Charged particle beam extraction system and method Number:7,385,203 from the United States Patent and Trademark Office (PTO) owispatent

Title: Charged particle beam extraction system and method

Abstract: A charged particle beam extraction system and method capable of ensuring higher safety when extraction of an ion beam is on/off-controlled during irradiation of the ion beam for treatment. The charged particle beam extraction system comprises a charged particle beam generator including a synchrotron, a range modulation wheel (RMW) for forming a Bragg peak width of a charged particle beam extracted from the charged particle beam generator, a gate signal generator for controlling start and stop of extraction of the charged particle beam from the charged particle beam generator in accordance with a rotational angle of the RMW, and an irradiation control/determination section for determining whether the start and stop of extraction of the charged particle beam is controlled at desired timing by the gate signal generator.

Patent Number: 7,385,203 Issued on 06/10/2008 to Nakayama,   et al.

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Inventors:	Nakayama; Takahide (Nara, JP), Natori; Takayoshi (Chiyoda, JP), Yanagisawa; Masaki (Hitachi, JP)
Assignee:	Hitachi, Ltd. (Tokyo, JP)
Appl. No.:	11/146,074
Filed:	June 7, 2005

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Current U.S. Class:	250/400 ; 250/492.3; 315/501; 315/505; 315/507
Field of Search:	250/492.3,400 315/501,505,507

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References Cited [Referenced By]

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U.S. Patent Documents

5260581	November 1993	Lesyna et al.
5363008	November 1994	Hiramoto et al.
2004/0118081	June 2004	Reimoser et al.
2006/0163496	July 2006	Hiramoto et al.

Foreign Patent Documents

	0 986 070		Mar., 2000		EP
	1 454 654		Sep., 2004		EP
	WO 96/25201		Aug., 1996		WO
	WO 2004/101070		Nov., 2004		WO

Other References

WT.Chu, B.A.Ludewigt and T.R.Renner, Review of Scientific Instruments vol. 64, No. 8, Aug. 1993, pp. 2055 to 2122. cited by examiner . "Review of Scientific Instruments," vol. 64, No. 8, pp. 2074-2084, Aug. 1993. cited by other.

Primary Examiner: Berman; Jack I.
Assistant Examiner: Sahu; Meenakshi S
Attorney, Agent or Firm: Dickstein Shapiro LLP

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Claims

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What is claimed is:

1. A charged particle beam extraction system for extracting a charged particle beam toward an irradiation target, the system comprising: a charged particle beam generator for generating the charged particle beam; an irradiation apparatus including a wheel having a thickness varied in the direction of travel of the charged particle beam extracted from said charged particle beam generator such that energy of the charged particle beam passing said wheel is changed to form a spread-out Bragg peak width in said irradiation target, said irradiation apparatus irradiating the charged particle beam having passed said wheel toward said irradiation target; a first control unit for controlling start and stop of extraction of the charged particle beam from said charged particle beam generator in accordance with a rotational angle of said wheel; and a determination unit for determining whether the start and stop of extraction of the charged particle beam is controlled at a desired timing by said first control unit.

2. The charged particle beam extraction system according to claim 1, wherein said first control unit controls the start and stop of extraction of the charged particle beam from said charged particle beam generator by turning on/off output of a first control signal in accordance with the rotational angle of said wheel.

3. The charged particle beam extraction system according to claim 2, wherein said determination unit determines whether the start and stop of extraction of the charged particle beam is controlled at the desired timing by said first control unit, by comparing on/off-timings of the output of the first control signal with respective target values of the on/off-timings.

4. The charged particle beam extraction system according to claim 2, further comprising a second control for turning on/off output of a second control signal in accordance with the rotational angle of said wheel.

5. The charged particle beam extraction system according to claim 4, wherein said determination unit determines whether the start and stop of extraction of the charged particle beam is controlled at the desired timing, by comparing the first control signal with the second control signal.

6. The charged particle beam extraction system according to claim 4, further comprising a storage for updating an address in accordance with turning-on/off of the second control signal, wherein said determination unit determines whether the start and stop of extraction of the charged particle beam is controlled at the desired timing, by comparing the address of said storage with the first control signal.

7. The charged particle beam extraction system according to claim 1, 3, 5 or 6, further comprising a third control unit for controlling said charged particle beam generator to stop extraction of the charged particle beam when said determination unit determines that the start and stop of extraction of the charged particle beam is not controlled at the desired timing.

8. The charged particle beam extraction system according to claim 3, further comprising a timer unit for measuring the on/off-timing of output of the first control signal.

9. The charged particle beam extraction system according to claim 3, further comprising a clock generator for generating clocks, and a counting unit for measuring the on/off-timing of output of the first control signal by counting the clocks generated from said clock generator.

10. The charged particle beam extraction system according to claim 9, wherein said clock generator is disposed in said determination unit and generates the clocks at a predetermined time cycle.

11. The charged particle beam extraction system according to claim 9, wherein said clock generator generates the clocks in sync with rotation of said wheel.

12. The charged particle beam extraction system according to claim 1, wherein said charged particle beam generator includes a synchrotron.

13. The charged particle beam extraction system according to claim 7, wherein said charged particle beam generator includes a synchrotron having an RF knockout electrode, and said third control unit stops application of an RF wave to said RF knockout electrode to stop extraction of the charged particle beam from said synchrotron when said determination unit determines that the start and stop of extraction of the charged particle beam is not controlled at the desired timing.

14. The charged particle beam extraction system according to claim 13, wherein said first control unit controls the start and stop of extraction of the charged particle beam by respectively starting and stopping supply of the RF wave to said RF knockout electrode.

15. A charged particle beam extraction method for allowing a charged particle beam extracted from a charged particle beam generator to be irradiated from an irradiation apparatus including a wheel having a thickness varied in the direction of travel of the charged particle beam such that energy of the charged particle beam passing said wheel to form a spread-out Bragg peak width in an irradiation target, the method comprising the steps of: controlling start and stop of extraction of the charged particle beam from said charged particle beam generator in accordance with a rotational angle of said wheel; and determining whether the start and stop of extraction of the charged particle beam is controlled at desired timing.

