JP7467145B2 - Radiation Therapy Planning Equipment - Google Patents

Description

The embodiments disclosed in this specification and the drawings relate to a radiation therapy planning system .

There is a known technology for formulating a radiation therapy plan based on X-ray CT images obtained by an X-ray computed tomography (CT) device for treatment planning. However, X-ray CT images have problems such as making it difficult to determine the extent of the tumor. For this reason, there is a demand for a technology that identifies the extent of the tumor using MR images obtained by a magnetic resonance imaging (MRI) device for treatment planning, and formulates a radiation therapy plan based on X-ray CT images that reflect the identified extent of the tumor. In radiation therapy, the extent of the tumor shrinks due to the administration of radiation, and the patient's weight and body shape change due to the effects of concurrent anticancer drug treatment. In such cases, in order to change (re-plan) the radiation therapy plan, X-ray CT images, which involve exposure to radiation when captured, are re-collected along with the MR images.

JP 2015-205110 A JP 2017-109099 A JP 2017-23551 A JP 2000-105279 A

One of the problems that the embodiments disclosed in this specification and the drawings attempt to solve is to perform processing related to replanning a radiation therapy plan accurately and with low radiation exposure. However, the problems that the embodiments disclosed in this specification and the drawings attempt to solve are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described below can also be positioned as other problems.

The radiation therapy planning device according to the embodiment includes a comparison unit and a generation unit. The comparison unit compares a first treatment planning medical image of the patient used in the radiation therapy plan of the patient with a post-planning medical image of the patient taken after the radiation therapy plan. The generation unit generates a treatment plan modification image based on a second treatment planning medical image used in the radiation therapy plan and the post-planning medical image according to a result of the comparison by the comparison unit.

FIG. 1 is a diagram showing an example of the configuration of a radiation therapy system including a radiation therapy planning apparatus according to an embodiment. FIG. 2 is a diagram showing an example of the configuration of the radiation therapy planning apparatus of FIG. FIG. 3 is a flowchart showing an example of the flow of radiation therapy performed in the radiation therapy system of FIG. FIG. 4 is a flow chart showing an example of a procedure for radiation therapy performed after an initial radiation therapy plan is made in the radiation therapy shown in FIG. FIG. 5 is a diagram for explaining each treatment session of the radiation therapy in FIG. FIG. 6 is a diagram showing an example of a display image including a superimposed image relating to radiation therapy in FIG. 3, in which a color image showing the calculated tumor area and the area indicated by the difference in body shape is superimposed on a newly acquired MR image for re-planning. FIG. 7 is a diagram showing an example of a display image relating to the radiation therapy of FIG. 3 in which a newly acquired re-planning MR image and a volume indicated by a calculated difference in the tumor area are displayed. FIG. 8 is a diagram showing an example of a display image relating to the radiation therapy of FIG. 3 in which a Dose Volume Histogram (DVH) relating to the calculated difference in tumor area is displayed together with a newly acquired re-planning MR image. FIG. 9 is a diagram showing image types used in each treatment session of radiation therapy according to the eleventh modified example. FIG. 10 is a diagram showing image types used in each treatment session of radiation therapy according to the twelfth modified example.

Below, embodiments of a radiation therapy planning device and a radiation therapy planning method will be described in detail with reference to the drawings. In the following description, components having the same or substantially the same functions as those described above with reference to the previous figures will be given the same reference numerals and will be described repeatedly only when necessary. Even when the same parts are shown, the dimensions and ratios of each part may be different depending on the drawing.

Figure 1 is a diagram showing an example of the configuration of a radiation therapy system 100 including a radiation therapy planning device 4 according to this embodiment. As shown in Figure 1, the radiation therapy system 100 has an X-ray computed tomography imaging device for treatment planning (X-ray CT device for treatment planning) 1, a magnetic resonance imaging device for treatment planning (MRI device for treatment planning) 2, a picture archiving and communication system (PACS) 3, a radiation therapy planning device 4, a radiation therapy information system 5, and a radiation therapy device 6, all of which are connected to each other via a network.

The treatment planning X-ray CT device 1 and the treatment planning MRI device 2 are medical modalities that generate three-dimensional medical images of the patient.

For example, the treatment planning X-ray CT device 1 irradiates a patient with X-rays from the X-ray tube while rotating a rotating frame holding an X-ray tube and an X-ray detector at high speed, and detects the X-rays that pass through the patient with the X-ray detector. Based on the projection data from the X-ray detector, the treatment planning X-ray CT device 1 generates a three-dimensional CT image that represents the spatial distribution of the X-ray attenuation coefficients of materials on the transmission path of the X-rays. The three-dimensional CT image obtained by the treatment planning X-ray CT device 1 is used for planning or changing (replanning) a radiation therapy plan. When capturing a three-dimensional CT image for use in planning or changing a radiation therapy plan, a tube voltage of predetermined conditions is set.

The treatment planning MRI device 2, for example, irradiates RF pulses from an RF coil to excite target nuclei present in a patient placed in a static magnetic field, and collects MR signals generated from the target nuclei using the RF coil. The treatment planning MRI device 2 then generates a three-dimensional MR image representing the spatial distribution of the target nuclei based on the MR signals from the RF coil. The three-dimensional MR image obtained by the treatment planning MRI device 2 is used to plan or change (replan) a radiation therapy plan. The MR image according to this embodiment may be generated by any contrast enhancement method, such as T1 weighting, T2 weighting, or diffusion weighting. The MR image according to this embodiment may also be a plurality of three-dimensional MR images captured using a plurality of protocols.

The treatment planning X-ray CT device 1 and the treatment planning MRI device 2 capture three-dimensional CT images and three-dimensional MR images for use in formulating or modifying a radiation therapy plan, respectively, while the patient is fixed to a bed or the like by a fixation device. The fixation device may be a device that fixes a part of the patient's body by covering it from above, like a mask, or may be a device that is fixed to a bed having a shape that fits the patient's body shape (shape) and fixes the patient by lying on it. In addition, the top plates of the treatment planning X-ray CT device 1 and the treatment planning MRI device 2 each have a flat shape similar to the top plate of the radiation therapy device 6 described later, so that the patient's position does not change between CT imaging, MR imaging, and radiation therapy. It is preferable that the shapes of the top plates of the treatment planning X-ray CT device 1, the treatment planning MRI device 2, and the radiation therapy device 6 are the same.

PACS3 is an image server that manages medical images. For example, PACS3 stores three-dimensional CT images from the treatment planning X-ray CT device 1 and three-dimensional MR images from the treatment planning MRI device 2.

Hereinafter, three-dimensional CT images and three-dimensional MR images will be collectively referred to as three-dimensional medical images. Three-dimensional medical images are image data composed of multiple voxels arranged in a three-dimensional shape. Furthermore, three-dimensional medical images obtained by the treatment planning X-ray CT device 1 will be referred to as treatment planning CT images. Similarly, three-dimensional medical images obtained by the treatment planning MRI device 2 will be referred to as treatment planning MR images.

The radiation therapy planning device 4 is a computer that uses three-dimensional medical images to create a radiation therapy plan for the patient. The radiation therapy plan information is supplied to the radiation therapy information system 5.

The radiation therapy information system 5 is an information system that manages radiation therapy schedule information, radiation therapy planning information, medical images, etc. One such information system is known as the Oncology Information System (OIS). The radiation therapy information system 5 supplies radiation therapy planning information to the radiation therapy device 6, for example.

The radiation therapy device 6 is a device that treats a patient by irradiating a target tumor or the like within the patient with radiation according to a radiation therapy plan. In this embodiment, the type of radiation is not particularly limited. Radiation such as X-rays, electron beams, and particle beams can be used.

Here, particle beams are a general term for proton beams and heavy particle beams. In other words, the radiation therapy planning device and radiation therapy planning method according to this embodiment include a particle therapy planning device and a particle therapy planning method for implementing radiation therapy using particle beams, respectively. Furthermore, the radiation therapy device 6 according to this embodiment includes a proton therapy device and a heavy particle therapy device.

Figure 2 is a diagram showing an example of the configuration of the radiation therapy planning device 4 in Figure 1. As shown in Figure 2, the radiation therapy planning device 4 is a computer for planning a radiation therapy plan for radiation therapy by the radiation therapy device 6 and changing (replanning) the radiation therapy plan. As shown in Figure 2, the radiation therapy planning device 4 has an arithmetic circuit 41, an image processing circuit 42, a communication circuit 43, a display circuit 44, an input circuit 45, and a memory circuit 46. The arithmetic circuit 41, the image processing circuit 42, the communication circuit 43, the display circuit 44, the input circuit 45, and the memory circuit 46 are connected to each other via a bus so as to be able to communicate with each other.

The arithmetic circuit 41 controls the overall operation of the radiation therapy planning device 4. The arithmetic circuit 41 executes a program related to radiation therapy planning (hereinafter referred to as a radiation therapy planning program) to develop a radiation therapy plan for a patient who is the subject of radiation therapy by the radiation therapy device 6, and generates radiation therapy planning information including an irradiation area, an irradiation method, a dose distribution, an irradiation direction, etc. The arithmetic circuit 41 has, as hardware resources, processors such as a Central Processing Unit (CPU), a Micro Processing Unit (MPU), and a Graphics Processing Unit (GPU), and memories such as a Read Only Memory (ROM) and a Random Access Memory (RAM).

The calculation circuit 41 according to this embodiment executes a treatment planning function 411, an image acquisition function 412, an image comparison function 413, a judgment function 414, and a display control function 415 using a radiation therapy planning program.

In the treatment planning function 411, the arithmetic circuit 41 uses CT images for treatment planning and MR images for treatment planning to create a radiation therapy plan, which is a plan for radiation therapy. Creating a radiation therapy plan includes changing (replanning) the radiation therapy plan. The arithmetic circuit 41 that realizes the treatment planning function 411 is an example of a planning unit and a generating unit.

In the image acquisition function 412, the arithmetic circuit 41 acquires CT images for treatment planning from the X-ray CT device 1 for treatment planning or the PACS 3. In the image acquisition function 412, the arithmetic circuit 41 acquires MR images for treatment planning from the MRI device 2 for treatment planning or the PACS 3. The arithmetic circuit 41 that realizes the image acquisition function 412 is an example of an acquisition unit.

