JP2009148494A - Radiotherapeutic dose distribution measuring apparatus and radiotherapeutic dose distribution measuring program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiotherapeutic dose distribution measuring apparatus or the like capable of preventing excessive irradiation to an affected area and excessive irradiation to a normal tissue by measuring an actually irradiated region in the patient and actual dose and providing the result in a predetermined form in external X-ray radiation therapy. <P>SOLUTION: A detector having a collimator in a position at a specific angle with respect to a therapeutic X-ray beam is mounted to selectively detect only scattering radiation in the direction. Since angles and amounts of X-rays scattered by Compton scattering are known theoretically, if scattering radiation at a certain angle can be detected, the number of scattering radiation at other angles can be also estimated. Further, to three-dimensionally obtain a distribution of places where scattering occurs in a patient body, the detector is rotated during irradiation and scattering radiation is measured from all directions. After that, a reconstructing process is performed, and a distribution of occurrence of scattering radiation in the subject is three-dimensionally imaged. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is a radiotherapy in which treatment is performed by irradiating radiation from the outside of the patient's body toward the lesioned part. Radiation therapy dose that can prevent over-irradiation of the lesion and over-irradiation of normal tissues by actually measuring the part and dose actually irradiated to the patient and providing the result in a predetermined form The present invention relates to a distribution measuring apparatus and a dose distribution measuring program for radiotherapy.

  In radiation therapy represented by external X-ray irradiation treatment, an irradiation plan (from which direction and how much dose is irradiated to the lesion) is planned on the patient image before treatment, and based on this The patient is irradiated. However, at present, there is no means to confirm whether the patient is actually receiving the position and dose as planned, and even if under-irradiation of the lesion or over-exposure to normal tissue occurs Is the current situation. It may be confirmed that irradiation can be performed as planned using a phantom and an X-ray detector before irradiation, but unlike a phantom that can be easily carried and adjusted freely, the patient can be placed on the bed. However, it is difficult to place them in the position as planned for irradiation, and these pre-irradiation confirmations do not completely guarantee the irradiation as planned for the patient.

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 X-ray of an 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.

  With increasing social interest in medical malpractice, over-irradiation of patients has also been reported in radiotherapy. It is expected that it will become more and more important in the future to record the “facts” of the medical practice performed, such as how much dose the patient has received. Recently, in the field of external X-ray irradiation therapy, a method of irradiating in sync with and following the movement of the tumor in the patient due to breathing, a method of collimating and irradiating a therapeutic X-ray beam according to the tumor shape, etc. Attempts have been made to irradiate the lesion more precisely. These precision irradiations are intended to concentrate the dose on the lesion. For this reason, in the unlikely event that the therapeutic X-ray beam deviates from the irradiation target, the normal tissue is seriously damaged. For this reason, it is important to confirm whether or not the irradiation is performed as planned as the irradiation becomes more precise.

  The present invention has been made in view of the above circumstances, and in X-ray external radiation treatment, actually measured which part of a patient was irradiated with how much dose, and the result in a predetermined form. It is an object of the present invention to provide a radiotherapy dose distribution measurement apparatus and a radiotherapy dose distribution measurement program that can prevent over-irradiation of a lesioned part and over-irradiation of a normal tissue.

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

  According to the first aspect of the present invention, there is provided irradiation means for irradiating a subject with a therapeutic radiation beam, and scattered rays having a predetermined scattering angle θ generated from the subject based on the therapeutic radiation beam. Detection means for detecting scattered radiation data at a plurality of positions, and scattered radiation showing a three-dimensional distribution of scattered radiation generation density in the subject based on the scattered radiation data for the detected plurality of positions Image reconstructing means for reconstructing volume data, image generating means for generating an image relating to the occurrence of scattering in the subject based on the scattered radiation volume data, and display means for displaying an image relating to the occurrence of scattering. A radiation distribution measuring apparatus for radiation therapy.

