Isocenter evaluation device, evaluation method, evaluation program, and gantry irradiation device

Abstract

We provide an isocenter evaluation technology that measures the position and size of the isocenter easily, quickly, and with high accuracy, minimizes the size, and achieves high reliability. The evaluation device (10) includes a laser tracker (15) that outputs a laser (30), a first probe (21) that is provided at three or more points on a support frame (25) and that reflects a first optical signal (11) when it receives the laser (30), a second probe (22) that is provided at three or more points on an intersection plane (36) of a beam (37) and that reflects a second optical signal (12) when it receives the laser (30), a calculation unit (16) that calculates a virtual point (38) of the isocenter based on information about the first optical signal (11), the second optical signal (12), and the radius R and rotation angle θ of the rotating frame (26), and a calculation unit (16) that calculates each of the calculated virtual points (38) of the isocenter by changing the rotation angle θ of the rotating frame (26). n It includes a recording unit 17 that records the data as point cloud data.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to an evaluation technique for isocenters where beams irradiated from an arc-shaped trajectory toward the center converge. [Background technology]

[0002] In radiotherapy equipment and CT scan equipment equipped with a rotating gantry, the radiation irradiation port moves along an arcuate trajectory to change the irradiation angle of the radiation to the patient. A rotating gantry consists of a support frame fixed to the building floor, a rotating frame that is constrained to the support frame via guide rollers or arcuate rails and rotates around its axis, and an irradiation port that is attached to the rotating frame and moves along an arcuate trajectory.

[0003] There are two types of rotating frames: those that rotate more than 360 degrees and those that rotate less than 360 degrees (C-shaped orbit). The structure consisting of the rotating frame and support frame is subject to assembly errors and deflection due to its own weight, so the irradiation port does not necessarily move ideally along a circular arc orbit.

[0004] In this way, if the irradiation port is moved on an arcuate trajectory to change the irradiation angle of the radiation, the beam will not be concentrated at a single point at the isocenter but will be dispersed. If the degree of beam concentration at the isocenter of the radiation is low, the effectiveness of the treatment and the accuracy of the examination position will be reduced.

[0005] Meanwhile, a method for mathematically determining the center of rotation using a calibration phantom is known, with the aim of eliminating concentric ring artifacts that appear in CT images of X-ray CT (computed tomography) examination equipment. According to this method, the positions of the X-ray tube and X-ray detector are calculated using a circular regression method based on the least squares method, using an image of the phantom. The center of rotation is determined by repeating this calculation at multiple different rotation angles (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2011-530372 Summary of the Invention [Problem to be solved by the invention]

[0007] When evaluating the degree of radiation beam concentration, it is necessary to measure the position and size of the isocenter with high precision, but this requires time and effort.

[0008] The embodiments of the present invention have been made in consideration of the above circumstances, and have an object to provide a technology for isocenter evaluation that can measure the position and size of the isocenter easily, quickly, and with high accuracy, minimize the size, and achieve high reliability. [Means for solving the problem]

[0009] An isocenter evaluation device according to an embodiment includes a laser tracker that outputs a laser from a predetermined spatial position, a first probe that is provided at three or more points on a support frame that supports a rotating frame that rotates on an axis, and each of the first probe reflects a first optical signal when it receives the laser, a second probe that is provided at three or more points on an intersection plane of a beam that is output in a direction that intersects with the rotation axis of the rotating frame, and each of the second probes reflects a second optical signal when it receives the laser, a calculation unit that calculates a virtual point of an isocenter based on information about the first optical signal, the second optical signal, and the radius and rotation angle of the rotating frame, and a recording unit that changes the rotation angle of the rotating frame and records each of the calculated virtual points of the isocenter as point cloud data. [Effects of the Invention]

