Virtual beam's-eye view imaging in radiation therapy for patient setup

A virtual beam's-eye view of a planning target volume is generated based on volumetric image data acquired immediately prior to radiation therapy by a radiation therapy system. The virtual beam's-eye view can then be displayed to confirm that, with the patient disposed in the current position, the planned beam-delivered treatment extends beyond the surface of the skin. In some embodiments, the virtual beam's-eye view can be displayed in conjunction with a beam's-eye view that is generated based on volumetric image data acquired during treatment planning, to create a blended beam's-eye view. In some embodiments, a field outline of a treatment beam can be superimposed on the blended beam's-eye view, thereby illustrating whether the planned beam-delivered treatment extends beyond the surface of the skin of the patient. The blended beam's-eye view can facilitate a manual confirmation process that verifies the planned beam-delivered treatment extends beyond the surface of the skin.

BACKGROUND

Radiation therapy is a localized treatment for a specific target tissue (a planning target volume), such as a cancerous tumor. Ideally, radiation therapy is performed on the planning target volume that spares the surrounding normal tissue from receiving doses above specified tolerances, thereby minimizing risk of damage to healthy tissue. Prior to the delivery of radiation therapy, an imaging system is typically employed to provide a three dimensional image of the target tissue and surrounding area. From such imaging, the size and mass of the target tissue can be estimated and an appropriate treatment plan generated and target volume determined.

So that the prescribed dose is correctly supplied to the planning target volume (i.e., the target tissue) during radiation therapy, the patient should be correctly positioned relative to the linear accelerator that provides the radiation therapy. 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 while radiation treatment is delivered to the planning target volume. IGRT incorporates imaging coordinates from the treatment plan to ensure the patient is properly aligned for treatment in the radiation therapy device.

SUMMARY

In accordance with at least some embodiments of the present disclosure, a virtual beam's-eye view of a planning target volume is generated based on volumetric image data acquired immediately prior to radiation therapy by a radiation therapy system. The virtual beam's-eye view can then be displayed to confirm that, with the patient disposed in the current position, the planned beam-delivered treatment extends beyond the surface of the skin. In some embodiments, the virtual beam's-eye view can be displayed in conjunction with a beam's-eye view that is generated based on volumetric image data acquired during treatment planning, to create a blended beam's-eye view. In some embodiments, a field outline of a treatment beam can be superimposed on the blended beam's-eye view, thereby illustrating whether the planned beam-delivered treatment extends beyond the surface of the skin of the patient. Thus, the blended beam's-eye view can facilitate a manual confirmation process that verifies the planned beam-delivered treatment extends beyond the surface of the skin.

DETAILED DESCRIPTION

When the tumor or clinical target volume is disposed near the surface of the skin, correct dosing of the specific target tissue, or the “planning target volume,” can be problematic. Consequently, a virtual bolus, sometimes referred to as a “skin flash region,” is employed in IGRT to ensure that the beam delivering treatment extends beyond the surface of the skin and the dosing of the planning target volume is accurate. For visualization of the skin flash region immediately prior to treatment, a beam's-eye view X-ray image is often generated for patient setup, in which a high-energy film is exposed to an X-ray source, such as the treatment beam itself or some lower energy X-ray beam. Because the X-rays employed to generate the beam's-eye view image mimic the path of the treatment beam during dosing, the beam's eye view enables a radiation therapist to ensure that the relative orientation and position of the patient and the treatment beam are correct. Alternatively, a field light can be employed for visualization of the skin flash region. With a field light, visible light that is coincident with the path of the treatment beam illuminates the planning target volume, and provides visual confirmation that the treatment beam extends beyond the surface of the skin.

However, these conventional approaches have multiple drawbacks. First, checking the skin flash region using a field light is time consuming, and requires a therapist to enter the treatment room and then return to the console area. In addition, some radiation therapy systems do not even include a field light. Second, setup images taken in the beam direction (i.e., beam's eye view images) can be difficult to use to verify the planned treatment area. Due to the unusual viewing angle of beam's-eye view images, matching the newly acquired beam's-eye view image to a previously acquired reference image is not a visually simple task. Third, the generation of beam's-eye view images requires additional patient dosing and time. Fourth, given the none-rigid nature of certain anatomy such as the breast, the current rigid matching based on cone-beam computed tomography (CBCT) in transversal, frontal, and sagittal display is not practical for setup.

