Radiotherapy apparatus controller and radiation irradiation method

A radiotherapy apparatus controller includes: a movement collection section; a sensor control section configured to change a first time interval in which a second sensor measures a position of an irradiation area in the subject, based on the movement information; and an irradiation control section. The movement collection section collects movement information indicating a movement of a subject from a first sensor. The sensor control section changes a first time interval in which a second sensor measures a position of an irradiation area in the subject, based on the movement information. The irradiation control section controls a radiotherapy apparatus such that therapeutic radiation irradiated to the irradiation area is changed based on the position.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority from Japanese patent application No. 2008-019801 filed on Jan. 30, 2008, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiotherapy apparatus controller and a radiation irradiation method, and especially relates to a radiotherapy apparatus controller and a radiation irradiation method used when a patient is treated by irradiating an affected area with a radiation.

2. Description of Related Art

Radiotherapy for treating a patient by irradiating a therapeutic radiation to an affected area (a tumor) is commonly known. A radiation generated by the bremsstrahlung is exemplified as the therapeutic radiation. A method of an irradiation for a wider area than the affected area in consideration of a moving region where the affected area moves, a respiratory-gated radiotherapy (a gated irradiation), and a method of a dynamic tumor-tracking irradiation are known as the radiotherapy. The respiratory-gated radiotherapy is a method for irradiating the therapeutic radiation and stopping the irradiation based on a position of an affected area. The radiotherapy of the dynamic tumor-tracking irradiation is a method for changing an emitting direction or an irradiation field of the therapeutic radiation based on a position of an affected area. The respiratory-gated radiotherapy and the radiotherapy of the dynamic tumor-tracking irradiation are desirable since a dose of the therapeutic radiation irradiated to normal cells other than the affected area is smaller as compared to the radiotherapy of the irradiation for the wider area than the affected area.

In the respiratory-gated radiotherapy and the radiotherapy of the dynamic tumor-tracking irradiation described above, the position of the affected area is required to be consecutively measured. As a measurement method, an X-ray photography method and a MRI (Magnetic Resonance Imaging) method are exemplified. For a target (a lung tumor is exemplified) rapidly moving because of a physiologic movement such as a breath and a pulsating, it is required to shorten a period in which a target position in a body is observed (to increase frequency of the observation) in order to accurately know the target position. The more frequency of the X-ray photography increases, the more a radiation exposure of X-ray for the X-ray photography of a patient increases. Radiotherapy is desired in which a radiation exposure of a patient other than the therapeutic radiation can be reduced.

The law restricts a simultaneous irradiation of the X-ray used for the X-ray photography and the therapeutic radiation to a patient. The MRI needs to operate for a long period of time in order to accurately measure a position of an affected area. The MRI further needs to time-share the observing an affected area by the MRI and the emission of the therapeutic radiation in order to generate a strong magnetic field. For this reason, the more frequency of the observing a position of an affected area increases, the more time for which the therapeutic radiation is irradiated is reduced, and a treatment time will become longer. It is desired to reduce the treatment time of the radiotherapy and to reduce a strain of a patient.

It is desired to more accurately observe a position of an affected area and to reduce frequency of the observing the position of the affected area.

U.S. Pat. No. 6,144,875 discloses a technique for, as for a target moving by a breath, intermittently obtaining a position of the target inside a body by a first sensor and subsequently obtaining a position of the target outside the body by a second sensor, relating the two positions, and estimating the position of the target inside the body based on the position of the target outside the body and irradiating.

U.S. Pat. No. 6,307,914 discloses a technique for, as for a target moving by a breath, performing an X-ray photography at a predetermined frame rate by using two imagers, calculating a three-dimensional position of a marker inside a body base on the images, and irradiating a radiation to the three-dimensional position to treat it.

SUMMARY

An object of the present invention is to provide a radiotherapy apparatus controller and a radiation irradiation method which more reduce frequency of observing a position of an affected area and observe the position of the affected area with more high accuracy.

Another object of the present invention is to provide a radiotherapy apparatus controller and a radiation irradiation method which reduce a radiation exposure by radiation other than the therapeutic radiation.

