Patent Description:
Radiation therapy, which is the use of ionizing radiation, is a localized treatment for a specific target tissue, such as a cancerous tumor. Ideally, radiation therapy is performed on target tissue (also referred to as the planning target volume) in a way that spares the surrounding normal tissue from receiving doses above specified tolerances, thereby minimizing risk of damage to the normal tissue. Both conformal radiotherapy and intensity-modulated radiotherapy have been developed so that a prescribed dose is correctly supplied to the planning target volume during radiation therapy.

In conformal radiotherapy, radiotherapy beams can be shaped around the target tissue, for example with a beam-limiting device, to give a high radiation dose to a cancerous tumor while minimizing dosing to the surrounding healthy tissue. In intensity-modulated radiotherapy, the intensity of a radiation beam is modulated so that a prescribed radiation dose conforms more precisely to the three-dimensional shape of the tumor. Both conformal radiotherapy and intensity-modulated radiotherapy can greatly reduce the risk of side effects and/or enable increased dosing of target tissue.

A commonly used beam-limiting device in conformal and intensity-modulated radiation therapy is the multileaf collimator (MLC). Generally, an MLC in a radiation therapy system includes a plurality of movable "leaves" of radiation-stopping material that are independently positioned within the path of a radiotherapy beam. In this way, an MLC enables targeted beam shaping and/or variation of the intensity of the radiotherapy beam.

So that a prescribed dose is correctly supplied to a planning target volume during radiation therapy, an MLC and each of the individual leaves included in the MLC must be precisely positioned relative to the linear accelerator that provides the radiation therapy. However, there are numerous drawbacks to the radiation-tolerant position sensors currently employed to measure the MLC and MLC leaf positions. For example, electromechanical position sensors have repeatability and reliability issues due to wear over time. In addition, some electromechanical position sensors can be subject to gravity-related inaccuracy when positioned at certain angles, adding further uncertainty to the output of such sensors.

In one aspect, the present invention provides a method of measuring a rotational position of an assembly, as defined in claim <NUM>. In a further aspect, the present invention provides a method of measuring a rotational position of an assembly, as defined in claim <NUM>. In another aspect, the present invention provides a radiation treatment system as defined in claim <NUM>. Optional features are specified in the dependent claims.

In accordance with at least some embodiments of the present disclosure, a radiation therapy system is configured to measure a position of a multileaf collimator carousel using a magnetoresistive sensor. In some embodiments, a rotational position of the multileaf collimator carousel is measured via a magnetoresistive sensor configured to detect the ferromagnetic teeth of a toothed ring coupled to a surface of the carousel.

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. The invention is defined in the following claims.

As noted above, beam shaping can play an important role in increasing the accuracy, efficiency, and quality of certain radiation treatments. To that end, multileaf collimators (MLCs) have been used in radiotherapy as beam shapers for conformal radiation therapy and as intensity modulators for intensity modulated radiotherapy (IMRT) and volumetrically modulated arc therapy (VMAT). In such therapies, accurate beam shaping depends on precise positioning of an MLC and the individual leaves in the MLC with respect to a treatment beam. According to various embodiments, improved and more reliable leaf positioning and MLC carousel positioning in a radiation therapy system is facilitated by measuring linear and/or rotational position with a magnetoresistive sensor as described below.

<FIG> is a perspective view of a radiation therapy system <NUM>, according to one or more embodiments. Radiation therapy (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) 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). Alternatively or additionally, RT system <NUM> can be configured to generate high-energy or very high-energy electrons, protons, heavy ions, and/or the like. By way of example, radiation therapy system <NUM> is described herein configured with a circular gantry. In other embodiments, RT system <NUM> can be configured with a C-gantry capable of infinite rotation via a slip ring connection or with a robotic arm.

Generally, RT system <NUM> is capable of kV imaging of a target volume during application of an MV treatment beam, so that an IMRT, VMAT, image-guided radiation therapy (IGRT) and/or conformal radiation therapy process can be performed. RT system <NUM> may include one or more touchscreens <NUM>, couch motion controls <NUM>, a bore <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. Base positioning assembly <NUM> is configured to precisely position couch <NUM> with respect to bore <NUM>, and motion controls <NUM> include input devices, such as button 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 bore <NUM>. Motion controls <NUM> also enable a user to manually position couch <NUM> to a predetermined location. In some embodiments, RT system <NUM> further includes one or more cameras (not shown) in the treatment room for patient monitoring.

<FIG> schematically illustrates a drive stand <NUM> and gantry <NUM> of RT system <NUM>, according to various embodiments. Covers, base positioning assembly <NUM>, couch <NUM>, and other components of RT system <NUM> are omitted in <FIG> for clarity. Drive stand <NUM> is a fixed support structure for components of RT treatment system <NUM>, including gantry <NUM> and a drive system <NUM> for rotatably moving gantry <NUM>. Drive 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. Gantry <NUM> is rotationally coupled to drive stand <NUM> and is a support structure on which various components of RT system <NUM> are mounted, including a linear accelerator (LINAC) <NUM>, an MV electronic portal imaging device (EPID) <NUM>, an imaging X-ray source <NUM>, and an X-ray imager <NUM>. During operation of RT treatment system <NUM>, gantry <NUM> rotates about bore <NUM> when actuated by drive system <NUM>.

