Treatment planning device, particle beam therapy system, and computer program

Abstract

To enable a correlation between a CT value and a water equivalent thickness ratio distribution for each patient to be corrected without increasing the treatment time, so that more accurate treatment can be realized.SOLUTION: A treatment planning system 112 generates a treatment plan for irradiating an irradiation target with a particle beam. The treatment planning system calculates a correction amount of a water equivalent thickness ratio of a first treatment plan created in advance, calculates a water equivalent thickness ratio distribution based on the correction amount and the first treatment plan, and creates a second treatment plan from the water equivalent thickness distribution.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a treatment planning apparatus, a treatment plan creation method, and a computer program.

Background Art

[0002] The present invention preferably relates to a particle beam therapy system for performing cancer treatment by irradiating a cancer affected area with a particle beam, a particle beam range measurement device, and a treatment planning apparatus.

[0003] Particle beams such as proton beams and carbon beams impart a large dose immediately before stopping in a patient's body. By utilizing this large dose, so-called Bragg peak, it is expected that a dose distribution matching the tumor shape can be easily formed compared to X-ray therapy, and high-precision radiation therapy can be realized.

[0004] In particle beam therapy, the range (position of the Bragg peak) for each particle beam is estimated from the distribution of the water equivalent thickness ratio (ratio of the thickness of water causing the same energy loss to the thickness of a local medium) in the patient's body, and the dose distribution is calculated. Based on this dose distribution, the irradiation position and irradiation amount of each beam for applying a target dose to each region in the patient's body are determined. This irradiation condition is called a prescription, and the procedure for determining the condition is called a treatment plan.

[0005] However, it is known that an error of several percent occurs between the range obtained by dose calculation and the actually measured range. The main causes of the error include changes in the internal structure and differences in the water equivalent thickness ratio for each patient.

[0006] The distribution of the water equivalent thickness ratio used for range calculation is calculated by converting the X-ray computed tomography (hereinafter referred to as CT) image of the patient taken in advance using a conversion table of CT values and water equivalent thickness ratio created using a phantom. The change in the water equivalent thickness ratio distribution due to the variation of the internal structure during CT image acquisition and particle beam irradiation is one of the main causes of range error. On the other hand, since the correlation between CT values and the water equivalent thickness ratio varies from patient to patient, even if there is no variation in the internal structure, an error between the actually converted water equivalent thickness ratio distribution from CT values and the actual distribution occurs. This is the second main cause of the error.

[0007] In a general treatment plan, in order to take into account the range error, a region with a margin (hereinafter referred to as a margin) added to the tumor is set as the target volume. However, when the margin is large, it becomes difficult to apply a high dose to a tumor surrounded by critical organs. Therefore, in order to expand the scope of application of particle beam therapy, it is required to suppress the range error, improve the treatment accuracy, and reduce the margin.

[0008] Regarding the variation of the internal structure, which is one of the main causes of the range error, it can be reflected in the treatment plan by observing the internal structure daily using CT or magnetic resonance imaging. On the other hand, in order to suppress the error due to the patient dependence of the water equivalent thickness ratio, it is necessary to obtain the distribution of the water equivalent thickness ratio for each patient.

[0009] As one of the methods for obtaining the distribution of the water equivalent thickness ratio, measurement of the water equivalent thickness ratio distribution by proton beam CT has been studied. In proton beam CT, a proton beam with higher energy than during treatment is irradiated three-dimensionally, and the transmitted beam is measured to directly measure the water equivalent thickness ratio distribution in the patient's body.

[0010] Patent Document 1 discloses a particle beam therapy system including a residual range measurement device that can irradiate proton beams and helium beams as charged particle beams and measures the energy of the proton beam transmitted through the patient, and a particle beam CT image generation device that obtains the stopping power ratio distribution of the patient with respect to the proton beam measured by the residual range measurement device and calculates the stopping power ratio distribution with respect to the helium beam based on the obtained stopping power ratio distribution.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] By obtaining the distribution of the water equivalent thickness ratio for each patient, the accuracy of particle beam therapy is improved. As disclosed in Patent Document 1, proton beam CT, which is one of the measurement methods for the water equivalent thickness ratio, uses the same beam type as the treatment, so the measurement accuracy of the water equivalent thickness ratio with respect to the treatment beam is high. In addition, since irradiation independent of the treatment is performed, there is a high degree of freedom in choices such as which part of the body to measure the water equivalent thickness ratio and what level of resolution to set.

[0013] However, in order to extract a proton beam with higher energy than that used in the treatment, a large accelerator is required. In addition, since proton beam CT is added to the treatment process, an increase in the treatment time is also assumed.

[0014] As described above, although proton beam CT is a high-performance measurement method for the water equivalent thickness ratio, there are some problems from a clinical perspective. In order to realize particle beam therapy with high accuracy, low cost, and high throughput, it is required to correct the correlation between the CT value and the water equivalent thickness ratio for each patient without increasing the treatment time by adding a measurement process other than the treatment.

[0015] The present invention has been made in view of the above circumstances, and an object thereof is to provide a treatment planning apparatus, a treatment planning method, and a computer program that can correct the correlation between the CT value and the water equivalent thickness ratio distribution for each patient without increasing the treatment time and can realize more accurate treatment.

Means for Solving the Problems

[0016] In order to solve the above problems, a treatment planning device according to one aspect of the present invention is a treatment planning device that generates a treatment plan for irradiating a particle beam to an irradiation target, calculates a correction amount of the water equivalent thickness ratio of a pre-created first treatment plan, calculates a water equivalent thickness ratio distribution based on the correction amount and the first treatment plan, and creates a second treatment plan from the water equivalent thickness ratio distribution.

Advantages of the Invention

[0017] According to the present invention, without increasing the treatment time, the correlation between the CT value for each patient and the water equivalent thickness ratio distribution can be corrected, and more accurate treatment can be realized.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0019] 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 limited, each component may be singular or plural.

[0020] 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.

[0021] The positions, sizes, shapes, ranges, etc. of the respective 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.

[0022] When there are a plurality of components having the same or similar functions, they may be described by attaching different subscripts to the same reference numeral. However, when it is not necessary to distinguish these plurality of components, the subscripts may be omitted in the description.

[0023] The particle beam therapy system having the treatment planning device of the present embodiment has the following configuration as an example.

[0024] That is, taking an example of the particle beam therapy system having the treatment planning device of the present embodiment, it is a particle beam therapy system that irradiates a particle beam to an irradiation target, including an irradiation device that irradiates the particle beam accelerated by an accelerator to the irradiation target, a range measurement device that is arranged on the side surface of the irradiation target and measures the actual measured range of each of the particle beams in synchronization with the irradiation device, and a treatment planning device that executes calculation and correction of the water equivalent thickness ratio distribution and creation of a prescription. The treatment planning device has a function of dividing the region of the patient X-ray CT image, a water equivalent thickness ratio calculation program that calculates the target volume and the water equivalent thickness ratio distribution based on the water equivalent thickness ratio correction result until the previous treatment, etc., a prescription creation program that creates a prescription for the particle beam from the water equivalent thickness ratio distribution, and a water equivalent thickness ratio correction program that determines the water equivalent thickness ratio correction amount for each region from information such as the actual measured range and the prescription.

