JP5590663B2 - Charged particle dose simulation apparatus, charged particle beam irradiation apparatus, charged particle dose simulation method, and charged particle beam irradiation method - Google Patents

Description

  The present invention relates to a charged particle dose simulation apparatus, a charged particle beam irradiation apparatus, and a charged particle dose for simulating a dose distribution of a charged particle beam in an irradiated body when the irradiated body is irradiated with a charged particle beam such as a proton beam. The present invention relates to a simulation method and a charged particle beam irradiation method.

  2. Description of the Related Art A proton beam therapy apparatus that treats a tumor by irradiating a charged particle beam such as a proton beam is known. In the treatment of such a tumor, it is necessary to formulate an irradiation plan such as an absolute dose, a dose distribution, and an irradiation position according to the shape and position of the tumor, and perform irradiation with a charged particle beam with high accuracy according to this irradiation plan. When making an irradiation plan, the dose distribution is calculated in advance by inputting the proton beam irradiation conditions into a simulation device installed in a proton beam therapy system, and the proton beam is accurately applied to the tumor based on this dose distribution. A simulation of whether or not the irradiation is performed As a method for determining the dose distribution, for example, methods called Monte Carlo Simulation and Pencil Beam Algorithm (PBA) are known (see Non-Patent Documents 1 to 4).

Harald Paganetti, Hongyu Jiang, Katia Parodi, Roelf Slopsema and Martijn Engelsman, IOP Publishing, Physics in Medicine and Biology, 53 (2008) 4825-4853. Department of Radiation Oncology, Massachusetts General Hospital & Harvard Medical School, Boston, MA 02114, USA, IOP Publishing, Physics in Medicine and Biology, 54 (2009) 4399-4421. Nobuyuki Kanematsu, Masataka Komori, Shunsuke Yonai1 and AzusaIshizaki, IOP Publishing, Physics in Medicine and Biology, 54 (2009) 2015-2027. Linda Hongyz, Michael Goiteiny, Marta Bucciolinix, Robert Comiskeyy, Bernard Gottschalkk, Skip Rosenthaly, Chris Seragoy and Marcia Urie, Phys. Med. Biol. 41 (1996) 1305-1330.

  However, the above-mentioned Monte Carlo Simulation has a problem in that the dose distribution is determined by statistical processing, so that the accuracy is high, but the calculation processing is heavy, and it takes several days, so it is not practical. It was. On the other hand, the PBA has a problem that the accuracy is apt to decrease compared to Monte Carlo Simulation, and it is difficult to ensure the desired accuracy.

  An object of the present invention is to solve the above-described problems, and a charged particle dose simulation apparatus capable of quickly calculating a dose distribution of a charged particle beam by reducing a burden of calculation processing while suppressing a decrease in accuracy. It is an object of the present invention to provide a charged particle beam irradiation apparatus, a charged particle dose simulation method, and a charged particle beam irradiation method.

The present invention assumes a case where a charged particle beam is irradiated on an irradiated object, assumes the charged particle beam as a virtual shape having a conical spread, and determines the dose of the charged particle beam in the irradiated body. In an apparatus for simulating a dose distribution of a charged particle beam in an irradiated body using a distribution kernel, an input unit that receives input of simulation data including material information of the irradiated body and irradiation information of the charged particle beam, and an input unit Calculating means for calculating the dose distribution of the charged particle beam in the irradiated body based on the simulation data and the dose distribution kernel, and the calculation means spread to a predetermined range in the middle of the traveling direction of the charged particle beam. subdividing a plurality of charged particle beams, a and subdivided position while assuming a plurality of virtual shapes having conical spread as a starting point, input Characterized in that to determine the dose distribution of the charged particle beam at the irradiated body based on the simulation data received in means and a plurality of virtual shape of the charged particle beam.

