Imaging controller, imaging system, imaging control method, and program

This imaging controller of the imaging controller includes: an imager position determination section that determines whether or not a first imager is located in an overlapping region where a rotation range of the first imager and a rotation range of a second imager overlap each other when a rotation mechanism rotates the first and second imagers by an angle greater than the predetermined angle; and an imaging timing control section that causes one or both of the first and second imagers to perform imaging when arrival of an imaging timing is detected and that causes only the second imager to perform imaging in at least one imaging timing whose arrival is detected in a state where the imager position determination section determines that the first imager is located in the overlapping region.

RELATED APPLICATIONS

The present application is National Phase of International Application No. PCT/JP2013/074670 filed Sep. 12, 2013, and claims priority from Japanese Application No. 2012-224248, filed Oct. 9, 2012, the disclosure of which is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to an imaging controller, an imaging system, an imaging control method, and a program.

Priority is claimed on Japanese Patent Application No. 2012-224248, filed on Oct. 9, 2012, the content of which is incorporated herein by reference.

BACKGROUND ART

In cone beam computed tomography (cone beam CT; CBCT), an imager in which an X-ray source and a two-dimensional detector form a pair captures a two-dimensional radiographic image by emitting cone-shaped X-rays from the X-ray source to the two-dimensional detector while rotating around an imaging target to change the irradiation angle. By using the cone-shaped X-rays, in the cone beam CT, it is possible to generate (reconstruct) a CT image (tomographic image) by capturing a two-dimensional radiographic image without the need to rotate the imaging target during imaging and without the need for multiple rotations.

Here, when performing a CT scan for the human body as a target, if subject blur due to the breathing of the imaging target occurs, this becomes a factor lowering the accuracy of the CT image. In order to prevent such a subject blur, a method is used in which an imaging target holds their breath during imaging. However, an increase in the breath-holding time becomes a burden for the imaging target. Therefore, in order to acquire a high-accuracy image while reducing the burden on the imaging target, it is preferable that the imaging time be short.

As an apparatus capable of reducing the imaging time, there is a CBCT for keeping the relatively small rotation angle of each imager by using a plurality of imagers, such as a dual-source CBCT using two pairs of imagers (for example, PTL 1).

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

If the radiation dose can be reduced in a CBCT using a plurality of imagers, such as a dual-source CBCT, it is possible to reduce the burden on the imaging target.

The present invention provides an imaging controller, an imaging system, an imaging control method, and a program that can reduce the radiation dose.

Solution to Problem

An imaging controller according to an aspect of the present invention is an imaging controller of an imaging apparatus which includes first and second imagers for capturing a radiographic image by emitting a cone beam toward a rotation axis and a rotation mechanism for rotating the first and second imagers integrally around the rotation axis and in which an angle between an irradiation axis of the first imager and an irradiation axis of the second imager with the rotation axis as a reference is a predetermined angle. The imaging controller includes: an imager position determination section that determines whether or not the first imager is located in an overlapping region where a rotation range of the first imager and a rotation range of the second imager overlap each other when the rotation mechanism rotates the first and second imagers by an angle greater than the predetermined angle; and an imaging timing control section that causes one or both of the first and second imagers to perform imaging when arrival of an imaging timing is detected and that causes only the second imager to perform imaging in at least one imaging timing whose arrival is detected in a state where the imager position determination section determines that the first imager is located in the overlapping region.

In addition, in an imaging controller according to another aspect of the present invention, in the imaging controller described above, a position specifying section that specifies a three-dimensional position of a position specification target based on a radiographic image captured by the first imager and a radiographic image captured by the second imager is included. When the imaging timing control section detects arrival of an imaging timing and causes both of the first and second imagers to perform imaging and the position specifying section succeeds in specifying the three-dimensional position of the position specification target based on the obtained radiographic images, if arrival of a next imaging timing is detected in a state where the imager position determination section determines that the first imager is located in the overlapping region, the imaging timing control section causes only the second imager to perform imaging.

In addition, in an imaging controller according to still another aspect of the present invention, in the imaging controller described above, a position specifying section that specifies a three-dimensional position of a position specification target based on a radiographic image captured by the first imager and a radiographic image captured by the second imager is included. When the imaging timing control section detects arrival of an imaging timing and causes both of the first and second imagers to perform imaging and the position specifying section fails to detect an image of the position specification target in at least one of the obtained radiographic images, if arrival of a next imaging timing is detected in a state where the imager position determination section determines that the first imager is located in the overlapping region, the imaging timing control section causes only the second imager to perform imaging.

In addition, in an imaging controller according to still another aspect of the present invention, in the imaging controller described above, the imaging timing control section causes only the second imager to perform imaging at all imaging timings whose arrival is detected in a state where the imager position determination section determines that the first imager is located in the overlapping region.

In addition, an imaging system according to still another aspect of the present invention includes: an imaging apparatus which includes first and second imagers for capturing a radiographic image by emitting a cone beam toward a rotation axis and a rotation mechanism for rotating the first and second imagers integrally around the rotation axis and in which an angle between an irradiation axis of the first imager and an irradiation axis of the second imager with the rotation axis as a reference is a predetermined angle; and an imaging controller configured to include an imager position determination section that determines whether or not the first imager is located in an overlapping region where a rotation range of the first imager and a rotation range of the second imager overlap each other when the rotation mechanism rotates the first and second imagers by an angle greater than the predetermined angle and an imaging timing control section that causes one or both of the first and second imagers to perform imaging when arrival of an imaging timing is detected and that causes only the second imager to perform imaging in at least one imaging timing whose arrival is detected in a state where the imager position determination section determines that the first imager is located in the overlapping region.

In addition, an imaging control method according to still another aspect of the present invention is an imaging control method of an imaging controller of an imaging apparatus which includes first and second imagers for capturing a radiographic image by emitting a cone beam toward a rotation axis and a rotation mechanism for rotating the first and second imagers integrally around the rotation axis and in which an angle between an irradiation axis of the first imager and an irradiation axis of the second imager with the rotation axis as a reference is a predetermined angle. The imaging control method includes: an imager position determination step of determining whether or not the first imager is located in an overlapping region where a rotation range of the first imager and a rotation range of the second imager overlap each other when the rotation mechanism rotates the first and second imagers by an angle greater than the predetermined angle; and an imaging timing control step of causing one or both of the first and second imagers to perform imaging when arrival of an imaging timing is detected and causing only the second imager to perform imaging in at least one imaging timing whose arrival is detected in a state where it is determined that the first imager is located in the overlapping region in the imager position determination step.