[0025] According to the present embodiment, since the correction amount of the water equivalent thickness ratio can be estimated from the actually measured range of the treatment particle beam, enlargement of the acceleration device and increase of the treatment time do not occur. Further, by using a method of dividing the CT image into regions and determining the water equivalent thickness ratio correction amount for each region, high-precision water equivalent thickness ratio correction is enabled from limited range error information. Furthermore, the correction accuracy can be improved by accumulating the range error information used for water equivalent thickness ratio correction for each treatment, and the improvement in the accuracy can be reflected in the treatment plan by reducing the margin.

[0026] The radiation treatment planning device of the embodiment (hereinafter simply referred to as the "treatment planning device") will be described with reference to FIGS. 1 to 11. 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 scatter body irradiation method or a treatment planning device for formulating a treatment plan for heavy particle beam therapy using carbon beams or the like. It is also applicable to a treatment planning device for X-ray therapy.

Example

[0027] Hereinafter, the treatment planning apparatus of this embodiment will be described with reference to FIGS. 1 to 10. First, the configuration of the particle beam therapy system having the treatment planning apparatus of this embodiment will be described with reference to FIGS. 1 to 5, and then the operation procedure of the same system in Example 1 will be described with reference to FIGS. 6 to 10.

[0028] First, the overall configuration of the particle beam therapy system will be described with reference to FIG. 1. FIG. 1 is a diagram showing the overall configuration of the particle beam therapy system of this embodiment.

[0029] The particle beam therapy system 101 of this embodiment employs spot scanning irradiation. Spot scanning irradiation is a method of forming a target dose distribution by irradiating each minute irradiation region (hereinafter, spot) in the irradiation target 102 with a pencil beam (a particle beam with a small spread, hereinafter, beam 103).

[0030] The particle beam therapy system 101 is a system for irradiating the irradiation target 102 with the beam 103. As shown in FIG. 1, it includes an accelerator system 104, a beam transport system 105, an irradiation nozzle 106, a treatment table 107, an overall control device 108, an accelerator / beam transport system control device 109, an irradiation nozzle control device 110, a range measurement device 111, and a treatment planning device 112.

[0031] The accelerator system 104 is a device for generating and accelerating the beam 103. In FIG. 1, examples of the accelerator are an injector 113, a synchrotron accelerator 114, and an ion source 115, but a cyclotron accelerator or a synchrocyclotron accelerator may also be used.

[0032] The beam transport system 105 is a group of devices that transports the beam 103 accelerated by the accelerator 104 to the irradiation nozzle 106 that irradiates the irradiation target 102, and connects the accelerator 104 and the irradiation nozzle 106. The beam 103 accelerated to the required energy by the accelerator 104 is transported to the irradiation nozzle 106 while being bent by a magnetic field in a vacuum by the deflection electromagnet 116 arranged in the beam transport system 105. The beam transport system 105 has a rotating gantry, but a fixed irradiation port may also be used.

[0033] The irradiation nozzle 106 is a device that adjusts the beam 103 transported from the beam transport system 105 and irradiates the irradiation target 102. The detailed configuration of the irradiation nozzle 106 will be described later with reference to FIG. 2.

[0034] The range measuring device 111 is a device that measures the range of the beam 103 in the irradiation target 102 and outputs it to the treatment planning device 112. As shown in FIG. 3, in this embodiment, an immediate gamma ray measuring device is shown as an example of the range measuring device, but any device that can measure the range in the irradiation target 102 for each beam 103 may be used, and other examples include an ultrasonic measuring device and an annihilation gamma ray measuring device. The detailed configuration of the range measuring device 111 and the method for determining the range will be described later with reference to FIGS. 3 and 4.

[0035] Again, in FIG. 1, the treatment planning device 112 implements a treatment plan to create a prescription, further transfers the prescription to the overall control device 108, and corrects the distribution of the water equivalent thickness ratio from the range measured by the range measuring device 111 and the like. The detailed configuration and operation of the treatment planning device 112 will be described later with reference to FIG. 5.

[0036] The accelerator and beam transport system control device 109 controls the operations of the various devices that make up the accelerator system 104 and the beam transport system 105.

[0037] The irradiation nozzle control device 110 controls the operations of the various devices that make up the irradiation nozzle 106.

[0038] The overall control device 108 is connected to the treatment planning device 112, the accelerator / beam transport system control device 109, the irradiation nozzle control device 110, the travel measurement device 111, and the treatment table 107, and controls the operations of each device.

[0039] The overall control device 108, the accelerator / beam transport system control device 109, the irradiation nozzle control device 110, the travel measurement device 111, and the treatment planning device 112 have a central processing unit (CPU) and a memory connected to the CPU.

[0040] Note that the control processing of the operations to be executed may be grouped into one program, may be divided into multiple programs respectively, or may be a combination thereof.

[0041] Part or all of the programs held by each device may be realized by dedicated hardware or may be modularized. Furthermore, various programs may be installed in each device by a program distribution server or an external storage medium, or existing devices may be updated.

[0042] Also, each device may be connected by a wired or wireless network as independent devices, or two or more of them may be integrated.

[0043] The treatment table 107 is a bed on which the patient to be irradiated, 102, is placed. The treatment table 107 can move in three orthogonal axes based on instructions from the overall control device 108, and can further rotate about each axis, that is, can move in a so-called six-axis direction. By these movements and rotations, the position of the irradiation target 102 can be moved to a desired position.

[0044] Next, the detailed configuration of the irradiation nozzle 106 will be described with reference to FIG. 2. FIG. 2 is a diagram showing the configuration of the irradiation nozzle 106.

[0045] Inside the irradiation nozzle 106, a scanning electromagnet 201A, 201B, a dose monitor 202, a position monitor 203, a ridge filter 204, and a range shifter 205 are arranged. Further, the irradiation nozzle control device 110 is connected to a dose monitor control device 206, a position monitor control device 207, and a scanning electromagnet control device 208.

[0046] The scanning electromagnets 201A, 201B scan the beam 103 in a plane perpendicular to the passing direction of the beam 103. The beam 103 scanned by the scanning electromagnets 201A, 201B is irradiated onto the target volume 209 within the irradiation target 102. When treating a patient such as with cancer, the irradiation target 102 represents the patient, and the target volume 209 represents a tumor 211 etc. taking into account a margin 210.

