Treatment planning device, particle beam therapy system, treatment plan generation method, and computer program

Abstract

To compare an original treatment plan with a new treatment plan in consideration of the influence of an error.SOLUTION: A treatment planning device 501 in a particle beam treatment system which irradiates a target with a particle beam calculates the first dose distribution of the particle beam on the basis of an X-ray image in planning obtained by imaging the target, calculates the second dose distribution of the particle beam on the basis of the prior X-ray image obtained by imaging the target subsequently to the X-ray image in planning, calculates the first and second dose indexes about the first and second dose distributions, and displays the variations of the first and second dose indexes.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a treatment planning apparatus, a particle beam therapy system, a treatment plan generation method, and a computer program.

Background Art

[0002] The present invention relates to a treatment planning apparatus, and particularly to a radiation therapy system that irradiates a diseased part with radiation centered on charged particle beams such as proton beams and carbon beams for treatment, and a treatment planning apparatus used therefor.

[0003] Radiation therapy, which aims to kill tumor cells by irradiating various types of radiation, has been widely performed in recent years. As the radiation used, not only X-rays, which are the most widely used, but also treatments using particle beams such as proton beams and carbon beams are spreading.

[0004] In radiation therapy, since a high dose is applied only to the tumor region, it is necessary to make a detailed treatment plan in advance. For example, in particle beam therapy, the energy, irradiation dose, and irradiation position are determined by a treatment planning apparatus so that a desired dose distribution to the diseased part and its surroundings can be obtained in advance.

[0005] As a means for checking the state of the patient's body during the prior planning, an X-ray CT image (hereinafter, a planning CT image) is the most common. The designation of the diseased part position and the calculation of the dose distribution in the body based thereon are often performed using CT images.

[0006] In radiation therapy, irradiation once a day is repeated over several days. Conventionally, the treatment plan was basically made first, and the same irradiation dose was applied to the same irradiation position every day. However, in recent years, the irradiation position and irradiation dose have begun to be changed according to the change in the internal state. Re-planning the treatment plan and irradiating is called adaptive irradiation.

[0007] Among adaptive irradiations, in particular, when the patient lies horizontally on the bed, imaging the affected area and re-planning the irradiation is called online adaptive irradiation. In online adaptive irradiation, Patent Document 1 discloses that after re-planning, the original treatment plan planned in advance is compared with the new treatment plan by re-planning, and radiation is irradiated based on a more preferable treatment plan.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] In the method of Patent Document 1, the original treatment plan or the new treatment plan is selected based on dose-based indicators, such as the maximum dose, minimum dose, etc. to the target and normal organs around the target. On the other hand, in online adaptive treatment, re-planning may be performed based on images obtained by Cone Beam CT (hereinafter referred to as CBCT). Although CBCT has a simple configuration, its image quality is inferior compared to the planned CT images taken for the prior treatment plan. Therefore, there is a method of deforming the planned CT images according to the CBCT images taken on the treatment day and performing re-planning based on those images. This method involves errors that were not present in the prior treatment plan, such as deformation errors of the planned CT images. In the comparison between the original treatment plan and the new treatment plan, there is a problem that a judgment considering the influence of this error must be made.

[0010] The present invention has been made in view of the above problems, and an object thereof is to provide a treatment planning device, a particle beam treatment system, a treatment plan generation method, and a computer program capable of comparing the original treatment plan and the new treatment plan while considering the influence of errors.

Means for Solving the Problems

[0011] To solve the above problems, a treatment planning device according to one aspect of the present invention is applied to a particle beam therapy system that irradiates a target with a particle beam, calculates a first dose distribution of the particle beam based on a planning X-ray image obtained by imaging the target, calculates a second dose distribution of the particle beam based on a pre-X-ray image obtained by imaging the target after the planning X-ray image, calculates first and second dose metrics related to these first and second dose distributions, and is characterized by displaying the variation of these first and second dose metrics.

Advantages of the Invention

[0012] According to the present invention, it becomes possible to compare the original treatment plan and the new treatment plan in consideration of the influence of errors.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description and drawings are examples for explaining the present invention, and for the sake of clarity of explanation, omissions and simplifications are made as appropriate. The present invention can be implemented in various other forms. Unless otherwise specifically limited, each component may be singular or plural.

[0015] In the drawings for explaining the embodiments, the same reference numerals are given to portions having the same function, and repeated explanations thereof are omitted.