  According to the eleventh aspect of the present invention, the computer detects scattered rays having a predetermined scattering angle θ from the inside of the subject generated based on the therapeutic radiation beam irradiated to the subject at a plurality of positions. Based on the detection function for generating scattered radiation data and the scattered radiation data for the plurality of detected positions, the scattered radiation volume data indicating the three-dimensional distribution of the scattered radiation generation density in the subject is reproduced. An image reconstructing function to be configured, an image generating function for generating an image relating to the occurrence of scattering in the subject based on the scattered radiation volume data, and a display function for displaying an image relating to the occurrence of scattering. Is a dose distribution measurement program for radiotherapy.

  As described above, according to the present invention, in the external X-ray irradiation treatment, by actually measuring which part of the patient is irradiated with how much dose, and providing the result in a predetermined form, It is possible to realize a radiotherapy dose distribution measurement apparatus and a radiotherapy dose distribution measurement program that can prevent over-irradiation of the body and over-irradiation of normal tissue.

  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 dose distribution measuring apparatus for radiotherapy according to the present embodiment measures scattered rays from the subject based on the radiation irradiated to the subject, and based on this, to which part of the subject, how much dose Information that objectively indicates whether or not is irradiated. The principle and method are as follows.

  FIG. 1 is a diagram for explaining the principle and method of measuring scattered radiation from a subject based on therapeutic radiation in the radiation therapy dose distribution measuring apparatus.

  The therapeutic effect of external X-ray irradiation is mainly brought about by X-ray scattering that occurs in the patient. That is, when the therapeutic X-ray beam is scattered by electrons in the patient, the electrons that have received energy fly through the tissue and then stop. At this time, the electrons radicalize the molecules in the tissue until they stop, damaging the DNA in the cells. Cells that are damaged and cannot be repaired eventually die. This is the therapeutic effect of X-ray irradiation. The more recoiled electrons are generated, the higher the probability that the cells constituting the tissue will die, so the therapeutic effect is proportional to the number of times the scattering reaction occurs.

  From the above, knowing the number of scatterings that have occurred in the tissue, it is possible to know the therapeutic effect (= how much the tissue has been damaged). The number of scattering that has occurred can be determined by measuring the number of scattered rays. Since most of the scattered X-rays are transferred to the outside of the patient after the traveling direction is changed by electrons, they can be measured by an X-ray detector installed outside the patient.

  In the radiation therapy dose distribution measuring apparatus according to the present embodiment, a detector having a collimator is installed at a position that forms a specific angle with respect to the treatment X-ray beam, and only scattered rays that come in that direction are selectively selected. To detect. Since it is theoretically possible to know how much X-rays are scattered at which angle by Compton scattering, if the scattered radiation at one angle can be detected, the number of scattered rays at other angles can be estimated. Furthermore, in order to obtain a three-dimensional distribution of the locations where scattering occurred in the patient, the detector is rotated during irradiation, and the scattered radiation is measured from all directions (see, for example, FIG. 3). Thereafter, reconstruction processing is performed, and the generation distribution of scattered radiation inside the subject is imaged three-dimensionally. As the reconstruction method, for example, a CT reconstruction method is used if the direction of the collimator is orthogonal to the scan axis, and a tomographic reconstruction method is used if the direction is not orthogonal.

[Constitution]
FIG. 2 shows a block diagram of the radiation therapy dose distribution measuring apparatus 1 according to the present embodiment. FIG. 3 is a view showing a measurement form of scattered radiation of the radiation therapy dose distribution measuring apparatus 1. As shown in the figure, the radiation treatment dose distribution measuring apparatus 1 includes a radiation irradiation system 2, a scattered radiation detection system 3, a data acquisition control unit 4, a data processing system 5, a display unit 6, a storage unit 7, and an operation unit. 8. Network I / F 9 is provided. The radiation irradiation system 2 and the scattered radiation detection system 3 are installed on a gantry, and can be arranged at arbitrary positions with respect to the subject by moving and rotating the gantry. In addition, 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 dose distribution measuring apparatus 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 a mechanism such as a linear accelerator (linac). In the irradiation unit 203, thermoelectrons emitted from the cathode are accelerated to several hundred keV by an electron gun provided at one end of the accelerating tube. Next, the microwave generated by the klystron is guided to the accelerating tube using a waveguide, where the thermoelectrons are accelerated until they reach several MeV energy. The accelerated thermoelectrons are changed in direction by the magnet and collide with the transmission target. At this time, X-rays with energy of several MeV are generated by bremsstrahlung. The irradiation unit 203 shapes the X-rays into a predetermined shape (for example, a conical shape) using a collimator, and irradiates the three-dimensional region of the subject placed on the bed.