In light of the above, there is a need in the art for improved systems and techniques for confirming that beam-delivered treatment in radiation therapy extends beyond the surface of the skin and accurately doses the planning target volume.

In image guided radiation therapy (IGRT), a manual or automatic matching process ensures that the relative orientation and position of the patient and the treatment beam are correct immediately before dosing by the treatment beam takes place. In the matching process, digitally constructed 2D views of the planning target volume are generated from digital volume data taken during the treatment planning process and from digital volume data acquired at the time of treatment; matching of the treatment planning 2D views and the time-of-treatment 2D views enables accurate positioning of the patient immediately prior to treatment. According to embodiments of the present disclosure, a virtual beam's eye view (BEV) image of the planning target volume is also generated from the digital volume data acquired at the time of treatment, so that the virtual BEV image can be employed in the matching process by the radiation therapist. Specifically, prior to delivery of planned radiation therapy, a virtual BEV image is displayed to a radiation therapist as part of an image match verification tool. The virtual BEV image can be a digitally reconstructed radiograph (DRR) projection image constructed from the point of view of the treatment beam at a certain point during the planned radiation treatment. Alternatively or additionally, the virtual BEV image can be a virtual 2D slice, where the slice is taken through the planning target volume and positioned orthogonal to the treatment beam. By viewing the virtual BEV image (or one or more virtual slices), the therapist can perform a matching process on a planning target volume without entering the treatment room for visual confirmation that a skin flash region is indicated by a field light. In addition, the patient is not dosed with additional radiation through the generation of a BEV X-ray image. Instead, the virtual BEV image employed in the match process is generated from image data that are already acquired as part of a radiation therapy workflow, such as CBCT. A radiation therapy system on which such a radiation therapy workflow can be performed is illustrated inFIG. 1.

FIG. 1is a perspective view of a radiation therapy system100, according to one or more embodiments of the present disclosure. Radiation therapy (RT) system100is 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 system100can include one or more of a linear accelerator (LINAC) that generates a megavolt (MV) treatment beam of high energy X-rays, a kilovolt (kV) X-ray source, an X-ray imager, and, in some embodiments, an MV electronic portal imaging device (EPID) (not shown for clarity). By way of example, radiation therapy system100configured with a circular gantry is described herein. Any other suitable radiation therapy system can also benefit from and be configured to implement the embodiments described herein, such as a radiation therapy system configured with a C-arm gantry.

Generally, RT system100is capable of MV and kV imaging techniques, to enable the treatment planner and physician to make clinical decisions that are most appropriate for the patient based on the anatomy of the patient. In some situations, a treatment plan can include kV imaging for improved visualization of soft tissue. In addition, iterative cone beam computed tomography (iCBCT) enhances image reconstruction and can further improve visualization of soft tissue in the kV images.

RT system100may include one or more touchscreens101, couch motion controls102, a bore103, a base positioning assembly105, a couch107disposed on base positioning assembly105, and an image acquisition and treatment control computer106, all of which are disposed within a treatment room. RT system100further includes a remote control console110, which is disposed outside the treatment room and enables treatment delivery and patient monitoring from a remote location. Base positioning assembly105is configured to precisely position couch107with respect to bore103, and motion controls102include input devices, such as button and/or switches, that enable a user to operate base positioning assembly105to automatically and precisely position couch107to a predetermined location with respect to bore103. Motion controls102also enable a user to manually position couch107to a predetermined location. In some embodiments, RT system100further includes one or more cameras (not shown) in the treatment room for patient monitoring.

FIG. 2is a conceptual block diagram illustrating a radiation therapy workflow, according to various embodiments of the present disclosure. Steps201-203take place during a treatment planning phase, in which dosimetry planning for a particular patient is performed. Steps211-216take place at the time of treatment, i.e., while the patient is positioned on the couch of the radiation therapy system at a time subsequent to the planned treatment phase. In some embodiments, the treatment planning phase is also performed on an imaging system that is different from RT system100.

In step201, planning 3D volume data (hereinafter referred to as “reference 3D volume data”) are acquired. In some embodiments, scanning software collects and reconstructs the planning 3D volume data. That is, the scanning software produces a so-called “digital volume” composed of three-dimensional voxels of anatomical data that can then be manipulated and visualized with appropriate software. For example, the patient is positioned in RT system100, or another suitable X-ray imaging system, and the 3D planning volume data is generated by, for example, CBCT. The reference 3D volume data includes volumetric reference image information and, when produced by the CBCT process, can include hundreds of distinct digital X-ray images. Alternatively or additionally, the 3D planning volume data can include volumetric image data generated by any other suitable medical imaging technology that can be employed to identify target tissues in radiation therapy planning and IGRT, such as computed tomography (CT), positron emission tomography (PET), ultrasound imaging, magnetic resonance imaging (MRI), or any combination thereof.