Another object of the present invention is to provide a radiotherapy apparatus controller and a radiation irradiation method which reduce a treatment time of the radiotherapy.

In a first aspect of the present invention, the present invention provides a radiotherapy apparatus controller including: a movement collection section configured to collect movement information indicating a movement of a subject from a first sensor; a sensor control section configured to change a first time interval in which a second sensor measures a position of an irradiation area in the subject, based on the movement information; and an irradiation control section configured to control a radiotherapy apparatus such that therapeutic radiation irradiated to the irradiation area is changed based on the position.

In the radiotherapy apparatus controller, the second sensor may measure the position based on a transmission radiation transmitted through the subject.

In the radiotherapy apparatus controller, the irradiation control section may control the radiotherapy apparatus such that an irradiation direction of the therapeutic radiation is changed based on the position.

In the radiotherapy apparatus controller, the first time interval may be longer than a second time interval in which the first sensor measures the movement of the subject.

The radiotherapy apparatus controller may further include: a target movement calculation section configured to calculate a rate of change of the position based on the movement information. The sensor control section may change the first time interval based on the rate of change.

The radiotherapy apparatus controller may further include: a correlation calculation section configured to calculate a table correlating a plurality of the movement information with a plurality of the positions based on the movement information and the position. The target movement calculation section may calculate the rate of change based on an estimation position corresponding to the movement information in the plurality of the positions with reference to the table.

The radiotherapy apparatus controller may further include: a target movement calculation section configured to calculate a period of the movement based on the movement information. The sensor control section may change the first time interval based on the period.

In the radiotherapy apparatus controller, the irradiation control section may control the radiotherapy apparatus such that the therapeutic radiation is irradiated in a plurality of time periods in which the second sensor does not measure the position. When a first time period of the plurality of time periods may be longer than a second time period of the plurality of time periods, a first irradiation period in which the therapeutic radiation is irradiated in the first time period may be longer than a second irradiation period in which the therapeutic radiation is irradiated in the second time period.

In a second aspect of the present invention, the present invention provides a radiotherapy system including: the radiotherapy apparatus controller according to any of those as mentioned above; the first sensor; the second sensor; and the radiotherapy apparatus.

In a third aspect of the present invention, the present invention provides a radiation irradiation method including: collecting movement information indicating a movement of a subject from a first sensor; changing a first time interval in which a second sensor measures a position of an irradiation area in the subject, based on the movement information; and controlling a radiotherapy apparatus such that therapeutic radiation irradiated to the irradiation area is changed based on the position.

In the radiation irradiation method, the second sensor may measure the position based on a transmission radiation transmitted through the subject.

In the radiation irradiation method, the controlling step may include: controlling the radiotherapy apparatus such that an irradiation direction of the therapeutic radiation is changed based on the position.

In the radiation irradiation method, the first time interval may be longer than a second time interval in which the first sensor measures the movement of the subject.

The radiation irradiation method may further include: calculating a rate of change of the position based on the movement information. The changing step may include: changing the first time interval based on the rate of change.

The radiation irradiation method may further include: calculating a table correlating a plurality of the movement information with a plurality of the positions based on the movement information and the position. The calculating the rate of change step may include: calculating the rate of change based on an estimation position corresponding to the movement information in the plurality of the positions with reference to the table.

The radiation irradiation method may further include: calculating a period of the movement based on the movement information. The changing step may include: changing the first time interval based on the period.

In the radiation irradiation method, the controlling step may include: controlling the radiotherapy apparatus such that the therapeutic radiation is irradiated in a plurality of time periods in which the second sensor does not measure the position. When a first time period of the plurality of time periods is longer than a second time period of the plurality of time periods, a first irradiation period in which the therapeutic radiation is irradiated in the first time period is longer than a second irradiation period in which the therapeutic radiation is irradiated in the second time period.

In a fourth aspect of the present invention, the present invention provides a computer program product with program code means for carrying out all steps according to any of those as mentioned above if the program runs on a computer. The computer program product with program code means according to that as mentioned above which are stored on a storage means which can be read by the computer.

