JP2009148495A - Radiotherapy information service system and radiotherapy information service program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiotherapy information service system and a radiotherapy information service program which can measure and display a radiation dose by acquiring scattered ray data in real time during radiotherapy, and by using the data. <P>SOLUTION: A detector having a collimator is installed in the position forming a prescribed angle (scattering angle) with respect to a therapeutic X-ray beam, scans a three-dimensional area of the interior of a subject by selectively detecting only scattered rays coming in that direction, and by executing the detection while maintaining the angle formed by the axis of a therapeutic X-ray beam radiated from the irradiation section and the detection surface of the detector. The system reorganizes scattered ray volume data by using three-dimensional scattered ray data relating to the obtained prescribed scattering angle, converts the scattered ray volume data to absorbed dose volume data showing the three-dimensional distribution of the absorbed radiation dose, and generates an absorbed radiation dose image. The generated radiation dose image is synthesized with a form image or the like (CT image or the like) for example and displayed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention measures the scattered X-rays generated when the therapeutic radiation is irradiated in the radiotherapy apparatus, and uses this to obtain the radiation for acquiring the absorbed dose three-dimensional distribution absorbed in the affected area with high accuracy. The present invention relates to a treatment information providing system and a radiation treatment information providing program.

  In order to perform radiotherapy accurately, there is a demand for monitoring the subject from the same viewpoint as the irradiation focus. In most radiotherapy devices currently in use, an image sensor called EPID (= Electronic Portal Imaging Device) that enables imaging with high-energy radiation is placed at a position facing the irradiation head across the isocenter. Thus, X-ray fluoroscopic images (hereinafter abbreviated as MV images) using MeV energy photons viewed from the same viewpoint as the irradiation focus can be taken. Using this, if transmission images are collected all around the rotation axis of the irradiation head, it is possible to perform image reconstruction by therapeutic radiation cone beam CT (= Mega-volt Cone Beam CT). It is possible to actually measure the 3D distribution of the total attenuation coefficient for photons with Another method is to obtain a “three-dimensional distribution image of the total attenuation coefficient for photons with keV energy” using normal diagnostic X-ray CT (= kilo-volt CT). From the quantitative relationship with the attenuation coefficient in MeV energy and the foreseeing information of "element distribution that constitutes an organ", "a three-dimensional distribution of total attenuation coefficient for photons having MeV energy" is also estimated.

By the way, when the subject is a living body, the tissue is roughly classified into bone, muscle, and fat, and their mass energy absorption coefficient [cm ² / g] is dependent on photon energy [MeV], as shown in FIG. Thus, there is a feature that there is almost no difference in the region of several MeV energy. For this reason, radiotherapy using X-rays with several MeV energy has a drawback that it hardly gives contrast to living tissue. Apart from this, a method of monitoring using X-rays of several tens of keV energy that is easy to contrast has also been put into practical use. However, since the radiation direction of the bremsstrahlung has energy dependency, there is a disadvantage that a keV energy X-ray tube and an X-ray image detector must be provided separately, and the viewpoint is different from the irradiation focus.

In addition, as a well-known document relevant to this application, there exist the following, for example.
JP, 5-146426, A The art which this patent document discloses detects a scattered ray of a X-ray subject, and obtains a tomographic image of a subject. It is characterized by reconstructing and obtaining a three-dimensional scattered radiation image of a subject by scanning with a pencil beam. In other words, this technology assumes only a pencil-shaped beam, and does not obtain a scattered image (spatial distribution of the dose of the treatment beam) of the region through which the beam with a finite width used in X-ray therapy has passed. . In addition, scattering of high-energy treatment beams (several MeV) within a subject is superior to forward scattering, so it is difficult to distinguish scattered and transmitted rays if a detector is placed in the direction of the incident X-ray, and scattered rays are detected. Correction processing is essential.

  However, in the conventional radiotherapy apparatus, it is assumed that the “total attenuation coefficient three-dimensional distribution” inside the subject created in advance by the above-described method and that the radiation is normally irradiated at the time of treatment in the same way as at the time of calibration. The absorption dose distribution is calculated from the "irradiation dose three-dimensional distribution" data created at the time of treatment planning, and the absorbed dose distribution image is displayed from the direction desired by the operator. .

  That is, the information provided by the prior art represents an “estimated absorbed dose distribution image” when it is assumed that radiation irradiation was performed as planned, and is not based on data actually measured during treatment. Therefore, it does not cover the information area at the time of treatment planning. For this reason, error factors such as “measurement error of total attenuation coefficient three-dimensional distribution”, “absorption dose calculation error”, and “error of radiation intensity during planning and treatment” may be introduced.

  The present invention has been made in view of the above circumstances, and obtains scattered radiation data in real time during radiotherapy, and uses this to provide a radiotherapy information providing system capable of actually measuring and displaying the absorbed dose, and The purpose is to provide a radiation therapy information provision program.

  In order to achieve the above object, the present invention takes the following measures.

  According to the first aspect of the present invention, an irradiation unit that irradiates a subject with a planar therapeutic radiation beam, and a scattered ray of the subject that is generated due to the therapeutic radiation beam is a predetermined scattering angle. Detection means for collecting scattered radiation data by detecting from the direction, and the position of the axis of the therapeutic radiation beam and the angle of the detection surface of the detection means with respect to the irradiation direction of the therapeutic radiation beam, while maintaining a constant angle The object is three-dimensionally scanned by moving the position of the detection surface of the detection means, and data acquisition control means for acquiring three-dimensional scattered radiation data, and based on the three-dimensional scattered radiation data, in the subject Image reconstruction means for reconstructing scattered radiation volume data indicating a three-dimensional distribution of scattered radiation generation density, and an absorbed dose image or an object in the subject based on the scattered radiation volume data Is a radiation therapy information providing system comprising: an image generating unit that generates a scattered radiation generation density image; and a display unit that displays the absorbed dose image or the scattered radiation generation density image.

