JPH08229031A - X-ray ct device - Google Patents

Abstract

PURPOSE: To provide an X-ray device requiring no X-ray simulator and suitable for a radiotherapy plan. CONSTITUTION: This X-ray CT device is provided with a tiltable gantry 1 storing an X-ray tube 2, a collimator 3, and an X-ray detector 4, a horizontally and vertically movable bed device 10 mounted with a testee on a top plate 11 and inserted into the center hole 1a of the gantry 1, a controller 15 horizontally and vertically moving the top plate 11 by the same distances as the horizontal and vertical displacements of the X-ray tube 2 when the gantry 1 is tilted, and an X-ray photographing film cassette 14 provided on the top plate 11.

Description

Detailed Description of the Invention

[0001]

This invention relates to an X-ray CT (Computed To
mography) device, and more particularly, to a device suitable for use in treatment planning in the field of radiation therapy and medical treatment.

[0002]

2. Description of the Related Art Conventionally, an X-ray apparatus for treatment planning is used to perform appropriate radiation treatment. One of them is an X-ray simulator (X-ray positioning device). This apparatus collects a plane image (X-ray image) of the affected area in order to confirm whether or not the radiation of the treatment apparatus is applied to the affected area without excess or deficiency. Therefore, in the X-ray simulator, the positional relationship of the X-ray tube, collimator, X-ray film, and the like is set so that the radiation treatment apparatus has the same geometrical conditions.

The geometrical relationship between the X-ray simulator and the radiotherapy apparatus will be described below with reference to FIG. The symbol P in FIG. 10 is the focus of the X-ray tube of the X-ray simulator,
It corresponds to a radiation source in a radiation treatment apparatus. The divergence angle θ of the conical X-ray beam (cone beam) CB emitted from the X-ray tube can be arbitrarily set by a collimator attached to the X-ray tube. Reference numeral B is an imaging surface of a region to be imaged (for example, a diseased part of a subject to be subjected to radiation therapy). The distance V ₁ from the X-ray tube (focus point P) to the imaging plane B is set to be the same as the distance from the radiation source of the radiotherapy apparatus to the irradiation target site (the same site as the imaging target site, for example, the affected part of the subject). To be done. Reference symbol F is the X-ray film surface of the X-ray simulator, and the distance from the photographing surface B is indicated by V ₂ .

With the X-ray beam CB having a divergence angle θ,
Distance L ₁ (L ₁ = V ₁ tan from the vertical axis VA passing through the focal point P)
On the film surface F, the point Q on the film surface F separated by θ) is a distance L ₂ (L ₂ = (V ₁ + V ₂ ) tan from the vertical axis VA.
The image is taken as a point R separated by θ). The X-ray image taken on the film surface F corresponds to the radiation irradiation area in the radiation therapy apparatus. Therefore, the optimum irradiation field of the radiation of the radiotherapy apparatus is determined by adjusting the correlator of the X-ray simulator and appropriately adjusting the divergence angle θ of the X-ray beam CB.

As described above, the X-ray simulator directly simulates the geometric relationship of radiation irradiation of the radiation treatment apparatus. Such a geometrical relationship is generally BEV.
(Beam's Eye View). In the following, an X-ray radiographic image (planar image) of the imaging target site obtained with the same geometrical relationship as the radiation irradiation of the radiotherapy apparatus is called a BEV image.

As another X-ray apparatus for treatment planning, there is an X-ray CT apparatus for taking a tomographic image of an affected area. Since it is not possible to know the depth information of the affected area only with the BEV image obtained by the X-ray simulator, the above-mentioned X-ray simulator and X-ray CT apparatus are usually used for radiation treatment planning.

However, when an X-ray simulator and an X-ray CT apparatus are used to carry out a radiation treatment plan, the purchase cost of the apparatus, maintenance costs, installation space, patient movement when in use, etc.
Various problems arise.

Therefore, recently, an apparatus having a function of using a CR image (also called a scout view) obtained by an X-ray CT apparatus as a substitute for a BEV image or reconstructing a BEV image from a plurality of tomographic images is proposed. Has been done. These will be briefly described below.