In addition, a program according to still another aspect of the present invention is a program causing a computer as an imaging controller of an imaging apparatus, which includes first and second imagers for capturing a radiographic image by emitting a cone beam toward a rotation axis and a rotation mechanism for rotating the first and second imagers integrally around the rotation axis and in which an angle between an irradiation axis of the first imager and an irradiation axis of the second imager with the rotation axis as a reference is a predetermined angle, to execute: an imager position determination step of determining whether or not the first imager is located in an overlapping region where a rotation range of the first imager and a rotation range of the second imager overlap each other when the rotation mechanism rotates the first and second imagers by an angle greater than the predetermined angle; and an imaging timing control step of causing one or both of the first and second imagers to perform imaging when arrival of an imaging timing is detected and causing only the second imager to perform imaging in at least one imaging timing whose arrival is detected in a state where it is determined that the first imager is located in the overlapping region in the imager position determination step.

Advantageous Effects of Invention

According to the imaging controller, the imaging system, the imaging control method, and the program described above, it is possible to reduce the radiation dose.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments are not intended to limit the invention defined in the appended claims. In addition, all combinations of the features described in the embodiments are not necessary for the solving means of the invention.

FIG. 1is a schematic block diagram showing the functional configuration of an imaging system in an embodiment of the present invention. In this diagram, a radiotherapy system1includes a radiotherapy apparatus controller2and a radiotherapy apparatus3.

The radiotherapy system1performs the emission (emission of radiation toward a certain target, such as an affected part) of radiation (may be a heavy particle beam) in radiation therapy or the generation of a CT image (tomographic image) for treatment planning. The radiotherapy system1corresponds to an example of an imaging system in the present embodiment.

The radiotherapy apparatus3emits radiation to the affected part in radiation therapy. In addition, the radiotherapy apparatus3captures a radiographic image (X-ray radiographic image) in order to generate a CT image. The radiotherapy apparatus3corresponds to an example of an imaging apparatus in the present embodiment.

The radiotherapy apparatus controller2controls the radiotherapy apparatus3to emit radiation and capture a radiographic image. In addition, the radiotherapy apparatus controller2generates a CT image based on the radiographic image captured by the radiotherapy apparatus3. The radiotherapy apparatus controller2corresponds to an example of an imaging controller in the present embodiment.

FIG. 2is a schematic diagram showing the apparatus configuration of the radiotherapy apparatus3. In this diagram, the radiotherapy apparatus3includes a rotary driving unit311, an O ring312, a traveling gantry313, a swing mechanism321, an irradiation unit330, a sensor array351, a sensor array361, a sensor array362, a couch381, and a couch driving unit382. The irradiation unit330includes a therapeutic radiation emission unit331, a multi-leaf collimator (MLC)332, a diagnostic X-ray source341, and a diagnostic X-ray source342.

The diagnostic X-ray source341and diagnostic X-ray source342will be referred to collectively as a “diagnostic X-ray source340” hereinafter. In addition, the sensor array361and the sensor array362will be referred to collectively as a “sensor array360” hereinafter.

The rotary driving unit311supports the O ring312on a base so as to be able to rotate around a rotation axis A11, and rotates the O ring312according to the control of the radiotherapy apparatus controller2. The rotation axis A11is an axis in a vertical direction.

The O ring312is formed in a ring shape having a rotation axis A12at the center, and supports the traveling gantry313so as to be able to rotate around the rotation axis A12. The rotation axis A12is an axis in a horizontal axis (that is, an axis perpendicular to the vertical direction), and is perpendicular to the rotation axis A11at the isocenter P11. The rotation axis A12is fixed to the O ring312. That is, the rotation axis A12rotates around the rotation axis A11with the rotation of the O ring312.

The traveling gantry313is formed in a ring shape having the rotation axis A12at the center, and is disposed inside the O ring312so as to be concentric with the O ring312. The radiotherapy apparatus3further includes a traveling driving device (not shown), and the traveling gantry313rotates around the rotation axis A12with power from the traveling driving device.

The traveling gantry313itself is rotated to integrally rotate each unit provided in the traveling gantry313, such as the diagnostic X-ray source341and the sensor array361or the diagnostic X-ray source342and the sensor array362. The traveling gantry313corresponds to an example of a rotation mechanism in the present embodiment.

The swing mechanism321is fixed inside the ring of the traveling gantry313, and supports the irradiation unit330on the traveling gantry313. The swing mechanism321rotates the irradiation unit330around a pan axis A21and rotates the irradiation unit330around a tilt axis A22according to the control of the radiotherapy apparatus controller2.

The pan axis A21is an axis parallel to the rotation axis A12, and is fixed to the traveling gantry313. The swing mechanism321causes the irradiation unit330to perform a swinging operation to the left and right with respect to the rotation axis A12(accordingly, to the left and right with respect to an imaging target T11shown inFIG. 2) by rotating the irradiation unit330around the pan axis A21.

The tilt axis A22is an axis perpendicular to the pan axis A21, and is fixed to the traveling gantry313. The swing mechanism321causes the irradiation unit330to perform a swinging operation in a direction of the rotation axis A12(accordingly, up and down with respect to the imaging target T11) by rotating the irradiation unit330around the tilt axis A22.

The irradiation unit330is disposed inside the traveling gantry313so as to be supported by the swing mechanism321, and emits therapeutic radiation B11or a diagnostic X-ray B21or B22.

The therapeutic radiation emission unit331emits the therapeutic radiation B11according to the control of the radiotherapy apparatus controller2. The therapeutic radiation emission unit331is supported by the traveling gantry313through the swing mechanism321. For this reason, once the therapeutic radiation emission unit331is directed toward the isocenter P11by adjustment of the swing mechanism321, the therapeutic radiation B11always passes through the isocenter P11in general even if the O ring312is rotated by the rotary driving unit311and even if the traveling gantry313is rotated by the traveling driving device. Therefore, the therapeutic radiation emission unit331can emit the therapeutic radiation B11toward the isocenter P11from various directions by rotating around the rotation axis A11or the rotation axis A12.

In addition, a case where deflection occurs in the traveling gantry313due to the weight of the irradiation unit330or the like or a case where the affected part to be irradiated does not necessarily match the isocenter P11may occur. In this case, after the therapeutic radiation emission unit331rotates around the rotation axis A11or the rotation axis A12, the swing mechanism321corrects the direction of the therapeutic radiation emission unit331. Accordingly, it is possible to perform high-accuracy positioning.

The multi-leaf collimator332matches the shape of the radiation field when the therapeutic radiation B11is emitted to the patient with the shape of the affected part by shielding a part of the therapeutic radiation B11according to the control of the radiotherapy apparatus controller2.

