JP2014023741A - Intensity modulation radiotherapy planning device, radiation beam coefficient computing method for the same, intensity modulation radiotherapy planning program, computer readable record medium, and recorded device - Google Patents

Abstract

[PROBLEMS] To reduce the calculation time and obtain a solution as a settable value while maintaining the positive value of the solution and the upper bound, and the optimization calculation having the convergence to the minimum solution. Realize an intensity-modulated radiation therapy plan.
A tomographic image acquisition unit for acquiring a tomographic image of an object to be subjected to radiation therapy, a display unit for displaying a tomographic image acquired by the tomographic image acquisition unit, and a tomographic image displayed on the display unit. The radiation volume designation means 34 for designating the target volume PTV to be irradiated and the area OAR to avoid radiation irradiation, the number of radiation beamlets irradiated by the intensity-modulated radiation irradiation apparatus 50, the radiation beamlet coefficient, A condition specifying means that specifies at least one of the dose transfer coefficient matrix, the number of areas, and the target irradiation dose, and a minimum solution of the target function using the following nonlinear ordinary differential equation solution according to the conditions specified by the condition specifying means Reverse treatment plan calculation means 70 for obtaining
[Selection] Figure 1

Description

  The present invention relates to an intensity-modulated radiation therapy planning apparatus, a radiation beam coefficient calculation method for the intensity-modulated radiation irradiation apparatus, an intensity-modulated radiation therapy planning program, a computer-readable recording medium, and a recorded device.

  In conventional radiotherapy by external irradiation, radiation RB is uniformly irradiated from a radiation source RS arranged around the treatment target as shown in FIG. 6, so that only the target tumor TM is irradiated with a high dose. Therefore, the important tissue OAR located around the tumor TM is also irradiated with a high dose. For this reason, it has been difficult to achieve both high-dose irradiation and important tissue preservation to the tumor. Therefore, in recent years, intensity modulated radiation therapy (IMRT) that enables intensity modulation of radiation as shown in FIG. 7 has been used. In this treatment method, a target volume (PTV: Planning Target Volume) is irradiated with a dose sufficient to treat a tumor such as a cancer cell, using a mechanism capable of freely controlling the angle and intensity of the radiation beam. In FIG. 7, the linac gantry (radiation output unit) can be rotated to irradiate radiation from any direction, and the radiation beam intensity irradiated from the gantry can be modulated by an MLC (Multi-Leaf Collimator). . According to this treatment method, the dose irradiated to the normal tissue can be suppressed to a low value, so that both high-dose irradiation to the tumor and preservation of important tissue can be achieved.

  However, in order to preserve such important tissues during IMRT, the radiation dose should be reduced in advance so that the dose to the surrounding risk organ (OAR) is minimized when the radiation beam is irradiated. It is important to develop an intensity-modulated radiation treatment plan that determines the irradiation intensity, irradiation direction, and the like. For this reason, a radiation treatment planning apparatus (RTPS) for making a treatment plan has been developed, and various radiation treatment planning methods have been proposed for such intensity-modulated radiation treatment plans (Patent Documents 1 to 3). 3).

  Intensity-modulated radiation therapy is realized by a computer-based inverse treatment plan (inverse plan) and a computer-controlled special irradiation method that enables irradiation according to the calculation result. The inverse plan is a method for calculating an optimal irradiation method using a computer. In this method, a radiation beam in one direction is divided into smaller segment units and irradiated to create an ideal beam pattern. In addition, the MLC is controlled by a computer to realize irradiation as calculated. Thus, an ideal dose distribution can be obtained by reproducing the beam pattern generated by the inverse plan and irradiating from multiple directions. In this intensity-modulated radiotherapy, although the irradiation dose from each radiation beam is different at each point in the irradiation field, the target dose distribution is finally realized by an integrated value obtained by summing the distributions of all the radiation beams.

  Before the start of treatment, the dose calculation is repeated many times using a three-dimensional treatment plan apparatus, and an optimum irradiation condition (treatment plan) is searched. Moreover, since it is a complicated irradiation method, the dose error is strictly confirmed by actually reproducing the three-dimensional dose distribution of the irradiation target part individually. Specifically, in performing radiotherapy, a tomographic image of a region to be irradiated is acquired in advance by a CT scan or the like, and PTV and OAR in the irradiation region are defined. And the parameter of radiation irradiation for obtaining desired irradiation is designated, and the intensity modulation radiation treatment planning apparatus is made to perform optimization calculation. Then, according to the obtained solution, the radiation irradiation parameters of the external irradiation apparatus are designated, and the radiation irradiation is actually performed. Moreover, based on the result obtained by actual irradiation, the irradiation conditions are changed again, and the intensity-modulated radiation therapy planning apparatus performs the calculation again as necessary. Thus, in the present situation, a complete solution cannot be obtained by a single calculation, and the user is actually changing the irradiation conditions so as to obtain a desired result while repeating trial and error.

  Such an intensity-modulated radiation therapy plan (IMRT plan) will be examined in detail. The intensity-modulated radiation therapy plan is a problem that the intensity of radiation irradiated from the outside is adjusted by using MLC so that the PTV is irradiated intensively and the OAR has a low dose. Here, the radiation beam incidence direction and dose distribution are set, and the intensity of the radiation beam is determined. That is, since it is necessary to obtain a radiation beamlet coefficient (input) for obtaining an optimum dose distribution (output), the problem belongs to a class called an inverse problem mathematically.

  In general, it is known that an inverse problem has a situation in which no solution exists or a situation in which a plurality of solutions exist even if there are solutions. For this reason, an objective function for obtaining an approximate solution (optimal solution) of a true solution is set and replaced with a problem (minimization problem) that minimizes it.

  The target function is the purpose of the above-mentioned IMRT plan, “To adjust the radiation intensity to be irradiated from the outside so as to reduce the dose to OAR while intensively irradiating PTV”. Is an expression that expresses a state in which the irradiation is concentrated and the OAR has a low dose. As such a target function, various target functions based on an irradiation dose, a dose-volume histogram (DVH), and an equivalent uniform dose (EUD) have been proposed. Further, as a method for performing the IMRT optimization calculation, a filter back projection method, pseudo annealing, a genetic algorithm, a random search technique, a gradient method, and the like are known. Among these, since the calculation speed is high, an iterative algorithm based on the gradient method is currently recommended for clinical implementation.