  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.

[Scattered radiation detection system]
The scattered radiation detection system 3 includes a detector 301, a collimator 303, a movement 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, an imaging plate, or the like, and detects scattered rays from the subject based on radiation irradiated to the subject. 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 collimator 303 is a diaphragm device for selectively detecting only scattered rays coming in a specific direction. A preferable shape, grid size, and the like of the 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.

<Size of detector 301>
4, 5, 6, 7, and 8 are diagrams for explaining the size of the detector 301. The size of the detector 301 is preferably a size that can cover the range in which scattered radiation comes out from the patient. As shown in FIG. 4 and FIG. 5, this size includes the width 2a of the treatment beam, the rotation angle (rotation angle of the gantry of the irradiation system) φ, the arrangement angle θ of the detector 301, and the thickness (width) of the patient's body. Determined by 2L. Using these values, the length L ₁ (of the detection surface) of the detector 301 can be expressed by the following equation (1).

Here, however, it was assumed that the treatment X-ray beam was a parallel beam and rotated about the middle of the patient's body thickness. L ₁ = 36.1 cm, assuming that the width of the treatment beam is 4 cm, the rotation angle is 35 °, the detector 301 is arranged at 120 ° (the same applies at 60 °), and the patient's body thickness is 30 cm. This value mainly depends on the arrangement angle of the detector 301. For example, when it is arranged at a position of 155 ° (same at 25 °), L ₁ = 20.3 cm, and the further away from 90 °, the more compact it can be made.

If the width of the patient's body is 2w, the length L ₁ of the detector 301 can be expressed by the following equation (2).

Here, however, the treatment X-ray beam is assumed to be a parallel beam. L ₂ = 36.6 cm (20.5 cm at 25 °) where the width of the treatment beam is 4 cm, the arrangement angle of the detector 301 is 120 ° (the same applies to 60 °), and the width of the patient's body is 40 cm.

In fact, it may tilt in both directions at the same time. For example, when tilted simultaneously at the angles as shown in FIGS. 4 and 7, it is about 57 cm (about 31 cm at 155 °) at the position of 120 °. The actual size L _{1 of the} detector 301 needs to be determined according to the tilt angle of the illumination system.

The other size L ₂ of the detector 301 is determined by the width of the treatment X-ray beam as shown in FIG. If it is assumed that there is no spread of the therapeutic X-ray beam, 2a is sufficient, but since it actually spreads, a size larger than this is necessary. It is generally known that the beam width at the therapeutic X-ray beam collimator is about three times near the center of the patient. Therefore, if the beam width at the collimator is used as a reference, it is necessary to make it at least three times larger, and in practice it is about four times larger. Considering the target size as a standard, the target size is about 3cm in the treatment aimed at radical cure, so a size of about 4cm is required. Irradiation aimed at symptomatic relief requires a size of about 13.3 cm because it irradiates a wide area of about 10 cm.

  As described above, the detector 301 is capable of detecting scattered radiation all assuming the arrangement angle of the detector 301, the width of the treatment beam (target size, irradiation range), the rotation angle, and the size of the patient's body. Determine the size. In a system that cannot realize such a size due to interference with an irradiation system or a patient, the scattered radiation data of only the range that can be covered is reconstructed.

<Arrangement angle of detector 301>
In the determination of the size of the detector 301 described above, it has been shown that the size of the detector that can cover the region where scattering occurs greatly varies depending on the arrangement angle. On the other hand, the likelihood of scattering also varies depending on the angle, and the number of scattered rays that can be detected varies depending on the arrangement angle. It is known that the degree of scattering at each angle (angular differential scattering cross section) is expressed by the Klein-Nishina equation shown in the following equation (3).

Here, α is the ratio between the incident energy of X-rays and the static energy of electrons, r ₀ is the classical radius of electrons, 2.82 × 10 ⁻¹⁵ [m], and θ is the scattering angle of X-rays.

