JP2017042311A - Neutron capture therapy system and control method for neutron capture therapy system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy in calculating the concentration of a boron-containing agent.SOLUTION: A neutron capture therapy system 1 for projecting a neutron beam N onto a patient M who is administered with a boron-containing agent comprises: a neutron beam projection unit 4 for projecting the neutron beam N to the patient M; a gamma ray information acquisition unit 30 for acquiring first gamma ray information about the gamma ray G discharged from the patient M by the projection of the neutron beam N; and an agent concentration calculation unit 40 for calculating the concentration of the agent in the body of the patient M, using the first gamma ray information. The gamma ray information acquisition unit 30 includes a pair of detectors 31a, 31b arranged in paired positions across a region R where the patient M rests. The agent concentration calculation unit 40 calculates the concentration of the agent, using third gamma ray information, the third gamma ray information being obtained by excluding, from the first gamma ray information, second gamma ray information which is about gamma rays of a given energy respectively detected by the detectors 31a, 31b at the simultaneous time.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a neutron capture therapy system and a control method for the system.

  As one of radiotherapy methods in cancer treatment or the like, there is boron neutron capture therapy (BNCT) that performs cancer treatment by irradiation of neutron beams. In boron neutron capture therapy, irradiating a patient with a boron-containing drug with neutron rays causes boron and neutrons to react in the cancer cells to release alpha rays and the like. Cancer cells and the like are destroyed by the alpha rays.

International Publication No. 2012/014671

  Since boron neutron capture therapy utilizes the reaction between neutrons and boron, it is desirable to measure the drug concentration in the patient in real time. As a method for measuring the drug concentration, for example, there is a method of collecting blood from a patient and measuring the drug concentration in the blood. However, in this method, since it takes about 15 minutes for one measurement, the drug concentration in the patient cannot be measured in real time.

  Therefore, as a method for measuring the drug concentration in real time, application of a single photoemission method (SPECT method) for evaluating the distribution of radioisotopes administered into a patient using a tomographic screen has been studied. When the SPECT method is applied to boron neutron capture therapy, gamma rays generated by the reaction between neutron rays and boron are used. However, when a patient is irradiated with neutrons, in addition to gamma rays associated with the reaction between neutron rays and boron, gamma rays associated with other factors are also generated. Therefore, it is difficult to improve the calculation accuracy of the drug concentration by measuring gamma rays using the SPECT method.

  An object of this invention is to provide the neutron capture therapy system which can aim at the improvement of the calculation precision of the chemical | medical agent containing boron, and the control method of the said system.

  One aspect of the present invention is a neutron capture therapy system for irradiating an irradiated body to which an agent containing boron is administered with a neutron capture therapy system, a neutron beam irradiation unit for irradiating the irradiated body with a neutron beam, A gamma ray information acquisition unit that acquires first gamma ray information related to gamma rays emitted from the irradiated body by irradiation, and a drug concentration calculation unit that calculates the concentration of the drug in the irradiated body using the first gamma ray information; The gamma ray information acquisition unit includes a pair of detectors provided at a pair of positions across the region where the irradiated object is disposed, and the drug concentration calculation unit detects from the first gamma ray information. The concentration of the drug is calculated using the third gamma ray information obtained by removing the second gamma ray information relating to the gamma ray of the predetermined energy detected at the same time in each of the vessels.

  When irradiating a subject to which a drug containing boron is administered with neutron rays, gamma rays accompanying the reaction between the drug and neutron rays and gamma rays containing components due to other factors are generated. The neutron capture therapy system calculates the drug concentration using the dose of gamma rays associated with the reaction between the drug and the neutron beam. However, gamma rays including components due to other factors can be noise in the calculation of the drug concentration. In the neutron capture therapy system, information on gamma rays that can be noise is acquired as second gamma ray information relating to gamma rays of a predetermined energy incident on each of the pair of detectors at the same time, and is obtained from the first gamma ray information. It is excluded. Therefore, the third gamma ray information from which the second gamma ray information is removed excludes information on gamma rays that can be noise. The drug concentration calculation unit calculates the drug concentration by using the third gamma ray information from which information related to gamma rays that can be noise is removed, so that the calculation accuracy of the drug concentration in real-time measurement is improved. Can do.