  The IMRT planning problem obtained by an optimization method such as the gradient method is input to the intensity-modulated radiation irradiation apparatus, and actual IMRT is performed.

  As described above, the IMRT planning problem can be mathematically reduced to a goal function minimization problem. A Newton method is known as a general method for solving such an optimization problem, but there is a problem that the amount of calculation becomes enormous. Specifically, in the optimization process, an operation for obtaining the Hessian matrix of the target function and its inverse matrix is required. In addition, the gradient method has a problem that it cannot be escaped if it is captured as a local minimum (minimum) solution. Furthermore, a treatment plan in which the radiation beam intensity is negative may be calculated. In this case, since a negative dose intensity cannot be set in reality, it must be cut to 0 at the end of the iterative process, and thus the possibility of causing a difference from the ideal in the final solution cannot be denied. Alternatively, even if the solution is a positive value, it may become a high value that cannot be set as a device, and there may be a problem that the value cannot be used as it is. Furthermore, there is a possibility that periodic points and quasi-periodic points may occur (see Non-Patent Document 1), and there is a problem that it is not practical to apply to the IMRT planning problem.

  On the other hand, a CQ algorithm has been proposed as a solution for the split feasibility problem (see Non-Patent Document 2). Similar to the gradient method, this CQ algorithm can also be applied to the optimization of IMRT planning problems. However, in order to speed up the calculation, it is necessary to set the step size value by trial and error, which is troublesome (see Non-Patent Document 3).

  Further, Patent Document 5 discloses a method and system for optimizing radiation dose delivery. According to this method, it is said that a direct solution can be determined by solving a nonlinear programming problem using a conventional quadratic objective function without imposing a positive beam weight constraint. However, in general, in a large-scale system, it is impossible to obtain a global minimum of the objective function.

  As described above, in the optimization of the current IMRT plan, calculation time is long, and a value obtained as a solution becomes a non-settable value such as a negative value. The realization of an intensity-modulated radiation therapy plan that can obtain reliable results in time has been desired.

JP 2006-175239 A Special table 2007-514499 gazette JP 2011-212395 A Japanese Patent No. 4425129 Special table 2007-516743 gazette

K. Fujimoto and T. Yoshinaga, Bifurcations in an Iterative Optimization Process for Intensity Modulated Radiation Therapy, Int. J. Bifurcation Chaos, Vol.19, No.3, pp.1087-1095, 2009. C. Byrne, Iterative oblique projection onto convex sets and the split feasibility problem, Inverse Probl., Vol.18, pp.441-453, 2002. Y. Censor, T. Bortfeld, B. Martin and A. Trofimov, A unified approach for inversion problems in intensity-modulated radiation therapy, Phys. Med. Biol., Vol. 51, No. 10, pp. 2353-2365, 2006. Kenichi Fujimoto, Tetsuya Yoshinaga "Mechanical properties of optimized iterative methods for intensity-modulated radiation therapy" IEICE Technical Report, vol.106, no.452, pp.17-21, 2007. Kenichi Fujimoto, Kenji Yamada, Tetsuya Yoshinaga “A Study on the Diagonal Newton Method for Optimization of Intensity-Modulated Radiation Treatment Plans Based on Equivalent Uniform Dose” IEICE Technical Report, vol.107, no.154, pp. 59-62, 2007. Kosuke Hashido, Kenichi Fujimoto, Tetsuya Yoshinaga “Intensity-modulated radiation therapy planning method using the continuous method”, IEICE Technical Report, Vol.111, No.62, pp.105-110, 2011. L. Portelance, KS Chao, PW Grigsby, H. Bennet, and D. Low, Intensity-modulated radiation therapy (IMRT) reduces small bowel, rectum, and bladder doses in patients with cervical cancer receiving pelvic and paraaortic irradiation, Int. J Radiat. Oncol. Biol. Phys., Vol.51, No.1, pp.261-266, 2001.

  The present invention has been made in view of such a background. The main object of the present invention is to achieve an optimization calculation with convergence to a minimal solution while maintaining the positive value and upper bound of the solution, while reducing the calculation time and solving as a settable value. It is an object of the present invention to provide an intensity-modulated radiation therapy planning apparatus, a radiation beam coefficient calculation method for the intensity-modulated radiation irradiation apparatus, an intensity-modulated radiation therapy planning program, a computer-readable recording medium, and a recorded device.

Means for Solving the Problems and Effects of the Invention

  To achieve the above object, according to the first intensity-modulated radiation therapy planning apparatus of the present invention, intensity modulation for determining radiation irradiation conditions for performing intensity-modulated radiation therapy using the intensity-modulated radiation irradiation apparatus. A radiotherapy planning apparatus, a tomographic image acquisition unit that acquires a tomographic image of an object to be subjected to radiotherapy, a display unit that displays a tomographic image acquired by the tomographic image acquisition unit, and displayed on the display unit Based on the tomographic image, an irradiation area designating unit for designating a target volume PTV to be irradiated with radiation and an area OAR to avoid radiation irradiation, the number of radiation beamlets irradiated by the intensity-modulated radiation irradiation apparatus, and a radiation beamlet A condition designating means for designating at least one of a coefficient, a dose transfer coefficient matrix, the number of regions, and a target irradiation dose, and a condition designated by the condition designating means. There, using the solution of the following nonlinear ordinary differential equations, it is possible and an inverse treatment planning calculation means for calculating a local minimum of the objective function.

Where x = (x ₁ , x ₂ ,..., X _J ) ^T is the radiation beamlet coefficient, J is the number of radiation beamlets, T is the transpose of the vector or matrix, and K is the dose transfer It is a coefficient matrix and is expressed by the following equation.

R ₊ represents a non-negative real number, and I represents the total number of pixels in the PTV and OAR areas. U is a unit matrix, X = diag (x), and γ> 0. The element of the initial value x (0) = x ⁰ is selected by the following equation.

Further, each element of Kx∈R ^I represents the irradiation dose for each pixel, P: R ^I → R ^I represents a projection for adjusting the difference between Kx and the target irradiation dose. The target irradiation dose may be set to a different value for each PTV and OAR.