FIG. 9 is a graph showing the Klein-Nishina equation calculated every 5 °. The incident energy is 5 MeV which is almost the same as the therapeutic X-ray beam used in normal X-ray irradiation. The unit of angle is deg, and the unit of cross-sectional area is b (10E-24 * m ² ). As can be seen from the figure, forward scattering, in which the traveling direction can be slightly changed by scattering, is superior. Therefore, in order to further increase the number of counts and improve the S / N ratio, it can be said that it is advantageous to detect at a position at a shallow angle with respect to the treatment beam X-ray (incident X-ray). Finally, based on the measured value at the angle θ at which the detector is placed, the value shown in FIG. 9 (the value calculated by the Klein-Nishina formula) is used to scatter x at other angles. Since a process for estimating the number of lines is required, the S / N ratio here affects the results.

At 0 degree (that is, the direction of travel does not change even after scattering with electrons) with the largest number of scattering, correction processing is necessary to distinguish it from transmitted rays that did not cause scattering in the patient. When the arrangement angles are as shown in FIGS. 10A and 10B, this correction processing is not necessary. That is, FIG. 10A shows an angular arrangement in which a large number of counts can be obtained by making θ as small as possible, and correction processing for distinguishing between transmitted rays and scattered rays is unnecessary. The count number also depends on the distance between the patient and the detection, and the smaller this distance, the more advantageous. In FIG. 10B, θ is slightly increased, but the distance can be reduced as compared with the left figure. However, if the detector placement angle is less than 90 ° (ie, forward scatter), scattered radiation passes through the bed and enters the detector. Assuming that the material of the bed is carbon fiber (density 1.9 g / cm ³ ) and the thickness is 2 cm, about 10% of scattered rays are scattered while passing through the bed, and the traveling direction changes. Therefore, in order to collect accurate scattered radiation data, there is a disadvantage in that additional processing such as collecting and correcting scattered data from a bed in advance is necessary.

  In the above, an example of the arrangement of detectors based on the idea of emphasizing the number of counts has been shown. However, in order to accurately estimate the effect of treatment, among scattered in all directions, scattered radiation that has made a significant contribution to treatment is particularly important. It is desirable to be able to measure accurately. In order to accurately count such scattered rays, it is better to increase θ. As described in [Principle and Method], the therapeutic effect of X-ray irradiation is mainly caused by electrons that receive energy from X-rays during scattering. The angle of X-rays that transfer more energy to electrons can be changed greatly, resulting in a larger scattering angle.

FIG. 11 shows the state of Compton scattering. The scattered rays and electron energies hν ′ and Te after scattering are expressed by the following equation (4) using the incident energy hν of X-rays and the scattering angle θ.

  FIG. 12 is a graph showing the relationship between the photon energy after Compton scattering and the scattering angle θ. As shown in the figure, scattered radiation with a large scattering angle is unlikely to occur and the number of counts is reduced, but it gives a lot of energy to the electrons, so it can be seen that it is an x-ray that made a large contribution to treatment . When the scattering angle θ satisfies 85 ° <θ <180 °, 90% or more of the energy of the incident therapeutic X-ray beam is transferred to the electrons and finally given to the living tissue. In order to accurately measure scattered radiation having a large contribution to treatment, such a detector arrangement angle is desirable.

  FIG. 13 is a diagram illustrating an example of a detector arrangement for more accurately detecting scattered radiation that has greatly contributed to treatment. According to such an arrangement, there is an advantage that the scattering correction process by the bed is not necessary and the size of the detector can be reduced.

  An error may also occur depending on the placement accuracy of the detector. Considering mechanical deflection etc., it is impossible to place it at the intended position without any error (and it is extremely difficult for the detector to measure how much deviation is caused by mechanical deflection etc. ). As shown in FIG. 9, the magnitude of the angle change of the scattering cross section varies depending on the angle. If the detector is arranged at an angle where the magnitude of this angle change is large, the error becomes large.

FIG. 14 is a diagram for explaining the correspondence between the detector arrangement position deviation Δd and the scattering angle deviation Δθ. In the figure, the scattering angle shift Δθ caused by the detector placement position shift Δd is expressed by the following equation (5), where l is the distance between the location where the scattering occurs and the detector.