[0016] The positions, sizes, shapes, ranges, etc. of the components shown in the drawings may not represent the actual positions, sizes, shapes, ranges, etc. in order to facilitate understanding of the invention. For this reason, the present invention is not necessarily limited to the positions, sizes, shapes, ranges, etc. disclosed in the drawings.

[0017] When there are a plurality of components having the same or similar functions, they may be described with the same reference numeral and different subscripts. However, when it is not necessary to distinguish these plurality of components, the subscripts may be omitted in the description.

[0018] A particle beam therapy system to which a radiation therapy treatment planning device (hereinafter simply referred to as "treatment planning device") according to an embodiment is applied will be described with reference to FIGS. 1 to 10. In the present embodiment, a treatment planning device for formulating a treatment plan for proton beam therapy by a scanning irradiation method, which is a kind of radiation therapy, will be described, but it is also applicable to a treatment planning device for formulating a treatment plan for proton beam therapy by a scatterer irradiation method or a heavy particle beam therapy using carbon beams or the like. Further, it is also applicable to a treatment planning device for X-ray therapy.

[0019] FIG. 1 is a schematic configuration diagram showing a particle beam therapy system to which a treatment planning device according to an example is applied.

[0020] FIG. 1 is a diagram showing the overall configuration of a particle beam therapy system. In FIG. 1, the particle beam therapy system includes a charged particle beam generator 301, a high-energy beam transport system 310, a rotational irradiation device 311, a control device 314 equipped with a treatment planning program 312 and a memory 313, a display device 315, an irradiation field forming device (irradiation device) 400, a bed 407, a treatment planning device 501, and a data server 502.

[0021] The charged particle beam generator 301 is composed of an ion source 302, a pre-stage accelerator 303, and a particle beam accelerator 304. In this embodiment, a synchrotron-type particle beam accelerator is assumed as the particle beam accelerator 304, but any other particle beam accelerator such as a cyclotron may be used as the particle beam accelerator 304. As shown in FIG. 1, the synchrotron-type particle beam accelerator 304 includes a deflection electromagnet 305, an accelerator 306, an output high-frequency application device 307, an output deflector 308, and a quadrupole electromagnet (not shown) on its circumferential orbit.

[0022] Using FIG. 1, the process until the particle beam is generated from the charged particle beam generator 301 using the synchrotron-type particle beam accelerator 304 and emitted toward the patient will be described.

[0023] The particles supplied from the ion source 302 are accelerated by the pre-stage accelerator 303 and sent to the synchrotron, which is a beam accelerator. An accelerator 306 is installed in the synchrotron, and a high frequency is applied to a high-frequency acceleration cavity (not shown) provided in the accelerator 306 in synchronization with the period when the particle beam orbiting inside the synchrotron passes through the accelerator 306 to accelerate the particle beam. In this way, the particle beam is accelerated until it reaches a predetermined energy.

[0024] After the particle beam is accelerated to a predetermined energy (e.g., 70 to 250 MeV), when an emission start signal is output from the control device 314, the high-frequency power from the high-frequency power supply 309 is applied to the particle beam orbiting inside the synchrotron by the high-frequency application electrodes installed in the high-frequency application device 307, and the particle beam is emitted from the synchrotron.

[0025] The high-energy beam transport system 310 connects the synchrotron and the irradiation field forming device 400. The particle beam extracted from the synchrotron is guided to the irradiation field forming device 400 installed in the rotation irradiation device 311 via the high-energy beam transport system 310. The rotation irradiation device 311 is for irradiating the beam from any direction of the patient 406, and the entire device can rotate in any direction around the bed 407 on which the patient 406 is installed.

[0026] The irradiation field forming device 400 rotates together with the rotation irradiation device. The tip of the irradiation field forming device is provided with X-ray detectors 420 and 421, and on the opposite side sandwiching the patient 406, X-ray generators 422 and 423 are provided. By acquiring the X-ray fluoroscopic image of the patient 406 while the X-ray generators 422 and 423 and the X-ray detectors 420 and 421 rotate together with the rotation irradiation device, a cone beam CT image can be reconstructed from the fluoroscopic image.

[0027] The irradiation field forming device 400 is a device for shaping the shape of the particle beam finally irradiated to the patient 406. The scanning method targeted in this embodiment irradiates the thin beam transported from the high-energy beam transport system 310 directly to the target and scans this three-dimensionally, so that a high-dose region can be finally formed only in the target.