[0010] According to an embodiment of the present invention, an isocenter evaluation technique is provided that can measure the position and size of the isocenter easily, quickly, and with high accuracy, minimize the size, and achieve high reliability. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a configuration diagram showing an isocenter evaluation device according to an embodiment of the present invention and a gantry irradiation device equipped with this evaluation device; [Figure 2] (A) A cross-sectional view of a rotating frame showing the ideal state in which a beam circulating around the isocenter and irradiating toward the center converges to a single point; (B) A cross-sectional view of a rotating frame in which the isocenter is defined by multiple point clouds as a result of the virtual points of the isocenter being dispersed depending on the irradiation angle. [Figure 3] (A) A diagram showing a virtual sphere of the isocenter formed by spherical fitting the point cloud using the least squares method. (B) A diagram showing a virtual sphere of the isocenter formed so that the spherical radius of the sphere containing the point cloud is the smallest. (C) A diagram showing a virtual sphere of the isocenter formed with the center of gravity of the point cloud as the center and the average distance from this center to each point in the point cloud as the sphere radius. [Figure 4] (A) An explanatory diagram of beam alignment adjustment in a gantry irradiation device to reduce the size of the virtual sphere formed by the point cloud of the isocenter, and (B) a magnified view of a portion showing the state in which the spherical radius of the virtual sphere of the isocenter becomes smaller due to beam alignment adjustment. [Figure 5] 1 is a flowchart illustrating steps of an isocenter evaluation method according to an embodiment and an algorithm of an isocenter evaluation program. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described based on the attached drawings. Figure 1 is a configuration diagram showing an isocenter evaluation device 10 and a gantry irradiation device 20 equipped with this evaluation device 10 according to an embodiment of the present invention.

[0013] The gantry irradiation device 20 is equipped with an irradiation port 35 for irradiating with a beam 37. By rotating this irradiation port 35 together with the rotating frame 26 around the rotation axis 28, the beam 37 can be irradiated towards the isocenter from any direction.

[0014] The rotating frame 26 is a large cylindrical structure that rotates on a rotating shaft 28 by the rotation of the rotation drive units 27 that are circumscribed on the outer peripheral surfaces of both edges of the rotating frame 26. The weight of the rotating frame 26 is supported by the support frame 25 via the rotation drive units 27.

[0015] In addition to the irradiation port 35, the rotating frame 26 is also provided with a number of beam transport ducts, beam bending magnets, and other control devices and structures (not shown). The beam 37 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 37 output from the circular accelerator is then transported through a beam transport system (not shown) and irradiated from the irradiation port 35 toward the isocenter.

[0016] The evaluation device 10 includes a laser tracker 15 that outputs a laser 30 from a predetermined spatial position, first probes 21 (21a, 21b, 21c) that are provided at three or more points on a support frame 25 that supports a rotating frame 26 that rotates on its axis, and each of the first probes 21 (21a, 21b, 21c) reflects a first optical signal 11 (11a, 11b, 11c) when it receives the laser 30, and second probes 22 (22a, 22b, 22c) that are provided at three or more points on an intersection plane 36 of a beam 37 that is output in a direction that intersects (is perpendicular to) the rotation axis 28 of the rotating frame 26, and each of the second probes 22 reflects a second optical signal 12 when it receives the laser 30.

[0017] 2A is a cross-sectional view of the rotating frame 26, showing an ideal state in which the beam 37 irradiated toward the center while orbiting the isocenter is focused at one point. FIG. 2B is a cross-sectional view of the rotating frame 26, showing the isocenter defined by a group of points as a result of the virtual point 38 of the isocenter being dispersed depending on the irradiation angle θ.

[0018] 1, the evaluation device 10 further includes a calculation unit 16 that calculates a virtual point 38 of the isocenter based on information on the first optical signal 11, the second optical signal 12, and the radius R and rotation angle θ of the rotating frame 26, and a calculation unit 17 that calculates a virtual point 38 of the isocenter based on information on the radius R and rotation angle θ of the rotating frame 26. n The virtual point 38 of each isocenter calculated by changing n It includes a recording unit 17 that records the data as point cloud data.