  If the object to be irradiated is composed only of a certain substance, the conventional PBA can be expected to have relatively high accuracy, but the actual object to be irradiated is composed of various substances intricately. With PBA, it is difficult to accurately determine the dose distribution of charged particle beams. However, according to the present invention, the conical virtual shape assumed as the charged particle beam is appropriately subdivided and assumed as a plurality of virtual shapes, so that the subdivided virtual shapes can be complicatedly arranged. Therefore, it is possible to determine the dose distribution of the charged particle beam while improving the accuracy of the dose distribution. Furthermore, in the present invention, since the charged particle beam is assumed to be a conical virtual shape and the dose distribution of the charged particle beam is obtained, the calculation processing is compared with Monte Carlo Simulation in which the dose distribution is derived by statistical calculation processing. The burden can be reduced. As a result, it is possible to determine the dose distribution at an early stage by reducing the burden of the arithmetic processing while suppressing the decrease in accuracy.

  Furthermore, the position where the charged particle beam is subdivided is preferably a position immediately before the charged particle beam enters the irradiated body. Immediately before entering the irradiated body, the charged particle beam can be subdivided into a plurality of virtual shapes corresponding to the internal structure, so that it becomes easier to further improve the accuracy in determining the dose distribution of the charged particle beam.

  Furthermore, it is preferable to further include output means for notifying the dose distribution determined by the calculation means. By notifying the output means of text information, image information, or voice information that can be viewed by the operator, the operator can easily grasp the dose distribution of the charged particle dose as the simulation result.

  Further, it is preferable that the output means informs the dose distribution by making it an isodose line or an isodose surface. It is possible to easily grasp the magnitude of the dose by reporting with an isodose line or isodose surface.

  Moreover, the charged particle beam irradiation apparatus according to the present invention includes the above-described simulation apparatus. According to the present invention, it is possible to irradiate a charged particle beam based on the dose distribution of the charged particle beam determined at an early stage by the simulation apparatus.

Further, the present invention assumes that the charged particle beam is irradiated onto the irradiated object, assumes the charged particle beam as a virtual shape having a conical expansion, and spreads the charged particle beam in the irradiated object. In the method of simulating the dose distribution of the charged particle beam in the irradiated body using the derived dose distribution kernel, the irradiation object information acquiring step for acquiring the substance information of the irradiated body and the irradiation information of the charged particle beam are determined. Based on the irradiation information setting process, the irradiation information determined in the irradiation information setting process, and the dose distribution kernel, a plurality of charged particle beams that have spread to a predetermined range in the middle of the traveling direction of the charged particle beam are subdivided and subdivided. Assuming a plurality of virtual shapes having a cone-shaped spread starting from the converted position, and based on the substance information acquired in the irradiated object information acquisition step and the plurality of virtual shapes of the charged particle beam Characterized in that it comprises a and a simulation step of determining the dose distribution of the charged particle beam irradiation body. According to the invention, it is possible to determine the dose distribution of the charged particle beam at an early stage while reducing the burden of calculation processing while suppressing the decrease in accuracy.

  According to the present invention, it is possible to determine the dose distribution at an early stage by reducing the burden of calculation processing while suppressing the decrease in accuracy.

It is explanatory drawing of the proton beam therapy apparatus carrying the simulation apparatus which concerns on embodiment of this invention. It is explanatory drawing which shows the effect of a proton beam treatment with a graph. It is explanatory drawing which shows a dose distribution calculation algorithm typically. It is explanatory drawing which shows the concept of a DMS-PBA method typically. It is explanatory drawing about the subdivision of the beamlet in a DMS-PBA method. About DMS-PBA method, the difference with the conventional PBA method is shown typically, (a) is explanatory drawing which shows PBA typically, (b) is explanatory drawing which shows DMS-PBA typically. . It is a figure which shows the difference of dose distribution of DMS-PBA method and the conventional PBA method, (a) is a figure which shows both differences by making an iso-dose line, (b) is both figures in the depth of 0 mm It is a graph which shows dose distribution, (c) is a graph which shows dose distribution in depth 115mm. It is a figure which compares and shows a dose distribution using a clinical image (sagittal cross section), (a) is an example of the image which shows the dose distribution calculated | required by PBA method as an isodose line, (b) is DMS. It is an example of the image which shows the dose distribution calculated | required by -PBA method by making it an iso-dose line. It is a figure which compares and shows a dose distribution using a clinical image (axial cross section), (a) is an example of the image which shows the dose distribution calculated | required by PBA method as an isodose line, (b) is DMS. It is an example of the image which shows the dose distribution calculated | required by -PBA method by making it an iso-dose line. It is a flowchart which shows the schematic procedure of a proton beam treatment. It is a flowchart which shows the operation | movement procedure of dose distribution simulation. 6 is a graph showing a simulation result of Experimental Example 1. 10 is a graph showing a simulation result of Experimental Example 2. 10 is a graph showing a simulation result of Experimental Example 3.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

