Patent Description:
Radiation therapy is a localized treatment for a specific anatomical target (a planning target volume, or PTV), 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 anatomical target and surrounding area. From such imaging, the size and mass of the anatomical target can be estimated, a planning target volume determined, and an appropriate treatment plan generated using a dedicated treatment planning system (TPS). The TPS has photon- and electron-beam models that accurately represent the beams generated by the radiation therapy delivery system.

Currently, the field of radiation oncology is moving to treating smaller planning target volumes, for example via stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT). Stereotactic radiosurgery and stereotactic radiation therapy are advanced forms of radiation therapy that involve delivery of a high radiation dose to a small focused region of a patient's anatomy. Because of the high radiation dose and small target volumes associated with these SRS treatments, high geometric accuracy of the delivered treatment is required. This high geometrical accuracy is required for both the predicted dose distribution provided by the beam model in the TPS and the delivered dose provided by the actual treatment delivery system.

"<NPL> disclose two distinct methods for determining the beam spot position and <CIT> discloses a method for monitoring in real time the electron beam spot position and shape.

According to one aspect of the invention, there is provided a computer-implemented method for tuning a beam spot in a radiation therapy system based on radiation field measurements, as defined in claim <NUM>. According to another aspect of the invention, there is provided a radiation therapy system, as defined in claim <NUM>. Optional features are specified in the dependent claims. The invention relates to a method and a system as defined in the appended claims. Embodiments, examples or aspects in the following disclosure which do not fall under the scope of the claims are presented for illustration purposes only and do not form part of the invention.

According to various embodiments, a computer-implemented procedure includes a direct measurement of beam spot size, shape, and intensity distribution in a radiation therapy system using an existing imaging panel of the radiation therapy system, and modification of one or more attributes of a beam spot based on such measurements. Specifically, a sequence of radiation projection images (e.g., X-ray projection images) are acquired with the imaging panel while a treatment beam is generated and a multi-leaf collimator is positioned to block a portion of the beam and rotated about the center axis of the beam. Based on the projection images, a two-dimensional (2D) image of the beam spot is reconstructed, which indicates the area, size, shape, location, and 2D intensity topography of the beam spot. Additionally, by shaping a small radiation field and using the existing imaging panel to measure the radiation field penumbra and output factor of the treatment beam can be determined. The computer-implemented procedure further includes modifying the size, shape, and/or location of the beam spot based on the reconstructed 2D beam spot image, so that the beam spot meets a threshold value for one or more predetermined quality metrics. In some embodiments, the beam spot can be modified by changing an existing value for a parameter of an electron-beam-generating component of the system to a new value. Additional iterations of beam spot measurement and electron-beam modifications can be performed until the beam spot meets such threshold values. Because each iteration can be performed in a few minutes as part of an automated process, the computer-implemented procedure of the embodiments can be employed as part of factory setup, an on-site quality-assurance tool, and/or as a periodic service tool. Thus, penumbra and/or output factor deviations and other issues created by asymmetric beam spots or beams that do not meet the necessary geometrical requirements can be prevented. Further, a radiation target energy density per unit beam area can be confirmed to be within acceptable limits, thereby ensuring reliable target power levels and extended target life for a radiation therapy system.

According to various embodiments, a computer-implemented procedure includes measurement of one or more attributes of a radiation field generated by a beam spot using an existing imaging panel of the radiation therapy system, and modification of one or more attributes of the beam spot based on such radiation field measurements. Attributes of the radiation field are quantified via one or more specific radiation field quality metrics, which can indicate whether a radiation beam originating from the beam spot is outside a specified quality range. Examples of such radiation field quality metrics include one or more of an area coincidence factor, a penumbra asymmetry factor, and a radiation beam output factor.

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.

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 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.

As noted above, for radiation treatments that involve a high radiation dose and/or a small target size, high geometric accuracy of the delivered radiation treatment is required. Many factors can affect the accuracy of a delivered radiation treatment, including the size, shape, and location of the beam spot, which is the area on a radiation target that is struck by an electron beam and generates the treatment radiation beam, such as an X-ray beam or other radiation beam, in linear-accelerator-based radiation therapy systems. For example, to achieve the high spatial accuracy required for certain image-guided radiation therapy (IGRT) treatments, the IGRT imaging isocenter must closely coincide with the treatment beam isocenter, and this isocenter coincidence is influenced by the alignment of the beam spot with the collimator rotation axis. In another example, percentage depth dose distribution and beam profiles of very small diameter (<NUM>-<NUM>) megavoltage (MV) radiosurgical beams have been shown to depend on the diameter of the beam spot. In a further example, controlling and minimizing dose fall-off at the edges of a treatment beam (i.e., the "penumbra") is important for sparing organs at risk in radiation therapy, and the size, shape, and symmetry of the beam spot all directly affect the size and shape of the penumbra. Moreover, the output factor of such small fields, which is also dependent on the beam spot characteristics, has to meet tight specifications. In light of the above, accurate knowledge of the geometry of a beam spot in a radiation therapy system is of high importance, particularly for treatments involving a smaller planning target volume (PTV) and/or a high radiation dose and/or a sharp dose fall-off.

Unfortunately, direct measurement of the beam spot in a radiation therapy system can be difficult to implement. As a result, fitting a planning target volume with a high, uniform dose while limiting the irradiation of neighboring healthy tissues can be difficult to achieve. Conventional techniques for measuring properties of the beam spot of a radiation therapy system are time-consuming to set up and perform, rely on measuring equipment that is external to the radiation therapy system, and/or provide incomplete information about the beam spot. For example, a spot camera positioned between the radiation source of n radiation therapy system and an electronic portal imaging device (EPID) of the radiation therapy system allows only parallel radiation from the radiation source to reach the EPID. As a result, the EPID can generate an image of the beam spot that shows the size, shape, and position of the beam spot. However, a spot camera is a bulky piece of specialized equipment external to the radiation therapy system, requiring precise and time-consuming setup and training to be used. In another example, a probe external to a radiation therapy system can be employed in conjunction with a water tank to traverse the radiation field of the radiation source and generate profiles of radiation intensity across the radiation field. Such profiles can provide relative information about the beam spot and penumbra symmetry. However, this approach also involves the time-consuming setup and manual operation of equipment external to the radiation therapy system, greatly limiting where and how frequently this approach can be employed. Further, the information obtained does not indicate the actual size of the penumbra or the intensity distribution of the beam spot itself.

According to various embodiments, a computer-implemented procedure includes a direct measurement of beam spot size, shape, location, orientation, and intensity distribution in a radiation therapy system, using an existing ("on-board") imaging panel of the radiation therapy system. Based on a sequence of projection images that are acquired with the on-board imaging panel, a two-dimensional (2D) image of the beam spot is reconstructed, which indicates the area, size, shape, location, orientation, and 2D intensity topography of the beam spot, including the radiation penumbra and the output factor of the treatment beam. Radiation penumbra is a parameter describing the dose delivered and the fall-off of dose profiles in the patient, and in some embodiments is given by the difference between the projected distances of the <NUM>% and <NUM>% dose values in a <NUM>-dimensional projection of the dose distribution. For the small fields employed in SRS treatments, penumbra is highly dependent on the radiation beam spot size, shape, and location with respect to the central axis of the collimator system of the radiation therapy system. Additionally, the radiation output factor of the SRS field is dependent on certain beam spot characteristics. Therefore, enforcing pre-determined quality metrics on the beam spot ensures that both the penumbra and output factors are tightly controlled and meet tight tolerances mandated by the geometrical accuracy of SRS treatments and small field dosimetry. The beam spot and penumbra of a treatment beam in a radiation therapy system are described in greater detail below in conjunction with <FIG>.

In some embodiments, the computer-implemented procedure further includes modifying the size, shape, and/or location of the beam spot and/or penumbra based on the reconstructed 2D beam spot image, so that the beam spot meets a threshold value for one or more predetermined beam spot quality metrics. In some embodiments, such beam spot quality metrics include one or more of a beam spot area, a beam spot elongation, a beam spot power per unit area factor, and/or a beam spot center point offset from an ideal center point location.

The herein-described embodiments facilitate tuning of a beam spot to achieve superior beam quality metrics and improve consistency between the attributes of the beam spot and the overall beam tuning of the treatment delivery system and pre-configured beam data that is included in a treatment planning model of a TPS. Pre-configured beam data is a set of beam measurements (e.g., beam profiles, percent depth dose and/or output factors) acquired using a dedicated <NUM>-dimensional water scanning system and radiation detectors. Generally, such pre-configured beam data resides in the TPS that is used for treatment plan creation. As a result, in the embodiments, performance of a radiation beam generated by the beam spot closely matches the performance assumed for the radiation beam in the TPS.