A radiotherapy apparatus controller and a radiation irradiation method according to the present invention can reduce a frequency of measuring a position of an irradiated part and measure the position of the irradiated part with high accuracy by lengthening a time interval for measuring the irradiated part when a movement of the irradiated part estimated on the basis of a motion of a subject is slow.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to drawings, an embodiment of a radiotherapy apparatus controller according to the present invention will be described. The radiotherapy apparatus controller2is applied for a radiotherapy system1as shown inFIG. 1. The radiotherapy system1includes the radiotherapy apparatus controller2, a radiotherapy apparatus3, and an infrared camera5. The radiotherapy apparatus controller2is a computer exemplified by a personal computer. The radiotherapy apparatus controller2is connected to the radiotherapy apparatus3and connected to the infrared camera5so as to transfer data bi-directionally.

The infrared camera5takes an infrared image of a patient by using a reflection of an infrared ray emitted to the patient and outputs the infrared ray image to the radiotherapy apparatus controller2.

FIG. 2shows the radiotherapy apparatus3. The radiotherapy apparatus3includes a revolution drive device11, an O-ring12, a traveling gantry14, a head swing mechanism15, and a therapeutic radiation irradiating device16. The revolution drive device11rotatably supports the O-ring12on a base centering around a rotational axis17, and rotates the O-ring12centering around the rotational axis17under a control of the radiotherapy apparatus controller2. The rotational axis17is parallel to a vertical direction. The O-ring12is formed in a ring shape centering around a rotational axis18, and rotatably supports the traveling gantry14centering around the rotational axis18. The rotational axis18is perpendicular to the vertical direction, and runs through an isocenter19included in the rotational axis17. The rotational axis18is further secured to the O-ring12, and, for this reason, rotates with the O-ring12centering around the rotational axis17. The traveling gantry14is formed in a ring shape centering around the rotational axis18, and is arranged so as to be a concentric circle with a ring of the O-ring12. The radiotherapy apparatus3further includes a traveling drive device not shown in the figure. The traveling drive device rotates the traveling gantry14centering around the rotational axis18under control of the radiotherapy apparatus controller2.

The head swing mechanism15is secured inside the ring of the traveling gantry14, and supports the therapeutic radiation irradiating device16on the traveling gantry14so that the therapeutic radiation irradiating device16can be arranged inside the traveling gantry14. The head swing mechanism15has a pan axis21and a tilt axis22. The tilt axis22is secured to the traveling gantry14, and is parallel to the rotational axis18without intersecting with the rotational axis18. The pan axis21is orthogonal to the tilt axis22. The head swing mechanism15rotates the therapeutic radiation irradiating device16centering around the pan axis21under the control of the radiotherapy apparatus controller2, and rotates the therapeutic radiation irradiating device16centering around the tilt axis21.

The therapeutic radiation irradiating device16radiates a therapeutic radiation23under the control of the radiotherapy apparatus controller2. The therapeutic radiation23is radiated almost along a straight line running on the intersection where the pan axis21and the tilt axis22intersect each other. The therapeutic radiation23is formed so as to have a uniform distribution of intensity. The therapeutic radiation irradiating device16includes a MLC (multi-leaf collimator)20. The MLC20changes a shape of its irradiation field by shielding a part of the therapeutic radiation23under the control of the radiotherapy apparatus controller2when the therapeutic radiation23is irradiated to the patient.

When the therapeutic radiation irradiating device16is once adjusted by the head swing mechanism15so as to face the isocenter19by being supported on the traveling gantry14as described above, the therapeutic radiation23constantly and basically passes through the isocenter19even when the O-ring12is rotated by the revolution drive device11or the traveling gantry14is rotated by the traveling driving device. That is to say, the therapeutic radiation23can be irradiated to the isocenter19from an arbitrary direction through the traveling and the rotating.