[0028] Figure 2 shows the configuration of the irradiation field forming device 400 corresponding to the scanning method.

[0029] Using FIG. 2, briefly describe the respective roles and functions of the devices within the irradiation field forming apparatus 400. The irradiation field forming apparatus 400 includes two scanning electromagnets 401 and 402, a dose monitor 403, and a beam position monitor 404 from the upstream side. The dose monitor 403 measures the amount of the particle beam that has passed through the monitor. On the other hand, the beam position monitor 404 can measure the position where the particle beam has passed. Based on the information from these monitors 403 and 404, the control device 314 can manage that the beam of the planned amount is irradiated at the planned position.

[0030] The thin particle beam transported from the charged particle beam generator 301 through the high-energy beam transport system 310 is deflected in its traveling direction by the scanning electromagnets 401 and 402. These scanning electromagnets are provided so that magnetic field lines are generated in a direction perpendicular to the beam traveling direction. For example, in FIG. 2, the scanning electromagnet 401 deflects the beam in the direction of the scanning direction 405, and the scanning electromagnet 402 deflects it in a direction perpendicular thereto. By using these two electromagnets, the beam can be moved to an arbitrary position within the plane perpendicular to the beam traveling direction, and beam irradiation to the target 406a becomes possible.

[0031] The control device 314 controls the amount of current flowing through the scanning electromagnets 401 and 402 via the scanning electromagnet magnetic field strength control device 411. The scanning electromagnets 401 and 402 are supplied with current from the scanning electromagnet power supply 410, and by exciting a magnetic field according to the amount of current, the deflection amount of the beam can be freely set. The relationship between the deflection amount of the particle beam and the amount of current is stored in advance as a table in the memory 313 in the control device 314 and is referred to.

[0032] There are two types of beam scanning methods for the scanning method. One is discrete scanning irradiation in which the particle beam is irradiated only while the irradiation position is stopped, and the irradiation of the particle beam is stopped while the irradiation position is changed. The other is continuous scanning irradiation in which the irradiation position is continuously changed without stopping the irradiation of the particle beam. In the present embodiment, discrete scanning irradiation will be described, but the present invention can also be applied to continuous scanning irradiation.

[0033] A conceptual diagram of irradiation by discrete scanning irradiation is shown in FIG. 3.

[0034] FIG. 3 is an example of irradiating a cubic target 801. Since the particle beam stops at a certain position in the traveling direction and most of the energy is imparted to the stop position, the energy is adjusted so that the depth at which the beam stops is within the target region. In FIG. 3, a beam of energy that stops near the surface 802 irradiated with the same energy is selected. On this surface, irradiation positions (spots) are arranged at spot intervals 803.

[0035] A spot represents a combination of an irradiation position and an irradiation amount. When a specified amount is irradiated with one spot, the irradiation is once stopped and moved to the next spot. When the movement is completed, the irradiation of the next spot is started, and when the specified amount is reached, the irradiation is stopped. Thereafter, this is repeated.

[0036] The spot 804 is irradiated with a beam passing through the trajectory 805 of the beam irradiating the spot 804. When the spots of the same energy arranged in the target are sequentially irradiated, the depth at which the beam is stopped is changed in order to irradiate other depth positions in the target. Here, it is assumed that a simple cubic target is irradiated with a constant irradiation amount, but in actuality, the irradiation amount for each spot is very different in order to form a dose distribution of a complex shape in the target.

[0037] In the example of FIG. 3, energy was mainly imparted to the region corresponding to the surface 802 irradiated with the same energy. By changing the energy, a situation as shown in FIG. 4 is obtained.

[0038] In FIG. 4, a beam having an energy lower than the energy used in FIG. 3 is irradiated. Therefore, the beam stops at a shallower position. This surface is represented by surface 901 irradiated with the same energy. One of the spots corresponding to the beam of this energy, spot 902, is irradiated with a beam passing through the trajectory 903 of the beam irradiating spot 902.

[0039] Another method of changing the beam energy is to insert a range modulator (not shown) into the irradiation field forming device 400. The thickness of the range modulator is selected according to the energy to be changed. The selection of the thickness may be by using a plurality of range modulators having a plurality of thicknesses, or by using opposing wedge-shaped range modulators.

[0040] In this embodiment, a set of irradiation positions irradiated with the same energy is called a layer.