[0019] Three or more first probes 21 and second probes 22 that receive the laser 30 output by the laser tracker 15 are installed on the support frame 25 and on the installation surface of the irradiation port 35 (intersection surface 36 of the beam 37). The laser tracker 15 receives the first optical signal 11 or the second optical signal 12 that is the result of the laser 30 being reflected by the first probe 21 or the second probe 22.

[0020] The laser tracker 15 calculates a coordinate system (X W ,Y W ,Z W ) can identify the positions of the first probe 21 (21a, 21b, 21c) and the second probe 22 (22a, 22b, 22c). The position measurement accuracy using a commercially available laser tracker 15 and probes 21, 22 is generally about ±0.1 mm for a length of 10 m. The probe serves as a source of reflected light (first optical signal 11 or second optical signal 12) of the laser 30 by combining multiple mirrors inside.

[0021] To create a coordinate system, first determine the origin using the coordinates of the first probe, which serves as the reference, out of a minimum of three probes that are not on the same line, and then create the first coordinate axis using the position coordinates of the second probe. Create a plane using the first coordinate axis and the position coordinates of the third probe, and determine the second coordinate axis from its normal vector. Furthermore, determine the third coordinate axis so that it intersects with the first and second coordinate axes (for example, perpendicular to them). Note that four or more probes may be used to ensure redundancy in case an obstacle gets in the probe's optical path and the reflected light signal cannot be obtained.

[0022] Continuing the explanation, returning to FIG. 1, the calculation unit 16 calculates the coordinates of the world coordinate system (X W ,Y W ,Z W ), a first defining unit 31 that defines a first position 41 where a first probe 21 (21a, 21b, 21c) is placed based on a first optical signal 11 (11a, 11b, 11c) and defines a second position 42 where a second probe 22 (22a, 22b, 22c) is placed based on a second optical signal 12, and a second coordinate system (X II ,Y II ,Z II ) based on the radius R of the rotation frame 26, the virtual point 38 of the isocenter n (FIG. 2), and a first coordinate system (X I ,Y I ,Z I ) is defined and the second coordinate system (X II ,Y II ,Z II ) in the first coordinate system (X I ,Y I ,Z I ) transformation rule 33 to transform it into a rotation angle θ n A generator 34 generates a virtual point 38 of the isocenter based on the transformation rule 33. n in the second coordinate system (X II ,Y II ,Z II ) to the first coordinate system (X I ,Y I ,Z I ) and a conversion unit 39 for converting the

[0023] As a result, a normal vector of the intersection plane 36 is obtained from the position coordinates of the second probe 22 (22a, 22b, 22c) installed on the installation surface of the irradiation port 35 (intersection plane 36 of the beam 37). Then, this normal vector is multiplied by the designed working distance (corresponding to the radius R of the rotating frame 26) to generate a virtual beam 37. Furthermore, point cloud data of the isocenter (virtual point 38) when the rotating frame 26 is rotated is obtained from the center coordinates (output position of the beam 37) of the irradiation port 35 obtained from the position coordinates of the second probe 22 (22a, 22b, 22c) and its tip coordinates. n ) is calculated.

[0024] The evaluation device 10 further includes an estimation unit 18 that estimates a virtual sphere 19 (19a, 19b, 19c) of the isocenter based on the point cloud data of the virtual points 38. The evaluation device 10 also includes an update unit (not shown) that updates the registration of the position information of the isocenter based on the center coordinate c of the newly estimated virtual sphere 19.

[0025] Fig. 3(A) shows a virtual sphere 19a (19) of the isocenter formed by spherical fitting the point cloud using the least squares method. Fig. 3(B) shows a virtual sphere 19b (19) of the isocenter formed so that the spherical radius r of the sphere containing the point cloud is the smallest. Fig. 3(C) shows a virtual sphere 19c (19) of the isocenter formed by setting the center of gravity of the point cloud as the central coordinate c and the average distance from this center to each point in the point cloud as the spherical radius r.