[0047] The dose monitor 202 is a monitor for collecting electrons generated by the passage of the beam 103 in order to measure the dose of the beam 103 irradiated at each spot position, and the detection signal is input to the dose monitor control device 206. The dose monitor control device 206 calculates the irradiation dose irradiated at each spot position based on the detection signal input from the dose monitor 202, and outputs the calculated irradiation dose to the irradiation nozzle control device 110.

[0048] The position monitor 203 is a monitor for collecting electrons generated by the passage of the beam 103 in order to measure each spot position. The detection signal (pulse signal obtained by collecting electrons) of the position monitor 203 is input to the position monitor control device 207. The position monitor control device 207 counts the dose at each spot position based on the detection signal input from the position monitor 203, and outputs the calculated count value to the irradiation nozzle control device 110.

[0049] The ridge filter 204 can be used when it is necessary to thicken the Bragg peak. Also, the range shifter 205 can be inserted when adjusting the arrival position of the beam 103.

[0050] In spot scanning irradiation, the irradiation nozzle control device 110 determines the passing position of the beam 103 based on the signal input to the position monitor control device 207, calculates the spot position from the obtained passing position data, and confirms the irradiation position of the beam 103. Further, when the irradiation dose input to the dose monitor control device 206 reaches the target dose, the irradiation nozzle control device 110 scans the beam 103 to the next spot via the scanning electromagnet control device 208. When the irradiation of all the spot groups (referred to as layers) with the same energy is completed, the irradiation nozzle control device 110 transmits a signal to the overall control device 108. When the overall control device 108 receives the signal indicating the completion of the irradiation to the layer from the irradiation nozzle control device 110, it sends a command to the accelerator / beam transport system control device 109 to change the energy of the beam 103 and start the irradiation to the next layer.

[0051] Next, the details of the range measuring device 111 will be described with reference to FIG. 3. In this embodiment, a range measuring device using prompt gamma rays is given as an example of the range measuring device, and FIG. 3 is a diagram showing an outline thereof.

[0052] The prompt gamma rays 301 are generated by the interaction between the beam 103 irradiated to the irradiation target 102 and the irradiation target 102.

[0053] The collimator 302 is installed on the side surface of the target volume 209 as viewed from the traveling direction of the beam 103. The collimator 302 shields everything other than the prompt gamma rays 301 passing through the slit 303. As the material of the collimator, for example, tungsten or lead blocks are used. In FIG. 3, the case where the inner wall of the slit 303 of the collimator 302 is triangular is shown, but the shape of the slit 303 may be such that the inner walls are parallel to each other, for example.

[0054] The array type detector 304 detects the prompt gamma rays 301 that have passed through the slit 303. The arrays are arranged in the beam traveling direction, and by distinguishing the signals for each array, the detection position of each prompt gamma ray 301 can be determined. As the array type detector 304, a semiconductor, a composite detector of a phosphor and a photodetector, or the like is used.

[0055] The detector control device 305 is connected to the array type detector 304, the overall control device 108, and the treatment planning device 112. The detector control device 305 receives information on the beam 103 being irradiated from the overall control device 108, and receives signals from the array type detector 304 for each beam 103. Next, the detector control device 305 determines the range from the detected signals and transmits it to the treatment planning device 112.

[0056] Fig. 4 shows an example of the detection signal of the array type detector 304. Since the number of prompt gamma rays 301 generated from the irradiation target 102 correlates with the applied dose, it increases rapidly near the range. Therefore, if each array of the array type detector 304 is numbered in the order of arrangement in real space and taken on the horizontal axis, and the coefficient rate for each array is plotted on the vertical axis, a shape corresponding to a Bragg peak such as the detection signal 401 is observed.

[0057] However, the distribution of the prompt gamma rays 301 detected by the array type detector 304 is inverted with the position of the slit 303 as the center compared to the distribution of the prompt gamma rays 301 in the target volume 209. The detector control device 305 determines the measured range 402 from the position of the peak of the detection signal 401.

[0058] Fig. 3 shows the case of measuring the distribution of the prompt gamma rays 301 with the collimator 302 fixed, but it may also be measured while moving the collimator 302 parallel to the traveling direction of the beam 103.

[0059] Next, the detailed configuration of the treatment planning device 112 will be described with reference to Fig. 5. Fig. 5 is a configuration diagram of the treatment planning device 112.

[0060] The treatment planning device 112 is configured as a computer system having, for example, a CPU 501, a memory 502, a storage device 503, a communication interface device 504, and a user interface (UI) device 505.

[0061] The memory device 503 is composed of, for example, a flash memory device, a hard disk drive (HDD), etc., and stores computer programs such as an operating system (OS) 506, a water equivalent thickness ratio calculation program 507, a prescription creation program 508, and a water equivalent thickness ratio correction program 509. Also, after the start of treatment, information used for water equivalent thickness ratio correction and treatment planning is stored. Details of the stored information will be described later in the explanation of the operation procedure.

[0062] By the CPU 501 reading out various programs (507, 508, 509) stored in the memory device 503 to the memory 502 and executing them, functions as a treatment planning device 112 (water equivalent thickness ratio calculation, prescription creation, water equivalent thickness ratio correction) are realized. Here, the CPU 501 is used as a representative of the arithmetic element for explanation, but as the arithmetic element, in addition to the CPU 501, a GPU (Graphic Processing Unit), an FPGA (Field-Programmable Gate Array), etc. may also be used.

[0063] The communication interface device 504 is a device for communicating with each device (overall control device 108, range measurement device 111) of the particle beam therapy system 101.

[0064] The UI device 505 is a device for exchanging information with a user (hereinafter referred to as a doctor) who uses the treatment planning device 112. The UI device 505 includes an information output device and an information input device. Examples of the information output device include a display, a printer, a voice synthesis device, etc. Examples of the information input device include a keyboard, a pointing device, a touch panel, a voice recognition device, etc. For example, the dose distribution calculation result of the prescription creation program 508 is displayed on the display.

[0065] The configuration of the particle beam therapy system 101 and the details of each device have been described above. Hereinafter, the operation procedure of the same system in Example 1 will be described.

[0066] The treatment procedure by the particle beam therapy system 101 will be mainly described with reference to FIG. 6. However, FIGS. 7 to 10 will be used as appropriate to supplement the detailed procedure. FIG. 6 is a diagram showing a flowchart of the entire particle beam therapy.

[0067] Generally, in particle beam therapy, fractionated irradiation is performed in which the target dose is applied in several portions. This is to prevent normal tissues from being damaged by the application of a high dose at once. In this embodiment, it is assumed that the target dose of 60 Gy is irradiated in 30 days at 2 Gy per day. However, if the number of fractions is two or more, the effects of the present invention will not be lost even if the number of fractions and the irradiation dose are changed. Also, the fractionation unit does not have to be one day, and the treatment in one day may be further subdivided into multiple treatments.

[0068] Since the treatment procedures are different on the first day, the days after the second day, and the 30th day, hereinafter, the description will be made in chronological order starting from the first day.