[0041] To change the depth at which the beam stops, the energy of the beam irradiating the patient 406 is changed. One method of changing the energy is to change the setting of the particle beam accelerator, that is, the synchrotron in this embodiment. The particles are accelerated until they reach the energy set in the synchrotron, but by changing this set value, the energy incident on the patient 406 can be changed. In this case, since the energy taken out from the synchrotron changes, the energy when passing through the high-energy beam transport system 310 also changes, and it is also necessary to change the setting of the high-energy beam transport system 310. In the case of a synchrotron, it takes about one second to change the energy.

[0042] FIG. 5 shows the configuration of the treatment planning device 501. The treatment planning device 501 is connected to the data server 502 and the control device 314 via a network.

[0043] As shown in FIG. 5, the treatment planning device 501 includes an input device 602 for inputting parameters for irradiating a particle beam, a display device 603 for displaying a treatment plan, a memory 604, an arithmetic processing device 605 (arithmetic unit) for performing dose distribution calculation, and a communication device 606. The arithmetic processing device 605 is connected to the input device 602, the display device 603, the memory (storage device) 604, and the communication device 606.

[0044] The treatment planning device 501 is a device capable of various information processes, and is composed of, for example, an information processing device such as a computer. The information processing device has an arithmetic unit 605, a storage device 604, and a communication interface which is the communication device 607, and further has an input device 602 such as a mouse and a keyboard, and a display device 603 such as a display.

[0045] The arithmetic unit 605 is, for example, a CPU (Central Processing Unit), a GPU (Graphic Processing Unit), an FPGA (Field-Programmable Gate Array), etc. The storage device 604 has, for example, a magnetic storage medium such as an HDD (Hard Disk Drive), a semiconductor storage medium such as a RAM (Random Access Memory), a ROM (Read Only Memory), and an SSD (Solid State Drive), etc. Also, a combination of an optical disk such as a DVD (Digital Versatile Disk) and an optical disk drive is also used as the storage device 604. In addition, known storage media such as magnetic tape media are also used as the storage device 604.

[0046] Programs such as firmware are stored in the storage device 604. When the treatment planning device 501 starts operating (for example, when power is turned on), programs such as firmware are read from this storage device 604 and executed to perform overall control of the treatment planning device 501. Also, in addition to programs, data etc. necessary for each process of the treatment planning device 501 are stored in the storage device 604.

[0047] Alternatively, some of the components that make up the treatment planning device 501 may be interconnected via a LAN (Local Area Network), or may be interconnected via a WAN (Wide Area Network) such as the Internet.

[0048] Next, the operation flow using the treatment planning device 501 will be described with reference to FIG. 6.

[0049] Prior to treatment, an image for treatment planning is taken. The most commonly used image for treatment planning is a CT image. The CT image reconstructs three-dimensional data from fluoroscopic images acquired from multiple directions of the patient.

[0050] The CT image taken by a CT device (not shown) is stored in the data server 502. In this embodiment, this CT image is referred to as the original plan CT image (planning X-ray image). The CT image holds information on electron density, and in the calculation of the dose distribution, the depth of penetration of the particle beam is calculated by converting the electron density information into water equivalent thickness. The relationship between the pixel value of the CT image and the water equivalent thickness is provided in advance as a table.

[0051] When the formulation of the treatment plan is started (step 101), the engineer (or doctor), who is the operator of the treatment planning device 501, reads the target CT data from the data server 502 using a device such as a mouse, which is the input device 602. That is, the treatment planning device 501 copies the CT image from the data server 502 onto the memory 604 through the network connected to the communication device 606 by operating the input device 602 (step 102).

[0052] When the loading of the three-dimensional CT image from the data server 502 to the memory 604 is completed and the three-dimensional CT image is displayed on the display device 603, the operator uses a device such as a mouse corresponding to the input device 602 while checking the three-dimensional CT image displayed on the display device 603 to input the slice of the three-dimensional CT image, that is, the region to be designated as the target for each two-dimensional CT image. Here, the target region to be input is a region determined to be a region where tumor cells exist or a region where a sufficient amount of particle beam should be irradiated because there may be tumor cells. This is called the target region. If there are other regions that require evaluation and control, such as when important organs where the irradiation dose should be minimized as much as possible exist near the target region, the operator also designates those regions such as the important organs in the same way. In addition, it may be executed on images of different modalities represented by MRI (step 103).