16. The charged particle beam extraction method according to claim 15, wherein the start and stop of extraction of the charged particle beam from said charged particle beam generator is controlled by turning on/off output of a first control signal in accordance with the rotational angle of said wheel.

17. The charged particle beam extraction method according to claim 16, wherein whether the start and stop of extraction of the charged particle beam is controlled at the desired timing is determined by comparing on/off-timings of the output of the first control signal with respective target values of the on/off-timings.

18. The charged particle beam extraction method according to claim 16, further comprising the step of turning on/off output of a second control signal in accordance with the rotational angle of said wheel.

19. The charged particle beam extraction method according to claim 18, wherein whether the start and stop of extraction of the charged particle beam is controlled at the desired timing is determined by comparing the first control signal with the second control signal.

20. The charged particle beam extraction method according to claim 18, wherein whether the start and stop of extraction of the charged particle beam is controlled at the desired timing is determined by comparing the first control signal with an address updated in accordance with turning-on/off of the second control signal.

21. The charged particle beam extraction method according to claim 15, 17, 19 or 20, further comprising the step of stopping the extraction of the charged particle beam when the determination shows that the start and stop of extraction of the charged particle beam is not controlled at the desired timing.

22. The charged particle beam extraction system according to claim 7, further comprising: a beam transportation line associated with said charged particle beam generator for transporting the charged particle beam extracted therefrom; and a beam shutter disposed in said beam transportation line; and wherein said third control unit controls said beam shutter to close while controlling said charged particle beam generator to stop extraction of the charged particle beam when said determination unit determines that the start and stop of extraction of the charged particle beam is not controlled at the desired timing.

23. The charged particle beam extraction system according to claim 7, wherein said charged particle beam generator includes a synchrotron, an RF knockout electrode disposed in the synchrotron for applying an RF wave to the charged particle beam circulating in said synchrotron, and a RF-power supply for supplying the RF wave to said RF knockout electrode through an on/off switch, and wherein said first control unit controls start and stop of extraction of the charged particle beam from said charged particle beam generator by controlling opening and closing of said on/off switch in accordance with a rotational angle of said wheel thereby to control starting and stopping of supply of the RF wave to said RF knockout electrode, and said third control unit controls said charged particle beam generator to stop extraction of the charged particle beam by opening said on/off switch thereby to stop supply of the RF wave to said RF knockout electrode when said determination unit determines that the start and stop of extraction of the charged particle beam is not controlled at the desired timing.

24. The charged particle beam extraction method according to claim 21, wherein a beam shutter is disposed in a beam transportation line associated with said charged particle beam generator for transporting the charged particle beam extracted therefrom, and said beam shutter is controlled to close while said charged particle beam generator is controlled to stop extraction of the charged particle beam when said determination unit determines that the start and stop of extraction of the charged particle beam is not controlled at the desired timing.

25. The charged particle beam extraction method according to claim 21, wherein said charged particle beam generator includes a synchrotron, an RF knockout electrode disposed in the synchrotron for applying an RF wave to the charged particle beam circulating in said synchrotron, and a RF-power supply for supplying the RF wave to said RF knockout electrode through an on/off switch, and wherein the start and stop of extraction of the charged particle beam from said charged particle beam generator is controlled by controlling opening and closing of said on/off switch in accordance with a rotational angle of said wheel thereby to control starting and stopping of supply of the RF wave to said RF knockout electrode, ar.d the extraction of the charged particle beam is stopped by opening said on/off switch thereby to stop supply of the RF wave to said RF knockout electrode when said determination unit determines that the start and stop of extraction of the charged particle beam is not controlled at the desired timing.

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Description

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a charged particle beam extraction system and method for irradiating a charged particle beam, e.g., a proton or carbon ion beam, to a diseased part (represented by a tumor) for treatment.

2. Description of the Related Art

There is known a therapy method for irradiating a charged particle beam (ion beam), e.g., a proton or carbon ion beam, to a tumor such as a cancer in the body of a patient. A charged particle beam extraction system (ion beam extraction system) for use in such therapy comprises a charged particle beam generator, a beam transportation line, and an irradiation apparatus. An ion beam accelerated by the charged particle beam generator reaches the irradiation apparatus through a first beam transportation line and a second beam transportation line, the irradiation apparatus and the second beam transportation line being installed in a rotating gantry. The ion beam is extracted from the irradiation apparatus and irradiated to the tumor in the patient body. Known examples of the charged particle beam generator include means for circulating the charged particle beam along an orbit, means for bringing betatron oscillation of the charged particle beam into a resonant state outside the separatrix of resonance, and a synchrotron (circular accelerator) provided with an extraction deflector for extracting the charged particle beam from the orbit (see, e.g., Patent Reference 1; U.S. Pat. No. 5,363,008).

The therapy using an ion beam, in particular, the treatment with irradiation of a proton beam to a tumor, is based on characteristics that most of energy of the proton beam is released at the time when protons are stopped, namely that a Bragg peak is formed upon the stop of protons. Then, the energy of the proton beam is selected to stop protons near the tumor so that most of the energy (absorbed dose) is given only to cells of the tumor.

Usually, a tumor has a certain thickness in the direction of depth from the body surface of a patient (hereinafter referred to simply as "the direction of depth", while it is coincident with the direction of travel of the ion beam). To effectively irradiate the ion beam over the entire thickness of the tumor in the direction of depth, the energy of the ion beam must be adjusted so as to form a comparatively wide and flat range of absorbed dose in the direction of depth (i.e., a spread-out Bragg peak width, hereinafter referred to as an "SOBP width").

From that point of view, a range modulation wheel (hereinafter abbreviated to "RMW") has already been proposed in which a plurality of blades each having a thickness varied step by step in the circumferential direction are disposed around a rotary shaft (see, e.g., Non-Patent Reference 1; "REVIEW OF SCIENTIFIC INSTRUMENTS", Vol. 64, No. 8, pp. 2074-2084 and FIGS. 30-32, in particular, p. 2077 and FIG. 30 (August 1993)). In the RMW, the plurality of blades are mounted to the rotary shaft, and a through opening is formed between adjacent two of the blades. By rotating the RMW in a state where, for example, the opening is positioned on a path of the ion beam (hereinafter referred to simply as a "beam path"), the opening and the blade alternately intersect the beam path. At the time when the ion beam passes the opening, the energy of the ion beam is not attenuated and therefore the Bragg peak is produced in the deepest position inside the patient body. At the time when the ion beam passes the blade, the energy of the ion beam is attenuated at a larger rate as the ion beam passes the blade having a larger thickness, and therefore the Bragg peak is produced in a portion closer to the body surface of the patient. With the rotation of the RMW, the position in the direction of depth where the Bragg peak is formed varies cyclically. As a result, the Bragg peak width being comparatively wide and flat in the direction of depth of the tumor can be obtained, looking at the beam energy integrated over time. Further, it is known that the SOBP width can also be formed by using a ridge filter (see, e.g., Non-Patent Reference 1; in particular, p. 2078 and FIG. 31).