The radiotherapy apparatus3further includes a plurality of imager systems. Concretely, the radiotherapy apparatus3includes diagnostic X-ray sources24and25and sensor arrays32and33. The diagnostic X-ray source24is supported by the traveling gantry14. The diagnostic X-ray source24is arranged inside the ring of the traveling gantry14. The diagnostic X-ray source24is arranged at a position where an angle configured by a line segment connecting the isocenter19with the diagnostic X-ray source24and a line segment connecting the isocenter19with the therapeutic radiation irradiating device16is an acute angle. The diagnostic X-ray source24radiates a diagnostic X-ray35to the isocenter19under the control of the radio therapy apparatus controller2. The diagnostic X-ray35is a conical corn beam which is radiated from one point included in the diagnostic X-ray source24and whose cone point is the one point. The diagnostic X-ray source25is supported by the traveling gantry14. The diagnostic X-ray source25is arranged inside the ring of the traveling gantry14. The diagnostic X-ray source25is arranged at a position where an angle configured by a line segment connecting the isocenter19with the diagnostic X-ray source25and a line segment connecting the isocenter19with the therapeutic radiation irradiating device16is an acute angle. The diagnostic X-ray source25radiates a diagnostic X-ray36to the isocenter19under the control of the radiotherapy apparatus controller2. The diagnostic X-ray36is a conical corn beam which is radiated from one point included in the diagnostic X-ray source25and whose cone point is the one point.

The sensor array32is supported by the traveling gantry14. The sensor array32receives the diagnostic X-ray35that is radiated by the diagnostic X-ray source24and transmits a subject around the isocenter19, and produces a transmission image of the subject. The sensor array33is supported by the traveling gantry14. The sensor array33receives the diagnostic X-ray36that is radiated by the diagnostic X-ray source25and transmits a subject around the isocenter19, and produces a transmission image of the subject. As the sensor arrays32and33, a FPD (Flat Panel Detector) and an X-ray II (Image Intensifier) are shown as examples.

According to these imager systems, a transmission image centering around the isocenter19can be produced on the basis of image signals obtained by the sensor arrays32and33.

The radiotherapy apparatus3further includes a sensor array31. The sensor array31is arranged so that a line segment connecting the sensor array31with the therapeutic radiation irradiating device16can run on the isocenter19, and is secured inside the ring of the traveling gantry14. The sensor array31receives the therapeutic radiation23radiated by the therapeutic radiation irradiating device16and transmitting a subject around the isocenter19, and produces a transmission image of the subject. As the sensor array31, the FPD (Flat Panel Detector) and the X-ray II (Image Intensifier) are shown as examples.

The radiotherapy apparatus3further includes a couch41and a couch driving device42. The couch41is used when a patient43to be treated by the radiotherapy system1lies down. The couch41includes holding fixtures that are not shown in the figure. The holding fixtures fix the patient to the couch41so that the patient cannot move. The couch driving device42supports the couch41on a base, and moves the couch41under the control of the radiotherapy apparatus controller2.

FIG. 3shows the patient43. The patient43has a target61in his/her body. The target61shows an affected part of the patient43and shows a portion to be irradiated by the therapeutic radiation23. A part of the lung is exemplified as the target61. The patient43further has an extracorporeal marker62on his/her body. The extracorporeal marker62is imaged in an infrared image taken by the infrared camera5and is attached on a body surface of the patient43.

FIG. 4shows the radiotherapy apparatus controller2. The radiotherapy apparatus controller2is a computer, and includes a CPU, a storage device, an input device, an output device, and an interface those are not shown in the figure. The CPU executes computer programs installed in the radiotherapy apparatus controller2, and controls the storage device, the input device, and the output device. The storage device stores the computer programs, stores information used by the CPU, and stores data produced by the CPU. The input device outputs information produced by a user's operation to the CPU. As the input device, a keyboard and a mouse are shown as examples. The output device outputs information produced by the CPU so as to be recognized by the user. As the output device, a display is shown as an example. The interface outputs data produced by an outside device connected with the radiotherapy apparatus controller2to the CPU, and outputs data produced by the CPU to the outside device. The outside device includes the infrared camera5, the revolution drive device11, the head swing mechanism15, the therapeutic radiation irradiating device16, the MLC20, the imager systems (the diagnostic X-ray sources24and25and the sensor arrays31,32, and33) of the radiotherapy apparatus3, and the couch driving device42.

The computer program includes a treatment planning section51, a movement collection section52, a correlation calculation section53, a target movement calculation section54, an imager control section55, and an irradiation control section56.

