Cone-beam reconstruction using an x-ray event detector

Abstract

An X-ray imaging system (400) includes an X-ray imaging source (506) for directing imaging X-rays to a region of patient anatomy, an X-ray event detector panel (505, 507) for receiving at least a portion of the imaging X-rays, and a controller. For each pixel of the X-ray event detector panel, the controller performs determining (1307) a cumulative sum of X-ray events detected at the pixel during an imaging interval, generating (1311) an X-ray event image of the region of patient anatomy based on the cumulative sum of X-ray events for each pixel, and updating (1312) a digital volume of the region of patient anatomy based on the X-ray event image.

Description

CONE-BEAM RECONSTRUCTION USING AN X-RAY EVENT DETECTOR CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of the United States Provisional Application No. 63 / 776,951, filed March 24, 2025, and the U.S. Provisional Application 63 / 800,456, filed May 6, 2025. These United States Provisional Applications, including any appendices or attachments thereof, are incorporated herein by reference in their entirety.BACKGROUND

[0002] Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.

[0003] Radiation therapy (also called radiotherapy) is a cancer treatment that employs high doses of ionizing radiation, such as X-rays or high-energy electrons, protons, or other heavy charged particles, to kill cancer cells. Generally, radiation therapy is a localized treatment for a specific target tissue, such as a cancerous tumor. Ideally, radiation therapy is performed on a planning target volume (i.e. , the target tissue) that spares the surrounding normal tissue from receiving doses above specified tolerances, thereby minimizing risk of damage to healthy tissue. For example, to accurately supply a planned radiation dose, the spatial distribution of delivered radiation dose within the patient must closely match the spatial distribution of the planned radiation dose. So that the planned radiation dose is correctly supplied to the planning target volume during radiation therapy, the patient should be correctly positioned relative to the radiation source that provides the radiation therapy immediately before and throughout the time that radiation is delivered to the target volume. To that end, patient position is oftentimes monitored before and during radiation delivery using X-ray imaging, for example with one or more onboard X-ray imaging systems.SUMMARY

[0004] According to various embodiments, an X-ray imaging system includes: an X-ray imaging source, an X-ray event detector panel, and a controller. In the embodiments, the controller performs the steps of: for each pixel of the X-ray event detector panel, determining a cumulative sum of X-ray events detected at the pixel during an imaging interval; generating an X-ray event image of the region of patient anatomy based on the cumulative sum of X-rayevents for each pixel; and updating a digital volume of the region of patient anatomy based on the X-ray event image.

[0005] According to various embodiments, a computer-implemented method for reconstructing a digital volume of a region of patient anatomy includes: for each pixel of an X-ray event detector panel, determining a cumulative sum of X-ray events detected at the pixel during an imaging interval; generating an X-ray event image of the region of patient anatomy based on the cumulative sum of X-ray events for each pixel; and updating a digital volume of the region of patient anatomy based on the X-ray event image. The method may be performed before treatment of the patient. The method may be performed before one treatment session or fraction of the patient. The method may be performed before each of a plurality of treatment sessions or fractions of the patient. The imaging interval may be before treatment of the patient. The imaging interval may be before one treatment session or fraction of the patient. The imaging interval may be before each of a plurality of treatment sessions or fractions of the patient.

[0006] Further embodiments include a non-transitory computer-readable storage medium comprising instructions that cause a computer system to cause the above steps to be carried out, as well as a computer system configured to cause the above steps to be carried out.

[0007] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. These drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope. The disclosure will be described with additional specificity and detail through use of the accompanying drawings.

[0009] FIG. 1 is a perspective view of a radiation therapy system, according to various embodiments.

[0010] FIG. 2 schematically illustrates a side view of the radiation therapy system of FIG. 1, according to various embodiments.

[0011] FIG. 3 schematically illustrates a digital volume that is constructed based on projection images generated by one or more X-ray images included in the radiation therapy system of FIG.1 , according to various embodiments.

[0012] FIG. 4 is a perspective view of another radiation therapy system, according to various embodiments.

[0013] FIG. 5 schematically illustrates a base stand and a gantry of the radiation therapy system of FIG. 4, according to various embodiments.

[0014] FIG. 6 schematically illustrates a conceptual view of an X-ray event detector panel, according to various embodiments.

[0015] FIG. 7 schematically illustrates a portion of a pixel array of the X-ray event detector panel of FIG. 6, according to various embodiments.

[0016] FIG. 8 schematically illustrates a cross-sectional view of the X-ray event detector panel of FIG. 6 when configured as an indirect conversion X-ray detector, according to various embodiments.

[0017] FIG. 9 schematically illustrates a cross-sectional view of the X-ray event detector panel of FIG. 6 when configured as a direct conversion X-ray detector, according to various embodiments.

[0018] FIG. 10 is a conceptual block diagram of a pixel circuit of an X-ray event detector panel, according to various embodiments.

[0019] FIG. 11 is a plot of changes in X-ray intensity measured at a pixel detector element and the associated rising and falling X-ray events generated by the pixel detector element, according to various embodiments.

[0020] FIG. 12 is a more detailed conceptual diagram of a pixel circuit when configured as a pixel of an indirect conversion X-ray detector, according to various embodiments.

[0021] FIG. 13 is a flowchart illustrating the steps of a computer-implemented process for CBCT reconstruction of a 3-dimensional (3D) image using an X-ray event detector panel, according to various embodiments.

[0022] FIG. 14 schematically illustrates an X-ray event image of a region of patient anatomy and a conventional X-ray projection image of the region of patient anatomy, according to various embodiments.

[0023] FIG. 15 is an illustration of a computing device configured to perform various embodiments.

[0024] FIG. 16 is a block diagram of an illustrative embodiment of a computer program product for implementing one or more embodiments.DETAILED DESCRIPTION

[0025] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.Introduction

[0026] In radiation therapy, a patient should be correctly positioned relative to the linear accelerator that provides the radiation therapy so that the prescribed dose is correctly supplied to the planning target volume (i.e. , the target tissue). Typically, dosimetric and geometric data are checked before and during the treatment, to ensure correct patient placement and that the administered radiotherapy treatment matches the previously planned treatment. This process is referred to as image guided radiation therapy (IGRT), and involves the use of an imaging system to view target tissues immediately before radiation treatment is delivered to the planning target volume. In many instances, as part of IGRT, to detect and / or compensate for patient motion during a particular radiation therapy session, or “fraction,” patient motion is monitored in real time or near-real time to detect intra-fraction motion of the patient and / or internal anatomy of the patient. A variety of methods have been used, including, but not limited to, breath-hold, active-breathing control with visual feedback, implanted fiducials with RF monitoring or X-ray imaging, tracking through a surrogate such as body surface, or other X-ray imaging techniqueswhich attempt to monitor the position of anatomy during a respiratory cycle or other internal motions, such as peristalsis or even muscle relaxation.