  For example, when l is 500 mm and Δd is shifted by 1 mm, Δθ is about 0.1 °. The error in the number of counts that occurs is the largest at about 0.6% when the scattering angle is around 18 °, decreases monotonously as the scattering angle increases, and becomes 0.0001% or less at 180 °. In consideration of avoiding interference with the therapeutic X-ray beam, it is difficult to place the detector at 180 ° in the actual detector arrangement. However, for example, the error is 0.05% or less, in the range of 140 ° ≦ θ <180 °. It is desirable to arrange.

The detector placement angle also affects the spatial resolution of the reconstructed image. FIG. 15 shows the relationship between the width of the reconstructed object, the detector arrangement angle (that is, the projection direction during the reconstruction process), and the spread R of the reconstructed object. From the figure, it can be seen that the magnitude of R can be expressed by the following equation.

  From the equation (6), when the 90 ° detector is arranged, the spatial resolution can be minimized, and the distance from 90 ° increases. The 90 ° and the vicinity thereof are extremely difficult to realize because they interfere with the patient and the bed, but it is desirable that the arrangement angle be as close to 90 ° as possible.

  From the viewpoint of the magnitude of contribution to treatment, the error that occurs in the count, and the spatial resolution after reconstruction, the detector placement angle θ is in the range of 140 ° ≦ θ <180 °, as described above. It is desirable that the value be as small as possible.

<Number of detectors>
In this embodiment, the detection surface is rotated around the axis of the radiation beam that irradiates the detector 301 while maintaining a predetermined angle with respect to the beam axis (in other words, the subject is scanned using scattered radiation). Thus, scattered radiation data at a plurality of positions (that is, multidirectional data for the same scattering angle) is acquired. However, regardless of this, in order to acquire multidirectional data for the same scattering angle, different rotation angles (ie, a circle centered on the beam axis and the center) are detected so as to detect scattered radiation having the same scattering angle. A plurality of detectors arranged at a plurality of positions on the circumference may be used. In addition, a plurality of detector positions arranged at different rotation angles as described above may be rotated around the axis of the radiation beam to obtain multidirectional data for the same scattering angle. By using a plurality of detectors like these, there is an advantage that the number of counts increases and the S / N ratio can be improved.

<Shape of collimator>
FIG. 16A is a diagram showing a collimator 303 provided on the detection surface of the detector 301. FIG. 16B is a side view of the detector 301 and the collimator 303. As shown in each figure, the detector 301 can detect only the scattered rays that are in the arrangement angle direction (that is, only the scattered rays having a scattering angle of θ can be detected), so that the grid-like collimator 303 can be detected. Is provided.

<Grid size of collimator>
The grid size determines the resolution of the reconstructed 3D distribution. The smaller the grid size, the better the spatial resolution, but the S / N ratio decreases because the number of scattered radiation counts decreases.

In the case of normal radical treatment, a total dose of about 60 to 70 Gy is irradiated to the target in about 30 days. That is, the irradiation dose for the target per day is about 2 Gy. The number of photons in the therapeutic X-ray beam required for 2Gy irradiation can be calculated by the following formula (7) (Source: Absorbed dose of human body, airborne dose of Fukuo Araki) 1.3 × 10 ¹¹ photons / cm ² . However, it was assumed that the energy E of the therapeutic X-ray was 5 MeV, the target was water, and μ _en / ρ was 0.0191.

Therefore, the number of scattering per 1 cm 3 (= number of scattered rays) can be calculated as in the following formula (8).

For example, the grid size and 1 cm, when located away 50cm detector from the target, the count number N _{1 cm @ 2} of 1 grid is represented by the following equation (9).

However, here, it is an average value when the angle dependency of scattering is ignored, and becomes a value close to two digits at a position where the scattering angle is large. In the case of diagnostic X-ray fluoroscopy (10 mR), it is about 2.4 × 10 ⁵ [counts / cm ² ]. However, the spatial resolution of X-ray fluoroscopy is as high as 0.2mm. If the spatial resolution is 1 cm, a count of 1/2500 (about 10 ² ) is sufficient. On the other hand, even when the detector is arranged at a position where the scattering angle is large as described above, a count of about 10 ³ can be obtained, which is one digit higher than fluoroscopy.
Also, the grid size must be an integer multiple or a fraction of an integer of the detector pixel size. However, the pixel size of the detector is desirably smaller than the grid size so that the count number is not lost. For example, when the grid size is 1 cm, the detector pixel size may be 1 cm, 0.5 cm, 0.2 cm, 0.1 cm, or the like.