[0026] 3(A) finds an equation so that as many points as possible are fitted to the surface of the virtual sphere 19a. However, if the distribution of the point cloud is distorted, the center coordinate c may be located far from the point cloud, and in this case, it may not necessarily become the virtual sphere 19a that represents the point cloud.

[0027] The method of Figure 3(B) obtains a virtual sphere 19b with the smallest radius that encompasses all point clouds, but the center coordinate c is easily affected by outliers in the virtual points 38, making it easier for the center coordinate c to fluctuate. The method of Figure 3(C) obtains a virtual sphere 19c by using the center of gravity of the point cloud as the center coordinate c and a representative value of the distance between the center of gravity and each point (a statistical value such as the mean, maximum, median, or quartile) as the radius r. By using the center of gravity, the method of Figure 3(C) can obtain a center coordinate c that represents all point clouds and is less affected by outliers in the virtual points 38. However, the radius r of the virtual sphere 19c is not necessarily the smallest (it may be larger than the method of Figure 3(B)). It is recommended that these methods for estimating the virtual sphere 19 of the isocenter be used appropriately depending on the specifications of the equipment being used.

[0028] 4(A) is an explanatory diagram of beam 37 alignment adjustment in the gantry irradiation system 20, which reduces the virtual sphere 19 formed by the point cloud of isocenter virtual points 38. FIG. 4(B) is a partially enlarged view showing the state in which the radius r of the isocenter virtual sphere 19 is reduced by beam 37 alignment adjustment.

[0029] Continuing the explanation, returning to Figure 1, the evaluation device 10 includes a derivation unit 45 that derives an adjustment amount 46 for the alignment of the rotating frame 26 or the support frame 25 so that the radius r of the phantom sphere 19 becomes even smaller.

[0030] The attachment of the irradiation port 35 to the rotating frame 26 requires adjustment (alignment) to minimize the size of the virtual sphere 19 at the isocenter. The derivation unit 45 determines this adjustment amount 46 through numerical calculation. The beam 37 is virtually shifted in three dimensions, and the shift amount (vector) that minimizes the size of the virtual sphere 19 at the isocenter is determined through optimization calculation. By using the adjustment amount 46 obtained through calculation, the attachment position of the irradiation port can be adjusted in a short time.

[0031] Although not shown, the gantry irradiation device 20 is equipped with a first holder (not shown) that detachably holds each of the first probes 21 and is fixed to the support frame 25, and a second holder (not shown) that detachably holds each of the second probes 22 and is fixed to the intersection surface 36 of the rotating frame 26.

[0032] In this way, by providing the first holder and the second holder, the repeatability of the installation positions of the first probe 21 and the second probe 22, which are attached to and detached from the support frame 25 and the crossing plane 36, is improved. While this embodiment originally allows the position and size of the isocenter to be measured with high repeatability, regardless of variations in the installation position of the laser tracker 15, the introduction of the first holder and the second holder further improves the repeatability of the measurement. As a result, even if the first probe 21 and the second probe 22 are repeatedly attached and detached when measurements are performed over different periods, such as during periodic inspections, the reliability of the isocenter evaluation is not lost.

[0033] The steps of the isocenter evaluation method and the algorithm of the isocenter evaluation program according to the embodiment will be described with reference to the flowchart in Figure 5. First, the laser tracker 15 emits a laser 30 from a predetermined spatial position (S11). Then, first probes 21 (21a, 21b, 21c) provided on the support frame 25 receive first optical signals 11 (11a, 11b, 11c) reflected from the laser 30 (S12). Then, second probes 22 (22a, 22b, 22c) provided on the intersection plane 36 of the beam 37 receive second optical signals 12 (12a, 12b, 12c) reflected from the laser 30 (S13).