FIG. 11 shows the principle for obtaining a CR image by the X-ray CT apparatus. X-ray CT system gantry 1
The X-rays emitted from the X-ray tube 2 housed inside are shaped by the collimator 3 and have a thin fan-shaped (fan) beam F.
It becomes B. The fan beam FB passes through the subject M and enters the X-ray detector 4, and the detection signal is detected by the image processing device 7.
Is given to the image monitor 8 via. In this state, when the subject M is moved in the x direction by horizontal movement of a top plate (not shown) on which the subject M is placed, a plane image of the subject M is displayed on the image monitor 8.

FIG. 12 shows the principle for reconstructing a BEV image from a plurality of tomographic images obtained by an X-ray CT apparatus. In FIG. 12, symbols S _{1 to} S _n are a plurality of slice planes of the subject M tomographically imaged by the X-ray CT apparatus. A two-dimensional distribution image (tomographic image) of CT values on each slice plane S _{1 to} S _n is obtained by tomography. The virtual X-ray focal point P of the same geometrical relationship with the radiation therapy device of the film plane F is assumed, the line B ₁ was assumed from the focal point P conically, B _2, ..., the CT values along the B _m The BEV image is reconstructed on the virtual film surface F by calculating the integrated value from the CT values of the respective slice surfaces S _{1 to} S _n .

[0011]

[Problems to be Solved by the Invention]

However, in the method shown in FIG.
Since the plane image is obtained by horizontally scanning the fan beam FB relative to the subject M, the image is enlarged in the diverging direction of the fan beam (direction s orthogonal to the paper surface of FIG. 11). On the other hand, in the x direction orthogonal to this, the image becomes distorted and the image is distorted. As a result, this method has a problem that a correct BEV image cannot be obtained.

Further, in the method shown in FIG. 12, the intervals between the slice planes S _{1 to} S _n cannot be made very fine due to the constraint of throughput, and the CT values become discrete, so that the lines B ₁ , B ₂ , ..., The image quality of the BEV image obtained from the integrated value of the CT values along B _m is very poor, and it is difficult to obtain accurate information on the affected area.

Although attempts have been made to substitute the X-ray simulator by the X-ray CT apparatus as described above,
Since neither of them is sufficient, both the X-ray simulator and the X-ray CT apparatus are still used for actual radiation treatment planning.

The present invention has been made in view of the above circumstances and does not require an X-ray simulator.
An object is to provide an X-ray CT apparatus suitable for a radiation treatment plan.

[0016]

The present invention has the following configuration to achieve the above object. That is, in the invention described in claim 1, the X-ray irradiating means for irradiating the fan-shaped X-ray beam and the tomographic X-ray detecting means for detecting the X-ray beam are housed and arranged so as to face each other. A gantry configured such that the X-ray irradiation means and the X-ray detection means for tomography rotate together, and the subject is placed on the top plate and the subject is inserted into the central hole of the gantry. An X-ray CT apparatus comprising a bed device capable of moving horizontally and vertically, and the gantry being configured to be tiltable around a horizontal axis substantially vertical to the axis of the central hole, in association with tilting motion of the gantry. And a control means for moving the tabletop horizontally and vertically by a distance equivalent to the horizontal displacement amount and the vertical displacement amount of the X-ray irradiating means associated with the tilting movement of the gantry, and attached to the tabletop of the bed apparatus. X-ray for flat image capture Characterized by comprising a means out.

According to a second aspect of the present invention, the X-ray irradiating means for irradiating the fan-shaped X-ray beam and the tomographic X-ray detecting means for detecting the X-ray beam are housed and arranged so as to face each other. A gantry configured such that the X-ray irradiating means and the X-ray detecting means for tomography rotate integrally, and a subject is placed on a top plate and the subject is inserted into a central hole of the gantry. An X-ray CT apparatus comprising a bed device capable of moving horizontally and vertically and tilting about a horizontal axis substantially vertical to the axis of the central hole. Then, the control means for moving the top plate horizontally and vertically by a distance equivalent to the horizontal displacement amount and the vertical displacement amount of the X-ray irradiating means associated with the tilting movement of the gantry, and the tilting movement of the gantry are interlocked. Detected by The two-dimensional coordinates of the image display position of the X-ray data of each detection element of the layer imaging X-ray detection means, that is, the coordinates on the first axis in the horizontal displacement direction of the top plate are determined in relation to the tilt angle of the gantry. When the coordinates on the horizontal second axis orthogonal to the first axis are assumed to be the arc-shaped detection elements constituting the X-ray detection means for tomography arranged horizontally, An image processing unit that is determined in relation to the position where the line beam is incident, and a display based on the X-ray detection data of each detection element of the X-ray detection unit for tomography is displayed at the image display position determined by the image processing unit. And a display means for performing.