  The predetermined energy may be 511 keV, and the third gamma ray information may be information regarding gamma rays having an energy of 478 keV. When the irradiated body is irradiated with a neutron beam, boron and neutron beam taken into the irradiated body react to release alpha rays and lithium. Gamma rays having an energy of 478 keV are emitted from the released lithium. Therefore, the dose of gamma rays with an energy of 478 keV corresponds to the drug concentration containing boron. On the other hand, when the irradiated object is irradiated with a neutron beam, electrons and positrons are generated by the reaction between the particles contained in the irradiated object and the neutron beam, and the neutron beam and particles (hydrogen, nitrogen, etc.) Electrons and positrons are generated by the reaction between high energy (1 MeV or more) gamma rays generated by the reaction and substances (structures such as lead in the irradiated object and apparatus). And the annihilation of these electrons and positrons occurs. In this pair annihilation, gamma rays having an energy of 511 keV are emitted. This pair production may be caused by a reaction between a particle other than boron and a neutron beam. Therefore, since the gamma ray whose energy is 511 keV includes a component accompanying a factor different from the reaction between the drug and the neutron beam, the gamma ray whose energy is 511 keV can be a noise when calculating the drug concentration. Therefore, in the neutron capture therapy system, except for information on gamma rays whose energy that can be noise is 511 keV, information on gamma rays whose energy associated with the reaction between the drug and neutron rays is 478 keV. Concentration calculation accuracy can be improved.

  The gamma ray information acquisition unit may further include a collimator disposed between the region where the irradiated object is disposed and the detector. The collimator transmits gamma rays emitted from the irradiated body and shields gamma rays not derived from the irradiated body. Therefore, the signal-to-noise ratio of the gamma ray information output from the detector can be increased.

  Another aspect of the present invention is a method for controlling a neutron capture therapy system for irradiating an irradiated body to which an agent containing boron is administered, the step of irradiating the irradiated body with a neutron beam, Obtaining a first gamma ray information relating to a gamma ray emitted from the irradiated body by irradiation with a neutron beam using a pair of detectors provided at a pair of positions across the region where the body is disposed; The step of calculating the concentration of the drug using the third gamma ray information obtained by removing the second gamma ray information relating to the gamma ray of the predetermined energy detected at the same time by each of the detectors from the first gamma ray information. And having.

  According to this control method, similarly to the neutron capture therapy system, it is possible to improve the calculation accuracy of the drug concentration containing boron in real-time measurement.

  ADVANTAGE OF THE INVENTION According to this invention, the neutron capture therapy system which can aim at the improvement of the calculation precision of the chemical | medical agent containing boron, and the control method of the said system are provided.

It is the schematic which shows the neutron capture therapy system of one Embodiment of this invention. It is a block diagram which shows the neutron capture therapy system of one Embodiment of this invention. It is a block diagram which shows the chemical | medical agent concentration calculation part in FIG. It is a flowchart which shows the main steps of the control method of the neutron capture therapy system in one Embodiment of this invention. It is a graph which shows the spectrum of the gamma ray emitted from a patient. It is a perspective view which shows the gamma ray information acquisition part with which the neutron capture therapy system which concerns on a modification is provided.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

A neutron capture therapy system 1 shown in FIG. 1 is a system that performs cancer treatment using boron neutron capture therapy. The neutron capture therapy system 1 irradiates a tumor of a patient (irradiated body) M, for example, to which a drug containing boron ( ¹⁰ B) is administered with neutron beams N.

  The neutron capture therapy system 1 includes an accelerator 2, a beam transport device 3, a neutron beam irradiation unit 4, and a drug administration unit 17. The accelerator 2 is, for example, a cyclotron. The accelerator 2 accelerates charged particles such as hydrogen ions to produce a proton beam (proton beam) as a charged particle beam P. Here, for example, the accelerator 2 has a beam radius of 40 mm and has a capability of generating a charged particle beam P of 60 kW (= 40 MeV × 2 mA). The accelerator 2 is not limited to a cyclotron, and may be, for example, a synchrotron, a synchrocyclotron, a linac, or the like.