[0053] When the input of regions for all the three-dimensional CT images is completed, the operator instructs the registration of the input regions. By registering, the regions input by the operator are stored in the memory 604 as three-dimensional position information (step 104). The position information of the regions can also be stored in the data server 502, and the information input in the past can be read together with the three-dimensional CT image when reading the three-dimensional CT image.

[0054] Next, the operator creates a treatment plan (original treatment plan) including information on the position and energy of the beam to be irradiated to the registered target region (step 104). First, the operator sets the irradiation direction. The particle beam therapy system to which this embodiment is applied can irradiate the beam from any direction of the patient by selecting the angles of the rotational irradiation device 311 and the bed 407. Multiple irradiation directions can be set for one target. Usually, it is positioned so that the vicinity of the center of the target region 706 coincides with the isocenter (the rotational center position of the rotational irradiation device 311).

[0055] Another parameter for irradiation that the operator needs to determine is the dose value (prescription dose) to be irradiated to the region registered in step 104. The prescription dose includes the dose to be irradiated to the target and the maximum dose that the important organs should avoid.

[0056] After the above parameters are determined, the treatment planning device 501 automatically performs calculations according to the operator's instructions (step 106). Details of the dose calculation performed by the treatment planning device 501 will be described below.

[0057] Here, an example will be described of creating a treatment plan for an irradiation method called intensity-modulated proton therapy by robust optimization. In normal irradiation, a uniform dose distribution is formed in the target for each irradiation direction. Therefore, even in optimizing the irradiation dose, the irradiation dose is optimized for each irradiation direction. On the other hand, in intensity-modulated proton therapy, the irradiation doses from all irradiation directions are simultaneously optimized so that a sufficient dose is irradiated to the target. In intensity-modulated proton therapy, since the degree of freedom is higher than in the normal case where the irradiation dose is optimized for each irradiation direction, it is possible to reduce the dose to the site to be avoided from irradiation while ensuring a sufficient dose to the target.

[0058] In creating a treatment plan, the positional error of the patient and the error in the depth at which the particle beam reaches are considered. That is, a treatment plan is created so that a sufficient dose is irradiated to the target even when these errors occur.

[0059] There are mainly two methods of considering errors. One is a method of setting a region larger than the target by the amount of the assumed error and optimizing the irradiation dose so that a sufficient dose is irradiated to that region. This method is suitable for the normal irradiation method that forms a uniform dose distribution for each irradiation direction. The other is a method called robust optimization that actually calculates the dose distribution when an error occurs and optimizes the irradiation dose so as to minimize the influence of the error on the dose distribution. This method is suitable for intensity-modulated proton therapy in which the dose distribution for each irradiation direction is not uniform.

[0060] First, the treatment planning device 501 determines the beam irradiation position. The irradiation position is set to cover the target region. The same operation is performed for each of a plurality of irradiation directions (the angle between the rotational irradiation device 311 and the bed 407).

[0061] When all the irradiation positions are determined, the treatment planning device 501 starts the optimization calculation of the irradiation dose.

[0062] First, the relationship between the irradiation dose and the dose distribution at each irradiation position is calculated for a plurality of cases. For example, in the case of no error, when the target position changes in a total of six directions, three mutually orthogonal directions and their reverse directions, and when the proton beam arrival position changes to the deeper side and the shallower side, a total of nine cases are considered.

[0063] Next, the irradiation dose to each irradiation position is determined. A method that uses an objective function that quantifies the deviation from the target dose with the irradiation dose for each irradiation position as a parameter is widely adopted. The objective function is defined such that, among the doses in a total of nine cases, the smaller the difference from the target prescription dose set in step 105, the smaller the value. The optimal irradiation dose is calculated by searching for the irradiation dose that minimizes the objective function through iterative calculations. When the iterative calculations are completed, the irradiation dose required for each irradiation position is finally determined.

[0064] Next, the treatment planning device 501 calculates the dose distribution (first dose distribution) using the obtained irradiation position and irradiation dose by the arithmetic processing unit 605. If necessary, the calculated dose distribution result is displayed on the display device 603.

[0065] The operator evaluates the displayed dose distribution and determines whether this dose distribution meets the target conditions and the degree of agreement with the target dose distribution (steps 107, 108).

[0066] As a result of evaluating the dose distribution, if the operator determines that the distribution is undesirable, the process returns to step 105 to reset the irradiation parameters. The parameters to be changed include the irradiation direction and the prescription dose. After a desirable result is obtained, the treatment planning device stores the spot data including the energy, irradiation dose, and irradiation position in the data server 502 through the network (steps 109, step 110).