  According to an eighth aspect of the present invention, a scattered light of a subject generated due to a planar therapeutic radiation beam irradiated to a subject is detected by a computer and scattered from a predetermined scattering angle direction. The detection function for collecting line data and the angle of the detection surface of the detection means with respect to the irradiation direction of the therapeutic radiation beam are kept constant, and the position of the axis of the therapeutic radiation beam and the detection surface of the detection means Based on the data acquisition control function for acquiring the three-dimensional scattered radiation data, and the three-dimensional scattered radiation data, the subject is three-dimensionally scanned by moving the position, and the scattered radiation generation density in the subject is measured. Based on the scattered ray volume data, an image reconstruction function for reconstructing scattered ray volume data showing a three-dimensional distribution, and an absorbed dose image or scattered ray emission in the subject. A radiotherapy information providing program comprising: an image generation function for generating a raw density image; and a display function for displaying the absorbed dose image or scattered radiation generation density image.

  As described above, according to the present invention, a radiation therapy information providing system and a radiation therapy information providing program capable of actually measuring and displaying an irradiation dose are obtained by acquiring scattered radiation data in real time during radiation therapy and using this. can do.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant description will be given only when necessary.

[Principle and method]
The radiation therapy information providing system according to the present embodiment measures scattered X-rays from the subject based on radiation irradiated to the subject, and based on this, how much dose is given to which part of the subject. Information that objectively indicates whether the irradiation has been performed is acquired. The principle and method are as follows.

FIG. 2 shows a graph representing a mass absorption coefficient [cm ² / g] with respect to photon (= X-ray) energy [MeV] in the case of water. FIG. 3 is a schematic diagram for explaining the principle of Compton scattering. According to FIG. 2, Compton scattering and electron pair generation among X-ray (= photon) biological tissue (approximately 70% by weight is water, so the whole can be regarded as almost water) with several MeV energy. Are comparable. In Compton scattering, the relational expression when the energy of the incident photon is E ₀ [MeV], the scattering angle is θ [deg], and the energy of the scattered photon is E _θ [MeV] is as follows: It is known.

Assuming that θ is a fixed angle of θ ≧ 90 [deg], if Compton scattering, for example, E ₀ = 5 [MeV], then scattered photons having an energy of E _θ ≦ 0.464 [MeV] (ie, scattered rays) ) Occurs. In addition to this, electron pair generation generates electrons and positrons of 0.511 [MeV] or more, and finally, photons of 0.511 [MeV] or more are generated by collision of the positrons and electrons, and the electrons cause bremsstrahlung. . That is, when viewed as a total, backscattered photons that are substantially proportional to the number of incident photons are detected.

  Since the subject is irradiated with photons with MeV energy during radiation therapy, if the image sensor can detect the scattered radiation that can identify the generation position during radiation irradiation, the "total attenuation coefficient 3D" By correcting using “distribution data”, “absorbed dose three-dimensional distribution” can be actually measured from data measured during radiation irradiation.

  The present invention provides an apparatus and method for acquiring a three-dimensional scattered image by acquiring a two-dimensional scattered radiation image and scanning it. Furthermore, by adding a correction, it is also possible to obtain an “absorbed dose three-dimensional distribution” due to therapeutic radiation.

[Constitution]
FIG. 4 shows a block diagram of the radiation therapy information providing system 1 according to this embodiment. FIG. 5 is a diagram showing a measurement form of scattered radiation of the radiation therapy information providing system 1. As shown in the figure, the radiation therapy information providing system 1 includes a radiation irradiation system 2, a radiation detection system 3, a data acquisition control unit 4, a data processing system 5, a display unit 6, a storage unit 7, an operation unit 8, and a network. I / F9 is provided. The radiation irradiation system 2 and the radiation detection system 3 are installed on a gantry, and can be arranged at an arbitrary position with respect to the subject by moving and rotating the gantry. Further, the data acquisition control unit 4, the data processing system 5, the display unit 6, the storage unit 7, the operation unit 8, and the network I / F 9 are installed in the main body (housing) of the radiation therapy information providing system 1, for example.

[Radiation irradiation system]
The radiation irradiation system 2 includes a power supply unit 201, an irradiation unit 203, a timing control unit 205, and a gantry control unit 207.

  The power supply unit 201 supplies power to the irradiation unit 203 according to the control from the data acquisition control unit 4.

  The irradiation unit 203 is a radiation irradiation apparatus having, for example, a linear accelerator (linac) mechanism. In particular, the irradiation unit 203 has a mechanism for shaping the radiation to be irradiated into a thin planar shape. Details of the configuration of the irradiation unit 203 will be described later.

  The timing control unit 205 controls the power supply unit 201 so that power is supplied to the irradiation unit 203 at a predetermined timing according to the control from the data acquisition control unit 4.

  The gantry control unit 207 controls the movement position / rotation position of the gantry in accordance with, for example, a control instruction from the operation unit 8 or the data acquisition control unit 4.