[0027] IGRT incorporates X-ray imaging coordinates from a treatment plan to ensure the patient is properly aligned for treatment in the radiation therapy device, thereby enabling an increase in accuracy and precision of treatment delivery, shorter treatment times (e.g., hypo-fractionated therapy and / or flash therapy), and patient-individualized therapy. Using IGRT, an adaptive therapy workflow with plan adaptation (“plan of the day”) can be performed, which is based on the actual patient anatomy on the day of treatment. For instance, during a course of radiotherapy, which can take place over many days, the planning target volume and / or neighboring patient anatomy can change in size or relative position due to tumor shrinkage, patient weight loss, and intra-fraction motion of the patient or internal anatomy of the patient. The X-ray imaging systems currently employed for IGRT are onboard imaging systems and fixed room-based systems. Onboard imaging systems are mounted on and rotate with the treatment gantry, while fixed room-based systems usually include a pair of room-mounted X-ray imagers.

[0028] In IGRT, a simulation step is generally performed prior to delivery of an X-ray dose. Typically, a series of machine instructions is created to deliver the course of radiation to the target. In order to prepare these machine instructions, 3D imaging (CT, CBCT, or MR ) of the region to receive the radiation is commonly performed. This can be done well in advance of treatment. Alternatively, with certain O-ring based systems, a patient can proceed directly to the treatment room and a CBCT of the day is taken and used to create the treatment plan and the machine instructions that are to be followed by the image-guided radiotherapy. Some systems can have fan-beam CT integrated on an O-ring or C-arm gantry.

[0029] In currently available X-ray detectors, which convert incident X-rays into electronic signals, increasing readout rates (frame rates) and more dense pixel counts create bandwidth limitations. This can impose latency limitations, for example when attempting to monitor internal patient motion with high temporal resolution. In addition, such latency limitations can limit cone and fan beam CT acquisition speeds. Further, the dynamic range of conventional X-ray detectors, which is the range of intensities that conventional X-ray detectors can record, can be limited. For example, the dynamic range of a typical conventional X-ray detector spans a range on the order of about 104or 105. As a result, the ability of conventional X-ray detectors to capture high-contrast images of both soft-tissue and dense bone structures can be limited.

[0030] One approach for reducing the effects of the high data rates and bandwidth limitations that can occur in conventional X-ray detectors is to reduce the data collected per frame when monitoring internal patient motion in real time. However, such an approach necessarily reduces the spatial resolution of the images being acquired. Another approach is the use of algorithmic compensations for incomplete or “sparse” data sampling, which involves acquiring data at fewer angular intervals and / or undersampling each image. Such an approach can reduce radiation dose, increase the speed of image acquisition, and reduce data storage and bandwidth issues. However, such an approach is well-known to introduce various uncertainties, including image artifacts (such as streaking) and reduced spatial resolution. Yet another approach is to dedicate increased computational power to process the large quantities of data acquired for real-time tracking of internal patient motion. While this approach can reduce latency to some degree, the change is generally incremental. Furthermore, greater computational power provides no increase in the dynamic range of an X-ray detector.

[0031] Accordingly, there is a need in the art for improved systems and methods for accurately imaging patient anatomy and detecting patient motion with X-ray imagers, including the onboard X-ray imagers of radiation therapy systems as well as other X-ray imagers.

[0032] According to various embodiments, one or more X-ray imagers of a radiation therapy system or other X-ray imaging system is configured as an X-ray event detector. In such embodiments, the basic concept of an event camera is incorporated into the one or more X-ray detectors, thereby forming an X-ray event detector. In the embodiments, instead of acquiring an X-ray projection image as a whole frame, an X-ray event detector reports changes in detected X-ray intensity (photons / unit time) at the individual pixel level. Thus, the X-ray event detector can output an asynchronous stream of pixel-specific detected X-ray events. X-ray event detection at a particular pixel is triggered when X-ray intensity at the pixel is determined to increase above or fall below a threshold with respect to the current reference value of X-ray intensity for that particular pixel. In some embodiments, this principle is applied to digital indirect X-ray detectors, such as charge-coupled devices (CCDs) and some thin-film transistor (TFT) devices. In other embodiments, this principle is applied to digital direct X-ray detectors, such as some TFT devices. Various embodiments can be implemented in the form of a digital circuit and / or logic, and can be applied to flat-panel and fan-beam detectors.

[0033] One technical advantage of the various embodiments is that X-ray projection images can be generated with much lower latency than conventional X-ray projection images. This is due tothe very low latency of pixel-level X-ray event detection, which can have a temporal resolution on the microsecond scale. Similarly, a digital volume of a region of patient anatomy that is based on such X-ray projection images can also be reconstructed more quickly than a digital volume that is based on conventionally acquired X-ray projection images of the region of patient anatomy. Another technical advantage of the various embodiments is that data bandwidth requirements within an X-ray imaging system are greatly reduced, since only local events are reported while unchanged portions of an X-ray projection image are not. Yet another technical advantage of the various embodiments is that the dynamic range of an X-ray event detector can be much greater than a corresponding conventional X-ray detector, thereby improving conebeam and fan-beam CT image quality regarding soft tissue contrast. Various embodiments are described below.C-Arm Gantry Overview

[0034] FIG. 1 is a perspective view of a radiation therapy system, according to various embodiments. Radiation therapy (RT) system 100 is a radiation system that may be configured to detect intra-fraction motion in near-real time using X-ray imaging techniques. Thus, in some embodiments, RT system 100 is configured to provide stereotactic radiosurgery and precision radiotherapy for lesions, tumors, and conditions anywhere in the body where radiation treatment is indicated. As such, RT system 100 can include one or more of a linear accelerator (LINAC) 104 that generates an MV treatment beam of high energy X-rays or other radiation, one or more kilovolt (kV) imaging X-ray sources 106, one or more imaging panels 107 (e.g., an X-ray imager), and a mega-Volt (MV) electronic portal imaging device (EPID) 105. In the embodiment illustrated in FIG. 1, RT system 100 is configured with a C-arm gantry 110. In the embodiment illustrated in FIG. 1, imaging panel 107 is depicted as a planar device, whereas in other embodiments, imaging panel 107 can have a curved configuration.

[0035] In some embodiments, RT system 100 is capable of X-ray imaging of a target volume immediately prior to and / or during application of an MV treatment beam. Consequently, RT system 100 can perform an image-guided radiation therapy (IGRT) and / or an intensity-modulated radiation therapy (IMRT) process using the X-ray imaging generated by RT system 100. For example, in some embodiments, such processes can include kV imaging of the target volume in conjunction with the supplemental X-ray imaging system. Alternatively or additionally, in some embodiments, such processes can include imaging generated by the MV treatment beam in conjunction with the supplemental X-ray imaging system.

[0036] RT system 100 may include one or more touchscreens (not shown) for patient information verification, couch motion controls 102, a radiation area 103, a couch-positioning assembly 101 , a treatment couch 108 disposed on couch-positioning assembly 101 , and an image acquisition and treatment control computer 109, all of which are disposed within a treatment room. RT system 100 further includes a remote control console 111, which is disposed outside the treatment room and enables treatment delivery and patient monitoring from a remote location. Couch-positioning assembly 101 is configured to precisely position treatment couch 108 with respect to radiation area 103, including rotating treatment couch 108 about an isocenter of RT system 100. In some embodiments, a center of rotation (not shown) of couch-positioning assembly 101 is vertically aligned with the treatment isocenter. Motion controls 102 include input devices, such as buttons and / or switches, that enable a user to operate couch-positioning assembly 101 to automatically and precisely position treatment couch 108 to a predetermined location with respect to radiation area 103. Motion controls 102 also enable a user to manually position treatment couch 108 to a particular location, such as a planned treatment position for a patient or an anatomical target.