[0067] Next, using the flows of FIGS. 7 and 8, a procedure for forming a dose distribution at a target by performing replanning using the control device 314 will be described.

[0068] Before starting irradiation, the operator places the irradiation target 51 on the couch 32 and moves it to the planned position. The control device 314 reads the information on energy, irradiation position, and irradiation dose registered in the data server 502 and registers it in the memory.

[0069] In step 201, the control device 314 performs fluoroscopy while rotating the gantry to obtain a cone beam CT image (pre-X-ray image). In step 202, the obtained cone beam image is compared with the CT image at the time of treatment planning to adjust the position of the patient.

[0070] In step 203, the treatment planning program 312 of the control device 314 replans the treatment plan and evaluates whether the replanned plan meets the target.

[0071] The details of the replanning in step 203 will be described according to the flowchart of FIG. 8.

[0072] The treatment planning program 312 of the control device 314 reads the cone beam CT image obtained in step 211 in step 211, and in step 212, reconstructs an image for treatment planning according to the patient body shape during irradiation. The original CT image for the original plan used in the previous treatment plan is compared with the obtained cone beam CT image. By performing deformation registration, the original CT image for the original plan at the time of treatment planning is deformed to match the cone beam CT image.

[0073] The CT image for the original plan used in the pre-treatment plan represents the electron density in the patient's body with high precision. In contrast, for the cone beam CT image, due to the large contribution of X-ray scattering, it is difficult to accurately represent the electron density. The accuracy of the electron density contributes to the calculation accuracy of the arrival position of the particle beam. Therefore, a new CT image for the new plan is created by deforming the CT image for the original plan, which measures the electron density in the patient's body with high precision, to match the cone beam CT image that measures the shape of the patient's body with high precision on the irradiation day. Together with the CT image for the original plan, the contour information drawn on the CT image for the original plan is also deformed.

[0074] Based on the new CT image for the new plan and the deformed contour information, a treatment plan is recreated. In step 213, the spot positions are arranged to cover the target based on the deformed contour information. When irradiating from multiple irradiation directions, the spots are arranged to cover the target for each irradiation direction. Also, in step 214, dose evaluation points are set for the target and the organs around the target. In step 215, target values are set for each dose evaluation point. The target values for each dose evaluation point can be determined in the same way as in step 105, which is the pre-treatment plan, or can be determined by deforming the dose distribution obtained in the pre-treatment plan in the same way as in step 203.

[0075] In step 216, the relationship between the irradiation dose for irradiating the spot positions and the dose values at the dose evaluation points is calculated, and the irradiation dose for each spot is optimized and adjusted so that the dose values at each dose evaluation point approach the target values. The result optimized in this way is registered as a new treatment plan (re-treatment plan).

[0076] In step 204, the operator compares the pre-created original treatment plan with the new treatment plan created immediately before irradiation and selects the more preferable treatment plan. The dose distributions formed by the original treatment plan and the new treatment plan are calculated using the planned CT image created in step 212. Furthermore, dose calculation considering the error, which is a feature of this embodiment, is performed.

[0077] The error mainly occurs during the creation of the planned CT image. The calculation considering specific errors will be described.

[0078] The first is to consider the density error. The water equivalent thickness obtained from the planned CT image is increased or decreased at a certain ratio, and the dose distribution is calculated based on that value. When increasing the water equivalent thickness, it represents the case where the arrival position of the particle beam is shallow, and when decreasing it, it represents the case where the arrival position of the particle beam is deep.

[0079] The second is to consider the position error. The positional relationship between the planned CT image and the irradiation device is moved in a plurality of directions, and the dose distribution is calculated based on that position.

[0080] The third is to consider the error of non - rigid registration that deforms the CT image to match the cone - beam CT image. For non - rigid registration, there are methods that deform based on pixel values, methods that deform based on the organ contour, and methods that consider both. Also, values representing the ease of bending of the deformation and the resolution exist as parameters. By changing these methods and parameters, results from different non - rigid registrations can be obtained. For each of the planned CT images obtained by these multiple non - rigid registrations, the dose distributions of the original treatment plan and the new treatment plan are calculated.

