JP2023023437A - Particle beam care system and treatment planning device - Google Patents

Abstract

To provide: a particle beam care system capable of improving quality of a gamma-ray source image in comparison with conventional ones, and improving range measurement accuracy; and a treatment planning device.SOLUTION: A particle beam care system includes a proton beam radiation device 101 for irradiating a target with a particle beam, a treatment planning device 210 for creating a radiation plan of a particle beam by the proton beam radiation device 101, and a gamma-ray detector 205 for detecting a gamma ray generated by radiation of the particle beam. The treatment planning device 210 determines a recommendation installation position of the gamma-ray detector 205 based on spatial resolution of the gamma-ray detector 205 at each angle set beforehand.SELECTED DRAWING: Figure 2

Description

The present invention relates to a particle beam therapy system and a treatment planning apparatus.

Non-Patent Document 1 describes the first clinical results and value evaluation of prompt γ-ray imaging for in vivo proton range confirmation in pencil beam scanning mode during proton therapy for brain tumor patients. Using a prototype of a trolley-mounted stand-alone prompt gamma camera employing a knife-edge slit collimator design to record the prompt gamma signal emitted along the track, the recorded individual pencil beam spot prompts. The results of comparing the gamma depth detection profile to the expected profile simulated from the treatment plan are described.

Xie Y., et al., “Prompt Gamma Imaging for In Vivo Range Verification of Pencil Beam Scanning Proton Therapy.” Int J Radiation Oncol Biol Phys, 99(1), 210-218, 2017

Under sufficiently low magnetic field conditions, charged particle beams such as proton beams and carbon beams, when they enter the human body, travel in a straight line while imparting doses to surrounding tissues, and finally lose all kinetic energy and stop.

The stopping position of the particle beam is called range, and a maximum dose area called Bragg peak is formed in the vicinity of the range. It is possible to either not apply a dose to regions deeper than the range, or to limit the dose to neutral ionizing radiation such as X-rays. Due to these characteristics, particle beam therapy can increase the dose concentration to the affected area compared to the conventionally widely used X-ray therapy, and it is expected to be a cancer treatment that suppresses damage to normal tissues. can.

As a method of irradiating the affected area with particle beams, the scanning irradiation method has been widely adopted in recent years because it does not require the manufacture of patient-specific instruments such as boluses and collimators, and because it is possible to form a dose distribution that matches the shape of the tumor.

In the scanning irradiation method, a large number of points (spots) are arranged three-dimensionally inside and outside the target area, especially a tumor, where a high dose is to be given, and each spot is targeted by a thin beam (pencil beam). etc.) are sequentially irradiated to form a uniform dose distribution in the target region.

The dose to each spot is optimized using a treatment planning system. Treatment planning involves calculating the dose distribution in the patient's body based on information obtained from the patient's CT images, etc., so that a uniform dose is given to the target area, and risk organs located near the target ( This is a procedure for optimizing the irradiation dose to each spot so as to avoid exposure to OAR (Organ At Risk) as much as possible.

The optimization places an infinite number of calculation points three-dimensionally inside and outside the target area and OAR. By setting a target dose for each calculation point and adjusting the irradiation dose to each spot and repeatedly calculating the dose at each calculation point, the irradiation dose for each spot that achieves the target value is obtained. . Note that the calculated points and the spot positions are not necessarily the same.

Therefore, treatment planning requires high dose calculation accuracy. However, even with a correctly calculated plan, there is a possibility that the planned irradiation will not occur. The factors are divided into external factors and internal factors.

External factors of calculation errors include positioning errors of the patient on the couch in the treatment room and variations in the irradiation position of the beam of the irradiation device.

Internal factors of calculation errors include deformation and movement of body structures including tumors due to respiration and heartbeat. The dose distribution of particle beams is greatly influenced not only by the position of the tumor but also by the structures along the path that the beam passes to reach it. For example, if areas with significantly different densities, such as bone and air layers, are on the beam path and these areas move significantly during beam irradiation due to respiration, etc., the dose distribution around the tumor may change significantly.

Furthermore, an important error factor is the uncertainty of CT value-stopping power conversion in dose calculation. In treatment planning, the CT value of each voxel on the CT image is converted into particle beam stopping power based on a conversion table prepared in advance, and the dose distribution is calculated. The CT value-stopping power conversion table is experimentally created using a phantom with a known stopping power. However, even if the CT value is the same, the stopping power varies depending on the site and the patient, so an error occurs in the calculation accuracy of the dose distribution.