[0018]

The operation of the invention described in claim 1 will be described. When viewed from the front of the gantry (a plane orthogonal to the axis of the central hole), the X-ray beam emitted from the X-ray irradiating means has a fan shape, and therefore the height of the top plate of the bed apparatus is adjusted to adjust the X-ray beam. The distance from the irradiation means to the imaging surface of the imaging target site (for example, the affected part of the subject who is about to undergo radiotherapy) is measured from the radiation source of the radiotherapy device to the irradiation target site (for example, the affected part of the subject). By setting the same as the distance, the geometric relationship of X-ray irradiation viewed from the front side of the gantry matches that of the radiotherapy apparatus.

On the other hand, the geometrical relationship seen from the side surface of the gantry (vertical plane including the axis of the central hole) matches that of the radiotherapy apparatus by horizontally and vertically displacing the top plate in conjunction with tilting movement of the gantry. Let That is, when the gantry is tilted from the vertical state in order to perform X-ray irradiation equivalent to the radiation beam (cone beam) of the radiotherapy apparatus, the X-ray irradiating means inside the gantry is accordingly moved horizontally and vertically. Because of the displacement, the geometrical relationship with the radiotherapy apparatus is deviated. Therefore, the control means interlocks with the tilt movement of the gantry and moves the top plate horizontally and vertically by a distance equivalent to the horizontal and vertical displacement amounts of the X-ray irradiation means associated with the tilt movement of the gantry. As a result, the imaging surface of the imaging target region on the top plate moves, so that the geometrical relationship between the X-ray irradiation means and the imaging surface matches that of the radiation therapy apparatus. Also,
Along with the movement of the tabletop, X for plane image shooting attached to the tabletop
The line detection means also moves. Therefore, by tilting the gantry while irradiating the X-ray beam, the X-ray detector for plane image capturing detects the X-ray image (planar image) of the region to be imaged in the same geometrical relationship as the radiotherapy apparatus. .

The operation of the invention described in claim 2 is as follows. Similar to the invention described in claim 1, regarding the geometrical relationship viewed from the front side of the gantry, the distance from the X-ray irradiation means to the imaging surface of the imaging target site is the distance from the radiation source of the radiotherapy apparatus to the irradiation target site. By adjusting the height of the top plate so as to be the same as, it is possible to match the geometrical relationship of the radiation therapy apparatus. Further, the geometrical relationship viewed from the side of the gantry can be matched with that of the radiotherapy apparatus by horizontally and vertically displacing the top plate in conjunction with the tilt movement of the gantry.

In the second aspect of the invention, since the BEV image of the subject is to be obtained by using the tomographic X-ray detecting means, each of the arc-shaped arrangements constituting the tomographic X-ray detecting means. In displaying the plane image based on the X-ray data detected by the detecting element, each plane image is displayed so that the plane image is the same as that photographed by the plane image photographing X-ray detecting means used in the invention of claim 1. It is necessary to determine the coordinates of the X-ray data. Therefore, the image processing means determines the coordinates on the first axis in the horizontal displacement direction of the top plate in relation to the inclination angle of the gantry,
The X-ray beam when the coordinates on the horizontal second axis orthogonal to the first axis are assumed to be the horizontal arrangement of the arc-shaped detection elements forming the X-ray detection means for tomography. Is determined in relation to the incident position of. By performing display based on the respective X-ray data at the position on the screen of the display means determined in this way, an X-ray image (planar image) of the imaging target region obtained with the same geometrical relationship as the radiotherapy apparatus. Is displayed.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 shows an X according to the first embodiment.
FIG. 2 is a side view showing a schematic configuration of the line CT apparatus, and FIG. 2 is a front view of the gantry.

