JP2001124857A - Positron camera system and beam irradiation position measurement method in the system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positron camera system capable of accurately measuring a beam irradiation position in a short time. SOLUTION: On the basis of a light emission distribution spread width (half- width Δr) of each of annihilation gamma beams 5a, 5b, a light emitting point depth position Δh of each of the annihilation gamma beams 5a, 5b in scintillators 2a, 2b of respective detectors 1a, 1b is found. From the found depth positions Δh of the light emitting points and incident angles θz, θy of the respective annihilation gamma beams 5a, 5b to the scintillators 2a, 2b of the respective detectors 1a, 1b, incident positions (calculated values of the center of gravity) Z, Y of the respective annihilation gamma beams 5a, 5b found as the centers (centers of gravity) of the signal distribution outputted from respective photoelectric multipliers 3a, 3b are corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positron camera system used for particle beam therapy and the like,
The present invention relates to a positron camera system capable of measuring an irradiation position (beam irradiation position) of a particle beam accurately and in a short time, and a beam irradiation position measuring method in the system.

[0002]

2. Description of the Related Art Conventionally, a treatment system for irradiating an affected part of a patient with a particle beam to perform treatment has been known. In such a treatment system, it is desired that the irradiation position of the particle beam (beam irradiation position) be accurately and quickly grasped in order to realize efficient treatment with less burden on the patient.

[0003] In such a treatment system, in general, a small amount of a focused positron emitter beam is irradiated into the body prior to treatment to measure the beam irradiation position, and the irradiation position is measured by a positron camera system. I have.

More specifically, as shown in FIG. 1 (a diagram showing the present invention), a positron emitter beam 4 is radiated into the body, and emitted by a positron emitter stopped at a predetermined position (point O) in the body. A pair of annihilation gamma rays (annihilation radiation) 5a and 5b (wavelength 511 keV) are detected. Here, the pair of annihilation gamma rays 5a and 5b are respectively detected by a pair of the detection devices 1a and 1b arranged opposite to each other, and the annihilation gamma rays 5a and 5b for the respective detection devices 1a and 1b are respectively detected.
The beam irradiation position (point O) is calculated by finding the intersection of the straight line connecting the incident positions 5b and the straight line formed by the beam axis L of the positron emitter beam 4.
Each of the detectors 1a and 1b is connected to each of the annihilation gamma rays 5a,
Scintillator 2a, 2b made of NaI (Tl) crystal or the like on which 5b is incident, and a plurality of photomultiplier tubes 3a for detecting the light quantity of annihilation gamma rays 5a, 5b emitting at an arbitrary depth position of the scintillator 2a, 2b. , 3b, and the center (center of gravity) of the signal distribution output from the plurality of photomultiplier tubes 3a, 3b is calculated for each of the detection devices 1a, 1b, like the Anger-type gamma camera.
Annihilation gamma rays 5a, 5 for scintillators 2a, 2b
The incident position of b is detected.

[0005]

By the way, the amount of the positron emitter beam 4 irradiated into the body in this way needs to be small in order to reduce the burden on the patient, and the measurement error of the beam irradiation position is small. The smaller the number of measurements (the number of measurement events), the smaller the number.
It is desirable that the size (thickness) of a and 2b be as large as possible.

However, when the thicknesses of the scintillators 2a and 2b are increased, the annihilation gamma rays 5a and 5 calculated based on the signals output from the photomultiplier tubes 3a and 3b are used.
b is changed according to the depth position of the light-emitting point in the scintillators 2a and 2b.
annihilation gamma ray 5 obliquely incident on a and 2b
There is a problem that a measurement error occurs at the beam irradiation positions a and 5b.

FIG. 8 is a diagram for explaining the relationship between the depth position of the light emitting point in the scintillators 2a and 2b and the measurement error of the beam irradiation position. In FIG. 8, the thickness of the scintillators 2a and 2b is D, and the position where the annihilation gamma rays 5a and 5b are generated is point O. The beam axis L of the positron emitter beam 4 is set to the Z axis for simplicity.