Tumor recurrence due to underdose may occur if irradiation is not delivered as planned. Also, high dose exposure of OAR can be caused. Therefore, it is necessary to improve positioning and irradiation accuracy, monitor internal body structures in real time using X-ray fluoroscopy and MRI, and take measures to eliminate the influence of uncertainties in CT value-stopping power conversion as much as possible. .

As one of the countermeasures, a method of directly observing the range in the body and comparing it with the result of treatment planning has been disclosed (see Non-Patent Document 1). If the observed range matches the treatment plan, it can be assured that the CT value-stopping power conversion table was appropriate for the patient. Moreover, even if the observed range differs from the treatment plan, the treatment plan for the next fraction and subsequent fractions can be corrected based on the difference, and high-precision particle beam therapy can be achieved throughout the entire treatment.

As described above, Non-Patent Document 1 discloses a method of observing the range by using high-energy gamma rays generated along the path of the beam.

Specifically, a radiation detector (line sensor) having a positional resolution in the direction of beam travel is installed, and gamma rays generated from the beam passage area are measured. By placing a knife-edge collimator directly above the line sensor, the direction of arrival of gamma rays is limited, making it possible to image the gamma ray source, that is, the beam passage path. The range can be estimated from the end of the beam passage path, that is, the position where the gamma ray intensity drops sharply. Here, the knife-edge collimator is represented by a shape obtained by projecting a pinhole collimator in a direction perpendicular to the beam traveling direction (hereinafter referred to as a lateral direction).

Here, the gamma rays generated along with the particle beam irradiation have high energy, and some of the gamma rays pass through the knife-edge portion of the collimator and reach the line sensor, causing the image of the gamma ray source to blur. In other words, there is a problem that the range measurement accuracy is lowered.

The present invention provides a particle beam therapy system and a treatment planning apparatus capable of improving the quality of gamma ray source images and improving the accuracy of range measurement compared to conventional systems.

The present invention includes a plurality of means for solving the above problems. To give an example, a particle beam irradiation device for irradiating a target with a particle beam, and an irradiation plan for the particle beam by the particle beam irradiation device. and a gamma ray detector that detects gamma rays generated by the irradiation of the particle beam, and the treatment planning device is based on the spatial resolution of the gamma ray detector for each preset angle, It is characterized by obtaining a recommended installation position of the gamma ray detector.

According to the present invention, it is possible to improve the quality of the gamma ray source image and improve the range measurement accuracy as compared with the conventional art. Problems, configurations and effects other than those described above will be clarified by the following description of the embodiments.

1 is a schematic diagram of a particle beam therapy system in an embodiment of the present invention; FIG. FIG. 2 is a schematic diagram of an irradiation field forming device, a gamma ray detector, and a treatment planning device using the scanning irradiation method in FIG. 1; FIG. 4 is a workflow diagram of treatment planning in the particle beam therapy system and the treatment planning apparatus in the embodiment. FIG. 2 is a schematic diagram showing the arrangement relationship of calculation points in a particle beam therapy system and a treatment planning apparatus in an embodiment; FIG. 4 is a schematic diagram showing the positional relationship of spots in the particle beam therapy system and the treatment planning apparatus in the embodiment; FIG. 2 is a schematic diagram showing an example of spatial resolution of a collimator in a particle beam therapy system and a treatment planning apparatus in an embodiment; FIG. 10 is a schematic diagram showing another example of the spatial resolution of the collimator in the particle beam therapy system and the treatment planning apparatus in the embodiment; FIG. 4 is a diagram showing an overview of how the positions of gamma ray detectors are determined based on the display screen of the display device in the particle beam therapy system and the treatment planning apparatus of the embodiment; FIG. 4 is a diagram showing an outline of another form of the particle beam therapy system and the treatment planning apparatus of the embodiment; FIG. 10 is a diagram showing another form of the collimator of the gamma ray detector in the particle beam therapy system and the treatment planning apparatus of the embodiment; FIG. 10 is a diagram showing still another form of the collimator of the gamma ray detector in the particle beam therapy system and the treatment planning apparatus of the embodiment;

An embodiment of a particle beam therapy system and a treatment planning apparatus according to the present invention will be described with reference to FIGS. 1 to 11. FIG. In the drawings used in this specification, the same or corresponding components are denoted by the same or similar reference numerals, and repeated descriptions of these components may be omitted.

First, an overview of the overall configuration of a particle beam therapy system according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram of a particle beam therapy system in this embodiment.

