JP6073609B2 - Positron emission nuclear position detector - Google Patents

Description

  The present invention relates to a positron emission nuclear position detection apparatus that estimates the emission position of γ rays within a particle beam irradiation target, such as a patient undergoing particle beam therapy.

  In the irradiation with particle beams, it is necessary to accurately irradiate the site to be irradiated. For example, in particle beam therapy, it is necessary to irradiate a target site with a particle beam while preventing the particle beam from affecting normal tissues. However, since the particle beam is not visible, the arrival position of the particle within the irradiation target is estimated.

  As an example, there is a method using a nuclide that undergoes positron decay (a kind of β decay that emits positrons) generated by particle beam irradiation (Non-patent Document 1). In this method, after the irradiation of the irradiation target is completed, the emission of positrons from the irradiation target is measured with a PET apparatus.

Enghardt, W. etal., The spatial distribution of positron-emitting nulei generated by relativistic light ion beams, Med. Phys. Biol., 37, pp. 2127-2131, 1992

  However, since the conventional method uses a PET apparatus, measurement during irradiation cannot be performed. Therefore, in order to measure the position of the positron decay nucleus even during particle beam irradiation, for example, the irradiation direction of the particle beam is set as the Z-axis direction, and the plane including this Z-axis (for example, the YZ plane; the Y-axis is orthogonal to the Z-axis) A method using a pair of PET detectors which are arranged so that the surfaces thereof are opposed to each other with the irradiation target interposed therebetween is conceivable.

In this method, for example, a pair of γ rays (energy 511 keV) generated when a positron generated by decay of ¹⁴ O causes pair annihilation with neighboring electrons is captured by these detectors. As illustrated in FIG. 5, the pair of γ-rays due to the pair annihilation jumps out in opposite directions, so that positron decay nuclei exist on the extension lines of the pair of positions where these γ-rays are detected. Therefore, the position of the positron decay nucleus can be measured with relatively high accuracy (accuracy of about 2 mm) in the YZ plane. However, in the direction orthogonal to the YZ plane (X-axis direction), the accuracy deteriorates to about 1 cm. For this reason, the current position and range of the positron decay nucleus cannot be estimated three-dimensionally. This is not limited to the case of particle beam irradiation, for example, at the time of administration of a drug containing ¹⁴ O, it is a problem when estimating the reach of the drug by detecting the position where the nucleus releases the positron. It becomes.

  The present invention has been made in view of the above circumstances, and it is one of its objects to provide a positron emission nucleus position detection device capable of improving the estimation accuracy of the existence position and range of a three-dimensional positron decay nucleus. To do.

  The present invention that solves the problems of the above-described conventional example is a positron emission nucleus position detection device, which has a pair of surfaces arranged with a particle beam irradiation target in between, and detects γ-rays in each of the surfaces. A pair of first detectors, a second detector that is arranged in a direction different from the first detector with respect to the irradiation target, and detects a direction of incidence of γ rays, and the second detector detects Using the incident direction of γ-rays and the information on the detection position of γ-rays detected by the first detector substantially simultaneously with the time when the second detector detects the incident direction of γ-rays, An estimation means for estimating the emission position of the γ-ray detected by the second detector, and an output means for outputting a result of estimation by the estimation means.

  In addition, the positron emission nucleus position detection device according to one aspect of the present invention has a pair of surfaces arranged with a particle beam irradiation target interposed therebetween, and generates an image representing a detection position of γ rays in each of the surfaces. A pair of first detectors, a second detector that is arranged in a direction different from the first detector with respect to the irradiation target, and detects the incident direction of γ rays, and the γ generated by the first detector An image of the detection position of the line, the incident direction of the γ-ray detected by the second detector, and the first detection at substantially the same time as the second detector detects the incident direction of the γ-ray Based on position information representing the emission position of γ rays in the irradiation object detected by the second detector, estimated using information on the detection position of the γ rays detected by the detector. Estimating means for estimating the emission range of the line, and output means for outputting a result of estimation by the estimating means And a step.

  According to the present invention, it is possible to improve the estimation accuracy of the position and range of a three-dimensional positron decay nucleus.

