Radiation irradiation system, beam path monitoring device, and beam path monitoring method

Abstract

A beam path monitoring and control device 41 for monitoring a density change upstream of a target 30 as viewed from a radiation irradiation direction calculates a density change in an irradiation object 26 on the basis of reference images 43A, 43B and current fluoroscopic images 44A, 44B captured by imaging X-ray generators 23A, 23B and X-ray measuring instruments 24A, 24B during treatment, and controls irradiation and interruption of radiation on the basis of a positional relationship between a three-dimensional density change region 51 and a beam path of radiation irradiation. As a result, it is possible to provide a radiation irradiation system, a beam path monitoring device, and a beam path monitoring method that can more accurately determine a change in dose distribution due to a density change on the upstream side of a target as viewed from the radiation irradiation direction.

Description

RADIATION IRRADIATION SYSTEM, BEAM PATH MONITORING DEVICE, AND BEAM PATH MONITORING METHOD

[0001] The present invention relates to a radiation irradiation system suitable for a radiation irradiation system that treats an affected area such as a tumor by irradiating it with radiation such as particle beams, a beam path monitoring device, and a beam path monitoring method.

[0002] Patent Document 1 describes an example of an image processing device and particle beam therapy device that contributes to irradiating a target, such as a tumor, with particle beams with higher accuracy than conventional devices, even when the position of the target periodically changes due to breathing or other factors. The device detects the position of high-density material that can be distinguished on a two-dimensional fluoroscopic image from soft tissue on a fluoroscopic X-ray image obtained by a fluoroscopic X-ray imaging control device and the position information of the high-density material in a CT image of a treatment planning device, resets the particle beam passage region in the shifted state on a previously prepared treatment planning CT image, calculates the change in water equivalent thickness of the reset particle beam passage region, and outputs a decision to allow particle beam irradiation only if the change is within a predetermined amount.

[0003] JP 2016-144573 A

[0004] There are known methods of irradiating patients with cancer and other conditions with radiation such as particle beams and X-rays. Particle beams include proton beams and carbon ions. The radiation irradiation system used for irradiation creates a dose distribution appropriate for the shape of the target, such as a tumor, inside the patient's body, who is fixed on a patient bed called a couch.

[0005] However, accurate irradiation of radiation becomes difficult when a target such as a tumor moves due to breathing or other factors. Therefore, gated irradiation, in which radiation is irradiated only when the target is within a predetermined range (gate range), has recently been realized.

[0006] Here, even if the target position is controlled with high precision using tumor-tracking irradiation, if the position of high-density materials such as bones located upstream of the target from the radiation irradiation direction changes, it may become difficult to achieve the dose distribution planned in the treatment plan.

[0007] In contrast, the technology described in the above-mentioned Patent Document 1 describes an image processing device that detects positional deviations of high-density materials from fluoroscopic images and evaluates changes in water equivalent thickness to determine whether particle beam irradiation is permitted.

[0008] On the other hand, with regard to changes upstream of the target from the perspective of radiation irradiation direction, not only changes in the position of high-density materials but also changes in low-density materials such as the gas-filling status in the digestive tract affect the feasibility of the dose distribution planned in the treatment plan.In addition, the accuracy of the water equivalent thickness evaluation has a significant impact on the decision to allow irradiation based on the evaluation of the water equivalent thickness.

[0009] Thus, there was a need to develop technology that could reflect changes upstream of the target from the perspective of radiation irradiation.

[0010] The present invention provides a radiation irradiation system, a beam path monitoring device, and a beam path monitoring method that can more accurately determine changes in dose distribution due to density changes upstream of the target as viewed from the radiation irradiation direction.

[0011] The present invention includes multiple means for solving the above-mentioned problems, and one example thereof includes a radiation irradiation device for irradiating a target with radiation, an irradiation control device for controlling the radiation irradiation device, an imaging device for acquiring an image of a tracked object within an object that contains the target, and a beam path monitoring device for monitoring density changes upstream of the target as viewed from the direction of irradiation of the radiation, wherein the beam path monitoring device calculates density changes within the object based on a reference image and an intra-treatment image captured by the imaging device during treatment, and controls the irradiation and stopping of the radiation by the irradiation control device based on the position where the density change occurred and the positional relationship between the beam path that irradiates the radiation.

[0012] According to the present invention, it is possible to more accurately determine changes in dose distribution due to density changes upstream of the target as viewed from the radiation irradiation direction. Objects, configurations, and effects other than those described above will become clear from the following description of the embodiments.