[0034] Next, the world coordinate system (X W ,Y W ,Z W ), a first position 41 where the first probe 21 (21a, 21b, 21c) is placed is defined based on the first optical signal 11 (11a, 11b, 11c) (S14). Similarly, in the world coordinate system (X W ,Y W ,Z W), the second position 42 where the second probe 22 (22a, 22b, 22c) is placed is determined based on the second optical signal 12 (12a, 12b, 12c) (S15).

[0035] Next, the first coordinate system (X I ,Y I ,Z I ) and a second coordinate system (X II ,Y II ,Z II ) is defined (S16). Then, a virtual point 38 of the isocenter is defined in the second coordinate system. n is defined based on the radius R of the rotating frame 26 (S17). II ,Y II ,Z II ) in the first coordinate system (X I ,Y I ,Z I ) transformation rule 33 is used to transform n Generated every time (S18).

[0036] Next, the rotation angle θ n Based on the transformation rule 33 generated for each point, the virtual point 38 of the isocenter is converted into the second coordinate system (X II ,Y II ,Z II ) to the first coordinate system (X I ,Y I ,Z I ) (S19), and all rotation angles θ n Virtual point 38 of the isocenter at n are recorded as point cloud data (S20).

[0037] Next, the virtual sphere 19 of the isocenter is estimated based on this point cloud data (S21), and the center coordinates c and sphere radius r of the virtual sphere 19 are determined (S22). If this sphere radius r is less than or equal to the target radius, the flow is terminated (S23; No, END). If the sphere radius r is greater than the target radius (S23; Yes), the adjustment amount 46 for the alignment of the rotating frame 26 or support frame 25 is derived so that the sphere radius r is minimized (S22; END).

[0038] In the embodiments described above, the focus was on a rotating frame 26 that rotates 360 degrees or more, but there are no particular limitations, and the invention can also be applied to a rotating frame with a C-shaped orbit that rotates less than 360 degrees. The present invention contributes to reducing the time and cost of checking for positional variations of isocenters that depend on the rotation angle of the rotating frame during on-site assembly and periodic inspection of radiotherapy equipment and CT scanning equipment having such a rotating frame.

[0039] Furthermore, in this embodiment, since there is no process for fine-tuning the jig used for isocenter measurement, the measurement time is shortened, and it also contributes to the stabilization of the measurement. In addition, alignment adjustment allows the irradiation port to be re-fixed to the theoretically optimal position, contributing to higher accuracy and increased product added value.

[0040] Furthermore, by shortening the time required for isocenter evaluation and equipment alignment adjustment, users (hospitals, etc.) can reduce regular maintenance time, thereby shortening the downtime (period when the equipment is unavailable for treatment) of radiation therapy equipment and CT scanners. From the equipment manufacturer's perspective, it becomes possible to perform highly reproducible regular inspections, further improving services such as aging deterioration inspections.

[0041] Furthermore, the present invention is applicable to devices other than the radiation-based treatment and inspection devices shown in the embodiments. For example, it can be applied to evaluate and adjust the degree of focus (degree of dispersion) in processing machines or measuring instruments that irradiate laser light from an arc-shaped trajectory, or measuring instruments that synthesize three-dimensional images by mounting a camera on an arc-shaped trajectory. [Example]

[0042] Hereinafter, an example of estimating the isocenter phantom sphere 19 (center coordinate c and radius r) and calculating the alignment adjustment amount 46 will be described. Note that the coordinate system is represented by the lower right subscript in the symbol notation of vectors. W This is the world coordinate system (X W ,Y W ,Z W ), pI is the first coordinate system (X I ,Y I ,Z I ), p II is the second coordinate system (X II ,Y II ,Z II ) and the rotation matrix between the coordinate systems is R W II and transform the vector from the coordinate system with the lower right subscript to the coordinate system with the upper right subscript. R W I is from the world coordinate system to the first coordinate system, R W II is from the world coordinate system to the second coordinate system, R II I represents the rotational transformation of a vector from the second coordinate system to the first coordinate system.