[0037] According to various embodiments, RT system 100 includes at least one onboard X-ray imaging system that is mounted on C-arm gantry 110 and a supplemental X-ray imaging system that is fixed in position while C-arm gantry 110 rotates about a treatment isocenter of RT system 100. In the embodiment illustrated in FIG. 1, one onboard X-ray imaging system that is mounted on C-arm gantry 110 of RT system 100 is implemented as imaging X-ray source 106 and imaging panel 107. In some embodiments, another onboard X-ray imaging system that is mounted on C-arm gantry 110 of RT system 100 is implemented as LINAC 104 (used as an X-ray source) and EPID 105 (used as an imaging panel).

[0038] FIG. 2 schematically illustrates a side view of RT system 100, according to various embodiments. As shown, RT system 100 includes a base stand 200, C-arm gantry 110, and couch-positioning assembly 101 with treatment couch 108. For clarity, in FIG. 2, EPID 105, imaging X-ray source 106, and imaging panel 107 are shown stowed and not deployed for use.

[0039] Base stand 200 is a fixed support structure for components of RT treatment system 100, including C-arm gantry 110 and a drive system (not shown) for rotatably moving C-arm gantry 110 about a horizontal rotation axis 202 and a treatment isocenter 203. Base stand 200 rests on and / or is fixed to a support surface that is external to RT treatment system 100, such as a floor 204 of an RT treatment facility. C-arm gantry 110 is rotationally coupled to base stand 200,for example via a bearing, and is a support structure on which various components of RT system 100 are mounted, including LINAC 104, EPID 105, imaging X-ray source 106, and imaging panel 107.

[0040] Couch-positioning assembly 101 is coupled to a turntable 201 that is mounted in floor 204 and rotates couch-positioning assembly 101 about treatment isocenter 203. Thus, couchpositioning assembly 101 in conjunction with turntable 201 enables rotational and linear motion of treatment couch 108 relative to isocenter 203. In some embodiments, couch-positioning assembly 101 is configured to rotate, pitch, roll, and / or translate treatment couch 108 relative to isocenter 203 to one or more treatment positions.

[0041] LINAC 104 is a radiation source, and typically includes one or more of an electron gun for generating electrons, an accelerating waveguide, an electron beam target, an electron beam transport means (such as a bending magnet) for directing the electron beam to the electron beam target, and / or a collimator assembly 208 for collimating and shaping a treatment beam 230 that originates from the electron beam target. Collimator assembly 208 typically includes one or more of a primary collimator that defines the largest available circular radiation field for treatment beam 230, a secondary collimator for providing a rectangular or square radiation field at isocenter 203 (for example via X-jaws and Y-jaws), and / or a multileaf collimator (MLC) for conforming treatment beam 230 to a planning target volume (PTV) or other anatomical target. In other embodiments, LINAC 104 can be any other radiation source suitable for radiation therapy.

[0042] During operation of RT treatment system 100, C-arm gantry 110 rotates about radiation area 103 (shown in FIG. 1) and isocenter 203 when actuated by the drive system for rotatably moving C-arm gantry 110 about horizontal rotation axis 202. Imaging X-ray source 106 is configured to direct a conical beam of X-rays, referred to herein as imaging X-rays (not shown in FIG. 2 for clarity), through isocenter 203 of RT system 100 to imaging panel 107. Ideally, isocenter 203 corresponds to the location of a target volume 209 to be treated, such as a PTV, a gross tumor volume (GTV), a clinical target volume (CTV), and / or an internal target volume (ITV), among others.

[0043] During radiation treatment, LINAC 104 is configured to generate treatment beam 230, which can include high-energy radiation (for example MV X-rays or MV electrons). In other embodiments, treatment beam 230 includes electrons, protons, and / or other heavy charged particles, ultra-high dose rate X-rays (e.g., for FLASH radiotherapy), and / or microbeams formicrobeam radiation therapy. In some embodiments, as treatment beam 230 is directed to isocenter 203 while C-arm gantry 110 rotates through a treatment arc, image acquisitions can be performed via EPID 105 to generate image data for target volume 209. For example, in such embodiments, EPID 105 generates one or more projection images of target volume 209 and / or a region of patient anatomy surrounding target volume 209. Thus, projection images (e.g., 2D X-ray images) of target volume 209 can be generated during portions of an IGRT process via imaging panel 107 and / or EPID 105. Such projection images can then be employed to reconstruct a digital volume that corresponds to a three-dimensional (3D) region that includes target volume 209. That is, a 3D image of such a 3D region is reconstructed from the projection images. In some embodiments, cone-beam computed tomography (CBCT) and / or digital tomosynthesis (DTS) can be used to process the projection images generated by imaging panel 107 and generate a digital volume of the region including target volume 209. One embodiment of such a digital volume is described below in conjunction with FIG. 3.

[0044] FIG. 3 schematically illustrates a digital volume 300 that is reconstructed based on a plurality of views acquired by imaging panel 107 and / or EPID 105, according to various embodiments. Digital volume 300 includes a plurality of voxels 301 (dashed lines) of anatomical image data, where each voxel 301 corresponds to a different location within digital volume 300. For clarity, only a single voxel 301 is shown in FIG. 3. Digital volume 300 corresponds to a 3D region that includes target volume 209. In FIG. 3, digital volume 300 is depicted as an 8x8x8 voxel cube, but in practice, digital volume 300 generally includes many more voxels, for example one or more orders of magnitude more than are shown in FIG. 3. Once reconstructed from a set of CT views, cross-sectional images of digital volume 300 can be generated at any location an in any of various planes, including the axial plane (which passes through patient anatomy from anterior to posterior, dividing the anatomy into superior and inferior sections), the coronal plane (which passes through patient anatomy from left to right and divides the anatomy into anterior and posterior sections, the sagittal plane (which passes through patient anatomy from anterior to posterior and divides the anatomy into left and right sections), and / or the oblique plane (which passes through patient anatomy at an angle to the axial, coronal, and / or sagittal planes).

[0045] For purposes of discussion, target volume 209 can refer to the gross tumor volume (GTV), clinical target volume (CTV), or the planning target volume (PTV) for a particular treatment. The GTV depicts the position and extent of the gross tumor, for example what can be seen or imaged; the CTV includes the GTV and an additional margin for sub-clinical diseasespread, which is generally not imageable; and the PTV is a geometric concept designed to ensure that a suitable radiotherapy dose is actually delivered to the CTV without adversely affecting nearby organs at risk. Thus, the PTV is generally larger than the CTV, but in some situations can also be reduced in some portions to provide a safety margin around an organ at risk. The PTV is typically determined based on imaging performed prior to the time of treatment, and alignment of the PTV with the current position of patient anatomy at the time of treatment is facilitated by X-ray imaging of digital volume 300.O-Ring Gantry Overview

[0046] In the embodiment illustrated in FIGS. 1 and 2, RT system 100 is configured with C-arm gantry 110. In other embodiments, a radiation therapy system can be configured with a ringbased gantry that is disposed about an isocenter of the radiation therapy system. One such embodiment is described below in conjunction with FIGS. 4 and 5.

