Radiation therapy system, its operating method and operating program

Abstract

To provide a radiotherapy technique that maximizes the absorbed dose in lesion tissue while minimizing the absorbed dose in normal tissue, even if the internal position of the lesion has changed since the treatment planning stage. [Solution] The system includes a storage unit (30) that stores first movement information (31) for moving a tabletop (26) so that a first position (21) of a lesion (15) identified from first voxel data (11) coincides with an isocenter (16) of a beam (20) that administers a dose to the lesion (15), and irradiation conditions (35) for the beam (20) that are set so that the lesion coverage rate of the patient (25) due to irradiation with the beam (20) is maximized at the first position (21); an identification unit (19b) that identifies a second position (22) of the lesion (15) from second voxel data (12) captured immediately before irradiating the beam (20); and an update unit (50) that updates the first movement information (31) to second movement information (32) so that the lesion coverage rate (40) at the position of the lesion (15) of the patient (25) is maximized without changing the irradiation conditions (35).

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to a radiation therapy technique for treating a lesion by beam irradiation. [Background technology]

[0002] Radiation therapy is a treatment technique that irradiates and destroys a patient's lesion (such as cancer) with a beam. When a particle beam, such as a carbon ion beam, passes through the patient's body, its kinetic energy decreases, and it suddenly stops when its speed drops to a certain value. Near this stopping point, the particle beam forms a dose distribution called a Bragg peak and releases energy.

[0003] The beam irradiation conditions and patient position are then determined so that the lesion is located at the end of the beam range where energy is emitted, i.e., at the Bragg peak, thereby achieving treatment that maximizes the absorbed dose in the lesion tissue while minimizing the absorbed dose in normal tissue due to beam irradiation.

[0004] Therefore, if the Bragg peak is not accurately aligned with the lesion, there is a risk of damaging normal tissue as well. Therefore, treatment planning is performed before the patient is irradiated with the beam. In this treatment planning, the patient is scanned with a CT scan to obtain voxel data, and the internal location and shape of the lesion are determined in three dimensions. The position of the tabletop on which the patient is immobilized and the beam irradiation conditions are then determined to minimize the radiation dose to normal tissue and deliver a sufficient dose to the lesion tissue.

[0005] However, it takes a certain amount of time to determine the setting position of the tabletop and the beam irradiation conditions. For this reason, it generally takes several days from the time of treatment planning to the time of treatment implementation. In addition, organs such as the pancreas, which are surrounded by the digestive tract, have the characteristic that their internal positions are not fixed depending on the amount of food eaten, body movements, etc. Lesions occurring in such organs may be displaced in the internal position at each stage of treatment planning and treatment implementation.

[0006] In such cases, images of the patient's body are taken during treatment to observe any lesions that have shifted since the treatment planning stage, and the position of the patient's table and the irradiation conditions of the beam are then adjusted based on the observed shift of the lesion before the beam is irradiated. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-172165 [Patent Document 2] Japanese Patent Application Publication No. 2019-147029 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-209012 Summary of the Invention [Problem to be solved by the invention]

[0008] The attenuation of the beam passing through the patient's body is significantly affected by gastrointestinal gas and the density of the tissue along the beam's range. Therefore, if the water equivalent length to the lesion assumed in the treatment plan differs, the beam range within the patient's body may differ from that expected in the original treatment plan.

[0009] This may result in the Bragg peak being formed at a position different from the actual position of the lesion imaged during treatment. For this reason, it has been pointed out that simply changing the setting position of the tabletop based solely on the displacement of the bone or lesion confirmed by X-ray imaging may result in an insufficient dose being delivered to the lesion tissue, and an increased radiation dose being delivered to normal tissue.

[0010] Furthermore, if the beam irradiation conditions are also modified to avoid an increase in the irradiation dose in normal tissue, the modification takes a lot of time, which places a burden on the patient and leads to an increase in treatment time.