In the image comparison function 413, the arithmetic circuit 41 compares two treatment planning MR images collected at different times. The two treatment planning MR images to be compared include the treatment planning MR image used to create the latest radiation therapy plan and the treatment planning MR image collected after the radiation therapy plan was created. The image comparison function 413 includes an alignment function for aligning the two treatment planning MR images, a specification function for specifying the tumor area in the aligned treatment planning MR image, and a calculation function for calculating the difference in the tumor area and/or body shape between the two treatment planning MR images. The arithmetic circuit 41 that realizes the image comparison function 413 is an example of a comparison unit. The arithmetic circuit 41 that realizes the alignment function, specification function, and calculation function are examples of the alignment unit, specification unit, and calculation unit, respectively.

In the judgment function 414, the arithmetic circuit 41 judges whether or not to change (replan) the latest radiation therapy plan at that time, depending on the comparison result of two MR images for treatment planning collected at different times. The arithmetic circuit 41 that realizes the judgment function 414 is an example of a judgment unit.

In the display control function 415, the arithmetic circuit 41 controls the operation of the display circuit 44. In the display control function 415, the arithmetic circuit 41 generates image data to be displayed on the display circuit 44. The arithmetic circuit 41 that realizes the display control function 415 is an example of a display unit.

The arithmetic circuit 41 may be realized by an ASIC (Application Specific Integrated Circuit) or a Field Programmable Gate Array (FPGA). The arithmetic circuit 41 may also be realized by another Complex Programmable Logic Device (CPLD) or a Simple Programmable Logic Device (SPLD).

Note that each of the functions 411 to 415 is not limited to being realized by a single processing circuit. A processing circuit may be configured by combining multiple independent processors, and each processor may execute a program to realize each of the functions 411 to 415.

The image processing circuit 42 has, as hardware resources, processors such as a CPU, a GPU, an MPU, and memories such as a ROM and a RAM. The image processing circuit 42 performs various image processing on three-dimensional medical images. For example, the image processing circuit 42 performs three-dimensional image processing such as volume rendering, surface rendering, image value projection processing, multi-planar reconstruction (MPR) processing, and curved MPR (CPR) processing on the three-dimensional medical images to generate two-dimensional medical images for display. The image processing circuit 42 may be realized by an ASIC, FPGA, CPLD, or SPLD capable of implementing the above image processing. The image processing circuit 42 may be expressed as an example of a display unit.

The communication circuit 43 communicates data between the treatment planning X-ray CT device 1, treatment planning MRI device 2, PACS 3, radiation therapy information system 5, and radiation therapy device 6 included in the radiation therapy system 100 via wired or wireless connections (not shown).

The display circuit 44 displays various display information related to the radiation therapy plan. For example, the display circuit 44 displays a display screen for the radiation therapy plan, such as a medical image generated by the arithmetic circuit 41 that realizes the display control function 415, and a GUI (Graphical User Interface) for receiving various operations from the operator. The display circuit 44 has a display interface circuit and a display device. The display interface circuit converts data (display information) representing the display object into a video signal. The display signal is supplied to the display device. The display device displays the video signal representing the display object. As the display device, any one or more of various displays can be used as appropriate. For example, as the display device, a CRT (Cathode Ray Tube) display, a liquid crystal display (LCD: Liquid Crystal Display), an organic EL display (OELD: Organic Electro Luminescence Display), an LED (Light Emitting Diode) display, or a plasma display can be used as appropriate. The display circuit 44 is provided, for example, in the pedestal body of a treatment pedestal installed in a treatment room not shown. The display circuit 44 may be described as an example of a display unit.

The display circuit 44 may be installed anywhere in the treatment room. The display circuit 44 may be a desktop type, or may be configured as a tablet terminal capable of wireless communication. One or more projectors may be used as the display device of the display circuit 44.

The input circuitry 45 accepts various commands from radiation therapy practitioners such as radiological technologists and doctors. The input circuitry 45 can be a keyboard, a mouse, various switches, etc. The input circuitry 45 supplies output signals corresponding to the various accepted commands to the arithmetic circuitry 41 via the bus.

The memory circuit 46 is a storage device such as a Hard Disk Drive (HDD), a Solid State Drive (SSD), or an integrated circuit storage device that stores various information. In addition to an HDD or SSD, the memory circuit 46 may also be a drive device that reads and writes various information to and from portable storage media such as a Compact Disc (CD)-ROM drive, a Digital Versatile Disc (DVD) drive, or a flash memory. The storage area of the memory circuit 46 may be in an external storage device connected via a network.

Below, an example of the operation of each part in the radiation therapy plan according to this embodiment will be described in detail with reference to the drawings. FIG. 3 is a flowchart showing an example of the flow of radiation therapy performed in the radiation therapy system 100 of FIG. 1.

In step S101, a fixation device specific to the patient who has been decided to receive radiation therapy is created. The fixation device is molded into a shape that fits the patient's body shape. A fixation device shaped to fit the patient's body shape can suppress the patient's bodily movements during treatment. The fixation device may be a device that covers part of the patient's body from above like a mask, or it may be a device that is fixed to a bed that has a shape that fits the patient's body shape (shape) and fixes the patient by lying on it.

One example is the Vac-Lok patient immobilization system. The immobilization device is a cushion of small polystyrene beads sealed in an airtight, stretchy bag. With the patient lying on the immobilization device, the pressure inside the device is reduced using an air compressor or similar device, causing the beads inside the device to pack together in a shape that fits the patient's body, and the immobilization device becomes hard. By keeping the pressure inside the device reduced throughout the treatment period, the hardness of the immobilization device is maintained throughout the treatment period.

For example, there is a patient fixation system that uses a mask sheet. The fixation device is a mask sheet that, in a hardened state, softens when heated to a temperature higher than room temperature and hardens again when cooled to room temperature. The entire mask sheet is warmed with hot water or the like to soften it. The softened mask sheet is placed on the patient's head and neck and molded to fit the shape of the patient's head and neck. The molded mask sheet hardens while maintaining the shape that fits the patient's head and neck when cooled to room temperature, and a patient mask that fits the patient's head and neck is molded. By using the hardened patient mask, it is possible to fix the patient's head and neck during radiation therapy and when taking CT images and MR images for treatment planning.

In step S102, a treatment planning CT image of the periphery of the tumor is captured using the treatment planning X-ray CT device 1. The treatment planning CT image is captured while the patient is fixed to the bed of the treatment planning X-ray CT device 1 by a fixture. The treatment planning CT image is captured by setting the imaging range of the treatment planning X-ray CT device 1 so that the tumor is included. The imaging range of the treatment planning X-ray CT device 1 is set so as to include all the trajectories through which the radiation beam passes during radiation therapy and to include organs that serve as indicators for positioning. In addition, the treatment planning CT image is captured by setting predetermined tube voltage conditions. Note that it is recommended that the tube voltage during imaging be uniquely fixed in relation to the creation of a conversion table for converting CT values into electron density or physical density. When the tube voltage is changed, it is necessary to create the conversion table for all tube voltages to be changed, which requires a large amount of preparation time. The captured treatment planning CT image is transferred to the radiation therapy planning device 4.

In step S103, a treatment planning MR image of the area around the tumor is captured using the treatment planning MRI device 2. The treatment planning MR image is captured while the patient is fixed to the bed of the treatment planning MRI device 2 using a fixture. The treatment planning MR image is captured by setting the imaging range of the treatment planning MRI device 2 to include the tumor. The imaging range of the treatment planning X-ray CT device 1 is set to include the entire trajectory of the radiation beam during radiation therapy and to include organs that serve as alignment indicators. The captured treatment planning MR image is transferred to the radiation therapy planning device 4.

Note that, although an example has been described in which the captured treatment planning CT images and treatment planning MR images are each transferred directly from each device to the radiation therapy planning device 4, this is not limiting. Each image may be transferred from each device to the PACS 3. The PACS 3 then transfers the treatment planning CT images and/or treatment planning MR images to the radiation therapy planning device 4.

In step S104, the radiation therapy planning device 4 creates a radiation therapy plan (initial radiation therapy plan). The radiation therapy plan is realized by the execution of a radiation therapy planning program by the arithmetic circuit 41. The radiation therapy plan involves creating a spatial dose distribution from information about the patient, and then considering its time distribution to determine the optimal treatment device, irradiation method, irradiation conditions, etc.

First, the arithmetic circuitry 41 that realizes the image acquisition function 412 collects a treatment planning CT image and a treatment planning MR image (first MR image) from the treatment planning X-ray CT device 1 and the treatment planning MRI device 2, respectively, for use in creating an initial radiation therapy plan. As described above, the arithmetic circuitry 41 that realizes the image acquisition function 412 may collect each image from the PACS 3. Each collected image is stored, for example, in the memory circuitry 46.

Next, the arithmetic circuitry 41 that realizes the treatment planning function 411 converts the CT values of the collected CT images for the treatment plan into electron density data or physical density data. In other words, the treatment planning function 411 includes a conversion function that converts the CT values of the collected CT images for the treatment plan into electron density data or physical density data. For this conversion, a conversion table between CT values and electron density data or physical density data is used. The conversion table is, for example, acquired in advance and stored in the memory circuitry 46.

Next, the arithmetic circuitry 41 that realizes the treatment planning function 411 performs distortion correction on the collected treatment planning MR image (first MR image). In other words, the treatment planning function 411 includes a correction function that performs distortion correction on the collected treatment planning MR image. A distortion map is used for this distortion correction. For distortion correction, a scan under the same conditions using a phantom for measuring the strain distribution (distortion map) may be performed in the treatment planning MRI device 2 prior to capturing the treatment planning MR image. The distortion map is, for example, acquired in advance and stored in the memory circuitry 46. Note that the distortion correction may be performed in the image processing circuitry 42.

Next, the arithmetic circuit 41 realizing the treatment planning function 411 generates a composite image by combining the distortion-corrected MR image for treatment planning (first MR image) with the collected CT image for treatment planning. The image processing circuit 42 generates a composite image for display (MPR image) by performing MPR processing on the composite image (three-dimensional medical image). The arithmetic circuit 41 realizing the display control function 415 displays the generated composite image for display on the display circuit 44.