<FIG> is a perspective view of a radiation therapy system <NUM> that can beneficially implement various aspects of the present disclosure. Radiation therapy (RT) system <NUM> is a radiation system may be configured to detect intra-fraction motion in near-real time using X-ray imaging techniques. Thus, in some embodiments, RT system <NUM> 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 <NUM> can include one or more of a linear accelerator (LINAC) <NUM> that generates an MV treatment beam of high energy X-rays or other radiation, one or more kilovolt (kV) X-ray sources <NUM>, one or more imaging panels <NUM> (e.g., an X-ray imager), and an MV electronic portal imaging device (EPID) <NUM>. By way of example, RT system <NUM> is described herein configured with a C-arm gantry <NUM> capable of infinite rotation via a slip ring connection. In other embodiments, RT system <NUM> can be configured with a circular gantry mounted on a drive stand, or any other technically feasible configuration that enables radiation therapy and imaging of a PTV.

In some embodiments, RT system <NUM> is capable of X-ray imaging of a target volume immediately prior to and/or during application of an MV treatment beam, so that an IGRT and/or an intensity-modulated radiation therapy (IMRT) process can be performed using X-ray imaging. For example, in some embodiments, RT system <NUM> includes kV imaging of a PTV in conjunction with imaging generated by the MV treatment beam. RT system <NUM> may include one or more touchscreens <NUM> for patient information verification, couch motion controls <NUM>, a radiation area <NUM>, a base positioning assembly <NUM>, a couch <NUM> disposed on base positioning assembly <NUM>, and an image acquisition and treatment control computer <NUM>, all of which are disposed within a treatment room. RT system <NUM> further includes a remote control console <NUM>, which is disposed outside the treatment room and enables treatment delivery and patient monitoring from a remote location. In some embodiments, image acquisition and treatment control computer <NUM> and/or remote control console <NUM> is configured to execute a treatment planning system that includes photon-beam, electron-beam, and/or other treatment planning models that accurately represent the beams generated by RT system <NUM>. Such models include pre-configured beam data that assumes specific attributes of the beam spot that generates a treatment beam. Base positioning assembly <NUM> is configured to precisely position couch <NUM> with respect to radiation area <NUM>, and motion controls <NUM> include input devices, such as buttons and/or switches, that enable a user to operate base positioning assembly <NUM> to automatically and precisely position couch <NUM> to a predetermined location with respect to radiation area <NUM>. Motion controls <NUM> also enable a user to manually position couch <NUM> to a predetermined location.

<FIG> schematically illustrates a side view of RT system <NUM>, according to various embodiments. As shown, RT system <NUM> includes a base stand <NUM> and C-arm gantry <NUM>. In <FIG>, base positioning assembly <NUM>, couch <NUM>, and X-ray source <NUM> are omitted for clarity. Base stand <NUM> is a fixed support structure for components of RT treatment system <NUM>, including C-arm gantry <NUM> and a drive system (not shown) for rotatably moving C-arm gantry <NUM> about a horizontal rotation axis <NUM>. Base stand <NUM> rests on and/or is fixed to a support surface that is external to RT treatment system <NUM>, such as a floor of an RT treatment facility. C-arm gantry <NUM> is rotationally coupled to base stand <NUM> and is a support structure on which various components of RT system <NUM> are mounted, including LINAC <NUM>, EPID <NUM>, imaging X-ray source <NUM> (not shown in <FIG>), and imaging panel <NUM>. During operation of RT treatment system <NUM>, C-arm gantry <NUM> rotates about radiation area <NUM> when actuated by the drive system.

Imaging X-ray source <NUM> is configured to direct a conical beam of X-rays, referred to herein as imaging X-rays (not shown in <FIG> for clarity), through an isocenter <NUM> of RT system <NUM> to imaging panel <NUM>. Isocenter <NUM> typically corresponds to the location of a target volume <NUM> to be treated, such as a PTV. In the embodiment illustrated in <FIG>, imaging panel <NUM> is depicted as a planar device, whereas in other embodiments, imaging panel <NUM> can have a curved configuration. In the embodiment illustrated in <FIG> and <FIG>, RT system <NUM> includes a single imaging panel and a single corresponding imaging radiation source in addition to EPID <NUM>. In other embodiments, RT system <NUM> can include two or more imaging panels, each with a corresponding imaging radiation source.

LINAC <NUM> 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 <NUM> for collimating and shaping a treatment beam <NUM> that originates from the electron beam target. Collimator assembly <NUM> typically includes one or more of a primary collimator that defines the largest available circular radiation field for treatment beam <NUM>, a secondary collimator for providing a rectangular or square radiation field at isocenter <NUM> (for example via X-jaws and Y-jaws), and a multileaf collimator (MLC) for conforming treatment beam <NUM> to a PTV or other target volume.

During radiation treatment, in some embodiments LINAC <NUM> is configured to generate treatment beam <NUM>, which can include high-energy radiation (for example MV X-rays or MV electrons). In other embodiments, treatment beam <NUM> includes electrons, protons, and/or other heavy charged particles, ultra-high dose rate X-rays (e.g., for FLASH radiotherapy), and/or microbeams for microbeam radiation therapy. In addition, imaging panel <NUM> is configured to receive imaging radiation and generate suitable projection images therefrom. Further, in some embodiments, as treatment beam <NUM> is directed to isocenter <NUM> while C-arm gantry <NUM> rotates through a treatment arc, image acquisitions can be performed via EPID <NUM> to generate image data for target volume <NUM>. For example, in such embodiments, EPID <NUM> generates one or more projection images of target volume <NUM> and/or a region of patient anatomy surrounding target volume <NUM>. Thus, projection images (e.g., 2D X-ray images) of target volume <NUM> can be generated during portions of an IGRT or IMRT process via imaging panel <NUM> and/or EPID <NUM>. Such projection images can then be employed to construct or update portions of imaging data for a digital volume that corresponds to a three-dimensional (3D) region that includes target volume <NUM>. 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 <NUM>.

As noted above, LINAC <NUM> is configured to generate treatment beam <NUM> during radiation treatment. For radiation treatments that involve a high radiation dose and/or a small target size, such as stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT), the required geometric accuracy of the delivery of treatment beam <NUM> can be adversely affected by the size, shape, location, and/or asymmetry of the treatment beam penumbra. A treatment beam penumbra is described below in conjunction with <FIG>.

<FIG> schematically illustrates treatment beam <NUM> with an associated treatment beam penumbra <NUM> for a particular beam-limiting device. As shown, treatment beam <NUM> is generated by a beam spot <NUM> (cross-hatched) on an electron beam target <NUM> that is located in a target plane <NUM>. Beam spot <NUM> is typically generated by an electron beam (not shown) that is directed onto electron beam target <NUM> by an accelerating waveguide and electron beam transport means (such as a bending magnet) of LINAC <NUM>. The electron beam creates beam spot <NUM> on electron beam target <NUM> from which treatment beam <NUM> originates. Beam spot <NUM> has a 3D distribution, which can be quantified via a 2D intensity distribution <NUM> that represents the electron beam distribution striking electron-beam target <NUM>. 2D intensity distribution <NUM> is depicted as a one-dimensional function in <FIG>, but in practice, 2D intensity distribution <NUM> of beam spot <NUM> varies over a 2D region of electron beam target <NUM>.

Treatment beam <NUM> is shaped by one or more MLCs <NUM> of RT system <NUM>, passes through isocenter <NUM> of RT therapy system <NUM>, and strikes EPID <NUM>. Ideally, a center axis <NUM> of treatment beam <NUM> is aligned with isocenter <NUM> and with collimator rotation axis <NUM>, about which MLC <NUM> may rotate. However, even when beam spot <NUM> is positioned on electron beam target <NUM> so that center axis <NUM> of treatment beam <NUM> is aligned with collimator rotation axis <NUM> (as shown in <FIG>), beam spot <NUM> produces penumbra <NUM>, which is a region at the edge of treatment beam <NUM> in which there is significant dose fall-off. Penumbra <NUM> is generated because beam spot <NUM> is not a single point, but instead is a 2D area on electron beam target <NUM>.