  Thereby, an upper limit can be added to the obtained solution in advance, and the solution can be obtained with a radiation dose that can be set by the intensity-modulated radiation irradiation apparatus.

  In addition, according to the second intensity-modulated radiation therapy planning apparatus, an iterative method in which the differential function of the target function is discretized as in the following equation can be used to obtain the minimum solution.

In the above equation, λ> 0, n is a discrete time (n = 0, 1, 2,...), And Φ _n is expressed by the following equation.

  Furthermore, according to the radiation beam coefficient calculation method of the third intensity-modulated radiation irradiation apparatus, in the intensity-modulated radiation treatment plan for determining the irradiation condition of radiation for performing the intensity-modulated radiation treatment using the intensity-modulated radiation irradiation apparatus. A method for calculating a radiation beam coefficient necessary for obtaining a desired dose distribution, the step of acquiring a tomographic image of an object to be subjected to radiation therapy, and displaying the acquired tomographic image on a display means A step, a step of designating a target volume PTV to be irradiated with radiation and a region OAR to avoid radiation irradiation based on the tomographic image displayed on the display means, and radiation irradiated by the intensity-modulated radiation irradiation apparatus Based on at least one of the number of beamlets, radiation beamlet coefficients, dose transfer coefficient matrix, number of regions, and target irradiation dose, the following nonlinear normal Using the solution of the equation can include a step of determining a local minimum of the objective function.

Where x = (x ₁ , x ₂ ,..., X _J ) ^T is the radiation beamlet coefficient, J is the number of radiation beamlets, T is the transpose of the vector or matrix, and K is the dose transfer It is a coefficient matrix and is expressed by the following equation.

R ₊ represents a non-negative real number, and I represents the total number of pixels in the PTV and OAR areas. U is a unit matrix, X = diag (x), and γ> 0. The element of the initial value x (0) = x ⁰ is selected by the following equation.

Further, each element of Kx∈R ^I represents the irradiation dose for each pixel, P: R ^I → R ^I represents a projection for adjusting the difference between Kx and the target irradiation dose. The target irradiation dose may be set to a different value for each PTV and OAR.

  Thereby, an upper limit can be added to the obtained solution in advance, and the solution can be obtained with a radiation dose that can be set by the intensity-modulated radiation irradiation apparatus.

  Furthermore, according to the radiation beam coefficient calculation method of the fourth intensity-modulated radiation irradiation apparatus, an iterative method in which the differential function of the target function is discretized as the following equation can be used to obtain the minimum solution. .

In the above equation, λ> 0, n is a discrete time (n = 0, 1, 2,...), And Φ _n is expressed by the following equation.

  Furthermore, according to the radiation beam coefficient calculation method of the fifth intensity-modulated radiation irradiation apparatus, the target function can be defined based on the dose distribution.

  Furthermore, according to the radiation beam coefficient calculation method of the sixth intensity-modulated radiation irradiation apparatus, the target function can be defined based on a dose-volume histogram or an equivalent uniform dose.

  Furthermore, according to the seventh intensity-modulated radiation therapy planning program, there is provided an intensity-modulated radiation therapy planning program for determining radiation irradiation conditions for performing intensity-modulated radiation therapy using an intensity-modulated radiation irradiation apparatus, Based on the tomographic image of the object to be treated, the function of designating the target volume PTV to be irradiated with radiation and the region OAR to avoid radiation irradiation, the number of radiation beamlets irradiated by the intensity-modulated radiation irradiation apparatus, A function that specifies at least one of the radiation beamlet coefficient, dose transfer coefficient matrix, number of regions, and target irradiation dose, and the solution of the following nonlinear ordinary differential equation according to the specified conditions, the minimum solution of the target function The desired function can be executed by the computer.

Where x = (x ₁ , x ₂ ,..., X _J ) ^T is the radiation beamlet coefficient, J is the number of radiation beamlets, T is the transpose of the vector or matrix, and K is the dose transfer It is a coefficient matrix and is expressed by the following equation.

R ₊ represents a non-negative real number, and I represents the total number of pixels in the PTV and OAR areas. U is a unit matrix, X = diag (x), and γ> 0. The element of the initial value x (0) = x ⁰ is selected by the following equation.

Further, each element of Kx∈R ^I represents the irradiation dose for each pixel, P: R ^I → R ^I represents a projection for adjusting the difference between Kx and the target irradiation dose. The target irradiation dose may be set to a different value for each PTV and OAR.

  Thereby, an upper limit can be added to the obtained solution in advance, and the solution can be obtained with a radiation dose that can be set by the intensity-modulated radiation irradiation apparatus.

  Furthermore, according to the eighth intensity-modulated radiation therapy planning program, an iterative method in which the differential function of the target function is discretized as in the following equation can be used to obtain the minimum solution.

In the above equation, λ> 0, n is a discrete time (n = 0, 1, 2,...), And Φ _n is expressed by the following equation.

  Furthermore, a ninth computer-readable recording medium or recorded device stores the program. Recording media can store CD-ROM, DVD, Blue-ray (registered trademark), flexible disk, optical disk such as MO, magnetic disk, magneto-optical disk, magnetic medium such as magnetic tape, semiconductor memory, and other programs. Media. The program includes a program distributed in a download manner through a network line such as the Internet, in addition to a program stored and distributed in the recording medium. Further, the recorded devices include general-purpose or dedicated devices in which the program is implemented in a state where it can be executed in the form of software, firmware, or the like. Furthermore, each process and function included in the program may be executed by program software that can be executed by a computer, or each part of the process or function may be executed by hardware such as a predetermined gate array (FPGA, ASIC), or program software. It may be realized in the form of a mixture of hardware and partial hardware modules that realize some elements of hardware.