[0047] FIG. 4 is a perspective view of an RT system 400, according to various embodiments. In some embodiments, RT system 400 can be consistent with RT system 100 of FIGS. 1 and 2, except that RT system 400 is configured with a circular or ring-based gantry. As such, RT system 400 can include one or more touchscreens 401, couch motion controls (not shown), a bore 403, a base positioning assembly 405, a treatment couch 407 disposed on base positioning assembly 405, and an image acquisition and treatment control computer 406, all of which are disposed within a treatment room. RT system 400 further includes a remote control console 410, which is disposed outside the treatment room and enables treatment delivery and patient monitoring from a remote location. Base positioning assembly 405 is configured to precisely position treatment couch 407 with respect to bore 403, and the motion controls include input devices, such as button and / or switches, that enable a user to operate base positioning assembly 405 to automatically and precisely position treatment couch 407 to a predetermined location with respect to bore 403. The motion controls also enable a user to manually position treatment couch 407 to a predetermined location.

[0048] FIG. 5 schematically illustrates a base stand 500 and gantry 510 of RT system 400, according to various embodiments. Covers, base positioning assembly 405, treatment couch 407, and other components of RT system 400 are omitted in FIG. 5 for clarity. Base stand 500 is a fixed support structure for components of RT system 400, including gantry 510 and a drive system 501 (dashed lines) for rotatably moving gantry 510. Base stand 500 rests on and / or isfixed to a support surface that is external to RT system 400, such as a floor of a radiotherapy treatment facility. Gantry 510 is rotationally coupled to base stand 500 and is a support structure on which various components of RT system 400 are mounted, including a LINAC 504, an EPID 505, an imaging X-ray source 506, and an X-ray imager 507.

[0049] During operation of RT system 400, drive system 501 rotationally actuates gantry 510, so that gantry 510 rotates about bore 403. LINAC 504 generates an MV treatment beam 530 of high energy X-rays (or in some embodiments electrons, protons, and / or other heavy charged particles, ultra-high dose rate X-rays (e.g., for FLASH radiotherapy) or microbeams for microbeam radiation therapy) and EPID 505 is configured to acquire X-ray images with treatment beam 530. Imaging X-ray source 506 is configured to direct a conical beam of X-rays, referred to herein as imaging X-rays 531, through an isocenter 503 of RT system 400 to X-ray imager 507, and isocenter 503 typically corresponds to the location of a target volume 509 to be treated. In the embodiment illustrated in FIG. 5, X-ray imager 507 is depicted as a planar device, whereas in other embodiments, X-ray imager 507 can have a curved configuration. In the embodiment illustrated in FIG. 5, RT system 400 includes a single X-ray imager 507 for kV imaging and a single corresponding imaging X-ray source 506. In other embodiments, RT system 400 can include two or more X-ray imagers 507, each with a corresponding imaging X-ray source 506.

[0050] In the embodiments described above, radiation therapy systems with a C-arm gantry and an O-ring gantry are described. In other embodiments, a radiation therapy system can include attributes of both a C-arm gantry system and an O-ring gantry system. For example, in such embodiments, a radiation therapy system with an O-ring gantry can be configured to rotate a C-arm about an isocenter that is disposed outside the bore of the O-ring gantry and in front of the face of the O-ring gantry. Sometimes referred to as a C-ring system, such a system can further include a treatment couch with a couch-positioning assembly that is similar to couchpositioning assembly 101 in FIG.1 , and thus has a center of rotation that is vertically aligned with the treatment isocenter of the system. Such systems allow a patient to extend within the bore and offer additional non-isocentric imaging to be used, such as fan-beam CT.X-Ray Event Detector Panel

[0051] According to various embodiments, an X-ray detector panel in a radiation therapy system or other X-ray imaging system is configured to operate as an X-ray event detector. Forexample, such an X-ray event detector can be implemented as one or more of imaging panel 107 or EPID 105 of FIG. 1 or X-ray imager 507 or EPID 505 of FIG. 5. In such embodiments, the X-ray event detector can be used to detect the relative motion of objects or anatomy as perceived by a rotating X-ray source and detector. This relative motion information can be used to determine spatial information perpendicular to the panel, allowing 3D image reconstruction. For example, in some embodiments, such spatial information can be employed to supplement or replace conventional filtered back projections. One embodiment of an X-ray event detector panel is described below in conjunction with FIG. 6.

[0052] FIG. 6 schematically illustrates a conceptual view of an X-ray event detector panel 600, according to various embodiments. As shown, X-ray event detector panel 600 includes a detector circuitry layer 601 formed on a substrate 602 and an X-ray receiving layer 603 formed on detector circuitry layer 601. Also shown are incident X-rays 609 that have passed through a patient, sample, or other object of interest after being generated by a suitable X-ray source. Together, detector circuitry layer 601 , substrate 602, and X-ray receiving layer 603 form an X-ray imaging array 605. It is noted that detector circuitry layer 601 is generally formed from a plurality of processing layers, and that X-ray imaging array 605 may include additional material layers not illustrated in FIG. 6.

[0053] Detector circuitry layer 601 is formed on substrate 602, and in some embodiments includes a plurality of photosensitive elements, such as photodiodes, photogates, phototransistors, or any other suitable circuitry suitable for operation as pixel detector elements in X-ray event detector panel 600. For example, in some embodiments, detector circuitry layer 601 includes TFTs for reading out the digital signals from photodiodes within the pixel detector elements of each pixel. Alternatively, in some embodiments, detector circuitry layer 601 includes CCDs for converting incident photons into electric charges and reading out the electric charges. Generally, each pixel detector element in detector circuitry layer 601 generates a signal for the corresponding pixel (e.g., a voltage or current that is proportional to incident light intensity). At each pixel detector element, events are detected and recorded based on the current light intensity signal incident at the pixel detector element. Collectively, detected event signals generated by the pixel detector elements can be used to form a digital image, for example of X-ray events detected over a specific time interval. For example, such a digital image can be generated via an encoder that interprets the detected event signals and assigns a value to each that is proportional to the number of detected events. One embodiment of a pixel array of pixel detector elements included in detector circuitry layer 601 is described below inconjunction with FIG. 7.

[0054] FIG. 7. schematically illustrates a portion of a pixel array 700 of X-ray event detector panel 600, according to various embodiments. As shown, pixel array 700 includes a plurality of pixel detector elements 701 that are arranged in a grid and are each individually connected to a first control circuit 710 and a second control circuit 720. In the embodiment illustrated in FIG. 7, a four-pixel by four-pixel portion of pixel array 700 is depicted, which includes pixels 1-1, 1-2, 1-3, 1-4, 2-1, 2-2, 2-3, 2-4, 3-1, 3-2, 3-3, 3-4, 4-1, 4-2, 4-3, and 4-4. In practice, pixel array 700 can include thousands of pixel detector elements 701 , such as an array of pixels that includes hundreds or thousands of columns of pixels and hundreds or thousands of rows of pixels.