In the instance illustrated in <FIG>, penumbra <NUM> is depicted as a geometric penumbra of treatment beam <NUM>. In other instances, penumbra <NUM>, when referenced herein, can further include a transmission penumbra of treatment beam <NUM>, which occurs when a portion of treatment beam <NUM> passes through an edge of a collimator (e.g., a jaw and/or MLC) before reaching the full attenuation point of the collimator. Thus, in some instances, the term "penumbra" can refer to a geometric penumbra of a treatment beam, a transmission penumbra of a treatment beam, and/or a total penumbra of a treatment beam, which is a combination of the geometric penumbra and the transmission penumbra.

The dose fall-off in a radiation therapy system associated with penumbra <NUM> can degrade the high spatial accuracy required for certain radiation therapy treatments using treatment beam <NUM>. As a result, radiation therapy systems are typically configured to minimize or otherwise reduce a width <NUM> of penumbra <NUM>. Further, when beam spot <NUM> is asymmetric and/or off-center from collimator rotation axis <NUM> and/or isocenter <NUM>, width <NUM> generally varies at different portions of penumbra <NUM>, which can complicate conforming treatment beam <NUM> to a PTV or other target volume. Consequently, precise and accurate knowledge of 2D intensity distribution <NUM> of beam spot <NUM> in a radiation therapy system can be highly beneficial, particularly for treatments involving a small PTV and/or a high radiation dose. According to various embodiments, such information regarding 2D intensity distribution <NUM> can be determined using a conventional radiation therapy system.

<FIG> schematically illustrates a beam-generating subsystem <NUM> of RT system <NUM> that can beneficially implement various embodiments. Beam-generating subsystem <NUM> includes components of RT system <NUM> for generating treatment beam <NUM> and for generating X-ray projection images of beam spot <NUM> according to various embodiments. In the embodiment illustrated in <FIG>, beam-generating subsystem <NUM> includes LINAC <NUM>, collimator assembly <NUM>, and EPID <NUM>. LINAC <NUM> includes an electron gun <NUM> for generating an electron beam <NUM>, an accelerating waveguide <NUM> for accelerating the electrons of electron beam <NUM>, a first beam-shaping solenoid <NUM>, a second beam-shaping solenoid <NUM>, electron beam target <NUM>, and/or an electron beam transport means (such as a bending magnet) <NUM>. While collimator assembly <NUM> may typically include one or more of a primary collimator, a secondary collimator, one or more filters, an ionization chamber, MLC <NUM>, and/or other components, for clarity the only portion of collimator assembly <NUM> shown in <FIG> is MLC <NUM>, which is configured to rotate about collimator rotation axis <NUM>. According to various embodiments, a computer-implemented procedure provides a direct measurement of beam spot size, shape, and intensity distribution in RT system <NUM> using beam-generating subsystem <NUM>. One such embodiment is illustrated below in conjunction with <FIG>.

<FIG> schematically illustrates a portion of beam-generating subsystem <NUM> while a beam-spot imaging procedure is performed, according to various embodiments. In the embodiments, a direct beam-spot measurement is performed that enables quantification of the size, shape, and location of 2D intensity distribution <NUM> of beam spot <NUM>. As shown, in the embodiments, a portion <NUM> of MLC <NUM> is parked so that a significant portion <NUM> (e.g., approximately half) of treatment beam <NUM> is blocked from reaching EPID <NUM>. A sequence of X-ray projection images are then acquired of beam spot <NUM> with EPID <NUM> while MLC <NUM> is rotated about collimator rotation axis <NUM>. Based on the X-ray projection images of the different portions of beam spot <NUM>, an image of beam spot <NUM> is reconstructed that indicates the size, shape, and location of 2D intensity distribution <NUM> of beam spot <NUM>. In some embodiments, a reconstruction algorithm (described below in conjunction with <FIG>) is employed that uses a parallel-beam computed tomography (CT) reconstruction technique to compute the image of beam spot <NUM>.

To generate the sequence of X-ray projection images of beam spot <NUM>, MLC <NUM> is positioned at a plurality of different rotational angles about collimator rotation axis <NUM>, so that at each different rotational angle, line of sight between beam spot <NUM> and a different portion of the radiation beam is blocked by portion <NUM>. Further, at each different rotational angle, an X-ray projection image of beam spot <NUM> is generated with LINAC <NUM>. Thus, for each X-ray projection image, a different portion of beam spot <NUM> is partially or completely viewable by EPID <NUM>. For example, with MLC <NUM> positioned as shown in <FIG>, a first region 505A of EPID <NUM> does not have line of sight to any of beam spot <NUM>, a second region 505B of EPID <NUM> has line of sight to a portion of beam spot <NUM>, a third region 505C of EPID <NUM> has line of sight to a different portion of beam spot <NUM>, and a fourth region 505D of EPID <NUM> does not have line of sight to any of beam spot <NUM>. As MLC <NUM> rotates about collimator rotation axis <NUM>, third region 505C and fourth region 505D of EPID <NUM> have lines of sight to different portions of beam spot <NUM>. Consequently, unless beam spot <NUM> is perfectly symmetric and precisely centered on collimator rotation axis <NUM>, each such X-ray projection image has a different intensity distribution of received X-rays from beam spot <NUM>. Based on the different intensity distribution of each X-ray projection image of beam spot <NUM>, a 2D image of beam spot <NUM> can be reconstructed. One embodiment of a 2D image of a beam spot is described below in conjunction with <FIG>.

<FIG> schematically illustrates a beam spot image <NUM>, according to various embodiments. Beam spot image <NUM> is an image of a beam spot of a radiation therapy system, such as beam spot <NUM> of <FIG>, and is generated using an imager of a conventional radiation therapy system, such as EPID <NUM> of RT system <NUM>. In the embodiments, beam spot image <NUM> is reconstructed based on the above-described sequence of projection images of the beam spot and a so-called "edge measurement" algorithm (described below in conjunction with <FIG>).

As shown in <FIG>, beam spot image <NUM> includes a 2D intensity distribution <NUM> (cross-hatching) of the beam spot depicted by beam spot image <NUM>, where denser cross-hatching indicates a higher intensity of X-rays (or other radiation) being generated. Thus, beam spot image <NUM> includes information indicating how X-ray radiation intensity varies within a beam spot of a radiation therapy system. In some embodiments, based on such information, one or more beam spot quality metrics are determined for a particular beam spot, including one or more of a beam spot area, a beam spot elongation, a beam spot power per unit area factor, and/or a beam spot center point offset <NUM>.

The beam spot area for a beam spot is a quantified measure of the size of a beam spot and is calculated based on an area of beam spot image <NUM>. In some embodiments, a beam spot area of a beam spot is calculated using all pixels (not shown) in beam spot image <NUM> that indicate greater than zero radiation intensity. Alternatively, in some embodiments, a beam spot area of a beam spot is calculated using the pixels in beam spot image <NUM> that indicate a radiation intensity that is greater than a predetermined radiation intensity level. In such embodiments, the predetermined radiation intensity level can be an absolute intensity level or a normalized intensity level, such as a percentage of a peak radiation intensity level indicated in beam spot image <NUM>. For example, in one such embodiment, a beam spot area of a beam spot is calculated using the pixels in beam spot image <NUM> that indicate a radiation intensity that is greater than <NUM>% of the peak radiation intensity level of beam spot image <NUM>.

The beam spot elongation for a beam spot is a quantified measure of the shape (e.g., roundness and/or symmetry) of a beam spot and is calculated based on attributes of the beam spot visible in beam spot image <NUM>. In some embodiments, a beam spot elongation of a beam spot is calculated using geometrical attributes of the beam spot that are detectable in beam spot image <NUM>, such as a length <NUM> of a major axis of the beam spot and a length <NUM> of a minor axis of the beam spot. In such embodiments, the beam spot elongation is the ratio of length <NUM> and length <NUM>. In such embodiments, length <NUM> and length <NUM> may be determined for the entire beam spot visible in beam spot image <NUM>. Alternatively, in such embodiments, length <NUM> and length <NUM> are determined for a higher-intensity portion of the beam spot visible in beam spot image <NUM>. For example, in the embodiment illustrated in <FIG>, length <NUM> and length <NUM> are determined for the portion of the beam spot visible in beam spot image <NUM> that is equal to or greater than <NUM>% of the peak radiation intensity level of beam spot image <NUM>. Thus, in such an embodiment, a lower-intensity portion of beam spot image <NUM> is ignored in determining length <NUM> and length <NUM>.