It is a block diagram showing an example of a positron emission nucleus position detection device according to an embodiment of the present invention. It is a block diagram showing an example of a control device of a positron emission nucleus position detection device according to an embodiment of the present invention. It is a schematic diagram showing the example of a structure which takes out the output signal from the detector of the positron emission nucleus position detection apparatus which concerns on embodiment of this invention. It is a schematic diagram showing another structural example which takes out the output signal from the detector of the positron emission nucleus position detection apparatus which concerns on embodiment of this invention. It is explanatory drawing showing the example of the discharge | release aspect of the gamma ray at the time of pair annihilation.

  Embodiments of the present invention will be described with reference to the drawings. As illustrated in FIG. 1, the positron emission nucleus position detection device 1 according to the embodiment of the present invention includes a pair of first detectors 11 a and 11 b arranged at intervals in the X-axis direction, and a second detection. The device 12 includes a control device 13. Here, as illustrated in FIG. 2, the control device 13 includes a control unit 31, a storage unit 32, an interface unit 33, and an output unit 34. In the following description, for the sake of easy understanding, the first detectors 11a and 11b are assumed to be planar (planar) detectors, the plane is in the YZ plane, and the Y axis is from the back side of the drawing sheet to the surface. Suppose that it is the normal direction of the direction. The normal direction of these YZ planes (the direction from the left to the right in the drawing) is the X-axis direction. The Z axis is the direction of the line segment drawn from the top to the bottom of the drawing, and these X, Y, and Z axes are orthogonal to each other. However, in the present embodiment, the first detectors 11a and 11b are not limited to planar detectors, and may be curved surfaces.

  The first detectors 11a and 11b are planar (planar) PET detectors in an example of the present embodiment. In the present embodiment, an irradiation target is arranged between the first detectors 11a and 11b. The PET detector has a plurality of scintillators that detect γ rays arranged on a plane. When the γ rays arrive, the scintillator at the position where the γ rays hit detects the γ rays. That is, the first detectors 11a and 11b can detect the position where the γ-rays arrive in this plane. The output signals of the first detectors 11a and 11b according to the present embodiment are planar image information in which the pixels at the positions where the γ rays have arrived and the positions where the γ rays have not been set have different pixel values. It becomes.

  The second detector 12 is, for example, a Compton camera, and detects the arrival direction of γ rays and the arrival direction of the γ rays. Specifically, the second detector 12 includes a plurality of γ-ray detection arrays in which a plurality of γ-ray detectors are arranged in a plane (for example, XY plane) different from the first detectors 11a and 11b. These γ-ray detection arrays are arranged in parallel to each other (XY plane) on which the γ-ray detectors are arranged. Of these, the incoming γ-rays are scattered by the γ-ray detection array closer to the arrival direction of the γ-rays, and the scattered γ-rays are absorbed by the other γ-ray detection arrays. When the energy of γ-rays at the time of scattering is measured at this time, if the energy of the incoming γ-rays is known, the scattering angle can be calculated by the Compton scattering equation, and therefore the cone containing the direction of arrival of the γ-rays (Compton cone) ) Can be obtained. The arrival direction of γ rays can be detected from the intersection range of Compton cones obtained from the detection results of a plurality of detectors included in the γ ray detection array. Since this Compton camera is widely known, further detailed explanation is omitted here. The output signal of the second detector 12 of the present embodiment is image information projected onto a plane parallel to the γ-ray detection array, and the pixels at the position where the γ-ray source is located and the positions where the γ-ray source is not located are different from each other. It will be set to the value.

  The control unit 31 of the control device 13 is a program control device such as a CPU, for example, and operates according to a program stored in the storage unit 32. In an example of the present embodiment, the control unit 31 receives information on the incident direction of γ rays detected by the second detector 12. The second detector 12 accepts information on the detected positions of the γ rays detected by the first detectors 11a and 11b substantially simultaneously with the time when the second detector 12 detects the incident direction of the γ rays. Then, using these received information, the γ-ray emission position in the irradiation object is estimated. Details of the operation of the control unit 31 will be described later.

  The storage unit 32 holds a program executed by the control unit 31. This program may be provided by being stored in a computer-readable recording medium such as a DVD-ROM and stored in the storage unit 32. In the present embodiment, the storage unit 32 also operates as a work memory of the control unit 31.

  The interface unit 33 receives information output from the first detectors 11 a and 11 b and the second detector 12 and outputs the information to the control unit 31. Specifically, as illustrated in FIG. 3, the interface unit 33 includes background removal units 21 a and 21 b corresponding to the first detectors 11 a and 11 b, a window setting unit 22, and an output control unit. 23.

