiation exposure. In this disclosure, the term "reference volume" may be used to refer to a volume that includes a target such as tumor tissue, organs at risk, reference structures, or surrogates as defined by the treatment planner. As Figure 4A As shown in , in a conventional radiotherapy machine equipped with a CBCT system, when the detector is centered, the reference volume may not be within the field of view (FOV). Figure 4B As shown in , the reference volume will not be visible at certain gantry angles. Advanced treatment techniques often use a rotating gantry to optimize dose distribution, such as in VMAT, IMRT, etc. Therefore, the reference volume may not be visible during most of the treatment. Figures 5A-5D As shown in , a radiotherapy machine equipped with a CBCT system according to an embodiment of the present disclosure can eliminate this problem so that a reference volume positioned away from the isocenter can be observed during the complete delivery process of the radiation used for treatment, which is described in more detail below.

[0020] refer to Figure 1 , an example CBCT system according to various embodiments of the present disclosure is now described. It should be noted that the CBCT system of the present disclosure can be implemented in a treatment system, a diagnostic system, a simulation system, a research and development system, or any other appropriate radiation system that includes imaging functionality. For example, embodiments of the present disclosure can be practiced in a radiation therapy machine that includes a radiation source that can operate at a megavolt voltage (MV) level (e.g., 4 to 20 VM) to produce radiation suitable for disease treatment. Thus, embodiments of the present disclosure can include a radiation therapy system suitable for performing intensity modulated radiation therapy (IMRT) or cubic modulated arc therapy (VMAT), wherein treatment delivery is monitored, supervised, or guided using the CBCT system of the present disclosure. Embodiments of the present disclosure can also include a radiation therapy system suitable for performing stereotactic radiation therapy (SRS) or stereotactic body radiation therapy (SBRT), wherein a reference volume can be viewed and tracked at any gantry angle throughout the treatment period. Embodiments of the CBCT system of the present disclosure can also be used to assist in patient placement, patient verification, and treatment planning.

[0021] like Figure 1 As shown, the example CBCT system 100 generally includes a radiation source 102, a regional detector 104, and an image processing device 106. The operation of the radiation source 102, the regional detector 104, and the image processing device 106 can be controlled by a computer and control system 108. The computer and control system 108 includes one or more displays (not shown) for displaying radiographic, fluoroscopic, or tomographic images generated by the system 100. A support device 110 (e.g., a patient support couch) can position an object 112, such as a patient or a portion of a patient, between the source 102 and the regional detector 104 to receive radiation for imaging.

[0022] Source 102 is operable to generate a cone beam 116 of radiation. As used herein, the term "cone beam" includes reference to a beam shaped in a conical manner or in an angular pyramidal manner. The shape and size of cone beam 116 can be determined by various collimation devices, such as a collimator module, a multi-leaf collimator (MLC), and the like. Cone beam 116 has an opening angle(s), which can be defined by a first fan angle in a first reference plane and a second fan angle in a second reference plane perpendicular to the first reference plane. By way of example, the opening angle of cone beam 116 can be referenced using two dimensions of flat panel imager 104. As used in this disclosure, the term "fan angle" refers to the opening angle of the beam in a reference plane perpendicular to the axis about which the source generating the beam rotates. Cone beam 116 has a beam axis 117, a central beam line passing through source 102 and the isocenter 101 of system 100. Area detector 104 can be centrally positioned by aligning the center of its active detection area with beam axis 117. Alternatively, the area detector 104 may be positioned laterally offset from the beam axis 117 .

[0023] The area detector 104 is operable to acquire a projection image of the object 112 as it is irradiated by the cone beam 116. The area detector 104 may include a flat panel imager comprising a plurality of detecting elements arranged in rows and columns forming an active detection area. The exemplary detector 104 comprises a 54 x 43 cm 2 Another example detector 104 includes an 86 x 43 cm active detection area. 2 Another example detector 104 includes an 86×65 cm active detection area. 2 The active detection area of ​​the further exemplary detector 104 comprises a 105 x 86 cm 2Detector 104 may include an active detection area having a size of approximately 54 centimeters or greater, or approximately 86 centimeters or greater, or a size ranging from approximately 54 to approximately 105 centimeters. Detector 104 may include an active detection area having a first size ranging from approximately 54 centimeters to approximately 105 centimeters and a second size ranging from approximately 43 centimeters to approximately 86 centimeters.