  When treating a tumor (cancerous lesion) by irradiating a proton beam (charged particle beam), an irradiation plan such as absolute dose, dose distribution, irradiation position, etc. is prepared according to the shape and position of the tumor. Proton irradiation is performed according to the plan. As shown in FIG. 1, a proton beam treatment apparatus (charged particle beam irradiation apparatus) 1 includes a simulation apparatus (charged particle dose simulation apparatus) 3 for creating an irradiation plan, and a subject such as a patient according to the simulation result. And an irradiation device 5 for irradiating the irradiation body X with the proton beam B.

  The irradiation device 5 adjusts the reach of the proton beam B according to the shape of the irradiation unit 51 that irradiates the proton beam B toward the irradiation object X, the collimator 52 that adjusts the irradiation range of the proton beam B, and the cancer lesion. A bolus 53 and the like are provided. The material of the bolus 53 is polyethylene or the like. Actual irradiation by the irradiation device 5 is performed based on an input operation of the irradiation device 5 by an operator.

  As shown in FIG. 2, in the case of a photon beam, the damage to the cell is the largest immediately after entering the patient's skin (body surface Xa) (before reaching the cancer lesion) (the therapeutic effect is the greatest). It reaches a peak and gradually decreases. On the other hand, in the case of heavy charged particles such as proton beams, a maximum portion called a Bragg peak appears at a predetermined depth. Therefore, by appropriately adjusting the shape of the bolus 53 through which the proton beam B passes and adjusting the depth at which the Bragg peak appears, the damage to the normal tissue is suppressed and the tumor tissue (cancer lesion) is obtained. Damage can be increased.

  The simulation apparatus 3 (see FIG. 1) includes a central processing unit. The central processing unit includes a CPU, a RAM, a ROM, and the like as hardware configurations, and includes an input unit (input means) 31 and a calculation unit (functional units). A calculation unit) 33 and an output unit (output unit) 35.

  The input unit 31 is an operation device such as a touch panel, a keyboard, or a mouse, and accepts data input based on an operation of the operator. In addition, the input unit 31 receives, for example, image data including a cancer lesion imaged by therapeutic CT (Computed Tomography), data related to an irradiation region, and irradiation parameter data. The irradiation parameter data is data such as an irradiation direction and a patient bed angle, for example. In the present embodiment, the image data (therapeutic CT image data) acquired by the therapeutic CT corresponds to the substance information of the irradiation object X, and the irradiation parameter data and the irradiation parameter data related to the irradiation region are the charged particle beam irradiation information. Equivalent to. Hereinafter, these are collectively referred to as simulation data.

  The computing unit 33 assumes that the irradiated body X is irradiated with the proton beam B, assumes the proton beam B as a virtual shape having a cone-shaped (pencil beam shape), and the inside of the irradiated body X. The function of simulating the dose distribution of the proton beam B inside the irradiated body X using the dose distribution kernel for deriving the spread of the proton beam B at Here, the conventional method for determining the dose distribution is, for example, the Pencil-beam method (PBA method). However, in this embodiment, the Delta-function Multi Segmented PBA method (DMS-PBA method) is a further evolution of the PBA method. ) To calculate the dose distribution. Hereinafter, after the PBA method is outlined, the DMS-PBA method will be described in detail.