[0043] First, the coordinates of three or more first probes 21 installed on the support frame 25 are measured to determine the origin O of the first coordinate system. I Position coordinate b in the world coordinate system W and the rotation matrix R from the world coordinate system to the first coordinate system W I Next, the coordinates of three or more second probes 22 installed on the installation surface of the irradiation port 35 (the beam intersection surface 36) are measured, and the irradiation port center coordinate c W and the rotation matrix R from the world coordinate system to the second coordinate system. W II , the normal vector n of the irradiation port installation surface W Using these, the center coordinate c of the irradiation port 35 on the first coordinate system is calculated. I is calculated as shown in equation (1).

[0044] p I =R W I ·p W (1)

[0045] When three probes are used, the normal vector can be easily found by creating two vectors and calculating their cross product. When four or more probes are used, the normal vector can be found by finding the equation of the plane using the least squares method or the like and then finding it from the coefficients of the polynomial. The second probes 22 installed on the installation surface of the irradiation port 35 (beam intersection surface 36) must be positioned so that at least three of them can be seen at the same time from the main body of the laser tracker 15. Therefore, if there is a difference in height between the installation position of the second probe 22 and the installation surface of the irradiation port 35, this dimension is subtracted in the direction of projection onto the installation surface before calculation. The normal vector n found in this way is W Using this, the normal vector n in the first coordinate system I This can be found using equation (2).

[0046] n I =R W I ·n W (2)

[0047] Isocenter coordinate q in the first coordinate system I This is the coordinate c of the irradiation port center in the first coordinate system. B The design working distance L and n from the isocenter. I It can be found using equation (3) as follows: L·n I This can be thought of as a virtual beam of radiation 37 irradiated from the center of the irradiation port installation surface (intersecting surface 36) toward the isocenter.

[0048] q I =p I +L·n I =R W I ·p W +L·R W I ·n W (3)

[0049] To determine the virtual sphere 19 of the isocenter from here, we need to find the virtual points 38 of the isocenter at multiple different irradiation angles. n Point cloud data is obtained. Irradiation angle θ of irradiation port 35. nis moved on a circular orbit at a specified pitch, and measurement of the second position 42 of the second probe 22 at that time is repeated n times to obtain n pieces of point cloud data representing the isocenter as shown in (Equation 4). For example, if measurements are taken at 5-degree pitches on a 360-degree rotating gantry, n=72 point clouds of isocenter coordinates can be obtained as shown in Equation (4). Using the obtained point cloud data, the central coordinate c of the virtual sphere 19 of the isocenter can be calculated. I and radius r are calculated numerically. Note that this calculation uses one of the three methods explained in Figure 3.

[0050] q I1 , q I2 ,…, q In (4)

[0051] Next, a method for adjusting the alignment of the irradiation port 35 to minimize the radius r of the virtual sphere 19 at the isocenter will be described. The adjustment amount 46 of the alignment of the irradiation port 35 in the second coordinate system is expressed as a vector e II It is expressed as e II represents the amount of fine adjustment (amount of shift in three-dimensional directions) of the position when installing the irradiation port 35 on the rotating frame. In practice, this is achieved by adjusting using a fine adjustment screw or a shim (thin plate). Since the irradiation port 35 is installed on the rotating frame and moves on an arc trajectory, the amount of alignment adjustment 46 on the first coordinate system is expressed by the vector e I Expressed as e I can be calculated as shown in equation (5).

[0052] e I = R II I ·e II (5)

[0053] e I is used, the isocenter coordinate q affected by the alignment adjustment amount 46 of the irradiation port 35 is I ´ can be expressed as equation (6).

[0054] q I ´=q I +e I =q I+R II I ·e II =q I +R W I (R W II ) -1 e II (6)

[0055] e II The n-piece point cloud data representing the isocenter when the irradiation port 35 is moved at a specified pitch on a circular arc trajectory can be expressed as follows: I , R W I and R W II This can be easily calculated because of the data.

