JP2002186678A - Radiotherapy system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiotherapy system enabling the execution of accurate radiotherapy by enabling the planning of the accurate radiotherapy even when the position or size of a lesion part is changed due to respiratory movement. SOLUTION: The radiotherapy system enables the superimpose-display of fluoroscopic images obtained during a prescribed time interval (the interval between exhalation and inhalation) by means of an X-ray simulator. Additionally, the setting and input of a target form (a radiation field) are conducted with respect to the superimpose-displayed lesion part T. Consequently, the proper target form (see, for example, R1 and R2) can be set according to a change in the size, etc., of the lesion part T due to the respiratory movement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation treatment planning system.

[0002]

2. Description of the Related Art Conventionally, radiation treatment aiming at healing by irradiating radiation to a lesion such as a cancer or a tumor to destroy or prevent the division of tissue cells in the lesion is widely performed. It has become. Here, as the radiation, for example, a linear accelerator (linear accelerator = L)
X-rays generated by irradiating electrons accelerated by INAC) onto a predetermined electron beam target (tungsten, gold, platinum, etc.) are used.

In performing such radiotherapy, it is necessary to irradiate (or dose) an appropriate amount of radiation to obtain a sufficient therapeutic effect on the above-mentioned lesion, and to perform other normal tissues other than the lesion. Must satisfy the condition that the allowable radiation dose must not be exceeded so that no damage occurs. At this time, especially when a tissue having high sensitivity to radiation (for example, thyroid gland or eyeball (lens)) exists near the lesion, higher attention is required.

Therefore, before the radiation treatment is actually started, in order to satisfy the above conditions, the position, size, shape, number, etc. of the lesion are accurately grasped (specifying the lesion), and the radiation is determined based on the information. Irradiation area (irradiation field), irradiation angle,
It is necessary to determine the number of irradiation portals and the like, and to formulate a radiation treatment plan so that the radiation is concentrated on the lesion and the dose distribution around the lesion is appropriate.

Conventionally, such a radiation treatment plan has been formulated by using, for example, an X-ray CT apparatus or a radiation treatment plan formulation apparatus, or an apparatus called an “X-ray positioning apparatus” or an “X-ray simulator”. Was implemented through use. Among them, the X-ray simulator is an X-ray tube and an X-ray detector (conventionally, image-in) that match the other geometrical arrangement such as the distance between the radiation source and the subject of the radiation therapy apparatus that actually performs the radiation therapy. It has a tensifier (a so-called “II” is used) and a top plate on which the subject is placed, and can acquire other X-ray images such as a fluoroscopic image of the subject. The device user determines a treatment plan with the radiation treatment plan formulation device and confirms that an irradiation field or the like based on the plan is superimposed and displayed on a fluoroscopic image or the like acquired by the X-ray simulator ( = Simulation), it is possible to check whether the radiotherapy to be performed from now on is performed as planned, or whether the radiotherapy is performed as planned.

[0006]

However, the conventional radiotherapy planning has the following problems. That is, in the stage of using the X-ray simulator, the apparatus user, in a fluoroscopic image or the like related to the acquisition, when the position or size of the diseased part changes every moment due to respiratory movement, A so-called “irradiation field margin” is also determined so that radiation irradiation according to the displacement can be performed, but this determination has a problem in that it must be based solely on the experience of a doctor or the like.

[0007] In determining the irradiation field margin as described above, a fixture is installed near the subject or the lesion, and the "amount" of respiratory movement of the lesion is observed. Has been operated such that if the movement amount is within a certain allowable value (for example, 1 cm), the treatment is carried out without any special change to the planned irradiation field. . In addition,
For the determination of such a movement amount, for example, a display of a cross board J as shown in FIG. 7 (in the figure, a symbol T is a lesion, and an arrow indicates respiratory movement of the lesion T) is used. As you can see from the figure, such a cross board J
Is used, the determination of the amount of movement must be relatively rough.

[0008] Eventually, in conventional radiation therapy planning,
Since the determination of the irradiation field margin or the determination of the amount of respiratory movement in the affected area is not quantitative, if the judgment is incorrect, the part to be irradiated is not irradiated, or the unnecessary part is irradiated. There was a case where such a trouble occurred.