  The charged particle beam P emitted from the accelerator 2 is introduced into the beam transport device 3. The beam transport device 3 includes a beam duct 5, a quadrupole electromagnet 6, a current monitor 7, and a scanning electromagnet 8. The accelerator 2 is connected to one end side of the beam duct 5, and the neutron beam irradiation unit 4 is connected to the other end side of the beam duct 5. The charged particle beam P travels through the beam duct 5 toward the neutron beam irradiation unit 4.

  A plurality of quadrupole electromagnets 6 are provided along the beam duct 5 and adjust the beam axis of the charged particle beam P using the electromagnets. The current monitor 7 detects the current value (charge, irradiation dose rate) of the charged particle beam P in real time. The current monitor 7 uses a non-destructive DCCT (DC Current Transformer) capable of measuring current without affecting the charged particle beam P. That is, the current monitor 7 can detect the current value of the charged particle beam P without contacting the charged particle beam P (without contact). “Dose rate” means a dose per unit time.

  Specifically, the current monitor 7 uses a quadrupole electromagnet 6 to eliminate the influence of the quadrupole electromagnet 6 in order to accurately detect the current value of the charged particle beam P irradiated to the target 9 of the neutron beam irradiation unit 4. It is provided immediately before the scanning electromagnet 8 on the downstream side (downstream side of the charged particle beam P). That is, since the scanning electromagnet 8 always scans the target 9 so that the charged particle beam P is not irradiated to the same place, a large current monitor 7 is required to dispose the current monitor 7 downstream of the scanning electromagnet 8. Is required. On the other hand, the current monitor 7 can be reduced in size by providing the current monitor 7 on the upstream side of the scanning electromagnet 8.

  The scanning electromagnet 8 scans the charged particle beam P and controls irradiation of the charged particle beam P to the target 9. The scanning electromagnet 8 controls the irradiation position of the charged particle beam P with respect to the target 9.

  The neutron beam irradiation unit 4 generates a neutron beam N by irradiating the target 9 with the charged particle beam P, and emits the neutron beam N toward the patient M. The neutron beam irradiation unit 4 includes a target 9, a shield 10, a moderator 11, and a collimator 12.

  The target 9 receives a charged particle beam P and generates a neutron beam N. The target 9 here is made of, for example, beryllium (Be), lithium (Li), tantalum (Ta), tungsten (W), or the like, and has a disk shape with a diameter of 160 mm, for example. The target 9 is not limited to a disk shape, but may be another solid shape or a liquid (liquid metal).

  The moderator 11 decelerates the energy of the neutron beam N by decelerating the neutron beam N generated by the target 9. The moderator 11 includes a first moderator 11A that mainly decelerates fast neutrons contained in the neutron beam N, and a second moderator 11B that mainly decelerates epithermal neutrons contained in the neutron beam N. It has a laminated structure.

  The shield 10 is generated when the moderator 11 decelerates the generated neutron beam N, secondary radiation such as gamma rays generated at the target 9 as the neutron beam N is generated, and the neutron beam N. Secondary radiation such as gamma rays generated in the moderator 11 is shielded, and release of these radiations to the irradiation room side where the patient M is present is suppressed. The shield 10 is provided so as to surround the moderator 11.

  The collimator 12 shapes the irradiation field of the neutron beam N, and has an opening 12a through which the neutron beam N passes. The collimator 12 is a block-shaped member having an opening 12a at the center, for example.

The drug administration unit 17 administers a drug containing boron ( ¹⁰ B) to the patient M while the patient M is irradiated with the neutron beam N. The drug administration unit 17 includes a delivery unit that delivers a drug containing boron, a needle unit that points to the patient, a transport unit that connects the delivery unit and the needle unit, and transports a drug containing boron, and the like. Since boron in the body of the patient M decreases due to the reaction with the neutron beam N, the drug administration unit 17 supplies and replenishes the patient M with boron during irradiation with the neutron beam N.

  The neutron capture therapy system 1 includes a control device 20 (see FIG. 2). The control device 20 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, and is an electronic control unit that comprehensively controls the neutron capture therapy system 1.