Drive system <NUM> rotationally actuates gantry <NUM>. In some embodiments, drive system <NUM> includes a linear motor that can be fixed to drive stand <NUM> and interacts with a magnetic track (not shown) mounted on gantry <NUM>. In other embodiments, drive system <NUM> includes another suitable drive mechanism for precisely rotating gantry <NUM> about bore <NUM>. LINAC <NUM> generates an MV treatment beam <NUM> of high energy X-rays (or in some embodiments electrons, protons, heavy ions, and/or the like) and EPID <NUM> is configured to acquire X-ray images via treatment beam <NUM>. Imaging X-ray source <NUM> is configured to direct a conical beam of X-rays, referred to herein as imaging X-rays <NUM>, through an isocenter <NUM> of RT system <NUM> to X-ray imager <NUM>. Isocenter <NUM> typically corresponds to the location of the target volume to be treated. X-ray imager <NUM> receives imaging X-rays <NUM> and generates suitable projection images therefrom. Such projection images can then be employed to construct or update portions of imaging data for a digital volume that corresponds to a 3D region that includes the target volume. In some embodiments, cone-beam computed tomography (CBCT) and digital tomosynthesis (DTS) can be used to process the projection images generated by X-ray imager <NUM>.

In the embodiment illustrated in <FIG>, X-ray imager <NUM> is depicted as a planar device. In other embodiments, X-ray imager <NUM> can have a curved configuration. In addition, in the embodiment illustrated in <FIG>, RT system <NUM> includes a single X-ray imager and a single corresponding imaging X-ray source. In other embodiments, RT system <NUM> can include two or more X-ray imagers, each with a corresponding imaging X-ray source.

LlNAC <NUM> includes and/or is operated in conjunction with a collimator assembly <NUM>. Collimator assembly <NUM> includes one or more collimators for shaping and/or modifying the intensity of MV treatment beam <NUM>. One embodiment of collimator assembly <NUM> is described below in conjunction with <FIG>.

<FIG> schematically illustrates collimator assembly <NUM>, according to an embodiment. In the embodiment illustrated in <FIG>, collimator assembly <NUM> includes a primary collimator <NUM> and an MLC carousel <NUM> that includes at least one MLC layer. Collimator assembly <NUM> is disposed proximate a radiation source (not shown) of LINAC <NUM> and between the radiation source and isocenter <NUM> of RT system <NUM>. Further, in some embodiments, primary collimator <NUM> is fixed in position relative to the radiation source, while MLC carousel <NUM> is configured to be moved with respect to the radiation source. In some embodiments, MLC carousel <NUM> is configured to be translated along one or more linear axes, such as a first axis of linear motion <NUM>, a second axis of linear motion <NUM>, and/or a third axis of linear motion <NUM> (out of page). In some embodiments, MLC carousel <NUM> is configured to be rotated about at least one axis of rotation, such as an axis of rotation <NUM>. In some embodiments, axis of rotation <NUM> is substantially parallel with a center line <NUM> of an X-ray field <NUM>. In the instance illustrated in <FIG>, axis of rotation <NUM> coincides with center line <NUM> of X-ray field <NUM>, but in many instances, axis of rotation <NUM> is displaced from center line <NUM> along first axis of linear motion <NUM> and/or third axis of motion <NUM>.

In some embodiments, MLC carousel <NUM> is configured with primary and secondary position detection for linear motion along first axis of linear motion <NUM>, second axis of linear motion <NUM>, third axis of linear motion <NUM>, and/or axis of rotation <NUM>. In some embodiments, primary motion detection with respect to one or more of the above axes is provided by a servo system associated with the motion. For example, in an embodiment, a servo system associated with linear motion of MLC carousel <NUM> along first axis of linear motion <NUM> includes certain position feedback that indicates the current position of MLC carousel <NUM> along first axis of linear motion <NUM>. In such embodiments, such position feedback is considered primary linear position detection along axis of linear motion <NUM>. In another example, in an embodiment, a servo system associated with rotational motion of MLC carousel <NUM> about axis of rotation <NUM> includes certain position feedback that indicates the current rotational position of MLC carousel <NUM> about axis of rotation <NUM>. In such embodiments, such rotational position feedback is considered primary rotational position detection.

In some embodiments, motion detection with respect to one or more of the above axes (for example, secondary motion detection) is provided by a respective magnetoresistive sensor. Thus, in such embodiments, MLC carousel <NUM> includes one or more of: a magnetoresistive sensor <NUM> for motion detection of MLC carousel <NUM> with respect to first axis of linear motion <NUM>; a magnetoresistive sensor <NUM> for motion detection of MLC carousel <NUM> with respect to second axis of linear motion <NUM>, a magnetoresistive sensor <NUM> for motion detection of MLC carousel <NUM> with respect to third axis of linear motion <NUM>, or a magnetoresistive sensor <NUM> for motion detection of MLC carousel <NUM> with respect to axis of rotation <NUM>. In such embodiments, magnetoresistive sensor <NUM> performs motion detection via a linear array <NUM> of magnets disposed on a surface <NUM> of MLC carousel <NUM>, magnetoresistive sensor <NUM> performs motion detection via a linear array <NUM> of magnets disposed on a surface <NUM> of MLC carousel <NUM>, magnetoresistive sensor <NUM> performs motion detection via a linear array <NUM> of magnets disposed on surface <NUM> of MLC carousel <NUM>, and/or magnetoresistive sensor <NUM> performs motion detection via a toothed ring <NUM> disposed on a peripheral region <NUM> of MLC carousel <NUM>. In such embodiments, an International Electrotechnical Commission (IEC) requirement for a secondary position sensor is for all LINAC carousel linear and rotational axes can be satisfied by a respective magnetoresistive sensor.