[0024] According to certain embodiments of the present disclosure, the area detector 104 can be designed and manufactured as a single imager comprising a plurality of detection elements arranged in rows and columns. Alternatively, the area detector can be constructed by tiling or combining two or more sensor discs or panels of standard sizes available from various manufacturers. The two or more sensor discs or panels can be arranged adjacent to each other or arranged with some overlap and enclosed in a housing. In combining two or more sensor panels to construct the area detector, when positioned in a CBCT system, the tiled or overlapping subareas are preferably located away from the middle of the combined active detection area or away from the isocenter. Artifacts caused by the tiling or overlapping of the sensor panels can be corrected or calibrated by computer software.

[0025] Various area detectors and methods of making the same are described in U.S. application Ser. No. 15 / 978,924, entitled “Method for Fabricating Pixelated Scintillators,” filed May 14, 2018. U.S. application Ser. No. 15 / 978,924 is incorporated herein by reference in its entirety.

[0026] The area detector 104 and the source 102 can move or rotate synchronously and acquire projection images of the object 112 from multiple angles. The area detector 104 and the source 102 can be supported or carried by a movable or rotatable gantry 114. Alternatively or additionally, the area detector 104 and the source 102 can be supported or carried by separate arm structures and move synchronously. The gantry 114 can include a ring gantry, a C-arm gantry, or a robotic arm gantry that is operable to synchronously rotate the source 102 and the area detector 104. Alternatively or additionally, the support device 110 can position the object 112 relative to the source 102 and the area detector 104 with multiple degrees of freedom (e.g., horizontal and / or vertical translation and / or rotation about various axes) before or during acquisition of the projection images. In certain embodiments of the present disclosure, the area detector 104 can be built into or attached to the support device 110, for example, a patient support bed. This can be advantageous in radiographic imaging for diagnostic applications where a large field of view (FOV) is required, for example, for the spine, skeleton, the entire body, etc. Placing a large area detector in the support bed can improve the handling of the detector by eliminating or reducing the risk of damage to the detector 104 when it is carried around as is currently the case with many digital radiography systems. As opposed to having the detector mechanically adjusted to the imaged patient or anatomy in the patient, the user can select a region of interest (ROI) on the area detector and image only the portion of the body of interest. In some embodiments, the area detector 104 can be mounted on a stand to allow the patient to sit or stand during the acquisition of the projection images.

[0027] The image processing device 106 may include a computer 118 and software 120 designed to reconstruct tomographic images based on the projection images acquired by the area detector 104 and the source 102. The reconstruction software 120 is known in the art and includes standard CBCT reconstruction software based on filtered backprojection techniques and iterative CBCT (iCBCT) reconstruction software based on algebraic reconstruction techniques. CBCT reconstruction generally requires projection images of the object over a range of 180 degrees plus the beam fan angle. The CBCT reconstruction volume or image volume refers to a volumetric space, typically cylindrical or spherical, within which tomographic images can be reconstructed based on the projection images. The diameter of the reconstruction volume is often referred to as the field of view (FOV). In practice, the FOV of the reconstruction volume corresponds to or covers at least the size of the object to be imaged. The FOV can be determined by data from the projection images acquired by the CBCT system and, if the distance between the source and the area detector is predetermined, can typically be determined by the size of the CBCT system's area detector and cone beam.