<Configuration of Irradiation Unit 203>
As shown in FIG. 5, in the irradiation unit 203, first, the thermal electrons emitted from the cathode are accelerated to an energy of several hundred keV by the electron gun 203b provided at one end of the acceleration tube 203a. Next, the microwave generated in the klystron 203c is guided to the accelerating tube 203a using a waveguide, where the thermal electrons are accelerated until reaching an energy of several MeV. The accelerated thermoelectrons are changed in direction by a bending magnet 203d and collide with the transmission target 203e. At this time, X-rays with energy of several MeV are emitted by the bremsstrahlung. This X-ray is adjusted so as to be an X-ray having substantially uniform intensity over the entire radiation direction by passing through an equalizer (flattening filter) 203f. The radiation direction of this X-ray is first narrowed by a collimator called “jaw” (described later), and then the shape of the affected area is further increased by a multileaf collimator (= multileaf collimator) (described later). Is shaped into an irradiation shape close to, and finally the affected area is irradiated.

  6 and 7 are diagrams for explaining a mechanism of the irradiation unit 203 for shaping the radiation to be irradiated into a thin planar shape.

  As shown in each figure, in the main irradiation unit 203, a planar X-ray beam having a very thin thickness using a jaw 203g in order to limit the irradiation region B0 of MeV energy X-rays that have passed through the equalizer 203f. Set to B1. A member that bisects the cylinder along the central axis is fitted on the end face of the jaw 203g, and the angle is always controlled by the timing control unit 205 so that the end face always passes through the irradiation focus. ing. Therefore, no “half shadow” is produced by the jaw 203g. Next, the X-ray beam B1 shaped into a thin flat shape is further narrowed by a multi-leaf collimator 203h controlled to have an opening shape that matches the contour of the treatment site, and shaped into a thin flat shape. An X-ray beam B2 (in the case of conformal irradiation, the opening shape is the same as the contour of the treatment site) is generated.

  Note that the inside of the irradiation region of the X-ray beam B2 shaped into a thin flat surface is a region where energy is irradiated and scattering is promoted. In this sense, the cross section of the subject irradiated with the X-ray beam B2 is X-rays. It can be understood as an excitation cross section due to.

[Radiation detection system]
The radiation detection system 3 includes a detector 301, a parallel collimator 303, a moving mechanism unit 305, and a position detection unit 307.

  The detector 301 is a semiconductor detector capable of detecting X-rays of several hundred keV, a detector composed of an imaging plate and an imaging device, and the like, and scattered X-rays from the subject based on radiation irradiated to the subject. Is detected. A preferable size of the detector, an arrangement angle with respect to the irradiation beam axis, the number of pixels, and the like will be described later.

  The parallel collimator 303 is a diaphragm device for selectively detecting only scattered rays coming from a predetermined direction. A preferable shape, grid size, and the like of the parallel collimator 303 will be described later.

  The moving mechanism unit 305 has an angle of the detection surface of the detector 301 with respect to the irradiation beam axis of the irradiation unit 203 (that is, an angle between the irradiation beam axis and the normal of the detection surface of the detector 301), and a radiation beam axis as a center. It is a moving mechanism unit for moving the position and angle of the detector 301 in order to control the rotation angle of the detector 301, the distance between the subject and the detection surface of the detector 301, and the like.

  The position detection unit 307 is an encoder for detecting the position of the detector 301.

<Detector 301 and parallel collimator 303>
FIG. 8 is a diagram for explaining the positions and angles of the detector 301 and the parallel collimator 303 with respect to the center line L that bisects the thickness of the X-ray beam B2 irradiated to the subject (shaped into a thin flat surface). FIG. FIG. 9A is a view of the parallel collimator 303 viewed from the incident side of the scattered radiation, and FIG. 9B is a perspective view of the detector 301 provided with the parallel collimator 303.

  X-rays focused in two stages are irradiated onto the patient's body, but pass through the path of the body surface → the affected area → the opposite body surface. In the case of radiation therapy, X-rays with MeV energy are irradiated, so it is considered that more than half of the scattered radiation is caused by “Compton scattering”. It is known that the relationship of the above-described formula (1) is established between the energy of the component resulting from the Compton scattering and the scattering angle θ. Therefore, in order to make the energy range of the scattered radiation to be measured substantially the same (that is, to detect only the scattered radiation in which the scattering angle θ can be regarded as substantially constant), the position shown in FIG. A detector 301 with a parallel collimator 303 (parallel grid) as shown in FIG.

A positional relationship in which an angle α (= 180−θ) [deg] formed by a center line L that bisects the thickness of the X-ray beam B2 and a straight line M indicating the viewing direction of the parallel collimator is always a constant value α _0. The scattered radiation shall be measured while keeping it. At this time, the focus of irradiation of therapeutic X-rays is F, and the isocenter is point O. When the angle formed by the straight line L ₀ and the straight line L passing through the focal point F and the point O is φ [deg], the scattered radiation data is collected by changing φ while always satisfying the condition of α = α ₀ (constant). . Through the above operation, scattered radiation images of the entire region irradiated with therapeutic radiation can be collected as volume data (= three-dimensional data).

<Movement mechanism unit 305>
FIG. 10 is a diagram illustrating an example of a moving mechanism unit 305 for moving the detector 301 and the parallel collimator 303. As shown in the figure, the moving mechanism unit 305 is a rail for allowing the detector 301 and the parallel collimator 303 to move on a concentric circle centered on the focal point F in front of the irradiation head of the radiation irradiation unit 203. To move along. At this time, the angle α formed by the straight line L and the line of sight M of the parallel collimator always maintains the relationship of α ₀ (constant) (that is, the relative positional relationship between the gravity center position of the irradiation unit 203 and the gravity center position of the detector 301). the by changing the angle φ between the bisector L and the straight line L ₀ of the thickness of the X-ray beam B2 which is shaped to hold the left) thin planar shape, for collecting scattered radiation image of the subject.