[0013] FIG. 1 is an overall configuration diagram of a proton beam irradiation system according to a first embodiment. FIG. 2 is a conceptual diagram of a beam path monitoring device according to a first embodiment acquiring a captured image. FIG. 3 is a flowchart of a beam path monitoring device according to a first embodiment determining whether irradiation is possible or not from a captured image. FIG. 4 is a schematic diagram of an image used to determine whether irradiation is possible or not in the beam path monitoring device according to the first embodiment. FIG. 5 is a conceptual diagram showing a method of calculating a three-dimensional density change region in the beam path monitoring device according to the first embodiment. FIG. 6 is a diagram of a display portion of a console when setting parameters used to determine whether irradiation is possible or not in the beam path monitoring device according to the first embodiment. FIG. 7 is a diagram of a display portion of a console showing a status of irradiation possibility or not determination in the beam path monitoring device according to the first embodiment. FIG. 8 is a flowchart of a beam path monitoring device according to a second embodiment determining whether irradiation is possible or not from a captured image. FIG. 9 is a flowchart of a beam path monitoring device according to a fourth embodiment determining whether irradiation is possible or not from a captured image.

[0014] Hereinafter, embodiments of the radiation irradiation system, the beam path monitoring device, and the beam path monitoring method of the present invention will be described with reference to the drawings. In the drawings used in this specification, identical or similar reference numerals are used to designate identical or corresponding components, and repeated description of these components may be omitted.

[0015] The present invention can be applied to a proton beam irradiation system 1 such as an X-ray irradiation system or a proton beam irradiation system. In the following first to fourth embodiments, a proton beam irradiation system will be described as an example.

[0016] First Embodiment A first embodiment of the radiation irradiation system, the beam path monitoring device, and the beam path monitoring method of the present invention will be described with reference to FIGS. 1 to 7. FIG.

[0017] First, the overall configuration of a proton beam irradiation system equipped with a beam path monitoring device will be described with reference to Fig. 1. Fig. 1 is an overall configuration diagram of a proton beam irradiation system according to a first embodiment.

[0018] 1 includes a proton beam generator 10, a beam transport system 20, an irradiation nozzle 22, a beam path monitor, a couch 27, and an irradiation controller 40. The proton beam irradiation system for irradiating a target 30 with a proton beam includes the proton beam generator 10, the beam transport system 20, and the irradiation nozzle 22.

[0019] The proton beam generator 10 includes an ion source 12, a linac 13, and a synchrotron 11. The synchrotron 11 includes a bending electromagnet 14, a quadrupole electromagnet (not shown for convenience), a radio-frequency accelerator 18, a radio-frequency extractor 19, and an extractor deflector 17. Of these, the ion source 12 is connected to the linac 13, and the linac 13 is connected to the synchrotron 11. In the proton beam generator 10, protons generated by the ion source 12 are pre-accelerated by the linac 13 and then enter the synchrotron 11. The proton beam further accelerated by the synchrotron 11 is extracted to a beam transport system 20.

[0020] The beam transport system 20 includes a plurality of bending electromagnets 21 and quadrupole electromagnets (not shown), and is connected to the synchrotron 11 and the irradiation nozzle 22. A part of the beam transport system 20 and the irradiation nozzle 22 are mounted on a cylindrical gantry 25 and can rotate together with the gantry 25. The proton beam extracted from the synchrotron 11 is converged by the quadrupole electromagnets while passing through the beam transport system 20, and then its direction is changed by the bending electromagnets 21 before it enters the irradiation nozzle 22.

[0021] The irradiation nozzle 22 for irradiating the target 30 with a proton beam is equipped with two scanning electromagnets, a dose monitor, and a position monitor (all not shown). The two scanning electromagnets are installed in directions perpendicular to each other, and generate a magnetic field using an excitation current, which can deflect the proton beam so that it reaches a desired position in a plane perpendicular to the beam axis at the position of the target 30. The dose monitor measures the amount of irradiated proton beam. The position monitor detects the position through which the proton beam has passed. The proton beam that has passed through the irradiation nozzle 22 reaches the target 30 within the irradiation object 26.

[0022] When treating a patient with cancer or the like, the irradiation subject 26 represents the patient, and the target 30 represents a tumor or the like.

[0023] The bed on which the irradiation target 26 is placed is called a couch 27. The couch 27 can move in the directions of three orthogonal axes and can also rotate around each axis based on instructions from the irradiation control device 40. These movements and rotations allow the irradiation target 26 to be moved to a desired position.

[0024] The irradiation control device 40 is connected to the proton beam generator 10, the beam transport system 20, the irradiation nozzle 22, the beam path monitoring and control device 41, the couch 27, the console 42, etc., and controls equipment such as the proton beam generator 10, the beam transport system 20, and the irradiation nozzle 22.

[0025] The beam path monitoring device includes a first X-ray imaging device, a second X-ray imaging device, and a beam path monitoring control device 41 .