[0069] When the treatment on the first day is started (step S601), first, the water equivalent thickness ratio calculation program 507 of the treatment planning device 112 calculates the water equivalent thickness ratio distribution (step S602).

[0070] The details of the water equivalent thickness ratio distribution calculation are shown with reference to FIG. 7. FIG. 7 is a flowchart showing the details of the operation of each program of the treatment planning device 112.

[0071] The water equivalent thickness ratio calculation program 507 first reads an X-ray CT image around the affected part of the patient taken by an X-ray CT device outside the particle beam therapy system 101 (step S701). The X-ray CT device may transmit the CT image to the treatment planning device 112 immediately after imaging, or the X-ray CT device may store the CT image in its own or an external storage device, and the treatment planning device 112 may read the CT image when starting the water equivalent thickness ratio calculation (step S602).

[0072] Next, the water equivalent thickness ratio calculation program 507 performs region classification of the CT image (step S702). However, since region classification information is not necessary for the calculation of the water equivalent thickness ratio on the first day, the region classification may be performed at any step up to the water equivalent thickness ratio correction (step S711) performed after particle beam irradiation.

[0073] Supplementary explanation of the region classification of the CT image is given with reference to FIG. 8. In FIG. 8, each pixel of the X-ray CT image 801 is represented by a grid, and the difference in CT values is indicated by the density of the color of the grid.

[0074] The classification of region 802 is determined based on the X-ray CT image 801. When determining the classification of region 802, the X-ray CT image 801 may be displayed on the UI device 505 and the physician may classify it for each type of internal tissue, or a program that groups pixels with similar CT values into one region may be incorporated into the treatment planning device 112 and automatically executed.

[0075] In FIG. 8, the boundary of region 802 is shown by a thick line and is divided into three regions (802A, 802B, 802C) from region 1 to region 3. The number of regions 802 is not limited to three and can be arbitrarily set. However, if the number of regions 802 is larger than the number of pieces of information of the actual measurement flight path 402, it is assumed that the application of the water equivalent thickness ratio correction amount determined by the method described later is not good, or the determination process of the water equivalent thickness ratio correction amount does not operate normally.

[0076] Returning to FIG. 7, next, the water equivalent thickness ratio calculation program 507 performs conversion of the X-ray CT image 801 into a water equivalent thickness ratio distribution and determination of the target volume 209 (step S704). Note that, since the water equivalent thickness ratio correction has not been performed at the time of step S704 in the treatment on the first day, the call of the water equivalent thickness ratio correction amount (step S703) is skipped.

[0077] Using FIG. 9, the conversion flow of the water equivalent thickness ratio distribution will be described. On the first day, only the pre-correction water equivalent thickness ratio distribution 905 is created among the two types of water equivalent thickness ratio distributions (pre-correction water equivalent thickness ratio distribution 905, corrected water equivalent thickness ratio distribution 906) shown in FIG. 9. The pre-correction water equivalent thickness ratio distribution 905 is calculated by reading the conversion table between the CT value and the water equivalent thickness ratio stored in advance in the treatment planning device 112 (step S901) and converting the X-ray CT image 801 using this conversion table (step S902). Here, the conversion table is created in advance by measurement using a phantom or the like and is constant regardless of the patient. Assuming a file in which the relational expression between the CT value and the water equivalent thickness ratio is recorded as the conversion table, the conversion is completed by substituting the CT value of each pixel of the X-ray CT image 801 into the relational expression and setting the return value as the water equivalent thickness ratio of that pixel (step S905). The conversion table may be a file in which the water equivalent thickness ratios corresponding to several CT values are discretely recorded. If the necessary CT value is not recorded in the file, it may be converted into the water equivalent thickness ratio after adding processing such as linear interpolation.

[0078] Return to step S704 in FIG. 7, and next, the target volume 209 is determined by the following procedure. First, based on the X-ray CT image 801 or the pre-correction water equivalent thickness ratio distribution 905 displayed on the UI device 505, the doctor extracts the contour of the tumor 211 (see FIG. 2). Considering a predetermined margin 210 for this contour, the contour of the target volume 209 is determined. For example, when the margin 210 is uniformly set to 10 mm within the target volume 209, the contour of the target volume 209 is set 10 mm outside the tumor 211 extracted by the doctor. The margin 210 may be uniform within the irradiation target 102 as in this embodiment, or may be varied according to parameters such as the depth from the surface of the irradiation target 102.

[0079] With the above, the calculation of the water equivalent thickness ratio distribution on the first day (step S602) is completed. Return to FIG. 6, and next, the prescription sheet creation program 508 of the treatment planning device 112 creates a prescription sheet (step S603).

[0080] Using FIG. 7 again, the procedure for creating a prescription sheet will be described.

[0081] First, the prescription creation program 508 reads the pre-correction water equivalent thickness ratio distribution 905 output from the water equivalent thickness ratio calculation program 507 and the setting of the target volume 209 (step S705).

[0082] Next, the prescription creation program 508 sets the target dose for the target volume 209. The target dose is input by the doctor via the UI device 505 (step S706).

[0083] Next, based on the pre-correction water equivalent thickness ratio distribution 905, the prescription creation program 508 calculates the dose to be applied by the beam 103 irradiated to each spot to each calculation point specified within the target volume 209, and outputs it in the form of a matrix having the number of elements equal to the product of the number of spots and the number of calculation points (hereinafter referred to as the dose matrix) (step S707).

[0084] Next, based on the dose matrix, the prescription creation program 508 performs an optimization calculation of the irradiation dose for applying the target dose, and determines the prescription, that is, the spot position and the irradiation dose of each beam 103 (step S708).

[0085] Next, the prescription creation program 508 calculates the dose distribution formed by the prescription determined by the optimization calculation of the irradiation dose (step S709). The calculation result is confirmed by the doctor via the UI device 505. When approved by the doctor, the prescription is stored in the treatment planning device 112 and also transmitted to the overall control device 108 (step S710). Thus, the prescription creation (step S603) is completed. If not approved, the process returns to step S706 to perform re-setting of the target dose.

[0086] Returning to FIG. 6 again, next, after placing the patient on the treatment table 107 and aligning the position to match that during the X-ray CT image acquisition, the particle beam therapy system 101 starts irradiating the beam 103 (step S604). The irradiation is performed for each beam 103 adjusted based on the prescription input to the overall control device 108. The overall control device 108 controls the accelerator / beam transport system control device 109 and the irradiation nozzle control device 110 to change the spot position and irradiation dose of each beam 103.

[0087] The range measuring device 111 measures the actual range 402 (see FIG. 4) for each beam 103 in parallel with the irradiation (step S605). In FIG. 3, an example of performing range measurement while distinguishing the beam 103 by reading the prescription from the overall control device 108 is shown. However, during range measurement, the beam 103 may not be distinguished, and the measurement results may be distinguished into the components of each beam 103 later by referring to the irradiation time of each beam 103 recorded in the overall control device 108.