[0011] The embodiments of the present invention have been made in consideration of the above circumstances, and aim to provide a radiation therapy technique that can maximize the absorbed dose in lesion tissues while minimizing the absorbed dose in normal tissues, even when changes in the internal position of the lesion or changes in the density of gastrointestinal gas or tissues along the beam range occur during the treatment planning stage. [Means for solving the problem]

[0012] In a radiation therapy system according to an embodiment, the system includes: first movement information for moving a tabletop to which a patient is fixed so that a first position of a focus identified from first voxel data obtained by imaging the inside of the patient's body coincides with an isocenter of a beam that administers a dose to the focus; irradiation conditions of the beam set so that the focus coverage rate of the patient by irradiating the beam is maximized at the first position; a storage unit that stores the irradiation conditions of the beam and the first movement information of the tabletop; an identification unit that identifies a second position of the focus from second voxel data obtained by imaging the inside of the patient's body immediately before irradiating the beam; and an update unit that updates the first movement information to second movement information so that the focus coverage rate at the position of the focus of the patient is maximized without changing the irradiation conditions. [Effects of the Invention]

[0013] Embodiments of the present invention provide a rapid radiation therapy technique that maximizes the absorbed dose to the lesion tissue while minimizing the absorbed dose to normal tissue, even when treatment planning involves changes in the location of the lesion within the body or changes in gastrointestinal gas or tissue density along the beam range. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a configuration diagram of a radiation therapy system according to a first embodiment of the present invention. [Figure 2] 3A and 3B are explanatory diagrams of rotational motion around an isocenter in the radiation therapy system according to each embodiment. [Figure 3] FIG. 10 is a configuration diagram of an update unit of a radiation therapy system according to a second embodiment. [Figure 4](A) A graph showing the dose distribution relative to the direction of incidence of the beam irradiated to the lesion at the first position of the first voxel data captured during the treatment planning stage. (B) A graph showing the dose distribution relative to the direction of incidence of the beam irradiated to the lesion at the second position of the second voxel data captured during the treatment implementation stage. (C) A graph showing the dose distribution relative to the direction of incidence of the beam irradiated to the lesion at a selected position selected by updating the isocenter position so that the lesion coverage rate is maximized. [Figure 5] 1 is a flowchart illustrating steps of an operation method of a radiation therapy system according to an embodiment and an algorithm of an operation program for the radiation therapy system. DETAILED DESCRIPTION OF THE INVENTION

[0015] (First embodiment) Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a configuration diagram of a radiation therapy system 10 according to a first embodiment of the present invention. Prior to a treatment 14 performed by this radiation therapy system 10, a treatment plan 13 is prepared in advance. This treatment plan 13 is performed in a location different from a treatment room 36 in which the treatment 14 is performed. In the treatment plan 13, a patient 25 assumes the same posture as when the patient 25 is fixed to a tabletop 26 and irradiated with a beam 20 in the treatment 14, and first voxel data 11 is captured. Then, in the treatment plan 13, first movement information 31 and irradiation conditions 35 are ultimately derived.

[0016] The first voxel data 11 is a three-dimensional image (stereoscopic image) of the inside of the body of a patient 25 captured at the stage of treatment planning 13 using a medical stereoscopic imaging device such as an X-ray CT (Computed Tomography) or MRI (Magnetic Resonance Imaging).

[0017] The first movement information 31 is data for moving the tabletop 26 on which the patient 25 is fixed so that the first position 21 of the lesion 15a identified from the first voxel data 11 obtained by imaging the inside of the patient 25 coincides with the isocenter 16 of the beam 20 that administers a dose to the lesion 15a.

[0018] The identification unit 19a (19) identifies the first position 21 of the lesion 15, which is different from normal tissue, in the first voxel data 11 in a coordinate system defined based on a non-displaced area such as bone or the reference position of the imaging device.