[0026] The first X-ray imaging device includes an imaging X-ray generator 23A and an X-ray measurement device 24A that capture a fluoroscopic image of the irradiation object 26. The second X-ray imaging device includes an imaging X-ray generator 23B and an X-ray measurement device 24B that capture a fluoroscopic image of the irradiation object 26. These imaging X-ray generators 23A and 23B and X-ray measurement devices 24A and 24B constitute an imaging device that acquires an image of a tracked object within the irradiation object 26 that contains the target 30.

[0027] 2 is a conceptual diagram illustrating how the beam path monitoring device acquires captured images in Example 1. The first X-ray imaging device and the second X-ray imaging device are installed so that the paths of their respective X-rays intersect, as shown in FIG. 2, and acquire images of the tracking target from two or more different directions.

[0028] The two pairs of imaging X-ray generators 23A, 23B and X-ray measuring devices 24A, 24B are preferably installed in directions perpendicular to each other, but they do not have to be perpendicular. However, by installing them perpendicular to each other as in this embodiment, it is possible to improve the accuracy of identifying the three-dimensional position of the irradiation target 26, and this can be said to be a more desirable arrangement.

[0029] Furthermore, the imaging X-ray generators 23A, 23B and the X-ray measuring devices 24A, 24B do not necessarily have to be placed inside the gantry 25, but may be placed in a fixed location such as on the ceiling or floor.

[0030] The beam path monitoring and control device 41 is a device that monitors density changes upstream of the target 30 as viewed from the radiation irradiation direction, and calculates density changes within the irradiation target 26 based on reference images 43A, 43B and current fluoroscopic images 44A, 44B taken by the imaging X-ray generators 23A, 23B and X-ray measurement devices 24A, 24B during treatment, and controls the start and stop of radiation irradiation based on the positional relationship between the three-dimensional density change region 51 and the beam path that irradiates radiation. This beam path monitoring and control device 41 preferably executes each step of the beam path monitoring method of the present invention.

[0031] In the configuration of this embodiment, for example, a determination is made as to whether or not to permit the emission of proton beams based on signals input from the first X-ray imaging device and the second X-ray imaging device, and a control signal (irradiation permission signal) indicating whether or not to irradiate the proton beams is transmitted to the irradiation control device 40.

[0032] The method for determining whether or not irradiation is permitted will be described in more detail below with reference to Fig. 3 and Fig. 4. Fig. 3 is a flowchart showing how the beam path monitoring device in Example 1 determines whether or not irradiation is permitted based on a captured image. Fig. 4 is a schematic diagram of an image used for determining whether or not irradiation is permitted by the beam path monitoring device in Example 1.

[0033] First, before determining whether irradiation is possible, reference fluoroscopic images (reference images 43A and 43B) are captured. A schematic diagram of the reference images 43A and 43B is shown in FIG.

[0034] When the determination of whether irradiation is possible is started in step S101, current fluoroscopic images 44A and 44B are captured by the two pairs of imaging X-ray generators 23A and 23B and X-ray measurement devices 24A and 24B in the beam path monitoring device in step S102. A schematic diagram of the current fluoroscopic images 44A and 44B is shown in Fig. 4(B). In this example, a state in which a low-density region that did not exist when the reference images 43A and 43B were captured is simulated.

[0035] It is desirable that the reference images 43A, 43B and the current fluoroscopic images 44A, 44B are acquired using the same device and under the same imaging conditions, but it is also possible to make them the same by adjusting these parameters through image processing.

[0036] In step S103, the beam path monitoring and control device 41 creates difference images 45A and 45B between the reference images 43A and 43B and the perspective images 44A and 44B. A schematic diagram of the difference images 45A and 45B is shown in FIG. 4C. By taking the difference in this way, images are obtained in which the two-dimensional density change regions 50A and 50B where the density has changed are emphasized.

[0037] In step S104, the beam path monitoring control device 41 identifies regions where density has changed in each of the difference images 45A and 45B. Specifically, it determines the portions where the change in pixel value in the grayscale is greater than a preset threshold as the two-dimensional density change regions 50A and 50B. In this way, the beam path monitoring control device 41 calculates the difference between the pixel values ​​of the reference images 43A and 43B and the pixel values ​​of the current perspective images 44A and 44B, and can calculate the regions where the difference is equal to or greater than a predetermined threshold as the two-dimensional density change regions 50A and 50B.

[0038] In addition, at this time, the beam path monitoring control device 41 can set different predetermined threshold values ​​for the increased areas where the pixel values ​​of the reference images 43A, 43B have increased to the pixel values ​​of the current perspective images 44A, 44B, and the decreased areas where the pixel values ​​of the reference images 43A, 43B have decreased to the pixel values ​​of the current perspective images 44A, 44B.