[0028] According to certain embodiments of the present disclosure, the area detector 104 and the cone-beam source 102 are configured to acquire projection images of a complete dataset for CBCT reconstruction at approximately 180 degrees plus the beam fan angle to provide an image volume having a FOV of at least about 20 centimeters or greater. This allows for rapid acquisition of the dataset with reduced image artifacts. Large anatomical structures may have a size of about 20 centimeters or greater, or about 30 centimeters or greater, or about 35 centimeters or greater, or about 40 centimeters or greater, or ranging from about 20 centimeters to about 50 centimeters. According to certain embodiments of the present disclosure, the area detector 104 and the cone-beam source 102 may be configured to acquire projection images at half a rotation plus the beam fan angle to provide a complete dataset for CBCT reconstruction, generating an image volume having a FOV of about 20 centimeters or greater, or about 30 centimeters or greater, or about 35 centimeters or greater, or about 40 centimeters or greater, or ranging from about 20 centimeters to about 50 centimeters. This is in contrast to conventional CBCT systems, with which the maximum size of an object that can be covered is typically about or less than 20 centimeters, where a complete data set for CBCT reconstruction is acquired at half a rotation plus a fan angle. Alternatively or additionally, according to certain embodiments of the present disclosure, the area detector 104 and the cone-beam source 102 can be configured to acquire projection images that cover a reference volume positioned about 10 centimeters or more, or about 15 centimeters or more, or about 17.5 centimeters or more, or about 20 centimeters or more from the isocenter at any gantry angle within 360 degrees, or a reference volume positioned from about 10 to about 25 centimeters from the isocenter at any gantry angle.

[0029] Now refer to Figure 2-3 , a CBCT system according to an embodiment of the present disclosure allows for rapid acquisition of projection images of large objects for CBCT reconstruction. For comparison purposes, Figure 2 The conventional CBCT system 200 is shown for obtaining projection images of a large object. The conventional CBCT system 200 includes a kV source 202 and a 43×43 cm 2The image detector 204 is sized. The image detector 204 is laterally offset from the beam axis 206 and positioned 150 centimeters from the kV source 202. To acquire projection images of a large object 208 (e.g., approximately 50 centimeters in size) for CBCT reconstruction, the image detector 204 and the kV source 202 begin scanning from a peripheral portion of the object 208. The object 208 must be scanned 360 degrees in order to acquire a complete data set for CBCT reconstruction. Reference numeral 210 indicates an image volume reconstructed based on the projection images of the object 208 acquired by the CBCT system 200. A full 360-degree rotation requires a long time, which increases the chance of patient motion and, therefore, the likelihood of image artifacts.

[0030] Figure 3 The acquisition of projection images of a large object using an example CBCT system 300 according to an embodiment of the present disclosure is illustrated. The example CBCT system 300 includes a kV source 302 and a 3D imager having a size of, for example, 86 x 43 cm. 2 302. The image detector 304 is positioned centrally on the beam axis 306 and approximately 150 cm from the kV source 302. To acquire projection images of a subject 308 (e.g., approximately 50 cm in diameter) for CBCT reconstruction, a scan of the subject 308 at approximately 180 degrees plus a fan angle (alpha) is sufficient to acquire a complete data set for CBCT reconstruction. Reference numeral 310 indicates an image volume reconstructed based on the projection images of the subject 308 acquired by the CBCT system 300 of the present disclosure. The ability to acquire a complete data set for a large subject in approximately half a rotation plus a fan angle significantly shortens acquisition time, reduces the chance of patient motion during image acquisition, and thus reduces or eliminates image artifacts caused by patient motion.

[0031] The ability to quickly acquire a complete data set for large objects for CBCT reconstruction in approximately half a rotation plus the beam fan angle enables the use of a deep inspiration breath hold (DIBH) technique, which can further help reduce the chance of patient motion and, therefore, reduce or eliminate image artifacts caused by patient motion. DIBH is a radiation therapy technique in which the patient takes a deep breath during treatment and holds that breath while radiation is delivered. In a radiation therapy machine equipped with a CBCT system of the present disclosure, the operation of the machine can be optimized to allow the gantry to rotate at a relatively fast speed, for example, at four revolutions per minute. At this rotation speed, a CBCT of the present disclosure will take 7-8 seconds to acquire a complete data set in a scan of approximately 180 degrees plus the beam fan angle, while allowing for a larger FOV of 50 centimeters or more. The 7-8 second acquisition time is within the application range of the DIBH technique, as most people are able to hold their breath for 6-9 seconds.

[0032] The ability to quickly acquire projection images for CBCT reconstruction allows for better use of the imaging source 302, such as an x-ray tube. For a given image quality, a CBCT system of the present disclosure requires only half the overall x-ray tube power compared to conventional systems. The generation of x-rays is isotropically controlled by physics. However, the x-ray beam must be collimated to irradiate the object onto the active detection area of ​​the image detector. Therefore, all generated radiation that does not hit the image detector is wasted. Large detectors can make more efficient use of the generated x-rays because they provide a large active detection area. The generation of x-rays is a very inefficient process, in which 99% of the required energy is wasted in the form of heat. A CBCT system of the present disclosure with a large detector (e.g., twice the size of a conventional imager) can provide double the dose for the same heat dissipation. This will allow the selection of a smaller x-ray tube, thereby reducing the cost for comparable image quality.