FIG. 11 is a diagram for obtaining a relational expression between the scattered radiation data acquired by the movement of the detector 301 and the parallel collimator 303 using the moving mechanism unit 305 shown in FIG. 10 and the coordinates of the scanning space. As shown in FIG. 11, the horizontal coordinate of the detector 301 with the parallel collimator 303 is x ′, the vertical coordinate is Y ′, the distance from the focal point F to the center point O ′ of the detector 301 is d ₀ , Let f be the distance between the focal point F of irradiation and the isocenter O. The Cartesian coordinate system with the isocenter O as the origin is O-XYZ, the X coordinate of any point Q in the coordinate system is x, the Y coordinate is y, and the Z coordinate is z. Other symbols should be used in accordance with what has been explained so far. From a simple geometric calculation, the coordinates of the arbitrary pixel S in the coordinate system O′-X′Y ′ in the scattered radiation image captured by the detector 301 is (x ′, y ′), and the corresponding object When the coordinates of the point Q in the coordinate system O-XYZ are set as (x, y, z), their correspondence is as shown in the following equations (2-1), (2-2), and (2-3). Led to.

  These equations mean that one-to-one mapping is possible between any pixel of the detector 301 and the treatment space of the radiation therapy apparatus, and three-dimensional information of the subject can be acquired. In addition, since the pixel value (luminance) is proportional to the number of photons of scattered radiation, if the correction is made based on the above-mentioned total attenuation coefficient three-dimensional distribution data, the absorbed dose three-dimensional distribution can also be obtained from the actually measured data during treatment.

FIG. 12 is a diagram illustrating another example of the moving mechanism unit 305 for moving the detector 301 and the parallel collimator 303. As shown in the figure, the moving mechanism unit 305 assumes that the center point O ′ (or the position of the center of gravity) of the detector 301 with the parallel collimator 303 is fixed with respect to the irradiation head, and the X-ray beam B2 The scattered line can be measured while maintaining the angular relationship that the angle α (= 180−θ) [deg] formed by the center line L and the straight line M indicating the viewing direction of the parallel collimator 303 is always a constant value α _0. In addition, in synchronization with the scanning angle φ of the center line L, imaging is performed while changing the line-of-sight direction of the detector 301 around the position of the center of gravity. That is, the detection surface of the detector 301 (and the opening surface of the parallel collimator 303) is rotated.

FIG. 13 is a diagram for obtaining a relational expression between the scattered radiation data acquired by the movement of the detector 301 and the parallel collimator 303 using the moving mechanism unit 305 shown in FIG. 12 and the coordinates of the scanning space. As shown in FIG. 13, the coordinates of the center point O ′ in the O-XYZ coordinate system are (0, y ₁ , z ₁ ), and O′-X′Y ′ at an arbitrary point S on the X-ray image detector. Let the coordinates in the coordinate system be (x ', y'). The other symbols should be used in the same way as before. From a simple geometric calculation, the coordinates of any pixel S in the scattered radiation image captured by the X-ray image detector is (x ', y'), and the coordinates of the corresponding point Q of the subject are (x , y, z), the corresponding relationship is obtained as in the following equations (3-1), (3-2), and (3-3).

  Although these relationships are slightly more complicated than the examples shown in FIGS. 10 and 11, it is possible to obtain three-dimensional information because they can also be handled one-to-one. In addition, since the pixel value (= luminance) is proportional to the number of photons of scattered radiation, if the correction is made based on the above-described total attenuation coefficient three-dimensional distribution data, the absorbed dose three-dimensional distribution can be obtained from the actually measured data during treatment. .

  In each example of the movement mechanism unit 305 described above, the opening / closing movement direction of the jaw 203g is the gantry rotation axis direction of the radiation therapy apparatus (the direction parallel to the X axis according to the coordinate method shown in FIGS. 11 and 13). Is shown only in the case of being parallel to the image, but the scattered radiation image is exactly the same even if the direction is orthogonal to this (the direction parallel to the Y axis in accordance with the method of taking the coordinates in FIGS. 11 and 13). Can be obtained, or absorbed dose three-dimensional distribution can be obtained.

[Data acquisition control unit]
The data acquisition control unit 4 performs comprehensive control relating to scattered radiation measurement during radiation therapy. For example, the data acquisition control unit 4 obtains a signal from the timing control unit 205 of the radiation irradiation system 2 and transmits a scattered radiation measurement start trigger or a detection data transmission trigger to the radiation detection system 3. The radiation therapy information providing system 1 is controlled statically or dynamically for scattered radiation measurement, data processing, image display, network communication, and the like. In addition, for example, the data acquisition control unit 4 optimizes the scan time according to the irradiation time of each irradiation based on the treatment plan received from the radiation treatment planning apparatus via the network, if necessary, or the radiation irradiation system. The beam axis of the X-ray beam B2 and the orientation of the detector 301 and the collimator 305 (that is, the angle formed by the beam axis of the X-ray beam B2 and the normal line of the detector 301) are made constant in accordance with the radiation irradiation timing 2. As such, the movement mechanism unit 305 is controlled.