[0081] The dose indices (first dose index, second dose index) are calculated from the dose distributions (first dose distribution, second dose distribution) calculated in this way, and are displayed together with the variation indicated by error bars as shown in FIG. 9. The screen shown in FIG. 9 may be displayed on either the display device 603 of the treatment planning device 501 or the display device 315 of the particle beam therapy system.

[0082] The dose index is a value represented by the maximum dose, minimum dose, or dose - volume histogram (DVH) in the target or normal organ. It may also be the dose uniformity within the target, the degree of dose - target coincidence, the tumor control probability (TCP), or the normal tissue complication probability (NTCP) calculated from the dose distribution.

[0083] The treatment planning device 501 calculates and displays the values of these dose metrics from the dose distributions calculated for a plurality of error cases. In the example of FIG. 9, the dose metrics at the time of planning are shown as references, and the values of the dose metrics for the original treatment plan and the new treatment plan are displayed with variations. In the example of FIG. 9(a), since the new treatment plan shows better values including the variations, it promotes the adoption of the new treatment plan. On the other hand, in the example of FIG. 9(b), although the new treatment plan is better as a value without errors, the new treatment plan has larger variations, and in the worst case, the old plan has better values, which promotes the adoption of the original treatment plan. A plurality of these metrics are displayed, and by comprehensively considering them, a plan to be used for irradiation is selected from the original treatment plan and the new treatment plan.

[0084] Note that here, it was shown that there are a number of methods for imparting errors. By calculating all of them, variations can be displayed with high accuracy. On the other hand, since it takes time to calculate the dose distribution, it is also effective to select the main ones among the calculations listed here and calculate the dose distribution.

[0085] If the previously created original treatment plan is preferred, irradiation is started in step 207.

[0086] On the other hand, if the new treatment plan created immediately before irradiation is selected, in step 205, the treatment plan is verified, and if it is approved in step 206, it is registered in the memory as the treatment plan to be irradiated, and the irradiation in step 207 is started.

[0087] The control device 314 sets the excitation current value of the scanning electromagnet in the irradiation device based on the energy, irradiation position, and irradiation amount information recorded in the memory.

[0088] A series of irradiations is started when the operator presses the irradiation start button on the operation console connected to the control device 314.

[0089] The irradiation procedure will be described with reference to FIG. 10.

[0090] In step 701, irradiation is started with energy number i = 1 and spot number j = 1.

[0091] In step 702, the control device 314 controls the synchrotron to accelerate the proton beam to the energy specified from the control device. The proton beam is incident from the linac on the synchrotron and is accelerated by the accelerator 306 while orbiting inside the synchrotron. Also, the control device 314 controls the beam transport system 310 and excites the electromagnet so that the proton beam can reach the irradiation device 400.

[0092] In step 703, the control device 314 excites the X-axis scanning electromagnet and the Y-axis scanning electromagnet respectively to irradiate the first irradiation position. In step 704, when the excitation of the scanning electromagnet is completed, the control device 314 controls the high-frequency application device 307 to apply a high frequency to the proton beam. The proton beam applied with the high frequency is scanned by the irradiation device 400 through the beam transport system 310 and reaches the first irradiation position.

[0093] The irradiation dose of the proton beam passing through the irradiation device is measured by the dose monitor 403. When the amount reaches the irradiation dose specified for the spot, the control device 314 stops the high-frequency application device 307 and stops the emission of the proton beam. After the emission of the proton beam is stopped, it returns to step 703 to irradiate the next irradiation position, and the control device 314 changes the excitation amount of the scanning electromagnets 401 and 402.

[0094] In step 705, when j = ns (ns is the number of spots included in the energy) is satisfied, in step 706, the control device 314 controls the synchrotron to decelerate and prepares for irradiation with the next energy in step 702.

[0095] When i = nr (nr is the number of energies) is reached in step 707, irradiation is completed in step 708.

[0096] By also writing the variation together with the value of the dose index as in this embodiment, it is possible to judge the selection of the treatment plan in consideration of the error. By visualizing the variation, a quick judgment becomes possible. In adaptive treatment, it is necessary to evaluate the dose distribution in consideration of the error due to non-rigid registration. The error of non-rigid registration is specific to adaptive treatment and does not need to be considered in the prior treatment plan. For an error that is not usually considered, the present invention supports the judgment by visualizing it.

[0097] Note that the present invention is not limited to the above-described embodiments, and includes various modifications. The above embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Also, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Also, it is possible to add, delete, or replace other configurations for a part of the configuration of each embodiment.

