Radiographic imaging devices and radiotherapy devices

Abstract

Reducing artifacts in tomographic images of a subject undergoing treatment that includes periodic motion. A radiographic imaging device includes a gantry that carries two pairs of radiation sources and detectors and rotates the radiation sources and detectors around the subject, and a reconstruction unit that reconstructs a tomographic image of the subject based on a plurality of projection images generated based on outputs from the detectors. The device further includes a phase calculation unit that calculates the phase of motion based on the periodic motion of the subject, a segmentation unit that separates a first projection image group (a plurality of projection images obtained from a first group) and a second projection image group (a plurality of projection images obtained from a second group) for each phase, and a condition setting unit that sets imaging conditions so that the first projection image group and the second projection image group, which are segmented into the same phase, complement each other at projection angles. The reconstruction unit reconstructs the tomographic image using the first projection image group and the second projection image group, which are segmented into the same phase.

Description

Technical Field

[0001] The present invention relates to a technique for capturing three-dimensional images of a subject and the subject when a subject that is periodically moving is treated by a radiotherapy apparatus, and more particularly to a technique for reducing artifacts included in the three-dimensional image. Background Art

[0002] In radiotherapy systems that deliver radiation to a target, such as a malignant tumor, it is crucial to focus the radiation on the target while minimizing exposure to normal tissue. This is especially true when the target moves periodically, for example due to breathing. Therefore, the timing and location of the radiation must be precisely controlled based on the target's movements.

[0003] Patent Document 1 discloses a radiotherapy system in which two imaging devices, each consisting of an X-ray source and a detector, are mounted on a rotating support device surrounding a subject, along with a therapeutic radiation source. In Patent Document 1, the three-dimensional position of the subject is determined based on two projection images acquired by the two imaging devices. A tomographic image is reconstructed using either only the projection images of a specific region of the subject or all of the projection images.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 6181459 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, in Patent Document 1, artifacts may sometimes occur in the reconstructed tomographic images. Specifically, when only projection images of a specific area of the treatment subject are used, artifacts may occur if the distribution of projection angles used to obtain the projection images is uneven. When all projection images are used, artifacts may occur due to the movement of the treatment subject.

[0009] Therefore, an object of the present invention is to provide a radiographic imaging apparatus and a radiotherapy apparatus capable of reducing artifacts in a tomographic image of a subject including a treatment target with periodic motion.

[0010] Means for solving problems

[0011] In order to achieve the above-mentioned purpose, the present invention is a radiation imaging device comprising: a frame, which carries a pair of radiation sources that irradiate radiation to a subject and detectors that detect radiation passing through the subject into two groups, and rotates the radiation source and the detector around the subject; a reconstruction unit, which reconstructs a tomographic image of the subject based on a plurality of projection images generated according to the output of the detector, and is characterized in that it also comprises: a phase calculation unit, which calculates the phase of the activity based on the periodic activity of the subject; a segmentation unit, which segments the plurality of projection images obtained by the first group, namely the first projection image group, and the plurality of projection images obtained by the second group, namely the second projection image group, respectively, according to each phase; a condition setting unit, which sets the shooting conditions in such a way that the first projection image group and the second projection image group divided into the same phase complement each other's projection angles, and the reconstruction unit uses the first projection image group and the second projection image group divided into the same phase to reconstruct the tomographic image.

[0012] Furthermore, the present invention provides a radiotherapy apparatus including a therapeutic radiation source for irradiating therapeutic radiation to a treatment target, characterized in that the radiotherapy apparatus includes the radiation imaging device.

[0013] Effects of the Invention

[0014] According to the present invention, it is possible to provide a radiographic imaging apparatus and a radiotherapy apparatus capable of reducing artifacts in a tomographic image of a subject including a treatment target with periodic motion. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a diagram of the overall structure of a radiotherapy device.

[0016] Figure 2 This is a diagram of the overall structure of a radiation imaging device.

[0017] Figure 3 This is a diagram explaining the calculation of the phase.

[0018] Figure 4 This is a diagram explaining a group of projection images that complement each other's projection angles.

[0019] Figure 5 A diagram illustrating the interval between projected images.