In the figure, reference numeral 1 is a gantry of an X-ray CT apparatus, and a central hole 1a for inserting a subject M to be imaged is formed in the center of the gantry. In Gantry 1,
The X-ray tube 2 and the collimator 3 are housed so as to face the X-ray detector 4. At the time of tomography, the X-ray tube 2, the collimator 3, and the X-ray detector 4 are integrally rotated. The caliber of the central hole 1a of the gantry 1 has a bed to be described later in order to match the geometrical relationship (BEV) between the X-ray tube 2 and the imaging region (for example, the affected part of the subject M) with that of the radiotherapy apparatus. The size is set so as not to hinder the movement of the top plate 11 of the device 10 when it is moved up and down.

The collimator 3 is the X-ray emitted from the X-ray tube 2.
A line beam is shaped into a thin fan-shaped beam.
Like the collimator provided in the radiotherapy device,
The divergence angle of the fan-shaped X-ray beam (fan beam) FB can be adjusted. The X-ray tube 2 and the collimator 3 correspond to the X-ray irradiation means in this invention.

As is well known, the X-ray detector 4 is constructed by arranging a large number of X-ray detecting elements such as scintillators and photomultiplier tubes in an arc shape. The X-ray detector 4 corresponds to the X-ray detection means for tomography in this invention.

The gantry 1 is driven by the tilt drive mechanism 5,
It is configured to be tiltable around a horizontal axis G that is substantially perpendicular to the axis of the central hole 1a.

The bed apparatus 10 includes a top plate 11 on which the subject M is placed. The top 11 is moved by the horizontal drive mechanism 12 and the vertical drive mechanism 13 provided in the bed apparatus 10,
It is configured to move horizontally and vertically. Each of the mechanisms 5, 12 and 13 described above is configured by a well-known rack and pinion mechanism or the like.

An X-ray film cassette 14 is attached to the lower surface of the top plate 11. Film cassette 14
Is for imaging the site (affected part) of the subject M placed on the top 11 to be subjected to radiation therapy, and can be attached at an arbitrary position according to the site to be imaged. There is. The film cassette 14 for X-ray photography corresponds to the X-ray detection means for plane image photography in this invention.

The control unit 15 interlocks with the tilting movement of the gantry 1 so that the geometric relationship (BEV) between the X-ray tube 2 and the region to be imaged coincides with that of the radiotherapy apparatus, and the top plate 11 is moved horizontally and vertically. It is for displacing. The control unit 15 corresponds to the control means in this invention. Details of the operation of the control unit 15 will be described later.

The operation for obtaining an X-ray image of the region to be imaged with the same geometrical relationship as the radiotherapy apparatus by using the apparatus of the first embodiment having the above-mentioned configuration will be described below.

First, the top plate 11 on which the subject M is placed is inserted into the center hole 1a of the gantry 1, and the X-ray tube 2 (specifically, the X-ray focal point P) is used to image the region of the subject M to be imaged. The height of the top plate 11 is adjusted so that the distance V ₁ to the distance from the radiation source of the radiotherapy apparatus to the treatment region of the subject M (the same as the imaging target region).

In this state, when viewed from the front side of the gantry 1 as shown in FIG. 2, the X-ray beam FB emitted from the X-ray tube 2 has a fan shape, and at this point, the radiation beam ( This beam is a conical beam, but is fan-shaped in a front view). Therefore, the geometrical relationship of X-ray irradiation when viewed from the front side of the gantry 1 matches that of the radiotherapy apparatus. This relationship is maintained even when the gantry 1 tilts, which will be described later.

Next, the gantry 1 is tilted while irradiating the X-ray beam FB from the X-ray tube 2 to photograph an X-ray image of the region to be photographed on the X-ray photographing film cassette 14. At this time, since the X-ray tube 2 inside the gantry 1 is displaced in the horizontal and vertical directions as the gantry 1 tilts, when viewed from the side surface of the gantry 1 (vertical surface including the axis of the central hole 1a), X The geometrical relationship between the radiation tube 2 and the part to be imaged deviates from that of the radiotherapy apparatus. Therefore, the control unit 15 interlocks with the tilt movement of the gantry 1 to horizontally and vertically displace the top plate 11 as described below.
The geometric relationship between the X-ray tube 2 and the part to be imaged is matched with that of the radiation therapy apparatus.