The PBA method is a method in which the proton beam B is regarded as a pencil beam shape, and calculation is performed using a dose distribution kernel that takes into account the spread of the proton beam B in the material due to multiple Coulomb scattering. Specifically, as shown in FIG. 3, the dose distribution in the depth direction from the irradiation point is obtained from actual measurements, and further, protons are considered in consideration of the beam spread obtained from a predetermined calculation (approximation by Gaussian). The dose distribution at a predetermined point in the traveling direction of the line B is derived. For example, it calculated as a spread sigma ₁ spread at the point Z ₁ by approximation by Gaussian, determine the spread at the point Z ₂ as spread sigma ₂ by approximation by Gaussian.

  Although the conventional PBA method is advantageous in that the dose distribution of the proton beam B can be derived in a calculation time of about several minutes, it is calculated based on the presence or absence of a heterogeneous substance (for example, a patient's bone) within the irradiation range. Since it is also assumed that the accuracy is lowered, there is room for improvement.

  The DMS-PBA method is a technique capable of improving accuracy while taking advantage of the reduction in calculation time, which is an advantage of the PBA method. There are at least two characteristic items of the DMS-PBA method, and the first is dose distribution calculation in consideration of scattering from the bolus 53 by the surface map analysis on the body surface Xa of the irradiated object (such as a patient) X. The second is a high-resolution dose distribution calculation by the beamlet Ba emitted from the body surface Xa.

  These features of the DMS-PBA method will be conceptually described with reference to FIGS. FIG. 4 is an explanatory diagram schematically showing the concept of the DMS-PBA method, and FIG. 5 is an explanatory diagram of beam segmentation in the DMS-PBA method. As shown in FIG. 4, the proton beam (beam) B input to the bolus 53 or the like travels to reach the body surface Xa while spreading due to side multiple Coulomb scattering. Here, the lateral emittance of the beam B to the body surface Xa is calculated. This calculation is similar to conventional PBA.

  Next, a surface map on the body surface Xa is created. The surface map is obtained by mapping the intensity (weight) of the combined beam B, the residual track, and the number of beams B having different residual tracks in each calculation grid on the body surface Xa. For example, when the bolus 53 is assumed to be a block body having an L-shaped cross section, a residual track on the body surface Xa of the beam B that has passed through the thick part is a residual scattering on the body surface Xa of the beam B that has passed through the thin part. Smaller than that. In addition, the dose (intensity) in the region where the beam B that has passed through the thick portion and the beam B that has passed through the thin portion overlap on the body surface Xa is larger than the region that does not overlap. A Surface Map on the body surface Xa is created in consideration of these factors. The above is the dose distribution calculation considering the scattering from the bolus 53 by the SurfaceMap analysis on the body surface Xa of the irradiated object X, and is the first feature of the DMS-PBA method. The residual track is a range corresponding to the kinetic energy of the proton beam.

  Next, the surface map is subdivided, and initial conditions of a plurality of proton beams (hereinafter referred to as “beamlets”) Ba that are virtually irradiated with each subdivided element (hereinafter referred to as “voxel”) as a starting point are defined as follows. Find out. For example, the dose of the beamlet Ba can be obtained by segmenting a dose distribution assumed to be incident on the body surface Xa into a delta function shape (see FIG. 5A). Also, the size of the beamlet Ba at the voxel is assumed to be extremely small.

  Next, the dose distribution calculation by the beamlet Ba irradiated into the body from the body surface Xa is performed. The dose distribution calculation by the beamlet Ba will be conceptually described with reference to FIG. FIG. 5A shows a lateral profile of the dose on the body surface Xa. As shown in FIG. 5A, the dose of the beamlet Ba is obtained by the above-described segmentation of the dose distribution. Assuming that the beamlet (segment) Ba is irradiated into the body, each segment expands as it goes deeper (see FIG. 5B). The dose distribution at an arbitrary depth in the body is derived by overlapping each segment (see FIG. 5C). FIG. 5C shows a lateral profile of the dose in the body.

  By integrating all the beamlets Ba, it becomes possible to determine the dose distribution in the body. The above is the high-resolution dose distribution calculation by the beamlet Ba emitted from the body surface Xa as the starting point, and is the second feature of the DMS-PBA method. The specific calculation of the beam size by the DMS-PBA method is based on the following equation (1).