  The neutron capture therapy system 1 further includes a gamma ray information acquisition unit 30 and a drug concentration calculation unit 40. The gamma ray information acquisition unit 30 acquires information on gamma rays emitted from the patient M. The drug concentration calculation unit 40 calculates the boron concentration (drug concentration) in the patient M using the information. The gamma ray information acquisition unit 30 and the drug concentration calculation unit 40 measure single energy gamma rays to measure the boron concentration distribution (PG (Prompt-γ) -SPECT (Single Photon Emission Computed Tomography). )).

  Here, the gamma rays emitted from the patient M will be described. FIGS. 5A and 5B are graphs A1 and A2 showing spectra of gamma rays emitted from the patient M when the patient M is irradiated with the neutron beam N. FIG. FIG. 5B is an enlarged view of the area S in FIG. The horizontal axes in FIGS. 5A and 5B indicate the energy of gamma rays. The vertical axis indicates the number of counts detected per unit time. As shown in FIG. 5A, when the patient M is irradiated with the neutron beam N, a plurality of types of gamma rays G1 to G5 having different energy are emitted. The plurality of types of gamma rays G1 to G5 are shown as first gamma ray information. Of these gamma rays G1 to G5, in the present embodiment, attention is paid to the gamma rays G1 and G2. In the following description, gamma rays G1 to G5 emitted from the patient M are referred to as gamma rays G.

  The gamma ray G1 has an energy of 478 keV and is generated by a reaction between boron (drug) and neutrons. Specifically, when boron reacts with neutron beam N, alpha rays and lithium are released. The released lithium is in an excited state, and gamma rays having an energy of 478 keV are emitted when transitioning from the excited state to the ground state. Information regarding this gamma ray G1 is indicated as third gamma ray information.

  The gamma ray G2 has an energy of 511 keV. It exists in the vicinity of the gamma ray G1 (478 keV). The gamma rays G2 are a pair of gamma rays, and their traveling directions are opposite to each other (180 degrees) and have an energy of 511 keV. Information regarding this gamma ray G2 is indicated as second gamma ray information. Two generation mechanisms are considered for this gamma ray G2. First, there are those caused by positrons accompanying β + decay caused by the reaction between particles (nuclei) and neutrons. In this case, it is unclear which element is the target of the reaction between particles and neutrons. The other is due to the positrons generated by the interaction between the gamma rays and the substance (a constituent such as an irradiated body or lead). The gamma rays in this case are generated by the reaction between neutrons and particles (hydrogen, nitrogen, etc.) and have an energy of 1 MeV or more. This generation mechanism is caused by gamma rays and can be generated anywhere there is a substance.

  As shown in FIG. 1, the gamma ray information acquisition unit 30 is connected to the drug concentration calculation unit 40 and outputs the acquired first gamma ray information to the drug concentration calculation unit 40. The gamma ray information acquisition unit 30 includes a pair of detectors 31 a and 31 b and a collimator 32. The detectors 31a and 31b output a signal that can be counted, such as a pulse signal, when a gamma ray G is detected, and scintillators, ionization chambers, and other various gamma ray detection devices can be used. The detectors 31a and 31b are disposed in the vicinity of the tumor of the patient M so as to sandwich the region R where the patient M is disposed. For example, the distance from the detector 31 to the patient M is about 40 cm. The detectors 31 a and 31 b are configured to be rotatable at a predetermined speed around the central axis of the opening 12 a of the collimator 12.

  The collimator 32 is disposed between the region R where the patient M is disposed and the detector 31a, and has a configuration capable of rotating together with the detector 31a while maintaining a relative positional relationship with the detector 31a. Accordingly, the gamma rays G emitted from the patient M enter the detector 31a via the collimator 32. The collimator 32 suppresses background gamma rays that may be noise not derived from the patient M from entering the detector 31a. The collimator 32 has a main body formed of a lead plate and a plurality of pores provided in the main body. The pore penetrates the main body along the direction from the patient M toward the detector 31. The collimator 32 is not limited to a configuration having a plurality of pores, and may employ various configurations that can suppress the incidence of background gamma rays on the detector 31a. For example, the collimator 32 may have a so-called pinhole type configuration.