1 schematically illustrates an exemplary radiotherapy device according to an embodiment of the present invention. FIG. FIG. 6 shows an exemplary grouping of 9 beam radiation delivery systems grouped into three groups for beam intensity modulation retrograde treatment planning. It is an image figure which shows the phantom used in Example 2. FIG. It is a graph which shows the image figure and DVH (lower stage) which show the dose distribution figure (upper stage) in case of (lambda) = 0.1. It is the graph which shows the image figure and DVH (lower stage) which show the dose distribution figure (upper stage) in case of (lambda) = 0.5. It is a schematic diagram which shows a mode that the conventional radiotherapy is performed. It is a schematic diagram which shows an intensity modulation radiation treatment plan.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiments described below are read by an intensity-modulated radiation treatment planning apparatus, a radiation beam coefficient calculation method of the intensity-modulated radiation irradiation apparatus, an intensity-modulated radiation treatment planning program, and a computer for embodying the technical idea of the present invention. This invention exemplifies a possible recording medium and recorded apparatus, and the present invention relates to an intensity-modulated radiation treatment planning apparatus, a radiation beam coefficient calculation method for the intensity-modulated radiation irradiation apparatus, an intensity-modulated radiation treatment planning program, and a computer-readable medium. The recording media and recorded equipment are not specified as follows. Further, the present specification by no means specifies the members shown in the claims to the members of the embodiments. In particular, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the embodiments are not intended to limit the scope of the present invention unless otherwise specified, and are merely explanations. It is just an example. Note that the size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation. Furthermore, in the following description, the same name and symbol indicate the same or the same members, and detailed description thereof will be omitted as appropriate. Furthermore, each element constituting the present invention may be configured such that a plurality of elements are constituted by the same member and the plurality of elements are shared by one member, and conversely, the function of one member is constituted by a plurality of members. It can also be realized by sharing.

In this specification, connection to a computer, printer, external storage device and other peripheral devices for operation, control, input / output, display, and other processing connected to the moving image encoding apparatus is, for example, IEEE 1394, RS- 232x, RS-422, RS-423, RS-485, serial connection such as USB, parallel connection, or electrically connected via a network such as 10BASE-T, 100BASE-TX, 1000BASE-T . The connection is not limited to a physical connection using a wire, but may be a wireless connection using radio waves such as IEEE802.1x, OFDM, etc., Bluetooth (registered trademark), infrared rays, optical communication, or the like. Further, a memory card, a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, or the like can be used as a recording medium for storing text and image data to be searched, database construction, setting for searching, and the like.
(Radiotherapy system 100)

FIG. 1 shows a schematic diagram of a radiation therapy system 100 according to an embodiment of the present invention. The radiotherapy system 100 includes a tomographic image acquisition unit 10 for obtaining a diagnostic image used for planning radiotherapy, an intensity-modulated radiation irradiation apparatus 50, and an operation unit 32. Here, a computer tomography (CT) scanner is provided as the tomographic image acquisition means 10. The CT scanner includes an X-ray source 14 that is attached to a rotating gantry 16. The X-ray source 14 emits a fan beam or a cone beam as X-rays that pass through the inspection region. On the other hand, the support 12 on which the subject OB is placed can move linearly in the target area within the examination region. Thereby, X-rays can interact with the target area of the subject OB supported by the support 12. The linear movement of the subject OB cooperates with the rotation of the X-ray source 14 by the rotating gantry 16 so as to cause a helical orbit of the X-ray source 14 relative to the subject OB. In addition, the X-ray detection array 18 is arranged so that X-rays can be received after passing through an examination region that is partially absorbed by the subject OB due to interaction with the subject OB. Therefore, the X-rays detected by the X-ray detection array 18 have absorption information related to the subject OB.
(CT scanner)

  The CT scanner is operated by the CT control means 20 so as to execute the selected imaging sequence for the selected target area in the subject OB to be treated by the radiotherapy. The CT scanner acquires imaging data of the target area by executing the imaging sequence. The acquired imaging data is stored in the imaging data memory 22. The reconstruction calculation unit 24 reconstructs a tomographic image of the target area from the acquired imaging data. The reconstructed image is stored in the image reconstruction memory 26.

The above-described tomographic image acquisition means is merely an example, and the present invention is not limited to the above configuration. For example, a single-slice or multi-slice fan beam CT scanner or other types of CT imaging scanners can be substituted for the CT scanner. Other types of tomographic scanners such as a magnetic resonance imaging (MRI) scanner, a proton emission tomography (PET) scanner, and a single photon emission computed tomography (SPECT) scanner can also be used in place of the CT scanner.
(Tomographic image acquisition means 10)

The tomographic image acquisition means 10 shown in FIG. 1 is provided apart from the intensity-modulated radiation irradiation apparatus 50. Preferably, a trust marker is given to the object OB before tomographic imaging, and the radiation irradiation performed following tomographic imaging is maintained at the same position so that alignment between tomographic imaging and radiation irradiation can be performed. . As another method for spatial alignment between tomographic image acquisition and radiation therapy, for example, an intrinsic anatomical marker can be used. Furthermore, it is possible to integrate the tomographic image acquisition means with the radiotherapy apparatus so as to reduce the alignment error between the tomographic imaging and the radiotherapy. On the other hand, according to the present invention, a tomographic image that has already been captured can be acquired in the form of data or the like using a tomographic image acquisition unit. The operation means 32 includes an input device such as a console for a user to perform various operations. In the example of FIG. 1, a PC is used as the operation means 32. The PC installs a dedicated program so that some or all of other functions such as the reconstruction calculation means 24, the density profile calculation means 30, the irradiation region designation means 34, the reverse treatment plan calculation means 70, etc. Can also be fulfilled. Further, the functions of the imaging data memory 22 and the image reconstruction memory 26 can be achieved using a PC hard disk or semiconductor memory. Further, the PC monitor can be used as a display means for displaying the tomographic image acquired by the tomographic image acquiring means.
(Density profile calculation means 30)

  The density profile calculation means 30 shown in FIG. 1 calculates the physical density of the structure in or around the target area of the subject designated on the operation means 32. The target and critical tissue are manually placed on the tomographic reconstruction display. Alternatively, various areas are automatically determined based on density or other characteristics. The physical density is used to calculate the absorption or attenuation of radiation used in radiation therapy as it passes into the subject.

  The irradiation region designating unit 34 designates the target volume PTV to be irradiated with radiation and the region OAR where radiation irradiation should be avoided based on the tomographic image displayed on the display unit. Here, a region of interest ROI for radiation therapy is defined. The region of interest ROI includes a target, an important tissue whose radiation dose should be minimized within the target area, or a radiation blocking structure. The contour for designating the irradiation area can be manually designated by the user using the operation means 32. Preferably, the boundary lines are electronically distinguished by automatically arranged density boundary surfaces. Alternatively, each tissue region may be distinguished based on characteristics such as density in the electronic tomographic image, and the region of interest may be automatically identified. As another method, the user can designate one or a few seed points in each region, and the density profile calculation means 30 defines a region in which surrounding voxels having the same density or other distinguishing characteristics are incorporated. Grow points to achieve. In general, the irradiation area designating unit 34 provides a radiation therapy purpose (target irradiation dose) including the target radiation dose distribution in the target area. This radiotherapy purpose may be constrained by the maximum dose in the selected critical tissue.