Next, the arithmetic circuit 41 that realizes the treatment planning function 411 creates a radiation therapy plan. The processing involved in creating the radiation therapy plan includes pre-processing and planning processing.

In pre-processing, the arithmetic circuit 41 realizing the treatment planning function 411 identifies the tumor region and the risk region based on the composite image. The risk region is a region including organs etc. that are at high risk of side effects occurring due to radiation exposure. The treatment planning MR image is suitable for identifying the tumor region. For this reason, for example, the tumor region extracted from the treatment planning MR image is used to identify the tumor region. Although the treatment planning CT image is generally used to extract the risk region in identifying the risk region, the treatment planning MR image may also be used if it has sufficient spatial resolution for risk region extraction. The extraction of the tumor region and risk region may also be performed in the image processing circuit 42.

The arithmetic circuit 41 that realizes the treatment planning function 411 determines the irradiation target area by adding a margin to the identified tumor area that takes into account patient movement, uncertainties of the treatment device, etc. The arithmetic circuit 41 that realizes the treatment planning function 411 also determines the expected dose distribution to the irradiation target area according to this plan, the upper limit of exposure to risk organs, etc.

The number of tumor regions and risk regions identified may each be two or more. In this case, for example, N tumor regions may be identified as tumor region 1, tumor region 2, ..., tumor region N, and M risk regions may be identified as risk region 1, risk region 2, ..., risk region M. In the following, for simplicity of explanation, it is assumed that the number of identified tumor regions and risk regions is one each.

In the planning process, the arithmetic circuit 41 that realizes the treatment planning function 411 creates a radiation therapy plan. The radiation therapy plan may be created by forward planning or inverse planning.

For example, when a radiation therapy plan is created by forward planning, conditions such as the number of irradiation directions for radiation therapy, the irradiation angle for each irradiation direction, the radiation intensity of irradiation, the collimator opening of irradiation, and the wedge filter are first set. The calculation circuit 41 that realizes the treatment plan function 411 calculates the radiation dose distribution based on the set conditions. For example, the planner checks the treatment plan CT image or the composite image for display on which the calculated dose distribution is superimposed to determine whether the irradiation conditions are optimal. The calculation circuit 41 that realizes the treatment plan function 411 determines whether the dose distribution is optimal based on the planner's judgment result obtained from the input circuit 45, for example. If it is not determined that the dose distribution is optimal, the calculation circuit 41 that realizes the treatment plan function 411 changes some or all of the above multiple conditions and calculates the dose distribution again. In this way, the dose distribution is changed little by little while changing the conditions, and a radiation therapy plan is created by repeatedly changing the conditions until the desired dose distribution is achieved.

For example, when a radiation therapy plan is created by inverse planning, the dose and tolerance range to be administered to the region to be irradiated are first set. In addition, a safe level of dose (dose constraint) is set for the risk region so that a dose exceeding the tolerance range for the risk region is not administered to the risk region. The arithmetic circuit 41 that realizes the treatment planning function 411 creates a radiation therapy plan that satisfies the set irradiation conditions while changing various parameters.

Next, the planner checks the created radiation therapy plan, radiation intensity distribution, Dose Volume Histogram (DVH), etc. The DVH is created, for example, from the radiation therapy plan. Note that these checks may be performed by the arithmetic circuitry 41 that realizes the treatment planning function 411. In this case, the various thresholds required for the checks may be stored, for example, in the memory circuitry 46, etc. If the check results in no problems, the created radiation therapy plan, etc. are approved and transferred to the radiation therapy information system 5.

The creation of a radiation therapy plan may include a simulation of a particle beam. The simulation of a particle beam is performed based on the expected dose distribution determined in the preprocessing. The particle beam has an ionization peak called a Bragg peak at a certain target depth. The depth of the Bragg peak of the particle beam is changed by changing the energy of the particle beam. In this situation, in order to uniformly irradiate the irradiation area, a Bragg peak expanded according to the size and depth of the irradiation area (expanded Bragg peak: SOBP) can be formed by using multiple particle beams with different energies. In other words, the simulation of a particle beam can be expressed as determining the number and energy of multiple particle beams to be irradiated in order to achieve the expected dose distribution.

In step S105, radiation therapy is performed based on the radiation therapy plan (initial radiation therapy plan). Radiation therapy is started by sending the radiation therapy plan for the first radiation therapy from the radiation therapy information system 5 to the radiation therapy device 6. When the planned administration of radiation is completed, the first radiation therapy is completed. Thereafter, multiple radiation therapy sessions are performed according to the radiation therapy plan. For example, assume that the total dose (total administered dose) for the tumor area planned in the initial radiation therapy plan is 60 Gy. In this case, radiation therapy in which radiation is administered to the tumor area at a dose of 2 Gy is performed five days a week for six consecutive weeks.

In general, the tumor area may shrink or change shape during multiple radiation therapy sessions. Radiation therapy may also be performed in parallel with anti-cancer drug therapy. During anti-cancer drug therapy, patients often feel nauseous and may lose their appetite. For this reason, the patient's weight may gradually decrease during multiple radiation therapy sessions. Weight loss is accompanied by changes in body shape. If the size or shape of the tumor area, or the patient's body shape, etc., changes, it is desirable to change (re-plan) the radiation therapy plan. However, capturing CT images for treatment planning involves exposure to radiation.

Therefore, in the radiation therapy system 100 according to this embodiment, a treatment planning MR image (second MR image) is captured after the radiation therapy plan has been created in order to grasp changes in the size and shape of the tumor area, the patient's body shape, etc.

In addition, in the radiation therapy system 100 according to this embodiment, the need to change (replan) the radiation therapy plan is determined by comparing the treatment planning MR image (first MR image) used to create the latest radiation therapy plan with the newly collected treatment planning MR image (second MR image).

In addition, in the radiation therapy system 100 according to this embodiment, a new radiation therapy plan is prepared (re-planned) using the treatment planning CT images used in preparing the radiation therapy plan and the newly collected treatment planning MR images (second MR images).

Below, an example of the operation of the radiation therapy planning device 4, which is realized by the execution of the radiation therapy planning program by the arithmetic circuit 41 after the initial radiation therapy plan has been made, will be described in detail with reference to the drawings. FIG. 4 is a flow chart showing an example of the flow of radiation therapy performed after the initial radiation therapy plan has been made in the radiation therapy of FIG. 3. FIG. 5 is a diagram for explaining each treatment session of the radiation therapy of FIG. 4. A treatment session refers to a radiation therapy performed on one day of radiation therapy performed five days a week for six weeks. In a treatment session, radiation is irradiated one or more times from one or more irradiation directions.

(About the first treatment session)
First, the first treatment session that is performed after the initial radiation treatment plan is made in step S104 in FIG. 3 will be described.

When the first treatment round is started, the latest radiation therapy plan is the initial radiation therapy plan drawn up in step S104 of FIG. 3. The initial radiation therapy plan is a radiation therapy plan drawn up using a treatment planning CT image CT_1 and a treatment planning MR image MR_1. Here, the treatment planning CT image CT_1 is a treatment planning CT image collected in step S102 of FIG. 3. The treatment planning MR image MR_1 is a treatment planning MR image collected in step S103 of FIG. 3. In this treatment round, the treatment planning MR image MR_1 is an example of a first MR image. Note that the treatment planning MR image MR_1 includes multiple 3D MR images captured using multiple protocols.

In step S201, the arithmetic circuitry 41 realizing the judgment function 414 judges whether or not to collect re-planning MR images. This judgment is made, for example, according to the judgment of a user such as a doctor. The judgment of the user such as a doctor is acquired, for example, based on a control signal output by the input circuitry 45. The control signal is generated according to an operation (user operation) or input by a user such as a doctor. It is assumed that MR images for treatment planning are captured, for example, once a week. At this time, in this judgment for the first treatment session, it is judged that re-planning MR images will not be collected. If it is judged that re-planning MR images will not be collected, the radiation therapy proceeds to step S208.

Here, the re-planning MR image is a treatment planning MR image that is used to determine whether or not re-planning of the radiation therapy plan is necessary and for re-planning the radiation therapy plan. The re-planning MR image is an image captured after the imaging range is determined in the same manner as in step S103 of FIG. 3. In other words, the treatment planning MR image used for the initial radiation therapy plan and the re-planning MR image collected in this step are three-dimensional medical images obtained using the same protocol.

The arithmetic circuit 41 that realizes the judgment function 414 may make the judgment in step S201 not only based on the judgment of a user such as a doctor, but also based on, for example, a preset collection schedule (planned schedule), patient information including weight measurements obtained from an in-hospital system, whether or not MR images have been sent, the administration schedule of an anticancer drug, etc.

In step S208, the radiation therapy device 6 performs radiation therapy based on the latest radiation therapy plan at that time. Note that when this step for the first treatment is executed, the latest radiation therapy plan is the initial radiation therapy plan devised in step S104 in FIG. 3.

First, preparation for radiation therapy begins based on the information received by the radiation therapy device 6. After preparing the patient-specific fixture created in step S101 of FIG. 3, the patient is welcomed into the treatment room. The patient lies on the bed and the fixture is set. Note that there may be cases where the patient lies on a bed to which the patient-specific fixture created in step S101 of FIG. 3 is attached.

Next, the bed position is adjusted according to the marks on the patient's body surface and a laser positioning device (not shown) that indicates the treatment iso-center, so that the tumor is approximately aligned with the iso-center. This positioning is called the first positioning.

Next, X-ray stereo images or cone beam (CB) CT images are taken. Using information on bones or organs obtained from the taken X-ray stereo images or CBCT images, the bed position and bed angle are adjusted so that the tumor is accurately aligned with the isocenter. This positioning is called the second positioning. The bed position is adjusted, for example, by moving the bed along the X-axis, Y-axis, or Z-axis. The bed angle is adjusted, for example, by rotating the bed around the X-axis, Y-axis, or Z-axis. Here, the X-axis, Y-axis, and Z-axis are respectively the left-right direction of the patient, the front-back direction of the patient, and the up-down direction (body axis) of the patient when the bed is in the home position.

Next, the radiation therapy device 6 administers radiation according to the initial radiation therapy plan for the first treatment session. After the planned administration of radiation is completed, the radiation therapy proceeds to step S209.