The particle beam therapy system includes a proton beam irradiation device 101 as shown in FIG. In this embodiment, a proton beam irradiation apparatus will be described as an example, but the present invention can also be applied to a heavy ion beam irradiation apparatus using particles having a mass heavier than that of protons (such as carbon beams).

A proton beam irradiation apparatus 101 is an apparatus for irradiating a target with a proton beam, and as shown in FIG. In this embodiment, the rotary irradiation device 104 having a rotating gantry will be described as an example, but a stationary irradiation device can also be used.

In FIG. 1 , the proton beam generator 102 has an ion source 105 , a pre-accelerator 106 (eg, linear accelerator), and a synchrotron 107 .

Proton ions generated by the ion source 105 are first accelerated by the pre-accelerator 106 . A proton beam (hereinafter referred to as a beam) emitted from the pre-accelerator 106 is accelerated to a predetermined energy by the synchrotron 107 and then emitted from the extraction deflector 108 to the proton beam transport device 103 . Finally, the beam passes through a rotary irradiation device 104 and is irradiated onto a target region 202 such as a tumor of a patient 201 to be irradiated.

In this embodiment, a synchrotron is used as a proton beam accelerator, but other accelerators such as a cyclotron and a linear accelerator can be used.

The rotating irradiation device 104 has a rotating gantry (not shown) and an irradiation field forming device 109 . An irradiation field forming device 109 installed on a rotating gantry rotates together with the rotating gantry. Part of the proton transport device 103 is attached to a rotating gantry.

Next, details of the irradiation field forming device 109 will be described with reference to FIG. FIG. 2 is a schematic diagram of an irradiation field forming device, a gamma ray detector, and a treatment planning device using the scanning irradiation method in FIG.

The irradiation field forming apparatus of this embodiment shown in FIG. 2 employs a scanning irradiation method. In the scanning irradiation method, a large number of points (hereinafter referred to as spots 203) are arranged three-dimensionally in and around a target area 202, such as a tumor, to which a high dose is to be applied, in the body of the patient 201, and each A uniform dose distribution is formed in the target region 202 by sequentially irradiating a thin pencil beam aiming at the spot 203 . When a certain spot 203 is given a predetermined dose, irradiation is stopped and the beam is scanned toward the next predetermined spot 203 .

A scanning electromagnet 204 mounted on the irradiation field forming device 109 is used for beam scanning in the horizontal direction (the X direction and the Y direction in FIG. 2). After applying a predetermined dose to all spots 203 for a certain depth in the Z direction, the field forming device 109 scans the beam in the Z direction. The scanning of the beam in the Z direction is performed by changing the acceleration conditions in the synchrotron 107, or changing the energy of the beam by passing the beam through a range shifter (not shown) mounted on the irradiation field forming device 109 or the like. do by doing A ridge filter (not shown) may be installed in the irradiation field forming device 109 in order to disperse the range of the passing beam in a Gaussian distribution and expand the width of the Bragg peak.

In the scanning irradiation method, a uniform dose distribution is finally formed over the entire target region 202 by repeating the procedure as described above. The lateral dose distribution of the beam for each spot 203 spreads in the form of a Gaussian distribution of 1σ=2 [mm]-20 [mm] on the XY plane.

Scanning irradiation includes a discrete system and a raster system, and although the discrete system will be described in this embodiment, the same effects can be obtained with either system. The discrete method is a method in which the beam is temporarily stopped when the spot 203 is switched, and the raster method is a method in which the beam is not stopped even during the movement of the irradiation position.

The dose delivered to each spot 203 is optimized using treatment planning system 210 . Treatment planning involves calculating the dose distribution in the patient's body based on information obtained from the patient's CT images, etc., so that a uniform dose is given to the target area, and risk organs located near the target ( This is a procedure for optimizing the irradiation dose to each spot 203 so as to avoid exposure to OAR) as much as possible. Detailed procedures for treatment planning will be described later.

The treatment planning device 210 is a device that creates a particle beam irradiation plan for the proton beam irradiation device 101, and preferably each device is composed of a computer or the like. The computer that constitutes these includes a CPU, a memory, an interface, a display device 211, an input device corresponding to a mouse and the like, a recording device, and the like. is executed based on These programs are stored in an internal recording medium, an external recording medium, a data server (not shown), or the like in each configuration, and are read and executed by the CPU.

Note that the operation control processing may be integrated into one program, may be divided into a plurality of programs, or may be a combination thereof. Also, part or all of the program may be realized by dedicated hardware, or may be modularized. Furthermore, various programs may be installed in each device from a program distribution server, an internal storage medium, or an external storage medium.