[0039] FIG. 6 is a diagram showing the display portion of the console when setting parameters used to determine whether irradiation is possible or not in the beam path monitoring device in the first embodiment.

[0040] 6, a parameter setting screen 420 is displayed on the console 42. The parameter setting screen 420 displays a density increase threshold setting area 421 for setting a density increase threshold used at an increased portion where the pixel values ​​of the current fluoroscopic images 44A and 44B have increased relative to the pixel values ​​of the reference images 43A and 43B, a density decrease threshold setting area 422 for setting a density decrease threshold used at an decreased portion where the pixel values ​​of the current fluoroscopic images 44A and 44B have decreased relative to the pixel values ​​of the reference images 43A and 43B, and an irradiation field overlap determination margin setting area 423 for setting an irradiation field overlap determination margin used when determining whether the beam path used in step S106 described later overlaps with the three-dimensional density change region 51.

[0041] The density increase threshold set in the density increase threshold setting area 421 contributes to improving the accuracy of excluding high-density materials such as bone, while the density decrease threshold set in the density decrease threshold setting area 422 contributes to improving the accuracy of excluding low-density areas such as gas.

[0042] The operator inputs the predetermined values ​​in each setting area and then presses the setting area 424a, which reflects the density increase threshold, density decrease threshold, and irradiation field overlap determination margin.To finish the settings, the operator presses the end area 424b.

[0043] Returning to FIG. 3, in step S105, the beam path monitoring and control device 41 calculates a three-dimensional density change region from the positions of the two-dimensional density change regions 50A and 50B on the respective difference images 45A and 45B.

[0044] FIG. 5 is a conceptual diagram showing a method for calculating a three-dimensional density change region in the beam path monitoring device in the first embodiment.

[0045] Specifically, as shown in Figure 5, a three-dimensional region formed by connecting the two-dimensional density change regions 50A, 50B and the radiation source is defined for each difference image 45A, 45B, and the region where these three-dimensional regions overlap is defined as a three-dimensional density change region 51.

[0046] In step S106, the beam path monitoring and control device 41 determines whether or not the beam path for irradiating the proton beam overlaps with the three-dimensional density change region 51. Specifically, this is determined based on whether or not there is an overlap between the region where the shape of the target 30 is projected onto the isocenter plane and the region where the three-dimensional density change region 51 is projected onto the isocenter plane.

[0047] At this time, when determining whether the three-dimensional density change region 51 is on the beam path, the beam path monitoring and control device 41 can enlarge or reduce either the three-dimensional density change region 51 or the beam path.

[0048] Specifically, the determination can be made after expanding or contracting the projection area of ​​the target 30 or the projection area of ​​the three-dimensional density change area 51 according to a preset margin amount. By expanding either the three-dimensional density change area 51 or the beam path, the possibility of being affected by the three-dimensional density change area 51 can be further reduced, thereby improving the accuracy of irradiation of the target 30. In contrast, by contracting either the three-dimensional density change area 51 or the beam path, radiation irradiation can be continued in a state where it can be determined that there is almost no influence even if the three-dimensional density change area 51 is located nearby, thereby realizing completion of irradiation in a shorter time.

[0049] If it is determined in step S106 that the beam path and the three-dimensional density change region 51 overlap and that the three-dimensional density change region 51 is on the beam path, the beam path monitoring control device 41 stops the irradiation of the proton beam by stopping the irradiation permission signal or outputting an irradiation stop signal in step S107.

[0050] On the other hand, if it is determined in step S106 that the beam path and the three-dimensional density change region 51 do not overlap and that the three-dimensional density change region 51 is not on the beam path, the beam path monitoring control device 41 permits proton beam irradiation by sending an irradiation permission signal or by stopping the output of the irradiation stop signal in step S108.

[0051] After step S107 or step S108 is completed, the determination as to whether irradiation is possible is completed in step S109. The determination as to whether irradiation is possible from step S101 to step S109 is repeatedly executed at a preset cycle.

[0052] In addition, in parallel with the flow of Figure 3, the beam path monitoring and control device 41 can display on the console 42 one or more of the reference images 43A, 43B, the current fluoroscopic images 44A, 44B, the two-dimensional density change regions 50A, 50B, and the irradiation and stopping of radiation.

[0053] FIG. 7 is a diagram showing a display portion of a console showing the status of irradiation propriety determination in the beam path monitoring device in the first embodiment.