The beam spot power per unit area factor for a beam spot is a quantified measure of the concentration of X-ray-generating power present in a particular beam spot. In some embodiments, the beam spot power per unit area factor for a beam spot quantifies the highest power concentration detected for a particular beam spot. In some embodiments, the beam spot power per unit area factor of a beam spot is calculated based on the beam spot area and on information associated with the electron beam employed to generate the beam spot. In such embodiments, the beam spot area may be calculated as described above, for example using the pixels in beam spot image <NUM> that indicate a radiation intensity that is greater than a particular percentage of the peak radiation intensity level of beam spot image <NUM>. In some embodiments, the beam spot power per unit area factor of a beam spot is calculated as a ratio of a power value per unit area. In such embodiments, the power value can be based on a peak power of the electron beam employed to generate the beam spot. Further, in such embodiments, the power value can be based on a frequency of the electron beam employed to generate the beam spot and a pulse width of the electron beam employed to generate the beam spot.

Beam spot center point offset <NUM> is a measure of a distance a center point <NUM> of a beam spot is located from an ideal center point location <NUM> of the beam spot. In some embodiments, center point <NUM> is determined based on the entire beam spot visible in beam spot image <NUM>. Alternatively, in some embodiments, center point <NUM> is determined based on a higher-intensity portion of the beam spot visible in beam spot image <NUM>, such as the portion of the beam spot visible in beam spot image <NUM> that is equal to or greater than <NUM>% of the peak radiation intensity level of beam spot image <NUM>. In some embodiments, ideal center point location <NUM> of the beam spot corresponds to a collimator rotation axis of RT system <NUM>, such as collimator rotation axis <NUM> in <FIG>, about which MLC <NUM> rotates. Thus, in such embodiments, beam spot center point offset <NUM> may indicate how aligned a center axis of a treatment beam (e.g., center axis <NUM> in <FIG> of treatment beam <NUM>) is with a collimator rotation axis (e.g., collimator rotation axis <NUM> in <FIG>). Alternatively, in such embodiments, beam spot center point offset <NUM> may indicate how aligned beam spot <NUM> is with a collimator rotation axis or some ideal or optimal location on an electron beam target (e.g., electron beam target <NUM> in <FIG>).

As noted above, beam spot image <NUM> can be reconstructed based on the different intensity distribution of each of the sequence of X-ray projection images generated of beam spot <NUM> as MLC <NUM> is rotated about collimator rotation axis <NUM>, as shown in <FIG>. In some embodiments, an edge measurement algorithm is employed to generate beam spot image <NUM> of beam spot <NUM>. In such embodiments, the resultant 2D image of beam spot <NUM> corresponds to a 2D beam spot intensity distribution on electron beam target <NUM>. It is noted that in each X-ray projection image of beam spot <NUM>, the relative intensity of received X-rays at any location in the X-ray projection image depends on how much of beam spot <NUM> was covered by MLC <NUM> during acquisition of that X-ray projection image. One such edge measurement algorithm is schematically illustrated in <FIG>.

<FIG> schematically illustrates various steps of an edge measurement algorithm for generating a 2D image of beam spot <NUM>, according to various embodiments. As shown, MLC <NUM> is rotated about collimator rotation axis <NUM>, and at each of a plurality of different rotational angles <NUM>, an X-ray projection image <NUM> of beam spot <NUM> is generated with LINAC <NUM>. As part of the edge measurement algorithm, each X-ray projection image <NUM> of beam spot <NUM> is rotated to be a rotated X-ray projection image <NUM>, so that an edge <NUM> formed by portion <NUM> in each rotated X-ray projection image <NUM> is oriented in the same way, for example from a top edge <NUM> of the rotated X-ray projection image <NUM> to a bottom edge <NUM> of the rotated X-ray projection image <NUM>. Assuming isotropic radiative emission from every point on beam spot <NUM>, the intensity distribution along any one horizontal row of a rotated X-ray projection image <NUM> is directly related to the fraction of beam spot <NUM> that was exposed when the corresponding X-ray projection image <NUM> was acquired. After averaging over all rows of pixels in a particular rotated X-ray projection image <NUM>, the resulting horizontal intensity distribution is like that of an edge spread function (ESF) <NUM>, one of which is generated for each rotated X-ray projection image <NUM>. A line spread function (LSF) <NUM> is then generated from each ESF <NUM> associated with a particular rotated X-ray projection image <NUM>, where LSF <NUM> for a particular rotated X-ray projection image <NUM> is a derivative of the ESF <NUM> for the particular rotated X-ray projection image <NUM>. Thus, for each rotated X-ray projection image <NUM> of beam spot <NUM>, a different LSF <NUM> is generated. A sinogram (not shown) is then constructed using the different LSFs <NUM>. When LSFs <NUM> are available from a sufficient number of projection angles, the sinogram can be used to recover the original 2D intensity distribution <NUM> of beam spot <NUM> as a beam spot image <NUM>. A more detailed description of an edge measurement algorithm is described in "<NPL>.

In some embodiments, one or more attributes of a beam spot in a radiation therapy system are controlled or otherwise modified based on the 2D intensity distribution determined for the beam spot as described above. In such embodiments, one or more parameters for an electron-beam-shaping component of the radiation system is modified based on the 2D intensity distribution for the beam spot, so that the size, shape, location, and/or intensity distribution of a beam spot is tuned to meet a predetermined specification. One such embodiment is described below in conjunction with <FIG>.

<FIG> sets forth a flowchart of a computer-implemented process <NUM> for tuning a beam spot in a radiation therapy system, according to one or more embodiments. Computer-implemented process <NUM> can be performed as a part of factory setup of a radiation therapy system, as an on-site quality-assurance tool for the radiation therapy system, and/or as a periodic service tool for the radiation therapy system.

Computer-implemented process <NUM> may include one or more operations, functions, or actions as illustrated by one or more of blocks <NUM> - <NUM>. 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 computer-implemented process <NUM> is described in conjunction with the X-ray imaging system described herein as part of RT system <NUM> and <FIG>, persons skilled in the art will understand that any suitably configured X-ray imaging system is within the scope of the present embodiments.

The control algorithms for the blocks of computer-implemented process <NUM> may be performed by any suitable computing device or devices. For example, in some embodiments, some or all of the control algorithms for the blocks of computer-implemented process <NUM> reside in image acquisition and treatment control computer <NUM>, remote control console <NUM>, a combination of both, or any other computing device communicatively coupled to RT system <NUM>. The control algorithms can be implemented in whole or in part as software- or firmware-implemented logic, and/or as hardware-implemented logic circuits.

In step <NUM>, a suitable computing device causes optimization of a particular treatment beam to be performed. In some embodiments, such treatment beam optimization includes confirming a maximum dose rate of treatment beam <NUM> using conventional techniques known in the art. In addition, in some embodiments, such treatment beam optimization further includes modifying one or more beam-generation parameters associated with the dose rate of treatment beam <NUM> for the particular configuration of treatment beam <NUM> until the particular treatment beam <NUM> is confirmed to have a specified dose rate. In some embodiments, the one or more beam-generation parameters include electron gun current, RF power, energy switch position, one or more bending magnet parameters, one or more gun driver parameters, and/or the like. In some embodiments, the maximum dose rate of treatment beam <NUM> includes a margin above a maximum specified dose rate that is used in practice. When treatment beam <NUM> is confirmed to provide a suitable maximum dose rate, the optimization of treatment beam <NUM> is complete and computer-implemented process <NUM> proceeds to step <NUM>.

In step <NUM>, the computing device causes beam spot <NUM> of RT system <NUM> to be measured, for example by the acquisition of a sequence of X-ray projection images of beam spot <NUM> and the application of an edge measurement algorithm, as described above in conjunction with <FIG>. In some embodiments, the output of such an algorithm includes a 2D intensity distribution <NUM> of beam spot <NUM>. In some embodiments, the output of such an algorithm includes information indicating a location of a beam spot center point <NUM>, for example relative to an absolute position on electron beam target <NUM>.

In step <NUM>, the computing device determines a value for one or more beam spot quality metrics for beam spot <NUM>, based on the output of step <NUM>. In some embodiments, the one or more beam spot quality metrics include a beam spot area, a beam spot elongation, a beam spot power per unit area factor, and/or a beam spot center point offset from an ideal center point location, among others.