[0088] When all the planned irradiations are completed, next, the water equivalent thickness ratio correction program 509 starts the water equivalent thickness ratio correction (step S606). The procedure of the water equivalent thickness ratio correction will be described again with reference to FIG. 7.

[0089] First, the water equivalent thickness ratio correction program 509 reads the region 802 and the pre-correction water equivalent thickness ratio distribution 905 determined during the water equivalent thickness ratio calculation, and the prescription input during the prescription creation (step S711). Note that the implementation of step S711 does not necessarily need to be after the completion of the irradiation and range measurement (step S605), and it may be performed in parallel with any step after the prescription creation in step S603 and before the determination of the water equivalent thickness ratio correction amount in step S713.

[0090] Next, the water equivalent thickness ratio correction program 509 receives the measured flight distances 402 of the respective beams 103 obtained in step S605 from the flight distance measuring device 111 (step S712). The measured flight distances 402 may be received for all the irradiated beams 103, or the statistic of the detection signal 401 used for determining the measured flight distances 402 may be acquired from the detector control device 305 for reliability determination of the measurement results, and the measured flight distances 402 may be received only for the beams 103 for which the statistic exceeds a certain value.

[0091] Next, based on the prescription, the water equivalent thickness ratio distribution 905 before correction, the region 802, and the measured flight distance 402, a water equivalent thickness ratio correction amount is determined (step S713). A method for determining the water equivalent thickness ratio correction amount will be described with reference to FIGS. 8 and 10.

[0092] First, the input amount used for determining the water equivalent thickness ratio correction amount is calculated. Before describing the specific calculation method, the principle for determining the water equivalent thickness ratio correction amount will be described with reference to FIG. 8 in order to show the required input amount.

[0093] When the difference between the flight distance estimated from the water equivalent thickness ratio distribution 905 before correction (hereinafter referred to as the flight distance 803 before correction) and the measured flight distance 402 is caused by an error in the water equivalent thickness ratio distribution, the error in the water equivalent thickness on the measured beam path is considered to coincide with the water equivalent thickness of the path between the flight distance 803 before correction and the measured flight distance 402 (hereinafter referred to as the difference path 804). At this time, the following formula (1) holds.

Equation

[0094] However, since the number of equations in Equation (1) obtained by range measurement is limited to be less than or equal to the number of beams 103 used for treatment, there are often not enough equations for the number of variables δw, that is, the number of pixels. Therefore, in this embodiment, the differential path length 805, the water equivalent thickness ratio 806 before correction, and the measured path length 807 of each region 802 of each pixel are used as input quantities, and the water equivalent thickness ratio correction amount for each region 802 formed by combining a plurality of pixels is determined by the least squares method. That is, δw that minimizes the following Equation (2) is obtained.

Equation

[0095] The description of the principle for determining the water equivalent thickness ratio correction amount is as above. Next, the calculation procedure for each input quantity will be described with reference to FIG. 8.

[0096] First, the measured path length 807 of each region 802 is calculated. Assuming that the beam 103 travels toward the spot position specified by the prescription, the path is determined by setting the position of the measured range 402 as the end of the beam 103 (the solid arrow in FIG. 8). From this path, the path length for each region 802 is calculated, and these are used as the measured path lengths 807 and stored in the treatment planning device 112. In the example of FIG. 8, since the path straddles three regions, the measured path lengths (807A, 807B, 807C) of the three regions are stored.

[0097] Next, the differential path length 805 for each pixel and the pre-correction water equivalent thickness ratio 806 on that path are calculated. To calculate these input amounts, the pre-correction range 803 is required. The pre-correction range 803 is obtained from the integrated distance until the value obtained by integrating the pre-correction water equivalent thickness ratio along the direction determined according to the prescription and along that direction matches the range in water. The differential path 804 is determined from the obtained pre-correction range 803 and the measured range 402, and the differential path length 805 and the pre-correction water equivalent thickness ratio 806 at each pixel are calculated. In the example of FIG. 8, since the differential path 804 passes through only three pixels from pixel 1 to pixel 3, the differential path lengths (805A, 805B, 805C) and the pre-correction water equivalent thickness ratios (806A, 806B, 806C) at these three pixels may be calculated.

[0098] The treatment planning device 112 stores the sum of the products of the differential path length 805 and the pre-correction water equivalent thickness ratio 806 for each pixel for all pixels (corresponding to the water equivalent thickness on the differential path 804, hereinafter referred to as the differential water equivalent thickness).

[0099] Thus, all the input amounts used to determine the water equivalent thickness ratio correction amount are stored in the treatment planning device 112.

[0100] Return to step S713 in FIG. 7. Next, the water equivalent thickness ratio correction program 509 determines the water equivalent thickness ratio correction amount for each region 802 from the input amounts stored in the treatment planning device 112 (step S714).

[0101] The procedure for determining the water equivalent thickness ratio correction amount will be described with reference to FIG. 10. FIG. 10 is a diagram showing the procedure for determining the water equivalent thickness ratio correction amount using the least squares method.

[0102] First, the measured path length 807 for each region 802 of each beam 103 and the differential water equivalent thickness 1001 of each beam 103 stored in the treatment planning device 112 are called. Next, a water equivalent thickness ratio correction amount 1002, which is an unknown quantity, is defined, and the water equivalent thickness ratio correction amount 1002 that minimizes Equation (2) is obtained. Through the above calculations, the water equivalent thickness ratio correction amount 1002 for each region 802 is determined. Note that the determination method is not limited to the least squares method, and the water equivalent thickness ratio correction amount 1002 may be obtained by other methods.

[0103] Returning to FIG. 7, by storing the water equivalent thickness ratio correction amount 1002 in the treatment planning device 112, the water equivalent thickness ratio calculation program 119 can be read during the next treatment (step S714). Thus, the water equivalent thickness ratio correction (step S606) is completed. Returning to FIG. 6, the treatment on the first day ends due to the completion of the water equivalent thickness ratio correction.

[0104] Next, the treatment procedures after the second day will be described again with reference to FIGS. 6 and 7. However, the description of the same procedures as on the first day will be simplified. Also, in this embodiment, the treatment procedure on the second day will be described as a representative, but the procedures are the same for the third day and later.