The treatment planning section51shows three dimensional data of the patient43, which are produced by a computer tomography apparatus not shown in the figure, so that the data can be browsed by a user. The treatment planning section51further designs a treatment plan on the basis of data inputted by using the input device. The treatment plan shows the three dimensional data of the target16of the patient43, and shows a combination of an irradiation angle and a radiation dose. The irradiation angle shows a direction of irradiating the therapeutic radiation to the affected area of the patient43, that is, shows a rotational angle of the O-ring and a rotational angle of the gantry. The rotational angle of the O-ring shows a direction of the O-ring12with respect to the base10. The rotational angle of the gantry shows a direction of the traveling gantry14with respect to the O-ring12. The radiation dose shows a dose of the therapeutic radiation irradiated to the affected area from the respective irradiation angles.

The movement collection section52periodically (for example, at every 0.01 sec. to 0.1 sec.) takes infrared images of the extracorporeal marker62of the patient43by using the infrared camera5. The movement collection section52relates the infrared image to an imaging time and temporarily stores the image in the storage device. The movement collection section52further calculates a position of the extracorporeal marker62based on the infrared image.

The correlation calculation section53calculates a position of the target61based on transmission images taken by imager systems of the radiotherapy apparatus3. Based on the position of the extracorporeal marker62calculated by the infrared image taken by the infrared camera5at the time near the time when the transmission image was taken, the correlation calculation section53further calculates a correlation between the position of the target61and the position of the extracorporeal marker62. The correlation calculation section53further produces a table showing the correlation.

The target movement calculation section54refers to the table calculated by the correlation calculation section53and calculates the position of the target61based on the position of the extracorporeal marker62calculated by the movement collection section52. The target movement calculation section54further calculates a rate of change of the position of the target61based on the calculated position of the target61and the imaging time of the infrared image used for the calculation of the position of the extracorporeal marker62.

The imager control section55controls an imager system of the radiotherapy apparatus3so that the diagnostic X-rays35and36can be intermittently emitted and a transmission image of the patient43can be taken. The imager control section55further calculates a time interval based on the rate of change calculated by the target movement calculation section54. The time interval is longer than or equal to a time interval when an infrared image is taken by the movement collection section52, for example, from 1/30 sec. to a few sec. The imager control section55further controls the imager systems of the radiotherapy apparatus3so that the diagnostic X-rays35and36can be emitted at the time interval and the transmission image can be taken at the time interval.

The irradiation control section56calculates the position of the target61based on the transmission image taken by the imager system of the radiotherapy apparatus3. The irradiation control section56drives the therapeutic radiation irradiating device16by using the head swing mechanism15so that the therapeutic radiation23can transmit the calculated position and controls a shape of an irradiation field of the therapeutic radiation23by using the MLC20. The irradiation control section56emits the therapeutic radiation23by using the therapeutic radiation irradiating device16after driving the head swing mechanism15and the MLC20. The longer a period when the diagnostic X-rays35and36are not emitted is, the longer a period when the therapeutic radiation23is emitted becomes. In addition, the irradiation control section56can also change a positional relation between the patient43and the therapeutic radiation irradiating device16by further using the revolution drive device11, the traveling drive device, or the couch drive device42so that the therapeutic radiation23can transmit the position of the affected area.

FIG. 5shows an example of a correlation chart between the position of the extracorporeal marker62calculated based on the infrared images taken by the infrared camera5and the position of the target61calculated based on the transmission images taken by the imager systems at the time near the time when the transmission image was taken. The correlation chart65shows a strong correlation and shows that the target61is synchronized with the extracorporeal marker62.

FIG. 5further shows a correlation. The correlation66is calculated by the correlation calculation section53based on the correlation chart65, and shows a correlation between the position of the extracorporeal marker62and the position of the target61. Specifically, the correlation calculation section53creates the correlation chart65within a predetermined time (for example, 10 sec.) based on the infrared images taken by the infrared camera5and the transmission images taken by the imager systems of the radiotherapy apparatus3. The correlation calculation section53calculates the correlation66based on the correlation chart65. The correlation calculation section53creates a table based on the correlation66and temporarily stores the table in the storage device. The table relates a position set of the extracorporeal marker62to a position set of the target61. Concretely, an arbitrary element in the position set of the extracorporeal marker62relates to one element in the position set of the target61.