In step <NUM>, the computing device determines whether beam spot <NUM> satisfies a predetermined beam spot quality specification. When the computing device determines that beam spot <NUM> satisfies the predetermined beam spot quality specification, computer-implemented process <NUM> proceeds to step <NUM>. When the computing device determines that beam spot <NUM> fails to satisfy the predetermined beam spot quality specification, computer-implemented process <NUM> proceeds to step <NUM>.

In some embodiments, in step <NUM> the computing device determines whether beam spot <NUM> satisfies the predetermined beam spot quality specification based on one or more beam spot quality metrics. For example, in one such embodiment, the computing device determines whether beam spot <NUM> satisfies the predetermined beam spot quality specification based on an eccentricity of beam spot <NUM>. In such an embodiment, when a value determined in step <NUM> for the eccentricity of beam spot <NUM> is less than a threshold eccentricity value (such as a specified maximum acceptable eccentricity for beam spot <NUM>), the computing device determines that beam spot <NUM> satisfies the predetermined beam spot quality specification. In another example, in an embodiment, the computing device determines whether beam spot <NUM> satisfies the predetermined beam spot quality specification based on a size (e.g., area) of eccentricity of beam spot <NUM>. In such an embodiment, when a value determined in step <NUM> for the area of beam spot <NUM> is less than a threshold maximum value (such as a specified maximum acceptable area for beam spot <NUM>), and is greater than a threshold minimum value (such as a specified minimum acceptable area for beam spot <NUM>), the computing device determines that beam spot <NUM> satisfies the predetermined beam spot quality specification. In yet another example, in an embodiment, the computing device determines whether beam spot <NUM> satisfies the predetermined beam spot quality specification based on a power per unit area of beam spot <NUM>. In such an embodiment, when a value determined in step <NUM> for the area of beam spot <NUM> is greater than a threshold maximum value (such as a specified maximum acceptable power per unit area for beam spot <NUM>), the computing device determines that beam spot <NUM> does not satisfy the predetermined beam spot quality specification.

In some embodiments, in step <NUM> the computing device determines whether beam spot <NUM> satisfies the predetermined beam spot quality specification based multiple beam spot quality metrics. For example, in some embodiments, when the value determined in step <NUM> for each of the multiple beam spot quality metrics satisfies a respective specified threshold or thresholds, the computing device determines that beam spot <NUM> satisfies the predetermined beam spot quality specification. In such embodiments, failure of a single value determined in step <NUM> to satisfy a respective specified threshold or thresholds indicates that beam spot <NUM> fails to satisfy the predetermined beam spot quality specification. Alternatively, in some embodiments, failure of one or more values determined in step <NUM> to satisfy a respective specified threshold or thresholds may not indicate that beam spot <NUM> fails to satisfy the predetermined beam spot quality specification. Instead, in such embodiments, a weighting scheme for each beam spot quality metric may be employed to quantify how well each particular beam spot quality metric is satisfied. In such embodiments, an overall quality score for beam spot <NUM> is determined that is based on such a weighting scheme as applied to the multiple values determined in step <NUM>. In such embodiments, a particular beam spot <NUM> may have an overall quality score indicating that the particular beam spot <NUM> satisfies the predetermined beam spot quality specification even though a value for one or more beam spot quality metrics determined in step <NUM> may not satisfy an associated threshold value for each of the one or more beam spot quality metrics. Further, in such embodiments, each beam spot quality metric may have a different score weighting, depending on the relative importance of each beam spot quality metric.

In some embodiments, a predetermined beam spot quality specification may include multiple threshold values for one or more beam spot quality metrics for beam spot <NUM>. In such embodiments, for a particular beam spot quality metric, the predetermined beam spot quality specification may include an upper threshold value and a lower threshold value for beam spot <NUM>. In such embodiments, the lower threshold value for a particular beam spot quality metric may indicate an ideal threshold that beam spot <NUM> may, but is not required to, satisfy. By contrast, the upper threshold value for the particular beam spot quality metric may indicate an undesired value at which beam spot <NUM> fails to satisfy the predetermined beam spot quality specification, regardless of the overall quality score for beam spot <NUM> with respect to other beam quality metrics. That is, in such embodiments, failure of beam spot <NUM> to satisfy the upper threshold indicates that the beam spot is not suitable for use and should be modified. Alternatively, in some embodiments, the upper threshold value for a particular beam spot quality metric indicates a value at which beam spot <NUM> accrues a more severe scoring penalty (higher scoring penalty or lower reward) than that associated with the lower threshold value for that particular beam spot quality metric. Alternatively, in some embodiments, the above-described roles of the upper threshold value and the lower threshold value for a particular beam spot quality metric are reversed, i.e., the upper threshold value for a particular beam spot quality metric indicate an ideal threshold value and the lower threshold value for the particular beam spot quality metric beam spot <NUM> indicates an undesired (or more heavily penalized) threshold value for the particular beam spot quality metric. For example, in the case of an area coincidence factor (described below in conjunction with FIGS. 10A- 10C), a lower threshold value may indicate an undesired value for a beam spot.

In step <NUM>, the computing device modifies one or more parameters of an electron-beam-shaping component of RT system <NUM> to a new value. As a result, one or more attributes of beam spot <NUM> are changed that affect 2D intensity distribution <NUM> of beam spot <NUM>, such as an eccentricity of beam spot <NUM>, an average diameter of beam spot <NUM>, an offset distance of beam spot <NUM>, a size or area of beam spot <NUM>, a power per unit area of beam spot <NUM>, and/or the like. In some embodiments, the one or more parameters modified in step <NUM> are selected based on which of the one or more beam spot quality metrics of the predetermined beam spot quality specification beam spot <NUM> failed to satisfy in step <NUM>. Upon completion of step <NUM>, computer-implemented process <NUM> returns to step <NUM> and the computing device causes beam spot <NUM> of RT system <NUM> to be measured again.

Examples of parameters of an electron-beam-shaping component of RT system <NUM> include a solenoid current for first beam-shaping solenoid <NUM>, a solenoid current for second beam-shaping solenoid <NUM>, a direction of current flow in first beam-shaping solenoid <NUM>, a direction of current flow in second beam-shaping solenoid <NUM>, and/or the like. Because the direction and magnitude of current flowing through first beam-shaping solenoid <NUM> and second beam-shaping solenoid <NUM> can affect the electron beam that generates beam spot <NUM> (and therefore treatment beam <NUM>), modification of such parameters also alters one or more attributes of beam spot <NUM>. Alternatively or additionally, in some embodiments, parameters of other beam-shaping components of RT system <NUM> are modified in step <NUM> to alter one or more attributes of beam spot <NUM>. Examples of other beam-shaping components of RT system <NUM> include electron gun <NUM>, accelerating waveguide <NUM>, and/or electron beam transport means <NUM>.

In step <NUM>, the computing device confirms that the maximum dose rate of treatment beam <NUM> continues to have a specified maximum dose rate. In instances in which the maximum dose rate of treatment beam is below the specified maximum dose rate, one or more beam-generation parameters associated with the dose rate of treatment beam <NUM> are modified until treatment beam <NUM> is confirmed to have a specified dose rate. Upon completion of step <NUM>, computer-implemented process <NUM> ends.

In some embodiments, steps <NUM> - <NUM> are performed over multiple iterations until specified attributes of treatment beam <NUM> satisfy a predetermined beam spot quality specification. Because each such iteration can be completed in an automated fashion in a relatively short time (e.g., <NUM> - <NUM> minutes) and without the use of equipment and/or measuring instruments external to RT system <NUM>, a particular treatment beam <NUM> can be tuned in a short time, for example in a fraction of an hour. Further, computer-implemented process <NUM> can be performed for each of a plurality of treatment beam energies that may be employed by RT system <NUM>. Because computer-implemented process <NUM> can be completed so quickly, computer-implemented process <NUM> can be performed as a part of factory setup of a radiation therapy system, as an on-site quality-assurance tool for the radiation therapy system, and/or as a periodic service tool for the radiation therapy system.

Implementation of computer-implemented process <NUM> enables precise control of beam spot shape and size in RT system <NUM>, thereby ensuring consistency in a pre-configured treatment beam <NUM>. Thus, treatment beam <NUM> can meet tight the geometric tolerances and small field penumbra required for forms of radiation therapy that involve delivery of a high radiation dose to a small focused region of a patient's anatomy. Further, treatment beam <NUM> can be assumed to have substantially the same attributes of the ideal treatment beam employed in treatment planning models.