One embodiment of a magnetoresistive sensor for linear motion detection of MLC carousel <NUM> is described below in conjunction with <FIG>. One embodiment of a magnetoresistive sensor for rotational motion detection of MLC carousel <NUM> is described below in conjunction with <FIG>.

<FIG> schematically illustrates a linear motion detection apparatus <NUM>, according to various embodiments of the invention. In the embodiment illustrated in <FIG>, linear motion detection apparatus <NUM> includes a magnetoresistive sensor <NUM> and a linear array <NUM> of magnets <NUM>. In some embodiments, linear array <NUM> is implemented as a magnetic scale of magnets <NUM> of alternating poles (i.e., N-S-N-S and so on), where magnets <NUM> are each separated from each other with a uniform pole pitch <NUM>.

Magnetoresistive sensor <NUM> is disposed proximate to and is separated from linear array <NUM> by an air gap <NUM>. Thus, magnetoresistive sensor <NUM> is not physically in contact with linear array <NUM>. As a result, neither magnetoresistive sensor <NUM> nor linear array <NUM> undergoes mechanical wear during use.

As shown, linear array <NUM> is configured as a linear array of magnets <NUM> that is longitudinally oriented in a particular linear travel direction <NUM>. Magnetoresistive sensor <NUM> is configured to detect motion of linear array <NUM> relative to magnetoresistive sensor <NUM> in linear travel direction <NUM> and/or to generate position information that enables detection of motion of linear array <NUM> relative to magnetoresistive sensor <NUM> in travel direction <NUM>. In some embodiments, magnetoresistive sensor <NUM> includes a magnetoresistive device <NUM>, a bias magnet <NUM>, and a resistive bridge (not shown). In some embodiments, the resistive bridge is included in magnetoresistive device <NUM>. In some embodiments, magnetoresistive device <NUM> includes at least one of an anisotropic magnetoresistive (AMR) sensor, a giant magnetoresistive (GMR) sensor, a tunnel magnetoresistive (TMR) sensor, or other magnetic position sensor that measures changes in a magnetic field that occur when magnets <NUM> of linear array <NUM> move relative to magnetoresistive sensor <NUM>.

Magnetoresistive sensor <NUM> generates position information based on the magnetoresistive effect, where an external magnetic field affects the electrical resistance of a magnetoresistive material in magnetoresistive sensor <NUM>. For example, in some embodiments, magnetoresistive sensor <NUM> is configured to operate as a sine encoder that generates position information of magnets <NUM> in the form of a sine output signal and a cosine output signal that are based on the current angle of a magnetic field. Based on the sine output signal and the cosine output signal, a position of magnetoresistive sensor <NUM> between two adjacent magnets <NUM> can be determined. In such embodiments, the sine and cosine output signals enable precise determination of the position of magnetoresistive sensor <NUM> between two adjacent magnets <NUM>. For example, in an embodiment in which magnetoresistive sensor <NUM> is configured to generate signals for resolving a position of magnetoresistive sensor <NUM> to within <NUM>° (where pole pitch <NUM> equates to <NUM>°), the position of magnetoresistive sensor <NUM> can be determined to within a fraction of <NUM> % of pole pitch <NUM>. Additionally, the repeating cycles of the sine output signal and/or the cosine output signal may be counted as the magnetoresistive sensor <NUM> moves from one end of the linear array <NUM> of magnets <NUM> to the other end of the linear array <NUM> of magnets <NUM>. This may allow the two adjacent magnets <NUM> between with the magnetoresistive sensor <NUM> is located to be determined. Thus, magnetoresistive sensor <NUM> can provide precise position information regarding linear array <NUM> relative to magnetoresistive sensor <NUM>.

It is noted that magnetoresistive sensor <NUM> does not actively generate a position signal, and instead is a passive device. As a result, the output of magnetoresistive sensor <NUM> is generally unaffected by the high-radiation environment of an X-ray field present in a radiation therapy system, such as X-ray field <NUM> in <FIG>.

Returning to <FIG>, primary collimator <NUM> is configured to define an outer limit of X-ray field <NUM>. Primary collimator <NUM> can be a fixed collimator or a collimator configured with one or more movable jaws. Typically, primary collimator <NUM> is disposed proximate the radiation source of LINAC <NUM>. In the embodiment illustrated in <FIG>, primary collimator <NUM> is depicted as a single collimating apparatus, but in other embodiments, primary collimator <NUM> includes multiple collimating apparatuses positioned in series within X-ray field <NUM>.

In some embodiments, MLC carousel <NUM> includes a proximal MLC layer <NUM> and a distal MLC layer <NUM>. In other embodiments, MLC carousel <NUM> includes a single MLC layer. Proximal MLC layer <NUM> includes a plurality of leaves <NUM> that are each independently movable into X-ray field <NUM> in a travel direction. Similarly, distal MLC layer <NUM> includes a plurality of leaves <NUM> that are each independently movable into X-ray field <NUM> in a travel direction. In the embodiment illustrated in <FIG>, each leaf <NUM> of proximal MLC layer <NUM> is movable in one particular travel direction, which is perpendicular to center line <NUM> of X-ray field <NUM>. Further, in the embodiment illustrated in <FIG>, the travel direction of leaves <NUM> is depicted to be along third axis of linear motion <NUM>, which is out of the page. Similarly, each leaf <NUM> of distal MLC layer <NUM> is movable in one particular travel direction that is perpendicular to center line <NUM> of X-ray field <NUM>. In the embodiment illustrated in <FIG>, the travel direction of leaves <NUM> is the same travel direction as that of leaves <NUM>, which is along axis of linear motion <NUM>. In <FIG>, leaves <NUM> and leaves <NUM> are viewed end-on, i.e., along the travel direction, which is parallel to third axis of linear motion <NUM>.