SUMMARY OF THE INVENTION

One of three inventors of this application has previously invented and filed a charged particle beam extraction system for performing on/off-control of extraction of an ion beam from a synchrotron during the rotation of the RMW. With that preceding invention, by rotating the RMW such that the ion beam passes the RMW for a comparatively long time, i.e., over a wider range of RMW rotational angle, the attenuation of the ion beam is varied to a large extent, and hence the SOBP width is increased. On the other hand, by rotating the RMW such that the ion beam passes the RMW for a comparatively short time, i.e., over a narrower range of RMW rotational angle, the attenuation of the ion beam is varied to a small extent, and hence the SOBP width is decreased. Thus, the on/off-control of extraction of the ion beam during the rotation of the RMW enables the SOBP width to be produced in various values by using one RMW. It is therefore possible to reduce the frequency at which the RMW is to be replaced, and to smoothly carry out the treatment for a larger number of patients.

Further studies conducted by the inventors of this application on the preceding invention, however, showed that the preceding invention had yet room for improvement in the point given below.

According to the preceding invention, by performing the on/off-control of the beam extraction for each patient, the SOBP width can be obtained depending on the tumor in the body of the relevant patient. However, there has not yet been established a method for confirming in real time during the beam irradiation whether the beam is turned on and off at the desired timing. In other words, a further improvement is demanded from the viewpoint of ensuring higher safety in treatment.

It is an object of the present invention to provide a charged particle beam extraction system and method, which are able to ensure higher safety when extraction of an ion beam is on/off-controlled during irradiation of the ion beam for treatment.

To achieve the above object, the charged particle beam extraction system of the present invention is featured in comprising a wheel having a thickness varied in the direction of travel of a charged particle beam extracted from a charged particle beam generator such that energy of the charged particle beam passing the wheel is changed to form a spread-out Bragg peak width in an irradiation target, a first control unit for controlling start and stop of extraction of the charged particle beam from the charged particle beam generator in accordance with a rotational angle of the wheel, and a determination unit for determining whether the start and stop of extraction of the charged particle beam is controlled at desired timing by the first control unit.

With the present invention, since whether the start and stop of extraction of the charged particle beam is controlled at the desired timing during irradiation for treatment is determined, safety in the irradiation for treatment can be increased.

Preferably, the system is controlled so as to stop the extraction of the charged particle beam when it is determined that the start and stop of extraction of the charged particle beam is not controlled at the desired timing. This feature contributes to positively increasing safety in the treatment using the charged particle beam irradiated to the irradiation target.

Thus, according to the present invention, higher safety can be ensured in the treatment using the charged particle beam irradiated to the irradiation target.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall block diagram of a charged particle beam extraction system according to a first embodiment of the present invention;

FIG. 2 is a vertical sectional view showing a detailed structure of an irradiation apparatus shown in FIG. 1;

FIG. 3 is a perspective view of an RMW shown in FIG. 1;

FIG. 4 is a plan view of the RMW shown in FIG. 3, the view showing, by way of example, ion beam extraction cases a to c;

FIG. 5 is a chart showing beam-on and beam-off periods in each of the cases a to c, shown in FIG. 4, on the time serial basis;

FIG. 6 is a graph showing a dose distribution and an SOBP width in the direction of depth in each of the cases a to c shown in FIG. 4;

FIG. 7 is a time chart showing the relationship between rotation of the RMW shown in FIG. 3 and a gate signal;

FIG. 8 is a functional block diagram showing the determining function of an irradiation control/determination section shown in FIG. 1;

FIG. 9 is a table for explaining one example of treatment plan information stored in a memory of an irradiation controller shown in FIG. 2;

FIG. 10 is a flowchart showing control steps executed by the irradiation control/determination section shown in FIG. 1;

FIG. 11 is a time chart showing the relationship between rotation of the RMW and a gate signal in a second embodiment of the present invention;

FIG. 12 is a functional block diagram showing the determining function of an irradiation control/determination section in the second embodiment of the present invention;

FIG. 13 is a vertical sectional view showing a detailed structure of an irradiation apparatus in a third embodiment of the present invention;

FIG. 14 is a time chart showing the relationship among rotation of the RMW, a gate signal, and a gate memory in the third embodiment of the present invention;

FIG. 15 is a functional block diagram showing the determining function of an irradiation control/determination section shown in FIG. 13; and

FIG. 16 is a functional block diagram showing the determining function of an irradiation control/determination section in a fourth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in detail below with reference to the drawings.

First Emobodiment

A charged particle beam extraction system as one preferred embodiment of the present invention will be described with reference to FIG. 1. The charged particle beam extraction system 24 of this embodiment comprises a charged particle beam generator 1, a beam transportation line 2 connected to the charged particle beam generator 1 at the downstream side thereof, and an irradiation apparatus 16 serving as an irradiation field forming apparatus. To be more specific, the charged particle beam extraction system 24 of this embodiment is a proton beam extraction system.