The present invention has been made in view of the above circumstances, and has as its object the purpose of changing the position or size of a diseased part by respiratory movement.
It is an object of the present invention to provide a radiation treatment system that can formulate a radiation treatment plan that accurately reflects the position, shape, and the like of such a lesion, and thus can perform more accurate radiation treatment. .

[0010]

The present invention adopts the following means to solve the above problems. That is, the radiation treatment planning system according to claim 1 is an X-ray simulator, a radiation treatment plan formulation device capable of formulating a radiation treatment plan based on an X-ray fluoroscopic image acquired by the X-ray simulator, and radiation. In a radiotherapy system at least constituted by a treatment device, a storage unit for storing a plurality of perspective images acquired during a predetermined time interval by the X-ray simulator, and an image display for superimposing and displaying the plurality of perspective images Means, and input means for setting and inputting a target shape that defines a radiation irradiation area of the radiation therapy apparatus with respect to a target portion on the superimposed display.

[0011] The radiation treatment planning system according to a second aspect is characterized in that, in the same system as the first aspect, a scale plate is further superimposed on the superimposed display. Furthermore, the radiation treatment planning system according to claim 3 is the radiation treatment planning system according to claim 1,
An X-ray tube that generates X-rays;
An X-ray detector that emits the X-ray tube and detects X-rays transmitted through the subject, wherein the X-ray detector is a planar detector having pixels arranged two-dimensionally. It is assumed that.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram illustrating a configuration example of the radiation treatment planning system according to the present embodiment. In FIG. 1, the radiation treatment planning system includes X
X-ray CT device 1 and radiation treatment plan formulation device (hereinafter “RTP”)
(Radio Therapy Planning) device. 2.) It is composed of four large components: an X-ray simulator 3 and a radiotherapy device 4.

The X-ray CT apparatus 1 is composed of a CT gantry 11 and a top board S1 provided on a bed and configured to be movable in the body axis direction of the subject P (vertical direction in FIG. 1). C
The T base 11 is provided with a cavity 11a into which the top plate S1 is inserted and removed as the top plate S1 moves.
An X-ray tube 12 and an X-ray detector 13 which are respectively disposed around the periphery of the subject 1a and inside the CT gantry 11 and are rotatable around the subject P around the cavity 11a.
Is provided. The X-ray tube 12 is connected to an X-ray generator (not shown) including a high-voltage power supply and the like, and the X-ray detector 13 is connected to a data acquisition unit 14. In addition, the data collection unit 14 and subsequent units are connected to well-known components (not shown) such as a preprocessing unit, a memory, and an image reconstruction unit.

In such an X-ray CT apparatus 1, X-rays emitted from the X-ray tube 12 are emitted to the subject P (see broken lines in FIG. 1), and the X-rays transmitted through the subject P X-rays are detected by the X-ray detector 13 and, based on this, appropriate amplification processing, A / D conversion processing, calibration processing,
Then, through the CT image reconstruction processing and the like, the CT inside the subject P is
An image or the like can be obtained.

The RTP device 2 includes an image display unit 21 for displaying a CT image or the like acquired by the X-ray CT device 1, a CT image displayed on the image display unit 21, and a lesion part appearing in the image. An input unit 22 capable of performing setting and input of a target shape and the like with respect to (“target portion” in the present invention) and the like, and inputting a position of an isocenter (described later); and an image display unit 21 and an input unit And a control unit 23 for controlling the control unit 22 and the like. As shown in FIG. 1, the input unit 22 includes a keyboard 22a, a pointing device such as a mouse or a trackball, and can designate and input a predetermined position on an image displayed on the image display unit 21. It has become.

In the RTP device 2, as described above,
A lesion or the like in the CT image displayed on the image display unit 21 is checked, and the input unit 22 is used to set and input a so-called “target shape” or the like so as to follow the shape of the lesion ( At this time, factors such as the position, size, and number of the affected part are also considered.) By setting the target shape, adjustment of the irradiation field defining means (for example, a multi-leaf collimator) of the radiation therapy apparatus 4 (to be described later) (that is, definition of the actual irradiation field) is automatically performed.

Further, in the present RTP device 2, in addition to the setting and input relating to the target shape, the irradiation angle, the number of irradiation gates,
Alternatively, by calculating or determining the radiation dose or the like to be bombarded on the subject P, planning is performed so that the radiation concentrates on the lesion and the dose distribution around the lesion becomes appropriate. In addition, it is possible to formulate a general radiation treatment plan necessary for performing radiation treatment.