[0020] Figure 6 This is a diagram showing an example of the process flow of Example 1.

[0021] Figure 7 This is a diagram showing another example of the processing flow of Example 1.

[0022] Figure 8This is a diagram illustrating an example of weights in the second embodiment.

[0023] Figure 9 This is a diagram explaining the difference in the range of the projection angle in rotation measurement. DETAILED DESCRIPTION

[0024] Hereinafter, embodiments of the radiographic imaging apparatus and radiotherapy apparatus according to the present invention will be described with reference to the accompanying drawings. In the following description and drawings, components having the same functional configuration are denoted by the same reference numerals to omit redundant description.

[0025] Example 1

[0026] use Figure 1 The overall structure of the radiotherapy apparatus will be described. The radiotherapy apparatus includes a therapeutic radiation source 101 , a bed 102 , an X-ray source 103 , a detector 104 , a gantry 105 , and a control unit 106 .

[0027] The therapeutic radiation source 101 is a device that irradiates therapeutic radiation to a subject 100 placed on a bed 102. It is connected to an electron beam accelerator or the like. If the subject is moving, the therapeutic radiation is irradiated when the subject enters the irradiation area, or the direction of the therapeutic radiation is changed to track the subject. The bed 102 is a device that moves the subject 100 to a position suitable for treatment, and it moves up, down, left, right, and forward.

[0028] The X-ray source 103 irradiates the subject 100 with X-rays. The detector 104 detects the two-dimensional distribution of X-rays transmitted through the subject 100 and is positioned opposite the X-ray source 103, sandwiching the subject 100. The pair of X-ray source 103 and detector 104 acquires a projected image of the subject 100, and the two-dimensional position of the treatment target on the projected image is extracted. Furthermore, in this embodiment, two pairs of X-ray source 103a and detector 104a, and X-ray source 103b and detector 104b, are provided. This allows the three-dimensional position of the treatment target to be calculated from the two-dimensional positions on the projected images acquired by each pair.

[0029] The gantry 105 is a device that carries a pair of X-ray sources 103 and detectors 104 and rotates them around the subject 100. The two pairs rotate together at the same speed via the gantry 105. The X-ray sources 103 and detectors 104 repeatedly emit and detect X-rays while rotating, thereby acquiring projection images from multiple directions. When acquiring projection images, the angle of the direction of X-ray emission is defined as the projection angle, with the direction of X-ray emission from a predetermined direction, such as directly above the subject 100, being defined as a projection angle of 0 degrees. Furthermore, the gantry 105 can carry three or more pairs of X-ray sources 103 and detectors 104, or it can also carry the therapeutic radiation source 101.

[0030] The control unit 106 is a device that controls each unit of the radiotherapy apparatus and is composed of a computer, etc. Conditions related to treatment are set by an operator via an input device such as a keyboard, a mouse, or a touch panel.

[0031] use Figure 2 The overall structure of the radiographic imaging device is described. The radiographic imaging device includes a bed 102, an X-ray source 103, a detector 104, a gantry 105, a body motion measurement unit 200, and a control unit 106. The bed 102, the X-ray source 103, the detector 104, and the gantry 105 are used as shown in FIG. Figure 1 As described above. Furthermore, the angle formed by the pair of X-ray source 103a and detector 104a and the pair of X-ray source 103b and detector 104b is denoted as Δθ. Δθ may be a constant value, such as 90 degrees, or may be changed to any value other than 0 degrees and 180 degrees.

[0032] The body motion measurement unit 200 is a device that measures the motion of the subject 100. For example, it irradiates the subject 100 with laser light, ultrasound waves, millimeter waves, near-infrared rays, or the like, and measures changes in the position of the outer surface of the subject 100 based on the measured value of the laser light or the like reflected from the outer surface of the subject 100. Alternatively, the body motion measurement unit 200 may irradiate the subject 100 with X-rays, ultrasound waves, magnetism, or the like, and measure changes in the position of the internal structure of the subject 100. Specifically, the body motion measurement unit 200 measures the periodic motion of the subject 100, such as motion based on breathing, by measuring the distance between a point of interest and a reference point on the subject 100 over time.