[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 scattered radiation detection system 3. The radiation therapy dose distribution measuring apparatus 1 is statically or dynamically controlled for irradiation, scattered radiation measurement, data processing, image display, network communication, and the like. In addition, 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 as necessary.

[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, and the like as necessary. The details of the correction process executed by the correction process 501 will be described in detail later.

  The reconstruction processing unit 503 executes image reconstruction processing using the scattered radiation image data detected in the scattered radiation detection system 3 and position information indicating the position where each scattered radiation image data is detected, and the number of scattering events ( Scattered ray volume data showing a three-dimensional distribution of the number of scattering occurrences) is acquired. As the reconstruction method, for example, a CT reconstruction method is used if the direction of the collimator is orthogonal to the scan axis, and a tomographic reconstruction method is used if the direction is not orthogonal.

  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.

[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, correction processing, image reconstruction processing, conversion processing, and display processing for acquiring (scanning) scattered radiation data while rotating the detector 301 around the axis of the radiation beam to be irradiated. Control program for executing the above, a dedicated program for displaying and editing a treatment plan in the system, scattered radiation volume data, absorbed dose volume data, absorbed dose acquired by the radiation treatment dose distribution measuring apparatus 1 Image data, image data acquired by other modalities such as an X-ray computed tomography apparatus, and the like are stored. 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 dose distribution measuring device 1 to another device via the network, and also, for example, the treatment plan created in the radiation treatment planning device. Obtain via the network.

(Operation)
Next, the operation of the radiotherapy dose distribution measuring apparatus 1 during radiotherapy will be described.

  FIG. 17 is a flowchart showing the flow of processing during radiotherapy including the operation of the radiation therapy dose distribution measuring apparatus 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 rotation angle for performing scattered radiation measurement, 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 image data in multiple directions: Step S2]
Next, the radiation irradiation system 2 generates therapeutic radiation for irradiating the subject with a three-dimensional region at a predetermined timing. Further, the scattered radiation detection system 2 detects the scattered radiation that comes out of the subject based on the irradiation radiation at a plurality of rotation angles around the axis of the radiation beam irradiated (step S2). For example, when irradiation can be performed for 3 minutes from one direction, data in 18 directions is collected for 10 seconds per direction. At this time, the 18 directions are preferably equiangular intervals with the beam axis as the center. The count number of scattered rays detected by the detector 303 in each direction and the position information of the detector 303 at the time of detecting scattered rays measured by the position detector 307 are transmitted to the data processing system 5.

  In the present embodiment, the detector 301 is arranged so that the arrangement angle of the detector 301 is such that backscattered rays having a scattering angle θ in a range of 120 ° ≦ θ ≦ 165 ° (for example, 155 °) are detected. It is assumed that an arrangement angle 301 is set.

In the above example, for example, when 2 Gy irradiation is performed from three directions, the number of counts per direction is 1.24 × 10 ⁵ × 1 / 3≈4 × 10 ⁴ [counts / cm ² ]. If it is irradiated for 180 seconds per direction and measured for 10 seconds, 4 × 10 ⁴ × 10/180 = 2 × 10 ³ [counts / cm ² ] is obtained, but there is no problem in the S / N ratio.

  In addition, the detection of scattered radiation requires at least two directions, but it is preferable to detect in as many directions as possible in practice. Moreover, it is preferable that the detection positions are arranged at equiangular intervals around the axis of the irradiation beam.

[Preprocessing (correction processing, etc.): Step S3]
In the collected data, only X-rays scattered in the detector installation angle direction are counted. However, actually, as shown in FIG. 9, X-rays are scattered in all directions. Finally, in order to calculate the dose [Gy] absorbed by the tissue, it is necessary to correct the count value of the detector and obtain the number of scatters in all directions.