[0033] The disclosed CBCT system 300 also reduces the mechanical complexity of the structure supporting the detector 304. Since no lateral movement would be required to move the detector 304 laterally out of the beam axis, the detector 304 could be mounted on a robotic wrist without a lateral movement mechanism.

[0034] refer to Figures 4A to 4B as well as 5A to 5D , embodiments of the present disclosure allow for monitoring or tracking of a reference volume during radiation therapy in extended source to axis distance (SAD) applications. There are instances where the reference volume is not placed at the isocenter of the radiation therapy system and a conventional standard image detector may be too small to cover the reference volume when it is positioned away from the isocenter. For example, due to the anatomy of the patient, the reference volume may have to be placed away from the isocenter. The clearance between the patient's body surface and the treatment head of the radiation therapy machine may be insufficient for some patients. Some treatments may require a constant source to skin distance (SSD). Further, VMAT with "couch kicks" (rotation of the patient support couch) has been demonstrated Treatment can spare organs at risk and allow for better dose deposition in the target. The small amount of table tilt allowed in conventional treatment systems limits the gantry rotation angle due to potential collision risk. Therefore, for example, moving the reference volume away from the isocenter by an additional 5 to 15 cm or even 20 cm will significantly help reduce the risk of collision and safely support VMAT with table tilt.

[0035] Figure 4A A conventional radiation therapy system 400 is depicted in an extended SAD application. The conventional radiation therapy system 400 includes an MV source 402, a kV source 404, and a detector 406 that generate therapeutic radiation for treatment. For reasons discussed above, a reference volume 408 is located at an offset from the isocenter 410 of the radiation system 400. A C-arm gantry 401 carries the MV source 402, which allows therapeutic radiation to be delivered to tumor tissue in the reference volume 408 while the MV source 402 rotates about an axis passing through the isocenter 410, as indicated by the arrows, to perform SRS, SBRT, or VMAT. The kV source 404 and image detector 406 are also supported by the rotating gantry 401, for example, via an extension arm (not shown), and operate to acquire images, such as planar images, radiographic images, or fluoroscopic images, for monitoring, supervision, or tracking of the reference volume during treatment. In Figure 4A In FIG4A , detector 406 is positioned at the center of the beam axis of kV source 404. Reference numeral 407 indicates the field of view (FOV) of detector 406 at any gantry angle. As shown in FIG4A , reference volume 408, positioned offset from isocenter 410, falls outside FOV 407 and cannot be imaged by detector 406 at certain gantry angles. Thus, reference volume 408 cannot be monitored or tracked by detector 406 on radiotherapy system 400 throughout treatment.

[0036] Figure 4B Another conventional radiation therapy system 450 is depicted in an extended SAD application. The conventional radiation therapy system 450 includes an MV source 452, a kV source 454, and a detector 456 that generate therapeutic radiation for treatment. For reasons discussed above, a reference volume 458 is located at an offset from the isocenter 460 of the radiation system 450. Figure 4A The radiation therapy system 400 is compared to Figure 4B The radiation therapy system 450 in FIG. 4 includes an annular gantry 451 carrying an MV source 452, a kV source 454, and a detector 456. The detector 456 is positioned laterally offset from the beam axis of the kV source 454. Reference numeral 457 indicates a volume that can be imaged by the detector 456 at certain gantry angles during a complete rotation. Figure 4B As shown in FIG, the portion of the reference volume 458 that is offset from the isocenter 460 falls outside of the volume 457 and, therefore, cannot be monitored or tracked by the detector 456 provided on the radiation therapy system 450 throughout the treatment. For stereotactic treatments such as SRS or SBRT, radiation is delivered in fewer high-dose fractions, and it is important to monitor the target volume throughout the radiation exposure. Since the dose per fraction is significantly higher, any positional error of the target volume is more severe.