In step S209, the arithmetic circuit 41 realizing the judgment function 414 judges whether or not to end the radiation therapy. This judgment is made according to the judgment of a user such as a doctor. The judgment of the user such as a doctor is acquired, for example, based on a control signal output by the input circuit 45. For example, assume that the initial radiation therapy plan includes radiation therapy that will continue for six weeks, five days a week. In this case, in this judgment for the first treatment session, it is judged that the radiation therapy will not be ended. If it is judged that the radiation therapy will not be ended, the radiation therapy returns to step S201.

The judgment in step S209 may be performed, for example, by the arithmetic circuit 41 that realizes the judgment function 414 judging whether all radiation treatments planned according to the latest radiation therapy plan have been completed. The arithmetic circuit 41 that realizes the judgment function 414 may also make a judgment depending on whether the total administration dose has reached the planned total administration dose. The various thresholds required for the judgment may be, for example, set in advance and stored in the memory circuit 46.

In addition, for the second and subsequent treatment sessions, in which it is determined in step S201 that replanning MR images will not be collected, radiation therapy will be performed based on the latest radiation therapy plan at that time, similar to the first treatment session described above.

(Regarding the Lth treatment session)
Next, the Lth treatment session in FIG. 5 will be described.

The latest radiation therapy plan at the time when the Lth treatment session is started is the initial radiation therapy plan prepared in step S104 of FIG. 3 using the treatment planning CT image CT_1 and the treatment planning MR image MR_1. In addition, in the Lth treatment session, a case will be described as an example in which a new radiation therapy plan is prepared (re-planned) after the re-planning MR image MR_L is collected. In this treatment session, the treatment planning MR image MR_1 is an example of a first MR image. Furthermore, the re-planning MR image MR_L is an example of a second MR image. Note that the re-planning MR image MR_L includes multiple 3D MR images captured using multiple protocols.

In step S201, the arithmetic circuit 41 realizing the judgment function 414 judges whether or not to acquire a re-planning MR image. In this judgment for the Lth treatment session, it is judged that a re-planning MR image MR_L is to be acquired. If it is judged that a re-planning MR image is to be acquired, the radiation therapy proceeds to step S202.

In step S202, the arithmetic circuitry 41 that realizes the image acquisition function 412 acquires a re-planning MR image MR_L from the treatment planning MRI apparatus 2. The re-planning MR image MR_L may be acquired via the PACS 3. The acquired re-planning MR image MR_L is stored in, for example, the memory circuitry 46.

In step S203, the arithmetic circuit 41 realizing the image comparison function 413 compares the two treatment planning MR images with respect to the tumor area and/or the patient's body shape. The two treatment planning MR images compared in this step are the treatment planning MR image used to create the latest radiation therapy plan and the re-planning MR image collected in step S202. That is, in this comparison for the Lth treatment session, the treatment planning MR image MR_1 and the re-planning MR image MR_L are compared.

This comparison consists of pre-processing and comparison processing. In pre-processing, the treatment planning MR image MR_1 and the re-planning MR image MR_L are aligned. Next, comparison processing is performed for at least one of the tumor region, body shape, and administered dose. Comparison of the tumor region is performed, for example, by comparing the representative length of the tumor region, such as the tumor diameter or maximum length, the volume, the area in any cross section, the position, the presence or absence, etc. Comparison of the body shape is performed, for example, by comparing the representative length of the soft tissue on the treatment planning MR image, such as the maximum length, the volume, the area in any cross section, the position, the presence or absence, etc.

First, the arithmetic circuit 41 realizing the image comparison function 413 performs alignment between the treatment planning MR image MR_1 and the re-planning MR image MR_L. The target structure for alignment differs depending on the imaging means used in the second alignment performed by the radiation therapy device 6. When X-ray stereo images are used for alignment, such as when the imaging means used is an X-ray stereo device, alignment is performed based on bone information or the shadows of large organs. When CBCT images are used for alignment, such as when the imaging means used is a cone beam (CB) CT device, alignment is performed based on organs that include or are near the tumor used for alignment.

Next, the arithmetic circuit 41 realizing the image comparison function 413 identifies the tumor region in the re-planning MR image MR_L. For example, the tumor region in the re-planning MR image MR_L can be identified by searching for the tumor region at the same site on the re-planning MR image MR_L based on the tumor region identified on the treatment planning MR image MR_1. Note that the tumor region in the treatment planning MR image MR_1 is assumed to have been identified when the initial radiation therapy plan was created, for example, in step S104 in FIG. 3.

Next, the arithmetic circuit 41 that realizes the image comparison function 413 calculates the difference between the tumor area identified in the re-planning MR image MR_L and the tumor area identified in the treatment planning MR image MR_1. The arithmetic circuit 41 that realizes the image comparison function 413 may calculate the difference in body shape between the re-planning MR image MR_L and the treatment planning MR image MR_1. The difference in tumor area and/or body shape calculated in this step includes, for example, the following four differences:

The first difference concerns soft tissue, which was present in the treatment planning MR image MR_1 but not in the re-planning MR image MR_L.

The second difference concerns soft tissue that was not present in the treatment planning MR image MR_1 but is present in the re-planning MR image MR_L.

The third difference concerns an area that was a tumor region on the treatment planning MR image MR_1 but is not a tumor region on the re-planning MR image MR_L.

The fourth difference concerns an area that was not a tumor area on the treatment planning MR image MR_1 but is a tumor area on the re-planning MR image MR_L.

In step S204, the arithmetic circuit 41 that realizes the display control function 415 displays the areas indicated by the four differences in the calculated tumor area and/or body shape in different colors. Figure 6 shows an example of a display image I13 including a superimposed image I12 relating to radiation therapy in Figure 3, in which a color image I11 indicating the areas indicated by the calculated tumor area and body shape differences is superimposed on the replanning MR image MR_L used to create the latest radiation therapy plan.

For example, the arithmetic circuit 41 realizing the display control function 415 assigns yellow, yellow-green, pink, and light blue to the area A1 indicated by the first difference, the area A2 indicated by the second difference, the area A3 indicated by the third difference, and the area A4 indicated by the fourth difference, respectively. The arithmetic circuit 41 realizing the display control function 415 generates a two-dimensional color image I11 for display such that the areas A1 to A4 indicated by the four differences are displayed semi-transparently in their respective color schemes on the re-planning MR image MR_L on which the MPR processing has been performed. The arithmetic circuit 41 realizing the display control function 415 generates a display image I13 including a superimposed image I12 in which the color image I11 is superimposed on the re-planning MR image MR_L on which the MPR processing has been performed. The arithmetic circuit 41 realizing the display control function 415 outputs the image data of the generated display image I13 to the display circuit 44. The display circuit 44 displays the display image I13 including the superimposed image I12 based on the image data of the display image I13.

Note that since the focus of interest is solely on the tumor region, it is acceptable for structures other than the target structure to be aligned to be slightly misaligned. In this case, distortion correction does not need to be performed.

By displaying the superimposed image I12 in this manner, a user such as a doctor can clearly understand the difference between the treatment planning MR image MR_1 that was used when the latest radiation therapy plan was created and the newly captured re-planning MR image MR_L (treatment planning MR image). This allows a user such as a doctor to easily determine whether or not re-planning is necessary.

As shown in FIG. 6, the high-dose risk region RA identified on the replanning MR image MR_L may be displayed in the superimposed image I12.

For example, in step S203, the arithmetic circuit 41 realizing the image comparison function 413 identifies a risk area RA in the replanning MR image MR_L. For example, the risk area RA in the replanning MR image MR_L can be identified by searching for the risk area RA in the same location on the replanning MR image MR_L based on the risk area identified on the treatment planning MR image MR_1. Note that the risk area in the treatment planning MR image MR_1 is assumed to have been identified when the initial radiation therapy plan was created, for example, in step S104 of FIG. 3. Next, the arithmetic circuit 41 realizing the image comparison function 413 calculates a high-dose risk area RA from among the risk areas RA identified in the replanning MR image MR_L. The high-dose risk area RA may be identified based on the latest radiation therapy plan at that time.

For example, in step S204, the arithmetic circuit 41 realizing the display control function 415 displays the calculated high-dose risk region RA in a color different from the calculated tumor region and/or the regions A1 to A4 showing the difference in body shape. The arithmetic circuit 41 realizing the display control function 415 assigns the color red to the high-dose risk region RA. The arithmetic circuit 41 realizing the display control function 415 generates a two-dimensional color image I11 for display such that the high-dose risk region RA is further displayed semi-transparently in red on the re-planning MR image MR_L that has been subjected to MPR processing.

In this way, the high-dose risk area RA identified on the replanning MR image MR_L is displayed on the superimposed image I12, allowing users such as doctors to more easily understand whether replanning is necessary.

In step S205, the arithmetic circuit 41 realizing the judgment function 414 judges whether or not to formulate a new radiation therapy plan (replan). The formulation of a new radiation therapy plan may be expressed as a change to the latest radiation therapy plan at that time. This judgment is made according to the judgment of a user such as a doctor who has viewed the superimposed image I12. The judgment of the user such as a doctor is acquired, for example, based on a control signal output by the input circuit 45. If it is judged that the radiation therapy should be replanned, the process proceeds to step S206.

The judgment in step S205 may be performed, for example, by the arithmetic circuit 41 that realizes the judgment function 414 judging whether the four differences related to the calculated tumor area and/or body shape are equal to or greater than a predetermined amount. The threshold values of each difference required for the judgment may be set in advance and stored in the memory circuit 46, for example.

In step S206, the arithmetic circuit 41 that realizes the display control function 415 generates a pseudo re-planning CT image that corresponds to the re-planning MR image MR_L. Hereinafter, the pseudo re-planning CT image is referred to as a virtual CT image. The virtual CT image is an example of a three-dimensional medical image.

First, the arithmetic circuit 41 that realizes the display control function 415 aligns the treatment planning MR image MR_1 used to create the initial radiation therapy plan with the re-planning MR image MR_L. The alignment of the two treatment planning MR images is performed based on organ information, tumor information, body shape, etc. Body shape and organ information are examples of soft tissue information that can be extracted from the treatment planning MR images. The soft tissue information may include tumor information. The arithmetic circuit 41 that realizes the display control function 415 identifies where an arbitrary point on the re-planning MR image MR_L corresponds on the treatment planning MR image MR_1 collected before the start of the first treatment. These processes are generally used in warping, which distorts images.