[0019] The generation unit 17 has a function of generating movement information to be input to a transport mechanism (not shown) that positions the top 26 in the treatment room 36. At the stage of the treatment plan 13, the generation unit 17 generates, as first movement information 31, a command to the transport mechanism (not shown) required to position the top 26 so that the first position 21 of the lesion 15a and the isocenter 16 of the beam 20 coincide with each other.

[0020] The transport mechanism (not shown) has an inherent function of adjusting the position and posture of the tabletop 26 in a coordinate system defined based on the treatment room 36. The generation unit 17 converts the first position 21 defined in the coordinate system of the first voxel data 11 into the coordinate system of the treatment room 36, and then generates first movement information 31 so as to align the first position 21 with the isocenter 16 originally defined in the coordinate system of the treatment room 36.

[0021] The adjustment unit 18 adjusts irradiation conditions 35, such as the radiation dose, irradiation angle, irradiation range, number of times, etc., of the beam 20 irradiated onto the lesion 15. In the treatment plan 13, the irradiation conditions 35 are set so that the lesion coverage rate 56a (FIG. 4) of the patient 25 irradiated with the beam 20 is maximized at the first position 21. Here, the lesion coverage rate 56 refers to the coverage rate of the prescribed dose at the lesion 15.

[0022] The radiation therapy system 10 operating during treatment implementation 14 includes a storage unit 30 that stores data on irradiation conditions 35 of the beam 20 and first movement information 31 of the tabletop 26, an identification unit 19b (19) that identifies the second position 22 of the lesion 15 from second voxel data 12 imaged from the inside of the patient 25 immediately before irradiating the beam 20, and an update unit 50 that updates the first movement information 31 to second movement information 32 so as to maximize the lesion coverage rate 56 at the position of the lesion 15 of the patient 25 without changing the irradiation conditions 35.

[0023] 2 is an explanatory diagram of the rotational movement of the radiation therapy system 10 of each embodiment about the isocenter 16. An irradiation port 27, which irradiates the beam 20, is fixed to the rotating gantry 28 of the radiation therapy system 10. By rotating this irradiation port 27 together with the rotating gantry 28 about the rotation axis, the beam 20 can be irradiated from any direction toward the lesion 15 (15a, 15b) of the patient 25 without tilting the tabletop 26. By rotating the irradiation port 27 about the body axis of the patient 25 in this way, the beam 20 can be irradiated toward the lesion 15 from multiple directions, minimizing the dose to normal tissue surrounding the lesion.

[0024] The rotating gantry 28 is a large structure generally having a cylindrical shape, and the outer peripheral surfaces of both edges of the rotating gantry 28 are The rotating gantry 28 rotates around the rotation axis by the rotational drive of a plurality of rotational drive units 37 circumscribing the rotating gantry 28. A treatment room 36 is formed inside a movable floor 38 that is provided along the inner peripheral surface of the rotating gantry 28 and moves in accordance with the rotation of the rotating gantry 28. The weight of the rotating gantry 28 is supported by a stationary system (not shown) via the rotational drive units 37.

[0025] In addition to the irradiation port 27, the rotating gantry 28 also has a beam transport port (not shown). There are numerous transmission ducts, beam deflection magnets, and other control equipment and structures. The beam 20 is generated by accelerating ions (heavy particles or proton ions) generated in an ion source (not shown) using a linear accelerator and then injecting them into a circular accelerator (not shown) to increase the energy to a set level. The beam 20 output from the circular accelerator is then transported through a beam transport system (not shown) and irradiated from an irradiation port 27 toward the isocenter 16 located on the rotation axis of a rotating gantry 28.

[0026] Returning to Figure 1, we continue the explanation. In the radiotherapy system 10, a stereoscopic imaging device consisting of two pairs of X-ray tubes 23 and X-ray detectors 24 is provided on a rotating gantry 28, crossing each other at a 90-degree angle. Here, the X-ray detector 24 has detection elements for X-rays 29 arranged in a two-dimensional array.