[0033] The control unit 106 is a device that controls the various components of the radiographic imaging apparatus and generates various images, such as tomographic images, based on the output of the detector 104. It is composed of a computer and includes a CPU (Central Processing Unit), a memory, etc. The conditions for imaging are set by the operator via an input device such as a keyboard, a mouse, or a touch panel, or by using a control panel. Figure 2After being set by the condition setting unit 203 described later, the condition is received by the control unit 106. Various images generated by the control unit 106 are displayed on a display device such as a liquid crystal display or stored in a storage device such as an HHD (Hard Disk Drive) or an SSD (Solid State Drive).

[0034] The control unit 106 includes a phase calculation unit 201, a division unit 202, a condition setting unit 203, a rotation control unit 204, and a reconstruction unit 205, which are the main components of this embodiment. These main components may be implemented by software operating in the control unit 106 or by dedicated hardware. The following description will describe the case where the main components of this embodiment are implemented by software.

[0035] The phase calculation unit 201 calculates the phase of the motion of the subject 100 based on the output of the body motion measurement unit 200. Specifically, the amplitude of the motion is divided into a plurality of parts, and a phase number is assigned to each of the divided amplitude ranges. Figure 3 An example of phase calculation is described below. Figure 3 The dotted line in the figure shows an example of an activity waveform. In addition, the vertical axis is the amplitude of the activity of the measurement point relative to an arbitrary reference point, and the horizontal axis is time. Figure 3 In the example, the phase calculation unit 201 divides the amplitude of the motion into five ranges, assigning phase numbers in order of increasing amplitude, and assigning the range with the smallest amplitude to phase 5. In other words, the phase is calculated based on the magnitude of the motion. Furthermore, the phase calculation unit 201 calculates the period of the motion of the subject 100.

[0036] The segmentation unit 202 segments the first projected image group (a group of projected images acquired by the pair of X-ray source 103a and detector 104a) and the second projected image group (a group of projected images acquired by the pair of X-ray source 103b and detector 104b) for each phase. While acquiring projection images at various projection angles, the subject 100 periodically moves. Therefore, each projection image is associated with the phase of the subject's 100 movement based on the timing of acquisition. In other words, the multiple projection images are segmented for each phase based on the projection angle.

[0037] Even when the subject 100 moves faster than the rotation speed of the gantry 105, it is possible to obtain an image with reduced artifacts caused by the movement of the subject 100 by dividing the plurality of projection images for each phase and reconstructing a tomographic image using a group of projection images of the same phase. Figure 3As shown, a weight of 1.0 is assigned to the projection images segmented into the projection angle corresponding to phase 5, while a weight of 0.0 is assigned to the projection images of phases 1 to 4. Consequently, the projection images of phases 1 to 4 are not used in tomographic image reconstruction, and tomographic images are reconstructed using only the projection image group of phase 5. However, artifacts may also occur if the distribution of projection angles of the acquired projection images is uneven. Therefore, in this embodiment, imaging conditions are set so that the projection angles of the projection images segmented into the same phase are uniform.

[0038] The condition setting unit 203 sets the imaging conditions so that the first projection image group and the second projection image group divided into the same phase complement each other in terms of projection angle. Figure 4 An example of a first projected image group and a second projected image group that complement each other's projection angles will be described. Figure 4 In the example, based on a certain phase, Figure 3 Phase 5, the solid line represents the weight set for the first projected image group, and the dotted line represents the weight set for the second projected image group. In addition, the vertical axis is the weight for the projected image group, and the horizontal axis is the projection angle. In addition, the imaging range of detector 104a is from the first starting angle θas to the first ending angle θae, and the imaging range of detector 104b is from the second starting angle θbs to the second ending angle θbe, and the two imaging ranges are offset by Δθ. Figure 4 In the embodiment of the present invention, the condition setting unit 203 sets the imaging conditions so that the weights of the first and second projected image groups complement each other's projection angles. By setting the imaging conditions in this way, the projection angles of the projected image groups divided into the same phase become uniform, thereby reducing artifacts in the reconstructed tomographic images.