The X-ray simulator 3 comprises an X-ray tube 31, X
It is composed of a line detector 32, a top plate S2, an image storage device 33, and the like. Among these, the geometrical arrangement relationship of the X-ray tube 31, the top plate S2, and the like is based on other geometrical arrangements such as the distance between the radiation source in the irradiation head of the radiation therapy apparatus 4 and the isocenter or the subject P, which will be described later. In consideration of the above, it is configured to be substantially similar to this. The image storage device 33 includes the X-ray tube 31 and the X-ray detector 3.
It is possible to store other X-ray imaging images such as a fluoroscopic image of the subject P acquired by the method 2.

In this embodiment, the X-ray detector 3
Reference numeral 2 denotes a pixel arranged in a two-dimensional, more specifically, two-dimensional matrix (for example, a pixel electrode, a pixel capacitor (capacitor), a thin film transistor as a switching element, etc.), and direct incidence of X-rays. A so-called “FPD” composed of a photoelectric conversion member for converting into a signal.
(Flat Panel Detector) (flat detector).

Further, this X-ray simulator 3
It is possible to exchange data with the RTP device 2. Thereby, for example, a fluoroscopic image or the like acquired by the X-ray simulator 3 can be displayed on the image display unit 21 of the RTP device 2, and the like.
As will be described later, it is possible to formulate a radiation plan by the cooperative operation of the X-ray simulator 3 and the RTP device 2. The fact that data can be exchanged between the two devices 2 and 3 in this way is also relevant to the present invention, and will be described in detail later in the description of operation.

In such an X-ray simulator 3, based on the radiation treatment plan formulated by the RTP device 2,
It is possible to acquire a fluoroscopic image or the like of the subject P and finally confirm whether radiation treatment can be actually performed according to the plan. In addition, the X-ray tube 31 and the X-ray detector 32 are rotated to obtain various fluoroscopic images and the like of the subject P. It is also possible for the RTP device 2 to make a new formulation or the like. Specifically, the device user determines or re-determines (= corrects) the “irradiation angle” and “the number of irradiation gates” through the input unit 22 of the RTP device 2 while checking the perspective image and the like. And so on. In addition, based on the perspective image and the like, geometric conditions such as the distance between the radiation source in the radiation therapy apparatus 4 and the rotation center of the rotating gantry 41, the aperture of the multi-leaf collimator 412, and the like can be set. It is.

Finally, the radiation therapy apparatus 4 comprises a rotary base 41, a rotary support table 42 for supporting the rotary base 41, and a treatment table 43 on which the subject P is placed. Rotating stand 4
As shown in FIG. 1, 1 is a solid whose cross section is substantially L-shaped, and has an irradiation head 411 for irradiating the subject P with X-rays at one end of the L-shape. The irradiation head 411 includes an electron accelerator (not shown), an electron beam target, and the like (not shown). The X-rays applied to the subject P are generated when the electrons accelerated by the electron accelerator are applied to the electron beam target (as described above, the X-rays are involved in the X-ray generation in the radiation therapy apparatus 4). A configuration including the electron accelerator, the electron beam target, and the like is simply referred to as a “beam source” in this specification.

The irradiation head 411 is also provided with an irradiation field stop (irradiation field defining means) not shown in FIG. 1 for defining in what area the generated X-ray is irradiated onto the subject P. Have been. The irradiation field stop is composed of, for example, a pair of stop blocks, a multi-leaf collimator that is arranged close to the stop blocks, and also includes a plurality of plate-like leaves provided in a pair. Of these, the stop block is a "stop" for roughly defining the irradiation field, each of a pair of opposing blocks having a unitary structure.

The multi-leaf collimator is an "aperture" for more precisely defining an irradiation field. More specifically, as shown in FIG. 2, the multi-leaf collimator 412 includes a plurality of plate-like leaves 412 a forming two sets of leaf groups 412 A and 412 B, and the plurality of plate-like leaves 4.
Each of the drive mechanisms 12a includes a drive mechanism (not shown) that moves each of the drive sections 12a separately and in a lengthwise direction facing each other or away from each other (see arrows Z1 and Z2 in the drawing).
According to the multi-leaf collimator 412 having such a configuration, it is possible to arbitrarily define an X-ray irradiation area that can almost match the lesion T having various shapes such as the elliptical shape shown in FIG. Is possible.