In step202, reference 2D views of the planning target volume and surrounding anatomy are generated based on the reference 3D volume data. Such reference 2D views can be used to visualize the planning target volume. Because RT system100generally performs alignment of couch107in three orthogonal planes (e.g., axial, sagittal, and coronal), for each of these three orthogonal planes, a plurality of reference 2D views (virtual slices) that are parallel to the plane are generated in step202. For example, to enable comprehensive visualization of the planning target volume along an axis perpendicular to the sagittal plane, a plurality of virtual slices are typically generated at different locations along such an axis. Similarly, to enable comprehensive visualization of the planning target volume along an axis perpendicular to the axial plane and to the coronal plane, a plurality of virtual slices is typically generated at different locations along the axis perpendicular to the axial plane and at different locations along the axis perpendicular to the coronal plane. Alternatively, in some embodiments, the above-described reference 2D views of the planning target volume are generated at the time of treatment using the reference 3D volume data.

In step203, dosimetry planning is performed based on the reference 3D volume data generated in step201, and the planning target volume to be radiated is determined.

In step211, which occurs at the time of treatment, the patient is positioned for radiation therapy on couch107of RT system100(shown inFIG. 1), for example using marks on the patient's skin that are aligned with treatment room alignment lasers.

In step212, time-of-treatment 3D volume data are acquired. Scanning software running on image acquisition and treatment control computer106(shown inFIG. 1) collects and reconstructs the time-of-treatment 3D volume data. Thus, a digital volume is produced of the planning target volume of the patient at the time of treatment.

In step213, time-of-treatment 2D views of the planning target volume and surrounding anatomy (hereinafter referred to as “time-of-treatment 2D views”) are generated based on the time-of-treatment 3D volume data acquired in step212. The time-of-treatment 2D views generated in step213include a plurality of virtual slices that are parallel to each of the axial, sagittal, and coronal planes. The time-of-treatment 2D virtual slices that are parallel to each of the axial, sagittal, and coronal planes can be subsequently used to assess quality assurance of the treatment plan and precisely align the patient prior to radiation treatment by comparing patient anatomical structures shown in the reference 2D virtual slices to the time-of-treatment 2D virtual slices. As noted above, in some embodiments, instead of being generated in step202, such reference 2D virtual slices can be generated at time-of-treatment (e.g., in step213) based on the reference 3D volume data acquired in step201.

In addition, according to some embodiments, the time-of-treatment 2D views generated in step213include a virtual BEV image and/or BEV-oriented virtual slices. Unlike the time-of-treatment 2D virtual slices that are parallel to each of the axial, sagittal, and coronal planes, the virtual BEV image and/or BEV-oriented virtual slices are well-suited to verify that the treatment beam extends past the skin of the patient. It is noted that the time-of-treatment virtual BEV image and BEV-oriented virtual slices are generated from time-of-treatment 3D volume data acquired in step212, and no additional acquisition time or dosing are needed. The time-of-treatment virtual BEV image and BEV-oriented virtual slices are described in greater detail below in conjunction withFIGS. 3 and 4.

In step214, an automated 3D matching process is performed. In the automated match process, RT system100performs the matching of time-of-treatment 3D volume data acquired in step212to corresponding reference 3D volume data generated in step201. For example, CBCT information acquired in step201and CBCT information acquired in step212are compared. RT system100then determines couch adjustments required to align the patient and planning target volume with the actual dosing location.

In step215, the time-of-treatment 2D views generated in step213are registered with the reference 2D views, i.e., a 2D matching process is performed. As part of the matching process, discrepancies between the position of anatomical structures in the reference 2D views and in the time-of-treatment 2D views are detected. Corrections to the patient setup position are then determined. For example, couch shift parameters can be calculated for positioning the actual location of patient anatomy relative to the radiation isocenter of RT system100. Specifically, the couch shift parameters are calculated so that the actual location of patient anatomy at the time-of-treatment coincides with the position of patient anatomy in the reference 2D images.