[0027] The imaging unit 45 irradiates X-rays 29 from the X-ray tube 23 toward the isocenter 16. The X-ray detector 24 detects the X-rays 29 that have passed through the patient 25 with detection elements based on the amount of energy attenuation, and causes the imaging unit 45 to receive a two-dimensional fluoroscopic image of the patient 25. The imaging unit 45 then instructs the rotation control unit 48 to rotate the rotating gantry 28 at least a quarter of a turn.

[0028] Furthermore, the imaging unit 45 acquires a plurality of two-dimensional fluoroscopic images of the patient 25 taken from different directions, and creates second voxel data 12. In this way, the imaging unit 45 captures the second voxel data 12 by rotating the combination of the X-ray tube 23 and the X-ray detector 24 around the isocenter 16 in synchronization with the rotating gantry 28.

[0029] Although the X-ray tube 23 and X-ray detector 24 are shown here as being integrated with the rotating gantry 28, they may be configured and controlled so that they can rotate independently without being synchronized. In this case, the rotating gantry 28, which is a large structure, does not need to be rotated, and therefore higher speeds in operation can be expected.

[0030] The identification unit 19b (19) identifies a second position 22 of the lesion 15b, which is different from normal tissue, in the second voxel data 12 in a coordinate system defined based on a non-displaced area such as bone or the reference position of the imaging device. Therefore, the identification unit 19b (19) in the treatment implementation 14 stage has the same function as the identification unit 19a (19) in the treatment planning 13 stage. As a result, the first voxel data 11 and the second voxel data 12 are expressed in a common coordinate system.

[0031] The storage unit 30 stores data of the irradiation conditions 35 of the beam 20 and the first movement information 31 of the tabletop 26 set in the treatment plan 13 as initial settings. The update unit 50 does not change the irradiation conditions 35, but updates the first movement information 31 to second movement information 32 so as to maximize the lesion coverage rate 56 at the position of the lesion 15 of the patient 25. Then, the setting unit 46 sets the tabletop 26, to which the patient 25 is fixed, in the coordinate system of the treatment room 36 based on the updated second movement information 32.

[0032] After setting the tabletop 26 based on the second movement information 32, the rotation control unit 48 rotates and displaces the rotating gantry 28 based on the irradiation conditions 35 set in the treatment plan 13. Then, the irradiation unit 47 irradiates the patient 25 with the beam 20 based on the irradiation conditions 35.

[0033] Here, the beam 20 refers to radiation that is irradiated onto lesion tissue such as cancer to kill cells, and examples of such radiation include X-rays, gamma rays, electron beams, proton beams, and heavy particle beams. Furthermore, although the irradiation port 27 of the beam 20 is exemplified as a rotating gantry 28 that rotates around the isocenter 16, the present invention is not limited to this, and the irradiation port 27 may be a fixed type that is fixed to the treatment room 36.

[0034] In addition, the imaging unit 45 for the second voxel data 12 has been exemplified as having a function of capturing a two-dimensional transmission image for comparison with a DRR (Digitally Reconstructed Radiograph), which is a two-dimensional image reconstructed from the first voxel data 11 used in the treatment plan 13, in order to accurately align the tabletop 26 on which the patient 25 is fixed. However, the imaging unit for the second voxel data 12 is not limited to this, and may be a general-purpose medical stereoscopic imaging device such as an X-ray CT or MRI, which is independently installed in a position outside the isocenter 16 inside or outside the treatment room 36.

[0035] (Second embodiment) Next, a second embodiment of the present invention will be described with reference to Figures 1 and 3. Figure 3 is a configuration diagram of the update unit 50 of the radiation therapy system 10 according to the second embodiment. The radiation therapy system 10 of the second embodiment is characterized by the configuration of the update unit 50, which is one of the configurations of the first embodiment described above.