The diagnostic X-ray source341emits the diagnostic X-ray B21toward the isocenter P11according to the control of the radiotherapy apparatus controller2. The diagnostic X-ray B21is a cone beam that is emitted from one point of the diagnostic X-ray source341and that has a conical shape, such as a cone or a pyramid, with the one point as an apex.

The diagnostic X-ray source342emits the diagnostic X-ray B22toward the isocenter P11according to the control of the radiotherapy apparatus controller2. The diagnostic X-ray B22is a cone beam that is emitted from one point of the diagnostic X-ray source342and that has a conical shape, such as a cone or a pyramid, with the one point as an apex.

FIG. 3is an explanatory diagram showing an example of the cone beam emitted from the diagnostic X-ray source340. As shown in the diagram, the cone beam emitted from the diagnostic X-ray source340spreads in both of the direction perpendicular to the rotation axis A12(left and right direction of the imaging target T11) and the direction of the rotation axis A12(up and down direction of the imaging target T11). Hereinafter, a fan angle, which is an angle indicating the spread of a cone beam in a direction perpendicular to the rotation axis A12, is expressed as “α”. In addition, a cone angle, which is an angle indicating the spread of a cone beam in a direction of the rotation axis A12is expressed as “β”.

InFIG. 2, both of the diagnostic X-rays B21and B22are shown as the irradiation axis. The irradiation axis of the cone beam referred to herein is the central axis of the cone formed by the cone beam (for example, when the cone beam has a conical shape, the rotation axis of the cone).

The diagnostic X-ray sources341and342are fixed to the irradiation unit330(for example, a housing of the multi-leaf collimator332) in a direction perpendicular to the irradiation axis. In particular, when the therapeutic radiation emission unit331is directed toward the isocenter P11(that is, when the therapeutic radiation emission unit331is directed toward a direction in which the therapeutic radiation B11passes through the isocenter P11), the irradiation axis of the diagnostic X-ray source341and the irradiation axis of the diagnostic X-ray source342are perpendicular to each other at the isocenter P11.

The sensor array351is disposed at a position hit by the therapeutic radiation B11from the therapeutic radiation emission unit331so as to face the therapeutic radiation emission unit331, and is fixed inside the ring of the traveling gantry313. The sensor array351receives the therapeutic radiation B11, which is emitted from the therapeutic radiation emission unit331and is transmitted through the subject, such as the affected part, and generates (captures) a radiographic image (radiation projection image) of the subject. The radiographic image of the subject generated by the sensor array351is used when checking the radiation position of the therapeutic radiation B11, when recording the treatment, and the like. Reception referred to herein is receiving the radiation.

As the sensor array351, it is possible to use various devices that can receive the therapeutic radiation B11and generate a radiographic image. For example, the sensor array351may be a flat panel detector (FPD), or may be an X-ray image intensifier (II).

The sensor array361is disposed at a position hit by the diagnostic X-ray B21from the diagnostic X-ray source341so as to face the diagnostic X-ray source341, and is fixed inside the ring of the traveling gantry313. The sensor array361receives the diagnostic X-ray B21, which is emitted from the diagnostic X-ray source341and is transmitted through the subject, such as the affected part, and generates a radiographic image of the subject. The radiographic image of the subject generated by the sensor array361and the radiographic image of the subject generated by the sensor array362are used when the radiotherapy apparatus controller2generates a CT image.

As the sensor array361, it is possible to use various devices that can receive the diagnostic X-ray B21and generate a radiographic image. For example, the sensor array361may be an FPD, or may be an X-ray II.

The sensor array362is disposed at a position hit by the diagnostic X-ray B22from the diagnostic X-ray source342so as to face the diagnostic X-ray source342, and is fixed inside the ring of the traveling gantry313. The sensor array362receives the diagnostic X-ray B22, which is emitted from the diagnostic X-ray source342and is transmitted through the subject, such as the affected part, and generates a radiographic image of the subject. The radiographic image of the subject generated by the sensor array362and the radiographic image of the subject generated by the sensor array361are used when the radiotherapy apparatus controller2generates a CT image.

As the sensor array362, it is possible to use various devices that can receive the diagnostic X-ray B22and generate a radiographic image. For example, the sensor array362may be an FPD, or may be an X-ray II.

When the traveling gantry313is made to travel along the O ring312, the diagnostic X-ray source341and the sensor array361, the diagnostic X-ray source342and the sensor array362, and the therapeutic radiation emission unit331and the sensor array351rotate around the rotation axis A12passing through the isocenter P11while maintaining the positional relationship therebetween.

Hereinafter, the combination of the diagnostic X-ray source341and the sensor array361is referred to as an “imager371”, and the combination of the diagnostic X-ray source342and the sensor array362is referred to as an “imager372”. Each of the imager371and the imager372corresponds to an example of an imager in the present embodiment. That is, the diagnostic X-ray source341emits the diagnostic X-ray B21of a cone beam toward the rotation axis A12, and the sensor array361captures a radiographic image based on the diagnostic X-ray B21. In addition, the diagnostic X-ray source342emits the diagnostic X-ray B22of a cone beam toward the rotation axis A12, and the sensor array362captures a radiographic image based on the diagnostic X-ray B22.

Here, emitting the cone beam toward the rotation axis is emitting the cone beam so that the cone beam and the rotation axis cross each other. Typically, the cone beam is emitted so that the irradiation axis of the cone beam and the rotation axis cross each other. However, the embodiment of the present invention is not limited to this.

Hereinafter, a case where the imager371is an example of a first imager and the imager372is an example of a second imager will be described as an example. However, the embodiment of the present invention is not limited to this. The imager372may be an example of the first imager, and the imager371may be an example of the second imager.

In addition, an angle between the irradiation axis of the imager371and the irradiation axis of the imager372is fixed at a predetermined angle with the rotation axis A12as a reference. In addition, the irradiation axis of the imager referred to herein is the irradiation axis of the cone beam emitted from the imager.

More specifically, when the swing mechanism321sets the direction of the irradiation unit330so that the therapeutic radiation B11passes through the isocenter P11, the irradiation axis of the diagnostic X-ray B21and the irradiation axis of the diagnostic X-ray B22are perpendicular to each other at the isocenter P11of the rotation axis A12. Also when the traveling gantry313rotates, the imager371(the diagnostic X-ray source341and the sensor array361) and the imager372(the diagnostic X-ray source342and the sensor array362) rotate while keeping the irradiation axes perpendicular to each other. In this regard, the traveling gantry313rotates the imager371and the imager372integrally.