The image display unit 21 of the RTP device 2
An image similar to that shown in FIG. 2 may be displayed in the plan formulation screen displayed above.

The irradiation head 411 has a rotatable portion as shown by an arrow A in FIG. 1, and adjusts an X-ray irradiation area through adjustment of the angle (or rotation) position of the multi-leaf collimator 412. It is also possible to do.

On the other hand, the rotation support base 42 is, as described above, a substantially L-shaped three-dimensional rotation base 41,
The arm 41a without the irradiation head 411 is
As shown by the arrow B in FIG. A point at which the axis of the rotation shaft 421 and the axis of the rotation axis of the irradiation head 411 (both are indicated by broken lines in FIG. 1) corresponds to the “isocenter” on the radiotherapy apparatus 4. In addition, the treatment table 43
A top plate S3 movable in the body axis direction of the subject P (arrow C1 in FIG. 1) is provided, and the top plate S3 is vertically moved as indicated by an arrow C2 in FIG. Rotational movement around the center is possible.

The X-ray CT apparatus 1 has a top S1 and the X-ray simulator 3 has a top S2.
And that the radiation therapy apparatus 4 is provided with the top plate S3, respectively.
S2 and S3 may be in a form commonly used in each of the devices 1, 3 and 4. That is, each device 1, 3
And 4, a common top plate is introduced into the cavity 11a of the CT gantry 11, and sometimes the X-ray simulator 3
May be arranged between the X-ray tube 31 and the X-ray detector 32, and in some cases, may be located in a region where the X-ray can be irradiated by the irradiation head 411 of the radiation therapy apparatus 4. . With such a configuration or operation, various operations as described with respect to the top plate S3 and the like are appropriately performed, and the X-ray CT apparatus 1, the X-ray simulator 3, and the radiation therapy apparatus 4
Can be easily realized by suitably arranging in the same space.

In the radiotherapy apparatus 4, the X-ray CT
Each plate leaf 412a constituting the multi-leaf collimator 412 based on a radiation treatment plan formulated using the apparatus 1, the RTP apparatus 2, and the X-ray simulator 3.
After performing other adjustments such as the arrangement of the X-rays, X-rays are emitted from the radiation source, and the X-rays are irradiated on the subject P to perform the treatment.

The operation and effect of the radiotherapy system according to the present embodiment, which is the above configuration example, will be described below with reference to the flowchart shown in FIG. It is an object of the present invention to formulate an appropriate radiation treatment plan when respiratory movement is observed in an organ or a lesion in the fluoroscopic image acquired by the X-ray simulator 3. Therefore, the following description will focus on this point.

First, as shown in step S1 of FIG.
An X-ray is emitted from the X-ray tube 31 of the X-ray simulator 3 and is emitted to the subject P, and a fluoroscopic image is created based on the result of the X-ray detector 32 detecting the X-ray transmitted through the subject P. I do. This perspective image is displayed on the image display unit 2 of the RTP device 2.
1 is displayed. It is assumed that this fluoroscopic image includes a lesion to be subjected to radiotherapy.

Next, as shown in step S2 in FIG. 3, in the X-ray simulator 3, a predetermined time corresponding to the interval between the expiration and the inspiration of the subject P with respect to the fluoroscopic image acquired as a so-called cine image. The perspective images acquired during the interval are recognized as so-called “plural perspective images” and stored in the image storage device 33, and the stored perspective images are superimposed on the image display unit 21. indicate. That is, "addition" of the perspective images acquired during the time interval is performed.

The above-mentioned predetermined time interval, ie, the interval between expiration and inspiration, is specifically, for example,
What is necessary is just to set "4 seconds" or the like. The setting of the time interval may be freely performed by the device user through the input unit 22 or the like.

When such superimposed display or addition of the perspective images is performed, an image as shown in FIG. 4 is obtained. That is, according to the image shown in FIG. 4, it is possible to confirm that the lesion T in the fluoroscopic image acquired during the interval changes its size due to the respiration of the subject P. From the state of the change, the affected part T becomes the largest (refer to the symbol Tb in the figure, hereinafter referred to as “maximum affected part Tb”) and the smallest (see the symbol Ts in the figure, hereinafter “minimum”). (Referred to as “lesioned portion Ts”).
Is indicated by a bold solid line).