Moreover, each device or system need not be independent, and two or more devices or systems may be integrated and made common to share only the processing. Also, at least part of the configuration may be connected via a wired or wireless network.

In this embodiment, the treatment planning system 210 obtains the recommended installation position of the gamma ray detector 205 based on the spatial resolution of the gamma ray detector 205 for each preset angle. Then, a signal is output to a driving device 208 capable of moving the installation position of the gamma ray detector 205 or a display device 211 displaying a screen for inputting the installation position of the gamma ray detector 205 . Their details will be described later.

In the particle beam therapy system of the present invention, in order to confirm the validity of the CT value-stopping power conversion table used for treatment planning, high-energy gamma rays generated along the beam passage path are used to generate real-time observation of the range position of the proton beam. For this purpose, the irradiation field forming device 109 is provided with a gamma ray detector 205 for detecting gamma rays generated along with the proton beam irradiation.

The gamma ray detector 205 is composed of a knife-edge collimator (hereinafter referred to as a collimator 206) and a radiation detector (hereinafter referred to as a line sensor 207) having a positional resolution with respect to the beam traveling direction (Z-axis). be done.

Here, the knife-edge collimator 206 is represented by a shape obtained by projecting a pinhole collimator in the Y-axis direction, and is formed of a substance such as tungsten or lead that has a high gamma-ray shielding capability.

The line sensor 207 is composed of a scintillation counter or a semiconductor detector that generates an electrical signal in response to incident radiation.

Furthermore, the gamma ray detector 205 has a driving device 208 capable of moving its installation position. In FIG. 2, it has a well-known configuration that can be moved in the X, Y, and Z-axis directions and finely adjusted and fixed in position. This driving device 208 can move the installation position of the gamma ray detector 205 during particle beam irradiation.

The driving device 208 is installed on the rotating gantry and can rotate around the origin together with the radiation field forming device 109 . Thereby, the gamma ray detector 205 can keep the angle parallel to the beam traveling direction (Z-axis) regardless of the rotation angle of the rotating gantry.

As shown in FIG. 2, the direction of arrival of the gamma rays observed by the line sensor 207 is limited by the collimator 206, so the gamma ray detector 205 can image the gamma ray source, that is, the beam passage path, based on the same principle as a pinhole camera. becomes possible. Imaging is performed by a signal processor 209 connected to the gamma ray detector 205 . Furthermore, the signal processing device 209 estimates the range from the acquired image. For example, an algorithm for estimation from the end of the beam passage path, that is, the position where the intensity of the gamma ray sharply drops is conceivable. However, in the present invention, the range estimation algorithm from the gamma ray source image is not limited to this method.

Next, the flow of treatment planning according to the present invention will be described with reference to FIGS. 3 to 5. FIG. FIG. 3 is a workflow diagram of treatment planning, FIG. 4 is a schematic diagram showing the arrangement relationship of calculation points, and FIG.

After starting treatment planning, first, as shown in FIG. Input the area to be specified (step 301). The input area is a target area to be irradiated with radiation and an OAR area to avoid radiation irradiation as much as possible. After completing the input for each slice, the area input by the operator is stored in the recording device within the treatment planning apparatus 210 as three-dimensional position information.

After step 301, as shown in FIG. 4, the treatment planning system 210 three-dimensionally arranges a total of M calculation points 402 inside and outside the target region 202 and the OAR region 401, and further N inside and outside the target region 202. spots 203 are arranged three-dimensionally (procedure 302).

Treatment planning system 210 then determines the energy of the beam to be directed at each spot 203 (step 303).

As a beam energy determination algorithm, for example, as shown in FIG. 5, a method of approximating that the beam travels straight from the scanning point 403 to each spot 203 and searching so that the range position and the spot 203 match. There is However, in the present invention, the beam energy determination algorithm is not limited to this method.

The beam energy and range for each spot 203 determined in step 303 are stored in the recording device. The position of the scanning point 403 is approximated by the central position of the scanning electromagnet.

Next, the treatment planning system 210 calculates the dose given to M calculation points by the pencil beam irradiated toward each spot 203, and saves it in the recording device as an M×N dose matrix A (step 304 ). Here, let d be an M-dimensional vector whose elements are the total applied dose for all the spots 203 to each calculation point, and d and an N-dimensional vector x whose elements are the doses to each spot 203 and can be expressed by the following equation (1).