[Data processing system]
The data processing system 5 includes a correction processing unit 501, a reconstruction processing unit 503, a conversion processing unit 505, and an image processing unit 507.

  The correction processing unit 501 performs data calibration processing, correction processing for removing noise, correction for signal attenuation caused by propagation of therapeutic radiation and scattered radiation in the subject (attenuation correction) as necessary. Perform processing. The details of the attenuation correction process executed by the correction process 501 will be described in detail later.

  The reconstruction processing unit 503 executes an image reconstruction process using the scattered radiation image data detected by the radiation detection system 3, and shows a scattered radiation volume indicating a three-dimensional distribution of the density of the number of scattering events (number of occurrences of scattering). Get the data. As the reconstruction formula, the relational expressions represented by the above (2-1), (2-2), (2-3), (3-1), (3-2), and (3-3) are given. Use the reconstruction method used.

  The conversion processing unit 505 converts the three-dimensional image data obtained by the image reconstruction process into absorbed dose volume data indicating a three-dimensional distribution of absorbed radiation dose (absorbed dose).

  The image processing unit 507 generates absorbed dose image data indicating the distribution of the absorbed radiation dose (absorbed dose) regarding a predetermined part of the subject using the absorbed dose volume data or the like. When the absorbed dose image is displayed by fusion, the image processing unit 507 performs image composition processing using the absorbed dose volume data or the like.

<Attenuation correction>
FIG. 14 is a diagram for explaining the concept of attenuation correction.

  The attenuation correction is executed based on the relative positional relationship between the subject and the scattered radiation detection system 3. Consider the process from when the X-ray beam B2 shaped into a thin flat surface enters the patient's body and then escapes. As shown in FIG. 14, the scattered radiation detected by each pixel of the detector 301 with the parallel collimator 303 is shaped into a thin line and a straight line N passing through the pixel and parallel to the line-of-sight direction M of the parallel collimator. Brightness considering the "collection of images from a perspective direction" and "attenuation effect by living tissue" because it can be identified as being emitted from the intersection P with the plane plane that bisects the thickness of the "X-ray beam" When the value is corrected, “scattered radiation at an arbitrary position in the living body” can be actually measured. The scattered radiation means that there was an interaction with the atom at the point Q where it was generated, and it also means that energy absorption occurred simultaneously with the scattering. Since this scattered radiation may be considered to be proportional to the absorbed dose D [Gy] (= D [J / kg]) at the point Q, the escape point R of the body surface from the point Q (these points are The integrated value of the total attenuation coefficient along the path to the above-mentioned straight line N) is calculated from “total attenuation coefficient three-dimensional distribution data” obtained in advance, and correction processing using this (= point Q) To the pixel value is calculated by multiplying the reciprocal of the total attenuation along the path from point to point R by the pixel value. The attenuation by the total attenuation coefficient can be easily obtained because it is expressed by an exponential function.

  The above correction alone is not sufficient to visualize the internal structure of the living body, and the total attenuation coefficient along the path from the entry point P to the point Q of the “thin X-ray beam shaped into a thin plane” is also corrected. It is obtained by attaching processing (= calculation of the reciprocal of the total attenuation along the path from the point P to the point Q and the reciprocal of the total attenuation along the path from the point Q to the point R to the pixel value). it can.

Other than this, the following method can be considered as a simple visualization method of the internal structure of the living body without using the “total attenuation coefficient three-dimensional distribution data”. First, as means for monitoring the irradiation X-ray intensity (that is, the X-ray intensity at the stage where no attenuation occurs immediately before irradiation of the subject), for example, between the equalizer 203f and the jaw 203g shown in FIG. A “dose monitor” (for example, a semiconductor radiation detector or a radiation-resistant camera with a scintillator) is provided to detect and record the irradiation X-ray intensity I ₀ in real time. This signal is proportional to the number of photons N ₀ of X-rays before being attenuated. If the proportionality constant is γ _0, it can be expressed as the following equation (4).

In the present system 1, as shown in FIG. 14, the X-ray beam shaped into a thin flat surface enters the subject from the intrusion point P, is scattered at the point Q where the main scattering occurs, and is “parallel” from the escape point R. There is a phenomenon of radiation toward an “X-ray image detector with a collimator”. Now assume that "the attenuation from point Q to point R is almost negligible", and further "the intensity of scattered radiation from point Q is proportional to the X-ray intensity reaching point Q while being attenuated," And considering that “scattered radiation is proportional to the energy lost by attenuation”, a model as shown in FIG. 15 can be considered. Let S _i be the signal value detected by the i-th pixel of the X-ray image detector. Also, pixel numbers are assigned in order from 1 from the entry point P to the scattering point Q. Then, using the proportional constant, it can be expressed as the following equation (5).

In order to visualize the internal structure of a living body, it is considered that an image having a pixel value proportional to “scattering intensity” (= ratio of scattered radiation intensity to X-ray intensity) corresponds to an anatomical structure more. The following correction is performed so that this can be displayed. That is, the image luminance value P _j corresponding to the i-th pixel is calculated and calculated as shown in the following equation (6). As a result, even when “total attenuation coefficient three-dimensional data” or the like cannot be obtained, the internal structure of the living body can be easily visualized more easily.

[Display unit, storage unit, operation unit, network I / F]
The display unit 6 displays the absorbed dose image in a predetermined form using the absorbed dose image data. For example, the display unit 6 displays the absorbed dose image by fusion with a plan image or an image obtained immediately before or during irradiation as necessary.