[0105] After the start of the treatment on the second day (step S601), the water equivalent thickness ratio calculation is performed (step S602). First, region division is performed based on the X-ray CT image taken again on the second day. Next, the conversion to the water equivalent thickness ratio distribution and the determination of the target volume 209 are performed. When converting to the water equivalent thickness ratio distribution, the pre-correction water equivalent thickness ratio distribution 905 is created in the same procedure as on the first day, and then the corrected water equivalent thickness ratio distribution 906 is created. The detailed procedure of the conversion is shown in FIG. 9 described above. The corrected water equivalent thickness ratio distribution 906 is a distribution that takes into account the water equivalent thickness ratio correction amount 1002 determined on the previous day (referring to the first day in the treatment on the second day). The conversion to the corrected water equivalent thickness ratio distribution 906 is completed by reading the water equivalent thickness ratio correction amount 1002 saved on the previous day (step S903) and adding the water equivalent thickness ratio correction amount 1002 determined for each region 802 to the pre-correction water equivalent thickness ratio distribution 905 (step S904).

[0106] Return to step S704 in FIG. 7, and next, determine the target volume 209 (see FIG. 2). Similar to the first day, the contour of the tumor 211 extracted by the doctor is used as the target volume 209 in a range expanded outward by the margin amount corrected based on the treatment result of the previous day. As a method for correcting the margin 210, in order to reflect the goodness of the application of the water equivalent thickness ratio correction amount 1002 determined on the previous day, for example, a coefficient inversely proportional to the value obtained by substituting the water equivalent thickness ratio correction amount 1002 determined for δw in Equation (2) (the smaller the value, the better the application) is integrated into the predetermined margin. Alternatively, a value proportional to the magnitude of the range error during the treatment on the previous day may be set, or it may be reduced according to the number of pieces of information on the measured range 402 stored in the treatment planning device 112 in the treatment up to the previous day.

[0107] Return to FIG. 6, and next, create a prescription (step S603). The procedure for creating the prescription is the same as on the first day. However, in order to reflect the effect of the water equivalent thickness ratio correction in the treatment plan, instead of the pre-correction water equivalent thickness ratio distribution 905, the corrected water equivalent thickness ratio distribution 906 created on the second day is read and used for creating the prescription.

[0108] After creating the prescription, perform particle beam irradiation and range measurement in the same procedure as on the first day (steps S604, S605), and then perform water equivalent thickness ratio correction (step S606).

[0109] In the water equivalent thickness ratio correction, first, calculate the differential water equivalent thickness 1001 of each beam 103 and the measured path length 807 for each region 802 from the prescription on the second day, the pre-correction water equivalent thickness ratio distribution 905, the measured range 402, and the region 802, and store them in the treatment planning device 112. Next, determine the water equivalent thickness ratio correction amount 1002 in the same procedure as on the first day. However, not only the differential water equivalent thickness 1001 and the measured path length 807 on the second day but also the differential water equivalent thickness 1001 and the measured path length 807 stored in the treatment planning device 112 up to the previous day are also used as the input amounts. By this method, it is expected that the correction will be more accurate than on the first day.

[0110] After determining the water equivalent thickness ratio correction amount 1002, follow the same procedure as on the first day, and the treatment on the second day will be completed. Repeat the treatment procedure described above until the 29th day.

[0111] Next, the treatment procedure on the 30th day will be described with reference to FIG. 6. From the start of treatment (step S601) to beam irradiation and range measurement (step S605), perform treatment in the same procedure as from the second day to the 29th day. In this embodiment, since the 30th day is the last day of treatment, the water equivalent thickness ratio correction (step S606) is skipped, and the treatment on the 30th day is completed.

[0112] In this embodiment, it is assumed that the water equivalent thickness ratio correction is performed every day from the first day to the 29th day. However, it is not necessary to perform the water equivalent thickness ratio correction every day, and for example, it may be performed every other day.

[0113] When the treatment on the 30th day is completed, the particle beam treatment in this embodiment ends.

[0114] Next, the effects of this embodiment will be described.

[0115] In the treatment planning device 112 of the above-described embodiment 1, using the actually measured path length 807 by the range measurement device 111 as an input quantity, it is possible to determine the water equivalent thickness ratio correction amount 1002 for each region 802 determined from the X-ray CT image 801. At the time of the next day's treatment, when converting the X-ray CT image 801 into a water equivalent thickness ratio distribution by dividing the region 802, by adding the water equivalent thickness ratio correction amount 1002 calculated during the previous day's treatment to the pre-correction water equivalent thickness ratio 806 of each pixel, it is possible to obtain a corrected water equivalent thickness ratio distribution 906 that takes into account the difference in the correlation between the CT value and the water equivalent thickness ratio for each patient. By performing the treatment plan using the corrected water equivalent thickness ratio distribution 906, it is possible to suppress the range error caused by the patient dependence of the water equivalent thickness ratio, and the treatment accuracy is improved. Furthermore, by reducing the margin 210 according to the improvement of the treatment accuracy, it is expected that the application of particle beam treatment to pancreatic cancer and the like, which was difficult to apply high-dose irradiation in conventional particle beam treatment without performing water equivalent thickness ratio correction, will become possible.

[0116] In the particle beam therapy system 101, the measurement of the actual range 402 necessary for water equivalent thickness ratio correction is carried out in parallel with beam irradiation. Also, since the water equivalent thickness ratio correction is automatically executed by the water equivalent thickness ratio correction program 509, it does not restrict patients or doctors. Therefore, the treatment time does not increase for water equivalent thickness ratio correction. Also, since beam irradiation other than treatment is not necessary, the size of the apparatus does not become larger than that of a general particle beam therapy system.

[0117] In water equivalent thickness ratio correction using the measurement of the range of the beam irradiated during treatment, since the number of information of the actual range 402 is limited to not more than the number of beams, it is often the case that the water equivalent thickness ratio cannot be corrected for each pixel of the X-ray CT image 801. To correct the water equivalent thickness ratio, it is necessary to divide the X-ray CT image 801 into at least the number of regions 802 equal to or less than the number of information of the actual range 402. However, in the method of uniformly determining the water equivalent thickness ratio for each region 802, the greater the difference in the water equivalent thickness ratio within the region 802, the lower the accuracy.

[0118] In this embodiment, instead of determining the water equivalent thickness ratio itself for each region 802, a method is used in which the water equivalent thickness ratio correction amount 1002 is determined and added to the water equivalent thickness ratio of each pixel before correction. Therefore, even if the difference in the water equivalent thickness ratio within the region 802 is large, the correction accuracy does not decrease as long as the magnitude and sign of the error are about the same. That is, by dividing the region 802 and determining the water equivalent thickness ratio correction amount 1002 for each region 802, it is possible to improve the treatment accuracy from a limited number of information.

Example

[0119] The treatment planning apparatus of Example 2 will be described with reference to FIG. 11. The same components as those in Example 1 are denoted by the same reference numerals, and the description thereof is omitted. FIG. 11 is a part of a flowchart showing the procedure of particle beam therapy in Example 2.