For example, an 80 Gy dose is targeted so that the area receives radiation therapy in critical tissues that are likely to be adversely affected by the irradiation, with a limit of at most 20% of this value (ie, 16 Gy). . Radiotherapy purposes may also be constrained by radiation source parameters. For example, the beam portion intensity is limited between the selected maximum intensity corresponding to the selected minimum intensity (eg, zero intensity) and the maximum power in the beam portion for the radiation source.
(Intensity modulated radiation irradiation device 50)

  The intensity-modulated radiation irradiation apparatus 50 shown in FIG. 1 includes a radiation irradiation apparatus 51 having a radiation source 54 attached to a rotating gantry 56. The rotating gantry 56 rotates the radiation source 54 around the rotation axis. The support 52 strictly positions the subject OB such that the target area is irradiated with the intensity-modulated radiation beam 60 generated by the radiation source 54.

  In helical tomotherapy, the support 52 moves the subject OB linearly while the rotating gantry 56 rotates the radiation source 54 so as to cause the helical trajectory of the radiation source 54 to rotate around the subject OB. An intensity-modulated radiation beam 60, such as a photon beam, forms a cross-sectional area with varying intensity and / or circumference. The radiation beam 60 is applied continuously during helical rotation or selectively during radiotherapy.

  Suitable radiation sources 54 include linear electron accelerators and linacs that produce an accelerated electron beam. In a preferred embodiment, an accelerated electron beam is irradiated using tungsten to produce an X-ray or gamma-ray photon beam for photon radiation therapy. It is also possible to apply other types of radiation, such as known proton and neutron beams, or an accelerated electron beam generated by linac to the subject during radiation therapy.

  The intensity modulation of the radiation beam 60 is suitably obtained using one or more multi-leaf collimators (MLC) 62. The MLC includes an array of pairs of leaves that block individually movable radiation, and all pairs together define a radiation aperture that is of a selectable size and shape. Preferably, the MLC is controlled to perform an operation that defines multiple aperture openings for a single radiation source. In FIG. 1, a linac device is illustrated as the radiation irradiation device 51. However, the present invention is not limited to this example, and it is also possible to use a plurality of non-rotating or step-and-shoot radiation sources that simultaneously or successively apply a plurality of radiation beams that intersect within the target area of the subject. it can. It is also possible to use helical tomotherapy that irradiates radiation by causing the radiation source to orbit around the patient in a helical manner. Multi-beam systems require complex MLC to obtain the proper spatial modulation of the combined beam intensity. In helical tomotherapy, the air dose modulation is obtained by opening or closing one leaf (or beamlet) 72 spatially and temporally during helical rotation, so a simple alternative to the conventional cone beam MLC. Binary fan beam MLC can be used.

A confidence marker is preferably used to align the previously acquired tomographic image with the radiation therapy. In a preferred embodiment, the detection means uses low power X-rays generated by the radiation source 54 to perform low resolution CT imaging that can be used to image a confidence marker placed on the subject prior to tomographic imaging. receive. For example, separate CT scanners, such as a separate X-ray source and detection array, can be integrated with the intensity modulated radiation delivery device. In this case, tomographic imaging can be performed in an intensity-modulated radiation irradiation device in order to reduce alignment errors between imaging and radiation therapy.
(Reverse treatment plan calculation means 70)

The reverse treatment plan calculation means 70 obtains a minimum solution of the target function using a solution of a nonlinear ordinary differential equation described later according to the specified condition. Various conditions for this purpose are designated by a condition designation means. Here, the operating means 32 is used as the condition specifying means, and the number of radiation beamlets, the radiation beamlet coefficients, the dose transfer coefficient matrix, the number of regions, the target irradiation dose, etc. irradiated by the intensity-modulated radiation irradiation apparatus 50 are controlled by the operating means 32. Specify from. Inverse planning computing means 70 shown in FIG. 1 calculates the radiation beam intensity modulation optimized for the intensity modulated radiation beam 60. In order to optimize the intensity modulation of one or more beams used for radiation therapy, the beam is mathematically divided into a plurality of beamlets. Parameters such as beamlet intensity are optimized continuously or iteratively.
(Multi-beam radiation irradiation equipment)

Next, an example of a multi-beam radiation irradiation apparatus will be described with reference to FIG. In multi-beam radiation therapy, a number of intersecting beams are typically applied to a target area sequentially to obtain the desired intensity modulation. FIG. 2 schematically illustrates the radiation beam of a typical 9-beam radiation system as the beams are evenly spaced at 40 ° angular spacing. Each beam is mathematically divided into a plurality of beamlets. For example, a 10 × 10 cm ² beam can be divided into 400 beamlets, each having an area of 0.5 × 0.5 cm ² . In a nine beam system, assuming that the angle and orientation of each beamlet is kept constant, it corresponds to 3600 beamlet intensity parameters.

  The beam shown in FIG. 2 is generated sequentially by one or more radiation sources attached to a rotating gantry operating in a rotating step-and-shoot mode. In this example, only nine beams with a corresponding large number of parameters (eg 3600) are shown, but fewer or more beams may be used. The beamlet resolution may also be increased to generate additional parameters. Radiation treatment plans that use more beamlets are considered to give accurate treatment plans, ie accurate dose distribution resolution and accuracy to the target area, in complex multi-beam radiation treatment procedures. Preferably, the beams are arranged so as not to oppose, i.e. neither of the two beams is arranged at an angular spacing of 180 °. In the example of FIG. 2, the nine beams are on the same plane. However, the present invention is not limited to this example, and beams that are not on the same plane can be used.

  In a helical tomotherapy device, at least one beam is helically rotated during radiation therapy. Continuously rotating beams are intensity modulated during helical rotation, and temporally intensity modulated beams can be represented by multiple virtual beams of short duration corresponding to the small angular spacing of the rotating beams. it can. Each virtual beam is divided into beamlets to optimize the temporal intensity modulation of the rotating beam. In the radiation therapy planning system of the present invention, the spatially and temporally modulated beam intensity to be applied during helical tomotherapy is appropriately resolved and optimized.