Next, the treatment planning device 210 sets a target irradiation dose D for M ( ^target ) calculation points included in the target region. Furthermore, an allowable dose value D _limit is set for M ^(OAR) points included in the OAR area. Here, when creating a treatment plan according to the present invention, the treatment planning device 210 determines the objective function F(x) as shown in the following equation (2) (step 305).

In equation (2), the first term is the portion corresponding to the target region, and the closer the dose value d _j ^(target) at M ( ^target ) calculation points is to the target irradiation dose D, the more the objective function F (x ) becomes smaller.

The second term relates to the dose constraint of OAR, and the dose value d_ _j ^(OAR) at M ^(OAR) calculation points does not exceed the allowable dose D _limit . θ(d _j ^(OAR) −D _limit ) is a step function and is 0 if d ^j(OAR)j <D _limit and 1 otherwise. Here, w ^(k) and w ^(OAR) are weights corresponding to the respective objective functions and are values input by the operator. A different weight can be set for each calculation point.

In order to more effectively obtain the effects of the present invention, the objective function for optimizing the irradiation dose for each spot 203 is not limited to the form shown in Equation (2).

In the treatment planning procedure of the present invention, after generating the objective function F(x), the treatment planning apparatus 210 repeats iterative calculations until the termination condition is satisfied, thereby finding x that minimizes the objective function F(x). Search (step 306). When the termination condition is reached, the iterative computation is terminated. Indices such as the calculation time, the number of iterations, and the amount of change in the objective function are set as the termination conditions. After the search is completed, the irradiation dose x for each spot 203 is stored in the recording device.

Next, the treatment planning device 210 optimizes the installation position r ^→ of the gamma ray detector 205 based on a preset objective function F2(r ^→ ). Although the center of the opening of the collimator 206 is defined as r ^→ in this embodiment, the effect of the invention can be obtained even if another position is defined as the position of the gamma ray detector 205 . In the present invention, the objective function F2(r ^→ ) is defined as in the following equation (3) (step 307).

Equation (3) is expressed as the product of the dose for each spot 203 and the resolution of the gamma ray detector 205, where xi is the irradiation dose for the i-th spot 203 obtained in step 306. As a result, the higher the dose, the higher the resolution area that can be observed. R represents the spatial resolution of the gamma ray detector 205 determined by the angle φ formed by the position r ^→ of the gamma ray detector 205 and the spot xi. From FIG. 2, φ is represented by the following formula (4).

In equation (4), r _⊥ ^→ is the X-axis component of r ^→ , and r _i ^→ is the position of spot i. The spatial resolution R of the gamma ray detector 205 with respect to φ is obtained in advance using experiments, simulations, or the like. Graphs 501 and 505 of spatial resolution R are shown in FIGS.

As shown in FIG. 6 or FIG. 7, in the gamma ray detector 205 using the knife-edge collimator 206, the gamma ray shielding performance of the collimator is improved as φ increases in the inside 502 of the field of view. Within the range of the inner side 502 of the field of view, the more distant the gamma rays come from the center of the field of view, the better the shielding performance of the collimator. It has been found by the studies of the present inventors that the distance is reduced and the range measurement accuracy is improved.

Therefore, the treatment planning system 210 can search for the recommended installation position so that the three-dimensional position of the target spot 203 is included in the high resolution region 503 where the spatial resolution of the gamma ray detector 205 is equal to or higher than a predetermined standard. A spot 203 for this purpose may preferably be a spot 203 where the exposure dose exceeds a pre-specified threshold.

Therefore, in step 307, the position r ^→ of the gamma ray detector 205 is optimized so that the spot 203 with a large irradiation dose is included in the high resolution area 503 as much as possible.

In addition, to further enhance the effect, the outside of the field of view, that is, the area 504 completely blocked by the collimator 206 can be strictly made to have no resolution (infinite). A large value is set for the area 504 as compared to the inside 502 of the field of view so that the spot 203 is not included as much as possible during optimization.

The spatial resolution R of the gamma ray detector 205 used for optimization can be a continuous graph directly using the resolution measurement results as shown in graph 501, as shown in FIG. In addition, as shown in FIG. 7, a discontinuous graph 505 in the form of a step function can be obtained in which a high-resolution area 503 satisfying a certain resolution or more is zero.

In addition, in order to consider only the high-dose spots 203 where a sufficient number of gamma rays are generated and whose range can be measured, for the optimization of r ^→ , the dose for each spot 203 used for calculating the objective function F2(r ^→ x can also be discretized such that less than a preset threshold value is zero, and x is greater than or equal to the threshold value.