Hereinafter, description will be made with reference to FIG. FIG. 3 is a view showing the geometrical relationship between the X-ray tube 2 and the imaging target site as seen from the side surface side of the gantry 1 (vertical plane including the axis of the central hole 1a). In the figure, reference symbol P indicates the focal point of the X-ray tube 2, reference symbol Θ indicates the tilt angle of the gantry 1, reference symbol B indicates the imaging surface of the imaging target region, and reference symbol F indicates the film surface of the X-ray imaging film cassette 14. .

As described above, when the gantry 1 is in the vertical state (tilt angle Θ = 0), the distance V ₁ between the focal point P and the imaging plane B is determined from the radiation source of the radiation treatment apparatus to the treatment site of the subject M. It is set to the same distance as (the same as the imaging target part). Further, there is a distance V ₂ between the shooting surface B and the film surface F. In this state, when the X-ray beam FB (which is viewed from the side surface of the gantry 1 is shown, the thin fan-shaped X-ray beam FB is represented by one broken line), the point Q on the imaging plane B is irradiated. ₀ is photographed as a point R ₀ on the film surface F.

Next, it is assumed that the gantry 1 is moved to the tilt angle Θ = θ. The X-ray focal point at this time is indicated by the reference symbol P ′, and the X-ray beam is indicated by FB ′. Here, for convenience of explanation, the center O of the tilt movement of the gantry 1 is set to the imaging plane B.
It is set above (corresponding to the point Q ₀ ). Since the radiation source of the actual radiation treatment apparatus does not move, the X-ray beam F
If the radiation having the same inclination angle as B'is shown in FIG. 3 as a reference, it becomes like the chain line indicated by the symbol FB ". The position Q" on the imaging plane B through which the virtual radiation FB "passes is the inclination angle Θ. Vertical line VA when = 0 (same line as radiation FB)
V ₁ from tan is in the θ apart position, a position R "is the same vertical line VA (V ₁ on the film plane F corresponding thereto
+ V ₂ ) tan θ. Therefore, when the gantry 1 is tilted by the tilt angle Θ = θ, the point Q ″, which is the original point to be imaged, is an X-ray separated by V ₁ tan θ from the vertical axis VA ′ based on the focus P ′. The shooting surface B (that is, the top plate 1) so as to come to the position Q'on the beam FB '.
It is sufficient to displace 1). Due to the displacement of the top plate 11, the film surface F (film cassette 14 for X-ray imaging) is also displaced by the same amount as the imaging surface B, so that the point R "on the film surface F corresponding to the point Q" is focused on the focal point P '. Standard vertical axis VA '
X-ray beam FB ′ separated by (V ₁ + V ₂ ) tan θ from
Move to position R'above. As a result, the imaging target site is imaged on the X-ray imaging film cassette 14 in the same geometrical relationship as the radiotherapy apparatus.

Displacement of the point Q ″ (point R ″) so as to come to the point Q ′ (point R ′) means that the vertical axis VA when the tilt angle Θ = 0 of the gantry 1 is the same as the photographing plane B. Crossing point Q ₀
Is the vertical axis VA 'when the tilt angle Θ of the gantry 1 is θ
Is equivalent to moving to a point Q ₀ 'that intersects the image plane B'after displacement. The horizontal displacement amount ΔH and the vertical displacement amount ΔV of the point Q _{0 at} this time can be expressed by the following equations, respectively. ΔH = V ₁ sin θ (1) ΔV = V ₁ (1-cos θ) (2)

Therefore, the control unit 15 shown in FIG.
Interlocking with the tilting movement of the gantry 1, with respect to the horizontal drive mechanism 12 of the bed apparatus 10, the top plate 11 is horizontally displaced as shown in the above formula (1), and with respect to the vertical drive mechanism 13. , The top plate 11 is controlled so as to be vertically displaced as shown in the above formula (2), so that a plane image of the imaging target portion is imaged on the X-ray film cassette 14 in the same geometrical relationship as the radiotherapy apparatus. To be done.