[0036] In the second embodiment, the update unit 50 includes a calculation unit 53 that calculates the dose distribution 40 of the patient 25 when the beam 20 is irradiated to each of a plurality of temporary positions 52 surrounding the second position 22 under irradiation conditions 35; a derivation unit 55 that derives a focus coverage rate 56 at the position of the focus 15 for each of the plurality of dose distributions 40; a selection unit 57 that selects the temporary position 52 with the maximum focus coverage rate 56 as the selected position 58 from among the plurality of temporary positions 52; a calculation unit 41 that calculates a difference vector 51 between the selected position 58 and the first position 21; and an addition unit 59 that adds the difference vector 51 to the first movement information 31 and outputs the second movement information 32.

[0037] The provisional setting unit 42 provisionally sets a plurality of provisional positions 52 in the coordinate system of the second voxel data 12 around and including the second position 22. That is, the provisional setting unit 42 provisionally sets a plurality of provisional positions 52 around and including the second position 22 identified from the second voxel data 12, using the coordinate system of the second voxel data 12. As a result, in the coordinate system of the second voxel data 12, a plurality of provisional positions 52 are set at regular intervals with the second position 22 as the center.

[0038] Fig. 4(A) is a graph showing a dose distribution 40a relative to the approach direction of the beam 20 irradiated to the focus 15a at the first position 21 of the first voxel data 11 captured during the treatment planning stage 13. Fig. 4(B) is a graph showing a dose distribution 40b relative to the approach direction of the beam 20 irradiated to the focus 15b at the second position 22 of the second voxel data 12 captured during the treatment implementation stage 14. Fig. 4(C) is a graph showing a dose distribution 40c relative to the approach direction of the beam 20 irradiated to the focus 15 at the selected position 58 selected by updating the position of the isocenter 16 so that the focus coverage ratio 56 is maximized.

[0039] The calculation unit 53 calculates a dose distribution 40b (FIG. 4(B)) inside the body of the patient 25 when the beam 20 is irradiated to the isocenter 16 at the second position 22 under the irradiation conditions 35 set in the treatment plan 13. Then, the derivation unit 55 derives a focus coverage ratio 56b in the focus 15 for this dose distribution 40b.

[0040] Similarly, the calculation unit 53 calculates a dose distribution 40 inside the body of the patient 25 when the beam 20 is irradiated to each of the plurality of temporary positions 52 under the irradiation conditions 35 set in the treatment plan 13. Then, the derivation unit 55 derives a focus coverage ratio 56 in the focus 15 for each of the plurality of dose distributions 40. Furthermore, the selection unit 57 selects, as a selected position 58, the one having the maximum focus coverage ratio 56c ( FIG. 4(C) ) from among the plurality of temporary positions 52 including the second position 22.

[0041] Returning to Figure 3, the explanation continues. The difference vector 51 calculated by the calculation unit 41 corresponds to the distance and direction of displacement of the lesion 15 in the first voxel data 11 or the second voxel data 12 from the treatment planning stage 13 to the treatment implementation stage 14. Then, the second movement information 32 obtained by adding the difference vector 51 to the first movement information 31 by the addition unit 59 corresponds to the position of the lesion 15 at the treatment implementation stage 14 in the coordinate system of the treatment room 36.

[0042] The setting unit 46 (FIG. 1) can set the position of the tabletop 26 based on the second movement information 32 to align the isocenter 16 with the selected position 58 of the focus 15 of the patient 25. It is necessary to determine the appropriateness of irradiating the patient 25 with the beam 20 for the second movement information 32 updated in this manner. This appropriateness can be determined based on the ratio between a focus coverage rate 56a (FIG. 4(A)) when the isocenter 16 is aligned with the first position 21 and a focus coverage rate 56c (FIG. 4(C)) when the isocenter 16 is aligned with the selected position 58. Specifically, it is ideal that the focus coverage rate 56c of the selected position 58 is 100% of the focus coverage rate 56a of the first position 21.

[0043] In the second embodiment, the update unit 50 is configured to update the first movement information 31 to the second movement information 32 using the difference vector 51. However, the embodiment of the update unit 50 is not limited to this configuration. As another embodiment, for example, a configuration in which the first movement information 31 is updated to the second movement information 32 by applying optimization with six degrees of freedom is also possible.