  Optimization of many beamlet parameters requires a great deal of computation. Thus, as shown in FIG. 1, the parameters are divided into a plurality of groups, ie, N beamlet parameter groups 1, 2,. . . , N. In the radiation treatment planning system of the present invention, the optimization is performed by dividing a vector composed of all beamlet coefficients into partial vectors and switching the partial systems (treatment planning systems) for each dose transfer matrix corresponding to each partial vector. And by combining the solutions (beamlet coefficients) obtained for each partial system. By dividing and optimizing the beamlet coefficients in this way, it is possible to save necessary calculation resources. In addition, compared with the optimization method shown in Patent Document 4 (a method in which beamlet coefficients are divided and optimization is performed for each group cumulatively), an error in cumulative beamlet intensity does not occur. Have

Further, the inverse treatment plan computing means 70 shown in FIG. 1 calculates optimized beamlet parameters, such as optimized beamlet intensity, representing intensity modulation of the radiation beam that is closely related to the radiation therapy purpose. To do. The conversion means 80 converts the beamlet intensity into a control parameter for the intensity-modulated radiation irradiation device 50, such as a selected time-varying setting for the MLC 62 of the radiation irradiation device 51, for example. Further, the radiation irradiation control means 82 controls the intensity-modulated radiation irradiation apparatus 50 in order to execute the selected radiation treatment plan.
(IMRT)

  For IMRT, a linear accelerator (particle beam irradiation device) as described above, a CT device for treatment planning, a three-dimensional radiation treatment planning device capable of reverse treatment planning, movement of the patient with respect to the irradiation center and internal movement of the organ , Devices that can change the irradiation intensity on a flat surface, micro-capacity ionization chamber dosimeter or semiconductor dosimeter (including diamond dosimeter) and water phantom or water equivalent individual phantom used in combination, two or more dimensions Equipment that can measure and compare relative dose distribution is required. Hereinafter, a procedure for searching for the optimum beam intensity in the backward treatment plan in the IMRT by performing the optimization calculation by the radiotherapy planning apparatus will be described.

The IMRT treatment plan is an inverse problem because it is necessary to obtain a radiation beam coefficient (input) for obtaining an optimal dose distribution (output) as described above. Now, when the unknown radiation beam coefficient is x∈R ^J and the irradiation dose and the dose transfer matrix are D∈R ^I and K∈R ^{I × J} , the following relationship is established.

In the above equation, D and K are doses of PTV and OAR (D _PTV ∈ R ^I1 , D _OAR ∈ R ^I2 ) and transfer matrix (K _PTV ∈ R ^{I1 × J} , K _OAR ∈ R ^{I2 × J} ) in the row direction. It has a side-by-side configuration (I ₁ + I ₂ = I). That is, it can be expressed by the following equation.

  The same applies to the case of targeting a plurality of PTVs and OARs. Moreover, the lower limit value and the upper limit value of the irradiation dose for PTV and OAR, respectively,

Specified by the projection

I ₁ = 1, 2,. . . , I ₁ , i ₂ = 1, 2,. . . , I ₂

  Defined in

  Here, a gradient method for obtaining a minimum value using a solution of a nonlinear ordinary differential equation can be applied. According to this method, the target function Hessian and its inverse matrix included in the conventional IMRT gradient system are not required, and convergence to a minimal solution can be achieved while maintaining the positive value and upper bound of the solution as a constraint of the beam coefficient. Features such as guaranteed. Here, continuous-time IMRT programming (hereinafter referred to as “continuous method”) is given as an initial value problem of the following differential equation.

In the above equation, U is a unit matrix, X = diag (x), and γ> 0. The element of the initial value x (0) = x ⁰ is

Select as. Hereinafter, the properties of the continuous process are listed below.
(Proposition 1)

  The solution trajectory of Equation 23 is closed in the partial state space of the following equation.

  Proof is omitted. Next, the stability of the equilibrium point set ε of the following equation is examined.

(Theorem 1)

  When the equilibrium point set ε exists in the system of Equation 23, the equilibrium point eεε is globally asymptotically stable.

That is, the solution trajectory x starting from the initial value x ⁰ converges toward the element e of the equilibrium point set ε that minimizes the target function defined by the following equation.

(Discrete method of continuous method)

  Next, we propose a discretization method derived from the continuous method and conduct a theoretical study. An iterative method discretized by the Euler method is defined as follows by assuming that γ → ∞ in the continuous method described above.

Here, Φ _n is expressed by the following equation.

N represents discrete time (n = 0, 1, 2,...). The non-diagonal elements of the square matrix Φ _n are 0, and the diagonal elements are 1 or less. By dividing the discretized step size as the product of the parameters λ and Φ _n , parameter conditions can be easily derived. If the parameter λ is selected to be a relatively small value, it is expected that the good property of the continuous method will be inherited, but the computation time required for iterating to sufficiently converge to a minimal solution (fixed point) becomes longer. Here, the value of λ is designed from the viewpoint of the upper limit of the parameter value that guarantees the convergence to the fixed point set. That is, note that the discretization method of Equation 28 is formally derived based on the Euler method, but is not a discretization for faithfully reproducing the solution trajectory of the original differential equation system.

  Next, the convergence of the iterative method with respect to the fixed point set ε expressed by the following equation is examined.

Here, let L be the maximum eigenvalue of K ^T K. Moreover, as a symbol used below, a positive real number is written as R ₊₊ , K _j is a j column of K, and u = (1, 1,..., 1) ^T ∈ R ^J. Here, it is assumed as follows.
(Proposition 2)
λ is

  Assume that At this time, if the element e of the fixed point set ε exists, the initial value

  The iterative solution given by satisfies the following equation.

(Proposition 3)

  And λ <2 / L. There exists an element e of the fixed point set ε,

  Then, the following equation holds.

  (System 1)

Under the assumption of Proposition 3, the iterative solution {x ⁿ } converges toward the element e of the fixed point set ε that minimizes the objective function of the following equation.