If the count on a grid is n _count , the scattering cross section at the detector installation angle θ ₀ is σ _θ0 , and the scattering cross section (total cross section) in all directions is Σ, then scattering in all directions is considered The corrected value N is obtained by the following equation (10).

[Image reconstruction processing: Step S4]
Next, the image reconstruction processing unit 503 of the data processing system 5 performs image reconstruction processing using multidirectional projection data, and acquires scattered radiation volume data (step S4). At this time, when the rotation axis of the detector 301 and the direction of the collimator are orthogonal and an image is captured in an angle range of 180 degrees (+ α) or more, a CT reconstruction method may be used. A tomographic reconstruction method is used. As a tomographic technique, for example, a filtered backprojection method in which a back projection process is performed after a filter process is applied to a projection image is used. As a filter configuration method, a classic Shepp-Logan filter or a filter disclosed in Japanese Patent Application Nos. 2006-284325 and 2007-269447 is used. In particular, if a method described in Japanese Patent Application Nos. 2006-284325 and 2007-269447 is used, a scatter source distribution image with a clear physical meaning can be generated.

  An image obtained by subjecting the detector image to filter processing and performing back projection has a scattered radiation generation density per unit volume (the number of scatterings per unit volume). Three-dimensional distribution of scattered radiation generation density in the vicinity where therapeutic radiation passes through the subject through all steps of the reconstruction process (various correction processes, filter processes, and back projection processes) (scattered volume data) Can be obtained.

[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. Converted into absorbed dose volume data indicating a three-dimensional distribution of (absorbed dose) (step S5).

The energy T _e (= energy absorbed by the tissue) received by the electrons by scattering can be expressed by the following equation (11).

Here, hν is the energy [eV] of the treatment X-ray beam, and is set at the time of treatment planning. Therefore, if the value of the i-th voxel (= the number of scattering per unit volume) is n _i , the absorbed energy E _{ab, i} [J] at this voxel can be expressed by equation (12).

Therefore, the absorbed dose D _i [Gy] = [J / kg] (= absorbed energy per unit mass) at the i-th voxel is the average density of living tissue existing in the voxel, d _i [g / cm ³ ], Where the volume of voxel is v [cm ³ ], it can be expressed as in equation (13).

Here, the average density d _i of the living tissue present in the voxel _[g / cm ^3], the human body is approximately considered as consisting of 100% water, it may be the 1 [g / cm ^3].

[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. 18 is a diagram showing a display form (fusion display) of the absorbed dose image. 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. A detector equipped with a collimator is installed at a specific angle (scattering angle) with respect to the therapeutic X-ray beam, and only the scattered radiation in that direction is selectively detected, and this detection is performed for the same scattering angle. Run in multiple directions. The scattered radiation volume data is reconstructed using the obtained multi-directional scattered radiation data relating to the predetermined scattering angle, and the scattered radiation volume data is converted into absorbed dose volume data indicating a three-dimensional distribution of the absorbed radiation dose. Convert and generate an absorbed dose image. The generated absorbed dose image is combined with, for example, a morphological image (CT image or the like) and displayed. 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.

  Further, according to the radiation treatment dose distribution measuring apparatus 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.

  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, in the external X-ray irradiation treatment, by actually measuring which part of the patient is irradiated with how much dose, and providing the result in a predetermined form, It is possible to realize a radiotherapy dose distribution measurement apparatus and a radiotherapy dose distribution measurement program that can prevent over-irradiation of the body and over-irradiation of normal tissue.