FIG. 6shows an example of a position change of the target61calculated by the target movement calculation section54. The change71shows that a rate of change of the position of the target61varies and that the target61moves largely periodically.FIG. 6further shows a timing when the imager systems of the radiotherapy apparatus3takes a transmission image (that is, a timing when emitting the diagnostic X-ray35or the diagnostic X-ray36) by a broken line and shows a time interval calculated by the imager control section55. Furthermore, the time interval is approximately equal to a period when the imager systems of the radiotherapy apparatus3do not emit the diagnostic X-rays35and36.FIG. 6shows that the time interval is not constant and that a time interval73calculated at a period when the rate of change of the position of the target61is large is small compared to a time interval72calculated at a period when the rate of change of the position of the target61is small.

On his occasion, the irradiation control section56emits the therapeutic radiation23at the period when the imager systems of the radiotherapy apparatus3do not emit the diagnostic X-rays35and36. The longer the period is, the longer time when the irradiation control section56can emit the therapeutic radiation23becomes. Specifically, the irradiation control section56can emit the therapeutic radiation23so that a time when the therapeutic radiation23is emitted at the time interval72can be longer than the time when the therapeutic radiation23is emitted at the time interval73.

An embodiment of the radiation irradiation method according to the present invention is performed by using the radiotherapy system1and includes an operation for creating a treatment plan and an operation for performing the radiotherapy.

In the operation for creating the treatment plan, a user inputs three dimensional data of the patient43created by the computer tomography apparatus into the radiotherapy apparatus controller2at first. The radiotherapy apparatus controller2creates an image showing the affected area of the patient and internal organs around the affected area based on the three dimensional data. The user brows the image by using the radiotherapy apparatus controller2and determines the position of the affected area. The user further creates the treatment plan based on the image and inputs the treatment plan into the radiotherapy apparatus controller2. The treatment plan shows an irradiation angle at which the therapeutic radiation is irradiated to the affected area of the patient and a dose and an aspect of the therapeutic radiation irradiated at the respective irradiation angles.

FIG. 7shows an operation for performing the radiotherapy. At first, the user fixes the patient43on the couch41of the radiotherapy apparatus3so that the patient43can take a position when the treatment plan has been created. The radiotherapy apparatus controller2periodically takes the infrared images of the extracorporeal marker62by using the infrared camera5, and periodically takes the transmission images of the target61of the patient43by using the imager system of the radiotherapy apparatus3in parallel with the taking of the infrared images. The radiotherapy apparatus controller2creates a table based on the infrared images and the transmission images and temporarily stores the table into the storage device (step S1). The table relates the position set of the extracorporeal marker62to the position set of the target61.

When the radiotherapy starts, the radiotherapy apparatus controller2periodically takes infrared images of the extracorporeal marker62by using the infrared camera5and periodically takes transmission images of the target61of the patient43by using the imager systems of the radiotherapy apparatus3. The radiotherapy apparatus controller2calculates the position of the extracorporeal marker62based on the infrared images (step S2). The radiotherapy apparatus controller2calculates the position of the target61based on the position of the extracorporeal marker62with referring to the table. The radiotherapy apparatus controller2further calculates a rate of change of the position of the target61based on an imaging time of the infrared images which were used for calculating the position of the extracorporeal marker62and the calculated position of the target61(step S3).

The radiotherapy apparatus controller2calculates the time interval based on the calculated rate of change. The time interval is a value allowing sufficiently accurate measurement of the position of the moving target61. That is, it shows that the larger an absolute value of the rate of change is, the smaller the value of the time interval is. The radiotherapy apparatus controller2controls the imager systems of the radiotherapy apparatus3so that the diagnostic X-rays35and36can be emitted at the time interval and that the transmission images can be taken at the time interval (step S4).