  The drug concentration calculation unit 40 measures the boron concentration in the body of the patient M in real time during irradiation with the neutron beam N. The drug concentration calculation unit 40 calculates the boron concentration by using information (third gamma ray information) regarding the gamma ray G1 (478 kev) generated by the reaction between the neutron beam N and boron. As shown in FIG. 3, the drug concentration calculation unit 40 includes a coincidence counting circuit 41, a noise determination unit 42, a counter 43, and a concentration calculation unit 44.

The coincidence counting circuit 41 has two input terminals 41a and 41b, and outputs a signal when a signal is input to both the input terminals 41a and 41b at the same time. The “simultaneous time” here is not limited to a strict simultaneous time, and a signal is input to both the input terminals 41a and 41b within a preset period (for example, ^10-8 seconds). Including. A detector 31a is connected to the input terminal 41a of the coincidence circuit 41, and a detector 31b is connected to the input terminal 41b. The coincidence counting circuit 41 outputs a signal to the noise determination unit 42 when signals are simultaneously input from the detectors 31a and 31b to the input terminals 41a and 41b, respectively. When a signal is input to one of the input terminals 41a and 41b, in other words, when it is not determined that the signals are input to the input terminals 41a and 41b at the same time, no signal is output. The signal output from the coincidence circuit 41 indicates that the gamma ray G detected by the detectors 31a and 31b is a gamma ray G2 (511 keV) generated by pair annihilation.

  The noise determination unit 42 is connected to the detectors 31 a and 31 b, the coincidence circuit 41, and the counter 43. The noise determination unit 42 selects the gamma ray signals input from the detectors 31a and 31b using the signal output from the coincidence counting circuit 41. When the gamma ray signal is input from the detectors 31a and 31b and the signal is input from the coincidence counting circuit 41, the noise determination unit 42 determines that the gamma ray signal input from the detectors 31a and 31b is noise. Ignoring the gamma ray signal. That is, the noise determination unit 42 does not output any signal in response to the input of the signal output from the coincidence counting circuit 41 and the gamma ray signal. On the other hand, when the gamma ray signal is input from one of the detectors 31a and 31b and the signal is not output from the coincidence counting circuit 41, the noise determination unit 42 does not ignore the gamma ray signal. That is, the noise determination unit 42 outputs the gamma ray signal input to one of the detectors 31 a and 31 b to the counter 43.

  The counter 43 is connected to the noise determination unit 42 and the density calculation unit 44. The counter 43 counts the number of gamma ray signals output from the noise determination unit 42. Then, for each predetermined period, the counter 43 outputs a combination of the energy included in the gamma ray signal and the count number of the energy.

  The concentration calculation unit 44 calculates the boron concentration using information periodically output from the counter 43. For example, the concentration calculation unit 44 calculates a gamma ray spectrum (see FIG. 5) from a plurality of combination data including the energy value included in the gamma ray signal and the count number of the energy. Then, in the spectrum, an integrated value (dose) of a predetermined energy band having a peak at gamma ray G1 (478 keV) is obtained. The boron concentration is calculated using this integrated value. Then, the concentration calculation unit 44 outputs the boron concentration to the control device 20.

  Next, the operation of the neutron capture therapy system 1 will be described with reference to the flowchart shown in FIG.

  First, administration of a drug containing boron is started from the drug administration unit 17 (step S1). Subsequently, irradiation with the neutron beam N is started from the neutron beam irradiation unit 4 (step S2). During irradiation with neutron beam N, boron and neutron beam N that have been taken into the cancer cells of patient M react with each other, and gamma rays G1 (478 keV), which are detection targets, are emitted. Further, during irradiation with the neutron beam N, gamma rays G2 (511 keV) to be removed are emitted. The gamma ray information acquisition unit 30 of the neutron capture therapy system 1 acquires first gamma ray information regarding the gamma rays G including these gamma rays G1 and G2 (step S3). The gamma ray information is output to the coincidence counting circuit 41 and the noise determination unit 42.

  Subsequently, it is determined whether or not a signal is output from the coincidence circuit 41 to the noise determination unit 42 (step S4). Here, when a signal is output, it can be seen that the acquired gamma ray information indicates a pair of gamma rays G2 (511 ekV). On the other hand, when no signal is output, the acquired gamma ray information indicates the gamma ray G1 (478 keV) or gamma rays G3 to G5. Hereinafter, a case where the acquired gamma ray information indicates the gamma ray G2 (511 ekV) and a case where the acquired gamma ray information indicates the gamma ray G1 (478 ekV) will be described individually.