[0044] The steps of the operation method of the radiation therapy system according to the embodiment and the algorithm of the operation program of the radiation therapy system will be described with reference to the flowchart in Figure 5. First, in the stage of treatment planning 13, first voxel data 11 inside the body of a patient 25 is captured using a medical stereoscopic imaging device (X-ray CT or MRI) (S11). Then, a first position 21 of a lesion 15 is identified from the first voxel data 11 (S12).

[0045] Next, first movement information 31 is generated to move the top 26 so that the isocenter 16 coincides with the first position 21 (S13). Furthermore, irradiation conditions 35 of the beam 20 are set so that the lesion coverage rate 56a of the patient 25 due to irradiation with the beam 20 is maximized at the first position 21 (S14; END).

[0046] Next, in the stage of treatment implementation 14, the irradiation conditions 35 and first movement information 31 set in the treatment plan 13 are stored as data (S15). Then, immediately before irradiating the beam 20, second voxel data 12 inside the body of the patient 25 is captured (S16). Furthermore, a second position 22 of the lesion 15 is identified from this second voxel data 12 (S17).

[0047] Next, the dose distribution 40 at the position of the lesion 15 of the patient 25 is calculated (S18) without changing the irradiation conditions 35. If the lesion coverage rate 56 at the position of the lesion 15 in the second movement information 32 indicates the maximum value (S19: No, Yes), the first movement information 31 is updated to the second movement information 32 (S20).

[0048] Next, the position of the tabletop 26 is adjusted based on the second movement information 32 (S21). Then, the beam 20 is irradiated onto the patient 25 based on the irradiation conditions 35 (S22; END).

[0049] According to at least one of the above-described embodiments of the radiation therapy system, by updating the gantry movement information so as to maximize the lesion coverage rate at the lesion position immediately before beam irradiation, it is possible to maximize the absorbed dose in the lesion tissue while minimizing the absorbed dose in normal tissue, even if the internal position of the lesion has shifted since the treatment planning stage, without changing the irradiation conditions. Furthermore, since there is no need to change the irradiation conditions and the time required to correct the irradiation conditions can be reduced, highly accurate treatment can be performed in a short time, which contributes to reducing the burden on the patient and improving treatment throughput.

[0050] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as the inventions described in the claims and their equivalents.

[0051] The radiation therapy system described above includes a control device with a highly integrated processor such as a dedicated chip, FPGA (Field Programmable Gate Array), GPU (Graphics Processing Unit), or CPU (Central Processing Unit), a storage device such as ROM (Read Only Memory) or RAM (Random Access Memory), an external storage device such as HDD (Hard Disk Drive) or SSD (Solid State Drive), a display device such as a monitor, input devices such as a mouse and keyboard, and a communication I / F, and can be realized with a hardware configuration using a normal computer. Therefore, the components of the radiation therapy system can be realized by a computer processor and can be operated by an operating program for the radiation therapy system.

[0052] This operating program may be provided by being pre-installed in a ROM, etc. Alternatively, this program may be provided by being stored in an installable or executable file format on a computer-readable storage medium such as a CD-ROM, CD-R, memory card, DVD, or flexible disk (FD).

[0053] The operating program for the radiation therapy system according to this embodiment may be stored on a computer connected to a network such as the Internet and provided by downloading it via the network. The radiation therapy system may also be configured by combining separate modules that independently perform the functions of the components and are interconnected via a network or dedicated lines. [Explanation of symbols]