  The storage unit 7 has a predetermined scan sequence for acquiring (scanning) scattered radiation data while keeping the angle between the axis of the irradiated radiation beam and the detection surface of the detector 301 constant, correction processing, image reconstruction processing, Control program for executing conversion processing, display processing, etc., dedicated program for displaying and editing treatment plan in the system, scattered radiation volume data, absorbed dose volume data acquired by the radiation treatment information providing system 1 , Stored absorbed dose image data, image data acquired by other modalities such as an X-ray computed tomography apparatus, and the like. Data stored in the storage unit 7 can also be transferred to an external device via the network I / F 90.

  The operation unit 8 includes various switches, buttons, a trackball 13s, a mouse 13c, and a keyboard for incorporating various instructions, conditions, a region of interest (ROI) setting instruction, various image quality condition setting instructions, and the like from the operator into the apparatus main body 11. 13d and the like.

  The network I / F 9 transfers the absorbed dose image data obtained by the radiation treatment information providing system 1 to another device via the network, and also, for example, the treatment plan created in the radiation treatment planning device via the network. Get in.

(Operation)
Next, operation | movement at the time of radiotherapy of this radiotherapy information provision system 1 is demonstrated.

  FIG. 16 is a flowchart showing the flow of processing at the time of radiotherapy including the operation of the present radiotherapy information providing system 1. Hereinafter, the processing content of each step will be described.

[Subject placement, etc .: Step S1]
First, the data acquisition control unit 4 acquires treatment plan information related to the subject via a network, for example, and displays it on the display unit 6. The surgeon arranges the subject on the bed according to the displayed treatment plan, and performs setting of the radiation irradiation time, setting of the scattering angle for measuring scattered radiation, selection of the scan sequence, etc. via the operation unit 8. (Step S1). Note that the setting of the radiation irradiation time and the like may be automatically performed based on the acquired treatment plan information.

[Radiation irradiation (acquisition of scattered radiation data): Step S2]
Next, the radiation irradiation system 2 irradiates the subject with an X-ray beam B2 shaped into a thin flat surface at a predetermined timing, and the radiation detection system 2 exits the subject based on the irradiation radiation. A scattered ray having a predetermined scattering angle is detected. In addition, the data acquisition control unit 4 moves the excitation cross section of the X-ray beam B2 while maintaining the angle formed by the axis of the therapeutic X-ray beam B2 irradiated from the irradiation unit 203 and the line-of-sight direction of the detector 301. The gantry control unit 207 or the movement mechanism unit 305 is controlled so as to scan the three-dimensional region in the subject (step S2). By scanning the three-dimensional region using the therapeutic X-ray beam B2, three-dimensional scattered radiation data including a plurality of two-dimensional scattered radiation data corresponding to the plane of the X-ray beam B2 is acquired.

[Preprocessing (correction processing, etc.): Step S3]
Next, the correction processing unit 501 of the data processing system 5 executes preprocessing including attenuation correction, and acquires projection data (step S3). The contents of the attenuation correction are as described above.

[Image reconstruction processing: Step S4]
Next, the image reconstruction processing unit 503 of the data processing system 5 performs image reconstruction processing using the acquired projection data, and acquires scattered radiation volume data (step S4).

[Conversion processing: Step S5]
Next, the conversion processing unit 507 of the data processing system 5 converts the number of scatterings n per unit volume calculated for each voxel into an absorbed dose, thereby absorbing the radiation dose absorbed by the scattered radiation volume data. It is converted into absorbed dose volume data indicating a three-dimensional distribution of (absorbed dose) (step S5). Here, the absorbed dose is the absorbed energy per unit mass and is represented by [Gy] = [J / kg]. Further, the optical depth n calculated by the reconstruction process, a number of scattering flew scattered radiation (photons) of a predetermined scattering angle theta _d direction.

That is, the energy (energy absorbed by the tissue) _{Te and θd} given to the electrons by the scattered radiation can be expressed by the following equation (7).

  Here, hν means the energy [eV] of the treatment X-ray beam, and is set at the time of treatment planning.

Thus, estimated from scattered radiation flew theta _d direction, tissue absorption energy of, n × T _e, is represented by _{[theta] d [eV].} However, since scattering in directions other than θ _d actually occurs, it is necessary to consider them. The number of scattered rays in a certain direction θ can be expressed as in Equation (8a), and the energy received by the tissue from these scattered rays is expressed as in Equation (8b).

Here, the differential scattering cross section is expressed as dσ / dΩ simply as σ (θ). Ω means solid angle. When this is used, the absorbed energy E _a [eV] in the voxel can be expressed by the following equation (9).

Furthermore, assuming that the volume of the voxel is V and the tissue is almost composed of water (density 1 g / cm ³ ), the absorbed dose D [Gy] of the voxel can be expressed as the following equation (10). Can do.

  By performing this calculation for all voxels, the absorbed dose distribution can be obtained.

[Generation of Absorbed Dose Image Data / Display of Image Data: Steps S6 and S7]
Next, the image processing unit 507 uses the absorbed dose volume data or the like to generate absorbed dose image data indicating the distribution of the absorbed radiation dose (absorbed dose) for a predetermined part of the subject, for example, for fusion display. Are combined with the CT image (step S6). The display unit 6 displays the absorbed dose image in a predetermined form (step S7).

  FIG. 17 is a diagram showing one form of display of an absorbed dose image (a fusion display in a lung field cross section including the heart). An absorbed dose image as shown in the figure can be displayed during treatment or at any timing before and after treatment. By observing the displayed image, the surgeon can visually and quantitatively grasp which part of the patient is actually irradiated and how much dose.