In addition, as will be described later, the angle between the diagnostic X-ray B21and the diagnostic X-ray B22is not limited to 90°.

The couch381is used for the lying down of the imaging target T11who is a patient to be treated. The couch381includes a fixture (not shown). By fixing the imaging target T11to the couch381using a fixed portion, it is possible to reduce subject blur (image blur due to subject movement) when the diagnostic X-ray source340emits a diagnostic X-ray to capture a radiographic image or the shift of the radiation position when the therapeutic radiation emission unit331emits the therapeutic radiation B11.

The couch driving unit382supports the couch381on a base, and moves the couch381according to the control of the radiotherapy apparatus controller2. By moving the couch381using the couch driving unit382, it is possible to locate the affected part of the imaging target T11at the isocenter P11or near the isocenter P11.

FIG. 4is a schematic block diagram showing the functional configuration of the radiotherapy apparatus controller2. In this diagram, the radiotherapy apparatus controller2includes an imaging processing unit210and a treatment control unit220. The imaging processing unit210includes an imager rotation control section211, an imager position determination section212, an imaging timing control section213, an imager image acquisition section214, a position specifying section215, an image correction section216, and a CT image reconstruction section217.

The imaging processing unit210controls the radiotherapy apparatus3(FIG. 2) to acquire a radiographic image of the imaging target T11, and generates a CT image based on the acquired radiographic image.

The CT image reconstruction section217generates (reconstructs) a CT image from the radiographic image that has been captured by the sensor array360and has an affected part position corrected by the image correction section216as will be described later. In addition, as the affected part position, for example, the center-of-gravity position corresponding to the shape (area) of the affected part image can be used.

FIGS. 5A to 5Care explanatory diagrams of the reconstruction of a CT image that the CT image reconstruction section217performs. As described with reference toFIG. 3, the cone beam emitted from the diagnostic X-ray source340has a spread of the fan angle α and the cone angle β. Therefore, the cone beam emitted from the diagnostic X-ray source340is projected onto the light receiving surface (surface that receives X-rays) of the sensor array360in a two-dimensional manner (for example, in a rectangular area of the light receiving surface of the sensor array360).

Here, the light receiving surface of the sensor array360is divided into pixels, and the CT image reconstruction section217acquires the density information of each pixel as radiographic image data. The density information indicates the intensity of the X-ray received by each pixel of the sensor array360(value after the correction of the image correction section216). Hereinafter, the pixel of the light receiving surface of the sensor array360is referred to as a “pixel of the sensor array360”.

In addition, the space of a target whose CT image is to be generated is classified into voxels corresponding to the pixels of the sensor array360. The CT image reconstruction section217converts the X-ray intensity of each pixel into the total value of the X-ray transmittance in each voxel through which the X-rays pass. Hereinafter, the process of converting the X-ray intensity of each pixel into the total value of the X-ray transmittance in each voxel through which the X-rays pass is referred to as “back projection”.

FIG. 5Ashows X-rays, which are emitted to the row of pixels of the sensor array360, as a surface, such as a surface F11. The row of pixels referred to herein is the arrangement of pixels in a direction perpendicular to the rotation axis A12(in the left and right direction of the imaging target T11shown inFIG. 2). In addition, sinceFIG. 5Ashows a state when viewed from the direction perpendicular to the rotation axis A12, each surface is shown by a line.

FIG. 5Bshows X-rays, which are emitted to the respective pixels of the sensor array360, as lines, such as line L11, in relation to the surface F11.

In addition,FIG. 5Cshows voxels through which line L11passes. Line L11passes through voxels B11, B12, and B13, and the CT image reconstruction section217performs back projection of the X-ray intensity in a pixel corresponding to line L11onto the total value of the X-ray transmittances of the voxels B11, B12, and B13.

The CT image reconstruction section217acquires a radiographic image by projecting X-rays onto the subject (affected part of the imaging target T11) from various angles, and performs back projection for each pixel of the sensor array360for each radiographic image.

Then, the CT image reconstruction section217calculates the X-ray transmittance of each voxel based on the obtained total value of the X-ray transmittances from various angles, and generates a CT image based on the obtained X-ray transmittance of each voxel.

In addition, each quantity or the positional relationship shown inFIGS. 5A to 5Cis an example for explanation, and the present invention is not limited thereto. For example, the fan angle α and the cone angle β of the cone beam emitted from the diagnostic X-ray source340, the number of pixels of the sensor array360, the number of voxels set in the space of the target whose CT image is to be generated, or the positional relationship between the diagnostic X-ray source340or the sensor array360and the voxels is not limited to those shown inFIGS. 5A to 5C.

The imager rotation control section211controls the traveling driving device of the radiotherapy apparatus3to rotate the traveling gantry313, thereby rotating the diagnostic X-ray source341and the sensor array361or the diagnostic X-ray source342and the sensor array362. Here, in order for the CT image reconstruction section217to generate a high-accuracy CT image by performing back projection, radiographic images of the subject from many angles are required. Therefore, the imager rotation control section211rotates the imager371and the imager372to locate the subject at various angles.

FIG. 6is an explanatory diagram showing an example of the angle by which the imager rotation control section211rotates an imager. Line L21shown in this diagram indicates the rotation range of the imager371, and line L22indicates the rotation range of the imager372. In addition, line L23indicates a combined range of the rotation range of the imager371and the rotation range of the imager372.

As described with reference toFIG. 2, the diagnostic X-ray source341and the diagnostic X-ray source342are disposed such that the irradiation axes thereof are perpendicular to each other. For this reason, when the imager rotation control section211controls the traveling driving device of the radiotherapy apparatus3to rotate the traveling gantry313by 90° or more, the rotation range of the imager371and the rotation range of the imager372overlap each other. Therefore, if the rotation range of the imager371and the rotation range of the imager372are combined, it is possible to rotate the subject in the range of an angle of 180° or more with respect to the subject. Thus, since the imager can be rotated in the range of an angle of 180° or more with respect to the subject by rotating the traveling gantry313by 90° or more, the imaging time can be reduced to approximately half of that when there is one imager.

Here, as shown inFIG. 6, the imager rotation control section211rotates the traveling gantry313(accordingly, the imager371and the imager372) by 90°+fan angle α (by an angle obtained by adding the fan angle α to 90°). Therefore, the traveling gantry313rotates the imager371and the imager372by an angle greater than 90° (angle between the irradiation axis of the imager371and the irradiation axis of the imager372when the rotation axis A12is a reference). This will be described with reference toFIG. 7.