Further, in the present embodiment, in addition to the display as shown in FIG. 4, a scale G may be displayed so as to surround the lesion T as shown in FIG. 5, for example. Good. The scale plate G (scale) is scale-converted in accordance with the degree of expansion or reduction of the image with respect to the real object. Therefore, the user of the device
Only by reading the scale, the degree of change of the lesion T, that is, the “actually measured value” of the respiratory movement amount can be accurately and easily estimated. In this regard, conventionally,
In view of the fact that only the cross board J is displayed (see FIG. 7), it is apparent that the movement amount is easily grasped.

Incidentally, it is convenient to display the scale plate G such that the display position can be freely and freely changed on the screen on the image display unit 21 (see arrows in FIG. 5, among them). The curved arrow also indicates that the scale G can be rotated. In this way, not only can the movement amount be confirmed and determined more accurately, but also the position of the subject P on the top plate S2 can be adjusted to match the (fixed) display position of the scale plate G. As the lesions overlap on the scale display,
It is not necessary to take unreasonable measures such as making changes.

Thereafter, as shown in step S3 in FIG. 3, the user of the apparatus checks the amount of respiratory movement of the changing lesion T based on the image shown in FIG.
Set and input the target shape (irradiation field) suitable for R
What is necessary is just to perform through the input part 22 in TP apparatus 2. In this case, “setting / inputting a target shape suitable for the lesion T” simply means, for example, as shown in FIG. 6, that the target shape R1 is set so as to surround the outer peripheral edge of the maximum lesion Tb. It is also conceivable to set a target shape R2 such as to sew an intermediate position between the outer peripheral edge of the maximum lesion Tb and the outer peripheral edge of the minimum lesion Ts. In short, regarding the setting of the target shape, a “preferred” one cannot be generally determined in accordance with the properties of the lesioned part T and the like, so that the discretion of a doctor or other device user can be appropriately reflected. It is preferable to keep it.

Further, with regard to the setting of the target shape, the outer peripheral edges of the maximum lesion Tb and the minimum lesion Ts are determined by using an appropriate image processing device or the like.
The control unit 23 of the TP device 2 may automatically recognize and the control unit 23 automatically sets the target shape based on the recognition. In this case,
If the device user determines that the automatically set target shape is preferable, the device user may use the target shape as it is, or if it determines that the target shape is not preferable, It goes without saying that correction input and the like may be performed.

Although only the case where the "size" of the lesion T changes has been described above, the "position" of the lesion T may change in some cases. Even in such a case, the use of the image as shown in FIG. 4 or FIG. 5 allows the setting and input of the movement amount or the target shape to be performed accurately as described above. Needless to say.

Further, in the image display of FIGS. 4, 5 and 6, etc., it is preferable that the arrangement of the plate-shaped leaves 412 of the multi-leaf collimator 412 is superimposed and displayed. In this case, in addition to the usage (new formulation of a radiation treatment plan) of superimposing the arrangement status corresponding to the set target shape, the plate-shaped leaf 412 based on the radiation treatment plan once planned in the RTP device 2. By superimposing the arrangement status of (1), it is possible to confirm (simulate) whether or not the plan is preferable (modification of the radiation treatment plan).

After that, the radiation treatment apparatus 4 refers to the target shape set as described above, determines the rotation angle of the rotary base 41 or the position of the top plate S3, and determines the multi-leaf collimator 412 in the irradiation head 411. Then, the setting of the irradiation area by the adjustment is performed, and the radiation treatment is actually performed.

As described above, according to the radiotherapy system or the X-ray simulator 3 of the present embodiment, even when the position or size of the lesion T changes due to respiratory movement, accurate radiotherapy planning can be performed. Formulation is possible. In addition, this makes it possible to accurately perform the actual radiation treatment scheduled later. In this regard, conventionally, the “estimation” of the irradiation field “margin”
It is clear that the superiority of the radiotherapy system and the like in the present embodiment (shift from the conventional judgment based on “experience” to the judgment based on quantitative measurement) is considered. .