In the embodiments described above, direct measurement of a beam spot enables tuning of one or more attributes of the beam spot in a radiation therapy system. For example, based on such beam spot measurements, one or more beam-shaping parameters that affect generation of the beam spot are modified so that the one or more attributes of the beam spot are changed. In other embodiments, measurement of one or more attributes of a radiation field generated by a beam spot enables similar tuning of the beam spot. In such embodiments, one or more beam-shaping parameters are modified based on the measured attributes of the radiation field, so that the one or more attributes of the beam spot are changed. The attributes of the radiation field are quantified via one or more specific radiation field quality metrics that indicate whether a radiation beam originating from the beam spot is outside a specified quality range. Examples of such radiation field quality metrics include one or more of an area coincidence factor, a penumbra asymmetry factor, and a beam output factor.

In some embodiments, values for one or more radiation field quality metrics are measured based on images that are generated using an existing imaging panel of the radiation therapy system, such as EPID <NUM> of RT system <NUM>. In such embodiments, one or more slit-field images are employed, in which a treatment beam (e.g., treatment beam <NUM> in <FIG>) originating from a beam spot (e.g., beam spot <NUM> in <FIG>) is shaped via a narrow rectangular aperture and imaged by EPID <NUM>. For example, the narrow rectangular aperture can be formed by an MLC of the radiation therapy system, such as MLC <NUM> of RT system <NUM>. As the MLC is rotated about a rotational axis, a different slit-field image is generated with the MLC at a different rotational orientation relative to the imaging panel. Quantitative analysis of the different slit-field images, as described herein, enables determination of the symmetry of a radiation field generated by a particular beam spot. One embodiment of an aperture for generating slit-field images is described below in conjunction with <FIG>, and one embodiment of a slit-field image is described below in conjunction with <FIG>.

<FIG> schematically illustrates an aperture <NUM> and imager <NUM> for generating slit-field images, according to various embodiments. In the embodiment illustrated in <FIG>, aperture <NUM> is formed by an MLC of a radiation therapy system, such as MLC <NUM> in <FIG>, and imager <NUM> is an imager included in the radiation therapy system, such as EPID <NUM> of RT system <NUM>. Aperture <NUM> and imager <NUM> are shown in a "beam's-eye" view in <FIG>, which is from the perspective of a source of a treatment beam, such as LINCAC <NUM> of RT system <NUM>.

In the embodiment illustrated in <FIG>, multiple additional orientations of aperture <NUM> with respect to imager <NUM> are shown that can each be employed to generate a slit-field image. The additional orientations include an orientation <NUM>, in which the MLC is positioned at a rotational angle of <NUM>° about an axis of rotation <NUM> of the collimator, an orientation <NUM>, in which the MLC is positioned at a rotational angle of <NUM>° about axis of rotation <NUM>, and an orientation <NUM>, in which the MLC is positioned at a rotational angle of <NUM>° about the axis of rotation <NUM>. In other embodiments, more or fewer orientations of aperture <NUM> may be employed to generate slit-field images.

<FIG> schematically illustrates a slit-field X-ray image <NUM> and an associated penumbra and output factor, according to various embodiments. Slit-field X-ray image <NUM> is an X-ray image generated using a treatment beam, an imager, and an MLC of a conventional radiation therapy system, such as treatment beam <NUM>, EPID <NUM>, and MLC <NUM> of RT system <NUM>. In some embodiments, slit-field image <NUM> is generated with EPID <NUM> positioned at or near isocenter <NUM> of RT system <NUM> rather than at a position employed during radiation treatment. In such embodiments, the added complication of treatment beam <NUM> and the associated penumbra being magnified is avoided.

As shown in <FIG>, slit-field X-ray image <NUM> includes a 2D intensity distribution <NUM> of the radiation intensity, depicted by cross-hatching, where denser cross-hatching indicates a higher intensity of X-rays being received by EPID <NUM>. Thus, slit-field X-ray image <NUM> includes information indicating how X-ray radiation intensity varies within a particular treatment beam <NUM>, such as a treatment beam that has a beam size similar to the width of the rectangular aperture employed to generate slit-field X-ray image <NUM>. In some embodiments, based on such information, one or more radiation field quality metrics are determined for a particular beam spot and aperture combination, including one or more of an area coincidence factor, a penumbra asymmetry factor, and an X-ray beam output factor. In the embodiments, values for the one or more radiation field quality metrics are compared to corresponding values of a predetermined radiation field quality specification to determine whether a treatment beam that generates slit-field X-ray image <NUM> is outside a specified quality range.

<FIG> further includes a one-dimensional X-ray intensity profile <NUM> that depicts X-ray dose along a linear portion <NUM> of slit-field X-ray image <NUM>. Thus, X-ray intensity profile <NUM> indicates how radiation intensity varies across 2D intensity distribution <NUM> of slit-field X-ray image <NUM>. In some embodiments, linear portion <NUM> is oriented along a major axis of slit-field X-ray image <NUM>. That is, linear portion <NUM> is oriented parallel to the rectangular aperture employed to generate slit-field X-ray image <NUM>. Alternatively or additionally, a one-dimensional X-ray intensity profile can be generated for other linear portions of slit-field X-ray image <NUM>, such as along a minor axis <NUM> (which is perpendicular to the rectangular aperture employed to generate slit-field X-ray image <NUM>). Further, in the embodiment illustrated in <FIG>, X-ray intensity profile <NUM> is normalized to a peak X-ray intensity value <NUM> of one-dimensional X-ray intensity profile <NUM>. Various radiation field quality metrics (area coincidence factor, penumbra asymmetry factor, and X-ray beam output factor) are now described with respect to slit-field X-ray image <NUM>.

The penumbra asymmetry factor is a quantified measure of the symmetry of the penumbra of an X-ray beam, such as an X-ray beam used to generate slit-field X-ray image <NUM>. In some embodiments, the penumbra asymmetry factor for an X-ray beam is based on a difference between a first penumbra portion <NUM> of one-dimensional X-ray intensity profile <NUM> and a second penumbra portion <NUM> of one-dimensional X-ray intensity profile <NUM>. In such embodiments, first penumbra portion <NUM> is disposed on a first side of one-dimensional X-ray intensity profile <NUM>, and second penumbra portion <NUM> is disposed on a second side of one-dimensional X-ray intensity profile <NUM>, where the first side is opposite the second side as shown in <FIG>.

In the embodiment illustrated in <FIG>, first penumbra portion <NUM> is defined as a width between a location <NUM> of a radiation intensity that corresponds to a beginning of a penumbra fall-off region on the first side of one-dimensional X-ray intensity profile <NUM> and a location <NUM> of a radiation intensity that corresponds to an ending of the penumbra fall-off region on the first side of one-dimensional X-ray intensity profile <NUM>. Similarly, second penumbra portion <NUM> is defined as a width between a location <NUM> of the radiation intensity that corresponds to the beginning of the penumbra fall-off region on the second side of one-dimensional X-ray intensity profile <NUM> and a location <NUM> of the radiation intensity that corresponds to the ending of the penumbra fall-off region on the second side of one-dimensional X-ray intensity profile <NUM>. For example, in the embodiment illustrated in <FIG>, the radiation intensity that corresponds to the beginning of the penumbra fall-off region (locations <NUM> and <NUM>) is <NUM>% of peak radiation intensity level <NUM> of one-dimensional X-ray intensity profile <NUM>, and the radiation intensity that corresponds to the ending of the penumbra fall-off region (locations <NUM> and <NUM>) is <NUM>% of peak radiation intensity level <NUM>. In other embodiments, the radiation intensities that correspond to the beginning and ending of the penumbra fall-off region can vary from those shown in <FIG>.

The X-ray beam output factor is a quantified measure of the radiation intensity associated with the X-ray beam that generates slit-field X-ray image <NUM> relative to a reference X-ray beam. In some embodiments, the X-ray beam output factor is a ratio of the radiation intensity associated with the X-ray beam of interest and the reference X-ray beam. Generally, the reference X-ray beam has a larger field than the X-ray beam that generates slit-field X-ray image <NUM>. For example, in an embodiment, the X-ray beam that generates slit-field X-ray image <NUM> has a field size of about <NUM> x <NUM>, and the reference X-ray beam has a field size of about <NUM> x <NUM>. As a result, the X-ray beam output factor for an X-ray beam that generates slit-field X-ray image <NUM> is generally less than <NUM>. In some embodiments, for a specific combination of rectangular aperture and treatment beam <NUM> that generates slit-field X-ray image <NUM>, the X-ray beam output factor is calculated for multiple orientations of the rectangular aperture (e.g., <NUM>°, <NUM>°, <NUM>°, and <NUM>°) around the beam collimator axis.