As can be understood from the above description, the horizontal displacement amount ΔH of the top plate 11 expressed by the above equation (1) is the same as that of the X-ray tube 2 when the gantry 1 is tilted by the tilt angle Θ = θ. It is the same as the horizontal displacement amount, and the vertical displacement amount ΔV of the top plate 11 expressed by the above equation (2) is the inclination angle Θ = θ of the gantry 1.
It is the same as the amount of vertical displacement of the X-ray tube 2 when it is tilted only. Therefore, in other words, the control unit 15 horizontally and vertically displaces the top plate 11 by distances equal to the horizontal and vertical displacement amounts of the X-ray tube 2 associated with the tilt movement of the gantry 1.

In the above-mentioned embodiment, the center O of the tilt movement of the gantry 1 is on the photographing surface B for convenience of explanation, but the center O of the tilt movement of the gantry 11 is on the photographing surface B. If not, the distance V ₁ in the above equations (1) and (2)
As the above, the distance from the focal point P of the X-ray tube 2 to the tilt movement center O of the gantry 1 may be used. The control in this case is also
This means that the top plate 11 is displaced horizontally and vertically by a distance equivalent to the amount of horizontal and vertical displacement of the X-ray tube 2 caused by the tilting movement of the gantry 1.

[Second Embodiment] FIG. 4 shows the X according to the second embodiment.
FIG. 5 is a side view showing a schematic configuration of the line CT apparatus, and FIG. 5 is a front view of the gantry. In these figures, the portions denoted by the same reference numerals as those shown in FIGS. 1 and 2 have the same configuration as that of the first embodiment apparatus, and therefore the description thereof is omitted here.

In the first embodiment, an X-ray film cassette 14 is attached to the top plate 11 to obtain a BEV image. However, in the present embodiment, the X-ray CT apparatus is essentially used without using the film cassette 14. A BEV image is obtained by using the X-ray detector 4 for tomography provided. Therefore, the image processing unit 16 for determining the position on the display screen of the X-ray data detected by each detection element of the X-ray detector 4.
And an image monitor 17 that displays a plane image of the imaging target region based on each X-ray data at the display position determined by the image processing unit 16. The image processing section 16 corresponds to the image processing means in this invention, and the image monitor 17 corresponds to the display means in this invention.

The operation for obtaining a plane image (BEV image) of the region to be imaged with this apparatus in the same geometrical relationship as the radiotherapy apparatus will be described below. Note that the gantry 1 is tilted while irradiating an X-ray beam from the X-ray tube 2, and in conjunction with this, the control unit 15 horizontally and vertically displaces the top plate 11 of the bed apparatus 10. The description is omitted here, and the processing of the image processing unit 16 for determining the display position of the X-ray data detected by each detection element of the X-ray detector 4 will be described below.

Referring to FIG. This figure shows a vertical plane including the axis of the central hole 1a of the gantry 1 (A ₀ -A ₀ in FIG. 5).
It is the figure which showed the geometrical relationship of the X-ray tube 2 and imaging target site | part in the arrow cross section). In the figure, reference symbols P and B denote the focus and imaging plane of the X-ray tube 2 when the inclination angle Θ of the gantry 1 is 0, and reference symbols P ′ and B ′ are those when the inclination angle Θ = θ of the gantry 1. The focus and imaging plane of the X-ray tube 2 are shown. For convenience of explanation, the tilting movement center O of the gantry 1 is set on the imaging plane B.