[0056] q I1 ', q I2 ',…, q In (7)

[0057] Using this point cloud data, e II The radius r' of the virtual sphere 19 at the isocenter can be calculated by varying the three-dimensional e II It can be said to be a scalar-valued function with vectors as variables.

[0058] r'=r(e II ) (8)

[0059] From this, the adjustment amount 46 of the alignment of the irradiation port 35, e II The adjustment method is a scalar-valued function r(e II Minimize the 3D vector e II This can be considered as a minimization problem to search for the following. up to r(e II ), e II ∈ R 3 (9)

[0060] Here, e IIis a three-dimensional vector, but the derivation of the optimal alignment adjustment amount 46 can be expressed one-dimensionally as e II is the input value, and r(e II ) is the optimal solution e II =e II * All we need to do is find ∇(r(e II )) is a scalar function r(e II ) represents the gradient vector (∇ is the nabla operator). II ) satisfies equation (10), where 0 is the zero vector.

[0061] ∇(r(e II ))=0 (10)

[0062] Such minimization problems can be solved using common mathematical optimization solvers, such as grid search, minimum gradient method, Newton's method, and quasi-Newton method. If the design tolerances of the rotating gantry are sufficiently small, the assembly precision is high, and the circularity of the circular arc trajectory of the rotating frame is high, the minimization problem of equation (10) will generally be a convex optimization problem, and the above solvers can generally obtain a globally optimal solution. However, in some cases, if the circularity of the circular arc trajectory cannot be made very high, multiple local optimal solutions may occur. In such cases, a global solution can be found by combining the annealing method or by performing a grid search near the local optimal solution.

[0063] In this embodiment, e II Using I In this example, the alignment is adjusted by translating the beam with three degrees of freedom, but this is not the only method. For example, the installation angle of the irradiation port 35 can be adjusted relative to the installation surface (intersection surface 36) of the irradiation port 35. In this case, the installation angles α and β in two directions and L·n I The adjustment is done by combining the amount of adjustment σ in the direction. In this case, too, it is an adjustment of three degrees of freedom, and by converting to polar coordinates, e II is equivalent to

[0064] However, there is no need to perform polar coordinate transformation each time you calculate an optimization problem. IITherefore, it is advantageous in terms of calculation cost to use the alignment mechanism of the actual device (α * ,β * ,γ * ) adjustment mechanism, first e II * After calculating (α * ,β * ,γ * ) is computationally less expensive.

[0065] Figure 4 shows the X coordinate system of the first coordinate system. I -Z I The figure shows conceptually how to estimate the imaginary sphere 19 of the isocenter as seen from a plane and calculate the alignment adjustment amount 46. The imaginary radiation beam L·n I Let the alignment vector e I =R II I ·e II It is shown that the radius r of the virtual sphere 19 at the isocenter can be reduced by shifting the axis by

[0066] Although detailed explanations are omitted, we will briefly introduce the results of optimization calculations of the alignment adjustment amount 46 for the prototype rotating gantry. The minimum containing sphere was used to calculate the radius r of the virtual sphere 19. The radius before the optimization calculation was 1.59 mm, but after the optimization calculation it became 0.44 mm. The position adjustment amount e of the irradiation port 35 at that time was II * was (-0.30, 2.10, -1.60). This shows that the present invention is a highly effective technique for isocenter evaluation.

[0067] According to at least one of the embodiments of the isocenter evaluation device described above, by having a first probe provided at three or more points on the support frame and reflecting the received laser light, and a second probe provided at three or more points on the beam intersection plane and reflecting the received laser light, it becomes possible to measure the position and size of the isocenter easily, quickly, and with high accuracy, minimize the sphere radius, and achieve high reliability.

[0068] 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.

[0069] The isocenter evaluation device 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, an input device such as a mouse or keyboard, and a communication I / F, and can be realized with a hardware configuration using a normal computer. Therefore, the components of the isocenter evaluation device can be realized by a computer processor and can be operated by an isocenter evaluation program.