In some embodiments, the match process performed by the therapist is a manual match process. In such a manual match process, the therapist can merge, overlay, blend, or otherwise compare the time-of-treatment 2D views and the reference 2D views of the three orthogonal views. In addition, according to embodiments of the present disclosure, in such a manual match process, the therapist can merge, overlay, blend, or otherwise compare a time-of-treatment virtual BEV image and/or time-of-treatment BEV-oriented virtual slice with a reference BEV image or virtual slice. In such embodiments, the time-of-treatment virtual BEV image (or time-of-treatment BEV-oriented virtual slice) is based on the volumetric time-of-treatment image information of the planning target volume and the reference virtual BEV image (or reference BEV-oriented virtual slice) is constructed based on the volumetric reference image information of the planning target volume. Since the time-of-treatment virtual BEV image and the reference BEV image can both be projection images of the planning target volume along the same specific viewing angle, a radiation therapist can visually perform a manual matching or alignment of the two images when displayed together in a blended fashion, i.e., in a “blended view.” When field outlines of the treatment beam are overlayed on such a blended view, the radiation therapist can then readily confirm that a treatment beam extends beyond the skin of the patient. In this way, dosing of the radiation therapy will be accurate. Alternatively, in some embodiments, field outlines of the treatment beam can be overlayed on the virtual BEV instead of the blended view.

Alternatively or additionally, in some embodiments, the match process performed by the therapist is a verification of the results of the automated match process performed in step214. In an automated match process, RT system100determines couch adjustments required to align the patient and planning target volume with the actual dosing location. Thus, in such embodiments, the radiation therapist visually confirms that the automated match process has accurately aligned the planning target volume with the dosing location of RT system100. This visual confirmation can be via comparison, merging, or blending of the time-of-treatment 2D views generated in step213and the reference 2D views generated in step202. In addition, the visual confirmation includes the comparison, merging, or blending of a time-of-treatment virtual BEV image (or virtual slice) with a reference BEV image. Alternatively or additionally, the visual confirmation includes the comparison, merging, or blending of time-of-treatment BEV-oriented virtual slices generated from the time-of-treatment 3D volume data with reference BEV-oriented virtual slices generated from the reference 3D volume data. For example, the virtual BEV image (generated based on the time-of-treatment 3D volume data) can be displayed together with a reference BEV image that is generated based on the reference 3D volume data of the planning target volume.

During the treatment phase, it is necessary to place the patient under the particle accelerator of RT system100exactly as considered in the dosimetry planning stage. Therefore, in step216, the calculated shift parameters are implemented by base positioning assembly105to reposition couch107so that the actual location of patient anatomy at the time-of-treatment coincide with the position of that anatomy in the reference 2D images (base positioning assembly105to reposition couch107are shown inFIG. 1). Delivery of treatment can then begin.

In some embodiments, the matching process of step215and the correction of the patient setup position of step216is performed by the radiation therapist using an image verification tool displayed on remote control console110(shown inFIG. 1). One example of such a match verification tool is illustrated inFIG. 3.

FIG. 3illustrates a match verification tool300that facilitates calculation of shift parameters for base positioning assembly105to automatically position couch107, according to an embodiment of the disclosure. As shown, match verification tool300includes imaging tools301, patient orientation indicators304, a taskbar305, multiple action buttons306, and a couch shift indicator307. Imaging tools301enable a radiation therapist to change the display of the images in various ways. For example, one such tool may apply filters that improve image quality and facilitate matching of images and/or verification of matched images. Another such tool is a blending slider for comparing the position of patient anatomy in a reference image and in an acquired image. Patient orientation indicators304indicate the anatomical position and relative relationship of an image to anatomical nomenclature in each view window of match verification tool300. Taskbar305provides options for selecting the imaging mode and a particular matching technique to be employed by RT system100and/or by the radiation therapist. The multiple action buttons306variously apply the calculated shift to the position of couch107, enable resetting of changes, perform adjustments to the match, cancel the current match, and reacquire a setup image, among other functions. Couch shift indicator307displays the distance each couch axis should move to correctly position the patient for treatment. As noted above, match results generated by RT system100can include values displayed by couch shift indicator307. In addition, when a radiation therapist adjusts the matching between a reference image and a time-of-treatment setup image, the couch shift values displayed by shift indicator307are updated.