The charged particle beam generator 1 comprises an ion source (not shown), a pre-accelerator (e.g., a linear accelerator) 3, and a synchrotron 4 serving as a main accelerator. The synchrotron 4 includes an RF knockout electrode 5 made of paired electrode members and an RF cavity 6, which are disposed on an orbit of a circulating ion beam. A first RF power supply 8 is connected to the paired electrode members of the RF knockout electrode 5 through on/off switches 9, 10. A second RF power supply (not shown) for applying an RF power to the RF cavity 6 is separately provided. Ions (e.g., proton ions (or carbon ions)) generated from the ion source are accelerated by the pre-accelerator 3. An ion beam (charged particle beam) emitted from the pre-accelerator 3 enters the synchrotron 4. The ion beam, i.e., the charged particle beam, is given with energy and accelerated by an electromagnetic field generated in the RF cavity 6 with application of the RF power supplied from the second RF power supply. The ion beam circulating in the synchrotron 4 is extracted from the synchrotron 4 upon closing of the on/off switch 9 after the ion beam has been accelerated to have energy at a setting level (e.g., 100 to 200 MeV). More specifically, when the on/off switch 9 is closed, an RF wave supplied from the first RF-power supply 8 is applied to the circulating ion beam from the RF knockout electrode 5 through the on/off switch 10 held in the closed state and the closed on/off switch 9. With the application of the RF wave, the ion beam circulating within the separatrix is forced to transit out of the separatrix and to exit from the synchrotron 4 through a beam extraction deflector 11. At the time of extracting the ion beam, currents supplied to quadrupole magnets 12 and bending magnets 13 both disposed in the synchrotron 4 are held at setting current values, and hence the separatrix is also held substantially constant. The extraction of the ion beam from the synchrotron 4 is stopped by opening the on/off switch 9 (or the on/off switch 10) to stop the application of the RF power to the RF knockout electrode 5.

The ion beam extracted from the synchrotron 4 is transported to a beam passage 17 on the downstream side by the beam transportation line 2. The beam transportation line 2 includes quadrupole magnets 14 and bending magnets 15, and it is connected to the beam passage 17 communicating with the irradiation apparatus 16. The irradiation apparatus 16 and the beam passage 17 are both mounted to a rotating gantry (not shown) installed in a treatment room (not shown). Further, quadrupole magnets 18, a bending magnet 19, and a bending magnet 20 are disposed along the beam passage 17 in this order. The ion beam in the beam passage 17 is transported to the irradiation apparatus 16. A patient 22 lies on a treatment couch 21 properly positioned in a treatment cage (not shown) that is formed within the rotating gantry. The ion beam extracted from the irradiation apparatus 16 is irradiated to a tumor K (see FIG. 2 described later), such as a cancer, in the body of the patient 22. The beam passage 17 including the magnets, such as the quadrupole magnets 18, can also be regarded as a beam transportation line. In addition, a beam shutter 38 is disposed upstream of the beam transportation line 2. The beam shutter 38 is usually opened, but it is closed by a later-described interlock device 72 in the event of an abnormality, to thereby shut off the extraction of the ion beam from the synchrotron 4 (as described later in detail).

The structure of the irradiation apparatus 16 will be described below with reference to FIG. 2. As shown in FIG. 2, the irradiation apparatus 16 has a casing 25 that is mounted to the rotating gantry and connected to the beam passage 17. Within the casing 25, the irradiation apparatus 16 has a beam profile monitor 26, a dose monitor 27, an RMW (range modulation wheel) device 28, a second scatterer device 29, a range adjustment device (e.g., a range shifter) 30, a dose monitor 31, a flatness monitor 32, a block collimator 33, a patient collimator 34, and a bolus 35, which are disposed to lie on a beam path (beam axis) m within the casing 25 in this order from the upstream side in the direction of travel of the ion beam.

The beam profile monitor 26 is a monitor for confirming whether the ion beam having entered the irradiation apparatus 16 from the beam transportation line 2 is positioned on the beam axis m. The dose monitor 27 is a monitor for detecting the dose of the ion beam having entered the irradiation apparatus 16. The beam profile monitor 26 and the dose monitor 27 are both installed on a support table 39 mounted to the casing 25.

The RMW device 28 comprises an RMW (wheel) 40, a rotation device (e.g., a motor) 42 for rotating the RMW 40, and an angle meter 51 for detecting the rotational angle of the RMW 40. The RMW 40, the rotation device 42, and the angle meter 51 are held by a support member 50 mounted to the casing 25. As shown in FIG. 3, the RMW 40 comprises a rotary shaft 43, a cylindrical member 44 disposed in a concentric relation to the rotary shaft 43, and a plurality of blades 45 (three blades 45A, 45B and 45C in this embodiment) each of which is mounted at one end to the rotatary shaft 43, is extended in the radial direction of the RMW 40, and is mounted at the other end to the cylindrical member 44. Each of the blades 45 has a circumferential width larger at the other end nearer to the cylindrical member 44 than at one end nearer to the rotary shaft 43. An opening 46 is formed between adjacent two of the blades 45 in the circumferential direction of the RMW 40. The opening 46 is also formed such that its circumferential width gradually increases toward an inner surface of the cylindrical member 44.

Each of the blades 45 has a plurality of plane areas (stepped portions) 47 arranged in the form of stairs in the circumferential direction of the RMW 40. Each of the plane areas 47 has a different thickness relative to a bottom surface of the RMW 40 in the axial direction of the rotary shaft 43 (i.e., the direction of the beam axis m). In other words, levels of the plane areas 47 relative to the bottom surface of the RMW 40 differ from one another. The thickness of each plane area 47 is called here the plane area thickness. More specifically, the plane area thickness of the blade 45 is increased in a stepwise way from each of the plane areas 47 adjacent to the openings 46, which are positioned on both sides of the relevant blade 45 in the circumferential direction, toward the plane area 47 positioned at a top portion 36 having the largest thickness in the direction of the beam axis m. Each plane area 47 is extended from the rotary shaft 43 toward the cylindrical member 44 and has a circumferential width gradually increasing toward the cylindrical member 44.

In an ideal form, the thickness of the RMW blade is changed continuously. However, an actual RWM is generally formed such that the blade thickness changes in a stepwise manner as described above. This is resulted from the viewpoint of tradeoff between an SOBP producing characteristic and workability in machining. Stated another way, the workability in machining (i.e., easiness in ensuring the machining accuracy) can be drastically improved in return for a slight reduction of the SOBP producing characteristic as compared with the case of the blade having the ideal form.