[0055] In some embodiments, first control circuit 710 provides a reference voltage to each pixel detector element 701. Together, first control circuit 710 and second control circuit 720 sequentially read outputs from individual pixel detector elements 701 or from rows of pixel detector elements 701. As noted previously, the output from each pixel detector element 701 is a detected event signal that is based on the current light intensity incident at the pixel detector element 701. In some embodiments, the detected event signals from pixel detector elements 701 are asynchronously generated during one or more X-ray imaging intervals that each have a specified duration. In such embodiments, the total detected events for a particular pixel detector element 701 are recorded for each X-ray imaging interval. Thus, in a given X-ray imaging interval, a different number of detected event signals can be recorded for each pixel detector element 701. In some embodiments, for the duration of an X-ray imaging interval, X-ray event detector panel 600 and pixel array 700 remain stationary relative to a region of interest of patient anatomy. In other embodiments, for the duration of an X-ray imaging interval, X-ray event detector panel 600 and pixel array 700 can rotate about the region of interest of patient anatomy. Thus, in such embodiments, motion (e.g., rotation) of the X-ray imaging system relative to the region of interest induces attenuation changes along rays that will be detected, thereby enabling CBCT and / or fan-beam 3D reconstruction of the region of interest.

[0056] In some embodiments, X-ray event detector panel 600 is configured as an indirect conversion X-ray detector. In such embodiments, X-ray event detector panel 600 includes a scintillator material that is excited by incident X-rays and emits light, which is detected by the photodiodes of a plurality of pixel detector element. One such embodiment is described below in conjunction with FIG. 8.

[0057] FIG. 8 schematically illustrates a cross-sectional view of X-ray event detector panel 600 when configured as an indirect conversion X-ray detector, according to various embodiments. The cross-sectional view of FIG. 8 is taken at section A-A in Figure 7. In the embodiment illustrated in FIG. 8, X-ray receiving layer 603 includes a scintillator material, and detector circuitry layer 601 includes pixel detector elements 701. The scintillator material of X-ray receiving layer 603 converts incident X-rays 609 into light photons 809 that are in turn detected and converted into charge by photodiodes included in pixel detector elements 701.

[0058] The scintillator material of X-ray receiving layer 603 may include one or more material layers including, but no limited to, gadolinium oxisulfide (Gd2O2S:Tb), cadmium tungstate (CdWOzi), bismuth germanate (Bi4Ge3Oi2or BGO), cesium iodide (Csl), or cesium iodide thallium (Csl :TI)), among others.

[0059] In some embodiments, X-ray event detector panel 600 is configured as a direct conversion X-ray detector. In such embodiments, X-ray event detector panel 600 includes a matrix or array of pixel detector elements that each convert incident X-ray photons to electrical charge via a photoconductor material. One such embodiment is described below in conjunction with FIG. 9.

[0060] FIG. 9 schematically illustrates a cross-sectional view of X-ray event detector panel 600 when configured as a direct conversion X-ray detector, according to various embodiments. The cross-sectional view of FIG. 9 is taken at section A-A in Figure 7. In the embodiment illustrated in FIG. 9, X-ray receiving layer 603 includes a photoconductor material, and detector circuitry layer 601 includes pixel detector elements 701. The photoconductor material of X-ray receiving layer 603 converts incident X-ray photons 609 into charge 909, and the resultant charge pattern therein is read out by suitable hardware included in detector circuitry layer 601.

[0061] In some embodiments, the photoconductor material of X-ray receiving layer 603 can include amorphous selenium and one of cadmium telluride (CdTe) or cadmium zinc telluride (CdZTe) for photon counting. In the embodiment illustrated in FIG. 9, detector circuitry layer 601 includes a TFT array, an active matrix array, microplasma line addressing, or the like for reading out detected event signals.Pixel Detector Elements

[0062] According to various embodiments, each pixel of an X-ray imaging system, such as X-ray event detector panel 600, is configured to generate signals based on event detection as described above. Embodiments of such pixels are described below in conjunction with FIGS.10 and 11.

[0063] FIG. 10 is a conceptual block diagram of a pixel circuit 1000 of an X-ray event detector panel, according to various embodiments. In some embodiments, pixel circuit 1000 can be implemented as a pixel detector element 701 of FIG. 7, and consequently is disposed within detector circuitry layer 601 of X-ray event detector panel 600 in FIG. 6. Pixel circuit 1000 can be implemented in an indirect conversion X-ray detector or a direct conversion X-ray detector. In the embodiment illustrated in FIG. 10, pixel circuit 1000 includes a photocurrent generator 1010, a differentiator 1020, a comparator 1030, associated interconnects, and, in some embodiments, an integrator 1070. As shown, pixel circuit 1000 is communicatively coupled to a data interface (l / F) 1040 and a data and control bus 1050.

[0064] Photocurrent generator 1010 produces an intensity signal 1001 that is proportional to the intensity of incident X-rays 609 on photocurrent generator 1010. Based on intensity signal 1001, differentiator 1020 determines a change in intensity and outputs a differential change signal 1005 to comparator 1030. Comparator 1030 compares differential change signal 1005 to a reference signal 1004. Comparator 1030 outputs a rising event signal 1002 when reference signal 1004 is exceeded by a positive threshold value and a falling event signal 1003 when reference signal 1004 is exceeded by a negative threshold value. In some embodiments, rising event signals 1002 and falling event signals 1003 can include a binary digital signal to define rising events and falling events, such as a transistor-transistor logic (TTL) signal. Rising event signals 1002 and falling event signals 1003 are transmitted to data interface 1040.

[0065] Data interface 1040 processes either positive or negative events that are detected. As shown, data interface 1040 can provide reference signal 1004 to comparator 1030, where reference signal 1004 corresponds to an X-ray intensity level for pixel circuit 1000 that is associated with a previous X-ray imaging interval. Thus, when an intensity of incident X-ray 609 increases during one particular X-ray imaging interval and then remains constant, comparator 1030 outputs a rising event signal 1002 only forthat X-ray imaging interval. The detection of rising and falling X-ray events is described below in conjunction with FIG. 11.

[0066] FIG. 11 is a plot 1100 of changes in X-ray intensity 1101 measured at a pixel detector element and the associated rising and falling X-ray events generated by the pixel detectorelement, according to various embodiments. In plot 1100, X-ray intensity 1101 measured at the pixel detector element varies over time, for example due to changes in attenuation of incident X-rays that have passed through a patient, sample, or other object of interest. In an embodiment in which the pixel detector element is included in an X-ray event detector panel that remains stationary with respect to a region of patient anatomy, such attenuation is caused by motion within the region of patient anatomy. By contrast, in an embodiment in which the pixel detector element is included in an X-ray event detector panel that moves with respect to a region of patient anatomy (e.g., rotates about the region), such attenuation is caused by the motion of the X-ray event detector panel. In such embodiments, CBCT and / or fan-beam 3D reconstruction of the region of interest can be performed based on such changes in attenuation over a plurality of imaging angles.