In some embodiments, proximal MLC layer <NUM> includes multiple banks of leaves <NUM> and distal MLC layer <NUM> includes multiple banks of leaves <NUM>. In such embodiments, MLC layer <NUM> includes two opposing banks of leaves <NUM> that are positioned on opposite sides of a center plane of X-ray field <NUM>, and distal MLC layer <NUM> includes two opposing banks of leaves <NUM> that are positioned on opposite sides of the center plane of X-ray field <NUM>.

Leaves <NUM> and <NUM> are typically formed from a high atomic number material, such as tungsten or an alloy thereof. In addition, in some embodiments, leaves <NUM> and <NUM> have a generally trapezoidal cross-section that matches the beam divergence that occurs in the direction perpendicular to leaf travel. In practice, the cross-section of leaves <NUM> and <NUM> may not exactly trapezoidal. In some embodiments, leaves <NUM> and leaves <NUM> may be configured to project to a same projected size at isocenter <NUM>. In such embodiments, leaves <NUM> have a smaller cross-section in the direction perpendicular to leaf travel than leaves <NUM>.

In some embodiments, motion detection of each of leaves <NUM> and leaves <NUM> along a direction of linear travel is enabled by a respective magnetoresistive sensor. In such embodiments, each leaf <NUM> and each leaf <NUM> includes a magnetoresistive sensor for linear motion detection of the corresponding leaf. One such embodiment is described below in conjunction with <FIG>.

<FIG> schematically illustrates a side view of a single leaf <NUM> of MLC carousel <NUM>, according to various embodiments. As shown, leaf <NUM> is positioned at a beginning edge <NUM> of a travel range in a particular direction of travel <NUM>, and is therefore disposed proximate to but outside X-ray field <NUM>. Leaf <NUM> is also shown (dashed lines) after traveling partially along the travel range in the direction of travel <NUM>.

Leaf <NUM> includes a magnetoresistive sensor <NUM> and a linear array <NUM> of magnets disposed on an edge surface <NUM> of leaf <NUM>. In some embodiments, magnetoresistive sensor <NUM> can be consistent in configuration with one or more embodiments of magnetoresistive sensor <NUM> in <FIG> and linear array <NUM> can be consistent in configuration with one or more embodiments of linear array <NUM> in <FIG>.

In operation, as leaf <NUM> moves along direction of travel <NUM>, magnetoresistive sensor <NUM> generates position information for precisely determining a current position of magnetoresistive sensor <NUM> between the two closest magnets included in linear array <NUM>. In some embodiments, magnetoresistive sensor <NUM> generates such position information in the form of a sine output signal and a cosine output signal. In some embodiments, such position information is employed for secondary motion detection of leaf <NUM> along direction of travel <NUM>. In such embodiments, a servo system associated with moving leaf <NUM> along direction of travel <NUM> provides primary linear motion detection. Thus, in such embodiments, an IEC requirement for all moving leaves in a radiation therapy system to have both primary and secondary position sensors is satisfied.

<FIG> is a perspective view of MLC carousel <NUM>, according to an embodiment. In <FIG>, an array <NUM> of magnetoresistive sensors <NUM> for proximal MLC layer <NUM> is shown exploded from MLC carousel <NUM>. In the embodiment illustrated in <FIG>, magnetoresistive sensors <NUM> are disposed on a printed circuit board (PCB) <NUM>. In some embodiments, array <NUM> of magnetoresistive sensors <NUM> is configured as a linear array that extends longitudinally in a direction <NUM> that is perpendicular to a linear travel direction <NUM> of leaves <NUM>. In the embodiment illustrated in <FIG>, array <NUM> includes multiple rows <NUM> of magnetoresistive sensors <NUM>. In some embodiments, magnetoresistive sensors <NUM> in multiple rows <NUM> are staggered, so that magnetoresistive sensors <NUM> can be more closely spaced along direction <NUM>.

Insertion of PCB <NUM> into MLC carousel <NUM> causes each of magnetoresistive sensors <NUM> to be disposed proximate a measurement surface of a respective leaf <NUM> of proximal MLC layer <NUM>.

<FIG> is a perspective view of PCB <NUM> when inserted into MLC carousel <NUM>, according to an embodiment. In <FIG>, portions of MLC carousel <NUM> are omitted for clarity, such as a housing that encloses leaves <NUM>. As shown, magnetoresistive sensors <NUM> are arranged on PCB <NUM> so that each of magnetoresistive sensors <NUM> is disposed proximate a measurement surface <NUM> of a respective leaf <NUM> of proximal MLC layer <NUM>. In the embodiment illustrated in <FIG>, each measurement surface <NUM> is an edge surface of a leaf <NUM> and each measurement surface <NUM> is an edge surface of a leaf <NUM>.