In the treatment planning procedure of the present invention, after generating the objective function F2(r ^→ ), the treatment planning apparatus 210 repeats iterative calculations until the end condition is met, and detects gamma rays with the smallest objective function F2(r ^→ ). position r ^→ of the device 205 (procedure 308).

When the termination condition is reached, the iterative computation is terminated. Indices such as the calculation time, the number of calculations, and the amount of change in the objective function are set as the termination conditions. After the search is completed, the installation position r ^→ of the gamma ray detector 205 is stored in the recording device, and the preparation of the treatment plan is completed.

FIG. 3 illustrates the case where the position r ^→ of the gamma ray detector 205 is optimized by the treatment planning device 210 by minimizing the objective function F2(r ^→ ), but the position r ^→ of the gamma ray detector 205 is searched manually. It is also possible to FIG. 8 is a diagram showing an overview of how the position of the gamma ray detector is determined based on the display screen of the display device.

As shown in FIG. 8, on the operation screen 701 displayed on the display device 211, in addition to the target region 202, the collimator 206, and the line sensor 207, the high resolution region 702 of the gamma ray detector 205, The predicted Bragg peak position of a spot (denoted as high dose spot 703) for which a sufficient number of statistics can be expected is displayed.

The high-dose spot 703 displayed on the operation screen 701 is preferably the spot 203 obtained in step 306 and having an irradiation dose exceeding a preset threshold value. The high resolution area 702 corresponds to the high resolution area 503 determined from the installation position r ^→ of the gamma ray detector 205 .

On such an operation screen 701, the position r ^→ of the gamma ray detector 205 can be freely moved using an input device such as a mouse. can be installed at

For example, the gamma ray detector 205 is positioned so that the high-dose spot 703 and the high-resolution region 702 overlap by determining the arrangement position so that as many spots whose irradiation dose exceeds a preset threshold value are included in the high-resolution region 702 as possible. can be ^determined . Also, placing importance on confirming that the range of the spot 203 in the area near the OAR is as planned, the arrangement position can be determined so that the spot 203 in the area near the OAR is included in the high resolution area 702. .

The installation position of the gamma ray detector 205 determined by the operation is also reflected in the actual device, and the driving device 208 is driven to set the gamma ray detector 205 at the determined installation position.

In the particle beam therapy system of the present invention, the driving device 208 is first used to move the gamma ray detector 205 toward the position r ^→ optimized by the treatment planning device 210 before treatment. Then, according to the irradiation dose x optimized by the treatment planning system 210, the target in the patient's body is irradiated with the beam for each spot 203. FIG.

Instead of using the driving device 208, the operator can refer to the screen of the display device 211 and manually install the gamma ray detector 205 at the desired position.

In the above procedure, the installation position of the gamma ray detector 205 is assumed to be fixed during irradiation. It can be captured in a high area. Advantageously, the beam energy, ie the placement position, can be varied from layer to layer. Description will be made below with reference to FIG. FIG. 9 is a diagram showing an overview of another form of the particle beam therapy system and the treatment planning apparatus of the embodiment.

In FIG. 9, the treatment planning device 210 outputs the estimated position information of the beam range of each spot 203 to the irradiation field forming device 109, and the irradiation field forming device 109 outputs the estimated position information of the range of the beam currently being irradiated. Based on the estimated position information, the driving device 208A adjusts the installation position of the gamma ray detector 205 so that the range of the beam is always within the high resolution region 503 during irradiation.

In FIG. 9 as well, the timing of measurement and driving may be limited to irradiation of spots 203 whose irradiation dose exceeds a predetermined threshold, instead of all spots 203, or irradiation of all spots 203 may be It is not particularly limited.

In the above description, a form using a bilaterally symmetrical knife-edge collimator 206 was shown. The shape of the collimator is not limited to symmetrical as long as it is possible to prepare in advance a graph of a spatial resolution with a sufficient spatial resolution.

Another example will be described below with reference to FIGS. 10 and 11. FIG. 10 and 11 are schematic diagrams of another form of the collimator of the gamma ray detector.

For example, as shown in FIG. 10, the effect of the present invention can be obtained even if the collimator 601 is left-right asymmetrical. With such a shape of the collimator 601, the distance between the high-dose spot 603 and the line sensor 207 can be shortened in observation in the high-resolution area 602, so the number of measured gamma rays increases. Therefore, the statistical error is reduced, and the range measurement accuracy can be improved.