[0037] Figures 5A-5D A radiation therapy system 500 according to an embodiment of the present disclosure is depicted in an extended SAD application. The radiation therapy system 500 includes a MV source 502, a kV source 504, and a regional detector 506. For reasons discussed above, a reference volume 508 is located at an offset from the isocenter 510 of the radiation therapy system 500, for example, 25 centimeters from the isocenter 510. A rotating gantry 501 carries the MV source 502, which allows therapeutic radiation to be delivered to tumor tissue in the reference volume 508 while the MV source 502 rotates about an axis passing through the isocenter 510 as indicated by the arrows, to perform SRS, SBRT, or VMAT. The rotating gantry 501 can be a C-arm gantry, a ring gantry, or a robotic gantry. The detector 506 and the kV source 504 can be supported by the gantry 501, for example, via an extension arm (not shown), and operated to acquire images from multiple angles as the gantry 501 rotates. Alternatively, the detector 506 and the kV source 504 can be supported by separate gantries. Figures 5A-5D In the embodiment shown in FIG, the detector 506 is located at the center of the beam axis of the kV source 504. As shown, an image containing the reference volume 508 can be acquired by the detector 506 and the kV source 504 at any gantry angle of the MV source 502, such as at Figure 5A The 0 degrees shown in Figure 5B 50 degrees shown in Figure 5C 170 degrees as shown in Figure 5D While positioned, for example, 25 centimeters from the isocenter 510, the reference volume 508 remains within the FOV of the image detector 506, which allows supervision and tracking of the reference volume 508 at any gantry angle of the MV source 502 within 360 degrees.

[0038] According to some disclosed embodiments, the kV source 504 can be synchronized with the MV source 502 to allow images to be acquired synchronously with a pause in the treatment being delivered to the target. For example, radiation from the MV source 502 can be paused for a short period of time to allow the kV source 504 to deliver the kV beam and acquire an image. This synchronization can reduce the effects of artifacts on the acquired image that would otherwise be caused by scattered treatment beams from the MV source 502. As an example, the treatment beam from the MV source 502 can be paused for 100 ms to allow the kV source 504 to deliver the kV beam and the detector 506 to read out image signals during this pause. Alternatively or additionally, the detector 506 can be synchronized with the MV source 502 to allow the detector 506 to read out signals synchronously with the pause in the treatment beam from the MV source 502. As an example, the treatment beam from the MV source 502 can be delivered in short pulses of, for example, 5 μs every 2.5 ms, and the line readout by the detector 506 can be performed synchronously with the treatment beam pulses. This will allow artifacts due to scattered therapy beams from the MV source 502 to appear at the same location in the detector 506, which can be corrected at least to some extent.

[0039] return Figure 1 The radiation source 102 may be a source operable to generate photons, protons or other heavy ions, and electrons. As an example, the source 102 may include an x-ray tube including a target that generates x-rays when struck by electrons. The x-ray tube 102 may include a collimator device to collimate the beam so that the beam exiting the x-ray tube has an overall conical or pyramidal shape. As another example, the source 102 may include a linear accelerator including a target that generates x-rays when struck by electrons, and various collimation devices for shaping and / or sizing the x-rays. As a further example, the source 102 may include a nozzle that emits photons, the photons being generated by a cyclotron or synchrotron and delivered to the nozzle. Generally, the source 102 may generate or emit radiation suitable for imaging. For example, the source may operate at a kilovolt (kV) level, such as in the range of 50 to 150 kV, to generate radiation suitable for diagnostic imaging. Alternatively, the source can be operated at megavolt (MV) levels for use, for example, with an electronic portal imaging device (EPID) to acquire images, for example, for determining patient placement or for interventional treatment or treatment planning iterations. In some embodiments, the source 102 can be a source capable of operating in two or more modes, for example, operating at kV or KV energy levels to produce radiation for various applications including dual-energy or multi-energy imaging.