Returning to FIG. 2, the support member 50 mounted to the casing 25 has supports 50A, 50B opposing to each other in the direction of the beam axis m, and it also has a support 50C located downstream of the support 50B. The supports 50A, 50B rotatably support rotary shafts 48, 49, respectively. The RMW 40 is disposed between the supports 50A and 50B, and the rotary shaft 43 of the RMW 40 is supported by the rotary shafts 48, 49 in a sandwiched relation. More specifically, the rotary shaft 43 of the RMW 40 is detachably mounted to the rotary shafts 48, 49 so that the RMW 40 is replaceable. Respective opposed ends of the rotary shafts 48, 49 are inserted in through holes formed in the rotary shaft 43. The supports 50A, 50B are disposed in positions not interfering with the beam path within the casing 25. The rotary shafts 43, 48 and 49 are also disposed in positions away from the beam path.

The rotation device 42 mounted to the support 50C is coupled to the rotary shaft 49. The angle meter 51 for detecting the rotational angle (rotational phase) of the RMW 40 is coupled to the rotary shaft 48 and is mounted to the support 50A. A measured value of the rotational angle of the RMW 40 detected by the angle meter 51 is outputted to a gate signal generator 37 described later.

In this embodiment, though not shown in FIGS. 2 and 3, a first scatterer is further disposed on the beam axis m between the RMW device 28 and the second scatterer device 29. The first scatterer is also mounted to the casing 25. The first scatterer has the function of spreading the ion beam having passed the RMW 40 in the direction perpendicular to the beam axis m.

The second scatterer device 29 comprises a plurality of second scatterers 55, a rotating table 56, and a motor 57. The motor 57 is installed on a support member 58 that is mounted to the casing 25. The plurality of second scatterers 55 for scattering the ion beam at degrees different from one another are arranged on the rotating table 56 side by side in the circumferential direction thereof. With the rotating table 56 rotated by the motor 57, a predetermined one of the second scatterers 55 is positioned on the beam axis m. Driving of the motor 57 is controlled by a driving control section 68.

The range adjustment device 30 comprises a plurality (four in this embodiment) of absorbers 60 differing in thickness from one another, and an absorber operating device 61 provided for each of the absorbers 60. The absorber operating device 61 is constituted as, e.g., an air cylinder driven by compressed air. Each absorber operating device 61 is driven by an absorber driver 62 that is controlled by the driving control section 68.

The dose monitor 31 detects the dose of the ion beam having entered the irradiation apparatus 16 and having passed the RMW device 28, the first scatterer, the second scatterer device 29, and the range adjustment device 30. The flatness monitor 32 is a monitor for confirming flatness (dose uniformity) of the ion beam in the direction perpendicular to the beam axis m after being scattered by the first scatterer and the second scatterer device 55. The dose monitor 31 and the flatness monitor 32 are disposed on a support table 63.

The block collimator 33 shapes the ion beam in the planar direction perpendicular to the beam axis m, thereby roughly collimating the irradiation field of the ion beam. The aperture size of the block collimator 33 is variably controlled by the driving control section 68. The patient collimator 34 finely collimates the ion beam in match with the shape of the tumor K in the body of the patient 22. The bolus 35 has the function of adjusting a penetration depth of the ion beam in match with the maximum depth of the tumor K (which represents the diseased part suffering from a cancer or a tumor) in the body of the patient 22 under treatment. Stated another way, the bolus 35 adjusts the range of the ion beam at each position on a plane perpendicular to the beam axis m in match with the shape of the tumor K as an irradiation target in the direction of depth thereof.

The charged particle beam extraction system 24 includes a gate signal generator (first control unit) 37 and an irradiation controller 64. The irradiation controller 64 comprises an irradiation control/determination section (determination unit and third control unit) 66, the driving control section 68, and a memory 69.

The gate signal generator 37 generates and outputs a gate signal (first control signal) depending on the rotational angle of the RMW 40, which is inputted from the angle sensor 51. More specifically, the gate signal generator 37 receives and counts output pulses outputted from an encoder (not shown). The encoder is incorporated in the angle sensor 51 and is rotated in sync with the RMW 40. Then, the output of the gate signal is turned on or off when the count value of the output pulses matches with a count target value of the encoder output pulses which corresponds to the timing of turning on or off the output of the gate signal and is stored in a memory (not shown) in the gate signal generator 37 beforehand. Also, the gate signal generator 37 outputs a reference signal (pulse signal) per rotation of the RMW 40, which serves as a reference for the output timing of the gate signal. More specifically, as in the above case outputting the gate signal, a count target value of the encoder output pulses corresponding to the timing of outputting the reference signal is stored in the gate signal generator 37 beforehand, and the reference signal is outputted when the count value of the output pulses matches with that count target value. While the gate signal generator 37 is shown in FIG. 2 as being separately disposed from the irradiation controller 64, it may be alternatively incorporated in the irradiation controller 64 as one function thereof.

The irradiation control/determination section 66 receives the gate signal outputted form the gate signal generator 37 and determines whether turning-on or -off of the output of the gate signal is made at the desired timing. If it is determined that the output timing is normal, the irradiation control/determination section 66 executes on/off-control of extraction of the ion beam from the charged particle beam generator 1 to form the SOBP width in accordance with the gate signal. If it is determined that the output timing is abnormal, the section 66 makes control to stop the extraction of the ion beam from the charged particle beam generator 1 and to close the beam shutter 38 via the interlock device 72. The driving control section 68 controls respective operations for driving the motor 57 of the second scatterer device 29, the absorber driver 62 of the range adjusting device 30, and the block collimator 33. The memory 69 stores various target values (described in more detail later) used for determining the on/off-timing of the output of the gate signal, and irradiation condition information outputted from a central controller 70. The charged particle beam extraction system 24 further includes the interlock device 72 (see FIG. 1).

In the charged particle beam extraction system 24 thus constructed, a plurality of SOBP widths can be formed by performing the on/off-control of extraction of the ion beam from the charged particle beam generator 1 depending on the rotational angle of the RMW 40. The principle of that on/off-control of the ion beam extraction will be described below with reference to FIGS. 4, 5 and 6.