  Here, the background removal unit 21 receives the signal output from the corresponding first detector 11 and the energy of the γ-ray detected by the first detector 11 exceeds a predetermined energy threshold (or two energy levels). If it is within the threshold range, the output signal of the first detector 11 is output. If the energy of the γ-ray detected by the corresponding first detector 11 does not exceed a predetermined energy threshold (or is not in the range of two energy thresholds), the background removal unit 21 performs the first detection. Control is performed so that the output signal of the device 11 is not output.

  The window setting unit 22 is connected to one of the background removal units 21a and 21b (referred to as the background removal unit 21a in FIG. 3), and the connected background removal unit 21 outputs a signal output from the first detector 11. When output, a pulse signal having a predetermined time width is output.

  The output control unit 23 receives signals output from the background removal units 21 a and 21 b and the second detector 12. When the window setting unit 22 outputs a pulse signal, the output control unit 23 outputs the received signals to the control unit 31 as they are.

  The output unit 34 is, for example, a display monitor, and displays and outputs information in accordance with instructions input from the control unit 31.

  Next, the operation of the control unit 31 will be described. In the present embodiment, signals received by the control unit 31 are as follows.

When the particle beam is irradiated to an irradiation object containing oxygen ( ¹⁶ O), the oxygen ¹⁶ O is converted to ¹⁴ O. This ¹⁴ O decays β and emits a positron, but this positron immediately causes pair annihilation with a nearby electron, and a pair of about 511 keV (value calculated by E = mec ² using the electron mass me, Here, c emits γ rays having energy of (the speed of light in vacuum). Also, due to this β decay, ¹⁴ O becomes a constant energy level of ¹⁴ N, but most ¹⁴ N immediately emits 2.3 MeV gamma rays (substantially simultaneously with the emission of 511 keV gamma rays). To do.

  Accordingly, in the present embodiment, when this reaction occurs, when a 2.3 MeV gamma ray is detected by the second detector 12, substantially each of the pair of 511 keV gamma rays is detected by the first detector. 11a and b. For this reason, for example, if 500 keV is set as the energy threshold value in the background removal unit 21, the background removal units 21 a and b are detected when the first detectors 11 a and 11 b detect 511 keV γ rays substantially simultaneously. Respectively output the output signals of the first detectors 11a and 11b as they are. The window setting unit 22 receives the output of the background removal unit 21a and outputs a pulse signal. When the above reaction occurs, the window setting unit 22 detects the second detection during the time width during which the pulse signal is output. Since the output signal indicating that the detector 12 has detected 2.3 MeV γ-rays is output, the output control unit 23 outputs the output signals of the first detectors 11 a and 11 b and the second detector 12 to the control unit 31. To do.

  In the present embodiment, the output signals of the first detectors 11a and 11b and the second detector 12 are both two-dimensional images as already described, and in the images of the first detectors 11a and 11b, The detection positions of γ rays in the YZ plane at the positions (Xa, Xb) on the X axis of the first detectors 11a, 11b are shown. The detection position of γ rays in the YZ plane based on the output signal of the first detector 11a is (Ya, Za), and the detection position of γ rays in the YZ plane based on the output signal of the first detector 11b is (Yb, Zb), the positron emitting nucleus is on a straight line represented by the following equation (1).

（ここでｔは実数パラメータ）。

(Where t is a real parameter).

  In addition, the output signal of the second detector 12 indicates the position of the γ-ray source in the XY plane. Therefore, assuming that the detection position of the γ-ray source in the XY plane based on the output signal of the second detector 12 is (Xd, Yd) (the coordinates of the first detector 11 and the second detector 12 are known positions). The control unit 31 sets the detection position (Xd, Yd) to either X or Y in the equation (1). The value of the parameter t is obtained by solving the substituted expression, for example, the following expression (2).

制御部３１は、ここで得たパラメータｔの値を（１）式に代入することで得たＸ，Ｙ，Ｚの値を、Ｘ，Ｙ，Ｚ軸で張られる三次元空間内での陽電子放出核の位置の推定結果として出力する。

The control unit 31 substitutes the value of the parameter t obtained here into the equation (1) to obtain the positrons in the three-dimensional space spanned by the X, Y, and Z axes. Output as the estimation result of the position of the emission nucleus.