The radiotherapy apparatus controller2calculates the position of the target61based on the taken transmission images (step S5). The radiotherapy apparatus controller2drives the therapeutic radiation irradiating device16by using the head swing mechanism15and controls the shape of an irradiation field of therapeutic radiation23by using the MLC20so that the therapeutic radiation23can transmit the calculated position. The radiotherapy apparatus controller2emits the therapeutic radiation23by using the therapeutic radiation irradiating device16at a period when the diagnostic X-rays35and36are not emitted after the head swing mechanism15and the MLC20are driven (step S6). On this occasion, the radiotherapy apparatus controller2further emits the therapeutic radiation23for a long time when the length of the time interval is longer.

The radiotherapy apparatus controller2repeatedly executes operations of step S1to step S6until an irradiation of the therapeutic radiation23of a dose indicated in the treatment plan is completed. At step S1in the repeating, the radiotherapy apparatus controller2updates a table based on the infrared images taken at a predetermined period and the transmission images taken at the predetermined period and temporarily stores the table into the storage device. The predetermined period is a period from a time backing a predetermined time period (for example, 10 sec.) from the present time to the present time. That is to say, the infrared images include an infrared image taken as step S2, and the transmission images include the transmission image taken at step S2.

According to these operations, the radiotherapy apparatus controller2can accurately measure the position of the moving target61, which is sufficiently useful for the dynamic tumor-tracking irradiation, and can reduce a frequency of measuring the position of the target61by the imager systems of the radiotherapy apparatus3in the total of the radiotherapy. The imager systems of the radiotherapy apparatus3generally radiate an electromagnetic wave when the diagnostic X-rays35and36are emitted, and the electromagnetic wave sometimes has harmful effects to other apparatuses. The radiotherapy apparatus controller2can reduce the harmful effects to apparatuses included in the radiotherapy apparatus3or apparatuses arranged in the vicinity of the radiotherapy apparatus3by reducing the frequency of the measurement by the imager systems of the radiotherapy apparatus3. The radiotherapy apparatus controller2can further reduce an amount of electric power consumed by the imager systems of the radiotherapy apparatus3in the total of the radiotherapy. The radiotherapy apparatus controller2can further reduce a dose of the diagnostic X-rays35and36irradiated to the patient43and reduce an exposure dose of the diagnostic X-rays35and36irradiated to the patient43in the total of the radiotherapy, and can reduce a strain of the patient43.

Since the longer the time interval when the diagnostic X-rays35and36are emitted, the longer the time when the therapeutic radiation23is emitted, the radiotherapy apparatus controller2can increase a dose of the therapeutic radiation23emitted per a unit of time and reduce a time for the radiotherapy in the total of the radiotherapy, and can reduce a strain of the patient43.

FIG. 8shows an example of a change of the position of the target61observed immediately before the radiotherapy. The change81shows that the position of the target61approximately periodically changes.FIG. 8further shows an example of a change of the position of the target61observed in the middle of the radiotherapy. The change82shows that the position of the target61approximately periodically changes, and shows that a period of the change is longer than a period of the change81. As described above, the position of the target61approximately periodically changes, however, its period may change.

According to the radiation irradiation method of the present invention, the radiotherapy apparatus controller2can measure the position of the moving target61at more appropriate time interval and accurately measure the position of the moving target61, which is sufficiently useful for the dynamic tumor-tracking irradiation.

FIG. 9shows another example of the change of the position of the target61observed immediately before the radiotherapy. The change83shows that the position of the target61approximately periodically changes.FIG. 9further shows another example of the change of the position of the target61observed in the middle of the radiotherapy. The change84shows that an average position85of the target61at a predetermined period (time of a natural number multiple of the period) moves as time passes. As described above, the position of the target61approximately periodically changes, however, its average position may change as time passes.

According to the radiation irradiation method of the present invention, even in a case where an average position of the target61changed, it is possible to measure the position of the moving target61at more appropriate time interval and to accurately measure the position of the moving target61, which is sufficiently useful for the dynamic tumor-tracking irradiation.