<In the case of gamma ray G2 (511 ekV): Step S4: YES>
When a pair of gamma rays G2 (511 keV) are generated by the annihilation of electrons and positrons, one is incident on the detector 31a and the other is incident on the detector 31b. With the incidence of the gamma ray G2, gamma ray information is input to the coincidence counting circuit 41 from the detectors 31a and 31b at the same time. Subsequently, an output signal is output from the coincidence circuit 41 to the noise determination unit 42. Subsequently, the noise determination unit 42 determines that the gamma ray signals output from the detectors 31a and 31b indicate a pair of gamma rays G2 based on the signal (step S4: YES). And the noise determination part 42 ignores the gamma-ray signal output from the detectors 31a and 31b (process S5), and implements process S3 and S4 again.

<In the case of gamma ray G1 (478 keV): Step S4: NO>
When boron and neutrons react to generate gamma rays G1 (478 keV), the gamma rays G1 enter, for example, only one detector 31a. The gamma ray information is input to the coincidence counting circuit 41 from the detector 31a by the incidence of the gamma ray G1. In this case, no signal is output from the coincidence counting circuit 41, and the signal is not output to the noise determination unit 42. Subsequently, based on the fact that no signal is input from the coincidence counting circuit 41 (step S4: NO), the noise determination unit 42 is information indicating that the gamma ray signal output from the detector 31a indicates the gamma ray G1 to be detected. judge. And the noise determination part 42 outputs gamma ray information to the counter 43 (process S6).

  Subsequently, the counter 43 increases the count number n by 1 (step S7). Subsequently, the drug concentration calculation unit 40 determines whether or not a predetermined time has elapsed (step S8). If the predetermined time has not elapsed (step S8: NO), steps S3 to S8 are performed again. When the predetermined time has elapsed (step S8: YES), the count number n and gamma ray information (energy value) are output to the concentration calculation unit 44 (step S9). Subsequently, the concentration calculation unit 44 calculates a boron concentration using a gamma ray spectrum obtained from the count number n and gamma ray information (step S10). Subsequently, the drug concentration calculation unit 40 determines whether or not the irradiation with the neutron beam N has been completed (step S11). If irradiation has not been completed (step S11: NO), the count number n is initialized (n = 0) (step S12), and steps S3 to S11 are performed again. When the irradiation is completed, the boron concentration calculation process is stopped (step S13).

  Next, the effect of the neutron capture therapy system 1 will be described.

  When a patient M to whom a drug containing boron is administered is irradiated with a neutron beam N, a gamma ray G1 (478 keV) associated with the reaction between boron and the neutron beam and a gamma ray G2 (511 keV) including a component associated with another factor are generated. To do. The neutron capture therapy system 1 calculates the boron concentration using the dose of the gamma ray G1 associated with the reaction between boron and the neutron beam, but the gamma ray G2 including a component due to another factor becomes noise in calculating the boron concentration. obtain. In the neutron capture therapy system 1, information on the gamma ray G2 that can be noise is second gamma ray information on the gamma ray G2 having a predetermined energy (511 keV) incident on each of the pair of detectors 31a and 31b at the same time. Acquired and excluded from the first gamma ray information. Accordingly, the third gamma ray information from which the second gamma ray information has been removed excludes information relating to the gamma ray G2 that may be noise. Then, the drug concentration calculation unit 40 calculates the boron concentration by using the third gamma ray information from which information related to the gamma ray G2 that can be noise is removed. Therefore, according to the control method of the neutron capture therapy system 1 and the neutron capture therapy system, it is possible to improve the calculation accuracy of the boron concentration in the real-time measurement.

  More specifically, as shown in FIG. 5B, there is a gamma ray G2 (511 keV) that can be noise in the vicinity of the gamma ray G1 (478 keV) for calculating the boron concentration. The gamma ray G2 is caused by a positron generated by β + decay, or a positron generated by the interaction between a gamma ray and a substance. Positrons generated by β + decay are not generated by the reaction of boron with neutrons, and can be noise. Moreover, the positron generated by the interaction between the gamma ray and the substance can be generated anywhere in the substance. In this case, it is considered that the number of positrons generated by the pair reaction due to the reaction with the neutron with a substance other than boron is larger than the number of positrons generated by the reaction between the boron and the neutron. Therefore, the count number of the gamma ray G2 becomes extremely larger than the count number of the gamma ray G1 (see graph A1), and the base of the gamma ray G2 overlaps the base of the gamma ray G1.