[0054] 10...Radiation therapy system, 11...First voxel data, 12...Second voxel data, 13...Treatment plan, 14...Treatment implementation, 15 (15a, 15b)...Lesion, 16...Isocenter, 17...Generation unit, 18...Adjustment unit, 19 (19a, 19b)...Identification unit, 20...Beam, 21...First position, 22...Second position, 23...X-ray tube, 24...X-ray detector, 25...Patient, 26...Tabletop, 27...Irradiation port, 28...Rotating gantry, 29...X-ray, 30...Holding unit, 31 ...First movement information, 32...Second movement information, 35...Irradiation conditions, 36...Treatment room, 37...Rotation drive unit, 38...Moving bed, 40 (40a, 40b, 40c)...Dose distribution, 41...Calculation unit, 42...Temporary unit, 45...Imaging unit, 46...Setting unit, 47...Irradiation unit, 48...Rotation control unit, 50...Update unit, 51...Difference vector, 52...Temporary position, 53...Calculation unit, 55...Derivation unit, 56 (56a, 56b, 56c)...Lesion coverage rate, 57...Selection unit, 58...Selected position, 59...Addition unit.

Claims

1. first movement information for moving a tabletop on which the patient is fixed so that a first position of a focus identified from first voxel data obtained by imaging the inside of the patient's body coincides with an isocenter of a beam for administering a dose to the focus; irradiation conditions of the beam set so that a lesion coverage rate of the patient by irradiation of the beam is maximized at the first position; a storage unit configured to store data of the irradiation conditions of the beam and the first movement information of the tabletop; an identification unit that identifies a second position of the lesion from second voxel data obtained by imaging the inside of the patient's body immediately before irradiating the beam; an updating unit that updates the first movement information to second movement information so as to maximize the lesion coverage rate at the position of the lesion of the patient without changing the irradiation conditions.

2. 2. The radiation therapy system according to claim 1, The update unit a calculation unit that calculates a dose distribution of the patient when the beam is irradiated to each of a plurality of temporary positions including the second position and surrounding the second position under the irradiation conditions; a derivation unit that derives a focus coverage ratio at the position of the focus for each of the plurality of dose distributions; a selection unit that selects, from the plurality of temporary positions, the temporary position having the maximum focus coverage rate as a selected position; a calculation unit that calculates a difference vector between the selected position and the first position; an adder that adds the difference vector to the first movement information and outputs the second movement information; a radiation therapy system that moves the tabletop so that the selected position coincides with the isocenter.

3. 3. The radiation therapy system according to claim 2, A radiation therapy system wherein irradiation of the beam to the patient is permitted based on a ratio of the lesion coverage rates derived when the isocenter is aligned with the selected position and the first position.

4. 4. The radiotherapy system according to claim 1, The second voxel data is A radiation therapy system in which imaging is performed around the isocenter by a combination of an X-ray tube and an X-ray detector that rotates together with the beam irradiation port in synchronization with a rotating gantry.

5. 4. The radiotherapy system according to claim 1, The second voxel data is A radiation therapy system in which imaging is performed with equipment located off-isocenter.

6. a step of storing first movement information as data for moving a tabletop on which the patient is fixed so that a first position of a focus identified from first voxel data obtained by imaging the inside of the patient's body coincides with an isocenter of a beam for administering a dose to the focus; storing data of irradiation conditions of the beam that are set so that the lesion coverage rate of the patient by irradiation of the beam is maximized at the first position; identifying a second location of the lesion from second voxel data obtained by imaging the inside of the patient immediately before irradiating the beam; and updating the first movement information to second movement information so as to maximize the lesion coverage rate at the position of the lesion in the patient, without changing the irradiation conditions.

7. On the computer, a step of storing first movement information as data for moving a tabletop on which the patient is fixed so that a first position of a focus identified from first voxel data obtained by imaging the inside of the patient's body coincides with an isocenter of a beam for administering a dose to the focus; a step of storing data of irradiation conditions of the beam that are set so that the lesion coverage rate of the patient by irradiation of the beam is maximized at the first position; identifying a second location of the lesion from second voxel data obtained by imaging the interior of the patient immediately before irradiating the beam; updating the first movement information to second movement information so as to maximize the lesion coverage rate at the position of the lesion in the patient without changing the irradiation conditions.

Images