[0067] As shown in plot 1100, rising events 1103 are recorded by the pixel detector element each time that X-ray intensity 1101 varies from a pixel reference level by more than a specified intensity threshold 1105, an X-ray event is recorded for the pixel detector element. The reference level is then updated from the previous value to a value corresponding to the current X-ray intensity level for the pixel detector element. For example, at a time t1 , an X-ray intensity 1101 measured at the pixel detector element exceeds a first reference level value 1104A for the pixel detector element by at least intensity threshold 1105. In response, a rising event 1102A is recorded for the pixel detector element, for example via rising event signal 1002 (shown in FIG.10). In addition, the pixel reference level is updated to a second reference level value 1104B for the pixel detector element. Then, at a time t2, an X-ray intensity 1101 measured at the pixel detector element exceeds a second reference level value 1104B by at least intensity threshold 1105. In response, a rising event 1102B is recorded for the pixel detector element, and the pixel reference level is updated to a third reference level value 1104C for the pixel detector element. Conversely, at a time t3, an X-ray intensity measured at the pixel detector element falls below third reference level value 1104C by at least intensity threshold 1105. In response, a falling event 1103A is recorded for the pixel detector element, and the pixel reference level is updated to a new reference level value for the pixel detector element, in this case second reference level value 1104B. Similarly, at a time t4, an X-ray intensity measured at the pixel detector element falls below second reference level value 1104B by at least intensity threshold 1105. In response, a falling event 1103B is recorded for the pixel detector element, and the pixel reference level is updated to reference level value 1104A for the pixel detector element.

[0068] As shown in plot 1100, the rising events and falling events are recorded asynchronously,and therefore can occur in different X-ray imaging intervals. For example, in the instance illustrated in FIG. 11, rising event 1102A and rising event 1102B occur in a first X-ray imaging interval 1110, while falling event 1103A and falling event 1103B occur in a second X-ray imaging interval 1120. Thus, in the instance illustrated in FIG. 11, rising event 1102A and rising event 1102B contribute to a first X-ray event image acquired during first X-ray imaging interval 1110, and falling event 1103A and falling event 1103B contribute to a second X-ray event image acquired during second X-ray imaging interval 1120. In other instances, any combination of rising events and falling events can occur within a given X-ray imaging interval.

[0069] It is noted that rising events and falling events can be detected and reported with microsecond time-scale latency. Consequently, an X-ray event detector panel that includes a plurality of pixel elements 1000 is well-suited for detecting motion, thereby enabling a paradigm shift in how internal patient motion can be detected and monitored. In the field of radiation therapy, X-ray event detectors can be applied to track patient motion in 2D, e.g., for patient safety during treatment beam delivery, fluoroscopy-based procedures, and the like.Embodiments can be applied to a static as well as rotating X-ray imaging system (such as a gantry mounted X-ray imaging system).

[0070] Returning to Figure 10, in some embodiments, data interface 1030 can operate differently than a data interface for a conventional X-ray detector panel. For example, in some embodiments, instead of passing all pixels for one frame to data control bus 1050 for image processing, data interface 1030 encodes each X-ray event with timestamp and location information and passes this information to data control bus 1050. As a result, control bus 1050 only transmits information for image processing for pixels for which an event (increase or decrease in X-ray intensity) is detected. In such embodiments, the timestamp for a particular X-ray event corresponds to the time at which that particular X-ray event is reported (e.g., t1 , t2, t3, and t4 in FIG. 11). In the embodiment illustrated in FIG. 10, data interface 1030 controls the behavior of pixel circuit 1000 by setting the value for reference signal 1004. In some embodiments, data interface 1030 also changes the operation of pixel element 1000 between event mode and integration mode when appropriate. For example, in integration mode, a conventional full-frame X-ray image can be generated when pixels of an X-ray event detector panel are in integration mode.

[0071] In some embodiments, integrator 1070 is included in pixel circuit 1000. In such embodiments, integrator 1070 enables conventional integration of intensity signal 1001 over aspecified time interval. Thus, in such embodiments, integrator 1070 enables an integration mode for pixel element 1000, in which pixel element 1000 intrinsically integrates by accumulating charge for a pixel. In such embodiments, integrator 1070 produces an integrated intensity value 1006 for the pixel that, when combined with intensity values for the other pixels of an X-ray event detector panel, can generate a conventional full-frame X-ray image.

[0072] FIG. 12 is a more detailed conceptual diagram of pixel circuit 1000 when configured as a pixel of an indirect conversion X-ray detector, according to various embodiments. As shown, pixel circuit 1000 includes a photodiode 1201 that generates intensity signal 1001, and differentiator 1020 and optional integrator 1070 both receive intensity signal 1001. Differentiator 1020 generates a differential change signal 1205 and transmits differential change signal to comparator 1030. Comparator 1030 compares differential change signal 1205 to reference signal 1004 and outputs either rising event signal 1002, falling event signal 1003, or no signal accordingly. Integrator 1070 outputs integrated intensity value 1006 at suitable intervals, for example once per X-ray imaging interval. In embodiments in which pixel circuit 1000 is configured as a pixel of a direct conversion X-ray detector, pixel circuit 1000 can include an X-ray photoconductor and associated readout circuitry instead of photodiode 1201.CBCT Reconstruction Using an X-Ray Event Detector

[0073] In some embodiments, an X-ray event detector as described herein can be employed for cone-beam computed tomography (CBCT) reconstruction. One example embodiment is described below in conjunction with FIG. 13.

[0074] FIG. 13 is a flowchart illustrating the steps of a computer-implemented process 1300 for CBCT reconstruction of a 3-dimensional (3D) image using an X-ray event detector panel, according to various embodiments. Computer-implemented process 1300 may include one or more operations, functions, or actions as illustrated by one or more of blocks 1301 - 1321. Although the blocks are illustrated in a specific order, these blocks may be performed in parallel, and / or in a different order than those described herein. Also, the various blocks may be combined into fewer blocks, divided into additional blocks, and / or eliminated based upon a specific implementation. Although the method is described in conjunction with radiation therapy systems 100 and 400, persons skilled in the art will understand that within the scope of the present disclosure any suitably configured radiation therapy system or X-ray imaging system can perform computer-implemented process 1300, such as non-rotating X-ray imaging systems.

[0075] In step 1301, an RT system (e.g., RT system 100 or 300) begins computer-implemented process 1300, which includes CBCT reconstruction of a region of patient anatomy. According to various embodiments, the CBCT reconstruction of computer-implemented process 1300 can generate a 3D image of a region of patient anatomy with higher dynamic range than conventional CBCT reconstructions, thereby improving CBCT image quality regarding soft tissue contrast.

[0076] In step 1301 , a patient is positioned for a CBCT imaging procedure. For example, in some embodiments, the patient is positioned so that a particular region of interest of patient anatomy is imagable by an X-ray event detector, such as X-ray event detector panel 600 in FIG.6.

[0077] In step 1302, the RT system acquires one or more integrated or full-frame CBCT X-ray projection images of the region of patient anatomy with X-ray event detector panel 600. In some embodiments, each full-frame X-ray projection image can be acquired conventionally, for example via integrator 1070 in each pixel circuit 1000. Alternatively, in some embodiments, each full-frame projection image can be acquired without integrator 1070. In such embodiments, intensity modulation of the X-ray imaging source for X-ray event detector panel 600 is employed to generate a full-frame projection image that is not an event detection image and instead corresponds to a conventional X-ray projection image. To facilitate the generation of an initial digital volume of the region of patient anatomy, in some embodiments, multiple fullframe CBCT X-ray projection images are acquired, each from a different viewing angle.

[0078] In step 1303, the RT system generates a digital volume or 3D image of the region of patient anatomy. Specifically, the voxels of the 3D image are populated with image information by performing filtered backprojection (FBP) with the one or more X-ray projection images acquired in step 1302. In embodiments in which a single X-ray projection image is acquired in step 1302, the 3D image is not a complete reconstruction of the region of patient anatomy and instead is a partial reconstruction. In embodiments in which a multiple X-ray projection images are acquired in step 1302, the 3D image can be a complete reconstruction of the region of patient anatomy that is used as an initial digital volume.