The area coincidence factor is a quantified measure of the variation in shape of a dose cloud of the X-ray beam that generates slit-field X-ray image <NUM>. The dose cloud is the geometrical enclosure of points with a dose larger or equal to a predefined intensity (e.g. an <NUM>% isodose contour). Specifically, the area coincidence factor quantifies the variation in shape of such a dose cloud as the rectangular aperture that forms the X-ray beam rotates through different angles. Thus, in some embodiments, for a particular treatment beam <NUM> and rectangular aperture, multiple values for the area coincidence factor are determined. For example, in one such embodiment, for the particular treatment beam <NUM> and rectangular aperture, a different value for the area coincidence factor is determined for each of multiple orientations of the rectangular aperture (e.g., <NUM>°, <NUM>°, <NUM>°, and <NUM>°). One such embodiment is described below in conjunction with <FIG>.

<FIG> schematically illustrate determination of an area coincidence factor for a particular combination of treatment beam <NUM>, rectangular aperture, and aperture orientation, according to various embodiments. <FIG> illustrates a first step in a process of generating the area coincident factor for the particular combination of treatment beam <NUM> and rectangular aperture; <FIG> illustrates a second step in the process of generating the area coincident factor; and <FIG> illustrates a third step in the process of generating the area coincident factor.

<FIG> shows a reference dose cloud <NUM> and an evaluated dose cloud <NUM> after acquisition of slit-field X-ray images <NUM> using the particular combination of treatment beam <NUM> and rectangular aperture. In the embodiment illustrated in <FIG>, reference dose cloud <NUM> is based on a reference slit-field X-ray image (not shown) generated with the rectangular aperture oriented at <NUM>°, and evaluated dose cloud <NUM> is based on an evaluated slit-field X-ray image (not shown) generated with the rectangular aperture oriented at <NUM>°. Further, in the embodiment illustrated in <FIG>, reference dose cloud <NUM> corresponds to a portion of the reference slit-field X-ray image that represents a radiation intensity of <NUM>% or more of a peak radiation intensity of the reference slit-field X-ray image. Thus, reference dose cloud <NUM> does not include portions of the reference slit-field X-ray image that indicate a radiation intensity of less than <NUM>% of the peak radiation intensity of the reference slit-field X-ray image. Likewise, in <FIG>, evaluated dose cloud <NUM> corresponds to a portion of the evaluated slit-field X-ray image that represents a radiation intensity of <NUM>% or more of a peak radiation intensity of the evaluated slit-field X-ray image. Thus, evaluated dose cloud <NUM> does not include portions of the evaluated slit-field X-ray image that indicate a radiation intensity of less than <NUM>% of the peak radiation intensity of the evaluated slit-field X-ray image. In other embodiments, reference dose cloud <NUM> and evaluated dose cloud <NUM> are defined based on a higher or lower radiation intensity cut-off than the <NUM>% level illustrated in <FIG> (e.g., <NUM>% of a peak radiation intensity, <NUM>% of a peak radiation intensity, etc.).

<FIG> shows evaluated dose cloud <NUM> after being rotated to align with reference dose cloud <NUM>. Thus, in the embodiment illustrated in <FIG>, evaluated dose cloud <NUM> is rotated <NUM>° as shown, since evaluated dose cloud <NUM> is based on an evaluated slit-field X-ray image generated with the rectangular aperture oriented at <NUM>°. In such embodiments, the area coincidence factor determined for evaluated dose cloud <NUM> enables variation in the shape of evaluated dose cloud <NUM> from reference dose cloud <NUM> to be captured, as shown in <FIG>.

In addition, in some embodiments, to align evaluated dose cloud <NUM> with reference dose cloud <NUM>, evaluated dose cloud <NUM> is rotated about a beam center point <NUM>, which corresponds to an ideal center point of a treatment beam. For example, in some embodiments, beam center point <NUM> corresponds to a collimator rotation axis (such as collimator rotation axis <NUM> in <FIG>). Alternatively, beam center point <NUM> corresponds to some other absolute position on the imager that generates the reference slit-field X-ray image and the evaluated slit-field X-ray image (e.g., EPID <NUM> of <FIG>). In such embodiments, beam center point <NUM> does not necessarily correspond to a center point (such as the centroid) of reference dose cloud <NUM> or of evaluated dose cloud <NUM>. In such embodiments, the area coincidence factor determined for evaluated dose cloud <NUM> captures the difference in the position of evaluated dose cloud <NUM> (e.g., relative to beam center point <NUM>) from the position of reference dose cloud <NUM>. That is, when evaluated dose cloud <NUM> is offset a different distance from beam center point <NUM> than reference dose cloud <NUM>, the area coincidence factor quantitatively captures the resulting reduction in coincidence (illustrated in <FIG>) between evaluated dose cloud <NUM> and reference dose cloud <NUM>.

<FIG> shows evaluated dose cloud <NUM> after being superimposed onto reference dose cloud <NUM>. In some embodiments, evaluated dose cloud <NUM> is superimposed onto reference dose cloud <NUM> based on the location of beam center point <NUM> in reference dose cloud <NUM> and in evaluated dose cloud <NUM>. In <FIG>, an area of coincidence <NUM> (cross-hatching) indicates a portion of evaluated dose cloud <NUM> that coincides with reference dose cloud <NUM>. It is noted that differences in shape and in position relative to beam center point <NUM> can both contribute to a smaller area of coincidence <NUM> between reference dose cloud <NUM> and evaluated dose cloud <NUM>. In some embodiments, a value of the area coincidence factor determined for a particular evaluated dose cloud <NUM> is a normalized value based on area of coincidence <NUM> and a total area of either reference dose cloud <NUM> or evaluated dose cloud <NUM>. Thus, in such embodiments, the value of the area coincidence factor determined for a particular evaluated dose cloud <NUM> is generally between <NUM> and <NUM>.

<FIG> sets forth a flowchart of a computer-implemented process <NUM> for tuning a beam spot in a radiation therapy system based on measurements of a radiation field, according to one or more embodiments. In the embodiments, as part of the beam-tuning process, one or more of the above-described radiation field quality metrics are employed to determine whether a beam spot is outside a specified quality range. Computer-implemented process <NUM> can be performed as a part of factory setup of a radiation therapy system, as an on-site quality-assurance tool for the radiation therapy system, and/or as a periodic service tool for the radiation therapy system.

In step <NUM>, a suitable computing device causes optimization of a particular treatment beam to be performed. In some embodiments, such treatment beam optimization in includes confirming a maximum dose rate of treatment beam <NUM> using conventional techniques known in the art and, when required, performing one or more beam output optimization procedures configure treatment beam <NUM> to have a suitable maximum dose rate. In some embodiments, step <NUM> is substantially similar to step <NUM> in computer-implemented process <NUM> of <FIG>.

In step <NUM>, one or more procedures are performed to ensure that treatment beam <NUM> is correctly aligned with respect to collimator rotation axis <NUM>, about which MLC <NUM> rotates. Additionally, in some embodiments, one or more procedures are performed to ensure that a filter included in collimator assembly <NUM> is positioned correctly with respect to collimator rotation axis <NUM>. In some embodiments, to complete step <NUM>, conventional procedures known in the art may be performed.

In step <NUM>, the computing device causes beam spot <NUM> of RT system <NUM> to be measured, for example by the acquisition of a sequence of X-ray projection images of beam spot <NUM> and the application of an edge measurement algorithm, as described above in conjunction with <FIG>. In some embodiments, step <NUM> is substantially similar to step <NUM> in computer-implemented process <NUM> of <FIG>.

In step <NUM>, the computing device determines a value for one or more beam spot quality metrics for beam spot <NUM>, based on the output of step <NUM>. In some embodiments, step <NUM> is substantially similar to step <NUM> in computer-implemented process <NUM> of <FIG>.

In step <NUM>, the computing device determines whether beam spot <NUM> satisfies a predetermined beam spot quality specification. When the computing device determines that beam spot <NUM> satisfies the predetermined beam spot quality specification, computer-implemented process <NUM> proceeds to step <NUM>. When the computing device determines that beam spot <NUM> fails to satisfy the predetermined beam spot quality specification, computer-implemented process <NUM> proceeds to step <NUM>. In some embodiments, step <NUM> is substantially similar to step <NUM> in computer-implemented process <NUM> of <FIG>.