  From the measurement result in which the base of the gamma ray G2 overlaps the base of the gamma ray G1, it is difficult to accurately extract the peak of the gamma ray G1 having a small count number by signal processing. According to the neutron capture therapy system 1, gamma ray information regarding the gamma ray G <b> 2 is ignored by the noise determination unit 42 of the drug concentration calculation unit 40. Accordingly, as shown in FIG. 5B, the peak of the count number can be reduced. Since the size of the count number and the spread of the base have a predetermined relationship, when the peak of the count number is small, the spread of the base is also narrowed. Therefore, the peak indicating the count number of the gamma rays G1 can be extracted with high accuracy, so that the calculation accuracy of the boron concentration can be improved. The detector 31 detects the gamma ray G with a predetermined counting efficiency. Then, when a pair of gamma rays G2 are emitted, there may occur a case where detection is performed by one detector 31a but not by the other detector 31b. In that case, the gamma ray G2 remains as noise.

  The predetermined energy is 511 keV, and the third gamma ray information is information on the gamma ray G1 having an energy of 478 keV. When the patient M is irradiated with the neutron beam N, boron and neutron beam N that have been taken into the body of the patient M react with each other, and alpha rays and lithium are released. From the released lithium, gamma rays G1 having an energy of 478 keV are released. Therefore, the dose of the gamma ray G1 whose energy is 478 keV corresponds to the boron concentration. On the other hand, when the patient M is irradiated with the neutron beam N, electrons and positrons are generated by the reaction between the particles contained in the patient M and the neutron beam N, and the neutron beam and particles (hydrogen, nitrogen, etc.). Electrons and positrons are generated by the reaction of high energy (1 MeV or more) gamma rays generated by the reaction with a substance (structure such as lead in the irradiated object or device). And the annihilation of these electrons and positrons occurs. In this pair annihilation, gamma rays G2 having an energy of 511 keV are emitted. This pair production may be caused by a reaction between a particle other than boron and the neutron beam N. Therefore, since the gamma ray G2 having an energy of 511 keV includes a component associated with a factor different from the reaction between boron and neutron rays, the gamma ray G2 having an energy of 511 keV can be a noise when calculating the boron concentration. Therefore, in the neutron capture therapy system 1, since information regarding the gamma ray G1 whose energy accompanying reaction with boron is 478 keV is used except for information regarding the gamma ray G2 whose energy that can be noise is 511 keV, boron is used. Concentration calculation accuracy can be improved.

  The gamma ray information acquisition unit 30 further includes a collimator 32 disposed between the region R where the patient M is disposed and the detector 31a. The collimator 32 transmits gamma rays G1 to G5 emitted from the body of the patient M and shields gamma rays not originating from the patient M. Therefore, the signal-to-noise ratio of the gamma ray information output from the detector 31a can be increased.

  The present invention is not limited to the above-described embodiments, and various modifications as described below are possible without departing from the gist of the present invention.

  For example, as illustrated in FIG. 6, the gamma ray information acquisition unit 40 </ b> A may include a plurality of detectors 33 and a plurality of collimators 34 disposed so as to surround a region R where the patient M is disposed. According to this configuration, the configuration for rotating the detector 33 and the collimator 34 is not required, so that the configuration of the gamma ray information acquisition unit 40A can be simplified.