For example, if the initial radiation therapy plan is the latest radiation therapy plan when processing in this step is performed, the alignment has been performed in step S203, so processing in this step does not need to be performed.

Next, the arithmetic circuit 41 that realizes the display control function 415 deforms the treatment planning CT image CT_1 used in the planning of the initial radiation therapy plan based on the positional correspondence between the identified treatment planning MR images. This deformation is performed under the constraint that bone information is not deformed. Bone information includes information on the shape, size, and position of bones. In other words, the deformation of the treatment planning CT image CT_1 is the deformation of at least one of the tumor region, organ region, and soft tissue region on the treatment planning CT image CT_1. The deformed treatment planning CT image CT_1 is a virtual CT image CT_L for replanning. Note that the positional correspondence between the treatment planning CT image CT_1 and the treatment planning MR image MR_1 used in the planning of the initial radiation therapy plan is identified when the initial radiation therapy plan is formulated.

In step S207, the arithmetic circuit 41 that realizes the treatment planning function 411 uses the replanning virtual CT image CT_L and the newly acquired replanning MR image MR_L to create (replan) a new radiation therapy plan. At this time, similar to step S104 in FIG. 3, the electron density distribution or physical density distribution is calculated using the virtual CT image CT_L and the replanning MR image MR_L.

In this way, in radiation therapy for the Lth treatment session, a virtual CT image CT_L for replanning is generated from the treatment planning CT image CT_1 used to create the initial radiation therapy plan, based on the positional correspondence between the treatment planning MR images. Here, the display control function 415 can be expressed as including a CT value conversion function that converts the MRI pixel values of the newly collected replanning MR image MR_L into CT pixel values. In addition, in radiation therapy for the Lth treatment session, the CT values of the generated virtual CT image CT_L are converted into an electron density distribution or physical density distribution, and a new radiation therapy plan is created using this distribution.

Note that, although an example has been described in which a virtual CT image CT_L for replanning is created, this is not limiting. For example, the arithmetic circuit 41 that realizes the treatment planning function 411 may directly identify the electron density distribution or physical density distribution from a newly acquired MR image for replanning. Even with this configuration, the same effects as the above-mentioned configuration can be obtained.

The arithmetic circuit 41 that realizes the treatment planning function 411 transfers the new radiation therapy plan that was created using the virtual CT image CT_L to the radiation therapy information system. Subsequent radiation therapy is started when the latest radiation therapy plan at that time is identified on the radiation therapy information system 5, and the latest radiation therapy plan for that treatment session is received from the radiation therapy information system 5 by the radiation therapy device 6.

In step S208, the radiation therapy device 6 performs radiation therapy based on the latest radiation therapy plan at that time. When this step for the Lth treatment session is executed, the latest radiation therapy plan is the radiation therapy plan re-planned in step S207.

In addition, for each treatment session after the Lth session, radiation therapy will be carried out based on the radiation therapy plan replanned in this treatment session until the next replanning is performed.

In step S209, the calculation circuit 41 that realizes the judgment function 414 judges whether or not to end the radiation therapy in the same manner as the first treatment session.

(About the Mth treatment session)
Next, the Mth treatment session in FIG. 5 will be described.

The latest radiation therapy plan at the time when the Mth treatment session begins is the radiation therapy plan replanned in the Lth treatment session using the replanning virtual CT image CT_L and the replanning MR image MR_L. In addition, in the Mth treatment session, a case will be described as an example in which a new radiation therapy plan is not formulated (replanned) after the replanning MR image MR_M is collected. In this treatment session, the replanning MR image MR_L is an example of a first MR image. In addition, the replanning MR image MR_M is an example of a second MR image.

The radiation therapy in steps S201 to S205 for this treatment is the same as the first and Lth treatments. In this treatment, it is determined in step S201 that a replanning MR image MR_M is to be acquired. Then, in step S202, the replanning MR image MR_M is acquired, and in step S203, the replanning MR image MR_L and the replanning MR image MR_M are compared, and in step S204, the comparison result between the two replanning MR images is displayed. Also, in step S205, it is determined that no replanning is to be performed. Then, in step S208, radiation is administered based on the radiation therapy plan replanned for the Lth treatment. After the administration of radiation for the Lth treatment is completed, it is determined in step S209 that the radiation therapy is not to be terminated.

In this way, after a new replanning MR image MR_M is collected, if it is determined that replanning is not necessary, radiation therapy is administered based on the latest radiation therapy plan at that time, just like the first and Lth treatments.

(Regarding the Nth treatment session)
Next, the Nth treatment in FIG. 5 will be described.

The latest radiation therapy plan at the time when the Nth treatment session begins is the radiation therapy plan replanned in the Lth treatment session using the replanning virtual CT image CT_L and the replanning MR image MR_L. In addition, in the Nth treatment session, a case will be described as an example in which a new radiation therapy plan is formulated (replanned) after the replanning MR image MR_N is collected. In this treatment session, the replanning MR image MR_L is an example of a first MR image. In addition, the replanning MR image MR_N is an example of a second MR image.

The radiation therapy in steps S201 to S209 for this treatment round is the same as that in the Lth treatment round.
In this treatment, it is determined in step S201 that a re-planning MR image MR_N is to be acquired. Then, in step S202, a re-planning MR image MR_N is acquired, and in step S203, the re-planning MR image MR_L and the re-planning MR image MR_N are compared, and in step S204, the comparison result between the two re-planning MR images is displayed. Also, it is determined in step S205 that re-planning is to be performed. Then, in step S206, the treatment planning MR image MR_1 used in the planning of the initial radiation therapy plan is aligned with the newly acquired re-planning MR image MR_N, and a re-planning virtual CT image CT_N related to the Nth treatment is generated from the treatment planning CT image CT_1 used in the planning of the initial radiation therapy plan. Then, in step S207, a new radiation therapy plan is created using the virtual CT image CT_N and the re-planning MR image MR_N. Thereafter, radiation is administered based on the re-planned radiation therapy plan for this treatment session. After the administration of radiation for the Nth treatment session is completed, it is determined in step S209 that the radiation therapy is not to be ended.

In this way, in the radiation therapy according to this embodiment, the radiation therapy plan is changed according to the replanning MR images collected after the initial radiation therapy plan is created, and radiation therapy for each treatment session is performed based on the latest radiation therapy plan at that time. Thereafter, steps S201 to S209 are repeated until it is determined in step S209 that radiation therapy should be terminated. Radiation therapy is terminated when it is determined in step S209 that radiation therapy should be terminated.

In this way, the radiation therapy planning device 4 according to this embodiment determines whether or not replanning of the latest radiation therapy plan at that time is necessary by comparing the treatment planning MR image used to plan the latest radiation therapy plan with the newly collected treatment planning MR image. In addition, the radiation therapy planning device 4 according to this embodiment replans the radiation therapy plan using the CT image used to plan the initial radiation therapy plan and the newly collected treatment planning MR image. With this configuration, the radiation therapy plan can be appropriately replanned without using the treatment planning CT image that involves exposure during imaging. Note that the newly collected treatment planning MR image is taken after the latest radiation therapy plan has been planned at that time, and before the start of radiation administration in the treatment session according to that radiation therapy plan.

(First Modification)
Hereinafter, a radiation therapy planning apparatus and a radiation therapy planning method according to this modification will be described with reference to the drawings. Here, differences from the embodiment will be mainly described. In the following description, components having the same or substantially the same functions as those in the embodiment will be given the same reference numerals and will be described repeatedly only when necessary.

In the embodiment, a radiation therapy planning device 4 has been described as an example in which the comparison between the two treatment planning MR images is performed by visual comparison. However, the comparison between the two treatment planning MR images may also be performed by numerical comparison.

The following explanation uses radiation therapy for the Lth treatment session as an example.

In step S203 of the radiation therapy according to this modification, the arithmetic circuit 41 that realizes the image comparison function 413 calculates the volume indicated by the difference in the tumor area and/or the patient's body shape between the treatment planning MR image MR_1 and the re-planning MR image MR_L. In step S204, the arithmetic circuit 41 that realizes the display control function 415 displays the volume indicated by the difference in the tumor area and/or the patient's body shape together with the treatment planning MR image used in the latest radiation therapy plan. FIG. 7 is a diagram showing an example of the display image I24 related to the radiation therapy of FIG. 3 in which the volume indicated by the calculated difference in the tumor area is displayed together with the newly acquired re-planning MR image MR_L. In the example shown in FIG. 7, a plurality of areas A4 indicated by a site that was not a tumor area on the treatment planning MR image MR_1 but is a tumor area on the re-planning MR image MR_L are shown. As shown in FIG. 7, the volume indicated by the calculated difference in the tumor area is displayed, for example, as a table. The arithmetic circuit 41 realizing the display control function 415 generates a two-dimensional color image I21 for display so that a plurality of areas A4 indicating differences in the tumor region are displayed semi-transparently in the assigned color scheme on the replanning MR image MR_L on which MPR processing has been performed. The arithmetic circuit 41 realizing the display control function 415 generates a superimposed image I22 in which the color image I21 is superimposed on the replanning MR image MR_L on which MPR processing has been performed. The arithmetic circuit 41 realizing the display control function 415 also generates a display image I23 including a table summarizing the volumes indicated by the calculated differences in the tumor region. The arithmetic circuit 41 realizing the display control function 415 generates an image for display (display image I24) including the superimposed image I22 and image I23, and outputs it to the display circuit 44.

By displaying the superimposed image (display image I24) in this manner, users such as doctors can more clearly grasp differences in the tumor area and/or the patient's body shape.

(Second Modification)
The radiation therapy planning apparatus and the radiation therapy planning method according to this modification will be described below. Here, the differences from the first modification will be mainly described. In the following description, the components having the same or substantially the same functions as those in the first modification will be given the same reference numerals and will be described repeatedly only when necessary.

The volume indicated by the difference in the tumor area and/or the patient's body shape may be calculated as a relative value, not limited to an absolute value. The arithmetic circuit 41 that realizes the image comparison function 413 calculates the ratio of the volume change in the body shape difference to the volume of the part corresponding to the human body. Also, the display image I23 in FIG. 7 calculates the ratio of the volume change in the tumor area to the volume of the tumor area. At this time, the display image I23 in FIG. 7 includes a table showing the calculated volume change ratios. Even with this configuration, the same effect as described above can be obtained.