[0054] 7, a current status screen 425 including reference images 43A and 43B, current fluoroscopic images 44A and 44B, and subtraction images 45A and 45B is displayed on the console 42. The contours of the two-dimensional density change regions 50A and 50B recognized in step S104 are displayed on the subtraction images 45A and 45B. Furthermore, a beam's eye view (BEV) image 46 including an irradiation range 52 viewed from the irradiation direction and a contour 53 of the three-dimensional density change region 51 is displayed. Also, a determination result 47 of whether irradiation is permitted in step S106 is displayed.

[0055] Next, the effects of this embodiment will be described.

[0056] The proton beam irradiation system 1 of the first embodiment of the present invention described above includes an irradiation nozzle 22 for irradiating radiation onto the target 30, an irradiation control device 40 for controlling the irradiation nozzle 22, imaging X-ray generators 23A, 23B and X-ray measurement devices 24A, 24B for acquiring images of a tracked target within an irradiation object 26 that includes the target 30, and a beam path monitoring control device 41 for monitoring density changes upstream of the target 30 as viewed from the direction of radiation irradiation. The beam path monitoring control device 41 calculates density changes within the irradiation object 26 based on the reference images 43A, 43B and current fluoroscopic images 44A, 44B taken by the imaging X-ray generators 23A, 23B and the X-ray measurement devices 24A, 24B during treatment, and controls the irradiation and stopping of radiation based on the positional relationship between a three-dimensional density change region 51 and the beam path that irradiates radiation.

[0057] In the conventional method, as described above, the position of high-density material present on the beam path is determined, and proton beam irradiation is controlled based on the results of evaluating the change in water equivalent thickness due to the change in the position of the high-density material. In this case, since the determination is made through a step of evaluating the change in water equivalent thickness, the determination result is significantly affected by calculation errors in the water equivalent thickness, making it difficult to capture the change in the position of low-density material, such as gas passing through the digestive tract during irradiation.

[0058] On the other hand, in this embodiment, density changes within the irradiation target 26 are calculated, and irradiation and termination of radiation are controlled based on the positional relationship between the three-dimensional density change region 51 and the beam path for irradiating radiation. This allows changes upstream of the target 30 as viewed from the radiation irradiation direction to be reflected, making it possible to determine positional changes of low-density materials. Therefore, changes in dose distribution can be determined more accurately than in the past, improving the feasibility of more accurate dose distributions. Furthermore, because the determination can be made based on the position of the density change region, it is not affected by calculation errors in the water equivalent thickness, allowing for more accurate determination of whether or not to permit radiation irradiation.

[0059] In addition, the beam path monitoring and control device 41 can more accurately irradiate the target 30 with radiation by stopping the irradiation of radiation when the three-dimensional density change region 51 is on the beam path and irradiating radiation when the three-dimensional density change region 51 is not on the beam path.

[0060] Furthermore, the beam path monitoring control device 41 takes the difference between the pixel values ​​of the reference images 43A, 43B and the pixel values ​​of the current perspective images 44A, 44B, and calculates the areas where the difference is greater than or equal to a predetermined threshold as the two-dimensional density change areas 50A, 50B, thereby enabling the two-dimensional density change areas 50A, 50B to be reliably captured.

[0061] Furthermore, the beam path monitoring control device 41 sets different predetermined thresholds for the increased portions where the pixel values ​​of the current fluoroscopic images 44A, 44B increase from the pixel values ​​of the reference images 43A, 43B and the decreased portions where the pixel values ​​of the current fluoroscopic images 44A, 44B decrease from the pixel values ​​of the reference images 43A, 43B. This makes it possible to achieve both settings suitable for excluding high-density substances such as bone and settings suitable for excluding low-density substances such as gas, thereby further improving the calculation accuracy of the two-dimensional density change regions 50A, 50B.

[0062] Furthermore, when determining whether the three-dimensional density change region 51 is on the beam path, the beam path monitoring and control device 41 can expand or reduce either the three-dimensional density change region 51 or the beam path, thereby reducing the effect of the three-dimensional density change region 51 and enabling irradiation in a short time or irradiation of the target 30 with greater accuracy.

[0063] In addition, the beam path monitoring control device 41 displays one or more of the reference images 43A, 43B, the current fluoroscopic images 44A, 44B, the two-dimensional density change areas 50A, 50B, and the irradiation and cessation of radiation on a display device, allowing an operator such as a doctor to grasp the status of radiation irradiation in real time.

[0064] Furthermore, the imaging X-ray generators 23A, 23B and the X-ray measurement devices 24A, 24B can improve the accuracy of identifying the three-dimensional position of the tracked object by acquiring images of the tracked object from two or more different directions.

[0065] Second Embodiment A radiation irradiation system, a beam path monitoring device, and a beam path monitoring method according to a second embodiment of the present invention will be described with reference to Fig. 8. Fig. 8 is a flowchart showing how the beam path monitoring device in the second embodiment determines whether irradiation is possible or not based on a captured image.