[0039] Furthermore, the rotation speed p of the gantry 105 , which is one of the imaging conditions set by the condition setting unit 203 , is calculated by, for example, the following equation.

[0040] p=2Δθ / (T·(2n-1))…(Formula 1)

[0041] Here, Δθ is the angle formed by the pair of X-ray source 103a and detector 104a, and the pair of X-ray source 103b and detector 104b, T is the period of motion of the subject 100, and n is a natural number. Specifically, the rotational speed p of the gantry 105 is set based on the angle formed by the two pairs of X-ray source 103 and detector 104 and the period of motion of the subject 100.

[0042] Furthermore, the irradiation timing t of X-rays from the X-ray source 103 , which is one of the imaging conditions set by the condition setting unit 203 , is calculated by, for example, the following equation.

[0043] t=2T / (2n-1)…(Formula 2)

[0044] That is, the X-ray irradiation timing t is set based on the cycle of the movement of the subject 100 .

[0045] In addition, it is preferable that the condition setting unit 203 sets the imaging conditions so that the first projection image group and the second projection image group divided into the same phase are equally spaced or complement each other's projection angles. Figure 5 The interval between the first projected image group and the second projected image group is described. Figure 5 In, with Figure 4 Similarly, the weights assigned to the first projected image group are represented by a solid line, and the weights assigned to the second projected image group are represented by a dotted line. Furthermore, interval A represents the distance between the center angles of the first projected image group with a weight of 1.0 and the center angles of the second projected image group with a weight of 1.0, and interval B represents the distance between the center angles of the second projected image group with a weight of 1.0 and the center angles of the next first projected image group with a weight of 1.0. As intervals A and B approach the same value, the closer the first and second projected image groups divided into the same phase are to being equally spaced, and the more uniform the projection angles of the projected image groups divided into the same phase become.

[0046] In addition, Figure 5 In the example, interval C is the distance between the end angle of the first projected image group with a weight of 1.0 and the start angle of the second projected image group with a weight of 1.0, and interval D is the distance between the end angle of the second projected image group with a weight of 1.0 and the start angle of the next first projected image group with a weight of 1.0. As interval C and interval D approach the same value, the first and second projected image groups divided into the same phase become more evenly spaced, and the projection angles of the projected image groups divided into the same phase become more uniform.

[0047] Furthermore, as the intervals C and D decrease, the projection angles between the first and second projected image groups, which are divided into the same phase, are filled by each other's projected images, thereby reducing artifacts caused by insufficient projection images. Furthermore, when the intervals C and D are negative, the first and second projected image groups, which are divided into the same phase, partially overlap, further reducing artifacts caused by insufficient projection images. Specifically, by setting the projection angle width of each projected image so that the first and second projected image groups, which are divided into the same phase, fill the projection angles between each other or partially overlap, artifacts can be reduced.

[0048] The rotation control unit 204 controls the rotation of the gantry 105 according to the rotation speed, which is one of the imaging conditions set by the condition setting unit 203 .

[0049] The reconstruction unit 205 reconstructs a tomographic image using the first and second projection image groups, which are segmented into the same phase. As described above, since the first and second projection image groups, which are segmented into the same phase, complement each other's projection angles, the tomographic image reconstructed by the reconstruction unit 205 has fewer artifacts.

[0050] use Figure 6 , an example of the process flow performed in this embodiment is described.

[0051] (S601)

[0052] Before acquiring the projected image, the body motion measurement unit 200 measures the motion of the subject 100. The measurement value of the body motion measurement unit 200 is sent to the phase calculation unit 201.

[0053] (S602)

[0054] The phase calculation unit 201 calculates the phase of the motion of the subject 100 based on the measurement value of the body motion measurement unit 200, and calculates the period of the motion. Figure 3 The maximum and minimum values are extracted from the waveform of the activity shown by the dotted line. The intervals between the maximum and minimum values are calculated multiple times. The average of these intervals is multiplied by 2 to calculate the period of the activity. The period of the activity calculated by the phase calculation unit 201 is sent to the condition setting unit 203.

[0055] (S603)

[0056] The condition setting unit 203 calculates a rotational speed, one of the imaging conditions, based on the period of motion calculated by the phase calculation unit 201. The rotational speed p of the gantry 105 is calculated using, for example, Equation 1. The calculated rotational speed is set as an imaging condition and sent to the rotation control unit 204.