In particular, in the X-ray simulator 3 of the present embodiment, the FPD is employed for the X-ray detector 32, so that the X-ray detector 32 is different from the conventional image intensifier (“II”). There is no problem of magnetostriction due to terrestrial magnetism, and since data related to images is digitally processed, there is no problem such as deterioration of image quality. According to the use of the FPD,
Unlike the related art, there is no need to perform target setting / input while performing fluoroscopic imaging, and an effect of reducing the amount of exposure to the subject P can be obtained. This effect is particularly effective in, for example, simulation of conformal irradiation (for example, images are collected in advance by the X-ray simulator 3 at every 2 ° change in inclination, and the RTP device 2 plans the images on the images. Similarly, the arrangement status of the plate-shaped leaf 412 of the multi-leaf collimator 412 for each change of the inclination angle of 2 ° is displayed in a superimposed manner).

In the radiotherapy system according to the above embodiment, the main purpose is to specify the shape or the like of the lesion T to be irradiated. However, in some cases, the radiotherapy system has high sensitivity to normal tissues and X-rays. A function of setting and inputting an area as a “non-irradiation area” may also be provided. The setting / input can be performed in exactly the same manner as the setting / input of the target shape R1 or R2 described above.

In the above embodiment, the case where only one target shape is set / input has been described. However, for example, when there are a plurality of lesions, or when the size of the lesion is relatively large, etc. A target shape corresponding to each of the plurality of lesions may be set, or a plurality of target shapes that divide the large lesion may be set.

Further, in the above description, the fluoroscopic image acquired by the X-ray simulator 3 is displayed on the image display unit 21 of the RTP device 2, but in the present invention, in such a form, For example, the image display unit and the input unit are provided on the X-ray simulator 3 side independently of those in the RTP device 2, and the confirmation of the final radiotherapy plan is performed by the X-ray simulator 3 alone. It is good also as a structure which can be performed.

[0047]

As described above, according to the radiotherapy system and the X-ray simulator of the present invention, an accurate radiotherapy plan can be obtained even when the position or size of a lesion changes due to respiratory movement. Therefore, more accurate radiation therapy can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration example of a radiotherapy system according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a configuration example of a multi-leaf collimator among irradiation field defining means installed in the radiation therapy apparatus shown in FIG.

FIG. 3 is a flowchart illustrating an example of a process of formulating a radiation treatment plan, particularly defining an irradiation field.

FIG. 4 is an explanatory diagram showing a state of a perspective image superimposed and displayed.

FIG. 5 is an explanatory diagram showing a state in which a scale plate is further superimposed on FIG. 4;

FIG. 6 is an explanatory diagram showing a state where setting and input of a target shape are performed with respect to FIG. 4;

FIG. 7 is an explanatory diagram showing a cross board used for estimating the amount of respiratory movement in conventional radiotherapy planning.

[Explanation of symbols]

 P subject 1 X-ray CT apparatus 11 gantry 11a cavity 12 X-ray tube 13 X-ray detector 14 data collection unit S1 top plate 2 RTP device (radiation treatment plan formulation device) 21 image display unit 22 input unit 23 control unit Reference Signs List 3 X-ray simulator 31 X-ray tube 32 X-ray detector S2 Top plate 4 Radiation therapy device 41 Rotation stand 411 Irradiation head 412 Multi-leaf collimator 412a Plate leaf 42 Rotation support table 43 Treatment table S3 Top plate G Scale plate

Claims (3)

[Claims] 1. An X-ray simulator, a radiation treatment plan formulation device capable of formulating a radiation treatment plan based on an X-ray fluoroscopic image acquired by the X-ray simulator, and radiation comprising at least a radiation treatment device In the treatment system, a storage unit that stores a plurality of perspective images acquired during a predetermined time interval by the X-ray simulator, an image display unit that superimposes and displays the plurality of perspective images, An input means for setting and inputting a target shape that defines a radiation irradiation area of the radiation therapy apparatus with respect to a target site in (1). 2. The radiation treatment planning system according to claim 1, wherein a scale plate is further superimposed and displayed on the superimposed display. 3. The X-ray simulator includes at least an X-ray tube that generates X-rays, and an X-ray detector that emits the X-ray tube and detects X-rays transmitted through a subject. The radiation treatment planning system according to claim 1, wherein the line detector is a planar detector having two-dimensionally arranged pixels.