  Moreover, the neutron capture therapy system 1 may include a neutron beam detection unit. The neutron beam detection unit is for measuring the neutron beam N irradiated to the patient M in real time during irradiation of the neutron beam N by the neutron beam irradiation unit 4. For example, the neutron beam detector detects the neutron beam N passing through the opening 12a of the collimator 12 in real time. The neutron beam detection unit includes a scintillator and a photodetector. The scintillator is a phosphor that converts incident radiation (neutron beam N, gamma beam) into light. In the scintillator, the internal crystal is excited according to the dose of incident radiation, and generates scintillation light. As the scintillator, a 6Li glass scintillator, a LiCAF scintillator, a plastic scintillator coated with 6LiF, a 6LiF / ZnS scintillator, or the like can be used. The photodetector detects light generated by the scintillator. As the photodetector, various types of photodetectors such as a photomultiplier tube and a photoelectric tube can be employed. The light detector outputs an electric signal (detection signal) to the control device 20 when light is detected.

  Moreover, the control apparatus 20 of the neutron capture therapy system 1 may include a boron concentration control unit. The control device 20 compares the set value of the boron concentration distribution in the information related to the treatment plan with the actual measured value of the boron concentration calculated by the drug concentration calculation unit 40, and whether or not both match or fall within a predetermined difference range. Determine whether. For example, when the difference between the set value of the boron concentration distribution in the information related to the treatment plan and the actual measured value of the boron concentration measured by the drug concentration calculation unit 40 is equal to or greater than the determination threshold, it does not fall within the predetermined difference range. Is determined. Since the boron concentration distribution is distribution data in a two-dimensional or three-dimensional predetermined space, the space is divided into a plurality of ranges, and a set value of boron concentration and an actual measured value of boron concentration are obtained for each divided range. Contrast. As a result of the comparison, when the measured value of the dose of neutron beam N and the measured value of the boron concentration distribution are determined to be in accordance with the treatment plan (or fall within a predetermined difference from the treatment plan), the control device 20 is left as it is. Continue irradiation with neutron beam N. On the other hand, when it is determined that the actual measured value of the dose of neutron beam N and the actual measured value of the boron concentration distribution are not in accordance with the treatment (or does not fall within a predetermined difference from the treatment plan), Adjustment of administration of boron or irradiation of neutron beam N is performed.

DESCRIPTION OF SYMBOLS 1 ... Neutron capture therapy system, 4 ... Neutron irradiation part, 17 ... Drug administration part, 20 ... Control apparatus, 30 ... Gamma ray information acquisition part, 31a, 31b ... Detector, 32 ... Collimator, 40 ... Drug concentration calculation part, DESCRIPTION OF SYMBOLS 41 ... Simultaneous counting circuit, 42 ... Noise determination part, 43 ... Counter, 44 ... Concentration calculating part, G1 ... Gamma ray (478 keV), G2 ... Gamma ray (511 keV), M ... Patient (irradiated body), N ... Neutron ray, R: Area where the patient is placed.

Claims (4)

A neutron capture therapy system that irradiates a subject to which a drug containing boron is administered with a neutron beam,
A neutron beam irradiation unit that irradiates the irradiated body with the neutron beam;
A gamma ray information acquisition unit for acquiring first gamma ray information related to gamma rays emitted from the irradiated body by irradiation of the neutron beam;
A drug concentration calculation unit that calculates the concentration of the drug in the irradiated body using the first gamma ray information,
The gamma ray information acquisition unit has a pair of detectors provided at a pair of positions across an area where the irradiated object is disposed,
The drug concentration calculation unit uses third gamma ray information obtained by removing second gamma ray information related to gamma rays of predetermined energy detected at the same time by the detectors from the first gamma ray information. A neutron capture therapy system for calculating the concentration of the drug. The predetermined energy is 511 keV,
The neutron capture therapy system according to claim 1, wherein the third gamma ray information is information relating to gamma rays having an energy of 478 keV.   The neutron capture therapy system according to claim 1, wherein the gamma ray information acquisition unit further includes a collimator disposed between a region where the irradiated object is disposed and the detector. A method for controlling a neutron capture therapy system that irradiates an irradiated body to which an agent containing boron is administered with a neutron beam,
Irradiating the irradiated body with the neutron beam;
First gamma ray information relating to gamma rays emitted from the irradiated object by irradiation of the neutron beam using a pair of detectors provided at a pair of positions across the region where the irradiated object is disposed A process of obtaining
The concentration of the drug is calculated using third gamma ray information obtained by removing second gamma ray information related to gamma rays of a predetermined energy detected at the same time by each of the detectors from the first gamma ray information. And a method of controlling the neutron capture therapy system.

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