Here, example has been described for detecting the γ rays emitted when a particle beam is converted to oxygen ⁽¹⁶ O) in ¹⁴ O, this embodiment is not limited thereto. For example, when a particle beam interacts with a carbon ( ¹² C) nucleus, the nucleus is converted to a nucleus ¹⁰ C capable of emitting a positron. When ¹⁰ C emits positrons and β decays, ¹⁰ B is formed, and the formed ¹⁰ B emits 718 keV gamma rays. Therefore, the first detectors 11a and 11b detect a pair of γ-rays (511 keV γ-rays) generated by the positrons emitted from ¹⁰ C annihilating with neighboring electrons. When the second detector 12 detects 718 keV gamma rays at the time, using the detected positions of the gamma rays and the positions of the gamma ray sources detected by the first detectors 11a and 11b and the second detector 12, respectively. The control unit 31 may estimate the position of the positron emission nucleus.

  In the above description, the example of solving the line segment formula has been described. However, the present embodiment is not limited to this, and the image information output from each of the first detectors 11a and 11b and the second detector 12 is projected. As an image, a three-dimensional image may be reconstructed by a method such as back projection. The three-dimensional image reconstructed here represents a range where the positron emission nucleus exists.

Furthermore, the pair of γ-ray emission accompanying the annihilation of positrons is not limited to the above-described β decay of oxygen ( ¹⁶ O) or carbon ( ¹² C). In other words, the reaction in which ¹⁴ N and ¹⁰ B are produced is only a part of the whole. Therefore, the number of 511 keV γ rays actually detected by the first detector 11 is larger than the number of γ rays detected by the second detector 12. Therefore, in the present embodiment, even when the second detector 12 is not detecting γ-rays, an image of 511 keV γ-rays detected by the first detector 11 is obtained. The position of the positron emission nucleus may be estimated by reconstructing a three-dimensional image using an image obtained when the two detectors 12 detect γ rays.

  In this example, as illustrated in FIG. 4, the interface unit 33 of the control device 13 includes background removal units 21 a and b provided corresponding to the first detectors 11 a and 11 b, and a first window setting. A unit 22 ', a second window setting unit 24, and an output control unit 23'.

  Here, the background removal unit 21 receives the signal output from the corresponding first detector 11 and the energy of the γ-ray detected by the first detector 11 exceeds a predetermined energy threshold (or two energy levels). If it is within the threshold range, the output signal of the first detector 11 is output. If the energy of the γ-ray detected by the corresponding first detector 11 does not exceed a predetermined energy threshold (or is not in the range of two energy thresholds), the background removal unit 21 performs the first detection. Control is performed so that the output signal of the device 11 is not output.

  The first window setting unit 22 ′ is connected to one of the background removal units 21 a and b (the background removal unit 21 a in FIG. 4), and the connected background removal unit 21 is connected to the first detector 11. When a signal to be output is output, a pulse-shaped signal having a predetermined time width Δt1 is output.

  The second window setting unit 24 outputs a pulse-like signal having a predetermined time width Δt2 when the second detector 12 outputs a signal indicating that γ rays have been detected. Here, the time widths Δt 1 and Δt 2 may be determined experimentally, and may be the same value or different values.

  The output control unit 23 ′ receives signals output from the background removal units 21 a and 21 b and the second detector 12 and pulse signals output from the first and second window setting units 22 ′ and 24. The output control unit 23 'operates as follows. That is, nothing is output when the first window setting unit 22 'does not output a pulse signal. When the first window setting unit 22 'outputs a pulse signal and the second window setting unit 24 does not output a pulse signal, the output control unit 23' uses the background removal units 21a, b. The output signals of the first detectors 11a and 11b received from the above are output to the control unit 31 as they are.

  Further, the output control unit 23 'receives the first detector received from the background removal units 21a and 21b when both the first window setting unit 22' and the second window setting unit 24 are outputting pulse signals. The output signals 11a and 11b and the signal received from the second detector 12 are output to the control unit 31 as they are.

  In the control unit 31, when the output control unit 23 ′ of the interface unit 33 outputs only the output signal of the first detectors 11 a and 11 b, the conventional detectors are used to output the first detectors 11 a and 11 b. A three-dimensional image (first three-dimensional image) representing the position of the positron emitting nucleus is reconstructed based on the output signal.