In the embodiment illustrated in <FIG>, PCB <NUM> are configured to position magnetoresistive sensors <NUM> proximate magnets <NUM> on measurement surfaces <NUM> of leaves <NUM>. In other embodiments, magnetoresistive sensors <NUM> are disposed on any other suitable surface of MLC carousel <NUM> that positions magnetoresistive sensors <NUM> proximate measurement surfaces <NUM> of leaves <NUM>.

<FIG> is an end view of MLC carousel <NUM> when PCB <NUM> is inserted into MLC carousel <NUM>, according to an embodiment. In <FIG>, portions of MLC carousel <NUM> are omitted for clarity, such as a housing that encloses leaves <NUM>. As shown, each linear array <NUM> (viewed end on in <FIG>) of magnets <NUM> is separated from a corresponding magnetoresistive sensor <NUM> by an air gap <NUM>. An embodiment of the configuration of magnets <NUM>, air gap <NUM>, leaves <NUM>, and magnetoresistive sensors <NUM> is described below in conjunction with <FIG>.

<FIG> is a partial end view of proximal MLC layer <NUM> and PCB <NUM>, according to an embodiment. As shown, leaves <NUM> of MLC layer <NUM> are spaced apart in direction <NUM> by a leaf pitch <NUM>, which is the on-center spacing (also referred to as the center-to-center distance) between two adjacent leaves <NUM>. In the embodiment illustrated in <FIG>, direction <NUM> is perpendicular to linear travel direction <NUM> of leaves <NUM>, and linear travel direction <NUM> is oriented into and out of the page. Leaf pitch <NUM> is typically selected based on a desired functionality of the radiotherapy system that includes MLC carousel <NUM>. In some embodiments, each magnetoresistive sensor <NUM> on PCB <NUM> is also spaced apart from adjacent magnetoresistive sensors <NUM> by leaf pitch <NUM>. Air gap <NUM> separating each linear array <NUM> of magnets <NUM> from a corresponding magnetoresistive sensor <NUM> is shown.

In some embodiments, to reduce crosstalk between magnetoresistive sensors <NUM> of proximal MLC layer <NUM>, a width <NUM> of a particular magnet <NUM> in a direction perpendicular to linear travel direction <NUM> is selected to be equal to or less than a threshold value. In some instances, the direction perpendicular to linear travel direction <NUM> is direction <NUM>, and in other embodiments, the direction perpendicular to linear travel direction <NUM> is another direction, such as a direction <NUM> that is also perpendicular to a length of the leaf <NUM> to which the particular magnet <NUM> is coupled. In some embodiments, the threshold value may be based on leaf pitch <NUM>, air gap <NUM>, a field strength of the particular magnet <NUM>, and/or one or more other factors associated with the configuration of proximal MLC layer <NUM>, such as the size, relative position, and/or orientation of the particular magnet <NUM>, magnetoresistive sensors <NUM>, and the like. For example, in one such embodiment, the threshold value for width <NUM> of the particular magnet <NUM> is one half of leaf pitch <NUM>. In another such embodiment, the threshold value for width <NUM> of the particular magnet <NUM> is determined based on a size of leaf pitch <NUM> and a size of air gap <NUM>. In yet another such embodiment, the threshold value for width <NUM> of the particular magnet <NUM> is determined based on a minimum distance between the particular magnet <NUM> and an adjacent magnetoresistive sensor <NUM>.

It is noted that when width <NUM> of magnets <NUM> is equal to or less than such a threshold value, crosstalk between adjacent magnetoresistive sensors <NUM> is reduced due to a greater distancing between magnets <NUM> coupled to one of leaves <NUM> and the magnetoresistive sensor <NUM> associated with an adjacent leaf <NUM>. For example, when width <NUM> of magnets <NUM> is reduced, magnet 721A of leaf 351A is located farther from the magnetoresistive sensor 651B that is associated with adjacent leaf 351B. As a result, magnetoresistive sensor 651B is less likely to erroneously detect motion of leaf 351A. In the same vein, reduction in width <NUM> of magnet 721B results in magnetoresistive sensor 651A being less likely to erroneously detect motion of leaf 351B.

In some embodiments, to reduce crosstalk between magnetoresistive sensors <NUM> of proximal MLC layer <NUM>, each magnet <NUM> in a particular linear array <NUM> is separated by a pole pitch (not visible in <FIG>) that is selected to be equal to or less than a threshold value. An example of pole pitch in a linear array of magnets is illustrated as pole pitch <NUM> in <FIG>. In some embodiments, the threshold value may be based on leaf pitch <NUM>, air gap <NUM>, a field strength of the magnets <NUM> included in the particular linear array <NUM>, and/or one or more other factors associated with the configuration of proximal MLC layer <NUM>, such as the size, width, relative position, and/or orientation of the magnets <NUM> included in the particular linear array <NUM>, magnetoresistive sensors <NUM>, and the like. For example, in some embodiments, the threshold value for the pole pitch separating magnets <NUM> in the particular linear array <NUM> is based on leaf pitch <NUM>. In one such embodiment, the threshold value for the pole pitch separating magnets <NUM> in the particular linear array <NUM> is equal to or less than leaf pitch <NUM>. In another such embodiment, the threshold value for the pole pitch separating magnets <NUM> in the particular linear array <NUM> is equal to or less than a specified fraction of leaf pitch <NUM>.