Next, as Examples 1-2, the results of numerical experiments are shown. Example 1 is a simplified setting based on a known fixed point set, and is intended to illustrate theoretical analysis results. Example 2 is intended for practical settings based on clinical cases, and evaluates the performance as an IMRT plan.
Example 1

Consider a setting in which single beam irradiation (x ₁ , x ₂ ,... X ₆ ) is applied to a planar region (d ₁ , d ₂ , d ₃ , d ₄ ) of size 2 × 2 from six directions, and (d ₁ , It is assumed that the area of d ₂ , d ₃ ) is PTV and the isolated point of d ₄ is OAR. Dose transfer coefficients for PTV and OAR, respectively

  and

And This is because the element corresponding to the irradiation in the horizontal or vertical direction is set to 1 / √2, and the element irradiated in the oblique direction is set to 1. Here, if the true value (fixed point) of the beam coefficient is e = (30, 10, 40, 5, 30, 10) ^T , the following equation is obtained as the target value of the dose distribution.

  From the condition of Equation 40,

  and

  Are set to 50 and 20, respectively, and the projections P in Expression 21 and Expression 22 are defined.

  At this time, a condition for satisfying the positive value of Proposition 2

  Can be expressed as λ <(√2) −1 = 0.414. In addition, the constraints λ <2 / L to λ <0.5 included in the proposition 3 are required. That is, if the value of λ is less than 0.414, the positive value of the solution and the monotonic decrease of the target function are theoretically guaranteed.

  Here, the objective function is

The value of the parameter λ was changed as follows, and the behavior of the target function in 10 iterations was observed. At this time, the initial value of the state variable was given a random number and executed several times. In experiments where the value of parameter λ is set to 0.01, 0.37, 0.38, 0.39 and 0.40, it is confirmed that all the elements of the state variable are always positive and the target function decreases monotonously. did it. On the other hand, when λ = 1, it was recognized that there was a repetition time at which the target function did not decrease monotonously.
(Example 2)

  Next, an IMRT planning problem given by a phantom (FIG. 3) having an image size of 532 × 446 (237272 pixels) based on the same problem setting as in Non-Patent Document 7 is targeted. Here, a single PTV and five OAR regions are considered, and the description and setting for each region in the figure are as shown in Table 1. Here, the total number of pixels in the PTV and OAR areas is I = 144352.

  Here, it is assumed that 699 parallel beam rows are irradiated from seven directions of 26 °, 77 °, 129 °, 180 °, 231 °, 283 °, and 334 ° (radiation beamlet number J = 4893). Conditions for satisfying the positive value of Proposition 2 in the above settings

  Becomes λ <0.9888, and in addition, the constraints λ <2 / L included in the proposition 3 are required from λ <2.6059. That is, if the value of λ is less than 0.9888, the positive value property and monotonic decrease property of the solution are theoretically guaranteed, so there are two setting values for the parameter λ, 0.1 and 0.5. It was. The experimental results for each parameter value are listed in FIGS. The dose distribution diagram and DVH when the value of the discrete time n is 100, 200, and 1000 are shown. When a general personal computer was used, the calculation time required for 1000 iterations was several tens of seconds, and a practical and high speed was obtained. In the dose distribution diagram, an image region irradiated with a dose of 30 Gy or more which is the same as the target lower limit dose of OAR2 (colon) and OAR3 (small intestine) is shown in black. It can be seen that as the number of iterative solutions increases, it is asymptotic to a good treatment plan. If the number of iterations is increased, the PTV is irradiated with a sufficiently high dose, and the result is appropriate. For OAR1 (kidney) and OAR3 (small intestine), according to Radiation Treatment Planning Guidelines 2008, the tolerated dose of one third of the kidney volume is 50 Gy, the tolerated dose is 40 Gy in all the small intestine volumes, and It can be judged that each is appropriate on the basis that there is a description that no obvious change is recognized at a volume of 50% or less. Compared with the result of Non-Patent Document 7 that is the source of the problem setting used in this experiment, it can be said that the result of the proposed method has a smaller area than the target upper limit dose value of each OAR.

  As described above, the IMRT programming method using the continuous method has a feature that the monotonic decrease of the target function along the solution is guaranteed while maintaining the positive value and the upper bound of the solution as the constraint of the irradiation beam coefficient. . In particular, according to the above embodiment, we propose an iterative method in which the continuous method is discretized, and by setting appropriate parameters, the solution trajectory of the iterative method keeps a positive value, and the distance from the ideal solution monotonously decreases by iteration. Prove that there is theoretically. Numerical examples of practical settings based on clinical cases were shown, and the performance as an IMRT plan was evaluated. For the set PTV and OAR, desirable treatment plans that enable irradiation with high and low doses were obtained, respectively, and the usefulness of the proposed method could be confirmed.

  As described above, according to the continuous method, the target function can be minimized while the solution trajectory of the differential equation naturally maintains a positive value and an upper bound. Furthermore, by using the discretization method of the continuous method, it is possible to monotonously decrease the target function while the iterative solution by the difference equation always maintains a positive value. With this method, it is not necessary to calculate the target function Hessian and its inverse matrix or solve simultaneous equations, and the amount of calculation can be drastically reduced.

  The multi-leaf collimator (MLC) is used for the intensity-modulated radiation therapy planning apparatus, the radiation beam coefficient calculation method of the intensity-modulated radiation irradiation apparatus, the intensity-modulated radiation therapy planning program, the computer-readable recording medium, and the recorded device of the present invention. It can be suitably used for an IMRT using an IMRT using a physical compensation filter, an IMRT using a binary collimator, an IMRT using a robot type treatment device, and the like.