[0070] The isocenter evaluation program may be provided by being pre-installed in a ROM, etc. Alternatively, the 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).

[0071] The isocenter evaluation program 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 isocenter evaluation device 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]

[0072] 10...isocenter evaluation device, 11...first optical signal, 12...second optical signal, 15...laser tracker, 16...calculation unit, 17...recording unit, 18...estimation unit, 19 (19a, 19b, 19c)...virtual sphere, 20...gantry irradiation device, 21...first probe, 22...second probe, 25...support frame, 26...rotating frame, 27...rotation drive unit, 28...rotation axis, 30...laser, 31...first determination unit, 32...second determination unit, 33...conversion rule, 34...generation unit, 35...irradiation port, 36...intersection plane, 37...beam, 38...virtual point, 39...conversion unit, 41...first position, 42...second position, 45...derivation unit, 46...adjustment amount.

Claims

1. A laser tracker that emits a laser from a predetermined spatial position, a first probe provided at three or more points on a support frame supporting a rotating frame that rotates around an axis, each of which reflects a first optical signal when it receives the laser beam; a second probe provided at three or more points on a crossing plane of the beam emitted in a direction crossing the rotation axis of the rotating frame, each of which reflects a second optical signal when it receives the laser; A calculation unit that calculates a virtual point of the isocenter based on the first optical signal, the second optical signal, and the information of the radius and rotation angle of the rotating frame, a recording unit that changes the rotation angle of the rotating frame and records the calculated virtual points of each of the isocenters as point cloud data.

2. In the isocenter evaluation apparatus according to claim 1, an isocenter evaluation device comprising an estimation unit that estimates a virtual sphere of the isocenter based on the point cloud data;

3. In the isocenter evaluation apparatus according to claim 2, The virtual sphere is estimated by fitting the point cloud using the least squares method, by finding an encompassing sphere of the point cloud with the smallest sphere radius, or by using the center of gravity of the point cloud as the center and taking the average distance from this center to each point in the point cloud as the sphere radius.

4. An isocenter evaluation apparatus according to claim 1 or claim 2, a first holder that detachably holds each of the first probes and is fixed to the support frame; a second holder that detachably holds each of the second probes and is fixed to the intersecting plane of the rotating frame.

5. In the gantry irradiation system according to claim 4 which relies on claim 2, a gantry irradiation device comprising an update unit that updates the registration of the position information of the isocenter based on the central coordinates of the virtual sphere;

6. In the gantry irradiation system according to claim 4 which relies on claim 2, a derivation unit that derives an adjustment amount for the alignment of the rotating frame or the support frame so that the radius of the virtual sphere becomes smaller.

7. The steps include: a laser tracker is used to output a laser from a predetermined spatial position; receiving a first optical signal obtained by reflecting the laser at each of three or more first probes provided on a support frame that supports a rotating frame that rotates on an axis; receiving a second optical signal obtained by reflecting the laser at each of three or more second probes provided on an intersection plane of a beam output in a direction intersecting the rotation axis of the rotating frame; calculating a virtual point of an isocenter based on the first optical signal, the second optical signal, and information about the radius and rotation angle of the rotating frame; and changing the rotation angle of the rotating frame and recording the calculated virtual points of each of the isocenters as point cloud data.

8. On the computer, outputting a laser from a predetermined spatial location by a laser tracker; receiving a first optical signal obtained by reflecting the laser at each of three or more first probes provided on a support frame that supports a rotating frame that rotates on an axis; receiving a second optical signal obtained by reflecting the laser at each of three or more second probes provided on an intersection plane of a beam output in a direction intersecting the rotation axis of the rotating frame; calculating a virtual point of an isocenter based on the first optical signal, the second optical signal, and information about the radius and rotation angle of the rotating frame; an isocenter evaluation program that executes a step of changing the rotation angle of the rotating frame and recording each calculated virtual point of the isocenter as point cloud data.

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