In addition, the infrared camera5can be replaced by another sensor for measuring movement of the patient43exemplified as the breath. A CCD (Charge-Coupled Device) camera, a body surface laser scanner, and a load cell are exemplified as the sensor. The CCD camera takes an image of the extracorporeal marker62by using a reflection of a visible ray emitted to the patient43and outputs movement information indicating the image to the radiotherapy apparatus controller2. The body surface laser scanner measures a position and a shape of the body surface of the patient43by scanning the body surface with using a laser light emitted to the body surface of the patient43, and outputs the movement information indicating the position and the shape of the body surface to the radiotherapy apparatus controller2. The load cell is arranged inside a belt wrapped around an abdomen of the patient43, measures a pressure applied with being sandwiched by the abdomen and belt, and outputs the movement information indicating the pressure to the radiotherapy apparatus controller2. On this occasion, the radiotherapy apparatus controller2can estimate the movement of the target61based on the movement information. That is to say, the radiotherapy apparatus controller2can measure the position of the target61with sufficiently high accuracy similarly even when the radiotherapy system1includes these sensors in place of the infrared camera52, and can reduce frequency of the measurement of the position of the target61by the imager systems of the radiotherapy apparatus3in the total of the radiotherapy.

In addition, the imager systems of the radiotherapy apparatus3can be replaced by another sensor for measuring a three dimensional position of the target61. A CT (Computed Tomography) apparatus and an MRI (Magnetic Resonance Imaging) apparatus are exemplified as the sensor.

The CT apparatus takes a plurality of transmission images based on a plurality of X-rays transmitting from a plurality of directions, creates a cross section image of the patient43after performing image processing on a plurality of the transmission images in a computer, and calculates the position of the target61of the patient43by performing image processing on a plurality of the transmission images in the computer. On this occasion, the radiotherapy apparatus controller2changes a time interval when the CT apparatus emits the X-ray based on the movement information of the patient43in the same way of the imager systems of the radiotherapy apparatus3.

The MRI apparatus gives a strong magnetostatic field to the patient43, create an image of three dimensional data of the patient43by using a nuclear magnetic resonance, and calculates the position of the target61of the patient43by performing the image processing on the image. On this occasion, the radiotherapy apparatus controller2changes a time interval when the MRI apparatus generates a strong magnetostatic field based on the movement information of the patient43in the same way of the imager systems of the radiotherapy apparatus3.

Consequently, the radiotherapy apparatus controller2can measure the position of the target61with sufficiently high accuracy in a same way even when the imager systems of the radiotherapy apparatus3is replaced by these sensors, and can reduce the frequency of the measurement of the position of the target61by the imager systems of the radiotherapy apparatus3in the total of the radiotherapy. The radiotherapy apparatus controller2can further reduce the harmful effects to apparatuses arranged in a vicinity of the sensor and can reduce an amount of electric power consumed by the sensor.

When the sensor is the CT apparatus, the radiotherapy apparatus controller2can further reduce a dose of the X-ray irradiated to the patient43by the CT apparatus and can reduce a strain of the patient43. When the sensor is the MRI apparatus, the radiotherapy apparatus controller2can further reduce a dose of the electromagnetic wave irradiated to the patient43by the MRI apparatus and can reduce a strain of the patient43.

In place of the changing the time interval based on the amount of change of the position of the target61, the radiotherapy apparatus controller2may change the time interval based on another value calculated in accordance with a measurement result of the infrared camera5. The position of the target61itself and the movement period of the target are exemplified as the value. It is possible to accurately measure the position of the target61similarly even under the control described above, and to reduce frequency of the measurement of the position of the target61by the imager systems of the radiotherapy apparatus3in the total of the radiotherapy.

Moreover, the technique according to the present invention can be applied to a radiotherapy which performs another radiation irradiation method where the therapeutic radiation23changes based on the position of the target61. A respiratory-gated radiotherapy is exemplified as the radiation irradiation method. On this occasion, the radiotherapy apparatus controller2irradiates and stops irradiating the therapeutic radiation23based on the measurement result by the imager systems of the radiotherapy apparatus3. The radiotherapy apparatus controller2can accurately measure the position of the target61similarly even when applied to the above mentioned radiation irradiation method, and to reduce frequency of the measurement of the position of the target61by the imager systems of the radiotherapy apparatus3in the total of the radiotherapy.

Although the present invention has been described above in connection with several exemplary embodiments thereof, it would be apparent to those skilled in the art that those exemplary embodiments are provided solely for illustrating the present invention, and should not be relied upon to construe the appended claims in a limiting sense.