In step <NUM>, the computing device modifies one or more parameters of an electron-beam-shaping component of RT system <NUM> to a new value. In some embodiments, step <NUM> is substantially similar to step <NUM> in computer-implemented process <NUM> of <FIG>.

In step <NUM>, the computing device causes one or more attributes of a radiation field generated by beam spot <NUM> to be measured. In some embodiments, in step <NUM> one or more slit-field X-ray images of a radiation field of a treatment beam <NUM> are generated using EPID <NUM>. In such embodiments, multiple slit-field X-ray images of the radiation field may be generated, one slit-field X-ray image for each of multiple evaluation angles. In such embodiments, for each slit-field X-ray image, a rectangular aperture formed by MLC <NUM> is oriented at a different evaluation angle.

In step <NUM>, the computing device radiation field analysis is performed. In such embodiments, one or more radiation field quality metrics are determined, such as an area coincidence factor, a penumbra asymmetry factor, and/or an X-ray beam output factor.

In step <NUM>, the computing device determines whether a radiation field of treatment beam <NUM> (which was used to generate the multiple slit-field X-ray images) satisfies a predetermined radiation field quality specification. When the computing device determines that the radiation field satisfies the predetermined radiation field quality specification, computer-implemented process <NUM> proceeds to step <NUM>. When the computing device determines that the radiation field fails to satisfy the predetermined radiation field quality specification, computer-implemented process <NUM> proceeds to step <NUM>.

In some embodiments, in step <NUM> the computing device determines whether the radiation field satisfies the predetermined radiation field quality specification based on one or more of the radiation field quality metrics determined in step <NUM>. In some embodiments, in step <NUM> the computing device determines whether the radiation field satisfies the predetermined radiation field quality specification based a scoring of multiple radiation field quality metrics. For example, in some embodiments, the radiation field fails to satisfy the predetermined radiation field quality specification when a total score associated with the radiation field does not meet or exceed a specified threshold value for the total score. Alternatively or additionally, in some embodiments, the radiation field fails to satisfy the predetermined radiation field quality specification when a value for at least one of the radiation field quality metrics associated with the radiation field fails to meet a minimum required threshold value or exceeds a maximum allowable threshold value for that radiation field quality metric. In some embodiments, each radiation field quality metric may have a different score weighting, depending on the relative importance of each radiation field quality metric.

Further, in some embodiments, a predetermined radiation field quality specification may include multiple threshold values for one or more radiation field quality metrics. Similar to the above-described beam spot quality metrics, in such embodiments, for a particular radiation field quality metric, the predetermined radiation field quality specification may include one or more upper control limits and one or more lower control limits for beam spot <NUM>. In such embodiments, the upper and lower control limit values can indicate different scoring penalties/rewards.

In step <NUM>, the computing device modifies one or more parameters of an electron-beam-shaping component of RT system <NUM> to a new value. As a result, one or more attributes of beam spot <NUM> are changed that affect 2D intensity distribution <NUM> of beam spot <NUM> and, in turn, the radiation field of the treatment beam <NUM> generated by beam spot <NUM>. In some embodiments, step <NUM> is substantially similar to step <NUM> described above.

In step <NUM>, the computing device causes optimization of the particular treatment beam to be performed. In some embodiments, the computing device confirms a maximum dose rate of treatment beam <NUM> using conventional techniques known in the art and, when required, performs one or more beam output optimization procedures configure treatment beam <NUM> to have a suitable maximum dose rate. In some embodiments, step <NUM> is substantially similar to step <NUM> described above.

In step <NUM>, one or more procedures are performed to ensure that treatment beam <NUM> is correctly aligned with respect to collimator rotation axis <NUM>, about which MLC <NUM> rotates. In some embodiments, step <NUM> is substantially similar to step <NUM> described above.

In step <NUM>, the computing device causes optimization of the particular treatment beam to be performed. In some embodiments, the computing device confirms a maximum dose rate of treatment beam <NUM> using conventional techniques known in the art and, when required, performs one or more beam output optimization procedures configure treatment beam <NUM> to have a suitable maximum dose rate. In some embodiments, step <NUM> is substantially similar to step <NUM> described above. Upon completion of step <NUM>, computer-implemented process <NUM> returns to step <NUM>.

In step <NUM>, computer-implemented process <NUM> ends.

In the embodiments described above, the examples of slit-field images depicted are generated using collimator aperture sizes associated with a small-field radiation treatment (e.g., treatments involving radiation fields on the order of a few millimeters). In other embodiments, slit-field images that are generated for measuring the herein-described radiation field quality metrics may be generated using different collimator apertures sizes, such as apertures associated with beam sizes on the order of one or more centimeters.

<FIG> is an illustration of a computing device <NUM> configured to perform various embodiments of the present disclosure. Computing device <NUM> 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 present disclosure. In operation, computing device <NUM> is configured to execute instructions associated with an edge measurement algorithm <NUM>, computer-implemented process <NUM>, computer-implemented process <NUM>, and/or a treatment planning system <NUM>, 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.

As shown, computing device <NUM> includes, without limitation, an interconnect (bus) <NUM> that connects a processing unit <NUM>, an input/output (I/O) device interface <NUM> coupled to input/output (I/O) devices <NUM>, memory <NUM>, a storage <NUM>, and a network interface <NUM>. Processing unit <NUM> 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 <NUM> may be any technically feasible hardware unit capable of processing data and/or executing software applications, including edge measurement algorithm <NUM>, computer-implemented process <NUM>, computer-implemented process <NUM>, and/or treatment planning system <NUM>.

I/O devices <NUM> 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 <NUM> 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 <NUM> may be configured to receive various types of input from an end-user of computing device <NUM>, and to also provide various types of output to the end-user of computing device <NUM>, such as displayed digital images or digital videos. In some embodiments, one or more of I/O devices <NUM> are configured to couple computing device <NUM> to a network.

Memory <NUM> may include a random access memory (RAM) module, a flash memory unit, or any other type of memory unit or combination thereof. Processing unit <NUM>, I/O device interface <NUM>, and network interface <NUM> are configured to read data from and write data to memory <NUM>. Memory <NUM> includes various software programs that can be executed by processor <NUM> and application data associated with said software programs, including edge measurement algorithm <NUM>, computer-implemented process <NUM>, computer-implemented process <NUM>, and/or treatment planning system <NUM>.

<FIG> is a block diagram of an illustrative embodiment of a computer program product <NUM> for implementing a method for segmenting an image, according to one or more embodiments of the present disclosure. Computer program product <NUM> may include a signal bearing medium <NUM>. Signal bearing medium <NUM> may include one or more sets of executable instructions <NUM> that, when executed by, for example, a processor of a computing device, may provide at least the functionality described above with respect to <FIG>.

In some implementations, signal bearing medium <NUM> may encompass a non-transitory computer readable medium <NUM>, 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 <NUM> may encompass a recordable medium <NUM>, such as, but not limited to, memory, read/write (R/W) CDs, R/W DVDs, etc. In some implementations, signal bearing medium <NUM> may encompass a communications medium <NUM>, 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 <NUM> may be recorded on non-transitory computer readable medium <NUM> or another similar recordable medium <NUM>.

In sum, embodiments described herein provide techniques for controlling the size, shape, and/or power intensity distribution of a beam spot in a radiation therapy system. The herein-described techniques facilitate tuning of the beam spot to improve consistency between the attributes of the beam spot and pre-configured beam data that is included in a treatment planning model. As a result, performance of an X-ray beam generated by the beam spot closely matches the performance assumed for the X-ray beam in the treatment planning system.

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 "circuit," "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.

Claim 1:
A computer-implemented method for tuning a beam spot in a radiation therapy system (<NUM>) based on radiation field measurements, the method comprising:
configuring an electron beam (<NUM>) to generate a first beam spot (<NUM>) on an electron-beam target (<NUM>) of the radiation therapy system (<NUM>);
determining a value for one or more radiation field quality metrics for a first radiation beam that originates from the first beam spot (<NUM>); and
based on the value, determining whether the first radiation beam is outside a specified quality range,
characterized by determining the value for the one or more radiation field quality metrics comprises configuring a collimator (<NUM>) of the radiation therapy system (<NUM>) to generate multiple slit-field images of the first radiation beam.