[0120] In this embodiment, an interlock based on error determination after the range measurement of each beam 103 is added to the particle beam therapy procedure shown in FIG. 6 (step S1101). After the irradiation and range measurement of each beam 103 (step S605), a range error is calculated. If the range error exceeds a set threshold (NO in S1101), the planned irradiation is stopped, and water equivalent thickness ratio correction (step S606) is performed based on the beam information irradiated until the stop, and the treatment session is ended. Next, a new treatment session is started, and the treatment plan is performed again based on the water equivalent thickness ratio correction amount 1002 obtained in step S606 of the previous treatment session and the irradiated dose, and the irradiation is resumed. Before the treatment plan, the patient X-ray CT image 801 may be re-taken, or the previously taken image may be used.

[0121] In order to perform the determination of the range error for each irradiation of each beam 103, it is necessary to calculate in advance for each beam 103 the range (hereinafter, planned range) assumed by the prescription creation program 508 until the start of irradiation. To calculate the planned range, the corrected water equivalent thickness ratio distribution 906 may be substituted for the uncorrected water equivalent thickness ratio distribution 905 in the calculation procedure of the uncorrected range 803. The planned range is calculated by the water equivalent thickness ratio correction program 509 after the prescription is created and stored in the treatment planning apparatus 112.

[0122] The determination of the range error is performed by calculating the difference between the stored planned range and the measured range 402. The threshold value of the range error may be set by a doctor via the UI device 505 for each treatment, or a program for calculating a threshold value depending on irradiation conditions such as the spot position may be introduced into the treatment planning apparatus 112 to automatically set it.

[0123] Next, the effects of this embodiment will be described.

[0124] In the treatment flow of Example 1, the prescription created at each treatment is carried out to the final spot regardless of the magnitude of the range error. Therefore, irradiation is not terminated due to the range measurement result, and the treatment time does not increase. However, especially on the initial treatment days when the water equivalent thickness ratio correction accuracy is not high, range errors on a scale larger than the margin 210 occur, and the risk of damage to dangerous organs and the like cannot be eliminated.

[0125] On the other hand, by adding an interlock after irradiation as in Example 2, it is possible to suppress the application of a large dose outside the target volume 209. Therefore, compared with the effect obtained by Example 1, although there is a possibility that the treatment time increases, further improvement in treatment accuracy, particularly reduction in the possibility of damage to dangerous organs, is expected.

[0126] Note that the present invention is not limited to the above-described embodiments and includes various modifications. The above-described 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. Further, it is possible to add, delete, or replace other configurations for a part of the configuration of each embodiment.

[0127] For example, although the case of using the water equivalent thickness ratio for the physical quantity to be corrected has been described, it is also possible to use the stopping power ratio (the ratio of the energy lost in the target tissue and the energy lost in the reference tissue while the particle beam passes through a unit length) instead of the water equivalent thickness ratio.

[0128] Also, although the target volume 209 obtained by adding the margin 210 to the tumor 211 has been cited as the target for setting the target dose, it is also possible to additionally set the target dose for dangerous organs and the like around the target volume 209.

[0129] Also, although the water equivalent thickness ratio correction was to be performed after the particle beam irradiation on each treatment day, information such as the prescription and the actually measured range on each treatment day may be stored until the next day and the correction may be performed before the calculation of the water equivalent thickness ratio on the next day.

[0130] In addition, each of the above-described configurations, functions, processing units, processing means, etc. may be realized in hardware by designing a part or all of them, for example, by using an integrated circuit. Also, each of the above-described configurations, functions, etc. may be realized in software by a processor interpreting and executing a program for realizing each function. Information such as a program, a table, and a file for realizing each function can be stored in a memory, a recording device such as a hard disk or an SSD, or a recording medium such as an IC card, an SD card, or a DVD.

[0131] Also, the control lines and information lines show those considered necessary for explanation, and not necessarily all the control lines and information lines are shown on the product. In practice, it may be considered that almost all the components are interconnected. (Appendix 1) A treatment planning device for generating a treatment plan for irradiating a particle beam to an irradiation target, calculating a correction amount for the water equivalent thickness ratio of a previously created first treatment plan, calculating a water equivalent thickness ratio distribution based on the correction amount and the first treatment plan, and creating a second treatment plan from the water equivalent thickness ratio distribution The treatment planning device is characterized by this. (Appendix 2) The treatment planning device according to (Appendix 1), characterized in that the correction amount is calculated based on the measured range of the particle beam measured along with the irradiation of the particle beam. (Appendix 3) The treatment planning device according to (Appendix 2), characterized in that the measured range is based on the measurement result of prompt gamma rays generated along with the irradiation of the particle beam. (Appendix 4) The first treatment plan includes irradiation conditions of the particle beam, The treatment planning device according to (Appendix 2), characterized in that the correction amount is calculated based on the measured range and the irradiation conditions. (Appendix 5) The treatment planning device according to (Appendix 2), characterized in that image data obtained by imaging the irradiation target is divided into a plurality of regions, and the correction amount for each region is calculated. (Appendix 6) The treatment planning device according to (Appendix 2), characterized in that the pre-correction range of the particle beam is obtained from the first treatment plan, and the correction amount is calculated based on the measured range and the pre-correction range. (Appendix 7) Image data composed of a plurality of pixels obtained by imaging the irradiation target is divided into a plurality of regions each having a plurality of the pixels. The measured path length in the region obtained based on the measured range, the difference path length which is the difference between the measured range and the pre-correction range for each pixel constituting the region, and the water equivalent thickness ratio for each pixel constituting the region are input, and the correction amount for each region is obtained by the least squares method. The treatment planning device according to (Appendix 6) is characterized by this. (Appendix 8) The treatment planning device according to (Appendix 2), characterized in that when the treatment plan irradiates the target dose of the particle beam by dividing it into a plurality of times, a plurality are created for each irradiation, and the second treatment plan is for irradiating the particle beam after the first treatment plan. (Appendix 9) The treatment planning device according to (Appendix 2), characterized in that the measured range is the measured range of the particle beam irradiated based on the first treatment plan. (Appendix 10) The treatment planning device described in (Appendix 1), an accelerator that accelerates a particle beam, an irradiation device that irradiates an irradiation target with the particle beam accelerated by the accelerator, a treatment planning device that generates a treatment plan for irradiating the irradiation target with the particle beam, a range measurement device that measures the range of the particle beam A particle beam therapy system having. (Appendix 11) The treatment planning device obtains the pre-correction range of the particle beam from the first treatment plan, When the difference range, which is the difference between the actually measured range of the particle beam measured by the range measurement device and the pre-correction range during the irradiation of the particle beam, exceeds a predetermined threshold value, the irradiation device stops irradiating the particle beam, After that, the treatment planning device calculates the correction amount The particle beam therapy system according to (Appendix 10), characterized in that. (Appendix 12) A treatment plan creation method by a treatment planning device that creates a treatment plan for irradiating an irradiation target with a particle beam, Calculating a correction amount of the water equivalent thickness ratio of a first treatment plan created in advance, Calculating a water equivalent thickness ratio distribution based on the correction amount and the first treatment plan, Creating a second treatment plan from the water equivalent thickness ratio distribution A treatment plan creation method characterized by that. (Appendix 13) A computer program executed by a computer that generates a treatment plan for irradiating a target with a particle beam, A function of calculating a correction amount of the water equivalent thickness ratio of a first treatment plan created in advance, A function of calculating a water equivalent thickness ratio distribution based on the correction amount and the first treatment plan, A function of creating a second treatment plan from the water equivalent thickness ratio distribution A computer program that realizes.