In some embodiments, to reduce crosstalk between magnetoresistive sensors <NUM> of proximal MLC layer <NUM>, each magnet <NUM> in a particular linear array <NUM> is configured with a field strength that is selected to be equal to or less than a threshold value. In some embodiments, the threshold value may be based on leaf pitch <NUM>, air gap <NUM>, and/or one or more other factors associated with the configuration of proximal MLC layer <NUM>, such as the size, width, relative position, and/or orientation of the magnets <NUM> included in the particular linear array <NUM>, magnetoresistive sensors <NUM>, and the like. Thus, in some embodiments, the threshold value for the field strength of magnets <NUM> in the particular linear array <NUM> is selected to have a field strength that, when measured by a magnetoresistive sensor <NUM> associated with an adjacent leaf <NUM>, is no greater than a particular fraction (e.g., <NUM>%) of a field strength measured by the magnetoresistive sensor <NUM> associated with an adjacent leaf <NUM> for magnets coupled to the adjacent leaf <NUM>. For example, in one such embodiment, a field strength for magnet 721A of leaf 351A measured by magnetoresistive sensor 651B is selected to be no greater than a particular fraction of the field strength for magnet 721B when measured by magnetoresistive sensor 651B. In such embodiments, the likelihood of a magnetoresistive sensor <NUM> erroneously measuring movement of magnets <NUM> coupled to an adjacent leaf <NUM> is greatly reduced or eliminated.

<FIG> schematically illustrates a linear rotational motion detection apparatus <NUM>, according to various embodiments. In the embodiment illustrated in <FIG>, rotational motion detection apparatus <NUM> includes magnetoresistive sensor <NUM> and toothed ring <NUM>, which is disposed on peripheral region <NUM> of MLC carousel <NUM>, as shown in <FIG>. Toothed ring <NUM> includes an array of ferromagnetic gear teeth <NUM>. In some embodiments, magnetoresistive sensor <NUM> performs secondary (or primary) rotational motion detection by detecting a position of magnetoresistive sensor <NUM> relative to ferromagnetic gear teeth <NUM> included in toothed ring <NUM>.

In the embodiment illustrated in <FIG>, magnetoresistive sensor <NUM> includes a bias magnet <NUM> coupled to a magnetoresistive device <NUM>. Magnetoresistive device <NUM> is configured to generate position information regarding the one or two ferromagnetic gear teeth <NUM> that are currently proximate magnetoresistive sensor <NUM>. Magnetoresistive device <NUM> is disposed proximate to ferromagnetic gear teeth <NUM> and is separated from ferromagnetic gear teeth <NUM> by an air gap <NUM>. Thus, magnetoresistive device <NUM> is not physically in contact with ferromagnetic gear teeth <NUM>. As a result, neither magnetoresistive device <NUM> nor ferromagnetic gear teeth <NUM> undergo mechanical wear during use.

In operation, as toothed ring <NUM> rotates with MLC carousel <NUM> (not shown), magnetoresistive sensor <NUM> generates rotational position information for precisely determining a current rotational position of magnetoresistive sensor <NUM> between the two closest ferromagnetic gear teeth <NUM> included in toothed ring <NUM>. In some embodiments, magnetoresistive sensor <NUM> generates such position information in the form of a sine output signal and a cosine output signal. In some embodiments, such position information is employed for secondary motion detection of toothed ring <NUM> (and consequently MLC carousel <NUM>) about an axis of rotation <NUM>. In such embodiments, a servo system associated with rotating MLC carousel <NUM> about axis of rotation <NUM> provides primary linear motion detection. Thus, in such embodiments, an IEC requirement for all rotational axes of an MLC carousel in a radiation therapy system to have both primary and secondary position sensors is satisfied.

Ideally, when position information in the form of a sine output signal and a cosine output signal are generated by magnetoresistive sensor <NUM>, the sine output signal and cosine output signal are each centered around the same value. For example, in an instance in which magnetoresistive sensor <NUM> includes a <NUM> V supply, the sine output signal and the cosine output signal are each ideally centered at <NUM> V and vary in amplitude from <NUM> V to <NUM> V over a single cycle. However, in practice, various factors typically produce a signal offset from an ideal output value, which can result in an inaccurate rotational position measurement for toothed ring <NUM>. One such instance is described below in conjunction with <FIG>.

<FIG> is a graph <NUM> illustrating output values for an ideal sine output signal <NUM>, an actual sine output signal <NUM>, and a cosine output signal <NUM> from magnetoresistive sensor <NUM>. As shown, ideal sine output signal <NUM> and cosine output signal <NUM> each vary from <NUM> V to <NUM> V, and ideal sine output signal <NUM> is out of phase from cosine output signal <NUM> by <NUM>°. In embodiments in which rotation of toothed ring <NUM> (shown in <FIG>) from one ferromagnetic gear tooth <NUM> to an adjacent ferromagnetic gear tooth <NUM> corresponds to a single <NUM>° cycle of magnetoresistive sensor <NUM>, the <NUM>° by which ideal sine output signal <NUM> is out of phase from cosine output signal <NUM> corresponds to <NUM>/<NUM> of the rotational displacement between the two adjacent ferromagnetic gear teeth <NUM>. Based on the <NUM>° phase offset between a sine output signal and a cosine output signal generated by magnetoresistive sensor <NUM>, a precise position of magnetoresistive sensor between two adjacent ferromagnetic gear teeth <NUM> of toothed ring <NUM> is determined. A control system may track which particular tooth <NUM> of toothed ring <NUM> is currently passing by the magnetoresistive sensor at any particular time, so that the two adjacent ferromagnetic gear teeth <NUM> of toothed ring <NUM> between which the magnetoresistive sensor <NUM> is located at any particular time can be determined.