(effect)
According to the configuration described above, the following effects can be obtained.

  In this radiation therapy information providing system 1, a detector equipped with a collimator is installed at a position that forms a predetermined angle (scattering angle) with respect to the therapeutic X-ray beam, and only the scattered radiation that comes in that direction is selectively detected. The detection is performed while moving the therapeutic X-ray beam and the detection surface while maintaining the angle formed between the axis of the therapeutic X-ray beam irradiated from the irradiation unit 203 and the detection surface of the detector 301. Then scan the 3D area in the subject. Using the obtained three-dimensional scattered radiation data for a given scattering angle, the scattered radiation volume data is reconstructed, and the scattered radiation volume data is converted into absorbed dose volume data indicating a three-dimensional distribution of absorbed radiation. Then, an absorbed dose image is generated. The generated absorbed dose image is combined with a morphological image (CT image or the like) and displayed, for example. The displayed absorption line image is generated based on multi-directional scattered radiation data that is objective data obtained by actual measurement. Therefore, the operator can visually and quantitatively grasp the position and amount of radiation actually irradiated by observing the absorbed dose image. Thereby, it is possible to determine whether or not radiation therapy is being performed as planned using an objective criterion, and it is possible to prevent over- and under-irradiation of a radiation treatment site and its surrounding area. As a result, it is possible to improve the effect of radiation therapy, reduce the amount of extra exposure to the subject, and contribute to improving the quality of radiation therapy.

  Moreover, according to the radiation therapy information provision system 1, the absorbed dose image can be observed in real time during the treatment. Further, by performing reconstruction processing and predetermined image processing using previously acquired scattered radiation volume data and absorbed dose volume data, an absorbed dose image can be observed at an arbitrary timing. Therefore, during treatment, the position and intensity of the currently irradiated radiation can be visually confirmed quickly and easily in real time. For example, during the course of treatment, It is possible to quickly and easily visually confirm the position where the radiation is applied and the accumulated radiation dose. That is, the surgeon can determine the appropriateness of the current treatment and the existing treatment based on objective criteria by observing the absorbed dose image in a desired situation.

  Further, according to the radiation therapy information providing system 1, based on the relative positional relationship between the subject and the scattered radiation detection system 3, the subject traveling from the X-ray scattering point of the radiation therapy toward the X-ray image detector. Attenuation correction is performed on the route to the escape point, or the entire route from the entry point of the radiotherapy X-ray to the subject to the exit point exiting the subject toward the detector via the scattering point Calculations such as attenuation correction for irradiated X-rays and scattered rays are performed at. Thereby, it is possible to correct the influence of energy attenuation caused by propagating inside the subject, and it is possible to acquire highly reliable scattered radiation volume data, absorbed dose volume data, and the like.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Specific examples of modifications are as follows.

  For example, the control function, the signal processing function, the display function, and the like according to the present embodiment can be realized by installing a program for executing the process on a computer such as a workstation and developing the program on a memory. . At this time, a program capable of causing the computer to execute the technique is stored in a recording medium such as a magnetic disk (floppy (registered trademark) disk, hard disk, etc.), an optical disk (CD-ROM, DVD, etc.), or a semiconductor memory. It can also be distributed.

  In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  As described above, according to the present invention, a radiation therapy information providing system and a radiation therapy information providing program capable of actually measuring and displaying an irradiation dose are obtained by acquiring scattered radiation data in real time during radiation therapy and using this. can do.

FIG. 1 shows a graph representing a mass absorption coefficient [cm ² / g] with respect to photon (ie, X-ray) energy [MeV] in a living tissue. FIG. 2 is a graph showing a mass absorption coefficient [cm ² / g] with respect to photon (= X-ray) energy [MeV] in the case of water. FIG. 3 is a schematic diagram illustrating the principle of Compton scattering. FIG. 4 shows a block diagram of the radiation therapy information providing system 1 according to this embodiment. FIG. 5 is a diagram showing a measurement form of scattered radiation of the radiation therapy information providing system 1. FIG. 6 is a side view for explaining a mechanism of the irradiation unit 203 for shaping the radiation to be irradiated into a thin planar shape. FIG. 7 is a perspective view for explaining a mechanism of the irradiation unit 203 for shaping the radiation to be irradiated into a thin planar shape. FIG. 8 is a diagram for explaining the positions and angles of the detector 301 and the parallel collimator 303 with respect to the center line L that bisects the thickness of the X-ray beam B2 irradiated to the subject (shaped into a thin flat surface). FIG. FIG. 9A is a view of the parallel collimator 303 as seen from the incident side of the scattered radiation. FIG. 9B is a perspective view of the detector 301 provided with the parallel collimator 303. FIG. 10 is a diagram illustrating an example of a moving mechanism unit 305 for moving the detector 301 and the parallel collimator 303. FIG. 11 is a diagram for obtaining a relational expression between the scattered radiation data acquired by the movement of the detector 301 and the parallel collimator 303 using the moving mechanism unit 305 shown in FIG. 10 and the coordinates of the scanning space. FIG. 12 is a diagram illustrating another example of the moving mechanism unit 305 for moving the detector 301 and the parallel collimator 303. FIG. 13 is a diagram for obtaining a relational expression between the scattered radiation data acquired by the rotation of the detector 301 and the parallel collimator 303 using the moving mechanism unit 305 shown in FIG. 12 and the coordinates of the scanning space. FIG. 14 is a diagram for explaining the concept of attenuation correction. FIG. 15 is a diagram for explaining another concept of simple attenuation correction. FIG. 16 is a flowchart showing the flow of processing at the time of radiotherapy including the operation of the present radiotherapy information providing system 1. FIG. 17 is a diagram showing one form of display of an absorbed dose image (a fusion display in a lung field cross section including the heart).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Radiation treatment information provision system, 2 ... Radiation irradiation system, 3 ... Radiation detection system, 4 ... Data acquisition control part, 5 ... Data processing system, 6 ... Display part, 7 ... Memory | storage part, 8 ... Operation part, 9 ... Network I / F, 201 ... power supply unit, 203 ... irradiation unit, 205 ... timing control unit, 207 ... gantry control unit, 301 ... detector, 303 ... parallel collimator, 305 ... moving mechanism unit, 307 ... position detection unit, 501 ... Correction processing unit, 503 ... Reconstruction processing unit, 505 ... Conversion processing unit, 507 ... Image processing unit