In addition, match verification tool300includes a coronal (or frontal) plane view320, a sagittal plane view330, an axial plane view340, and a virtual BEV window350. Thus, in the embodiment illustrated inFIG. 3, match verification tool300allows reference and time-of-treatment images to be matched in four views. Coronal plane view320enables the display and matching of reference 2D images and time-of-treatment 2D images in a coronal view (i.e., a view along an axis perpendicular to the coronal plane), sagittal plane view330enables the display and matching of reference 2D images and time-of-treatment 2D images in a sagittal view, and axial plane view340enables the display and matching of reference 2D images and time-of-treatment 2D images in an axial view. Furthermore, virtual BEV window350enables the display and matching of reference 2D views and time-of-treatment 2D views in a beam's-eye view (i.e., a view along an axis parallel to a specific path of the planned treatment beam).

For the reference 2D views and time-of-treatment 2D views displayed in coronal plane view320, sagittal plane view330, or axial plane view340, the image plane is considered the physical plane corresponding to the location of the 2D virtual slice. For virtual BEV images displayed by virtual BEV window350, the image plane is considered the projection plane of the virtual BEV image.

It is noted that virtual BEV window350is configured to display reference 2D BEV views and time-of-treatment 2D BEV views for any beam angle of the planned treatment beam. By contrast, each of coronal plane view320, sagittal plane view330, and axial plane view340, is configured to display reference 2D images and time-of-treatment 2D images from a single fixed point of view (or viewing angle). Thus, the image plane for each reference 2D image or time-of-treatment 2D image displayed in, for instance, sagittal plane view330is parallel with the image plane of any other reference 2D view or time-of-treatment 2D view displayed in sagittal plane view330, while the image plane for each 2D BEV view displayed by virtual BEV window350is generally not parallel with the image plane of other 2D BEV images displayed by virtual BEV window350.

Each of coronal plane view320, sagittal plane view330, axial plane view340, and virtual BEV window350displays a portion of patient anatomy310. In coronal plane view320, sagittal plane view330, axial plane view340, patient anatomy310is displayed as a 2D image, which is a virtual slice through patient anatomy310. By contrast, in embodiments in which virtual BEV window350displays a projected DRR image, patient anatomy is shown as a virtual projected view in virtual BEV window350, simulating a conventional X-ray image. Alternatively or additionally, in some embodiments, virtual BEV window350can display a 2D virtual slice of patient anatomy instead of a projected DRR image, where the 2D virtual slice is positioned along and perpendicular to a particular planned path of the treatment beam. In either case, the image displayed in virtual BEV window350has an image plane that is perpendicular to a path of a particular planned treatment beam that passes through the image plane.

In some embodiments, some or all of coronal plane view320, sagittal plane view330, axial plane view340, and virtual BEV window350can be selected to display a time-of-treatment 2D image of patient anatomy310, a reference 2D image of patient anatomy, a time-of-treatment 2D image superimposed on a reference 2D image, or a blended view of patient anatomy310, in which a radiation therapist can simultaneously view a reference 2D image and a time-of-treatment 2D image. In the blended view, the radiation therapist can employ one of imaging tools301to enable a slider function that facilitates comparison and matching of a reference 2D image and a time-of-treatment 2D image. For example, a slider tool included in imaging tools301can be activated that enables the comparison, at a selected location, of a reference 2D image and a corresponding time-of-treatment 2D image. Thus, when the slider tool is activated for a window displaying a view of a particular planar slice of a planning target volume (e.g., a view toward one of the axial, sagittal, or coronal planes), actuation of the slider selects a reference image (2-D slice) and a corresponding time-of-treatment image (2-D slice) at a specific planar location.

According to embodiments of the disclosure, virtual BEV window350can be used to verify that the treatment beam extends past the skin for any selected beam angle of the treatment beam that is programmed to occur during treatment. Specifically, match verification tool300is configured to display, when an appropriate imaging tool301is selected (e.g., a field outlines tool), the extents351of the planned treatment beam relative to the anatomy of the patient. In the embodiment illustrated inFIG. 3, extents351of the planned treatment beam are displayed in each of coronal plane view320, sagittal plane view330, axial plane view340, and virtual BEV window350. However, when only viewing coronal plane view320, sagittal plane view330, and axial plane view340, visually determining the location of extents351of the planned treatment beam relative to surface352of patient skin in these views can be unreliable and/or time-consuming. By contrast, in virtual BEV window350, surface352of patient skin relative to extents351of the planned treatment beam is readily determined visually for any angle of the planned treatment, due to the positioning of the image plane for views shown in virtual BEV window350. One embodiment of an image plane for a view displayed in sagittal plane view330is shown inFIG. 4A, one embodiment of an image plane for a view displayed in virtual BEV window350is shown inFIG. 4B, and one embodiment of an image plane for a 2D projected view displayed in virtual BEV window350is shown inFIG. 4C.