FIG. 7is an explanatory diagram showing the angle of an X-ray passing through the end of the fan angle of a cone beam when the rotation range of the imager is 180°. A point P21shown in this diagram is located on line L31at the end of the fan angle α of the cone beam, which is emitted from the diagnostic X-ray source340, when the diagnostic X-ray source340starts to rotate. When the diagnostic X-ray source340is present at a position rotated by 180° from the position at the start of rotation, the point P21is located on line L32at the end of the fan angle α of the cone beam emitted from the diagnostic X-ray source340.

As shown inFIG. 7, the direction of the X-ray passing through the point P21changes in a range of an angle obtained by subtracting the fan angle α from 180°. On the other hand, in order for the CT image reconstruction section217to generate a high-accuracy CT image, it is preferable to acquire information (density information of each pixel of the sensor array360) by emitting X-rays to all voxels from the respective directions in the range of 180° or more.

Therefore, the imager rotation control section211controls the traveling driving device to rotate the traveling gantry313by 90°+fan angle α. Then, the combined rotation range of the rotation range of the imager371and the rotation range of the imager372becomes 180°+fan angle α. Accordingly, the CT image reconstruction section217can acquire the information by emitting X-rays to all voxels from the respective directions in the range of 180° or more.

The imager position determination section212acquires the position information of the imager371(information indicating the amount of rotation of the imager371), and determines whether or not the imager371is located in an overlapping region where the rotation range of the imager371and the rotation range of the imager372overlap each other (hereinafter, simply referred to as an “overlapping region”).

Here, as a method used when the imager position determination section212acquires the position information of the imager371, it is possible to use various methods. For example, the imager position determination section212may acquire the control information of the traveling driving device from the imager rotation control section211, and calculate the rotation angle from the reference position (for example, the position at the start of rotation) of the diagnostic X-ray source340, as the position information of the imager371, based on the control information. Alternatively, when a shift occurs between the control information from the imager rotation control section211and the actual rotation angle of the traveling gantry313, the traveling gantry313may measure the rotation angle, and the imager position determination section212may acquire the rotation angle as the position information of the imager371(rotation angle of the imager371).

In addition, the imager position determination section212determines whether or not the imager371is located in the overlapping region by determining whether or not the amount of rotation of the imager371is equal to or greater than 90° based on the position information of the imager371. That is, when the amount of rotation of the imager371is equal to or greater than 90°, the imager371is located in the overlapping region.

The imaging timing control section213causes one or both of the imager371and the imager372to perform imaging when detecting the arrival of imaging timing. Specifically, the imaging timing control section213outputs control information instructing one or both of the imager371and the imager372to perform imaging every time set in advance as an imaging period.

In this case, the imaging timing control section213causes only the imager372to perform imaging in at least one imaging timing whose arrival is detected in a state where the imager position determination section212determines that the imager371is located in the overlapping region. For example, the imaging timing control section213causes only the imager372to perform imaging at all of the imaging timings whose arrival is detected in a state where the imager position determination section212determines that the imager371is located in the overlapping region. That is, when the imager position determination section212determines that the amount of rotation of the imager371is equal to or greater than 90°, the imaging timing control section213outputs control information for the instruction of imaging only to the imager372.

Hereinafter, “only one of the imager371and the imager372performs imaging at one imaging timing” is referred to as “one-sided imaging”. In addition, “both of the imager371and the imager372perform imaging at one imaging timing” is referred to as “simultaneous imaging”.

FIG. 8is an explanatory diagram of a first example of the control of the imaging timing. In the example shown in this diagram, 13 imaging timings are set while the imager371or the imager372rotates by 90°+fan angle α. Here, line L41indicates the rotation range of the diagnostic X-ray source341, and line L42indicates the rotation range of the diagnostic X-ray source342.

At the first to ninth imaging timings, the imaging timing control section213instructs the imager371and the imager372to perform simultaneous imaging.

On the other hand, the imager371is located in the overlapping region at the tenth and subsequent imaging timings. Therefore, even if the imager371stops imaging, the CT image reconstruction section217can acquire a radiographic image for the 180°+fan angle α. As a result, it is possible to acquire the information by emitting X-rays to all voxels from the respective directions in the range of 180° or more.

Therefore, at the tenth and subsequent imaging timings, the imaging timing control section213instructs only the imager372to perform imaging (one-sided imaging).

Thus, when the imager position determination section212determines that the amount of rotation of the imager371is equal to or greater than 90°, the imaging timing control section213instructs only the imager372to perform imaging (stops the imaging of the imager371), thereby being able to reduce the radiation dose. In the example shown inFIG. 8, compared with a case where the imager371emits radiation even at the tenth to thirteenth imaging timings, it is possible to reduce the four-time radiation dose for the imager371.

In addition, the imaging timing shown inFIG. 8is an example for explanation, and is not limited thereto.

For example, the number of imaging timings whose arrival is detected by the imaging timing control section213is not limited to 13 times.

Alternatively, when the imager position determination section212determines that the amount of rotation of the imager371is equal to or greater than 90°, the imaging timing control section213may instruct the imager371and the imager372to perform simultaneous imaging at some imaging timings.

FIG. 9is an explanatory diagram of a second example of the control of the imaging timing. Similar to the case shown inFIG. 8, in the example shown inFIG. 9, 13 imaging timings are set while the imager371or the imager372rotates by 90°+fan angle α. In addition, similar to the case shown inFIG. 8, line L41indicates the rotation range of the diagnostic X-ray source341, and line L42indicates the rotation range of the diagnostic X-ray source342.

In addition, similar to the case shown inFIG. 8, the imaging timing shown inFIG. 9is an example for explanation, and is not limited thereto.

In the example shown inFIG. 9, similar to the case shown inFIG. 8, at the first to ninth imaging timings, the imaging timing control section213instructs the imager371and the imager372to perform simultaneous imaging.

In addition, at the eleventh and thirteenth imaging timings of the tenth and subsequent imaging timings at which the imager371is located in the overlapping region, similar to the case shown inFIG. 8, the imaging timing control section213instructs only the imager372to perform imaging (one-sided imaging).

On the other hand, at the tenth and twelfth imaging timings, unlike the case shown inFIG. 8, the imaging timing control section213instructs the imager371and the imager372to perform simultaneous imaging.

As will be described later, the position specifying section215can specify the position of a position specification target (in the present embodiment, an affected part that is a target to which the therapeutic radiation B11is to be emitted) in a three-dimensional manner due to the simultaneous imaging of the imager371and the imager372. Therefore, as will be described later, the image correction section216can correct a radiographic image even if the position specification target moves in a direction of the diagnostic X-ray B21or in a direction of the diagnostic X-ray B22.