At the time when the ion beam passes the opening 46 of the RMW 40, the beam energy is not attenuated and therefore the Bragg peak is formed in a first deep position away from the body surface. At the time when the ion beam passes the plane area 47 of the blade 45 which is positioned at the top portion 36 and has the largest thickness, the beam energy is maximally attenuated and therefore the Bragg peak is formed in a second shallow position close to the body surface. At the time when the ion beam passes the plane area 47 positioned between the opening 46 and the top portion 36, the beam energy is attenuated at a rate depending on the blade thickness at the position where the relevant plane area 47 is present, and therefore the Bragg peak is formed in a third position between the first position and the second position. Accordingly, when the ion beam is always turned on all over a 360.degree.-region of the rotational angle in the circumferential direction of the RMW 40 as the case a shown in FIGS. 4 and 5, the Bragg peak cyclically varies between the first position and the second position with the rotation of the RMW 40. As a result, looking at the dose integrated over time, the case a can provide a comparatively wide SOBP width ranging from a position near the body surface to a deep position as indicated by a dose distribution a in the direction of depth, as shown in FIG. 6. The term "beam-on" means a state in which the ion beam is extracted from the synchrotron 4 and irradiated from the irradiation apparatus 16 after passing the RMW 40. On the other hand, the term "beam-off" means a state in which the ion beam is not extracted from the synchrotron 4 and hence not irradiated from the irradiation apparatus 16.

In the case b shown in FIGS. 4 and 5, the ion beam is turned off in a comparatively thick region (near the top portion 36) of each blade 45 in the circumferential direction of the RMW 40, while the ion beam is turned on in the other region of the rotational angle. Because no Bragg peak is formed in a shallow portion near the body surface, the case b provides an SOBP width indicated by a dose distribution b in the direction of depth and having a narrower flat zone than the dose distribution a, as shown in FIG. 6.

In the case c shown in FIGS. 4 and 5, the ion beam is turned on in the opening 46 and a comparatively thin region of each blade 45 near the opening 46 in the circumferential direction of the RMW 40, while the ion beam is turned off in the other region of the rotational angle. Because the attenuation rate of the beam energy is small as a whole, the Bragg peak is formed in a deep position away from the body surface in the case c. Therefore, the case c provides an SOBP width indicated by a dose distribution c in the direction of depth and having a narrower flat zone than the dose distribution b, as shown in FIG. 6.

Thus, the charged particle beam extraction system 24 can form a plurality of different SOBP widths with one unit of RMW by performing the on/off-control of extraction of the ion beam depending on the rotational angle of the RMW 40 as described above.

The capability of forming various SOBP widths by the on/off-control of extraction of the ion beam performed during the rotation of the RMW 40 is much merit as described later. On the other hand, a capability of confirming whether the on/off-control of extraction of the ion beam is actually performed at the desired timing or not is one of important factors required for the charged particle beam extraction system from the viewpoint of increasing safety in the treatment using the ion beam. The inventors of this application have conducted various studies with intent to overcome such a problem. Results of the studies conducted by the inventors will be described below.

FIG. 7 is a time chart showing the relationship between the rotation of the RMW 40 and the gate signal. While the thickness of the RMW blade is changed in a stepwise manner in the above description with reference to FIGS. 3 through 5, such a blade shape is resulted, as mentioned above, from the restriction in ensuring high machining accuracy with ease. In the following description with reference to FIG. 7 and subsequent drawings, it is assumed that the RMW blade has a mountain-like sectional shape with the thickness changing ideally linearly. From the viewpoint of description, there is no essential difference between the case of the blade having a mountain-like sectional shape and the case of the blade having the thickness changed in a stepwise manner. As described above with reference to FIG. 3, the RMW 40 has the three blades 45A, 45B and 45C, and therefore has a section projecting in three mountain-like shapes in the circumferential direction as shown in FIG. 7. In the illustrated example, there are three mountains (blade portions each having the maximum thickness) and three valleys (portions having zero thickness (i.e., portions corresponding to the openings 46 in FIG. 4)). The gate signal is controlled such that it is turned on within a certain range about the bottom of each valley as in the case b described above with reference to FIG. 4. When the gate signal inputted from the gate signal generator 37 is turned on, the irradiation control/determination section 66 outputs an extraction start signal to the on/off switch 9 if there is no abnormality in later-described determinations. The extraction start signal closes the on/off switch 9 so that the RF wave supplied from the first RF-power supply 8 is applied to the circulating ion beam from the RF knockout electrode 5. When the gate signal inputted from the gate signal generator 37 is turned off, the irradiation control/determination section 66 outputs an extraction stop signal to the on/off switch 9, whereby the on/off switch 9 is opened to stop the application of the RF wave supplied from the first RF-power supply 8 to the ion beam from the RF knockout electrode 5.

With reference to FIG. 8, a description is now made of the function of determining the on/off-timing of the gate signal (hereinafter referred to simply as the "gate timing"), which is executed in the irradiation control/determination section 66. FIG. 8 is a functional block diagram showing the determining function of the irradiation control/determination section 66. As shown in FIG. 8, the gate signal (denoted by (1) in FIG. 8) and the reference signal (denoted by (2) in FIG. 8) are inputted to the irradiation control/determination section 66 from the gate signal generator 37. The reference signal inputted from the gate signal generator 37 is applied to a phase determination circuit 83, whereupon the phase determination circuit 83 starts up a not-shown timer (timer unit). On the other hand, the inputted gate signal is applied to an input processing circuit 81 where a rise or a fall of the gate signal is detected. When a fall of the gate signal is detected (in the illustrated example, when a rise of the gate signal is detected via a NOT circuit), a gate pulse-1 signal (denoted by (3) in FIG. 8) is inputted from the input processing circuit 81, via a hold circuit 82, to the phase determination circuit 83 for determination of a time Tp. The time Tp means a period of time from the reference signal to the first fall of the gate signal (see FIG. 7). More specifically, the phase determination circuit 83 compares the time Tp from the reference signal to the first fall of the gate signal with a target value, thereby determining a phase difference between the whole of the gate signal and the rotation of the RMW 40. In practice, the time Tp is determined as being normal if the following condition (i) is satisfied:

Tp determination: Tp limit-Etp.ltoreq.Tp.ltoreq.Tp limit+Etp (i)

In the condition (i), "Tp limit" is the target value of Tp, and Etp is an allowable value of Tp, e.g., a value stored in the memory 69 of the irradiation controller 64 beforehand. Because the hold circuit 82 holds the gate pulse 1 until the reference signal is reset, the Tp determination is executed on the gate pulse 1 only once immediately after the reference signal per rotation of the RMW 40.