[0079] In step 1304, the RT system begins rotation of a rotatable gantry (e.g., C-arm gantry 110 or gantry 510) about the region of patient anatomy.

[0080] In step 1305, while the RT system continues to rotate the rotatable gantry, the RTsystem determines whether the rotatable gantry is at an imaging position. If yes, X-ray imaging of the region of patient anatomy begins; if no, computer-implemented method 1300 returns to step 1305. For example, in some embodiments, each imaging position corresponds to a specific angle of rotation of the rotatable gantry. In some embodiments, an imaging position can be implemented as a finite arc of rotation of the rotatable gantry rather than a single point. In such embodiments, the arc of rotation can be a very small rotational arc due to rising events and falling events being detected and reported with microsecond time-scale latency. Thus, in the time needed for the rotatable gantry to rotate through a small arc (e.g., 1 degree), a sufficient number of X-ray events can be collected to detect patient motion and / or to collect 3D information for the region of patient anatomy.

[0081] In step 1306, the RT system begins X-ray imaging, for example by directing imaging X-rays through the region of patient anatomy and towards X-ray event detector panel 600. The imaging X-rays can be directed to the region of patient anatomy in pulses or continuously. In step 1307, X-ray event detector panel 600 accumulates X-ray events at each pixel. As noted previously, rising events and falling events are reported asynchronously throughout the duration of an imaging interval that occurs at each imaging position.

[0082] In step 1310, the RT system determines whether imaging for the current imaging position is complete. For example, in some embodiments, imaging for a given gantry position occurs over a specified arc of rotation of the rotatable gantry. In some embodiments, imaging for a given gantry position occurs over a specified time interval. In some embodiments, imaging for a given gantry position occurs for a specified number of pulses of imaging X-rays. When the RT system determines imaging for the current imaging position is complete, computer-implemented method 1300 proceeds to step 1311; when the RT system determines imaging for the current imaging position is not complete, computer-implemented method 1300 returns to step 1307.

[0083] In step 1311 , X-ray event detector panel 600 performs a readout of the accumulated X-ray events associated with each pixel, thereby generating a full-frame X-ray event image. One embodiment of an X-ray event image is described below in conjunction with FIG. 14.

[0084] FIG. 14 schematically illustrates a conventional X-ray projection image 1400 of a region of patient anatomy and an X-ray event image 1450 of the region of patient anatomy, according to various embodiments. Conventional X-ray projection image 1400 is a two-dimensional imageof a 3D region 1401 of patient anatomy, where each pixel (not shown) of conventional X-ray projection image 1400 includes density information for a different portion of region 1401. Such density information can be captured with a different gray-scale value for each pixel of conventional X-ray projection image 1400. For clarity, region 1401 is depicted with discrete lines in conventional X-ray projection image 1400, but in practice, conventional X-ray projection image 1400 is typically a grayscale image. In contrast to conventional X-ray projection image 1400, a pixel of X-ray event image 1450 includes information event information when one or more X-ray events are detected for the pixel, for example due to motion of certain portions 1402 of region 1401. Otherwise, there is no information associated with a pixel of X-ray event image 1450. Thus, in the embodiment illustrated in FIG. 14, the majority of pixels include no information. Similar to conventional X-ray projection image 1400, in X-ray event image 1450, pixels that are associated with X-ray event information are depicted with discrete lines that imply a binary change between either no X-ray events being reported for a pixel of some non-zero number of X-ray events being reported for the pixel. In practice, many different non-zero values can be associated with a given pixel in X-ray event image 1450.

[0085] Returning to FIG. 13, in step 1312, the RT system updates the digital volume of the region of patient anatomy based on the X-ray event image. For example, in some embodiments, the RT system performs FBP with the X-ray event image generated or acquired in step 1312. In this way, a CBCT reconstruction of the region of patient anatomy is one step closer to being completed. Computer-implemented method 1300 then proceeds to step 1320. It is noted that the reconstruction performed in step 1312 can run in parallel with rotation of the rotatable gantry and acquisition of X-ray event data. Thus, while the reconstruction of step 1312 is being performed, the rotatable gantry can continue to rotate and an additional iteration of steps 1305 - 1310 can be performed.

[0086] It is noted that, in some embodiments, the X-ray event signal associated with each pixel of an X-ray event image will have a unique rotation angle. In such embodiments, the concept of a common plane of detector signals at a specific gantry angle no longer applies. Instead, in such embodiments, there is an ensemble of detector signal points in a shell around the patient. Effectively, this is a continuous stream of detector events that must be combined using adaptations of existing algorithms to reconstruct a 3D image. In such embodiments, a row of pixel detector elements sees (roughly) a Radon transform across a full rotation, and the event nature of the X-ray event detector send the derivative (change) information. Consequently, in some embodiments, updating the digital volume of the region of patient anatomy in step 1312based on an X-ray event image includes a modified procedure compared to a conventional reconstruction algorithm for updating a digital volume with a conventional intensity X-ray projection. In a conventional reconstruction algorithm that employs a radon transform, each column of a sinogram corresponds to a different projection angle, and includes intensity information for reconstructing or partially reconstructing a digital volume. By contrast, in some embodiments, each column of a sinogram generated based on an X-ray event image represents the change with respect the preceding column, and thus can be considered a derivative with respect to time or angle of X-ray intensity. In such embodiments, an intensity signal that can be employed in a conventional radon transform can be generated by numeric integration. For example, for a ray u that is attenuated by an object, intensity recorded at a pixel detector element in an X-ray event detector panel can be determined by integrating over the attenuations along ray u. In one embodiment, intensity Ipixdrecorded at a pixel detector element can be determined with Equation 1 :Ipixei ~ f e~^du (1)In determining an intensity value Ipixdfor each pixel detector element in an X-ray event detector panel, an inverse of a Radon transform can then be employed in a conventional manner to reconstruct the original density from the X-ray event data.

[0087] In step 1320, the RT system determines whether there are any remaining imaging positions from which an X-ray event image is to be acquired. When the RT system determines there are one or more such imaging positions, computer-implemented method 1300 returns to step 1305 and the RT system continues to rotate the rotatable gantry about the region of patient anatomy. When the RT system determines there are no remaining imaging positions, computer-implemented method 1300 proceeds to step 1321. In step 1321, the RT system ends rotation of the rotatable gantry and computer-implemented method 1300 terminates.Example Computing Device

[0088] FIG. 15 is an illustration of a computing device 1500 configured to perform various embodiments of the present disclosure. For example, in some embodiments, computing device 1500 can be implemented as image acquisition and treatment control computer 109 of RT system 100 or image acquisition and treatment control computer 406 of RT system 400.Computing device 1500 may be a desktop computer, a laptop computer, a smart phone, or any other type of computing device suitable for practicing one or more embodiments of the presentdisclosure. In operation, computing device 1500 is configured to execute instructions associated with computer-implemented process 1300, as described herein. It is noted that the computing device described herein is illustrative and that any other technically feasible configurations fall within the scope of the present disclosure.