In practice, the sine and cosine output signals generated by magnetoresistive sensor <NUM> are not ideal. For example, the sine and cosine output signals generated by magnetoresistive sensor <NUM> typically include a signal offset. For example, in the case of the sine output signal, a signal offset <NUM> is present between ideal sine output signal <NUM> and actual sine output signal <NUM>. As shown, signal offset <NUM> causes an output value of actual sine output signal <NUM> to cross over the output value of cosine output signal <NUM> at an actual crossover point <NUM>. In the instance depicted in <FIG>, signal offset <NUM> is depicted as approximately +<NUM> V, but in practice is typically much smaller. Actual crossover point <NUM> occurs at a different rotational position R1 than an ideal crossover point <NUM>, which occurs at rotational position R2. The difference between rotational position R1 and rotational position R2 corresponds to an inaccuracy in the phase shift between the sine output signal and the cosine output signal generated by magnetoresistive sensor <NUM>. As a result, when determining a rotational position of magnetoresistive sensor <NUM> between two adjacent ferromagnetic teeth <NUM> based on actual sine output signal <NUM> and cosine output signal <NUM>, the determined rotational position may be inaccurate. Factors that can contribute to and/or cause signal offset <NUM> include variations in the resistance of resistors included in a resistive bridge of magnetoresistive sensor <NUM>, other artifacts of the electronics included in magnetoresistive sensor <NUM>, and/or physical tooth-to-tooth variations of ferromagnetic teeth <NUM>.

According to various embodiments, a calibration process is performed to determine a first signal offset value for a sine output signal generated by magnetoresistive sensor <NUM> and a second signal offset value for a cosine output signal generated by magnetoresistive sensor <NUM>. In the embodiments, one or more dummy cycles are performed to enable quantification of the first and second signal offset values. The first and second signal offset values can then be employed to compensate for the inaccuracy in rotational position that otherwise results from non-ideal sine output signals and cosine output signals generated by magnetoresistive sensor <NUM>.

In some embodiments, in a dummy cycle, an excitation is applied to an actuator for rotating toothed ring <NUM> so that toothed ring <NUM> rotates a specified rotational displacement, such as the rotational displacement between two adjacent ferromagnetic teeth <NUM>. In some embodiments, the specified rotational displacement corresponds to a rotational displacement of toothed ring <NUM> in which a first ferromagnetic tooth <NUM> proximate magnetoresistive sensor <NUM> is rotated from a first rotational position to a second rotational position and a second ferromagnetic tooth <NUM> that is adjacent to the first ferromagnetic tooth <NUM> is rotated from the second rotational position to a third rotational position. Thus, over specified rotational displacement, the first ferromagnetic tooth <NUM> moves to the position occupied by the second ferromagnetic tooth <NUM> at the beginning of the cycle. Thus, during a dummy cycle, values are collected for a sine output signal and a cosine output signal generated by magnetoresistive sensor <NUM> as toothed ring <NUM> rotates through a rotational displacement that corresponds to one tooth pitch of toothed ring <NUM>. One such embodiment is described below in conjunction with <FIG>.

<FIG> sets forth a flowchart of a calibration process for rotational position detection via a magnetoresistive sensor, according to one or more embodiments. The method 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 the method is described in conjunction with the systems of <FIG>, persons skilled in the art will understand that any suitably configured radiation therapy system is within the scope of the present disclosure. In some embodiments, the control algorithms for the method steps may reside in image acquisition and treatment control computer <NUM>, remote control console <NUM>, or a combination of both. The control algorithms can be implemented in whole or in part as software- or firmware-implemented logic, and/or as hardware-implemented logic circuits.

A method <NUM> begins at step <NUM>, when RT system <NUM> begins a calibration process. In some embodiments, method <NUM> is performed a single time for a particular radiation therapy system, for example during commissioning, acceptance testing, and/or installation of the radiation therapy system. In alternative embodiments, method <NUM> is performed periodically for a particular radiation therapy system, for example upon powering up of the radiation therapy system, upon completion of a specified duration of operation by the radiation therapy system, and/or upon completion of a specified number of procedures by the radiation therapy system.

In step <NUM>, RT system <NUM> begins applying an excitation to the rotational actuator configured to rotate MLC carousel <NUM> about axis of rotation <NUM>. In some embodiments, the excitation may correspond to a rotational displacement of toothed ring <NUM> in which a first ferromagnetic tooth <NUM> proximate magnetoresistive sensor <NUM> is rotated from a first rotational position to a second rotational position and a second ferromagnetic tooth <NUM> that is adjacent to the first ferromagnetic tooth <NUM> is rotated from the second rotational position to a third rotational position. One such specified rotational displacement is also referred to herein as an excitation cycle.

In step <NUM>, RT system <NUM> determines whether a measurement location has been reached. In some embodiments, a plurality of measurement locations are disposed across a specified rotational displacement, or excitation cycle. In one embodiment, <NUM> or <NUM> of measurement locations are passed through over the rotational displacement that corresponds to an excitation cycle. In such embodiments, a highly accurate curve of output vales for magnetoresistive sensor <NUM> can be generated across a single excitation cycle. As a result, an accurate signal offset value can be determined based on such a curve.

When RT system <NUM> determines that a measurement location has been reached, method <NUM> proceeds to step <NUM>; when RT system <NUM> determines that a measurement location has not been been reached, method <NUM> proceeds to step <NUM>.