Next, the difference between the PBA method and the DMS-PBA method will be described with reference to FIGS. FIG. 6A is an explanatory diagram schematically showing PBA, and FIG. 6B is an explanatory diagram schematically showing DMS-PBA. As shown in FIG. 6, in the PBA method, the beam B that has reached the body surface Xa is the initial condition of the beam B that is irradiated into the body as it is. That is, in the PBA method, it is assumed that the beam B that has passed through the bolus 53 and has reached the body surface Xa as the beam sizes σ ₁ and σ ₂ and the residual tracks R ₁ and R ₂ is irradiated into the body under the same conditions. The On the other hand, in the DMS-PBA method, the beam B input to the body surface Xa as the beam sizes σ ₁ and σ ₂ and the residual tracks R ₁ and R ₂ is subdivided by the body surface Xa, so that the beam size σ It is assumed that ₀ is subdivided into a plurality of beamlets Ba that are extremely smaller than σ ₁ and σ ₂ , and each beamlet Ba is irradiated into the body.

  FIG. 7 shows the result of calculating the dose distribution using the DMS-PBA method and the PBA method on the assumption that the beam B is irradiated to the model of the irradiated object X in which the bone equivalent material is arranged in the water equivalent material. (A) is a diagram showing the difference between the two in an isodose line, (b) is a side profile of both at a depth of 0 mm, and (c) is a side profile of both at a depth of 115 mm. It is a profile.

  As shown in FIG. 7B, when the depth d is “0 mm”, that is, the size and the dose of the beam B on the body surface Xa are the same. On the other hand, as shown in FIG. 7C, when the depth d is “115 mm”, there is a large difference between the dose distribution obtained by the PBA method and the dose distribution obtained by the DMS-PBA method. Has occurred. The difference is that the dose distribution is calculated without considering the presence of bone equivalent in the PBA method, whereas the dose distribution is calculated in consideration of the presence of bone equivalent in the DMS-PBA method. Due to being.

  The output unit 35 is an output device such as a monitor or a speaker, and outputs (notifies) the simulation result in the arithmetic unit as an image that can be visually recognized by an operator or the like, or outputs (notifies) it as sound data. In other words, the output unit 35 receives dose distribution data based on the calculation result in the DMS-PBA method from the calculation unit 33, and based on the received dose distribution data, for example, the treatment CT image is converted into an isodose line or isodose surface. The dose distribution images thus synthesized are combined to generate and display (notify) image data (image information) that can be viewed by an operator or the like.

  Here, the image data displayed from the output unit 35 will be specifically described with reference to FIGS. 8 and 9. 8 and 9 show an example of an image in which the dose distribution is made into an isodose line, and the output unit 35 displays an image as shown in FIG. 8B or FIG. 9B, for example. To do. 8A and 9A are images showing the dose distribution derived by the PBA method, and FIGS. 8B and 9B are derived by the DMS-PBA method. It is an image which shows dose distribution.

  When comparing the dose distribution image obtained by the PBA method (FIG. 8A) and the dose distribution image obtained by the DMS-PBA method (FIG. 8B), the dose distribution image obtained by the DMS-PBA method is obtained by the PBA method. It can be inferred that the dose distribution is accurately determined corresponding to the inhomogeneous substance because each of the isolines is intricately complicated in comparison with the dose distribution image of the above. Similarly, as shown in FIG. 9, the dose distribution image by the DMS-PBA method (FIG. 9B) is equal to the dose distribution image by the PBA method (FIG. 9A). It is inferred that the dose line has a complicated and complicated shape, and that the dose distribution has been accurately calculated for heterogeneous substances.

  Next, an outline of an actual proton beam treatment method will be described, and a dose distribution simulation method and a proton beam irradiation method (charged particle beam irradiation method) performed therein will be described with reference to FIGS. 10 and 11. FIG. 10 is a flowchart showing a schematic procedure of proton beam treatment, and is a flowchart showing an operation procedure of dose distribution simulation.