The gate pulse-1 signal (denoted by (3) in FIG. 8) from the input processing circuit 81 is further inputted to a gate determination-1 circuit 84. Then, when a rise of the gate signal is detected, a gate pulse-2 signal (denoted by (4) in FIG. 8) from the input processing circuit 81 is inputted to the gate determination 1 circuit 84 for determination of a time T1. The time T1 means a period of time from the gate pulse-1 signal to a gate pulse-2 signal (i.e., a time during which the gate signal is turned off) (see FIG. 7). More specifically, the gate determination-1 circuit 84 compares the time T1 from the gate pulse-1 signal to the gate pulse-2 signal with a target value, thereby determining the time T1 during which the gate signal is turned off. In practice, the time T1 is determined as being normal if the following condition (ii) is satisfied:

T1 determination: T1 limit-Et1.ltoreq.T1.ltoreq.T1 limit+Et1 (ii)

In the condition (ii), "T1 limit" is the target value of T1, and Et1 is an allowable value of T1, e.g., a value stored in the memory 69 of the irradiation controller 64 beforehand. Because the blades 45 of the RMW 40 have a rotationally symmetric structure, the determination is repeatedly executed per blade 45 during one rotation of the RMW 40.

The gate pulse-2 signal (denoted by (4) in FIG. 8) from the input processing circuit 81 is further inputted to a gate determination-2 circuit 85. Then, when a fall of the gate signal is detected, the gate pulse-1 signal (denoted by (3) in FIG. 8) from the input processing circuit 81 is inputted to the gate determination-2 circuit 85 for determination of a time T2. The time T2 means a period of time from the gate pulse-2 signal to the gate pulse-1 signal (i.e., a time during which the gate signal is turned on) (see FIG. 7). More specifically, the gate determination-2 circuit 85 compares the time T2 from the gate pulse-2 signal to the gate pulse-1 signal with a target value, thereby determining the time T2 during which the gate signal is turned on. In practice, the time T2 is determined as being normal if the following condition (iii) is satisfied:

T2 determination: T2 limit-Et2.ltoreq.T2.ltoreq.T2 limit+Et2 (iii)

In the condition (iii), "T2 limit" is the target value of T2, and Et2 is an allowable value of T2, e.g., a value stored in the memory 69 of the irradiation controller 64 beforehand. Because the blades 45 of the RMW 40 have a rotationally symmetric structure, the determination is repeatedly executed per blade 45 during one rotation of the RMW 40.

If the determination is not satisfied in any of the determination circuits 83, 84 and 85, a signal indicating detection of an abnormality is inputted to an OR circuit 86 which produces a gate phase/gate timing abnormality signal. This abnormality signal is applied to a succeeding AND circuit 87 via a NOT circuit. With such an arrangement, the AND circuit 87 provides the gate signal from the gate signal generator 37, as the beam extraction start signal or the beam extraction stop signal, to the on/off switch 9 only when the gate timing is normal, whereby the on/off-control of the beam extraction can be performed. Thus, if an abnormality of the gate timing is detected in any of the determination circuits 83, 84 and 85, the gate signal is not outputted to the on/off switch 9 (namely, the beam extraction stop signal is outputted). As a result, the on/off switch 9 is opened and the beam extraction from the synchrotron 4 is stopped. At the same time, an interlock signal is outputted to the interlock device 72, whereupon the interlock device 72 closes the beam shutter 38 to prevent the ion beam from being transported toward the irradiation apparatus 16.

Prior to starting the treatment using the charged particle beam extraction system 24, a doctor makes a diagnosis based on a tomogram of the tumor K and thereabout in the body of the patient 22, which is taken by using an X-ray CT apparatus (not shown). The doctor confirms the position and size of the tumor K with the diagnosis, and inputs information indicating the direction of irradiation of the ion beam, the maximum irradiation depth, etc. to a treatment planning unit 71. Based on the input information such as the direction of irradiation of the ion beam and the maximum irradiation depth, the treatment planning unit 71 computes the SOBP width, the irradiation field size, the target dose to be irradiated to the tumor K, etc. by using treatment planning software. Further, the treatment planning unit 71 computes various operation parameters (such as the energy of the ion beam at the time when it is extracted from the synchrotron 4 (i.e., the incident energy to the irradiation apparatus 16), the angle of the rotating gantry, and the rotational angles of the RMW 40 when the extraction of the ion beam is turned on and off), and then selects the RMW 40 suitable for the treatment. Those various items of treatment plan information including not only the rotational angles and the target dose, but also other items listed in FIG. 9, i.e., the irradiation field size, the range, the incident energy (incident Eg), the thickness of the first scatterer (SC1 thickness), the SOBP width, the type of the second scatterer 55 (SC2 type), the thickness of the absorber 60 positioned in the beam path within the range adjustment device 30 (RS thickness), and the aperture size of the block collimator 33 (BC aperture size), are inputted to the central controller 70 of the charged particle beam extraction system 24 and stored in a memory (not shown) of the central controller 70. The above-stated treatment plan information is stored in the memory 69 of the irradiation controller 64 as well from the central controller 70.

In accordance with the rotating gantry angle information inputted from the memory 69, a gantry controller (not shown) rotates the rotating gantry to direct the beam path within the irradiation apparatus 16 toward the patient 22. Then, the treatment couch 21 on which the patient is lying is moved and positioned such that the tumor K lies on an extension of the beam path within the irradiation apparatus 16.

By using the information stored in the memory 69 and regarding the irradiation field size, the range and the incident energy, the driving control section 68 of the irradiation controller 64 selects respective values of the thickness of the first scatterer, the SOBP width, the type of the second scatterer, the absorber thickness, and the aperture size of the block collimator from the irradiation condition information stored in the memory 69 beforehand, which is shown, by way of example, in FIG. 9. In accordance with the information regarding the thickness of the first scatterer, the driving control section 68 moves the first scatterer having the selected thickness to be positioned on the beam axis m. Then, the driving control section 68 drives the motor 57 to rotate the rotating table 56 such that the selected second scatterer 55 is positioned on the beam axis m. Further, the driving control section 68 actuates the absorber operating device 61 through the absorber driver 62 such that the selected absorber 60 is positioned on the beam axis m. In accordance with the information regarding the selected aperture size of the block collimator 33, the driving control section 68 controls a not-shown driver to move blocks of the block collimator 33 for setting the aperture size to a predetermined value.