Claims (8)

An irradiation means for irradiating the subject with a planar therapeutic radiation beam;
Detecting means for collecting scattered radiation data by detecting scattered radiation of the subject generated due to the therapeutic radiation beam from a predetermined scattering angle direction;
By moving the position of the axis of the therapeutic radiation beam and the position of the detection surface of the detection means while keeping the angle formed by the detection surface of the detection means with respect to the irradiation direction of the therapeutic radiation beam constant, Data acquisition control means for three-dimensionally scanning a specimen and acquiring three-dimensional scattered radiation data;
Based on the three-dimensional scattered radiation data, image reconstruction means for reconstructing scattered radiation volume data indicating a three-dimensional distribution of scattered radiation generation density in the subject;
An image generating means for generating an absorbed dose image or a scattered radiation generation density image in the subject based on the scattered radiation volume data;
Display means for displaying the absorbed dose image or scattered radiation generation density image;
A radiation therapy information providing system comprising: A moving mechanism for moving a spatial position of the irradiation unit and the detection unit while fixing a relative positional relationship between the irradiation unit and the detection unit;
The data acquisition control means performs the three-dimensional scanning by controlling the moving mechanism,
The radiation therapy information providing system according to claim 1. A moving mechanism for moving the spatial position of the detection surface of the detection means;
The data acquisition control unit executes the three-dimensional scanning by controlling the moving mechanism so that the position of the detection surface of the detection unit moves in conjunction with the movement of the position of the axis of the therapeutic radiation beam. To do,
The radiation therapy information providing system according to claim 1. Based on the three-dimensional distribution of the X-ray attenuation coefficient acquired in advance and the relative positional relationship between the subject and the detection means, the subject exits from the scattered radiation generation position toward the detection means. By integrating the X-ray attenuation coefficient along the path to the position, to obtain a correction coefficient, using the correction coefficient, further comprising a correction means for performing attenuation correction for the three-dimensional scattered radiation data,
The image reconstruction means reconstructs scattered radiation volume data indicating a three-dimensional distribution of scattered radiation generation density in the subject, based on the corrected three-dimensional scattered radiation data.
The radiation therapy information provision system according to any one of claims 1 to 3. Based on the three-dimensional distribution of the X-ray attenuation coefficient acquired in advance and the relative positional relationship between the subject and the detection means, scattered radiation is generated from the entry position of the therapeutic radiation beam into the subject. By integrating the X-ray attenuation coefficient along the path from the position to exit the subject toward the detection means via the position, a correction coefficient is obtained, and using the correction coefficient, the 3 A correction means for performing attenuation correction related to the two-dimensional scattered radiation data;
The image reconstruction means reconstructs scattered radiation volume data indicating a three-dimensional distribution of scattered radiation generation density in the subject, based on the corrected three-dimensional scattered radiation data.
The radiation therapy information provision system according to any one of claims 1 to 3. Based on the intensity information of the planar therapeutic radiation beam and the three-dimensional scattered radiation data, X is generated in the path from the position where the therapeutic radiation beam enters the subject to the scattered radiation generation position. A correction coefficient for correcting the line attenuation is estimated, and the correction coefficient is further used, and correction means for performing attenuation correction related to the three-dimensional scattered radiation data is further provided.
The image reconstruction means reconstructs scattered radiation volume data indicating a three-dimensional distribution of scattered radiation generation density in the subject, based on the corrected three-dimensional scattered radiation data.
The radiation therapy information provision system according to any one of claims 1 to 3.   The radiation treatment information providing system according to claim 1, wherein the display unit displays an image related to the occurrence of scattering in combination with a morphological image. On the computer,
A detection function that collects scattered radiation data by detecting scattered radiation of the subject generated from a planar therapeutic radiation beam irradiated to the subject from a predetermined scattering angle direction;
By moving the position of the axis of the therapeutic radiation beam and the position of the detection surface of the detection means while keeping the angle formed by the detection surface of the detection means with respect to the irradiation direction of the therapeutic radiation beam constant, A data acquisition control function that scans a specimen three-dimensionally and acquires three-dimensional scattered radiation data;
Based on the three-dimensional scattered radiation data, an image reconstruction function for reconstructing scattered radiation volume data indicating a three-dimensional distribution of scattered radiation generation density in the subject,
Based on the scattered radiation volume data, an image generation function for generating an absorbed dose image or scattered radiation generation density image in the subject,
A display function for displaying the absorbed dose image or scattered radiation generation density image;
A radiation therapy information providing program characterized by comprising:

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