[0057] (S604)

[0058] The control unit 106 begins measuring the rotation of the projected images. More specifically, the rotation control unit 204 rotates the gantry 105 at the rotation speed set by the condition setting unit 203. As the gantry 105 rotates, a set of projected images is acquired from the X-ray source 103 and detector 104. Furthermore, as each projected image is acquired, the body motion measurement unit 200 measures the motion of the subject 100. Furthermore, the phase calculation unit 201 calculates the phase of the subject 100's motion based on the measurement values from the body motion measurement unit 200. The calculated phase is associated with each projected image.

[0059] (S605)

[0060] When the projection images in the angle range required for reconstruction of the tomographic image are acquired, the control unit 106 ends the rotation measurement, that is, stops the irradiation of X-rays from the X-ray source 103 and the rotation of the gantry 105 .

[0061] (S606)

[0062] The division unit 202 divides the projected image group into phases based on the phase of the motion calculated by the phase calculation unit 201 .

[0063] (S607)

[0064] The reconstruction unit 205 sets the weight based on the phase of the reconstructed tomographic image. In addition, the phase of the reconstructed tomographic image can be selected from the phase with the smallest amplitude of the activity, or can be set in advance by the operator via the input device. In the case of selecting the phase with the smallest amplitude of the activity, the weight is set. Figure 3 The weights are like the solid line.

[0065] (S608)

[0066] The reconstruction unit 205 reconstructs the tomographic image using the projected image group obtained by multiplying the weights set in S607. Figure 3 If the weights are as shown by the solid line, only the projection image group corresponding to the phase with the smallest amplitude of the motion is used for reconstructing the tomographic image, so that artifacts caused by the motion can be suppressed.

[0067] Through the processing flow described above, the first projection image group and the second projection image group divided into the same phase are obtained in a manner that complements each other's projection angles, thereby reducing artifacts in the tomographic image of the subject 100 including the periodically moving treatment target.

[0068] use Figure 7 , another example of the process flow executed in this embodiment, that is, the case where the rotation speed of the gantry 105 is changed according to the change in the movement of the object 100 during the rotation measurement, will be described. Figure 6 The same processing is performed, so the description is omitted.

[0069] (S711)

[0070] The body motion measurement unit 200 measures the motion of the subject 100 during the rotation measurement. The measurement value of the body motion measurement unit 200 is sent to the phase calculation unit 201.

[0071] (S712)

[0072] The phase calculation unit 201 calculates the phase of the motion of the subject 100 and the period of the motion based on the measurement value of the body motion measurement unit 200. The period of the motion calculated by the phase calculation unit 201 is sent to the condition setting unit 203.

[0073] (S713)

[0074] The condition setting unit 203 calculates the rotation speed of the gantry 105 based on the period of motion calculated by the phase calculation unit 201 , for example, using Equation 1. The calculated rotation speed is set as an imaging condition and sent to the rotation control unit 204 .

[0075] (S714)

[0076] If the motion of the subject 100 changes, for example, if the difference between the motion periods calculated in S602 and S712 is significantly large, the rotation control unit 204 corrects the rotation speed of the gantry 105. Furthermore, while the rotation speed is being accelerated or decelerated, X-ray irradiation from the X-ray source 103 is stopped.

[0077] (S715)

[0078] Based on the angular range of the acquired projection images, the control unit 106 determines whether to complete the rotation of the gantry 105. If projection images within the angular range required for reconstruction of tomographic images have been acquired, the process proceeds to S606; otherwise, the process returns to S711.

[0079] Through the processing flow described above, even if the movement of the subject 100 changes during the rotation measurement, the first projection image group and the second projection image group divided into the same phase can be obtained in a manner that complements each other's projection angles, thereby reducing artifacts in the tomographic image.

[0080] Example 2

[0081] In Example 1, the weights used for tomographic image reconstruction were described as rectangular waveforms. Rectangular waveforms can sometimes cause artifacts due to discontinuities in the projected image. This example describes a case where the weights are continuous waveforms in the projection angle direction. Components having the same functions as in Example 1 are denoted by the same reference numerals, and their descriptions are omitted.