[0040] In a particular embodiment, the source 102 comprises an x-ray tube operable to generate x-rays. X-ray tubes are well known in the art and therefore a detailed description of them is omitted herein. Briefly and generally, an x-ray tube comprises an electron source such as a filament (cathode) and a target such as metal tungsten on a rotating plate (anode) enclosed in a vacuum envelope. The provision of an electric current causes the filament to be heated to generate electrons. A voltage applied to the vacuum envelope accelerates the electrons toward the anode, bombarding the target to generate x-rays. The small surface area on the target where the x-rays are generated is called the focus of the x-ray tube or source, and its size can be determined by the electron beam from the cathode. The generated x-rays can then be shaped by a collimator and exit through a window in the envelope. Although Figure 1 Not shown, the x-ray controller and generator sets signals such as current, voltage, exposure time, and other operating parameters of the x-ray tube and generates voltage to be supplied to the x-ray tube. The x-ray controller and generator, in turn, can be controlled by the computer and control system 108.

[0041] Still refer to Figure 1 , the area detector 104 detects radiation transmitted through the object 112, which is indicative of attenuation properties or structures of the imaged portion of the object 112. The area detector 104 may be coupled to a data acquisition system (not shown), which includes electronic circuitry for providing control signals, receiving and processing data signals, and outputting data to the image processing device 106. The data acquisition system and area detector 104 may be separate units or integrated into a single unit controlled by a computer and control system 108.

[0042] The area detector 104 includes a plurality of detector elements arranged in rows and columns in a two-dimensional area. In a specific embodiment, the area detector 104 includes a planar plate imager having a planar plate detector surface. In an alternative embodiment, the area detector 104 has a curved detector surface.

[0043] In some embodiments, the area detector 104 may include an anti-scatter grid or be used in conjunction with an anti-scatter grid. Since the image detector has a sufficiently large active detection area, a two-dimensional grid can be used to reduce scattering from two directions, and even for larger objects, no movement of the area detector about the grid is required. The anti-scatter grid can be focused or non-focused. Various embodiments of the anti-scatter grid are described in U.S. Patent No. 9,620,256, entitled "X-Ray Imaging Device Including Anti-Scatter Grid," issued to Varian Medical Systems. The disclosure of U.S. Patent No. 9,620,256 is incorporated herein by reference in its entirety.

[0044] In some embodiments, the regional detector 104 may be a multi-slice image detector. A multi-slice image detector includes two or more detection layers arranged one on top of the other, or two or more imagers arranged one on top of the other. A multi-slice image detector can improve overall dose efficiency and allow the use of dual-energy imaging techniques. For example, the detection layer closer to the source can be configured to read the low-energy portion of the image signal, and the detection layer farther from the source can be configured to read the high-energy portion of the image signal. Through flexible processing of these sub-images, more information about the imaged anatomical structure, such as density, Z value, electron density, etc., can be obtained. CBCT reconstruction can be constructed for the energy of a virtual single energy beam. Various embodiments of a multi-slice image detector are described in U.S. Patent No. 9,268,037, entitled "Universal kV-MV Imagers," issued to Varian Medical Systems. The disclosure of U.S. Patent No. 9,268,037 is incorporated herein by reference in its entirety.

[0045] In certain disclosed embodiments, the area detector 104 may be a flat panel imager. The flat panel imager may include a radiation conversion layer and a detector matrix. The conversion layer converts radiation, such as x-ray photons, into visible light. The detector array detects the visible light and converts it into an electrical signal. The conversion layer may include a scintillator material that is capable of generating visible light photons in response to x-ray radiation. Thus, the detector array may include photosensitive elements that are capable of generating electrical signals in response to illumination photons generated by the scintillator material. Suitable scintillator materials include gadolinium oxysulfide (Gd2O2S:Tb), cadmium tungstate (CdWO4), bismuth germanate (Bi4Ge3O4), and tungstate (Tb). 12or BGO), cesium iodide (CsI), cesium thallium iodide (CsI:Tl), thallium-doped cesium iodide Na1(Tl), or any combination thereof. Suitable photosensitive elements may include photodiodes, photogates, or phototransistors, etc. Alternatively, the conversion layer may include a photoconductor material that can directly convert x-ray photons into charges (electron-hole pairs). In this way, the detector array may include electrodes on either side of the photoconductor material to collect the charges generated by the photoconductor material. Suitable photoconductor materials include, but are not limited to, mercury iodide (HgI2), lead iodide (PbI2), bismuth iodide (BiI3), cadmium zinc antimony (CdZnTe), amorphous selenium (a-Se), etc.