The various items of the treatment plan information are displayed on a display installed in a control room for the charged particle beam extraction system 24. The RMW 40, the bolus 35, and the patient collimator 34, which are suitable for the patient 22 who is going to take the treatment, are installed in the casing 25 of the irradiation apparatus 16, as shown in FIG. 2, by an operator.

The irradiation control/determination section 66 of the irradiation controller 64 reads, from the memory 69, rotational angle information (e.g., .alpha.1 to .alpha.6 described later) of the RMW 40 installed in the casing 25, the target dose, the target values "Tp limit", "T1 limit" and "T2 limit" and the allowable values Etp, Et1 and Et2 used in the above-described Tp, T1 and T2 determinations, which are suitable for the patient 22 who is going to take the treatment.

A manner of treating the tumor K by using the charged particle beam extraction system 24 will be described below. The synchrotron 4 is operated by repeating the steps of introducing the ion beam from the pre-accelerator 3, and then accelerating, extracting and decelerating the ion beam. When the ion beam is accelerated until reaching the extraction energy at a setting level, the acceleration of the ion beam is brought to an end and the ion beam comes into a state ready for extraction from the synchrotron 4 (i.e., an ion beam extractable state). Information indicating the end of acceleration of the ion beam is transmitted to the central controller 70 from a magnet power supply controller that monitors states of the magnets, etc. of the synchrotron 4 by using sensors (not shown).

The on/off-control of extraction of the ion beam for forming the SOBP width, as described above, in the charged particle beam extraction system 24 will be described below with reference to FIGS. 1, 2, 4 and 10. The following description of the on/off-control of extraction of the ion beam is made, by way of example, in connection with the case b shown in FIG. 5. In the example of the case b, black points 52A, 52B and 52C each represent the timing of the extraction-on (start of extraction) of the ion beam, and white points 53A, 53B and 53C each represent the timing of the extraction-off (stop of extraction) of the ion beam. When the irradiation control/determination section 66 executes the control for the case b, it receives, from the memory 69, the rotational angles .alpha.1 to .alpha.6 (.alpha.3 to .alpha.6 being not shown), i.e., the setting values of the rotational angles. The rotational angle al represents an angle from a reference line 41 to the point 52A, and the rotational angle .alpha.2 represents an angle from the reference line 41 to the point 53A. The rotational angle .alpha.3 represents an angle from the reference line 41 to the point 52B, and the rotational angle .alpha.4 represents an angle from the reference line 41 to the point 53B. The rotational angle .alpha.5 represents an angle from the reference line 41 to the point 52C, and the rotational angle .alpha.6 represents an angle from the reference line 41 to the point 53C. The rotational angles .alpha.1 to .alpha.6 each represent an angle on the basis of the state in which the reference line 41 is positioned on the beam axis m. In FIG. 4, the position of each black point represents a position where the extraction of the ion beam is started, while the position of each white point represents a position where the extraction of the ion beam is stopped.

The irradiation control/determination section 66 executes the on/off-control of extraction of the ion beam in accordance with a control flow shown in FIG. 10. First, the irradiation control/determination section 66 receives a signal indicating the end of acceleration in the accelerator (synchrotron 4) (i.e., a signal indicating that the ion beam is in the extractable state) (step 73). The end-of-acceleration signal is inputted from the central controller 70. Then, the section 66 outputs a start-of-rotation signal to the rotation device 42 (step 74). The rotation device 42 is rotated in accordance with the start-of-rotation signal. The torque of the rotation device 42 is transmitted to the rotary shaft 43 through the rotary shaft 49, whereby the RMW 40 is rotated. The number of rotations of the RMW 40 is set to a value in the range of 100 to 200 rotations per second. It is determined whether a measured value of the rotational angle matches with a first setting value of the rotational angle (step 75). More specifically, a value of the rotational angle of the RMW 40 measured by the angle sensor 51 is inputted to the gate signal generator 37. It is then determined whether the input measured value matches with the first setting value of the rotational angle (any of the rotational angles .alpha.1, .alpha.3 and .alpha.5) at which the beam extraction start signal is to be outputted. If the measured value of the rotational angle matches with the first setting value, the gate signal is outputted from the gate signal generator 37 to the irradiation control/determination section 66. Then, if the gate timing is determined as being normal based on the Tp, T1 and T2 determinations, the beam extraction start signal is outputted from the irradiation control/determination section 66 (step 76). The on/off switch 9 is closed in response to the beam extraction start signal. The on/off switch 10 is held in the closed state. The RF wave outputted from the first RF-power supply 8 is applied to the circulating ion beam from the RF knockout electrode 5, whereupon the ion beam is extracted from the synchrotron 4. The extracted ion beam is transported to the irradiation apparatus 16.

The transported ion beam travels along the beam axis m within the irradiation apparatus 16. The ion beam passes the beam profile monitor 26 and the dose monitor 27. The ion beam having passed the rotating RMW 40 is spread out by the first scatterer in the direction perpendicular to the beam axis m. Then, the dose distribution of the ion beam is flattened by the second scatterer 55 in the direction perpendicular to the beam axis m. By subsequently passing the absorber 60 of the range adjusting device 30, the energy of the ion beam is reduced for adjustment of the range to be obtained in the body of the patient 22. The dose of the ion beam having passed the absorber 60 is measured by the dose monitor 31, and the flatness of the ion beam in the direction perpendicular to the beam axis m is confirmed by the flatness monitor 32. The ion beam further passes the block collimator 33, the patient collimator 34, and the bolus 35, followed by being irradiated to the tumor K.

It is determined whether the dose having been irradiated to the tumor K has reached the target dose (step 77). Further, it is determined whether the measured value of the rotational angle matches with a second setting value of the rotational angle (step 78). The dose having been irradiated to the tumor K is measured by the dose monitor 31 and is inputted to the irradiation control/determination section 66. In step 77, it is determined whether a total of the dose value measured by the dose monitor 31 has reached the target dose. If this determination result is "YES", the processing of step 82 is executed in precedence to the processing of step 78 and the beam extr