DESCRIPTION OF SYMBOLS 100 ... Radiation therapy system 10 ... Tomographic image acquisition means 12 ... Support body 14 ... X-ray source 16 ... Rotating gantry 18 ... X-ray detection array 20 ... CT control means 22 ... Imaging data memory 24 ... Reconstruction calculation means 26 ... Image reconstruction Configuration memory 30 ... density profile calculation means 32 ... operation means 34 ... irradiation area designation means 50 ... intensity modulated radiation irradiation apparatus 51 ... radiation irradiation apparatus 52 ... support 54 ... radiation source 56 ... rotating gantry 60 ... radiation beam 62 ... MLC
70 ... Reverse treatment plan calculation means 80 ... Conversion means 82 ... Radiation irradiation control means OB ... Subject RS ... Radiation source RB ... Radiation TM ... Tumor OAR ... Important tissue PTV ... Target volume

Claims (9)

An intensity-modulated radiation therapy planning device that determines radiation irradiation conditions for performing intensity-modulated radiation therapy using an intensity-modulated radiation irradiation device,
A tomographic image acquisition means for acquiring a tomographic image of an object to be subjected to radiation therapy;
Display means for displaying a tomographic image acquired by the tomographic image acquisition means;
Based on the tomographic image displayed on the display means, an irradiation area designation means for designating a target volume PTV to be irradiated with radiation and an area OAR to avoid radiation irradiation;
Condition designation means for designating at least one of the number of radiation beamlets, radiation beamlet coefficients, dose transfer coefficient matrix, number of regions, and target irradiation dose irradiated by the intensity-modulated radiation irradiation device;
Intensity-modulated radiation treatment planning apparatus comprising: an inverse treatment plan calculation means for obtaining a minimum solution of a target function using a solution of the following nonlinear ordinary differential equation according to a condition designated by the condition designation means .
(Where x = (x ₁ , x ₂ ,..., X _J ) ^T is the radiation beamlet coefficient, J is the number of radiation beamlets, T is the transpose of the vector or matrix, and K is the dose A transfer coefficient matrix, expressed as
R ₊ represents a non-negative real number, I represents the total number of pixels in the PTV and OAR regions, U represents a unit matrix, X = diag (x), γ> 0, and an initial value x (0) = x ⁰ The element is selected by
Each element of Kx∈R ^I represents the irradiation dose for each pixel, P: R ^I → R ^I represents a projection for adjusting the difference between Kx and the target irradiation dose. ) The intensity-modulated radiation therapy planning device according to claim 1,
An intensity-modulated radiation therapy planning apparatus characterized by using an iterative method in which a differential function of a target function is discretized as in the following equation in order to obtain the minimal solution.
(In the above equation, λ> 0, n is a discrete time (n = 0, 1, 2,...), And Φ _n is expressed by the following equation.)
This is a method for calculating the radiation beam coefficient necessary for obtaining a desired dose distribution in an intensity-modulated radiation therapy plan for determining the irradiation conditions for performing intensity-modulated radiation therapy using an intensity-modulated radiation irradiation apparatus. And
Acquiring a tomographic image of an object to be subjected to radiation therapy;
Displaying the acquired tomographic image on a display means;
Designating a target volume PTV to be irradiated with radiation and a region OAR to avoid radiation irradiation based on the tomographic image displayed on the display means;
Based on at least one of the number of radiation beamlets, radiation beamlet coefficients, dose transfer coefficient matrix, number of regions, and target irradiation dose irradiated by the intensity-modulated radiation irradiation device, the target function is calculated using the solution of the following nonlinear ordinary differential equation. A method for calculating a radiation beam coefficient of an intensity-modulated radiation irradiating apparatus.
(Where x = (x ₁ , x ₂ ,..., X _J ) ^T is the radiation beamlet coefficient, J is the number of radiation beamlets, T is the transpose of the vector or matrix, and K is the dose A transfer coefficient matrix, expressed as
R ₊ represents a non-negative real number, I represents the total number of pixels in the PTV and OAR regions, U represents a unit matrix, X = diag (x), γ> 0, and an initial value x (0) = x ⁰ The element is selected by
Each element of Kx∈R ^I represents the irradiation dose for each pixel, P: R ^I → R ^I represents a projection for adjusting the difference between Kx and the target irradiation dose. ) A radiation beam coefficient calculation method for an intensity-modulated radiation irradiation apparatus according to claim 3,
A radiation beam coefficient calculation method for an intensity-modulated radiation irradiation apparatus, characterized by using an iterative method in which a differential function of a target function is discretized as in the following equation in order to obtain the minimum solution.
(In the above equation, λ> 0, n is a discrete time (n = 0, 1, 2,...), And Φ _n is expressed by the following equation.)
A radiation beam coefficient calculation method for an intensity-modulated radiation irradiation apparatus according to claim 3 or 4,
The method for calculating a radiation beam coefficient of an intensity-modulated radiation irradiation apparatus, wherein the target function is defined based on a dose distribution. A radiation beam coefficient calculation method for an intensity-modulated radiation irradiation apparatus according to claim 3 or 4,
A radiation beam coefficient calculation method for an intensity-modulated radiation irradiation apparatus, wherein the target function is defined based on a dose-volume histogram or an equivalent uniform dose. An intensity-modulated radiation therapy planning program for determining radiation irradiation conditions for performing intensity-modulated radiation therapy using an intensity-modulated radiation irradiation apparatus,
A function for designating a target volume PTV to be irradiated with radiation and a region OAR to avoid radiation irradiation based on a tomographic image of an object to be subjected to radiation therapy;
A function for designating at least one of the number of radiation beamlets, radiation beamlet coefficients, dose transfer coefficient matrix, number of regions, and target irradiation dose irradiated by the intensity-modulated radiation irradiation device;
According to the specified conditions, using the solution of the following nonlinear ordinary differential equation, the function to obtain the minimum solution of the target function,
An intensity-modulated radiation treatment planning program characterized by causing a computer to execute.
(Where x = (x ₁ , x ₂ ,..., X _J ) ^T is the radiation beamlet coefficient, J is the number of radiation beamlets, T is the transpose of the vector or matrix, and K is the dose A transfer coefficient matrix, expressed as
R ₊ represents a non-negative real number, I represents the total number of pixels in the PTV and OAR regions, U represents a unit matrix, X = diag (x), γ> 0, and an initial value x (0) = x ⁰ The element is selected by
Each element of Kx∈R ^I represents the irradiation dose for each pixel, P: R ^I → R ^I represents a projection for adjusting the difference between Kx and the target irradiation dose. ) The intensity-modulated radiation therapy planning program according to claim 7,
An intensity-modulated radiation therapy planning program characterized by using an iterative method in which a differential function of a target function is discretized as in the following equation in order to obtain the minimal solution.
(In the above equation, λ> 0, n is a discrete time (n = 0, 1, 2,...), And Φ _n is expressed by the following equation.)
  A computer-readable recording medium or a recorded device storing the program according to claim 7 or 8.