[0046] In some embodiments, the example flat panel imager 104 may include a large number of detector pixels (such as hundreds of thousands or millions). The large number of detector pixels may be arranged in multiple rows and columns to form an active detector area. In some specific embodiments, each detector pixel may include an addressable photosensitive element such as a photodiode and a switching transistor such as a thin film transistor (TFT) or a complementary metal oxide semiconductor (CMOS) transistor.

[0047] The detector array may further include a plurality of address lines and a plurality of data lines. Each address line in the plurality of address lines can connect a plurality of detector pixels in a row to a drive control assembly of a data acquisition system. Each data line in the plurality of data lines can connect a plurality of detector pixels in a column to a readout control assembly of the data acquisition system. The drive control assembly provides a control signal for accessing a selected pixel row. The readout control assembly provides a control signal for reading out a signal from the pixel. As an example, when it is desired to capture an image signal from the detector array, the control signal from the drive control assembly drives the gate of a switching element such as a TFT in the selected pixel row, and the signal stored in the selected pixel row is read out by the readout control assembly. The signal from the selected pixel can be buffered, amplified and converted by an analog-to-digital converter (ADC) of the electronic device of the data acquisition system. The resulting digitized data signal can then be multiplexed, buffered and transmitted to an image processing device for further processing.

[0048] During operation of the detector array, a control signal from the driver control circuitry for a row of pixels can be asserted on the address line within a predetermined period, or line time. During the assertion of this control signal, the signal from each pixel in the selected row is transmitted via the column data line to the readout control circuitry, where the signal on each data line is received and buffered by the corresponding charge-sensitive amplifier. Thus, the data image for an entire row can be captured within a line time cycle. With each subsequent line time cycle, image data for subsequent rows is captured. At the end of the "frame time" cycle, the entire image can be captured. In this way, pixels encompassing the entire active detection area can be read out row by row, each row within a line time cycle. In an alternative embodiment, the flat panel imager can employ split data lines, where the top and bottom halves of the array are read out simultaneously. This allows for faster readout of the flat panel imager, requiring, for example, only half the "frame time" to read out pixels. By way of example, the flat panel imager can operate at speeds ranging from 15 to 50 frames per second (fps), depending on dose requirements, image resolution, and the number of projection data sets.

[0049] Still refer to Figure 1 The image processing device may include a computer 118 and software 120 for processing the projection images and reconstructing the tomographic images based on the projection images. The computer 118 may include a processor, a memory, an optional user interface, and a network interface. The processor may include a central processing unit (CPU) as is generally known in the art, such as a CPU. processor processor, or such The processor may retrieve and execute computer-executable instructions from a memory, which may cause the processor to perform any of the methods and / or steps described above according to the embodiments of the present disclosure.

[0050] The memory may include any one or a combination of volatile memory elements and non-volatile memory elements. The memory may include a random access memory (RAM) or other dynamic memory device for storing information and instructions to be executed by the processor and for storing temporary variables or other intermediate information during the execution of the instructions by the processor. The memory may also include a read-only memory (ROM) or other static storage device for storing static information and instructions for the processor. The memory may further include a data storage device such as a magnetic disk or optical disk for storing information and instructions. The memory (e.g., a non-transitory computer readable medium) may include a program (logic) for operating a computer system and for executing an application, including dosimetry projections and dose calculations or other treatment planning applications as described above. In addition, the memory may include a database that stores any information that can be selected by a user such as a radiation oncologist or radiation therapist.

[0051] Various embodiments of CBCT systems and radiation therapy machines including CBCT systems are described with reference to the accompanying drawings. It should be noted that some of the drawings are not necessarily drawn to scale. The drawings are intended only to facilitate the description of specific embodiments and are not intended to be exhaustive or to limit the scope of the present disclosure.

[0052] Unless specifically limited otherwise, all technical and scientific terms used herein have the meanings commonly understood by those skilled in the art. As used in this description and the appended claims, unless the context clearly dictates otherwise, the singular forms "a", "an", and "the" include plural references. Unless the context clearly dictates otherwise, the term "or" refers to a non-exclusive "or". Unless the context clearly dictates otherwise, the terms "first" or "second" are used to distinguish one element from another when describing various similar elements and should not be understood to have any particular order. Further, certain specific dimensions are provided for a comprehensive understanding of various aspects of this disclosure. It should be noted that these specific dimensions are not intended to limit the scope of the claims. The specified dimensions or parameters should be understood to mean "about", "approximately" rather than "completely". For example, the term "about" can be used to indicate a numerical value, which can include a variation of ±15% of the numerical value modified by the term.