First, it is assumed that light is emitted at a point α _{1 on} the surface of the scintillator 2a on the first detecting device 1a side and light is emitted at a point β _{1 on} the bottom surface of the scintillator 2b on the second detecting device 1b side. In this case, conventionally, the scintillators 2a, 2
Since the thickness D of the b is negligible and both are calculated as emitting light at an intermediate position between the scintillators 2a and 2b, the emission points α ₁ and β ₁ are both calculated at the point α ′. , Β ′. Therefore, these two
The intersection of the straight line connecting the points α ′ and β ′ and the straight line formed by the beam axis L is point O ′, and ΔZ (= + D / 2 · tan θ _z ) between the point O which is the actual beam irradiation position. Measurement error will occur. Here, θ _z is a direction perpendicular to the plane of the scintillators 2a and 2b (X axis) and two points α
_1, it is the angle between a straight line connecting the beta _1.

Next, it is assumed that light is emitted at the point α _{2 on} the bottom surface of the scintillator 2a on the first detecting device 1a side, and is emitted at the point β _{2 on} the surface of the scintillator 2b on the second detecting device 1b side. In this case, both the emission points α ₂ and β ₂
In calculation, they are recognized as points α ″ and β ″. Therefore, the intersection of the straight line connecting these two points α ″ and β ″ and the straight line formed by the beam axis L is point O ″, and −ΔZ (= −D / 2 · tan θ
A measurement error of only _z ) will occur.

That is, the measurement error at the point O, which is the generation position of the annihilation gamma rays 5a and 5b, is ± ΔZ = ± D / 2 · at maximum.
tan θ _z , and the measurement accuracy decreases as the thickness D of the scintillators 2a and 2b increases.

The present invention has been made in view of the above points, and provides a positron camera system capable of measuring a beam irradiation position accurately and in a short time, and a method of measuring a beam irradiation position in the system. With the goal.

[0012]

According to a first aspect of the present invention, there is provided a pair of detectors for detecting a pair of annihilation radiations emitted by a positron emitter beam, respectively, wherein A pair of detection devices having a scintillator to which each annihilation radiation is incident, a plurality of light amount detectors for detecting the amount of annihilation radiation emitted at an arbitrary depth position of the scintillator, and the respective light amount detection of each of the detection devices Based on the signal detected by the detector, the incident position calculation means for calculating the incident position of each of the annihilation radiation to the scintillator of each of the detection devices, and the signal detected by each of the light amount detector of each of the detection devices A light emission distribution calculating means for calculating a spread width of a light emission distribution of each of the annihilation radiations in the scintillator of each of the detection devices, Based on the spread width of the emission distribution of each annihilation radiation calculated by the calculation means, the depth position of the emission point of each annihilation radiation in the scintillator of each detection device is obtained, and the obtained emission point is obtained. Based on the depth position and the incident angle of each of the annihilation radiations to the scintillator of each of the detection devices, based on the incident position correction means for correcting the incident position of each annihilation radiation calculated by the incident position calculation means, An irradiation position calculation for calculating a beam irradiation position based on an intersection of a straight line connecting the incident positions of the respective annihilation radiations corrected by the incident position correcting means and a straight line formed by the beam axis of the positron emitter beam. Means for providing a positron camera system.

In the above-mentioned first solving means, the signal converting means for converting a signal detected by each of the light quantity detectors of each of the detecting devices into a digital signal for each channel corresponding to each of the light quantity detectors. And distribution signal discriminating means for discriminating a channel through which a signal having a peak value equal to or more than a predetermined value flows among channels through which the signal converted by the signal converting means flows. It is preferable to calculate the spread width of the emission distribution of each annihilation radiation based on the signal flowing through the channel discriminated by the discriminating means. Further, it is preferable that the emission distribution calculating means calculates the spread width of the emission distribution of each of the annihilation radiations by a function approximation method. Further, it is preferable that the scintillator of each of the detection devices has a blackening process performed on an incident surface thereof.

According to a second aspect of the present invention, there is provided a pair of detectors for respectively detecting a pair of annihilation radiations emitted by a positron emitter beam, each of which receives the respective annihilation radiations. A pair of detectors having a scintillator, a plurality of light detectors for detecting the amount of annihilation radiation emitted at an arbitrary depth position of the scintillator, and signals detected by the respective light detectors of the respective detectors. Based on the incident position calculation means for calculating the incident position of each annihilation radiation to the scintillator of each detection device, and a straight line connecting the incident positions of each annihilation radiation calculated by the incident position calculation means, An irradiation position calculation method for calculating a beam irradiation position based on an intersection of a straight line formed by the beam axis of the positron emitter beam. Wherein the scintillator of each of the detection devices has a substantially circular cross-section centered on the generation position of each of the annihilation radiations so that each of the annihilation radiations enters substantially perpendicularly. I will provide a.