Also, as shown in FIG. 11, a multi-leaf collimator 606 composed of a plurality of metal leaves 605 connected to a leaf driving device 604 can also obtain the effects of the present invention. The advantage of this multi-leaf collimator 606 is that the shape of the knife edge can be adjusted based on the size of the target area 202, so that the driver 208 of the gamma ray detector 205 is not required. Also, by adjusting the knife edge shape for each spot 203 or for each beam energy (layer), it is easy to place all the spots 203 in the high resolution region 503 of the gamma ray detector 205 for observation.

An appropriate aperture shape of the multi-leaf collimator 606 for each spot 203 is obtained by calculating and measuring the spatial resolution R of the gamma ray detector 205 for each aperture shape in advance and minimizing the objective function F2(r ^→ ). can ask. At this time, the position r ^→ of the gamma ray detector 205 is a fixed value. Also, the aperture shape of the multi-leaf collimator 606 can be manually determined by a position operator.

Next, the effects of this embodiment will be described.

In the particle beam therapy system of the present embodiment described above, the proton beam irradiation device 101 that irradiates the target with the particle beam, the treatment planning device 210 that creates the irradiation plan of the particle beam by the proton beam irradiation device 101, and the particle beam irradiation and a gamma ray detector 205 that detects gamma rays generated along with the treatment planning apparatus 210, based on the spatial resolution of the gamma ray detector 205 for each preset angle, obtains the recommended installation position of the gamma ray detector 205 .

This makes it possible to adjust the position of the gamma ray detector 205 and perform gamma ray measurement using an area with high spatial resolution, thereby improving the quality of the gamma ray source image and improving the range measurement accuracy. Therefore, the validity of the CT value-stopping power conversion table for each patient can be confirmed more accurately. In addition, even if the observed range differs from the treatment plan, the treatment plan for subsequent fractions can be corrected based on the difference, and particle beam therapy can be achieved with higher precision than before throughout treatment.

In addition, since the gamma ray detector 205 has a driving device 208 capable of moving its installation position, it is possible to position the gamma ray detector 205 with high accuracy.

Furthermore, in the scanning irradiation method in particle beam therapy, the majority of the spots 203 have a small irradiation dose and do not emit a sufficient number of gamma rays, so statistical errors may degrade the quality of the gamma ray source image. In other words, just as there is room for improvement in the above-described lack of gamma-ray shielding performance of the collimator, there is room for further improvement in range measurement accuracy.

Here, in order to confirm that the CT value-stopping power conversion table used in the dose calculation is appropriate for each patient and that irradiation has been performed as planned, at least one or more spots 203 must be used. In the course of the above investigation, the inventors found that it is sufficient to observe and compare with the treatment plan, and that it is not necessary to measure the range for all the spots 203 .

Therefore, the treatment planning system 210 extracts the high-dose spots 603 and 703 where the irradiation dose exceeds a predetermined threshold, thereby identifying regions that can be measured with high accuracy, and determining the timing of irradiation at highly-accurate locations. Therefore, it becomes possible to confirm the validity of a more accurate CT value-stopping power conversion table for each patient.

In addition, the treatment planning apparatus 210 determines the recommended installation positions so that the three-dimensional positions of the high-dose spots 603 and 703 are included in the high-resolution region 503 of the gamma-ray detector 205 where the spatial resolution of the gamma-ray detector 205 is equal to or greater than a predetermined standard. By searching, more measurement data can be obtained at locations with high accuracy, and the quality of the gamma ray source image can be further improved.

Furthermore, by further providing a display device 211 that displays the three-dimensional position of the spot 203 and the high resolution region 702 where the spatial resolution of the gamma ray detector 205 is equal to or higher than a predetermined standard, the operator can obtain the measurement result at the desired position. It can be a form suitable for the case where it is desired to obtain

In addition, the driving device 208 moves the installation position of the gamma ray detector 205 during irradiation of the particle beam, so that more highly accurate measurement data can be acquired, and the quality of the gamma ray source image is greatly improved. be able to.

Furthermore, the spatial resolution is a continuous graph directly using the measurement result of the resolution, or a step function discontinuous graph in which the high resolution region 503 of the gamma ray detector 205 that satisfies a certain level of resolution is zero. It is possible to search for recommended installation positions based on accurate spatial resolution or spatial resolution defined by a simpler function.

<Others>
The present invention is not limited to the above embodiments, and various modifications and applications are possible. The above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the described configurations.