FIG. 1 is a diagram for explaining the principle and method of measuring scattered radiation from a subject based on therapeutic radiation in the radiation therapy dose distribution measuring apparatus. FIG. 2 shows a block diagram of the radiation therapy dose distribution measuring apparatus 1 according to the present embodiment. FIG. 3 is a view showing a measurement form of scattered radiation of the radiation therapy dose distribution measuring apparatus 1. FIG. 4 is a diagram for explaining the size of the detector 301. FIG. 5 is a diagram for explaining the size of the detector 301. FIG. 6 is a diagram for explaining the size of the detector 301. FIG. 7 is a diagram for explaining the size of the detector 301. FIG. 8 is a diagram for explaining the size of the detector 301. FIG. 9 is a graph showing the Klein-Nishina equation. FIGS. 10A and 10B are diagrams showing examples of detector arrangement angles, respectively. FIG. 11 shows the state of Compton scattering. FIG. 12 is a graph showing the relationship between the photon energy after Compton scattering and the scattering angle θ. FIG. 13 is a diagram showing an example of a detector arrangement for more accurately detecting scattered radiation. FIG. 14 is a diagram for explaining the correspondence between the detector arrangement position deviation Δd and the scattering angle deviation Δθ. FIG. 15 is a diagram for explaining the arrangement angle of the detector, the size of the object, and the spatial extent of the reconstructed object. FIG. 16A is a diagram showing a collimator 303 provided on the detection surface of the detector 301. FIG. 16B is a side view of the detector 301 and the collimator 303. FIG. 17 is a flowchart showing the flow of processing during radiotherapy including the operation of the radiation therapy dose distribution measuring apparatus 1. FIG. 18 is a diagram showing a display form (fusion display) of the absorbed dose image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Radiation therapy dose distribution measuring apparatus, 2 ... Radiation irradiation system, 3 ... Scattered ray 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 ... Collimator, 305 ... Movement mechanism unit, 307 ... Position detection 501... Correction processing unit 503... Reconstruction processing unit 505... Conversion processing unit 507.

Claims (10)

Irradiation means for irradiating the subject with a therapeutic radiation beam;
Detecting means for detecting scattered radiation at a predetermined scattering angle θ from the subject generated based on the therapeutic radiation beam at a plurality of positions and generating 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 based on the scattered radiation data for the plurality of detected positions;
An image generating means for generating an image related to the occurrence of scattering in the subject based on the scattered radiation volume data;
Display means for displaying an image relating to the occurrence of scattering;
A radiation distribution measuring apparatus for radiation therapy, comprising:   2. The radiation therapy dose distribution measuring apparatus according to claim 1, wherein the detection means is installed so as to detect scattered radiation having a scattering angle θ of 140 ≦ θ <180 °.   3. The radiotherapy dose distribution measuring apparatus according to claim 1, wherein the detection means includes control means for controlling an angle of a detection surface with respect to an axis of the therapeutic radiation beam.   The said detection means has a rotation means which detects the scattered-radiation data about these said several positions by rotating a detection surface centering on the axis | shaft of the said radiation beam for a treatment, The 1st thru | or 3 characterized by the above-mentioned. The dose distribution measuring apparatus for radiotherapy as described in any one of them.   The said detection means has a some detector arrange | positioned in the some position on the circumference centering on the axis | shaft of the said therapeutic radiation beam, The any one of Claim 1 thru | or 4 characterized by the above-mentioned. Dose distribution measuring device for radiotherapy.   The reconstruction means reconstructs the scattered radiation volume data by performing image reconstruction used in X-ray computed tomography using the scattered radiation data of the detected plurality of positions. The dose distribution measuring apparatus for radiotherapy according to any one of claims 1 to 5.   The reconstructing means reconstructs the scattered radiation volume data by executing a back projection process after the filtering process using the scattered radiation data for the plurality of detected positions. The dose distribution measuring apparatus for radiotherapy according to any one of 1 to 6. The image generating means includes
Converting the scattered radiation volume data into absorbed dose volume data showing a three-dimensional distribution of absorbed radiation,
Using the absorbed dose volume data to generate an absorbed dose image as an image relating to the occurrence of scattering;
The dose distribution measuring device for radiotherapy according to any one of claims 2 to 7.   9. The radiotherapy dose distribution measurement apparatus according to claim 2, wherein the display unit displays an image related to the occurrence of scattering with a morphological image. On the computer,
A detection function for generating scattered radiation data by detecting scattered radiation of a predetermined scattering angle θ from within the subject generated based on a therapeutic radiation beam irradiated to the subject at a plurality of positions;
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 data for the detected plurality of positions;
Based on the scattered radiation volume data, an image generation function for generating an image related to the occurrence of scattering in the subject,
A display function for displaying an image relating to the occurrence of scattering;
A dose distribution measuring program for radiotherapy, comprising:

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