According to a third aspect of the present invention, there is provided a pair of detectors for respectively detecting a pair of annihilation radiations emitted by a positron emitter beam, each of which receives the respective annihilation radiations. In a beam irradiation position measurement method in a positron camera system including a scintillator and a pair of detection devices having a plurality of light amount detectors for detecting the amount of annihilation radiation emitted at an arbitrary depth position of the scintillator, the detection of the respective Calculating the incident position of each of the annihilation radiations to the scintillator of the device; calculating the spread width of the emission distribution of each annihilation radiation in the scintillator of each of the detection devices; and calculating the calculated each annihilation. Based on the spread width of the emission distribution of radiation, based on the scintillator of each of the detection devices Calculating the depth position of the emission point of the annihilation radiation, the calculated depth position of the emission point, and the angle of incidence of each of the annihilation radiation with respect to the scintillator of each of the detection devices, the calculated. Correcting the incident position of each of the annihilation radiations, and irradiating the beam based on an intersection of a straight line connecting the corrected incident positions of the annihilation radiations and a straight line formed by the beam axis of the positron emitter beam. Calculating the position.

According to the first and third solutions of the present invention, the spread width of the emission distribution detected by each light amount detector of each detection device is determined by the depth position of the emission point of each annihilation radiation in each scintillator. The depth position of the emission point of each annihilation radiation in the scintillator of each detection device is obtained based on the spread width of the emission distribution of each annihilation radiation utilizing the fact that it changes in accordance with the following.
Then, based on the obtained depth position of the light emitting point and the incident angle of each annihilation radiation to the scintillator of each detection device, it was calculated as the center (center of gravity) of the signal distribution output from each light amount detector. The incident position of each annihilation radiation is corrected. Thus, even when the annihilation radiation enters the scintillator from an oblique direction, the incident position of each annihilation radiation can be detected accurately and in a short time. Therefore,
The beam irradiation position can be measured accurately and in a short time, so that an efficient treatment with less burden on the patient can be realized.

According to the second solution of the present invention, since the scintillator has a substantially circular cross section centered on the position where each annihilation radiation is generated, each annihilation radiation is oblique to the scintillator. Thus, even if the incident position of each annihilation radiation is not corrected, the measurement error of the beam irradiation position can be effectively reduced.

[0018]

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

First, an embodiment of a positron camera system according to the present invention will be described with reference to FIGS.

First, the overall configuration of the positron camera system according to the present embodiment will be described with reference to FIG.

As shown in FIG. 1, the positron camera system comprises a pair of detectors 1a, 1b for detecting a pair of annihilation gamma rays (annihilation radiation) 5a, 5b emitted by the positron emitter beam 4, Each detection device 1a,
1b, positron camera circuits 11, 12 connected to
A positron camera computer 13 connected to the positron camera circuits 11 and 12 is provided. Note that the detection devices 1a and 1b are arranged to face each other with a pair of annihilation gamma rays 5a and 5b generated positions (point O) interposed therebetween. The detectors 1a and 1b respectively include scintillators 2a and 2b made of NaI (Tl) crystal or the like, on which the annihilation gamma rays 5a and 5b are incident, respectively, and the scintillators 2a and 2b.
A plurality of photomultiplier tubes (light amount detectors) 3a, which are arranged at the backs of the light emitting devices a and 2b and detect the light amounts of the annihilation gamma rays 5a and 5b which emit light at arbitrary depth positions of the scintillators 2a and 2b.
3b.

Next, the details of the positron camera system shown in FIG. 1 will be described with reference to FIG. Since the configurations of the positron camera circuits 11 and 12 are basically the same, the configuration of the first positron camera circuit 11 will be mainly described below.

As shown in FIG. 2, a pair of detectors 1a,
1b, the plurality of photomultiplier tubes 3 of the first detection device 1a
The signal detected by a is input to the first positron camera circuit 11.

The first positron camera circuit 11 has a signal processing unit 15 for processing signals detected by the plurality of photomultiplier tubes 3a of the first detector 1a for each channel corresponding to each photomultiplier tube 3a. are doing. Signal processing unit 15
Is a waveform shaping circuit 16 and an ADC (Analog Digital C
and a converter 17 for converting a signal detected by each photomultiplier tube 3a into a digital signal for each channel corresponding to each photomultiplier tube 3a. The signal processing unit 15 also includes a memory 18 and a DSP (Digital Sign) for processing the ADC value converted by the ADC 17.
al Processor) circuit (signal processing circuit) 19.

Further, the first positron camera circuit 11 includes:
A distributed signal discriminating circuit 20 for discriminating a channel in which a signal having a peak value equal to or more than a predetermined value among signals processed by the signal processing unit 15 flows, and a sum of the signals processed by the signal processing unit 15 is set to a predetermined value. A signal addition discriminating circuit 21 for judging whether or not the coincidence has occurred, and a coincidence circuit 22 for judging whether coincidence with the second positron camera circuit 12 are simultaneously established.

Further, the first positron camera circuit 11
Has a photomultiplier tube high-voltage power supply 23 for supplying power to each photomultiplier tube 3a, and a circuit low-voltage power supply 24 for supplying power to the positron camera circuit 11 itself.

Further, the first positron camera circuit 1
1 has a bus 25 to which the signal processing unit 15 and the circuit low-voltage power supply 24 are connected, and a CPU board 26 connected to the bus 25. The CPU board 26 is controlled by the upper sequencer 14.

In the present embodiment, the waveform shaping circuit 16 of the signal processing unit 15 and the AD
The signal conversion means is realized by C17, and the distributed signal discrimination means is realized by the distributed signal discrimination circuit 20. Also, C
The PU board 26 implements an incident position calculating means,
The SP circuit 19 and the CPU board 26 implement a light emission distribution calculation unit. Further, the positron camera computer 13 realizes an incident position correcting unit and an irradiation position calculating unit.

Next, the operation of the positron camera system shown in FIGS. 1 and 2 will be described.

As shown in FIGS. 1 and 2, signals detected by a plurality of photomultiplier tubes 3a and 3b of a pair of detectors 1a and 1b are input to positron camera circuits 11 and 12, and are output from the positron camera circuit. In 11 and 12,
The incident positions of the annihilation gamma rays 5a and 5b with respect to each of the scintillators 2a and 2b of the detection devices 1a and 1b and the spread width of the emission distribution are calculated.

The positron camera circuits 11 and 12 respectively shape the signals detected by the photomultiplier tubes 3 a and 3 b by the waveform shaping circuit 16 of the signal processing unit 15, and then, via the ADC 17, the waves proportional to the amount of light. Outputs a pulse (digital signal) with a high value.

At this time, the signal of each channel output from the waveform shaping circuit 16 of the signal processing unit 15 is branched and distributed signal discrimination circuit 20 provided outside the signal processing unit 15
Is input to Then, in the distribution signal discrimination circuit 20, a channel through which a signal having a peak value equal to or more than a predetermined value flows among channels through which the signal output from the waveform shaping circuit 16 flows is discriminated by a comparator or the like. In the ADC 17 of the processing unit 15,
Only signals having a peak value equal to or greater than a predetermined value among the signals output from the waveform shaping circuit 16 and flowing through each channel are converted into digital signals. The ADC value converted by the ADC 17 is transmitted to the memory 18 and the DSP circuit 19.

The signals of the respective channels (signals output from the respective photomultiplier tubes 3a) input to the distribution signal discriminating circuit 20 are input to the signal adding discriminating circuit 21. Only when the sum of the signals output from the multipliers 3a and 3b is a predetermined value (a value corresponding to an annihilation gamma ray having a wavelength of 511 keV), discrimination is performed. Thereby, annihilation gamma ray (wavelength 511 keV)
It is possible to remove gamma rays (background noise) having different energies other than the above. Further, in the coincidence circuit 22 connected to the signal addition discrimination circuit 21, it is determined whether coincidence is simultaneously established between the first positron camera circuit 11 and the second positron camera circuit 12, and the coincidence is determined between the two. The ADC value converted by the ADC 17 is written to the memory 18 only when the conditions are satisfied at the same time.

Thereafter, the DSP circuit 19 of the signal processing unit 15
Thus, a plurality of signals output from each photomultiplier tube 3a are approximated by a function (eg, polynomial approximation). Note that the DSP circuit 1
9 and the ADC value (including the channel number) of the signal flowing through the channel discriminated by the distribution signal discrimination circuit 20 via the bus 25 for each measurement event. 26.

Here, for example, when the polynomial approximation method is used as the function approximation method, each of the photomultiplier tubes 3a, 3b
The distance between the center (center of gravity) of the signal distribution output from the photomultiplier tubes 3a and 3b is denoted by r, and each scintillator 2
The spread of the emission distribution of the annihilating gamma rays 5a and 5b at a and 2b is approximated by a polynomial P (r) = a + br + cr ² + dr ³ +... Then, coefficients a, b, c,.
The data is written into the memory 18 of the signal processing unit 15.

Here, in the CPU board 26, A
Each photoelectron amplifier tube 3a, 3b converted by DC17
Is multiplied by the position information (determined by the channel number) of each photomultiplier tube 3a and output from each photomultiplier tube 3a. By calculating the centers (centroids) of the signal distributions, the incident positions of the annihilation gamma rays 5a and 5b with respect to the scintillators 2a and 2b of the detection devices 1a and 1b are calculated.

In the CPU board 26, DS
Each annihilation gamma ray 5a, 5b calculated by the P circuit 19
The spread width of the emission distribution of the annihilated gamma rays 5a and 5b in the scintillators 2a and 2b of the detection devices 1a and 1b is calculated based on the emission distribution of the detection devices 1a and 1b.

When the above-described polynomial approximation technique is used as the function approximation technique, the CPU board 26 indicates the spread of the light emission distribution of the annihilated gamma rays 5a and 5b written in the memory 18 of the signal processing unit 15. Coefficient a
, A half-value width Δr that satisfies P (Δr) = a / 2 (2) is obtained as the spread width of the light emission distribution.

The incident positions (calculated center of gravity) of each of the annihilation gamma rays 5a and 5b and the spread width of the light emission distribution calculated by the CPU board 26 of the positron camera circuits 11 and 12 in this manner are determined by the bus for each measurement event. 25 to the positron camera computer 13.

In the positron camera computer 13, the scintillators 2a and 2b of the detectors 1a and 1b are controlled based on the incident positions of the annihilation gamma rays 5a and 5b calculated by the CPU boards 26 of the positron camera circuits 11 and 12. The incident angles of the annihilation gamma rays 5a and 5b are obtained. The scintillators 2a, 2b of the detectors 1a, 1b are based on the spread width of the light emission distribution of the annihilation gamma rays 5a, 5b calculated by the DSP circuit 19 of the positron camera circuits 11, 12 and the CPU board 26.
The depth position of the emission point of each annihilation gamma ray 5a, 5b at b is obtained.

More specifically, as shown in FIG. 3A, the case where the annihilation gamma ray 5a is emitted on the ZX plane will be described as an example.
_z is obtained, and Δh is obtained as the depth position of the emission point of the annihilation gamma ray 5a.

The positron camera computer 13 has:
Experimentally determined spread of emission distribution (half-width Δr)
Is stored in advance in the form of a function or a table, and the depth position Δh of the light emitting point is obtained based on the stored relationship. FIGS. 4 and 5 are diagrams showing an example of the relationship between the spread width (half width Δr) of the light emission distribution and the depth position Δh of the light emission point, which are experimentally obtained. FIG. 4 shows the scintillator 2a,
The height position (distance h (= D−Δh): distance between the light emitting point and the surface of the photomultiplier tube) of the light emitting point in 2b is 2.5c
m, 3.0cm, 3.5cm, 4.0cm, 4.5c
FIG. 5 is a diagram showing an example of a light emission distribution when the light emission point is changed to 5.0 cm and 5.0 cm. FIG. 5 shows the height position (distance h (D) of the light emission point on the scintillators 2a and 2b in the case shown in FIG.
FIG. 4 is a diagram illustrating an example of a relationship between -Δh)) and a spread width of the emission distribution (half-width Δr).

Then, in the positron camera computer 13, the depth position Δ
h and the scintillators 2a and 2b of the respective detection devices 1a and 1b.
The incident position (calculated center of gravity) of each of the annihilation gamma rays 5a, 5b calculated by the CPU board 26 of the positron camera circuits 11, 12 is corrected based on the incident angle θ _{z of} each of the annihilation gamma rays 5a, 5b with respect to.

Here, the incident position in the Z direction of the annihilation gamma ray 5a calculated by the CPU board 26 (calculated center of gravity)
Is Z = Z0, the incident position Z is corrected as an incident position Z ′ according to the following equation (3) (FIG. 3).
(A)).

Z ′ = Z0 + tan θ _z · (D / 2−Δh) (3) Here, for simplicity of description, the annihilation gamma ray 5
Although it is assumed that the emission direction of a is on the ZX plane, if the emission direction of the annihilation gamma ray 5a is not on the ZX plane, the correction in the Z direction and the Y direction is performed simultaneously. That is, the incident angles of the annihilation gamma rays 5a and 5b with respect to the scintillators 2a and 2b of the detection devices 1a and 1b are obtained as θ _z and θ _y for each of the Z and Y directions, and the Z and Y directions are obtained.
The incident position (calculated center of gravity) Z, Y is corrected for each direction.
At this time, the incident position Z in the Z direction is corrected according to the above equation (3). On the other hand, the incident position Y in the Y direction
Assuming that the incident position in the Y direction of the annihilation gamma ray 5a calculated by the circuit 19 is Y = Y0, this incident position Y
Is corrected as the incident position Y ′ according to the following equation (4).

Y ′ = Y 0 + tan θ _y · (D / 2−Δh) (4) Thereafter, in the positron camera computer 13, a straight line connecting the incident positions of the annihilated gamma rays 5 a and 5 b corrected in this manner is used. The beam irradiation position is calculated by finding the intersection of the positron emitter beam 4 and the straight line formed by the beam axis L.

As described above, according to the present embodiment, the spread width of the light emission distribution detected by each photomultiplier tube 3a, 3b of each detection device 1a, 1b is determined by each annihilation gamma ray 5a at each scintillator 2a, 2b. , 5b (the emission distribution becomes wider as the light is emitted at a point farther from each of the photomultiplier tubes 3a, 3b), and the extinction gamma rays 5a, 5b The depth position Δh of the emission point of each annihilation gamma ray 5a, 5b in each of the scintillators 2a, 2b of each of the detection devices 1a, 1b is obtained based on the spread width of the emission distribution (half width Δr). Then, the obtained depth position Δh of the light emitting point and each annihilation gamma ray 5a, 5 with respect to the scintillator 2a, 2b of each detection device 1a, 1b.
b based on the incident angles θ _z and θ _y of the respective photomultipliers 3
The incident positions (center-of-gravity calculated values) Z, Y of the annihilation gamma rays 5a, 5b calculated as the centers (centroids) of the signal distributions output from the signals a, 3b are corrected. Thus, even when the annihilation gamma rays 5a, 5b enter the scintillators 2a, 2b from oblique directions, the incident positions Z ', Y' of the annihilation gamma rays 5a, 5b can be detected accurately and in a short time. Therefore, the irradiation position of the beam can be measured accurately and in a short time, so that an efficient treatment with less burden on the patient can be realized.

Further, according to the present embodiment, of the signals output from the waveform shaping circuit 16 and flowing through each channel, only the signal having a peak value equal to or greater than a predetermined value is determined by the signal distribution discriminating circuit 2.
Since the signal is discriminated by 0 and input to the ADC 17, the range of the signal to be processed by the DSP circuit 19 and the CPU board 26 can be narrowed. Therefore, the disappearing gamma rays 5a and 5b in the DSP circuit 19 and the CPU board 26 can be narrowed down.
Can be calculated efficiently.

In the above embodiment, the incident position calculating means is realized by the CPU boards 26 of the positron camera circuits 11 and 12, and the DSP circuit 19 and the C
Although the light emission distribution calculation means is realized by the PU board 26, these incident position calculation means and light emission distribution calculation means can be realized at any place. Specifically, for example, A converted by the ADC 17 of the signal processing unit 15
Positron camera calculator 1 for each measurement event
3 and the positron camera computer 13 can realize a light emission distribution calculating means. In this case, the positron cameras 11 and 12 shown in FIG.
The circuit 19 can be eliminated (see FIG. 6). In the positron camera system shown in FIG.
In the ADC 17, only signals having a peak value equal to or greater than a predetermined value among the signals flowing through the respective channels output from the waveform shaping circuit 16 are converted into digital signals, and the respective annihilating gamma rays 5 a and 5 b calculated by the CPU board 26. Signal discrimination circuit 2 along with the incident position (calculated value of the center of gravity)
The ADC value (including the channel number) of the signal flowing through the channel discriminated by 0 is transmitted to the positron computer 13, and the positron camera computer 13 calculates the spread width of the emission distribution of each annihilation gamma ray 5 a, 5 b. Similarly, C of the positron camera circuits 11 and 12
The incident position calculation means realized by the PU board 26 can be realized by the positron camera computer 13.

In the above-described embodiment, it is preferable that the scintillators 2a and 2b of each of the detectors 1a and 1b have their incident surfaces blackened. In the scintillators 2a and 2b, a radial direction (4π direction) from the light emitting point
About half of the light uniformly radiated to the photomultiplier tubes 3a, 3
Irradiated on the b side, the other half is the scintillator 2 on the opposite side
Irradiation is performed on the surfaces (incident surfaces) of a and 2b. Conventionally, in order to increase the amount of light measured by the photomultiplier tubes 3a and 3b, a white pigment or the like is generally applied to the incident surfaces of the scintillators 2a and 2b. However, scintillator 2
When the incident surfaces of the a and b are subjected to the whitening process, of the light emitted from the light emitting points of the annihilation gamma rays 5a and 5b, the light applied to the incident surfaces of the scintillators 2a and 2b is irregularly reflected, and An error easily occurs in the relationship between the spread of the emission distribution detected by the multipliers 3a and 3b and the depth position Δh of the emission point. On the other hand, when the incident surfaces of the scintillators 2a and 2b are blackened, the photomultiplier tubes 3a and 3
The spread of the emission distribution detected by b and the depth position Δ of the emission point
h can be accurately grasped, and the incident positions of the annihilation gamma rays 5a and 5b with respect to the scintillators 2a and 2b can be accurately corrected.

Next, another embodiment of the positron camera system according to the present invention will be described with reference to FIG. The present embodiment is substantially the same as the above-described positron camera system shown in FIGS. 1 to 6 except that the shape of the scintillator of the detection device is different.

As shown in FIG. 7, the detectors 1a and 1b according to the present embodiment have a spherical scintillator 2a having a substantially circular cross-sectional shape centered on the generation positions (point O) of the annihilation gamma rays 5a and 5b. , 2b and the scintillators 2a,
And a plurality of photomultiplier tubes 3a and 3b arranged on the back of the scintillator 2a along the shape of the scintillator 2a.
The annihilation gamma rays 5a and 5b are incident almost perpendicularly to 2b.

As described above, according to the present embodiment, the scintillators 2a and 2b have a substantially circular cross-section centered on the positions (points O) where the annihilating gamma rays 5a and 5b are generated. Gamma ray 5 extinguished for 2b
Since a and 5b do not enter from an oblique direction, even when the incident positions of the annihilation gamma rays 5a and 5b are not corrected, the measurement error of the beam irradiation position can be effectively reduced.

[0054]

As described above, according to the present invention, the beam irradiation position can be measured accurately and in a short time.
For this reason, it is possible to realize an efficient treatment with a small burden on the patient.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an embodiment of a positron camera system according to the present invention.

FIG. 2 is a block diagram showing details of the positron camera system shown in FIG. 1;

FIG. 3 is a diagram for explaining a method of correcting an incident position of an annihilation gamma ray to a scintillator.

FIG. 4 shows the position of a light emitting point on a scintillator (distance h (= D
-Δh): distance between the light emitting point and the surface of the photomultiplier tube)
The figure which shows an example of the light emission distribution at the time of changing.

5 is a diagram showing an example of the relationship between the position (distance h (= D−Δh)) of a light emitting point in a scintillator and the spread width (half width Δr) of a light emission distribution in the case shown in FIG. 4;

FIG. 6 is a block diagram showing a modification of the positron camera system shown in FIG. 1;

FIG. 7 is a block diagram showing another embodiment of the positron camera system according to the present invention.

FIG. 8 is a diagram for explaining a relationship between a depth position of a light emitting point in a scintillator and a measurement error of a beam irradiation position.

[Explanation of symbols]

 1a, 1b Detector 2a, 2b Scintillator 3a, 3b Photomultiplier tube (light quantity detector) 4 Positron emitter beam 5a, 5b Annihilation gamma ray (annihilation radiation) 11, 12 Positron camera circuit 13 Positron camera computer 14 Upper sequencer 15 Signal processing Unit 16 waveform shaping circuit 17 ADC 18 memory 19 DSP circuit (signal processing circuit) 20 distributed signal discrimination circuit 21 signal addition discrimination circuit 22 coincidence circuit 23 high voltage power supply for photomultiplier tube 24 low voltage power supply for circuit 25 bus 26 CPU board O Annihilation gamma ray generation position L Beam axis

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shunichiro Makino 2-1 Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture F-term in the Toshiba Hamakawasaki Plant (reference) 2F067 AA04 AA31 CC19 EE10 FF11 HH10 JJ04 LL14 RR00 RR01 RR02 RR12 RR21 RR31 TT01 2G088 EE01 FF04 FF14 GG16 GG20 JJ06 KK15 KK29 KK35 LL13 4C082 AA01 AC02 AC04 AE01 AJ04 AJ13 AP12

Claims (6)

[Claims] 1. A pair of detectors for respectively detecting a pair of annihilation radiations emitted by a positron emitter beam, each comprising a scintillator to which each of said annihilation radiations enters, and an arbitrary depth of said scintillator. A pair of detecting devices having a plurality of light amount detectors for detecting the amount of annihilation radiation emitted at the position, based on signals detected by the respective light amount detectors of the respective detecting devices, Incident position calculating means for calculating an incident position of each of the annihilation radiations with respect to the scintillator; and, based on a signal detected by each of the light amount detectors of each of the detection devices, each of the annihilations in the scintillator of each of the detection devices. A light emission distribution calculating means for calculating a spread width of the light emission distribution of the radiation, and the light emission of each of the annihilation radiations calculated by the light emission distribution calculating means Based on the spread width of the cloth, the depth position of the emission point of each annihilation radiation in the scintillator of each detection device, and the depth position of the obtained emission point, An incident position correcting unit that corrects an incident position of each of the annihilation radiations calculated by the incident position calculating unit, based on an incident angle of each of the annihilation radiations to a scintillator; and each of the positions corrected by the incident position correction unit. A positron camera comprising: an irradiation position calculation unit that calculates a beam irradiation position based on an intersection point of a straight line connecting incident positions of annihilation radiation and a straight line formed by the beam axis of the positron emitter beam. system. 2. A signal conversion means for converting a signal detected by each of the light quantity detectors of each of the detection devices into a digital signal for each channel corresponding to each of the light quantity detectors, wherein the signal is converted by the signal conversion means. Distribution signal discriminating means for discriminating a channel in which a signal having a peak value equal to or more than a predetermined value flows among channels in which the signal flows, wherein the light emission distribution calculating means includes a signal flowing in the channel discriminated by the distribution signal discriminating means. 2. The positron camera system according to claim 1, wherein the spread width of the emission distribution of each of the annihilation radiations is calculated based on the following formula. 3. The positron camera system according to claim 2, wherein said emission distribution calculating means calculates the spread width of the emission distribution of each said annihilation radiation by a function approximation method. 4. A positron camera system according to claim 1, wherein said scintillator of each of said detection devices has a blackening process applied to an incident surface thereof. 5. A pair of detectors for respectively detecting a pair of annihilation radiations emitted due to a positron emitter beam, each comprising a scintillator to which each said annihilation radiation enters, and an arbitrary depth of said scintillator. A pair of detecting devices having a plurality of light amount detectors for detecting the amount of annihilation radiation emitted at the position, based on signals detected by the respective light amount detectors of the respective detecting devices, An incident position calculating means for calculating an incident position of each of the annihilation radiations with respect to the scintillator; a straight line connecting the incident positions of the respective annihilation radiations calculated by the incident position calculation means with a beam axis of the positron emitter beam; An irradiation position calculation unit that calculates a beam irradiation position based on an intersection point where the straight line intersects, Nchireta is positron camera system characterized by having a substantially circular cross-sectional shape around the generation position of the annihilation radiation to each annihilation radiation is incident substantially perpendicularly. 6. A pair of detection devices for respectively detecting a pair of annihilation radiations emitted due to a positron emitter beam, each comprising a scintillator to which said annihilation radiation enters, and an arbitrary depth of said scintillator. A beam irradiation position measuring method in a positron camera system including a pair of detection devices having a plurality of light amount detectors for detecting the amount of annihilation radiation emitted at the position, wherein each of the annihilation radiations to the scintillator of each of the detection devices Calculating the incident position of; and calculating the spread width of the emission distribution of each annihilation radiation in the scintillator of each of the detection devices; based on the calculated spread width of the emission distribution of each annihilation radiation. The depth position of the emission point of each of the annihilation radiations in the scintillator of each of the detection devices. Correcting the calculated incident position of each of the annihilation radiations based on the obtained depth position of the light emitting point and the incident angle of each of the annihilation radiations to the scintillator of each of the detection devices. And calculating a beam irradiation position based on an intersection of a straight line connecting the corrected incident positions of the annihilation radiations and a straight line formed by the beam axis of the positron emitter beam. A beam irradiation position measuring method.