  As shown in FIG. 10, first, a diagnosis by an operator such as a doctor is performed (step S1), and then an image of the vicinity of the cancer lesion is acquired by the therapeutic CT (step S2). Next, an irradiation area is determined (step S3) and an irradiation parameter is determined (step S4). The process in which the CT image for treatment in step S2 is acquired corresponds to the irradiation object X information acquisition process in which the substance information of the irradiation object X is acquired, and the irradiation region determination and the irradiation parameter determination in steps S3 and S4 are performed. The step of performing is equivalent to an irradiation information setting step of determining irradiation information of a charged particle beam.

  Next, processing related to dose distribution simulation is executed in the simulation apparatus 3 (step S5), and a dose distribution image as a simulation result is displayed (notified) from the output unit 35. Step S5 corresponds to a simulation process.

  The operator confirms the dose distribution image displayed on the output unit 35. For example, the operator determines whether the Bragg peak of the proton beam B has accurately reached the target region (cancer lesion) and whether it has not reached the target region (simulation result) Determination). Here, if the operator determines that the Bragg peak of the proton beam B has not reached the cancer lesion accurately, the process returns to step S4. The operator repeatedly executes the irradiation parameter determination (step S4) and the dose distribution simulation (step S5) until it is determined that the Bragg peak of the proton beam B accurately reaches the cancer lesion, and accurately reaches the cancer lesion. If it is determined, the irradiation apparatus 5 is operated to perform actual proton beam irradiation (step S7). Step S7 corresponds to a proton beam irradiation method (charged particle beam irradiation method) for irradiating the proton beam B.

  Next, a dose distribution simulation executed by the simulation apparatus 3 will be described. This dose distribution simulation assumes that the irradiated body X is irradiated with the proton beam B, assumes the proton beam B as a virtual shape having a beam pencil shape (conical shape), and the inside of the irradiated body X. This is a method for simulating the dose distribution of the proton beam B in the irradiated body X using the dose distribution kernel for deriving the spread of the proton beam B at the same time, and is executed by the DMS-PBA method which is a further evolution of the above-mentioned PBA method. Is done.

  The simulation apparatus 3 executes processing related to dose distribution simulation by receiving simulation data. The input unit 31 of the simulation apparatus 3 accepts input of simulation data including therapeutic CT image data, irradiation region data, and irradiation parameter data (step S11).

  When the simulation data is received by the input unit 31, the calculation unit 33 assumes that the proton beam B is irradiated to the irradiated object X, and irradiates irradiation region data and irradiation parameter data (substance information) and a dose distribution kernel. Based on this, it is assumed that the proton beam B is a beam having a beam pencil shape (conical shape) (virtual shape) and that such a beam has been emitted (step S12).

  Next, the calculation unit 33 calculates the lateral emittance of the beam to the body surface Xa using a dose distribution kernel that derives the spread of the beam in the irradiated object X. Further, the calculation unit 33 assumes that the beam that has spread to a predetermined range in the middle of the beam traveling direction (body surface) has reached the body surface Xa, and creates a Surface Map on the body surface Xa (step S13). .

  Next, the calculation unit 33 subdivides the surface map on the body surface Xa and assumes a plurality of voxels in order to subdivide the beam on the body surface Xa (step S14). Further, the calculation unit 33 assumes a plurality of beamlets (virtual shapes) having a pencil beam shape (conical shape) from a plurality of voxels as a starting point, and assumes that a subdivided beamlet is fired ( Step S15). Further, the calculation unit 33 calculates the dose distribution of the proton beam B in the irradiation object X based on the therapeutic CT image data and the plurality of beamlets (step S16). This completes the dose distribution simulation.

  Next, effects of the simulation apparatus 3 and the dose distribution simulation method according to the present embodiment will be described.

  For example, when the irradiated object X is composed of only a certain substance, relatively high accuracy can be expected even with the conventional PBA method. However, since the actual irradiated object X such as a patient is composed of various substances intricately, it is difficult to accurately determine the proton beam (charged particle beam) dose distribution by the conventional PBA method. However, according to the simulation apparatus 3 and the dose distribution simulation method according to the present embodiment, a virtual shape of the pencil beam shape (conical shape) assumed as the proton beam B is appropriately subdivided, and a plurality of beamlets (virtual shape) are obtained. Therefore, it is possible to determine the dose distribution of the proton beam B while corresponding to the complicated configuration of each of the subdivided beamlets, which is effective in improving the accuracy of the dose distribution.