[0082] use Figure 8 , the waveform of the weight of this embodiment is described. In addition, Figure 8 (a) is a waveform in which the weight is set based on a waveform obtained by inverting the amplitude of the waveform of the motion of the subject 100. Figure 8 (b) is a waveform of weights set by approximating the inverse waveform of the motion of the subject 100 using a trigonometric function or the like.

[0083] Figure 8 The weight waveform shown in (a) is the waveform obtained by normalizing the inverse waveform of the activity waveform to a value with a maximum value of 1.0 and a minimum value of approximately 0.0, that is, a range that can reduce the influence of the activity. Figure 8 In (a), the dotted line shows the waveform of the activity, and the dotted line shows Figure 3 The weight of . Figure 8 As shown in (a) of FIG, by setting the weight to a waveform that is continuous in the projection angle direction, artifacts caused by discontinuity of the projected image can be reduced. In addition, by using weights that are linked to the movement of the subject 100, artifacts caused by movement can be reduced.

[0084] Figure 8 The weighted waveform shown in (b) is a waveform of weights set by approximating the inverse waveform of the active waveform using a trigonometric function. Figure 8 In (b), the dotted line represents the inversion waveform of the activity, and the dotted line represents Figure 3 The weight of . Figure 8 In the case of an approximate waveform such as (b) in FIG, weights are set according to a mathematical formula. Therefore, even if there are sudden changes in the motion of the subject 100, their effects can be suppressed, and the risk of the weights representing abnormal values can be avoided. Furthermore, since the weight waveform is continuous in the projection angle direction, artifacts caused by discontinuities in the projected image can be reduced. Furthermore, the formula used in the approximation is not limited to trigonometric functions; polynomials can also be used.

[0085] use Figure 9 , the difference in the range of the projection angle of the rotation measurement is explained. Figure 9 (a) is the case where the range of the projection angle of the rotation measurement is 110 degrees. Figure 9 (b) is the case of 180 degrees, with the solid line representing the weight of detector 104a and the dotted line representing the weight of detector 104b. Furthermore, when Δθ = 90 degrees, the weight of detector 104b after a projection angle of 180 degrees is equivalent to that after a projection angle of 0 degrees.

[0086] exist Figure 9 In (a), at projection angles of 0 and 90 degrees, the weight of detector 104a and the weight of detector 104b complement each other's projection angles, thus making up for the deficiency of the projected image. Figure 9 In (b), the weights of detectors 104a and 104b complement each other across the entire projection angle range, compensating for any deficiencies in the projected image. In other words, by expanding the range of projection angles for rotational measurement, artifacts caused by deficiencies in the projected image can be reduced.

[0087] Furthermore, in the first embodiment, the case where projection images are acquired by irradiating X-rays at all projection angles and a tomographic image is reconstructed using only a projection image group corresponding to a certain phase in the acquired projection image group is described. Projection images not used in the reconstruction of tomographic images compress the capacity of the storage device and become a major factor in increasing ineffective coverage of the subject 100. Therefore, it is preferable to limit the range of projection angles for acquiring projection images. Therefore, it is also possible to Figure 3 or Figure 8 The X-rays are irradiated with the weights shown to limit the range of projection angles for obtaining projection images.

[0088] The imaging conditions set by the condition setting unit 203 are not limited to the rotational speed calculated by Equation 1 and the X-ray irradiation timing calculated by Equation 2. For example, the angle Δθ formed by the pair of X-ray source 103a and detector 104a, or the pair of X-ray source 103b and detector 104b, may be set as an imaging condition based on the period T of the subject 100's movement and the rotational speed p of the gantry 105. The angle Δθ formed is calculated using the following equation derived from Equation 1.

[0089] Δθ=T·p·(2n-1) / 2...(Formula 3)

[0090] Here, n is a natural number. By setting the angle Δθ to the value calculated by Equation 3, the first and second projected image groups, which are divided into the same phase, can be obtained so that the first and second projected image groups complement each other at the projection angle, thereby reducing artifacts in the tomographic images.