As is clear from FIG. 6, when the inclination angle Θ = θ of the gantry 1, the X-ray detector 4 moves from the vertical axis VA ′ passing through the focal point P ′ to Vtan θ (where V is the gantry 1).
When the inclination angle Θ of 0 is 0, the distance V _{1 in the} first embodiment is
Similarly, the X-ray data of the point Q'on the imaging plane B ', which is separated by the set distance between the focus P and the imaging plane B), is sampled. This means that the geometrical relationship of the radiotherapy apparatus matches the geometrical relationship of the X-ray simulator shown in FIG. The above geometrical relationship is established within the cross section taken along the line A ₀ -A ₀ in FIG. On the other hand, even with respect to the A ₁ -A ₁ cross-section parallel to the A ₀ -A ₀ arrow cross-section, a virtual X-ray in which the X-ray detector 4 is tentatively arranged in a straight line rather than an arc If it is a detector (shown by reference numeral 4'in FIGS. 5 and 7), it has the same geometrical relationship as shown in FIG.
Therefore, in the present embodiment, the image processing unit 16 performs a process for correcting the height h (see FIG. 5) of each detection element forming the X-ray detector 4. This will be described below with reference to FIGS. 7 and 8.

FIG. 8 shows the geometrical relationship shown in perspective in FIG.
FIG. 3 is a view seen from the −s plane (T is the central axis of the gantry 1 that connects the focal point P to the central detection element of the X-ray detector 4, and s is the tangent to the central detection element of the X-ray detector 4). X-ray detector 4
The detection element in the center of E is indicated by E ₀ , and the detection element of the X-ray detector 4 separated from the central axis T by an angle φ is indicated by E. The detection element E is
It corresponds to the detection element E'on the virtual X-ray detector 4'for obtaining the BEV image. When the distance from the focus P of the X-ray tube 2 to the X-ray detector 4 is R, s of the virtual detection element E ′ is
The coordinate on the axis is expressed by the following equation (3). s = Rtan φ ……… (3)

If the position of each detection element of the X-ray detector 4 is represented by an arc-shaped coordinate axis t along the arc-shaped array of detection elements, the X-ray data detected by each detection element is μ (t). Can be expressed as The position t of each detection element is given by the following equation (4). t = Rφ ………… (4)

When φ is eliminated from the above equations (3) and (4), s = Rtan (t / R) (5) is obtained. That is, the X-ray data μ (t) detected by the detection element at the position t on the X-ray detector 4 is B
On the virtual X-ray detector 4 ′ for obtaining the EV image, s
= Rtan (t / R) position data.

FIG. 9 shows the corrected position of the X-ray data detected by each detection element of the X-ray detector 4 described above. In the figure, μ (t, θ) is X-ray data detected by the detection element at the position t in the X-ray detector 4 when the gantry 1 has an inclination angle Θ = θ. The coordinate x of the X-ray data μ (t, θ) on the first axis in the horizontal movement direction of the top 11 is given by Vtan θ, as described with reference to FIG. The coordinates on the horizontal axis s orthogonal to the x-axis are given by the above equation (5).

That is, when the image processing unit 16 is given the tilt angle θ of the gantry 1 from the control unit 15 and the position t of the detection element from the X-ray detector 4, the X-ray data μ ( As the display coordinates (x, s) of (t, θ), x = Vtan θ and s = Rtan (t / R) are calculated.
Then, from the image processing unit 16 to the image monitor 17, the X-ray data μ (t, θ) of each detection element and the display coordinates (x,
By giving s), a plane image (BEV image) of the imaging target region that matches the geometrical relationship of the radiation therapy apparatus is displayed on the image monitor 17.

[0052]

As is apparent from the above description, the present invention has the following effects. That is, according to the first aspect of the invention, the top plate is horizontally / vertically displaced by a distance equal to the horizontal displacement amount and the vertical displacement amount of the X-ray irradiating means in association with the tilt movement of the gantry. Therefore, the X-ray detecting means for flat image capturing attached to the top plate can obtain an X-ray image (plan image) of good image quality having the same geometrical relationship (BEV) as the radiation irradiation of the radiotherapy apparatus. Therefore, an X-ray simulator conventionally used for radiotherapy planning is not required, and an X-ray CT image and a tomographic image of the affected area of the subject can be obtained by one X-ray CT apparatus according to the present invention. Therefore, the purchase cost, maintenance cost, installation space, and patient movement during use can be suppressed as much as possible.

According to the invention of claim 2, claim 1
In addition to obtaining the same effect as the invention described in claim 1, for tomography originally provided in the X-ray CT apparatus without using the plane image imaging X-ray detection means used in the invention of claim 1. Since the X-ray image (planar image) of the affected part of the subject can be obtained using the X-ray detection means, the configuration of the apparatus can be further simplified.