FIG. 4Aschematically illustrates an image plane401for a 2D view displayed in, for example, sagittal plane view330ofFIG. 3, according to an embodiment of the disclosure. The 2D view being displayed can be a reference 2D view of a planning target volume410, a time-of-treatment 2D view of the planning target volume410, or a blended 2D view that includes a reference 2D view and a corresponding time-of-treatment 2D view of the planning target volume410. As shown, image plane401for the 2D view being displayed passes through planning target volume410and corresponds to the location of the 2D virtual slice being displayed in sagittal view330. Further, image plane401is perpendicular to a virtual viewing direction402. As a result, a 2D slice404(cross-hatched area of planning target volume410) that is parallel to the sagittal plane and perpendicular to virtual viewing direction402is displayed in sagittal plane view330ofFIG. 3. Similarly, an image plane (not shown) for the 2D view being displayed in axial plane view340corresponds to the location of a 2D virtual slice that passes through planning target volume410, is perpendicular to a virtual viewing direction, and is displayed in axial plane view340. Furthermore, an image plane (not shown) for the 2D view being displayed in coronal plane view320corresponds to the location of a 2D virtual slice that passes through planning target volume410, is perpendicular to a virtual viewing direction, and is displayed in coronal plane view320.

FIG. 4Bschematically illustrates an image plane421for a 2D view displayed in virtual BEV window350ofFIG. 3, according to an embodiment of the disclosure. The 2D view being displayed in virtual BEV window350is represented by the cross-hatched region405, and can be a reference 2D BEV slice of planning target volume410, a time-of-treatment 2D BEV slice of the planning target volume410, or a blended 2D BEV slice that includes a reference 2D BEV slice and a corresponding time-of-treatment 2D BEV slice of the planning target volume410. As shown, image plane421for the 2D view displayed in virtual BEV window350passes through planning target volume410and corresponds to the location of the 2D BEV view being displayed in virtual BEV window350. Further, image plane421is perpendicular to a virtual viewing direction that is coincident with a planned treatment beam path422. In contrast to image plane401depicted inFIG. 4A, image plane421is generally not parallel to a coronal plane, a sagittal plane, or an axial plane associated with RT treatment of planning target volume410. Instead, image plane421is perpendicular to planned treatment beam path422that passes through planning target volume410. It is noted that planned treatment beam path422can be the path of a treatment beam at any portion of a particular RT treatment of planning target volume410. For example, in a volumetric modulated arc therapy (VMAT) treatment of planning target volume410, planned treatment beam path422of the treatment beam is continuously changing over time during delivery of radiation therapy. Alternatively or additionally, planned treatment beam path422can be the path of any other treatment beam path for treatment of planning target volume410.

FIG. 4Cschematically illustrates an image plane431for a 2D projected view430displayed in virtual BEV window350ofFIG. 3, according to an embodiment of the disclosure. In the embodiment illustrated inFIG. 4C, 2D projected view430being displayed in virtual BEV window350can be a reference DRR of planning target volume410, a time-of-treatment DRR of the planning target volume410, or a blended DRR BEV that includes a reference DRR BEV and a corresponding time-of-treatment DRR BEV of the planning target volume410. As shown, image plane431for 2D projected view430corresponds to the projection plane that is employed in generating the above DDR BEVs of the planning target volume410. Thus, in such embodiments, image plane431for 2D projected view430does not pass through planning target volume410, but is perpendicular to a planned treatment beam path432.

FIG. 5sets forth a flowchart of an example method for viewing a planning target volume for radiation therapy, according to one or more embodiments of the present disclosure. The method may include one or more operations, functions, or actions as illustrated by one or more of blocks501-508. Although the blocks are illustrated in a sequential 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 the desired implementation. Although the method is described in conjunction with the systems ofFIGS. 1-4C, persons skilled in the art will understand that any suitably configured radiation therapy system is within the scope of the present disclosure.