(Third Modification)
Hereinafter, a radiation therapy planning apparatus and a radiation therapy planning method according to this modification will be described with reference to the drawings. Here, differences from the embodiment will be mainly described. In the following description, components having the same or substantially the same functions as those in the embodiment will be given the same reference numerals and will be described repeatedly only when necessary.

In the embodiment, a radiation therapy planning device 4 has been described as an example in which the comparison between the two treatment planning MR images is performed by visual comparison. However, the comparison between the two treatment planning MR images may also be performed by numerical comparison.

The following explanation uses radiation therapy for the Lth treatment session as an example.

In step S203 of the radiation therapy according to this modification, the arithmetic circuit 41 that realizes the image comparison function 413 calculates the ratio of the change volume indicated by the difference in the tumor area and/or the patient's body shape between the treatment planning MR image MR_1 and the re-planning MR image MR_L. In step S204, the arithmetic circuit 41 that realizes the display control function 415 displays the DVH related to the volume indicated by the difference in the tumor area and/or the patient's body shape together with the newly acquired re-planning MR image MR_L. FIG. 8 is a diagram showing an example of the display image I34 related to the radiation therapy of FIG. 3 in which the newly acquired re-planning MR image MR_L and the calculated DVH related to the difference in the tumor area are displayed. The arithmetic circuit 41 that realizes the display control function 415 generates a two-dimensional color image I31 for display so that the tumor area TA and the risk area RA are displayed semi-transparently in the assigned color scheme on the re-planning MR image MR_L that has been subjected to MPR processing. In addition, the color image I31 further includes a dose distribution. The dose distribution is, for example, a dose distribution calculated based on a newly acquired re-planning MR image MR_L and a treatment planning CT image CT_1 used in planning the initial radiation therapy plan (the latest radiation therapy plan at that time). The arithmetic circuit 41 realizing the display control function 415 generates a superimposed image I32 in which the color image I31 is superimposed on the re-planning MR image MR_L that has been subjected to MPR processing. The arithmetic circuit 41 realizing the display control function 415 also generates a display image I33 including the DVH based on the volume ratio indicated by the calculated difference in the tumor area and/or the patient's body shape. For example, the DVH is expressed by taking the dose on the horizontal axis and the volume % on the vertical axis. For example, when 54 Gy or more of radiation is administered to 100% of the tumor area TA, the DVH is 100% from 0 to 54 Gy. Furthermore, if 90% of the tumor area TA is administered radiation of 60 Gy or more, the radiation gradually decreases from there to 90% at 60 Gy. Furthermore, if there is no tumor area TA administered radiation of 63 Gy or more, the radiation rapidly decreases from there to 0 at 63 Gy. The arithmetic circuit 41 that realizes the display control function 415 generates an image for display (display image I34) including the superimposed image I32 and image I33, and outputs it to the display circuit 44. Note that the display image I34 may further include an image for display including the DVH of the risk area.

By displaying the superimposed image (display image I34) in this manner, users such as doctors can more clearly grasp differences in the tumor area and/or the patient's body shape.

(Fourth Modification)
The radiation therapy planning apparatus and the radiation therapy planning method according to this modification will be described below. Here, the differences from the embodiment will be mainly described. In the following description, components having the same or substantially the same functions as those in the embodiment will be given the same reference numerals and will be described repeatedly only when necessary.

In the embodiment, the radiation therapy planning device 4 is described as an example in which the comparison of two treatment planning MR images is performed for areas showing differences in tumor area and/or patient body shape. However, the comparison of two treatment planning MR images may also be performed by comparing numerical values related to dose distribution.

The following explanation uses radiation therapy for the Lth treatment session as an example.

For example, the dose distribution according to the initial radiation therapy plan (the latest radiation therapy plan at that time) is compared with the dose distribution calculated based on the newly collected replanning MR image MR_L and the treatment planning CT image CT_1 used in the planning of the initial radiation therapy plan (the latest radiation therapy plan at that time). In this comparison, the arithmetic circuit 41 that realizes the image comparison function 413 aligns the treatment planning MR image MR_1 corresponding to the treatment planning CT image CT_1 with the replanning MR image MR_L. After that, the arithmetic circuit 41 that realizes the image comparison function 413 recalculates the dose distribution (administered dose) based on the initial radiation therapy plan (the latest radiation therapy plan at that time) and the newly collected replanning MR image MR_L. For example, when the patient's body shape changes, the human body passage length of radiation irradiation changes. In other words, in the radiation therapy according to this modified example, the change in this passage length can be calculated to compare the patient's body shape. For example, the arithmetic circuit 41 realizing the image comparison function 413 calculates the length of the path of radiation passing through the human body based on the recalculated dose distribution (administered dose). The arithmetic circuit 41 realizing the image comparison function 413 further calculates the amount of change between the length of the path of radiation passing through the human body according to the initial radiation therapy plan (the latest radiation therapy plan at that time) and the length of the path of radiation passing through the human body calculated in this step. In the radiation therapy according to this modified example, for example, the largest value among the calculated changes in the path length is displayed together with the replanning MR image MR_L that has been subjected to MPR processing. In other words, the arithmetic circuit 41 realizing the display control function 415 generates a display image that displays the calculated amount of change together with the replanning MR image MR_L that has been subjected to MPR processing. Even with this configuration, the treatment planning MR images can be compared in the same manner as described above.

The identified tumor area or risk area may be further superimposed. The DVH of the tumor area or risk area may also be further displayed. With this configuration, a user such as a doctor can grasp the differences in the tumor area and/or the patient's body shape in more detail.

(Fifth Modification)
The radiation therapy planning apparatus and the radiation therapy planning method according to this modification will be described below. Here, the differences from the fourth modification will be mainly described. In the following description, the same reference numerals are used for components having the same or substantially the same functions as those in the fourth modification, and the description will be repeated only when necessary.

The dose distribution may be compared in more detail. For example, a dose distribution based on the latest treatment plan is calculated based on the newly acquired replanning MR image MR_L and the treatment planning CT image CT_1 used in the planning of the first radiation therapy plan (the latest radiation therapy plan at that time). The calculated dose distribution is displayed on the newly acquired replanning MR image MR_L together with the tumor area and the risk area, for example, as shown in FIG. 8. Furthermore, in the radiation therapy according to this modified example, a transformation map is created that transforms the treatment planning MR image MR_1 used in the planning of the first radiation therapy plan (the latest radiation therapy plan at that time) into the newly acquired replanning MR image MR_L based on the body shape, organ shape, tumor area shape, etc. The calculated dose distribution is compared between positions identified as being approximately the same site in the created transformation map. At this time, the result of the comparison is the change in dose [Gy] between the same positions identified by the created transformation map. In radiation therapy according to this modified example, for example, the calculated change in dose is displayed on the replanning MR image MR_L that has been subjected to MPR processing. With this configuration, it is possible to compare the treatment planning MR images in even more detail.

The identified tumor area or risk area may be further superimposed. The DVH of the tumor area or risk area may also be further displayed. For example, the DVH of the tumor area or risk area identified when the latest radiation therapy plan was created is displayed as a red and black dotted line, respectively. Furthermore, the DVH considering the dose change caused by the change in body shape or the change in the tumor area is displayed as a red and black solid line, respectively. In other words, the DVH related to the latest radiation therapy plan at that time is displayed at the same time as the calculated DVH. With this configuration, a user such as a doctor can grasp the differences in the tumor area and/or the patient's body shape in more detail.

(Sixth Modification)
The radiation therapy planning apparatus and the radiation therapy planning method according to this modification will be described below. Here, the differences from the embodiment will be mainly described. In the following description, components having the same or substantially the same functions as those in the embodiment will be given the same reference numerals and will be described repeatedly only when necessary.

In the embodiment, a radiation therapy planning device 4 has been described as an example that generates a virtual CT image for replanning by deforming a CT image for treatment planning based on the positional correspondence between two MR images for treatment planning. However, the generation of a virtual CT image for replanning is not limited to this.

The following explanation uses radiation therapy for the Lth treatment session as an example.

For example, in the radiation therapy according to this modified example, a conversion table between MRI pixel values and CT values is created based on the treatment planning CT image CT_1 and the treatment planning MR image MR_1 used in the planning of the first radiation therapy plan (latest radiation therapy plan). That is, the treatment planning function 411 includes a CT value conversion function that converts the MRI pixel values of the newly collected treatment planning MR image to CT values. Then, using the created conversion table, the MRI pixel values of the newly collected re-planning MR image MR_L are converted to CT values. Re-planning is performed based on the converted CT values. However, bone information cannot be sufficiently extracted from the MR image. On the other hand, unlike changes in body shape, bone information does not change significantly in a few weeks. Therefore, in the radiation therapy according to this modified example, bone information is extracted from the treatment planning CT image CT_1 used in the planning of the first radiation therapy plan (latest radiation therapy plan). The extracted bone information is synthesized with the newly collected re-planning MR image MR_L and displayed. In addition, a virtual CT image for replanning may be generated based on the converted CT values, and the extracted bone information may be synthesized into the virtual CT image. Even with this configuration, the same effect as described above can be obtained.

The bone information used for synthesis is not limited to bone information extracted from the treatment planning CT image CT_1, but may be, for example, a standard hip joint, etc., if it is a part with little individual variation, such as the hip joint.

(Seventh Modification)
The radiation therapy planning apparatus and the radiation therapy planning method according to this modification will be described below. Here, the differences from the sixth modification will be mainly described. In the following description, the same reference numerals are used for components having the same or substantially the same functions as those in the sixth modification, and redundant description will be given only when necessary.

The relationship between MRI pixel values and CT values may differ depending on the organ. For this reason, a conversion table between MRI pixel values and CT values may be created for each part. The MRI pixel values of the newly acquired re-planning MR image MR_L are converted to CT values using the conversion table created for each part. With this configuration, a virtual CT image for re-planning can be generated with greater accuracy.

(Eighth Modification)
The radiation therapy planning apparatus and the radiation therapy planning method according to this modification will be described below. Here, the differences from the embodiment will be mainly described. In the following description, components having the same or substantially the same functions as those in the embodiment will be given the same reference numerals and will be described repeatedly only when necessary.