[0053] Those skilled in the art will recognize that various other modifications may be made. All these and other changes and modifications are contemplated by the inventors and are within the scope of the invention.

Claims

1. A cone-beam computed tomography (CBCT) system, comprising: a supporting device configured to support an object to be irradiated; a source operable to generate a cone beam of radiation, the source being rotatable about an axis to irradiate the object from a plurality of angles; an area detector rotatable in synchronization with the source, the area detector operable to acquire projection images of the object while the object is irradiated by the cone beam of radiation, wherein the area detector and the source are configured to allow acquisition of a plurality of projection images at only 180 degrees plus a fan angle of the cone beam during an image acquisition cycle to provide a complete data set for CBCT reconstruction to generate an image volume having a field of view (FOV) of at least 20 centimeters; and wherein the support device is configured not to move during the entire image acquisition cycle; Wherein the area detector comprises a flat panel imager having an active detection area, the active detection area comprising dimensions ranging from 54 centimeters to 105 centimeters.

2. The system of claim 1 , wherein the area detector and the source are configured to enable acquisition of the plurality of projection images at 180 degrees plus the fan angle to provide the complete data set for CBCT reconstruction to generate the image volume having a FOV ranging from 20 cm to 50 cm. 3 . The system of claim 1 , wherein the area detector is centrally positioned on the beam axis of the radiation cone beam.

4. The system according to claim 1, further comprising: A source operable to generate radiation suitable for treatment of a disease and rotatable about said axis.

5. The system of claim 4, wherein the source operable to generate radiation suitable for treatment is rotatable about the axis at a speed of at least one revolution per minute.

6. The system of claim 1 , wherein the source is rotatable about the axis to irradiate a patient containing the object, and the area detector and the source are configured to acquire the plurality of projection images at 180 degrees plus a fan angle of the cone beam while the patient holds his breath.

7. The system of claim 6, wherein the area detector comprises two or more sensor discs or sensor panels forming the active detection area.

8. A cone-beam computed tomography (CBCT) system comprising: a supporting device configured to support an object to be irradiated; a first source rotatable about an axis and operable to generate radiation suitable for treatment; a second source operable to generate radiation suitable for imaging; as well as an area detector operable to acquire an image of the object while the object is irradiated by the radiation from the second source, the object comprising a reference volume located at least 10 centimeters from the axis and comprising a target to be irradiated by the radiation from the first source, the area detector being rotatable in sync with the second source, wherein the area detector and the second source are configured to allow acquisition of the image encompassing the reference volume at any angle of the first source during an image acquisition cycle, Wherein the support device is configured not to move during the entire image acquisition cycle, wherein the area detector comprises a planar plate imager having an active detection area, the active detection area comprising dimensions ranging from 54 centimeters to 105 centimeters.

9. The system of claim 8, wherein the reference volume in the subject is located between 10 cm and 25 cm from the axis and the area detector and the second source are configured to allow acquisition of the image encompassing the reference volume at any angle of the first source.

10. The system of claim 8, wherein the first source is configured to generate the radiation suitable for stereotactic radiosurgery (SRS) or stereotactic body radiation therapy (SBRT).

11. The system of claim 8, wherein the area detector is centrally located on a beam axis of the radiation.

12. The system of claim 8, wherein the second source is synchronized with the first source to allow the second source to deliver radiation and acquire the image of the object while the first source is paused, thereby reducing the effect of artifacts on the image caused by scattering of the radiation from the first source.

13. The system of claim 8, wherein the area detector is synchronized with the first source to allow the area detector to acquire the image of the object in synchronization with a pulse pattern of the first source.

14. The system of claim 8, wherein the area detector comprises two or more detection layers configured for dual-energy or multi-energy imaging.

15. The system of claim 8, wherein the area detector comprises a planar plate imager having an active detection area formed by two or more sensor disks or sensor panels.

Images