101 ... proton beam irradiation device (particle beam irradiation device)
DESCRIPTION OF SYMBOLS 102... Proton beam generator 103... Proton beam transport apparatus 104... Rotary irradiation apparatus 105... Ion source 106... Pre-stage accelerator 107... Synchrotron 108... Departure deflector 109... Irradiation field forming apparatus 201... Patient 202... Target area 203... Spot 204... Scanning electromagnet 205... Gamma ray detector 206... Collimator 207... Line sensor 208, 208A... Driving device (position adjusting unit)
209 Signal processing device 210 Treatment planning device 211 Display device 301 Procedure for inputting a region on the CT image 302 Procedure for arranging calculation points and spots inside and outside the region 303 Calculation of beam energy and range for each spot Procedure 304 for calculating a dose matrix Procedure 305 Procedure for setting an objective function for searching prescription dose for each spot Procedure 306 Procedure for searching prescription dose for each spot by iterative calculation 307 Procedure for searching for the installation position of the gamma ray detector Procedure 308 for setting the objective function for : Procedure 401 for searching the installation position of the gamma ray detector by iterative calculation OAR area 402 Calculation point 403 Scanning point 501 Indicating the spatial resolution of the gamma ray detector for each angle φ Graph 502: Field of view of gamma ray detector (gamma ray detectable area)
503...High resolution area of gamma ray detector 504...Outside field of view of gamma ray detector (gamma ray undetectable area)
505... Graph discretizing the spatial resolution of the gamma ray detector for each angle φ with a threshold value 601... Left-right asymmetric collimator 602... High resolution area of gamma ray detector 603... High dose spot 604... Leaf driving device 605... Metal leaf 606 ... multi-leaf collimator 701 ... operation screen 702 ... high-resolution area 703 ... high-dose spot

Claims (12)

a particle beam irradiation device that irradiates a target with a particle beam;
a treatment planning device that creates an irradiation plan for the particle beam by the particle beam irradiation device;
a gamma ray detector that detects gamma rays generated along with the irradiation of the particle beam,
A particle beam therapy system, wherein the treatment planning device obtains a recommended installation position of the gamma ray detector based on a spatial resolution of the gamma ray detector for each angle set in advance. In the particle beam therapy system according to claim 1,
A particle beam therapy system, wherein the gamma ray detector has a position adjuster capable of moving its installation position. In the particle beam therapy system according to claim 1,
A particle beam therapy system, wherein the treatment planning device extracts spots where the irradiation dose exceeds a predetermined threshold. In the particle beam therapy system according to claim 3,
A particle beam therapy system, wherein the treatment planning apparatus searches for the recommended installation position so that the three-dimensional position of the spot is included in an area where the spatial resolution of the gamma ray detector is equal to or greater than a predetermined standard. In the particle beam therapy system according to claim 3,
A particle beam therapy system, further comprising a display device for displaying a three-dimensional position of the spot and an area where the spatial resolution of the gamma ray detector is equal to or higher than a predetermined standard. In the particle beam therapy system according to claim 2,
A particle beam therapy system, wherein the position adjustment unit moves an installation position of the gamma ray detector during irradiation of the particle beam. In the particle beam therapy system according to claim 1,
A particle beam therapy system, wherein the spatial resolution is a continuous graph directly using the measurement result of the resolution, or a discontinuous step function graph in which an area satisfying a resolution of a certain level or more is set to zero. A treatment planning device for creating a particle beam irradiation plan by a particle beam irradiation device that irradiates a target with a particle beam,
A treatment planning apparatus, wherein a recommended installation position of said gamma ray detector is obtained based on the spatial resolution of said gamma ray detector for detecting gamma rays generated in association with said particle beam irradiation for each angle set in advance. 9. A treatment planning device according to claim 8, wherein
A treatment planning apparatus, wherein the treatment planning apparatus extracts a spot where the irradiation dose exceeds a predetermined threshold. 10. The treatment planning device of claim 9, wherein
The treatment planning apparatus searches for the recommended installation position so that the three-dimensional position of the spot is included in a region height where the spatial resolution of the gamma ray detector is equal to or higher than a predetermined standard. . 9. A treatment planning device according to claim 8, wherein
A treatment planning apparatus, wherein the spatial resolution is a continuous graph directly using the measurement result of the resolution, or a discontinuous step function graph in which an area satisfying a resolution of a certain level or more is set to zero. 9. A treatment planning device according to claim 8, wherein
The treatment planning device outputs a signal to a position adjustment unit capable of moving the installation position of the gamma ray detector, or a display device that displays a screen for inputting the installation position of the gamma ray detector. Device.

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