A method500begins at step501, in which a computing device associated with RT system100(such as image acquisition and treatment control computer106) receives initial digital volume data of a planning target volume. The digital volume data can include sets of images, where each set includes a plurality of image slices taken through the planning target volume and surrounding anatomy. The plurality of image slices are taken orthogonal to a single viewing direction, so that the image slices included in one set are parallel to one of axial, sagittal, or coronal planes. In some embodiments, the digital volume data can include one or more reference 2D BEV images that each include an image plane that is perpendicular to a planned treatment beam path that passes through that image plane. Alternatively or additionally, the digital volume data can include a set of 2D BEV virtual slices that each include an image plane that is perpendicular to a planned treatment beam path that passes through the image plane.

In optional step502, the computing device generates a first 2D view of the planning target volume based on the initial digital volume data. Specifically, the computing device generates one or more virtual BEV images of the planning target volume, based on the initial digital volume data generated prior to radiation therapy. The one or more BEV images are also generated to appear to be taken from the direction of the treatment beam and from the point of view of the source of the treatment beam. The first 2D view has a first image plane that is perpendicular to a planned treatment beam path that passes through the image plane. In embodiments in which the initial digital volume data includes such a 2D view of the planning target volume, step502is not performed.

In step503, the planning target volume is positioned for acquisition of time-of-treatment digital volume data of the planning target volume. That is, the patient associated with the initial digital volume data is positioned on couch107of RT system100so that the planning target volume is located as close as possible to the planned treatment isocenter.

In step504, the computing device causes RT system100to acquire time-of-treatment digital volume data of the planning target volume. For example a CBCT process may be performed by RT system100.

In step505, the computing device generates a second 2D view of the planning target volume based on the time-of-treatment digital volume data. Thus, the computing device generates one or more virtual BEV images of the planning target volume, based on the time-of-treatment digital volume data acquired in step504, and also on a planned treatment that includes at least one treatment beam. The one or more virtual BEV images (time-of-treatment virtual BEV images) are generated to appear to be taken from the direction of the treatment beam and from the point of view of the source of the treatment beam. Any suitable DRR generation algorithm or other software for processing digital volume data can be employed in step505to generate such virtual BEV images.

In step506, the computing device causes a time-of-treatment virtual BEV image that is generated in step505to be displayed in a blended view, for example on remote control console110. Step506may be performed in response to a user input selecting a particular virtual BEV image to be displayed. For example, the user may perform the input via a suitable imaging tool301. In some embodiments, the time-of-treatment virtual BEV image that is displayed in step506is displayed without a corresponding reference virtual BEV image. In other embodiments, the time-of-treatment virtual BEV image that is displayed in step506is displayed superimposed on a corresponding reference virtual BEV image. In other embodiments, the time-of-treatment virtual BEV image that is displayed in step506is displayed in a blended view, which includes the time-of-treatment virtual BEV image and the corresponding reference virtual BEV image. Thus, the blended view includes a virtual BEV image that is generated based on time-of-treatment digital volume data and a virtual BEV image that is generated based on reference digital volume data.

In step507, the computing device determines a field outline for the treatment beam included in the planned treatment. The field outline is determined based on the particular time-of-treatment virtual BEV image that is selected in step506and a corresponding treatment beam and treatment beam angle. The treatment beam angle is that angle associated with the treatment beam when the treatment beam is applied to the planning target volume, passes through the image plane of the selected virtual BEV image, and is perpendicular to the image plane of the selected virtual BEV image.

In step508, the computing device causes the field outline to be displayed with the virtual BEV image displayed in step505. That is, the field outline is superimposed on the virtual BEV image(s) displayed in step505. In some embodiments, anatomical structures associated with the planning target volume are also overlayed on the blended view. It is noted that virtual BEV window350displays a projection image of patient anatomy310that is a virtual BEV image from whatever viewing angle is requested by the radiation therapist. Generally, the viewing angle used to generate the 2D virtual BEV image corresponds to the angle of the treatment beam or beams employed in the current treatment plan. Consequently, the radiation therapist can readily determine visually whether the extents351of the planned treatment beam extend beyond the surface352of a patient's skin for any selected treatment beam angle.

Implementation of method500as described above provides a match verification tool that enables fast and accurate visual confirmation that the patient is correctly positioned relative to the planned treatment isocenter, so that a planned treatment beam extends beyond the surface of the patient's skin. Furthermore, the virtual BEV image employed in the above-described match verification tool is generated without the additional dosing associated with a conventional X-ray BEV image.