[0066] The beam path monitoring device and radiation irradiation system of this embodiment differ from those of the first embodiment in the method of determining the irradiation permission signal.

[0067] Specifically, the beam path monitoring and control device 41 of this embodiment determines the three-dimensional position of the target 30 from the current fluoroscopic images 44A and 44B, and determines and controls the irradiation and stopping of radiation based on the three-dimensional position.

[0068] 8, after a fluoroscopic image is captured in step S102, the position of the target 30 is calculated based on the fluoroscopic image in step S201 in parallel with the determination of density changes on the beam path in step S103 and subsequent steps. The method for calculating the position of the target 30 may be the same as the conventional calculation method. In step S202, it is determined whether the calculated position of the target 30 is within a predetermined irradiation permission range.

[0069] If it is determined in step S202 that the target 30 is within the irradiation permission range, and if it is determined in step S106 that the beam path and the three-dimensional density change region 51 do not overlap, an irradiation permission signal is sent in step S108, or the output of the irradiation stop signal is stopped.

[0070] On the other hand, if it is determined in step S202 that the target 30 is not within the irradiation permission range, or if it is determined in step S106 that the beam path overlaps with the three-dimensional density change region 51, the irradiation permission signal is stopped or an irradiation stop signal is output in step S107.

[0071] After step S107 or step S108 is completed, the determination as to whether irradiation is possible is completed in step S109. The determination as to whether irradiation is possible from step S101 to step S109 is repeatedly executed at a preset cycle.

[0072] Here, we have shown the flow of performing so-called double gate irradiation, in which the position is identified in parallel and radiation is irradiated only when the beam path and the three-dimensional density change region 51 do not overlap.However, when the beam path and the three-dimensional density change region 51 do not overlap, it is also possible to perform so-called gate and tracking irradiation, in which the position is identified in parallel and the radiation irradiation parameters are changed as in step S201.

[0073] This example will be described as being implemented during immediate adaptive radiation therapy.

[0074] In real-time adaptive radiation therapy, a 3D image of the patient is taken at the start of treatment, and a treatment plan is created on the spot based on that 3D image, making it possible to irradiate radiation according to a treatment plan that is tailored to the patient's internal conditions at the start of treatment.

[0075] On the other hand, since it takes several tens of minutes from creating a treatment plan to completing irradiation, it is not possible to respond to changes during treatment. In contrast, by using a known tumor tracking technique in combination, irradiation control that responds to changes due to movement of the target 30 becomes possible, but it is not possible to respond to density changes on the beam path.

[0076] When the method of this embodiment is applied to real-time adaptive radiation therapy, reference images 43A and 43B are captured when capturing the three-dimensional images used to create a treatment plan. By monitoring the beam path based on these reference images 43A and 43B, it becomes possible to stop irradiation if a density change occurs on the beam path compared with the internal body structure at the time of treatment planning, and it becomes possible to realize the dose distribution of the treatment plan with higher accuracy.

[0077] The other configurations and operations are substantially the same as those of the radiation irradiation system, beam path monitoring device, and beam path monitoring method of the first embodiment, and therefore details thereof will be omitted.

[0078] The radiation irradiation system, beam path monitoring device, and beam path monitoring method of the second embodiment of the present invention also provide substantially the same effects as those of the radiation irradiation system, beam path monitoring device, and beam path monitoring method of the first embodiment described above.

[0079] In addition, the beam path monitoring and control device 41 determines the three-dimensional position of the target 30 from the current fluoroscopic images 44A, 44B, and controls the irradiation and stopping of radiation based on the three-dimensional position, thereby enabling radiation to be irradiated in response to changes in the position of the target 30, thereby enabling more accurate irradiation.

[0080] Third Embodiment A radiation irradiation system, a beam path monitoring device, and a beam path monitoring method according to a third embodiment of the present invention will be described.

[0081] The beam path monitoring device and radiation irradiation system of this embodiment differ from those of the first and second embodiments in the method of acquiring the reference image.

[0082] In this embodiment, based on the CT images used in the treatment plan, reconstructed images (DRR: Digitally Reconstructed Radiograph) corresponding to the imaging angles of the imaging X-ray generators 23A and 23B and the X-ray measurement devices 24A and 24B are calculated and used as reference images 43A and 43B.

[0083] The other configurations and operations are substantially the same as those of the radiation irradiation system, beam path monitoring device, and beam path monitoring method of the first embodiment, and therefore details thereof will be omitted.

[0084] The radiation irradiation system, beam path monitoring device, and beam path monitoring method of the third embodiment of the present invention also provide effects substantially similar to those of the radiation irradiation system, beam path monitoring device, and beam path monitoring method of the first embodiment described above.