Here, as a criterion for performing switching between one-sided imaging and simultaneous imaging by the imaging timing control section213in a state where the imager371is located in the overlapping region, various criteria can be used.

For example, when the imaging period is sufficiently shorter than the breathing cycle of the imaging target T11, the image correction section216can correct a radiographic image for the subject blur in the diagnostic X-ray direction due to the breathing of the imaging target T11even if the position specifying section215does not specify a three-dimensional position every imaging timing.

For example, at an imaging timing up to a predetermined time after the position specifying section215specifies the three-dimensional position of the position specification target, the image correction section216may use the three-dimensional position. Alternatively, in a period of time for which the movement of the position specification target can be regarded as linear uniform motion after the position specifying section215specifies the three-dimensional position of the position specification target, the position specifying section215may calculate the three-dimensional position of the position specification target every imaging timing.

Therefore, when the imager371is located in the overlapping region, the imaging timing control section213may cause only the imager372to perform imaging (one-sided imaging) at a predetermined number (1 or more) of imaging timings after the position specifying section215succeeds in specifying the three-dimensional position of the position specification target.

Thus, when the imaging timing control section213detects the arrival of the imaging timing and causes both of the imager371and the imager372to perform imaging (simultaneous imaging) and the position specifying section215succeeds in specifying the three-dimensional position of the position specification target based on the obtained radiographic image, if the arrival of the next imaging timing is detected in a state where the imager position determination section212determines that the imager371is located in the overlapping region, the imaging timing control section213may cause only the imager372to perform imaging (one-sided imaging).

Alternatively, when the imaging period is short, once the position specification target is hidden by bone or the like in the radiographic image of the imager371or the imager372, the state where the position specification target is hidden continues for a while. In the meantime, even if the imager371and the imager372perform simultaneous imaging, the position specifying section215may continuously fail to specify a three-dimensional position.

Therefore, when the imager371is located in the overlapping region, the imaging timing control section213may cause only the imager372to perform imaging (one-sided imaging) at a predetermined number (1 or more) of imaging timings after the position specifying section215fails to specify the three-dimensional position of the position specification target.

Thus, when the imaging timing control section213detects the arrival of the imaging timing and causes both of the imager371and the imager372to perform imaging (simultaneous imaging) and the position specifying section215fails to detect the image of the position specification target in at least one of the obtained radiographic images, if the arrival of the next imaging timing is detected in a state where the imager position determination section212determines that the imager371is located in the overlapping region, the imaging timing control section213may cause only the imager372to perform imaging (one-sided imaging).

Alternatively, the imaging timing control section213may store an imaging plan determined by a doctor or the like in advance, and perform switching between simultaneous imaging and one-sided imaging according to the imaging plan when the imager371is located in the overlapping region.

The imager image acquisition section214acquires a radiographic image (radiographic image data) captured by the imager371and a radiographic image (radiographic image data) captured by the imager372from the radiotherapy apparatus3, and outputs the radiographic images to the position specifying section215.

The position specifying section215specifies the three-dimensional position of the position specification target (hereinafter, will be described as an affected part) based on the radiographic image captured by the imager371and the radiographic image captured by the imager372. That is, it is not possible to specify the position of the affected part in a depth direction from only one radiographic image, but the position specifying section215can also detect the position of the affected part in the depth direction by using another radiographic image that has been simultaneously captured from another direction.

For example, first, the position specifying section215specifies the position of an affected part by image matching (template matching) for each radiographic image obtained by simultaneous imaging of the imager371and the imager372. Information (template) of the shape of the affected part for image matching is generated, for example, by a doctor based on the radiographic image (Roentgen image) captured in advance, and is given to the position specifying section215.

When the position specifying section215succeeds in specifying the position of the affected part in both of the radiographic image captured by the imager371and the radiographic image captured by the imager372, the position specifying section215specifies the three-dimensional position of the affected part based on the position information of the affected part in both of the images. As a method used when the position specifying section215specifies the three-dimensional position of the affected part, it is possible to use known methods, such as a method disclosed in Japanese Patent No. 404952.

The image correction section216corrects the position of the affected part in the radiographic image captured by the imager371or the radiographic image captured by the imager372.

Here, in the radiographic image captured by the imager371or the imager372, from the difference in imaging timing, the position of the affected part may shift due to the breathing of the imaging target T11or the like. Due to the shift of the affected part, there is a possibility that the accuracy of the CT image will be lowered. Therefore, the image correction section216corrects the position of the affected part (performs correction for acquiring a radiographic image close to a radiographic image when the affected part does not move), thereby reducing the lowering of accuracy of the CT image.

Specifically, the image correction section216moves the position of an image of the affected part in the radiographic image.

FIG. 10is a diagram showing an example of a radiographic image when the position of an affected part is shifted. An image M111of an affected part and bone images M121and M122are included in the radiographic image shown in this diagram. In the example shown inFIG. 10, the position of the affected part moves according to the breathing of the imaging target T11. On the other hand, the position of the bone shown in the image M121or M122does not move.

Therefore, the image correction section216moves the position of the affected part image while keeping the positions of the bone images M121and M122in the radiographic image, thereby reducing the influence of the shift of the affected part position on the CT image. As a method used when the image correction section216moves the position of the affected part image, it is possible to use known methods, such as a method using an optical flow shown in Japanese Unexamined Patent Application Publication 2001-259059. In the method using the optical flow, the image correction section216translates the position of the affected part image to a shift vector and an inverse vector of the affected part shown in the optical flow.

When the information of the three-dimensional position of the affected part is acquired from the position specifying section215, the image correction section216also corrects the radiographic image for the movement of the position of the affected part in the diagnostic X-ray direction.

FIGS. 11A and 11Bare explanatory diagrams showing an example of the correction of a radiographic image for the movement of the position of the affected part in the diagnostic X-ray direction that is performed by the image correction section216.FIG. 11Ashows an example of a radiographic image before correction, andFIG. 11Bshows an example of a radiographic image after correction.

In the example shown inFIGS. 11A and 11B, the affected part is shifted to the side of the diagnostic X-ray source340. For this reason, in the image shown inFIG. 11A, an image M211of the affected part is relatively large. Therefore, the image correction section216performs correction for reducing the image of the affected part as an image M212of the affected part inFIG. 11B, according to a case where the affected part is located closer to the sensor array360side. As a method of correcting the radiographic image for the movement of the position of the affected part in the diagnostic X-ray direction that is performed by the image correction section216, it is possible to use known methods, such as a method of calculating the optical flow in a three-dimensional manner.