  In addition, when the output control unit 23 ′ of the interface unit 33 outputs the output signals of the first detectors 11 a and 11 b and the second detector 12, the control unit 31 uses these methods as described above. Based on the output signals of the first detectors 11a and 11b and the output signal of the second detector 12, a three-dimensional image (second three-dimensional image) representing the position of the positron emission nucleus is reconstructed.

  Here, as described above, in the first three-dimensional image, the accuracy of the estimated position of the positron emission nucleus in the X-axis direction is lower than the accuracy in the other axis (Y-axis, Z-axis) directions. Yes. On the other hand, in the second three-dimensional image, the accuracy of each axis of the estimated position of the positron emission nucleus is not inferior to the accuracy of the Y-axis or Z-axis in the first three-dimensional image, but the number of detection is the first three-dimensional image. There are few compared with the detection result of the gamma ray used for reconstruction.

  The control unit 31 performs super-resolution synthesis of the first three-dimensional image and the second three-dimensional image, and generates and outputs a three-dimensional image representing the estimated position of the positron emission nucleus. Since a widely known method for super-resolution processing by combining a plurality of images can be used, detailed description thereof is omitted.

  The output of the three-dimensional image may be performed by receiving a designation of an arbitrary cross section from the user and generating and displaying a cross-sectional image of the arbitrary cross section.

  The positron emission nucleus position detection device 1 of the present embodiment is used as follows, for example, at a site where particle beam therapy is performed. The first detectors 11a and 11b of the positron emission nucleus position detecting device 1 are arranged so as to face each other across the particle beam irradiation site of the patient (the surface of the first detector 11 at this time is on the YZ plane) To do). The second detector 12 is arranged on the back side of the patient's particle beam irradiation site (position facing the particle beam irradiation device with the patient sandwiched, XY plane).

  When the particle beam is irradiated here, a positron emission nucleus is generated at a position where the particle beam is irradiated (particles are stopped) in the patient's body, and a positron is emitted therefrom. Then, the first detector 11 captures a pair of γ-rays emitted when the emitted positron annihilates with an electron in the vicinity of the positron emitting nucleus.

  The second detector 12 capable of detecting the direction of arrival of γ-rays captures the γ-rays emitted when the atoms having nuclei after the positron-emitting nuclei emit positrons and β-decay change the energy state.

  Then, the control device 13 obtains a projection image representing the detection position of the γ-ray in the YZ plane obtained by the first detector 11, and the γ-ray in the XY plane obtained by the second detector 12. A virtual projection image representing the position of the source is obtained. Then, a three-dimensional image representing a position where γ rays are estimated to be generated is reconstructed from these projected images by a method such as back projection. The reconstructed three-dimensional image is output.

  The user refers to this three-dimensional image, determines the position where the particle beam is irradiated in the patient's body (irradiation target), and uses it to adjust the intensity and irradiation direction of the particle beam.

As described above, in this embodiment, the emitted positron generates a pair of annihilation γ-rays and emits one or more transition γ-rays when transitioning from the excited level to the predetermined level. Imaging is realized by measuring the detection position and the arrival direction of the pair of annihilation gamma rays and one or more transition gamma rays. As a result, it is possible to realize the determination of the irradiation position at the time of particle beam irradiation, the estimation of the reach of the medicine containing ¹⁴ O, etc. with higher accuracy.

DESCRIPTION OF SYMBOLS 1 positron emission nucleus position detection apparatus, 11 1st detector, 12 2nd detector, 13 control apparatus, 21 background removal part, 22 window setting part, 22 '1st window setting part, 23, 23' output control part , 24 Second window setting unit, 31 control unit, 32 storage unit, 33 interface unit, 34 output unit.

Claims (1)

A pair of first detectors each having a pair of surfaces arranged with a particle beam irradiation target interposed therebetween, each generating an image representing a detection position of γ-rays within the surface;
A second detector that is arranged in a direction different from the first detector with respect to the irradiation target, and that generates an image indicating an incident direction of γ rays;
Means for reconstructing a first three-dimensional image based on an image generated by the first detector when the first detector detects gamma rays and the second detector does not detect gamma rays ;
A second three-dimensional image based on images respectively generated by the first detector and the second detector when the first detector and the second detector detect γ rays substantially simultaneously. Means for reconfiguring,
Means for super-resolving and outputting the first three-dimensional image and the second three-dimensional image;
A positron emitting nuclear position detecting device.

Images