[0085] Furthermore, the beam path monitoring and control device 41 calculates reconstructed images corresponding to the imaging angles of the imaging X-ray generators 23A and 23B and the X-ray measurement devices 24A and 24B based on the CT images used in the treatment plan, and uses these as reference images 43A and 43B, thereby making it possible to omit imaging for obtaining the reference images, thereby shortening the treatment time and reducing the amount of radiation exposure to the patient due to imaging.

[0086] Fourth Embodiment A radiation irradiation system, a beam path monitoring device, and a beam path monitoring method according to a fourth embodiment of the present invention will be described with reference to Fig. 9. Fig. 9 is a flowchart showing how the beam path monitoring device in the fourth embodiment determines whether irradiation is possible or not from a captured image.

[0087] The beam path monitoring device of this embodiment differs from those of Embodiments 1 to 3 in the method of acquiring reference images 43A, 43B. Specifically, the beam path monitoring control device 41 acquires reference images 43A, 43B for one respiratory cycle, determines the current respiratory phase from current fluoroscopic images 44A, 44B, and uses the reference images 43A, 43B that are most suitable for the corresponding respiratory phase.

[0088] First, before determining whether irradiation is possible, a reference fluoroscopic image is captured. At this time, a plurality of fluoroscopic images are captured. Furthermore, for each of these captured fluoroscopic images, the respiratory phase is determined based on the positions of the diaphragm and fiducial markers on the fluoroscopic image. Then, each fluoroscopic image is stored in a storage device within the beam path monitoring and control device 41 as a reference image associated with the determined respiratory phase.

[0089] Thereafter, as shown in FIG. 9, when a determination as to whether irradiation is possible or not is started in step S101, a fluoroscopic image is taken in step S102.

[0090] Then, in step S301, the respiratory phase of the fluoroscopic image captured in step S102 is determined based on the positions of the diaphragm and fiducial markers on the fluoroscopic image that have been prepared beforehand before determining whether irradiation is possible. Furthermore, based on the determined respiratory phase, a reference image to be used in step S103 and subsequent steps is selected.

[0091] Steps S103 and thereafter are the same as those in the first to third embodiments.

[0092] The other configurations and operations are substantially the same as those of the radiation irradiation system, beam path monitoring device, and beam path monitoring method of the first embodiment, and therefore details thereof will be omitted.

[0093] The radiation irradiation system, beam path monitoring device, and beam path monitoring method of the fourth embodiment of the present invention also provide substantially the same effects as those of the radiation irradiation system, beam path monitoring device, and beam path monitoring method of the first embodiment described above.

[0094] Furthermore, the beam path monitoring and control device 41 acquires reference images 43A, 43B for one respiratory cycle, determines the current respiratory phase from the current fluoroscopic images 44A, 44B, and uses the reference images 43A, 43B that are most suitable for the corresponding respiratory phase. This allows for more accurate evaluation of density changes within the body, even in cases where the internal structure changes periodically due to breathing, such as in cases of the chest or abdomen.

[0095] In this embodiment, the three-dimensional position of the target 30 can be obtained from the current fluoroscopic images 44A and 44B, and the start and stop of radiation irradiation can be determined and controlled based on the three-dimensional position as well, as in embodiment 2. Furthermore, reference images 43A and 43B can be generated from the DRR as in embodiment 3. Furthermore, both embodiment 2 and embodiment 3 can be implemented.

[0096] <Others> The present invention is not limited to the above-described examples, and includes various modifications. The above-described examples have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those having all of the described configurations.

[0097] It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of one embodiment to the configuration of another embodiment.It is also possible to add, delete, or replace part of the configuration of each embodiment with the configuration of another embodiment.

[0098] For example, in the above embodiment, an example is described in which two X-ray imaging devices are used to image a target, but two X-ray imaging devices are not necessarily required. For example, images of the tracked target may be captured from two different directions by moving one X-ray imaging device. Also, instead of an X-ray imaging device, ultrasound or MRI may be used for imaging.

[0099] Furthermore, although the above embodiment has been described using a proton beam irradiation system as an example, the radiation irradiation system of the present invention can be similarly applied to systems that irradiate particle beams other than proton beams, such as carbon beams, X-rays, electron beams, etc. For example, when X-rays are used, the radiation irradiation device is composed of an X-ray generator, a beam transport system, and an irradiation nozzle.

[0100] In the case of a particle beam irradiation system, the particle beam generator may be an accelerator such as a cyclotron or synchrocyclotron in addition to the synchrotron described in the above embodiment.