[0098] As an example, in this embodiment, proton beams are described as an example, but the same calculation is possible when irradiating carbon beams or X-rays.

[0099] Also, in this embodiment, an example using cone beam CT is shown, but CT images of a device called InRoomCT in which a normal CT device is placed indoors may be used, or MRI images by an MRI device may be used.

[0100] Furthermore, in this example, the processes of FIGS. 7 and 8 were performed by the treatment plan program 312 of the control device 314, but a treatment planning device 501 outside the control device 314 may perform this process.

[0101] In addition, some or all of the above-described components, functions, processing units, processing means, etc. may be realized in hardware, for example, by designing them in an integrated circuit or the like. Further, the above-described components, functions, etc. may be realized in software by a processor interpreting and executing a program for realizing each function. Information such as a program, table, file, etc. for realizing each function can be stored in a memory, a recording device such as a hard disk or SSD, or a recording medium such as an IC card, SD card, or DVD.

[0102] Also, the control lines and information lines show those considered necessary for explanation, and not necessarily all control lines and information lines are shown on the product. In reality, it may be considered that almost all components are interconnected.

Description of Reference Numerals

[0103] 501…Treatment planning device 602…Input device 603…Display device 604…Memory 605…Database 606…Arithmetic processing unit 607…Communication device

Claims

1. A treatment planning device applied to a particle beam therapy system for irradiating a target with a particle beam, calculating a first dose distribution of the particle beam based on a planning X-ray image obtained by imaging the target, calculating a second dose distribution of the particle beam based on a pre-treatment X-ray image obtained by imaging the target after the planning X-ray image, calculating first and second dose metrics for these first and second dose distributions, and displaying the variation of these first and second dose metrics A treatment planning device characterized by the above.

2. The treatment planning device according to claim 1, wherein the variation is obtained by calculating the first and second dose distributions by imparting an error in the density of the target.

3. The treatment planning device according to claim 1, wherein the variation is obtained by calculating the first and second dose distributions by imparting an overlay error between the planning X-ray image and the pre-treatment X-ray image.

4. The treatment planning device according to claim 1, wherein the variation is obtained by calculating the first and second dose distributions by deforming the planning X-ray image based on the pre-treatment X-ray image.

5. The treatment planning device according to claim 1, wherein the first and second dose metrics in the case where there is no such variation are displayed, and the variation with respect to the first and second dose metrics is displayed as error bars.

6. Calculating the irradiation dose of the particle beam based on the first dose distribution to create an original treatment plan, Calculating the irradiation dose of the particle beam based on the second dose distribution to create a re-treatment plan, After displaying the variation of the first and second dose metrics, allowing selection of whether to irradiate the particle beam using either the original treatment plan or the re-treatment plan A treatment planning device characterized by the above according to claim 1.

7. The treatment planning device according to claim 1, wherein the pre-treatment X-ray image is an image captured immediately before irradiation of the particle beam by the particle beam therapy system.

8. A particle beam therapy system that irradiates a target with a particle beam and has a treatment planning device, The treatment planning device is, Calculating a first dose distribution of the particle beam based on a planning X-ray image obtained by imaging the target, Calculating a second dose distribution of the particle beam based on a pre-treatment X-ray image obtained by imaging the target after the planning X-ray image, Calculate first and second dose metrics for these first and second dose distributions and display the variations of these first and second dose metrics A particle beam therapy system characterized by the above.

9. The particle beam therapy system according to claim 8, characterized in that the particle beam therapy system irradiates the target with X-rays.

10. A treatment plan generation method by a treatment planning device applied to a particle beam therapy system that irradiates a target with a particle beam, Calculating a first dose distribution of the particle beam based on a planning X-ray image obtained by imaging the target, Calculating a second dose distribution of the particle beam based on a pre-treatment X-ray image obtained by imaging the target after the planning X-ray image, Calculate first and second dose metrics for these first and second dose distributions and display the variations of these first and second dose metrics A treatment plan generation method characterized by the above.

11. A computer program executed by a computer applied to a particle beam therapy system that irradiates a target with a particle beam, A function of calculating a first dose distribution of the particle beam based on a planning X-ray image obtained by imaging the target, A function of calculating a second dose distribution of the particle beam based on a pre-treatment X-ray image obtained by imaging the target after the planning X-ray image, A function of calculating first and second dose metrics for these first and second dose distributions and displaying the variations of these first and second dose metrics A computer program that causes the computer to implement the above.

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