[0089] As shown, computing device 1500 includes, without limitation, an interconnect (bus) 1540 that connects a processing unit 1550, an input / output (I / O) device interface 1560 coupled to input / output (I / O) devices 1580, memory 1510, a storage 1530, and a network interface 1570. Processing unit 1550 may be any suitable processor implemented as a central processing unit (CPU), a graphics processing unit (GPU), an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), any other type of processing unit, or a combination of different processing units, such as a CPU configured to operate in conjunction with a GPU or digital signal processor (DSP). In general, processing unit 1550 may be any technically feasible hardware unit capable of processing data and / or executing software applications, including computer-implemented process 1300.

[0090] I / O devices 1580 may include devices capable of providing input, such as a keyboard, a mouse, a touch-sensitive screen, and so forth, as well as devices capable of providing output, such as a display device and the like. Additionally, I / O devices 1580 may include devices capable of both receiving input and providing output, such as a touchscreen, a universal serial bus (USB) port, and so forth. I / O devices 1580 may be configured to receive various types of input from an end-user of computing device 1500, and to also provide various types of output to the end-user of computing device 1500, such as displayed digital images or digital videos. In some embodiments, one or more of I / O devices 1580 are configured to couple computing device 1500 to a network.

[0091] Memory 1510 may include a random access memory (RAM) module, a flash memory unit, or any other type of memory unit or combination thereof. Processing unit 1550, I / O device interface 1560, and network interface 1570 are configured to read data from and write data to memory 1510. Memory 1510 includes various software programs that can be executed by processor 1550 and application data associated with said software programs, including computer-implemented process 1300.Example Computer Program Product

[0092] FIG. 16 is a block diagram of an illustrative embodiment of a computer program product1600 for implementing a method for imaging a region of patient anatomy for a radiation therapy system that includes a rotatable gantry operable to rotate about a treatment isocenter of the radiation therapy system, according to various embodiments. Computer program product 1600 may include a signal bearing medium 1604. Signal bearing medium 1604 may include one or more sets of executable instructions 1602 that, when executed by, for example, a processor of a computing device, may provide at least the functionality described above with respect to FIGS.1 - 15.

[0093] In some implementations, signal bearing medium 1604 may encompass a non-transitory computer readable medium 1608, such as, but not limited to, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, memory, etc. In some implementations, signal bearing medium 1604 may encompass a recordable medium 1610, such as, but not limited to, memory, read / write (R / W) CDs, R / W DVDs, etc. In some implementations, signal bearing medium 1604 may encompass a communications medium 1606, such as, but not limited to, a digital and / or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link, etc.). Computer program product 1600 may be recorded on non-transitory computer readable medium 1608 or another similar recordable medium 1610.

[0094] The descriptions of the various embodiments have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.

[0095] Aspects of the present embodiments may be embodied as a system, method, or computer program product. Accordingly, aspects of the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “module” or “system.” Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.

[0096] Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readablestorage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable readonly memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.

[0097] Aspects of the present disclosure are described above with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, enable the implementation of the functions / acts specified in the flowchart and / or block diagram block or blocks. Such processors may be, without limitation, general purpose processors, special-purpose processors, application-specific processors, or field-programmable processors or gate arrays.

[0098] The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and / or flowchart illustration, andcombinations of blocks in the block diagrams and / or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

[0099] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

1. CLAIMS:

1. An X-ray imaging system, comprising:an X-ray imaging source for directing imaging X-rays to a region of patient anatomy; an X-ray event detector panel for receiving at least a portion of the imaging X-rays; and a controller, wherein the controller performs the steps of:for each pixel of the X-ray event detector panel, determining a cumulative sum of X-ray events detected at the pixel during an imaging interval; generating an X-ray event image of the region of patient anatomy based on the cumulative sum of X-ray events for each pixel; and updating a digital volume of the region of patient anatomy based on the X-ray event image.

2. The X-ray imaging system of claim 1, wherein each pixel comprises a photocurrent generator, a differentiator, and a comparator.

3. The X-ray imaging system of claim 2, wherein the comparator of each pixel is configured to generate a rising event signal when a first X-ray intensity that is received by the photocurrent generator exceeds a pixel reference value by a threshold value.

4. The X-ray imaging system of claim 3, wherein the reference value corresponds to a second X-ray intensity received by the photocurrent generator prior to receiving the first X-ray intensity.

5. The X-ray imaging system of claim 2, 3 or 4, wherein the comparator of each pixel is configured to generate a falling event signal when a first X-ray intensity that is received by the photocurrent generator falls below a pixel reference value by a threshold value.

6. The X-ray imaging system of claim 5, wherein the reference value corresponds to a second X-ray intensity received by the photocurrent generator prior to receiving the first X-ray intensity.

7. The X-ray imaging system of any one of claims 1 to 6, further comprising generating the digital volume based on an initial full-frame X-ray image of the region of patient anatomy.

288. The X-ray imaging system of claim 7, further comprising acquiring the initial full-frame X-ray image with each pixel of the X-ray event detector panel.

9. The X-ray imaging system of claim 8, wherein acquiring the initial full-frame X-ray image with each pixel of the X-ray event detector panel comprises switching each pixel of the X-ray detector panel to an integration mode.

10. The X-ray imaging system of any one of claims 1 to 9, further comprising generating the digital volume based on a plurality of 2D X-ray projection images of the region of patient anatomy.

11. The X-ray imaging system of any one of claims 1 to 10, wherein the X-ray event detector panel is configured to assign timestamp information to each X-ray event detected at each pixel of the X-ray event detector panel.

12. The X-ray imaging system of any one of claims 1 to 11 , wherein updating the digital volume of the region of patient anatomy comprises determining an intensity signal for each pixel of the X-ray event image that has a non-zero value.

13. The X-ray imaging system of claim 12, wherein determining the intensity signal for each pixel comprises integrating over attenuations along a ray that corresponds to the pixel.

14. The X-ray imaging system of any one of claims 1 to 13, wherein generating the X-ray event image comprises reading out the cumulative sum of X-ray events for each pixel of the X-ray event detector panel.

15. A computer-implemented method for reconstructing a digital volume of a region of patient anatomy, the method comprising:for each pixel of an X-ray event detector panel, determining a cumulative sum of X-ray events detected at the pixel during an imaging interval;generating an X-ray event image of the region of patient anatomy based on the cumulative sum of X-ray events for each pixel; andupdating a digital volume of the region of patient anatomy based on the X-ray event image.

16. The computer-implemented method of claim 15, further comprising generating the digital volume based on a plurality of 2D X-ray projection images of the region of patient anatomy.

17. The computer-implemented method of claim 15 or 16, wherein the X-ray event detector panel is configured to assign timestamp information to each X-ray event detected at each pixel of the X-ray event detector panel.

18. The computer-implemented method of claim 15, 16 or 17, wherein updating the digital volume of the region of patient anatomy comprises determining an intensity signal for each pixel of the X-ray event image that has a non-zero value.

19. The computer-implemented method of claim 18, wherein determining the intensity signal for each pixel comprises integrating over attenuations along a ray that corresponds to the pixel.

20. The computer-implemented method of any one of claims 15 to 19, wherein generating the X-ray event image comprises reading out the cumulative sum of X-ray events for each pixel of the X-ray event detector panel.

Images