  Further, in the simulation apparatus 3 and the dose distribution simulation method according to the present embodiment, the dose distribution of the proton beam B is obtained after assuming the proton beam (charged particle beam) B as a virtual shape of a pencil beam shape (cone shape). Compared to Monte Carlo Simulation, which derives the dose distribution by statistical calculation processing, the calculation processing load can be reduced. As a result, it is possible to determine the dose distribution at an early stage by reducing the burden of the arithmetic processing while suppressing the decrease in accuracy.

  Furthermore, in the present embodiment, the position where the proton beam B is subdivided is the position (body surface Xa) immediately before the proton beam B enters the irradiated body X, and thus immediately before entering the irradiated body X. Since the proton beam B can be subdivided into a plurality of beamlets (virtual shapes) corresponding to the internal structure, high accuracy in determining the dose distribution of the proton beam B can be expected.

  Furthermore, in this embodiment, the output part 35 which alert | reports the dose distribution calculated | required by the calculating part 33 is provided, The character information, image information, audio | voice information, etc. which an operator can view are alert | reported from the output part 35. be able to. Therefore, the operator can easily grasp the dose distribution of the proton beam B as a simulation result.

  Furthermore, since the output unit 35 notifies the operator by outputting an image in which the dose distribution is made into an isodose line or isodose surface, the operator can easily grasp the magnitude of the dose.

  Next, experimental results for demonstrating the superiority of the present embodiment will be described with reference to FIG. 12, FIG. 13, and FIG. 12, 13, and 14 show the verification results using the experimental geometry, and each figure (a) schematically shows the traveling direction of the proton beam B with respect to the phantom that is the irradiated object model. Each figure (b) is a graph which shows the dose distribution profile of the depth direction of the to-be-irradiated body X, and each figure (c) is a graph which shows the side dose distribution profile in predetermined depth.

  In Experimental Example 1, Experimental Example 2, and Experimental Example 3, a bolus 61 having an L-shaped cross section, a polystyrene phantom 62 that reproduces the boundary between air and soft tissue found in the paranasal sinuses, and a phantom 62 below Experimental apparatus (FIGS. 12 (a) and 13 (a), FIG. 12 (a), FIG. 12 (a), and FIG. 13 (a), including a two-dimensional dosimeter (2D-ARRAY)) 63 and a proton patient treatment patient bed 64 that supports the phantom 62 and 2D-ARRAY. A verification experiment is performed using FIG. Further, in each of Experimental Examples 1, 2, and 3, assuming that the beam B passes through the phantom 62, dose distribution profiles are derived by the PBA method and the DMS-PBA method.

  As shown in FIG. 12B, FIG. 13B, and FIG. 14B, the simulation results (deep direction dose distribution profiles) of Experimental Example 1, Experimental Example 2, and Experimental Example 3 show the Bragg peak. The dose derived by the DMS-PBA method is smaller than the dose derived by the PBA method. Moreover, FIG.12 (c) has shown the side dose distribution profile in the Bragg peak depth (depth d is 123 mm) of Experimental example 1, and the value (2D-ARRAY63 of said experimental apparatus measured ( In Measured), hot spots are observed. FIG. 13C shows a side dose distribution profile at the Bragg peak depth (depth d is 142 mm) in Experimental Example 2, and a cold spot is observed in the measured value (Measured). . FIG. 14C shows a side dose distribution profile at the Bragg peak depth (depth d is 162 mm) in Experimental Example 3, and a hot spot is observed in the measured value (Measured). . A hot spot is a spot with a high dose, and a cold spot is a spot with a low dose.

Next, the content inferred from the verification results of Experimental Example 1, Experimental Example 2, and Experimental Example 3 will be described.
(1) In each of the experimental examples 1, 2, and 3, the appearance of a hot spot or cold spot at the Bragg peak depth can be considered to be due to the influence of the proton detour effect.
(2) In the PBA method, the accuracy drop of about 12% at the maximum was observed in the hot spot or cold spot of each Bragg peak. This is considered to be due to the fact that the expanded pencil beam shape considers only the lateral spread along the central axis.
(3) The DMS-PBA method can take into account the influence of inhomogeneous substances in the body by the segmentation of the beam B on the body surface. In consideration of the geometric misalignment, it was confirmed that there was a match with an accuracy of 3%.