[0091] Furthermore, the timing of the subject 100's respiration may be displayed based on a period T calculated from the angle Δθ formed by the pair of X-ray source 103a and detector 104a, and the pair of X-ray source 103b and detector 104b, and the rotational speed p of the gantry 105. The following equation derived from equation 1 is used to calculate the period T.

[0092] T = 2Δθ / (p·(2n-1)) (Formula 4)

[0093] By prompting the subject 100 to breathe based on the period T calculated by Formula 4, the first and second projected image groups divided into the same phase are acquired so as to complement each other's projection angles, thereby reducing artifacts in the tomographic image.

[0094] Furthermore, the radiographic imaging device and radiotherapy apparatus of the present invention are not limited to the above-described embodiments. Modifications and modifications to the structural elements are possible without departing from the spirit of the invention. Furthermore, multiple structural elements disclosed in the above-described embodiments may be appropriately combined. Furthermore, some structural elements may be deleted from all the structural elements shown in the above-described embodiments.

[0095] Description of Reference Numerals

[0096] 100: Subject, 101: Therapeutic radiation source, 102: Bed, 103: X-ray source, 104: Detector, 105: Gantry, 106: Control unit, 200: Body motion measurement unit, 201: Phase calculation unit, 202: Segmentation unit, 203: Condition setting unit, 204: Rotation control unit, 205: Reconstruction unit.

Claims

1. A radiographic imaging device comprising: a gantry that carries two pairs of radiation sources for irradiating radiation to a subject and detectors for detecting radiation transmitted through the subject, and rotates the radiation sources and detectors around the subject; a reconstruction unit that reconstructs a tomographic image of the object based on a plurality of projection images generated based on outputs of the detector, It is characterized in that The radiation imaging device further comprises: a phase calculation unit for calculating the phase of the activity based on the periodic activity of the subject; a dividing unit for dividing the first projection image group, which is a plurality of projection images obtained from the first group, and the second projection image group, which is a plurality of projection images obtained from the second group, for each phase; and a condition setting unit that sets the imaging conditions so that the first projection image group and the second projection image group divided into the same phase complement each other at projection angles; The reconstruction unit reconstructs a tomographic image using the first projection image group and the second projection image group divided into the same phase; The shooting conditions set by the condition setting unit include the rotation speed of the frame. setting the rotation speed based on the angle formed by the first group and the second group and the period of the activity; When the angle formed by the first group and the second group is Δθ, the period of the activity is T, the rotation speed of the rack is p, and the natural number is n, p=2Δθ / (T·(2n-1)).

2. The radiation imaging device according to claim 1, wherein The imaging conditions set by the condition setting unit include the timing of irradiation of radiation, The irradiation timing is set based on the cycle of the activity.

3. The radiation imaging device according to claim 2, wherein When the cycle of the activity is T, the radiation irradiation timing t is t=2T / (2n-1).

4. The radiation imaging device according to claim 1, wherein The condition setting unit sets the projection angle width of each projection image so that the first projection image group and the second projection image group divided into the same phase fill the space between each other's projection angles.

5. The radiation imaging device according to claim 1, wherein The condition setting unit sets the projection angle width of each projection image so that a first projection image group and a second projection image group divided into the same phase partially overlap each other.

6. The radiation imaging device according to claim 1, wherein The shooting conditions set by the condition setting unit include the angle Δθ formed by the first group and the second group, The angle Δθ formed by the first group and the second group is set based on the period T of the activity and the rotation speed p of the gantry, Wherein, Δθ=T·p·(2n-1) / 2.

7. The radiation imaging device according to claim 1, wherein The periodic activity of the subject is the subject's breathing, The radiation imaging device further includes a display unit configured to display and prompt the subject's breathing timing. The timing of the subject's breathing is set based on the angle Δθ formed by the first group and the second group and the rotation speed p of the gantry, Here, the timing of the subject's breathing = the period of the activity T = 2Δθ / (p·(2n-1)).

8. A radiotherapy device, characterized in that: have: The radiation imaging device according to claim 1; and A therapeutic radiation source irradiates therapeutic radiation toward a treatment target included in the subject.

Images