In the embodiment, a radiation therapy planning device 4 has been described as an example that generates a virtual CT image for replanning by deforming a CT image for treatment planning based on the positional correspondence between two MR images for treatment planning. However, the generation of a virtual CT image for replanning is not limited to this.

The following explanation uses radiation therapy for the Lth treatment session as an example.

For example, in radiation therapy according to this modified example, the treatment planning MR image MR_1 used in creating the initial radiation therapy plan is aligned with the newly acquired re-planning MR image MR_L in the same manner as in the above embodiment. The alignment is performed based on organ information, tumor information, body shape, and the like. Next, it is identified where an arbitrary point on the re-planning MR image MR_L corresponds on the treatment planning MR image MR_1. These processes are generally used in warping and the like. Here, the correspondence between the treatment planning CT image CT_1 and the treatment planning MR image MR_1 is identified when the initial radiation therapy plan is created, etc. After that, the following process is performed for each voxel on the re-planning MR image MR_L.

First, voxels are identified on the treatment planning MR image MR_1. Next, voxels are identified on the treatment planning CT image CT_1. Next, the CT values of the identified voxels on the treatment planning CT image CT_1 are assigned to voxel values in the re-planning MR image MR_L. In radiation therapy according to this modified example, these processes are performed on all voxels in the re-planning MR image MR_L, thereby generating a virtual CT image for re-planning that corresponds to the current patient condition.

(Ninth Modification)
The radiation therapy planning apparatus and the radiation therapy planning method according to this modification will be described below. Here, the differences from the embodiment will be mainly described. In the following description, components having the same or substantially the same functions as those in the embodiment will be given the same reference numerals and will be described repeatedly only when necessary.

The following explanation uses radiation therapy for the Lth treatment session as an example.

For example, in the radiation therapy according to this modification, a virtual CT image CT_L for replanning may be generated from a newly collected replanning MR image MR_L using mutual information. At this time, the alignment between the treatment planning MR image MR_1 used in the planning of the initial radiation therapy plan and the newly collected replanning MR image MR_L is identified using mutual information. Here, the mutual information represents, for example, the amount of information about the pixel values of the replanning MR image MR_L obtained by knowing the pixel values of the treatment planning MR image MR_1. In other words, when the mutual information is high, the correlation between the two treatment planning MR images is high. Also, as in the sixth modification, the extracted bone information is synthesized in the replanning MR image MR_L. Even with such a configuration, the same effect as described above can be obtained. Also, here, the virtual CT image CT_L is created from the replanning MR image MR_L using mutual information, but it may be created using deep learning. One example of the deep learning algorithm used in this case is GAN (Generative Adversarial Network). Although the virtual CT image created with GAN contains bone information, the reliability of the bone information is low. Therefore, it is desirable to replace the bone information with the information of the treatment planning CT image CT_1 in the virtual CT image created with GAN.

(Tenth Modification)
The radiation therapy planning apparatus and radiation therapy planning method according to this modification will be described below. Here, differences from the embodiment will be mainly described. In the following description, components having the same or substantially the same functions as those in the embodiment will be given the same reference numerals and will be described repeatedly only when necessary.

In the radiation therapy according to this modified example, when it is determined that replanning of the radiation therapy plan is necessary, a replanning CT image may be collected at any timing. At this time, replanning is performed using a newly collected replanning CT image. Here, the replanning CT image is a recollected treatment planning CT image, and is a treatment planning CT image used for replanning the radiation therapy plan. With this configuration, for example, even if there is a possibility that bone information has changed, appropriate replanning can be performed, and the patient's exposure can be reduced compared to when a replanning CT image is captured for each replanning. Alternatively, a site estimated to be bone may be extracted from the first MR image and the second MR image, and the bone structures may be compared, and a replanning CT image may be collected only when the difference in bone structure between the MR images is large (when it is determined that the bone information has changed).

In the above-mentioned embodiment and modified example, the case where the radiation therapy plan is created in the radiation therapy planning device 4 has been described as an example, but this is not limited to the above. For example, some or all of the functions realized by the arithmetic circuit 41 executing the radiation therapy planning program may be realized in the treatment planning X-ray CT device 1, the treatment planning MRI device 2, the radiation therapy device 6, or a server provided outside the radiation therapy system 100. In other words, some or all of the arithmetic circuit 41 may be provided in these. In addition, the function of converting the CT value into the attenuation coefficient in the beam used for radiation therapy may be executed by the treatment planning X-ray CT device 1 or the radiation therapy planning device 4.

The radiation therapy system 100 may further include a Positron Emission Tomography (PET) device, a Single Photon Emission Computed Tomography (SPECT) device, a PET-CT device, an ultrasound diagnostic device, an X-ray angiography device, etc. On the other hand, the treatment planning MR images and treatment planning CT images may be acquired from outside the radiation therapy system 100. In other words, the radiation therapy system 100 does not need to include a treatment planning X-ray CT device 1 or a treatment planning MRI device 2.

(Eleventh Modification)
The radiation therapy planning apparatus and the radiation therapy planning method according to this modification will be described below. Here, the differences from the embodiment will be mainly described. In the following description, components having the same or substantially the same functions as those in the embodiment will be given the same reference numerals and will be described repeatedly only when necessary.

9 is a diagram showing the image types used in each treatment of radiation therapy according to the eleventh modified example. As shown in FIG. 9, in the first radiation therapy plan, a treatment planning CT image CT_1 is acquired, and a radiation therapy plan is made based on the treatment planning CT image CT_1. No treatment planning MR image is acquired. In any treatment from the second time onwards, a planning MR image is collected as in the above embodiment, and the tumor area and/or the patient's body shape are compared between the re-planning MR image and the treatment planning CT image CT_1. Next, the presence or absence of re-planning is determined based on the user's judgment or the magnitude relationship between the difference in the tumor area and/or the patient's body shape and a threshold value. If it is determined that re-planning is necessary, a virtual CT image, which is a pseudo CT image corresponding to the re-planning MR image, is generated based on the re-planning MR image and the treatment planning CT image CT_1. Then, the radiation therapy plan is re-planned based on the virtual CT image. In addition, an electron density image or a physical density image may be generated based on the virtual CT image, and the radiation therapy plan may be re-planned based on the electron density image or the physical density image.

As described above, according to the eleventh modified example, the tumor area and/or the patient's body shape is compared between the treatment planning CT image and the re-planning MR image. This method makes it possible to detect changes in the shape of the tumor area and/or the patient's body shape between the time of treatment planning and each treatment session, even if the treatment planning MR image does not exist.

(Twelfth Modification)
The radiation therapy planning apparatus and the radiation therapy planning method according to this modification will be described below. Here, the differences from the embodiment will be mainly described. In the following description, components having the same or substantially the same functions as those in the embodiment will be given the same reference numerals and will be described repeatedly only when necessary.

Figure 10 is a diagram showing the types of images used in each radiation therapy session in the 12th modified example. As shown in Figure 10, in the 12th modified example, both MR images and ultrasound images are used to assist in creating a treatment plan.

As shown in FIG. 10, for example, a treatment planning CT image CT_1 and a treatment planning MR image MR_1 are acquired, and an initial radiation therapy plan is created based on the treatment planning CT image CT_1 and the treatment planning MR image MR_1.

In any treatment session from the second onwards, the patient is ultrasonically imaged using an ultrasonic diagnostic device in order to monitor the tumor area and/or the patient's body shape. For example, a processing circuit of the ultrasonic diagnostic device ultrasonically images multiple three-dimensional regions within the patient's body via an ultrasonic probe, and generates multiple three-dimensional ultrasonic images (volume data) corresponding to the multiple three-dimensional regions. For example, a three-dimensional region corresponding to the imaging area of the treatment planning CT image CT_1 and the treatment planning MR image MR_1 is divided and ultrasonically imaged multiple times. Note that the three-dimensional region to be ultrasonically imaged may be larger or smaller than the imaging area of the treatment planning CT image CT_1 and the treatment planning MR image MR_1.

The ultrasound probe is provided with a position sensor, which detects the position of the ultrasound probe during ultrasound imaging. The position data of the ultrasound probe is associated with each three-dimensional ultrasound image. The processing circuit of the ultrasound diagnostic device stitches together multiple three-dimensional ultrasound images according to the position data of the ultrasound probe, thereby generating a three-dimensional ultrasound image of a wide three-dimensional area corresponding to the imaging area of the treatment planning CT image CT_1 and the treatment planning MR image MR_1. Hereinafter, the generated three-dimensional ultrasound image will be referred to as a re-planning ultrasound image. The generated re-planning ultrasound image is acquired by the radiation therapy planning device 4.

The tumor area and/or the patient's body shape are compared between the re-planning ultrasound image of each treatment session and the treatment planning MR image MR_1. Note that since the ultrasound probe is in contact with the patient, the patient's body surface is hardly drawn in the re-planning ultrasound image. Therefore, the calculation circuit 41 only needs to compare the tumor area between the re-planning ultrasound image of each treatment session and the treatment planning MR image MR_1.

Next, it is determined whether or not there has been a change in the shape of the tumor region based on the user's judgment and the magnitude relationship between the difference in the tumor region and the threshold value. If it is determined that there has been a change in the shape of the tumor region, a replanning MR image MR_N is generated by the treatment planning MRI device 2 and acquired by the radiation therapy planning device 4 in order to observe the shape change in more detail. As in the embodiment, the arithmetic circuit 41 of the radiation therapy planning device 4 compares the tumor region and/or the patient's body shape between the treatment planning MR image MR_1 and the replanning MR image MR_N. Then, based on the user's judgment and the magnitude relationship between the difference in the tumor region and the threshold value, it is determined whether or not there is a need for replanning.

If it is determined that replanning is necessary, a virtual CT image, which is a pseudo CT image corresponding to the replanning MR image MR_N, is generated based on the replanning MR image MR_N and the treatment planning CT image CT_1. Then, the radiation therapy plan is replanned based on the virtual CT image. Note that an electron density image or a physical density image may be generated based on the virtual CT image, and the radiation therapy plan may be replanned based on the electron density image or the physical density image. Also, a virtual CT image may be generated based on the replanning MR image MR_N, the treatment planning CT image CT_1, and the replanning ultrasound image US_N, or a virtual CT image may be generated based on the treatment planning CT image CT_1 and the replanning ultrasound image US_N.