In step <NUM>, RT system <NUM> continues to apply the excitation to the rotational actuator and the rotational actuator continues to cause MLC carousel <NUM> (and toothed ring <NUM>) to rotate.

In step <NUM>, RT system <NUM> measures one or more output signals from magnetoresistive sensor <NUM>. In some embodiments, RT system <NUM> measures a sine output signal and a cosine output signal at the current rotational position. In some embodiments, RT system <NUM> measures multiple sine output signals (e.g., <NUM>, <NUM>, <NUM>, etc.) and multiple cosine output signals (e.g., <NUM>, <NUM>, <NUM>, etc.) at the current rotational position. In such embodiments, the multiple sine output signals are averaged to generate a single average sine output signal for the current rotational position, and the multiple cosine output signals are averaged to generate a single average cosine output signal for the current rotational position. It is noted that rotation of toothed ring <NUM> generally occurs at a relatively low rotational frequency (e.g. on the order of about <NUM> to <NUM>). As a result, the multiple sine output signals and the multiple cosine output signals can be acquired sequentially during step <NUM> at a sufficiently high acquisition rate that toothed ring <NUM> does not significantly rotate during step <NUM>. Thus, the multiple sine output signals and the multiple cosine output signals are effectively measured at the same rotational position.

In step <NUM>, RT system <NUM> determines whether the current rotational position of toothed ring <NUM> is at the final measurement location for the excitation cycle. If yes, method <NUM> proceeds to step <NUM>; if no, method <NUM> proceeds to step <NUM>.

In step <NUM>, RT system <NUM> determines whether additional excitation cycles are to be performed during the calibration process. In some embodiments, steps <NUM> - <NUM> are performed for a single excitation cycle. In other embodiments, steps <NUM> - <NUM> are performed for multiple excitation cycles, e.g., <NUM> - <NUM>, so that signal offset values (e.g., for the sine output signal and the cosine output signal) can be averaged over the multiple excitation cycles. In yet other embodiments, steps <NUM> - <NUM> are performed for each ferromagnetic tooth <NUM> of toothed ring <NUM>. In such embodiments, a different signal offset value can be determined for rotational motion being measured between each ferromagnetic tooth <NUM> of toothed ring <NUM>. In such embodiments, each signal offset value can provide compensation for a different rotational position inaccuracy associated with the physical variations between ferromagnetic teeth <NUM>.

<FIG> sets forth a flowchart of a process for rotational position detection via a magnetoresistive sensor, according to one or more embodiments. The method 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 the method is described in conjunction with the systems of <FIG>, persons skilled in the art will understand that any suitably configured radiation therapy system is within the scope of the present disclosure. In some embodiments, the control algorithms for the method steps may reside in image acquisition and treatment control computer <NUM>, remote control console <NUM>, or a combination of both. The control algorithms can be implemented in whole or in part as software- or firmware-implemented logic, and/or as hardware-implemented logic circuits.

A method <NUM> begins at step <NUM>, when RT system <NUM> begins operation. For example, in one instance, MLC carousel <NUM> is rotated about axis of rotation <NUM> during a radiation therapy session.

In step <NUM>, RT system <NUM> begins applying an excitation to the rotational actuator configured to rotate MLC carousel <NUM> about axis of rotation <NUM>.

In step <NUM>, RT system <NUM> measures one or more output signals from magnetoresistive sensor <NUM>. In some embodiments, RT system <NUM> measures a sine output signal and a cosine output signal at the current rotational position.

In step <NUM>, RT system <NUM> generates one or more corrected output signals by modifying each of the one or more output signals measured in step <NUM> with a corresponding signal offset value determined during a calibration process, such as method <NUM>. Thus, in some embodiments, a sine output signal measured in step <NUM> is modified with a first signal offset value and a cosine output signal measured in step <NUM> is modified with a second signal offset value.

In step <NUM>, RT system <NUM> determines a current rotational position of toothed ring <NUM> based on the one or more corrected output signals generated in step <NUM>.

After step <NUM>, method <NUM> generally continues as RT system <NUM> rotates MLC carousel <NUM> during operation.

<FIG> is an illustration of 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. For example, in some embodiments, computing device <NUM> can be employed as image acquisition and treatment control computer <NUM> and/or remote control console <NUM>. 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 a calibration process <NUM> consistent with method <NUM> and/or a rotational position detection process <NUM> consistent with method <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 calibration process <NUM> and/or rotational position detection process <NUM>.

<FIG> is a block diagram of an illustrative embodiment of a computer program product <NUM> for implementing various 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 enable precise and repeatable position measurement of an MLC and of the individual leaves of an MLC in a high-radiation environment. In addition, position measurement as described herein is non-contact, reducing wear-based inaccuracies and hysteresis.

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 method of measuring a rotational position of an assembly, the method comprising:
applying an excitation signal to an actuator that is coupled to the assembly that includes an array of ferromagnetic teeth that are arranged circumferentially about the assembly, wherein the excitation signal causes a first rotational displacement of a first ferromagnetic tooth included in the array from a first rotational position to a second rotational position;
measuring one or more signal outputs from a magnetoresistive sensor when the first ferromagnetic tooth is disposed at the second rotational position;
generating one or more corrected signals by modifying each of the one or more signal outputs with a respective signal offset value; and
based on the corrected signals, determining a rotational position of the assembly.