[0101] REFERENCE SIGNS LIST 1... Proton beam irradiation system 10... Proton beam generator 11... Synchrotron 12... Ion source 13... Linac 14... Bending electromagnet 17... Extraction deflector 18... High frequency accelerator 19... High frequency extractor 20... Beam transport system 21... Bending electromagnet 22... Irradiation nozzle (radiation irradiation device) 23A, 23B... Imaging X-ray generator (imaging device) 24A, 24B... X-ray measuring device (imaging device) 25... Gantry 26... Irradiation object (object) 27... Couch 30... Target 40... Irradiation control device (control system) 41... Beam path monitoring control device (beam path monitoring device) 42... Console 43A, 43B... Reference image (baseline image) 44A, 44B... Current fluoroscopic image (treatment image) 45A, 45B... Difference image 46... BEV image 47... Irradiation permission determination result 50A, 50B... Two-dimensional density change area (position where density change occurred) 51... Three-dimensional density change area (position where density change occurred) 52... Irradiation range 53... Contour 420... Setting screen 421... Density increase threshold setting area 422... Density decrease threshold setting area 423... Irradiation field overlap determination margin setting area 424a... Setting area 424b... End area 425... Current status screen

Claims

1. A radiation irradiation system comprising: a radiation irradiation device for irradiating a target with radiation; an irradiation control device for controlling said radiation irradiation device; an imaging device for acquiring an image of a tracked object within an object that contains said target; and a beam path monitoring device for monitoring density changes upstream of said target as viewed from the direction of irradiation of said radiation, wherein said beam path monitoring device calculates density changes within said object based on a reference image and an image during treatment taken by said imaging device during treatment, and controls start and stop of irradiation of said radiation by said irradiation control device based on the positional relationship between the position where the density change occurred and the beam path that irradiates said radiation.

2. A radiation irradiation system according to claim 1, wherein the beam path monitoring device stops irradiation of the radiation when the position where the density change occurs is on the beam path.

3. A radiation irradiation system according to claim 1 or 2, wherein the beam path monitoring device irradiates the radiation when the position where the density change occurs is not on the beam path.

4. A radiation irradiation system according to any one of claims 1 to 3, wherein the beam path monitoring device calculates the difference between the pixel values ​​of the reference image and the pixel values ​​of the treatment image, and calculates the area where the difference is equal to or greater than a predetermined threshold as the position where the density change has occurred.

5. A radiation irradiation system according to claim 4, wherein the beam path monitoring device sets different predetermined threshold values ​​for an increase point where the pixel value of the image during treatment increases from the pixel value of the image during reference time and a decrease point where the pixel value of the image during treatment decreases from the pixel value of the image during reference time.

6. A radiation irradiation system according to any one of claims 1 to 5, wherein the beam path monitoring device, when determining whether the position where the density change occurred is on the beam path, expands or contracts either the position where the density change occurred or the beam path.

7. A radiation irradiation system according to any one of claims 1 to 6, wherein the beam path monitoring device displays on a display device one or more of the reference image, the treatment image, the position where the density change occurred, and irradiation and cessation of the radiation.

8. A radiation irradiation system according to any one of claims 1 to 7, wherein the beam path monitoring device determines the three-dimensional position of the target from the treatment image and controls the start and stop of irradiation of the radiation based also on the three-dimensional position.

9. A radiation irradiation system according to any one of claims 1 to 8, wherein the beam path monitoring device calculates a reconstructed image corresponding to the imaging angle of the imaging device based on the CT image used in the treatment plan, and uses the reconstructed image as the reference image.

10. A radiation irradiation system according to any one of claims 1 to 9, wherein the beam path monitoring device acquires the reference image for one respiratory cycle, determines the current respiratory phase from the treatment image, and uses the reference image that is most suitable for the corresponding respiratory phase.

11. A radiation irradiation system according to any one of claims 1 to 10, wherein the imaging device acquires images of the tracked object from two or more different directions.

12. A beam path monitoring device that monitors density changes upstream of a target when viewed from the direction of radiation irradiation within an object containing the target, the beam path monitoring device calculates density changes within the object based on a reference time image and an image during treatment captured by an imaging device that acquires an image of a tracked object within the object containing the target during treatment, determines whether to irradiate the radiation or not based on the position where the density change occurred and the positional relationship of the beam path that irradiates the radiation, and outputs a control signal to a control system of a radiation irradiation device that irradiates the target with the radiation.

13. A beam path monitoring method for monitoring density changes upstream of a target when viewed from the direction of radiation irradiation within an object containing the target, the method comprising: calculating density changes within the object based on a reference time image and an image during treatment captured by an imaging device that acquires an image of a tracked object within the object containing the target during treatment; determining whether to irradiate the radiation or not based on the positional relationship between the position where the density change occurred and the beam path that irradiates the radiation; and outputting a control signal to a control system of a radiation irradiation device that irradiates the radiation to the target.

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