In addition, since the image correction section216calculates the optical flow in a three-dimensional manner, it is possible to eliminate the influence of the shift of the imaging angle at each imaging timing.

For example, inFIG. 9, a shift in the imaging direction occurs between a radiographic image captured by the imager371at the first imaging timing and a radiographic image captured by the imager371at the second imaging timing. The shift in the imaging direction may become an error when calculating the two-dimensional optical flow. In contrast, when the position specifying section215specifies the position of the affected part with the three-dimensional coordinates fixed to the imaging target T11, the three-dimensional coordinates are fixed irrespective of the imaging direction. Accordingly, it is possible to eliminate the influence of the shift in the imaging direction when calculating the optical flow.

In addition, based on the radiographic images obtained by simultaneous imaging, the image correction section216may correct the direction of the rotation axis A12(body axis direction).

For example, due to the contour of the image of the affected part being unclear, or due to deformation of the affected part, or due to the shadow of other organs being reflected on the affected part, there is a possibility that an error may occur in the direction of the rotation axis A12when calculating the position of the affected part by image matching for determining the position of the affected part.

In such a case, for example, by taking the average of the position of the affected part in the direction of the rotation axis A12in the radiographic image captured by the imager371and the radiographic image captured by the imager372in simultaneous imaging, it is possible to reduce the magnitude of the error.

In addition, when an organ hidden by the affected part is visible by the correction of the radiographic image for the movement of the position of the affected part in the diagnostic X-ray direction, the image correction section216may acquire an image of the organ from another radiographic image and add the image to the radiographic image to be corrected.

The treatment control unit220controls the radiotherapy apparatus3when emitting the therapeutic radiation B11. For example, the treatment control unit220performs various kinds of control, such as the control of the position of the therapeutic radiation emission unit331, the control of the emission time of the therapeutic radiation B11, or the control of the multi-leaf collimator332, according to the treatment plan made by the doctor based on the CT image generated by the CT image reconstruction section217.

As the radiotherapy apparatus controller2, for example, a computer can be used. In this case, functions of each unit of the radiotherapy apparatus controller2can be realized by causing a central processing unit (CPU) provided in the computer to read a program from a storage device provided in the computer and execute the program.

However, it is also possible to use apparatuses other than the computer as the radiotherapy apparatus controller2. For example, each unit of the radiotherapy apparatus controller2can be formed by dedicated hardware.

Next, the operation of the radiotherapy system1when generating a CT image will be described with reference toFIG. 12.

FIG. 12is a flowchart showing the procedure of the process performed by the imaging processing unit210. The imaging processing unit210starts the process shown in this diagram when the radiotherapy apparatus controller2receives a user operation for instructing the generation of a CT image.

In the process shown inFIG. 12, the imaging processing unit210performs a calibration first (step S101). For example, the imager rotation control section211adjusts the position of each of the imager371and the imager372to the initial position, and adjusts the direction of the irradiation axis of each of the imager371and the imager372to a direction passing through the isocenter P11. In addition, the imaging timing control section213performs a response performance calibration for matching the response performance of the sensor array361and the sensor array362.

Then, the imager rotation control section211controls the traveling driving device to rotate the traveling gantry313at a fixed speed (step S102).

Then, the imaging timing control section213determines whether or not the imaging timing has arrived (step S103). Specifically, the imaging timing control section213has a timer function, and detects the arrival of the imaging timing every predetermined time set in advance as an imaging period.

When the imaging timing control section213determines that the imaging timing has arrived in step S103(step S103: YES), the imaging timing control section213selects one-sided imaging or simultaneous imaging (step S111). Specifically, as described above, when the imager position determination section212determines that the imager371is not located in the overlapping region, the imaging timing control section213instructs the imager371and the imager372to perform simultaneous imaging. On the other hand, when the imager position determination section212determines that the imager371is located in the overlapping region, the imaging timing control section213selects one-sided imaging or simultaneous imaging based on the imaging plan acquired in advance or a program set in advance, and gives an imaging instruction according to the selection.

When one or both of the imager371and the imager372capture radiographic images according to the instruction of the imaging timing control section213, the imager image acquisition section214acquires the radiographic images (radiographic image data) (step S112).

When the imager371and the imager372perform simultaneous imaging, the position specifying section215calculates the three-dimensional position of the affected part as described above (step S113).

Then, the image correction section216corrects the position of the affected part as described above for the image captured by the imager371or the image captured by the imager372. In particular, when the information of the three-dimensional position of the affected part is acquired from the position specifying section215, the image correction section216also corrects the position of the affected part for the movement of the affected part in the diagnostic X-ray direction (step S114).

Then, the CT image reconstruction section217performs a calculation for reconstructing the CT image (step S115). Specifically, the CT image reconstruction section217performs the above-described back projection based on the projection image corrected by the image correction section216.

Then, the imaging processing unit210determines whether or not the imaging at all angles has been completed (step S116). For example, the imager position determination section212acquires the amount of rotation of the traveling gantry313, and determines whether or not the amount of rotation is equal to or greater than 90°+α.

When it is determined that the imaging at all angles has not been completed (step S116: NO), the process returns to step S102.

On the other hand, when it is determined that the imaging at all angles has been completed (step S116: YES), the CT image reconstruction section217reconstructs a tomographic image by calculating the amount of transmitted radiation for each voxel from the result of the back projection, and outputs the obtained tomographic image (step S121). For example, the CT image reconstruction section217stores the tomographic image in a storage device provided in the radiotherapy apparatus controller2, and displays the tomographic image on a display screen provided in the radiotherapy apparatus controller2.

In this case, the imager rotation control section211ends the output of the rotation instruction in step S102, and accordingly, the traveling gantry313is stopped (rotation is ended).

On the other hand, when the imaging timing control section213determines that the imaging timing has not arrived in step S103(step S103: NO), the process proceeds to step S116.

As described above, the imaging timing control section213causes only the imager372to perform imaging in at least one imaging timing whose arrival is detected in a state where the imager position determination section212determines that the imager371is located in the overlapping region.

Since the imaging timing control section213causes only the imager372to perform imaging, it is possible to reduce the radiation dose equivalent to the radiation from the imager371at the imaging timing.

In particular, in a state where the imager371is not located in the overlapping region, the imaging timing control section213causes the imager371and the imager372to perform simultaneous imaging, so that a radiographic image of 180°+fan angle α can be captured. In this regard, the imaging timing control section213can reduce the radiation dose without lowering the accuracy of the CT image.