[Brief description of drawings]

FIG. 1 is a side view showing a schematic configuration of a first embodiment device.

FIG. 2 is a front view of a gantry of the first embodiment device.

FIG. 3 is a diagram showing a geometrical relationship during X-ray imaging by the apparatus of the first embodiment.

FIG. 4 is a side view showing a schematic configuration of a second embodiment device.

FIG. 5 is a front view of a gantry of the second embodiment device.

FIG. 6 is a diagram showing a geometrical relationship during X-ray photography by the apparatus of the second embodiment.

FIG. 7 is a perspective view showing a geometrical relationship during X-ray photography by the apparatus of the second embodiment.

FIG. 8 is a diagram for explaining position correction of X-ray data of the second embodiment device.

FIG. 9 is a diagram for explaining an image display position of X-ray data of the second embodiment device.

FIG. 10 is a diagram showing a geometric relationship of a conventional X-ray simulator.

FIG. 11 is a diagram for explaining CR image capturing by a conventional X-ray CT apparatus.

FIG. 12 is a diagram for explaining reconstruction of a BEV image by a conventional X-ray CT apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Gantry 1a ... Center hole 2 ... X-ray tube 3 ... Collimator 4 ... X-ray detector 5 ... Tilt drive mechanism 10 ... Bed device 11 ... Top plate 12 ... Horizontal drive mechanism 13 ... Vertical drive mechanism 14 ... For X-ray imaging Film cassette 15 ... Control unit 16 ... Image processing unit 17 ... Image monitor P ... X-ray focus B ... Shooting surface F ... Film surface

Claims (2)

[Claims] 1. An X-ray irradiating means for irradiating a fan-shaped X-ray beam and a tomographic X-ray detecting means for detecting the X-ray beam are housed and arranged to face each other, and the X-ray irradiating means and the tomographic section are arranged. A gantry configured to rotate together with an imaging X-ray detecting means, and a horizontal and vertical movement in which a subject is placed on a top plate and the subject is inserted into a central hole of the gantry. An X-ray CT apparatus including a bed device and configured such that the gantry can be tilted about a horizontal axis substantially perpendicular to the axis of the central hole, the tilting of the gantry being linked with the tilting motion of the gantry. Control means for moving the top plate horizontally and vertically by a distance equivalent to the horizontal displacement amount and the vertical displacement amount of the X-ray irradiating means associated with movement, respectively.
An X-ray CT apparatus comprising: an X-ray detection unit for capturing a plane image attached to a top plate of the bed apparatus. 2. An X-ray irradiating means for irradiating a fan-shaped X-ray beam and a tomographic X-ray detecting means for detecting the X-ray beam are housed and arranged so as to face each other, and the X-ray irradiating means and the tomographic section are arranged. A gantry configured to rotate together with an imaging X-ray detecting means, and a horizontal and vertical movement in which a subject is placed on a top plate and the subject is inserted into a central hole of the gantry. An X-ray CT apparatus including a bed device and configured such that the gantry can be tilted about a horizontal axis substantially perpendicular to the axis of the central hole, the tilting of the gantry being linked with the tilting motion of the gantry. Control means for moving the top plate horizontally and vertically by a distance equivalent to the horizontal displacement amount and the vertical displacement amount of the X-ray irradiating means associated with movement, respectively.
The two-dimensional coordinates of the image display position of the X-ray data of each detection element of the X-ray detection unit for tomography, which is detected in conjunction with the tilt movement of the gantry, that is, the first in the horizontal displacement direction of the top plate.
The coordinate on the axis is determined in relation to the tilt angle of the gantry, and the coordinate on the horizontal second axis orthogonal to the first axis is arranged in an arc shape constituting the X-ray detection means for tomography. Further, assuming that the respective detection elements are arranged horizontally, an image processing unit which is determined in relation to a position where the X-ray beam is incident, and the tomographic X-ray at the image display position which is determined by the image processing unit. An X-ray CT apparatus comprising: a display unit that displays based on X-ray data of each detection element of the line detection unit.