Explanation of Symbols

[0132] 101…Particle beam therapy system 102…Irradiation target 103…Beam 104…Accelerator system 105…Beam transport system 106…Irradiation nozzle 107…Treatment table 108…Overall control device 109…Accelerator / beam transport system control device 110…Irradiation nozzle control device 111…Range measurement device 112…Treatment planning device 209…Target volume 210…Margin 211…Tumor 301…Prompt gamma ray 302…Collimator 303…Slit 304…Array type detector 305…Detector control device 402…Measured range 501…CPU 502…Memory 503…Storage device 504…Communication interface 505…UI device 507…Water equivalent thickness ratio calculation program 508…Prescription creation program 509…Water equivalent thickness ratio correction program 801…X-ray CT image 802A, 802B, 802C…Regions 803…Range before correction 804…Differential path 805A, 805B, 805C…Differential path length 806A, 806B, 806C…Water equivalent thickness ratio before correction 807A, 807B, 807C…Measured path length 905…Water equivalent thickness ratio distribution before correction 906…Corrected water equivalent thickness ratio distribution 1001…Differential water equivalent thickness 1002…Water equivalent thickness ratio correction amount

Claims

1. A treatment planning device, a first prescription indicating each irradiation condition of each of the particle beams when irradiating a subject with a plurality of particle beams, each measured actual range of the particle beams measured as each of the particle beams is irradiated to the subject based on the first prescription, a pre-correction water equivalent thickness ratio distribution in the subject, and calculates a water equivalent thickness ratio correction amount in the subject based on the classification of regions related to the subject, creates a corrected water equivalent thickness ratio distribution in the subject based on the pre-correction water equivalent thickness ratio distribution and the water equivalent thickness ratio correction amount, and is a treatment planning device that creates a second prescription indicating each irradiation condition of each of the particle beams when irradiating the subject with a plurality of particle beams based on the corrected water equivalent thickness ratio distribution in the subject, wherein the classification of the regions related to the subject is based on the classification of regions for each type of internal tissue by a doctor based on the X-ray CT image data of the subject, or by grouping pixels with close CT values in the X-ray CT image data of the subject into one region, the treatment planning device.

2. The treatment planning device according to claim 1, wherein each of the measured actual ranges is based on the measurement result of prompt gamma rays generated with each irradiation of each of the particle beams. The treatment planning device is characterized by this.

3. The treatment planning device according to claim 1, when classifying the subject into a plurality of regions, the X-ray CT image data obtained by imaging the subject is classified into a plurality of regions, and when calculating the water equivalent thickness ratio correction amount in the subject, calculates the water equivalent thickness ratio correction amount for each region. The treatment planning device is characterized by this.

4. The treatment planning device according to claim 1, obtains each pre-correction range of each of the particle beams based on the first prescription and the pre-correction water equivalent thickness ratio distribution, and when calculating the water equivalent thickness ratio correction amount in the subject based on the first prescription, each of the measured actual ranges, the pre-correction water equivalent thickness ratio distribution, and the classification of regions related to the subject, calculates the water equivalent thickness ratio correction amount based on each of the measured actual ranges, each of the pre-correction ranges, the pre-correction water equivalent thickness ratio distribution, and the classification of regions related to the subject. The treatment planning device is characterized by this.

5. The treatment planning device according to claim 4, When dividing the irradiation target into a plurality of regions, X-ray CT image data composed of a plurality of pixels obtained by imaging the irradiation target is divided into a plurality of regions each having a plurality of the pixels. A treatment planning apparatus, wherein when calculating the water equivalent thickness ratio correction amount based on each of the actually measured ranges, each of the correction-before ranges, the correction-before water equivalent thickness ratio distribution, and the division of the region regarding the irradiation target, the actually measured path length in the region obtained based on each of the actually measured ranges, the difference path length which is the difference between each of the actually measured ranges and each of the correction-before ranges for each of the pixels constituting the region, and the correction-before water equivalent thickness ratio for each of the pixels constituting the region are input, and the water equivalent thickness ratio correction amount for each region is obtained by the least squares method.

6. The treatment planning apparatus according to claim 1, wherein when the treatment planning apparatus irradiates the target particle beam by dividing the target beam dose into a plurality of times, a plurality of prescriptions are created for each irradiation. The treatment planning apparatus, wherein the second prescription is for irradiating the particle beam after the irradiation of the particle beam based on the first prescription.

7. A particle beam therapy system, comprising the treatment planning apparatus according to claim 1, an accelerator for accelerating the particle beam, an irradiation apparatus for irradiating the irradiation target with the particle beam accelerated by the accelerator, and a range measuring apparatus for measuring the range of the particle beam. A particle beam therapy system having the above components.

8. The particle beam therapy system according to claim 7, wherein the treatment planning apparatus obtains the planned range of the particle beam based on a prescription indicating irradiation conditions when irradiating the irradiation target with the particle beam and the water equivalent thickness ratio distribution in the irradiation target, the irradiation apparatus stops the irradiation of the particle beam when a range error, which is the difference between the actually measured range of the particle beam measured by the range measuring apparatus and the planned range, exceeds a predetermined threshold value during the irradiation of the particle beam, and after the stop of the irradiation of the particle beam, the treatment planning apparatus calculates the water equivalent thickness ratio correction amount. A particle beam therapy system characterized by the above.

9. A computer program, for a computer, A first prescription indicating the respective irradiation conditions of the plurality of particle beams when irradiating an irradiation target, each of the measured flight paths of the particle beams measured as the particle beams are irradiated on the irradiation target based on the first prescription, the pre-correction water equivalent thickness ratio distribution in the irradiation target, and a function of calculating the water equivalent thickness ratio correction amount in the irradiation target based on the classification of the region related to the irradiation target. A function of creating a corrected water equivalent thickness ratio distribution in the irradiation target based on the pre-correction water equivalent thickness ratio distribution and the water equivalent thickness ratio correction amount. A computer program for realizing a function of creating a second prescription indicating the respective irradiation conditions of the plurality of particle beams when irradiating the irradiation target, based on the corrected water equivalent thickness ratio distribution in the irradiation target. The classification of the region related to the irradiation target is based on the region being classified by a doctor for each type of internal tissue based on the X-ray CT image data of the irradiation target, or by grouping pixels with close CT values in the X-ray CT image data of the irradiation target into one region. Computer program.

Images