For example, when the imaging timing control section213detects the arrival of the imaging timing and causes the imager371and the imager372to perform simultaneous imaging and the position specifying section215succeeds in specifying the three-dimensional position of the position specification target based on the obtained radiographic image, if the arrival of the next imaging timing is detected in a state where the imager position determination section212determines that the imager371is located in the overlapping region, the imaging timing control section213may cause only the imager372to perform imaging (one-sided imaging).

In this case, at the imaging timing at which the imager372has performed one-sided imaging, the image correction section216can perform correction for the movement of the position specification target in the diagnostic X-ray direction based on the three-dimensional position of the position specification target specified by the position specifying section215based on simultaneous imaging or based on a new three-dimensional position calculated from the three-dimensional position.

In this regard, it is possible to reduce the radiation dose while increasing the accuracy of the CT image.

Alternatively, when the imaging timing control section213detects the arrival of the imaging timing and causes the imager371and the imager372to perform simultaneous imaging and the position specifying section215fails to detect the image of the position specification target in at least one of the obtained radiographic images, if the arrival of the next imaging timing is detected in a state where the imager position determination section212determines that the imager371is located in the overlapping region, the imaging timing control section213may cause only the imager372to perform imaging (one-sided imaging).

In this case, since the imaging timing control section213stops simultaneous imaging at an imaging timing at which there is a high possibility that the position specifying section215will fail to specify the three-dimensional position of the position specification target even if the imager371and the imager372perform simultaneous imaging, it is possible to reduce the radiation dose.

Alternatively, the imaging timing control section213causes only the imager372to perform imaging (one-sided imaging) at all of the imaging timings whose arrival is detected in a state where the imager position determination section212determines that the imager371is located in the overlapping region.

In this manner, it is possible to further reduce the radiation dose.

In addition, a control target in the present embodiment is not limited to the radiotherapy apparatus. For example, a CT dedicated apparatus can also be the control target in the present embodiment. As the configuration of a CT dedicated apparatus, for example, it is possible to adopt a configuration in which each unit (the therapeutic radiation emission unit331, the multi-leaf collimator332, or the sensor array351) for emission of the therapeutic radiation B11has been removed from the configuration shown inFIG. 2. In addition, for the configuration on the controller side, it is possible to adopt a configuration in which the treatment control unit220has been removed from the configuration shown inFIG. 4.

In addition, the imager371may correspond to an example of the second imager, and the imager372may correspond to an example of the first imager. In this case, only the imager371may perform one-sided imaging in at least a part of the timing at which the imager372is located in the overlapping region, so that the imaging from the overlapping region is performed by the imager371.

In addition, both of the imager371and the imager372may correspond to any example of the first imager and the second imager. For example, imaging in the overlapping region may be alternately performed by the imager371and the imager372.

In addition, as long as the rotation range of the imager371and the rotation range of the imager372overlap each other, the angle between the irradiation axis of the imager371and the irradiation axis of the imager372with the rotation axis A12as a reference is not limited to 90° described above, and may be an arbitrary angle.

In addition, the number of imagers provided in the radiotherapy apparatus or the CT dedicated apparatus that is a control target is not limited to 2 described above, and three or more imagers may be provided. For example, the radiotherapy apparatus3may include a third imager in addition to the imagers371and372. In this case, for example, the angle between the irradiation axis of the imager371and the irradiation axis of the imager372with the rotation axis A12as a reference may be 60°, and the angle between the irradiation axis of the imager372and the irradiation axis of the third imager with the rotation axis A12as a reference may be 60°.

By arranging the imagers as described above, if the traveling gantry313rotates 60° or more, a rotation range when the rotation ranges of the three imagers are combined is equal to or greater than 180°. Therefore, it is possible to reduce the time required to capture a radiographic image. In addition, in the same manner as described with reference toFIG. 7, an overlapping region of the rotation ranges of the imagers occurs from the relationship with the fan angle. In the overlapping region, the imaging timing control section213can select one of imaging by one imager, imaging by two imagers, and imaging by three imagers every imaging timing.

In addition, it is preferable that both the irradiation axis of the imager371and the irradiation axis of the imager372pass through the vicinity of the isocenter P11, however, the irradiation axis of the imager371and the irradiation axis of the imager372do not necessarily need to pass through the isocenter P11. In addition, the irradiation axis of the imager371and the irradiation axis of the imager372do not necessarily need to cross each other (may be in a relationship of twisted position).

In addition, as described above, a computer can be used as the radiotherapy apparatus controller2. Accordingly, the processing of each unit may be performed by recording a program for realizing the functions of all or some of the units of the radiotherapy apparatus controller2in a computer-readable recording medium, reading the program recorded in the recording medium into a computer system, and executing the read program. In addition, the “computer system” referred to herein may include an OS or hardware, such as a peripheral device.

In addition, the “computer system” may also include a homepage presenting environment (or display environment) if a WWW system is used.

In addition, examples of the “computer-readable recording medium” include portable media, such as a flexible disk, a magneto-optic disc, a ROM, and a CD-ROM, and a storage device, such as a hard disk built in a computer system. In addition, examples of the “computer-readable recording medium” may include a recording medium that stores a program dynamically for a short period of time like a network, such as the Internet, or a communication line when a program is transmitted through a communication line, such as a telephone line, and include a recording medium that stores a program for a predetermined period of time like a volatile memory in a computer system that serves as a server or a client in this case. In addition, the above program may be a program for realizing some of the functions described above or may be a program capable of realizing the above functions by combination with a program already recorded in the computer system.

While the embodiment of the present invention has been described in detail with reference to the diagrams, the specific configuration is not limited to the above-described embodiment, and various changes may be made in design without departing from the spirit of the present invention.

INDUSTRIAL APPLICABILITY

The present invention relates to an imaging controller of an imaging apparatus which includes first and second imagers for capturing a radiographic image by emitting a cone beam toward a rotation axis and a rotation mechanism for rotating the first and second imagers integrally around the rotation axis and in which an angle between an irradiation axis of the first imager and an irradiation axis of the second imager with the rotation axis as a reference is a predetermined angle. The imaging controller includes: an imager position determination section that determines whether or not the first imager is located in an overlapping region where a rotation range of the first imager and a rotation range of the second imager overlap each other when the rotation mechanism rotates the first and second imagers by an angle greater than the predetermined angle; and an imaging timing control section that causes one or both of the first and second imagers to perform imaging when arrival of an imaging timing is detected and that causes only the second imager to perform imaging in at least one imaging timing whose arrival has been detected in a state where the imager position determination section determines that the first imager is located in the overlapping region.

According to the present invention, it is possible to reduce the radiation dose.

REFERENCE SIGNS LIST