  Moreover, the following verification results can be obtained from the results shown in Table 1.

(1) The larger the irradiation field area, the longer the calculation time (time for calculation processing) in both the PBA method and the DMS-PBA method.
(2) In the PBA method and the DMS-PBA method, the ratio to the calculation time decreases as the ratio of the total volume calculated by the beam decreases.
(3) When the irradiation field area is 100 × 100 mm ² , the calculation time of the DMS-PBA method is shorter than the calculation time of the PBA method.

From the above verification results, compared with the PBA method currently implemented in clinical practice, the DMS-PBA method is equivalent to the accuracy of the dose distribution calculation result (simulation result) in the inhomogeneous region in the phantom 62 in the same calculation time. Was confirmed to be excellent.
Moreover, although it was initial verification using a phantom, the possibility that the DMS-PBA method was useful in clinical use was confirmed.

  The present invention has been described above by taking the simulation apparatus and the dose distribution simulation method according to the embodiments as examples. However, the present invention is not limited to the above-described embodiments. For example, the mode notified from the output unit 35 is not limited to predetermined image data, and may be audio data. The simulation apparatus is not limited to the one provided in the proton beam therapy apparatus, and may be provided separately from the proton beam therapy apparatus.

  DESCRIPTION OF SYMBOLS 3 ... Simulation apparatus, 31 ... Input part (input means), 33 ... Calculation part (calculation means), 35 ... Output part (output means), B ... Proton beam, beam (charged particle beam), X ... Irradiation body.

Claims (6)

Assuming that a charged particle beam is irradiated on an irradiated object, assuming that the charged particle beam is a virtual shape having a conical spread, and a dose for deriving the spread of the charged particle beam in the irradiated body In an apparatus for simulating a dose distribution of a charged particle beam in the irradiated body using a distribution kernel,
Input means for receiving input of simulation data including material information of the irradiated object and irradiation information of the charged particle beam;
Calculating means for calculating a dose distribution of the charged particle beam in the irradiated body based on the simulation data received by the input means and the dose distribution kernel;
The arithmetic means subdivides a plurality of the charged particle beams that have spread to a predetermined range in the middle of the traveling direction of the charged particle beam, and a plurality of virtual shapes having a cone-shaped spread starting from the subdivided position And calculating a dose distribution of the charged particle beam in the irradiated body based on the simulation data received by the input means and a plurality of virtual shapes of the charged particle beam. apparatus.   The simulation apparatus according to claim 1, wherein the position where the charged particle beam is subdivided is a position immediately before the charged particle beam enters the irradiated body.   The simulation apparatus according to claim 1, further comprising output means for notifying the dose distribution determined by the calculation means.   4. The simulation apparatus according to claim 3, wherein the output means notifies the dose distribution by forming an isodose line or an equivalent dose surface.   A charged particle beam irradiation apparatus comprising the simulation apparatus according to claim 1. Assuming that a charged particle beam is irradiated on an irradiated object, assuming that the charged particle beam is a virtual shape having a conical spread, and a dose for deriving the spread of the charged particle beam in the irradiated body In a method of simulating a dose distribution of charged particle beams in the irradiated body using a distribution kernel,
An object information acquisition step of acquiring material information of the object to be irradiated;
An irradiation information setting step for determining irradiation information of the charged particle beam;
Based on the irradiation information determined in the irradiation information setting step and the dose distribution kernel, a plurality of the charged particle beams that have spread to a predetermined range in the middle of the traveling direction of the charged particle beam are subdivided and subdivided Assuming a plurality of virtual shapes having a cone-shaped spread starting from the position that has been made, and based on the substance information acquired in the irradiated object information acquisition step and the plurality of virtual shapes of the charged particle beam A simulation method for determining a dose distribution of a charged particle beam in an irradiated body, and a simulation method comprising: