Patent Application
20160015338
The present invention relates to dosimeters of measuring a dose of radiation such as an X-ray.
A dosimeter is conventionally known (Non-Patent Literature 1), in which a cadmium (Cd) scintillator is used for a detection unit of detecting a radiation and light generated by the detection unit is transmitted through an optical fiber and detected. Since the detection unit and the optical fiber have a satisfactory transparency to an X-ray, this dosimeter is, for example, capable of measuring an absorption dose on a skin surface of a human body in real time while suppressing influence on an X-ray image when taking or fluoroscopically viewing the X-ray image. Therefore, the dosimeter has been widely used particularly in the field of medical image diagnosis.
Non-Patent Literature 1: Hwang E, Gaxiola E, Vlietstra R E, et al.: Real-time measurement of skin radiation during cardiac catheterization. Cathet Cardiovasc Diagn, 43 (4), pp. 367-370 (1998).
However, the conventional dosimeter has an environmental problem because the scintillator used in the detection unit includes cadmium (Cd).
A dosimeter according to an aspect of the present invention is a dosimeter of measuring a dose of radiation and comprises a radiation detection part including a phosphor made of Y2O2S as a matrix with at least Eu as an activating agent, an optical fiber of transmitting light emitted from the phosphor of the radiation detection part by receiving a radiation, and a light detection part of detecting the light transmitted through the optical fiber.
In this dosimeter, when the radiation detection part receives a radiation, the phosphor included in the radiation detection part emits light. The light emitted from the radiation detection part is entered into the optical fiber and transmitted. This light transmitted with the optical fiber is detected by the light detection part. The dose of radiation can be measured based on the detection result of the light detection part.
Herein, since the light that is emitted from the radiation detection part by receiving a radiation can be transmitted to the light detection part away from the radiation detection part by the optical fiber, the radiation is not blocked by the light detection part. Furtheremore, the foregoing phosphor made of Y2O2S as a matrix with at least Eu as an activating agent has a satisfactory transparency to the radiation and the optical fiber has also a satisfactory transparency to the radiation unlike a cable and lead wire made of normal metal. Accordingly, when taking or fluoroscopically viewing an image by using a radiation, it is capable of suppressing an influence on the image taken or fluoroscopically viewed. Therefore, it is capable of measuring a radiation dose in real time when taking or fluoroscopically viewing the image while suppressing influence on the image taken by using the radiation.
Moreover, since the phosphor in the radiation detection part is the phosphor made of Y2O2S as a matrix with at least Eu as an activating agent and does not include cadmium (Cd), it is capable of providing a dosimeter with an environmental safety.
In the foregoing dosimeter, the radiation may be an X-ray emitted from an X-ray generating apparatus with a tube voltage of 40 kV or more and 150 kV or less, and the phosphor may emit light of red area including a bright line spectrum in the wavelength range of 600 nm or more and 630 nm or less. In this dosimeter, it is capable of suppressing influence on an image taken or fluoroscopically viewed by using an X-ray which is emitted from the X-ray generating apparatus with the foregoing predetermined range of tube voltage and has energy and species of radiation suitable for medical image diagnosis, and measuring a dose of the X-ray in real time during taking or fluoroscopically viewing the X-ray image. Furthermore, the light emitted from the phosphor when receiving the X-ray has a bright line spectrum in the wavelength range of 600 nm or more and 630 nm or less corresponding to a transmitting wavelength range of an easily available optical fiber. Accordingly, it is capable of providing a dosimeter with low price, by which sensitivity and accuracy for the dose of X-ray to be measured can be enhanced.
In the foregoing dosimeter, an end surface of a light incident side part of the optical fiber may be an inclined surface inclined with respect to the optical axis of the optical fiber and the phosphor of the radiation detection part may be disposed to face a peripheral surface in opposition to the inclined surface of the optical fiber so that the light emitted from the phosphor enters from the peripheral surface and reaches the inclined surface. In this dosimeter, the light emitted from the phosphor of the radiation detection part is condensed so as to direct to a core around the optical axis of the optical fiber due to refraction on the peripheral surface, when entering from the peripheral surface in opposition to the inclined surface of the optical fiber. The light passing through the inside of the optical fiber while being condensed in this way reaches the inclined surface from inside of the optical fiber, and is reflected at the inclined surface and transmitted in the core around the optical axis so as to be directed to a light-outgoing end part. By entering the light from the peripheral surface of the optical fiber and reflecting the light from the inside at the inclined surface in this way, it is capable of efficiently guiding and transmitting the light, which is emitted from the phosphor, in the core of optical fiber, in comparison with a case of directly entering the light from outside into the end surface of light-incoming end part of the optical fiber. Accordingly, it is capable of further improving sensitivity and accuracy for the dose of radiation to be measured.
In the foregoing dosimeter, the inclined surface of the light-incoming end part of the optical fiber may be mirror finished and applied with a light reflective coating to enhance reflectivity to the foregoing light. In this dosimeter, since the inclined surface of the optical fiber is mirror finished, light scattering at the inclined surface can be reduced. Moreover, since the inclined surface is applied with the light reflective coating to enhance light reflectivity, it is capable of enhancing the reflectivity of light when the light entered from the peripheral surface of the optical fiber and transmitted inside of the optical fiber is reflected at the inclined surface. Accordingly, it is capable of further efficiently guiding and transmitting the light, which is emitted from the phosphor, in the core of optical fiber and further improving the sensitivity and accuracy of the dose of radiation to be measured.
In the foregoing dosimeter, the foregoing optical fiber may be an optical fiber made of a fluororesin. In this dosimeter, by using the optical fiber made of a fluororesin, it is capable of having a satisfactory transparency to an X-ray and transmitting a red light emitted from the phosphor made of Y2O2S as a matrix with at least Eu as an activating agent, with low transmission loss.
According to the present invention, it is capable of providing a dosimeter with an environmental safety, by which a dose of radiation can be measured in real time when taking or fluoroscopically viewing an image by using the radiation while suppressing influence on the image taken or fluoroscopically viewed.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. It is noted that, although the present embodiment will be described with respect to an example in which the present invention is applied to a dosimeter of measuring a dose of X-ray, the present invention is applicable to a dosimeter of measuring a dose of radiation except for an X-ray.
The X-ray detection part 100 has a phosphor that emits light by receiving an X-ray as a radiation.
The optical fiber 200 has a light-incoming end part 201 where the light emitted from the phosphor of the X-ray detection part 100 is entered and a light-outgoing end part 202 where the light entered and transmitted from the light-incoming end part 201 exits. By using the optical fiber 200, since the light that is emitted from the phosphor of X-ray detection part 100 when receiving an X-ray can be transmitted to the light detection part 310 away from the X-ray detection part 100, the X-ray is not blocked by the light detection part 310.
Furtheremore, the light detection part 310 detects the light that exits from the light-outgoing end part 202 of the optical fiber 200. The light detection part 310 includes an optical fiber connection part 311 that is detachably connected with the light-outgoing end part 202 of the optical fiber 200, and a cable connection part 312 that is detachably connected with an end of a cable 315. Another end of the cable 315 is detachably connected with a cable connection part 301 of the main body apparatus 300. The cable 315 has a function of transmitting a signal detected with the light detection part 310 to the main body apparatus 300. As the light detection part 310, for example, a photomultiplier tube (PMT), a photodiode, or the like can be used. It is noted that electric power required for the light detection part 310 may be supplied from a battery, which is installed in the light detection part 310, or may be supplied from the main body apparatus 300 side via the cable 315.
Moreover, the light detection part 310 may be configured so that two or more sets of the X-ray detection probes 50 can be detachably connected therewith. In the example of
The X-ray detection part 100 includes a base member 110 made of, for example, plastic material, and a phosphor sheet 140 provided on the base member 110 in the form of a layer or a plate. The phosphor sheet 140, for example, has a two-layered structure and includes a phosphor 120 and a support 130 of supporting the phosphor 120.
As the support 130, for example, a support having the shape of a thin plate, which is made of plastic material such as acrylic, polyethylene, etc. can be used. The thickness of the support 130 is, for example, in the range of 0.05-1.0 [mm] and preferably in the range of 0.1-0.5 [mm]. It is noted that, with respect to the material and thickness of the support 130, it is enough to have a satisfactory transparency to an X-ray to the extent that influence on an image taken or fluoroscopically viewed by using the X-ray can be suppressed, and it is not limited to the foregoing examples.
The mass per unit area of the layer-shaped phosphor 120 coated and dried on a surface (upper surface in the figure) perpendicular with respect to the thickness direction of the support 130 is, for example, in the range of 20-400 [mg/cm2] and preferably in the range of 100-300 [mg/cm2]. The thickness of the phosphor 120 is, for example, in the range of 0.5-1.5 [mm] and preferably in the range of 0.8-0.9 [mm]. It is noted that, with respect to the quantity and thickness of the phosphor 120, it is enough to acquire a satisfactory fluorescent light necessary for taking or fluoroscopically viewing an image by using an X-ray and have a satisfactory transparency to the X-ray to the extent that influence on an image taken or fluoroscopically viewed by using the X-ray can be suppressed, and it is not limited to the foregoing examples.
There are several methods to forming the foregoing phosphor sheet 140 and the phosphor sheet can be formed, for example, by using following methods. To start with, binder with organic synthetic resin dissolved in organic solvent, etc. is added to phosphor powder, and coating liquid like paint slurry with the phosphor turbidly mixed in the binder is prepared. By coating this coating liquid on the support 130 so as to have a predetermined coated mass and drying it, the phosphor sheet 140 having the phosphor 120 of the foregoing mass per unit area can be acquired. In coating of the foregoing coating liquid, in addition to a method with a brush or spray used in painting, various kinds of a coating tool, coating machine or printing machine, which is called a coater used in printing or the like, may be used. The coated film may be dried by heating in addition to drying at room temperature. The phosphor sheet 140 may be formed by a method except for the foregoing exemplified method.
The phosphor sheet 140 with the foregoing configuration is, for example, fixed on the base member 110 with an adhesive material so that the side near the support 130 is attached to the base member 110. On the surface (lower surface in the figure) of the base member 110, which is opposite to the phosphor sheet 140, a layer of adhesive may be formed so as to easily attach on a skin of a human body and so on. The shape in a surface direction perpendicular to a thickness direction of the base member 110, on which the phosphor sheet 140 is formed, may be, for example, a square with the sides of about several mm to ten and several mm, or a circular shape with a diameter of about several mm to ten and several mm. Each of these surfaces may have a planar shape or a curved surface shape.
The light-incoming end part 201 of the optical fiber 200 is fixed on the phosphor sheet 140 formed on the base member 110 with, for example, an adhesive material. As shown with a dashed line in
The phosphor 120 is a phosphor made of Y2O2S as a matrix with at least Eu as an activating agent and emits light by receiving an X-ray as a radiation. In this embodiment, a phosphor made of Y2O2S:Eu,Sm, in which a small amount of Sm for improving characteristics is further added, is used as the phosphor 120. It is noted that a phosphor made of Y2O2S:Eu without Sm added may be used as the phosphor 120.
The phosphor 120 made of the foregoing predetermined material emits light in a red region, which has a bright line spectrum in the wavelength range of 600 nm or more and 630 nm or less, when receiving an X-ray from an X-ray generating apparatus in which, for example, a target of tungsten, molybdenum or the like is used and a tube voltage is set to 40 kV or more and 150 kV or less. The wavelength range of 600 nm or more and 630 nm or less corresponds to a transmittable wavelength range of an easily available optical fiber. Since the phosphor 120 made of the foregoing predetermined material does not include cadmium (Cd), it is capable of configuring the dosimeter that includes the X-ray detection part 100 having an environmental safety.
The foregoing phosphor 120 made of Y2O2S as a matrix with at least Eu as an activating agent has a satisfactory transparency to an X-ray. For example, when receiving an X-ray from the aforementioned X-ray generating apparatus in which a target of tungsten, molybdenum or the like is used and a tube voltage is set to 40 kV or more and 150 kV or less, the absorbance A of the phosphor 120 to the X-ray is 1.3 or less. When the absorbance A is 1.3 or less like this, an image of the phosphor 120 does not appear in the X-ray image taken or fluoroscopically viewed, or there is no influence of the image of the phosphor 120 on a treatment and diagnosis using the X-ray image taken or fluoroscopically viewed even when the image of the phosphor 120 appears on the X-ray image. It is noted that, when the intensity of X-ray made incident on the phosphor 120 is I0 and the intensity of X-ray passing through the phosphor 120 is I, the absorbance A is defined by the following formula (1).
A=−log10(I/I0) (1)
The foregoing phosphor 120 made of Y2O2S as a matrix with at least Eu as an activating agent has small degradation in brightness due to damage (radiation damage) when an X-ray is irradiated. For example, when an X-ray from the foregoing X-ray generating apparatus is irradiated to the phosphor 120 in the present embodiment so that the accumulated absorption dose become 2 [Gy], the degradation in brightness of luminescence from the phosphor 120 after irradiation is within 10% of the brightness before irradiation.
The optical fiber 200 in the present embodiment is a step-index type optical fiber including a core 210 that forms the portion around the optical axis (central axis) and a clad 220 that is formed so as to surround the core 210. The outer surface (peripheral surface) of the clad 220 is protected with a coating 230. At the boundary between the core 210 and clad 220 of the optical fiber 200, a refractive index changes stepwise and the core 210 has a higher refractive index than the clad 220. Light entered from the light-incoming end part 201 of the optical fiber 200 passes mainly in the core 210 and is transmitted toward the light-outgoing end part 202. It is noted that a graded index type optical fiber formed so that a refractive index changes continuously from the core to the clad, may be used as the optical fiber.
The material of the optical fiber 200 preferably has a satisfactory transparency to an X-ray and is preferably capable of transmitting red light in the wavelength range of 600 nm or more and 630 nm or less, which is emitted from the phosphor 120, with low transmission loss. As such an optical fiber, an optical fiber made of acrylic resin such as polymethyl methacrylate (PMMA), etc., and an optical fiber made of fluororesin can be exemplified. The optical fiber 200 made of such material also has a satisfactory transparency to an X-ray, unlike a cable and lead wire made of normal metal. Particularly, the optical fiber made of fluororesin is preferably capable of transmitting red light emitted from the phosphor 120 with lower transmission loss compared to the optical fiber made of acrylic resin such as PMMA and so on, since the optical fiber 200 made of such material does not have an absorption peak in the wavelength range of 600 nm or more and 630 nm or less.
The end surface of the light-incoming end part 201 of the optical fiber 200 is an inclined surface 201a inclined by a predetermined angle θ with respect to a virtual plane S perpendicular to the optical axis La of the optical fiber 200. The inclination angle θ of the inclined surface 201a is, for example, an angle in the range of 30 degrees-60 degrees, and more preferably, an angle in the range of 40 degrees-50 degrees. The inclined surface 201a of the optical fiber 200 is mirror polished to reduce scattering of light emitted from the phosphor 120. A light reflective coating (for example, silver color coating) to enhance reflectivity to the light emitted from the phosphor 120 is applied.
At the light-incoming end part 201 of the optical fiber 200, the coating 230 is removed and the peripheral surface 201b of the clad 220 is exposed. The phosphor 120 of the X-ray detection part 100 is disposed in opposition to the peripheral surface 201b so that the light L emitted from the phosphor 120 enters from the peripheral surface 201b of the clad 220 in opposition to the inclined surface 201a of the optical fiber 200 and reaches the inclined surface 201a. By entering the light L from the peripheral surface 201b of the optical fiber 200 and reflecting the light L from the inside at the inclined surface 201a in this way, an incident efficiency of the light L to the optical fiber 200 is enhanced. The aspect where the incident efficiency of the light L to the optical fiber 200 is enhanced in the configuration of
In
It is noted that, although the light L emitted from the phosphor 120 is entered from the peripheral surface 201b side of optical fiber 200 in the present embodiment as described above, a configuration for entering the light L emitted from the phosphor 120 into the optical fiber 200 is not limited to the configuration in the present embodiment. For example, the phosphor 120 may be disposed so as to be attached or close to the exposed inclined surface 201a of the optical fiber 200 and the light L emitted from the phosphor 120 may be directly entered into the inclined surface 201a. The configuration such as the present embodiment, in which the light form the phosphor 120 is entered from the peripheral surface 201b side of optical fiber 200, may be combined with the configuration of directly entering the light from the phosphor 120 into the inclined surface 201a.
The main body apparatus 300 also includes a control part 320 which functions as control means and computation means, a display part 330 as output means of outputting a measurement result, and so on. The control part 320 is configured with a microcomputer including, for example, a CPU, a ROM, a RAM, an I/O interface, etc. and connected with each part such as the light detection part 310, the display part 330 and so on.
The control part 320 controls each part and calculates values of various doses of X-rays (for example, absorption dose [Gy], dose equivalent [Sv], exposure dose [C/kg]) or a value of dose rate [Gy/h] that is a dose per unit hour based on an output signal of the light detection part 310, by executing a predetermined program. The control part 320 also memorizes calibration data and values of various coefficients and parameters for calculating the foregoing various doses and dose rate. The calibration data is a conversion table or data of a conversion formula, which is used when converting the output signal of the light detection part 310 to values of the foregoing various doses and dose rate, and is acquired by a calibration performed before starting the use.
In a case that two or more X-ray detection probes 50 are used and the characteristics of X-ray detection probes 50 are different each other, two or more kinds of calibration data acquired for each of the X-ray detection probes 50 are memorized in advance. In this case, the control part 320 identifies the X-ray detection probe connected with the light detection part 310 or the main body apparatus 300 and calculates the foregoing various doses and dose rate by using the corresponding calibration data. Furtheremore, in a case that the main body apparatus 300 is connected with two or more light detection parts 310 or the main body apparatus 300 is provided with two or more light detection parts 310 and the characteristics of light detection parts 310 are different each other, two or more kinds of calibration data acquired for each of the light detection parts 310 or two or more kinds of calibration data acquired for each combination set of the X-ray detection probes 50 and the light detection parts 310 are memorized in advance. It is noted that, since the aforementioned calibration data possibly changes after starting the use, the acquisition and update may be periodically performed after starting the use.
The display part 330 is configured with, for example, a liquid crystal display or the like, which is capable of displaying a value of dose or dose rate calculated by the control part 320 in real time and displaying a change of dose or dose rate as a graph with time axis in real time.
Accordingly, in the example in
In
As described above, according to the present embodiments, when the X-ray detection part 100 receives an X-ray, the phosphor 120 included in the X-ray detection part 100 emits light, and the light emitted from the phosphor 120 of the X-ray detection part 100 enters from the light-incoming end part 201 of the optical fiber 200, transmits in the optical fiber 200 and exits from the light-outgoing end part 202. This light exited from the light-outgoing end part 202 of the optical fiber 200 is detected with the light detection part 310. Based on a result of the light detection part 310, a dose of X-ray can be measured.
Herein, the light that is emitted from the phosphor 120 of the X-ray detection part 100 by receiving the X-ray can be transmitted to the light detection part 310 away from the X-ray detection part 100 by the optical fiber 200. Accordingly, when measuring a dose of X-ray while taking or fluoroscopically viewing an X-ray image, it is not necessary to locate the light detection part 310 at the region where the X-ray for taking or fluoroscopically viewing is passing through and the X-ray for taking or fluoroscopically viewing is not blocked by the light detection part 310. Furtheremore, the foregoing phosphor 120 made of Y2O2S as a matrix with at least Eu as an activating agent has a satisfactory transparency to the X-ray and the optical fiber 200 has also a satisfactory transparency to the X-ray unlike a cable and lead wire made of normal metal. Accordingly, when taking or fluoroscopically viewing an image by using the X-ray, it is capable of suppressing an influence on the image taken or fluoroscopically viewed. Therefore, it is capable of measuring a dose of X-ray in real time when taking or fluoroscopically viewing the image while suppressing influence on the image taken or fluoroscopically viewed by using the X-ray.
Moreover, the foregoing phosphor 120 of the X-ray detection part 100, which is made of Y2O2S as a matrix with at least Eu as an activating agent, does not include cadmium (Cd). Accordingly, it is capable of providing a dosimeter with an environmental safety.
In particular, the dosimeter 10 of the present embodiment can measure a dose of X-ray in real time when taking or fluoroscopically viewing the X-ray image while suppressing influence on the image taken or fluoroscopically viewed by using the X-ray with energy and species suitable for medical image diagnosis, which is emitted from the X-ray generating apparatus with the predetermined range of tube voltage and has energy and species for medical image diagnosis. Accordingly, the dosimeter 10 of the present embodiment is preferable as a safe real-time dosimeter used for medical image diagnosis such as a real-time measurement of a skin exposure dose when performing an angiography, a vascular IVR, a non-vascular IVR, or the like.
Further, the dosimeter 10 of the present embodiment can also used as a dosimeter of measuring an exposure dose for a medical staff such as an IVR medical operator.
It is noted that the description of embodiments disclosed in the present specification is provided so that the present disclosures can be produced or used by those skilled in the art. Various modifications of the present disclosures will be readily apparent to those skilled in the art and general principles defined in the present specification can be applied to other variations without departing from the spirit and scope of the present disclosures. Therefore, the present disclosures should not be limited to examples and designs described in the present specification and should be recognized to be in the broadest scope corresponding to principles and novel features disclosed in the present specification.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-044772 | Mar 2013 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/054706 | 2/26/2014 | WO | 00 |