In this way, according to the 12th modified example, it is possible to obtain replanning images using ultrasound imaging, which is simpler and less burdensome for the patient than MR imaging.

In the above process, if a change in the shape of the tumor area is determined by comparing the re-planning ultrasound image of each treatment session with the treatment planning MR image MR_1, a re-planning MR image MR_N is generated, but the re-planning MR image MR_N does not have to be generated. In this case, a virtual CT image may be generated based on the treatment planning CT image CT_1 and the re-planning ultrasound image US_N.

In addition, in the above process, it is assumed that ultrasound images are not acquired for the treatment plan. However, ultrasound images for the treatment plan may be acquired. In this case, the initial radiation therapy plan may be created based on the CT images for the treatment plan, or based on the CT images for the treatment plan and the ultrasound images for the treatment plan, or based on the CT images for the treatment plan, the ultrasound images for the treatment plan, and the MR images for the treatment plan. Also, the re-planning ultrasound images may be compared with the ultrasound images for the treatment plan for the tumor area.

In the above process, MR images for treatment planning do not need to be acquired. In this case, the initial radiation therapy plan may be created based on the CT images for treatment planning. Furthermore, the re-planning ultrasound images may be compared with the CT images for treatment planning for the tumor area.

(General remarks)
According to some of the above-mentioned embodiments and modifications, the radiation therapy planning device 4 includes a comparison unit and a generation unit. The comparison unit compares a first treatment planning medical image of a patient used in the radiation therapy plan of the patient with a post-planning medical image of the patient captured after the radiation therapy plan. The generation unit generates a modified treatment plan image based on the second treatment planning medical image and the post-planning medical image used in the radiation therapy plan according to a result of the comparison by the comparison unit.

The contrast of the treatment plan change image corresponds to that of the second treatment plan medical image, and the patient's internal body structures depicted correspond to those depicted in the post-planning medical image. In other words, after planning, a medical image can be generated that corresponds to the contrast of the second treatment plan medical image and depicts the patient's internal body structures in the post-planning medical image, without imaging the patient with a medical imaging diagnostic device for generating the second treatment plan medical image.

As an example, the first medical image for treatment planning is a treatment planning MR image or a treatment planning ultrasound image of the patient, the second medical image for treatment planning is a treatment planning CT image of the patient, and the post-planning medical image is a post-planning MR image or a post-planning ultrasound image of the patient. In this case, the comparison unit compares the treatment planning MR image with the post-planning MR image or the post-planning ultrasound image. As another example, the first medical image for treatment planning and the second medical image for treatment planning are treatment planning CT images of the patient, and the post-planning medical image is a post-planning MR image or a post-planning ultrasound image of the patient. In this case, the comparison unit compares the treatment planning CT image with the post-planning MR image or the post-planning ultrasound image. According to these examples, it is possible to generate a modified treatment plan image that corresponds to the contrast of X-ray CT and depicts the internal structure of the patient in the post-planning medical image without exposing the patient to X-rays.

Specifically, the generating unit generates a virtual CT image, an electron density image, or a physical density image as a treatment plan change image based on the treatment planning CT image and the planned MR image or the planned ultrasound image. More specifically, the generating unit generates a virtual CT image, an electron density image, or a physical density image based on the bone region in the treatment planning CT image and the tumor region and/or the patient's body shape in the planned MR image or the planned ultrasound image. The generating unit converts the pixel values of the tumor region into CT values, and synthesizes the bone region with the replaced planned MR image or the planned ultrasound image to generate a virtual CT image. The generating unit generates an electron density image or a physical density image by converting the CT value of each pixel of the virtual CT image into electron density or physical density.

According to at least one of the embodiments described above, processing related to replanning a radiation therapy plan can be performed accurately and with low radiation exposure.

The term "processor" used in the above description means, for example, a circuit such as a CPU, a GPU, an application specific integrated circuit (ASIC), or a programmable logic device (PLD). PLDs include simple programmable logic devices (SPLDs), complex programmable logic devices (CPLDs), and field programmable gate arrays (FPGAs). The processor realizes its function by reading and executing a program stored in a memory circuit. The memory circuit in which the program is stored is a non-transitory computer-readable recording medium. Note that instead of storing a program in a memory circuit, the program may be directly embedded in the circuit of the processor. In this case, the processor realizes its function by reading and executing the program embedded in the circuit. Also, instead of executing a program, a function corresponding to the program may be realized by a combination of logic circuits. Note that each processor in this embodiment is not limited to being configured as a single circuit for each processor, but may be configured as a single processor by combining multiple independent circuits to realize its function. Furthermore, multiple components in Figures 1 and 2 may be integrated into a single processor to achieve the functions.

Although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are within the scope of the invention and its equivalents as set forth in the claims, as well as the scope and spirit of the invention.

1... X-ray computed tomography (CT) device for treatment planning 2... Magnetic resonance imaging (MRI) device for treatment planning 3... PACS
4...Radiation therapy planning device 5...Radiation therapy information system 6...Radiation therapy device 41...Arithmetic circuit 42...Image processing circuit 43...Communication circuit 44...Display circuit 45...Input circuit 46...Memory circuit 100...Radiation therapy system 411...Treatment planning function 412...Image acquisition function 413...Image comparison function 414...Judgment function 415...Display control function

Claims (15)

a comparison unit that compares a first treatment planning medical image of the patient used in a radiation therapy plan for the patient with a post-planning medical image of the patient taken after the radiation therapy plan;
a generating unit that generates a modified treatment plan image based on the second treatment planning medical image used in the radiation therapy plan and the post-planning medical image according to a result of the comparison by the comparing unit ,
the first medical image for treatment planning is a magnetic resonance (MR) image or an ultrasound image for treatment planning of the patient;
the second treatment planning medical image is a treatment planning CT image of the patient;
the planned medical images are planned MR images or planned ultrasound images of the patient;
the comparison unit compares the treatment planning MR image with the post-planning MR image or the post-planning ultrasound image;
the generating unit generates, as the treatment plan change image, a virtual CT image, an electron density image, or a physical density image based on the treatment planning CT image and the post-planning MR image or the post-planning ultrasound image;
Radiation treatment planning equipment. a comparison unit that compares a first treatment planning medical image of the patient used in a radiation therapy plan for the patient with a post-planning medical image of the patient taken after the radiation therapy plan;
a generating unit that generates a modified treatment plan image based on the second treatment planning medical image used in the radiation therapy plan and the post-planning medical image according to a result of the comparison by the comparing unit ,
the first medical image for treatment planning and the second medical image for treatment planning are CT images for treatment planning of the patient;
the planned medical images are planned MR images or planned ultrasound images of the patient;
the comparison unit compares the treatment planning CT image with the post-planning MR image or the post-planning ultrasound image;
the generating unit generates, as the treatment plan change image, a virtual CT image, an electron density image, or a physical density image based on the treatment planning CT image and the post-planning MR image or the post-planning ultrasound image;
Radiation treatment planning equipment. The radiation therapy planning device according to claim 1, further comprising a planning unit that changes the radiation therapy plan based on the treatment plan change image. 3. The radiation therapy planning device according to claim 1, wherein the generation unit generates the virtual CT image, electron density image, or physical density image based on a bone region in the treatment planning CT image and a tumor region and/or a patient body shape in the post-planning MR image or the post-planning ultrasound image. 5. The radiation therapy planning device according to claim 4, wherein the generation unit converts pixel values of the tumor region into CT values to generate a converted post-planning MR image or a post-planning ultrasound image, and combines the converted post-planning MR image or the converted post-planning ultrasound image with the bone region to generate the virtual CT image. The radiation therapy planning apparatus according to claim 5 , wherein the generating unit generates the electron density image or the physical density image by converting a CT value of each pixel of the virtual CT image into an electron density or a physical density. The comparison unit identifies a tumor region and/or a patient body shape of the patient between the first treatment planning medical image and the post-planning medical image,
The generating unit generates the treatment plan change image when the degree of change in the identified tumor area and/or the patient's body shape exceeds a standard.
The radiation therapy planning system according to any one of claims 1 to 6 . Further comprising a display unit,
the comparison unit aligns the first treatment planning medical image and the post-planning medical image, and calculates a first difference in a tumor area and a second difference in a patient body shape between the first treatment planning medical image and the post-planning medical image;
the display unit displays an area indicated by the first difference and an area indicated by the second difference in different colors on a display image based on the post-planning medical image.
The radiation therapy planning system of claim 1. Further comprising a display unit,
the comparison unit aligns the first treatment planning medical image and the post-planning medical image, and calculates a first difference in a tumor area and a second difference in a patient body shape between the first treatment planning medical image and the post-planning medical image;
the display unit displays at least one of a volume of an image region corresponding to the first difference and the second difference and a ratio occupied by the image region corresponding to the first difference and the second difference together with a display image based on the post-planning medical image.
The radiation therapy planning system of claim 1. 2. The radiation therapy planning device according to claim 1, wherein the comparison unit aligns the first treatment planning medical image and the post-planning medical image, and calculates an administration dose based on the latest radiation therapy plan at that time, the first treatment planning medical image, and the post-planning medical image. Further comprising a display unit,
the comparison unit calculates an amount of change in a length of a trajectory of radiation passing through a human body between the first treatment planning medical image and the post-planning medical image based on the calculated administration dose;
The display unit displays the amount of change together with a display image based on the post-planning medical image.
The radiation therapy planning system of claim 10 . Further comprising a display unit,
The comparison unit further calculates DVH of the tumor region and/or the risk region based on the post-planning medical image,
The display unit displays the DVH together with a display image based on the post-planning medical image.
The radiation therapy planning system of claim 10 . The radiation therapy planning apparatus according to claim 12 , wherein the display unit displays a DVH related to a currently latest radiation therapy plan together with the DVH. The radiation therapy planning device according to claim 1, further comprising a planning unit that deforms the second treatment planning medical image based on the post-planning medical image and re-plans the radiation therapy plan using the deformed second treatment planning medical image. 15. The radiation therapy planning apparatus according to claim 14, wherein the planning unit performs distortion correction on the planned medical image, and deforms at least one of a tumor region, an organ region, and a soft tissue region included in the second treatment planning medical image based on the distortion- corrected planned medical image.