Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/20—Measuring radiation intensity with scintillation detectors
  • G01T1/201—Measuring radiation intensity with scintillation detectors using scintillating fibres

Definitions

• the present invention relates to a method for real-time measurement of the dose of radiological radiation received by a region subjected to a flux of radiological radiation.
• Document EP 1 167 999 describes a real-time dosimeter based on a matrix of silicon detectors. This dosimeter allows a mapping of the dose received thanks to the
• Another technique making it possible to obtain in real time the dose received by an area subjected to radiation during an examination consists in finding this area by calculation from the dose measured at the output of the radiation emission device.
• this method is not suitable for determining radiation mapping, because the irradiation geometry is not fixed.
• a method for real-time measurement of a dose of radiological radiation absorbed by a region to be inspected subjected to a flow of radiological radiation comprising the steps consisting in:
• a position is determined where the radiological radiation is detected along said measuring optical fiber, and the dose of radiological radiation received in this position as a function of at least one specific parameter F ° k of this optical fiber;
• the at least one parameter F ° has been obtained by a preliminary calibration step in which a dose has been detected at at least one point in the region to be inspected using a non-radiolucent radiation detector radiation received at this point;
• step (b) is carried out using a detection device comprising at least one cell, and the parameter F ° k takes into account at least the optical fiber and at least one cell of the detection device associated with this fiber;
• step (a) is also carried out using a second optical fiber bundle, containing at least one second measurement optical fiber, adapted to generate a light signal when it receives radiological radiation, and extending along a second direction forming an angle with the first direction;
• steps (b) and (c) are carried out, for at least one overlap point (i, j) between a first optical fiber for measuring i of the first beam and a second optical fiber for measuring j of the second beam, from radiation detected by at least the first optical fiber i among the fibers of the first beam, radiation detected by the second optical fiber j, and the position of this overlap point (i, j) along the second optical fiber j ;
• steps (b) and (c) are carried out, for at least one overlap point (i, j) between a first optical fiber for measuring i of the first beam, and a second optical fiber for measuring j of the second beam, from the radiation detected by at least the second optical fiber j among the fibers of the second beam, the radiation detected by the first optical fiber i, and the position of this overlap point ( i, j) along the first optical fiber i;
• the method further comprises the step (d) of issuing an alarm signal if the cumulative dose of radiation received exceeds a pre-established threshold;
• the method further comprises the step (e) of displaying on a monitor the dose of radiation received at at least one point in the region to be inspected;
• the method further comprises the step (f) of detecting the radiation transmitted by the region to be inspected and displaying on a monitor the radiographic image thus detected;
• step (f) the radiographic image obtained in step (f) and the image of the received radiation dose obtained in step (e) are displayed on the same monitor; - At least steps (a), (b) and (c) are repeated for several points in the region to be inspected,. allowing to obtain a map of the dose received by the region to be inspected;
• steps (a), (b) and (c) are repeated for several measurement time intervals, making it possible to obtain a temporal variation of the dose received at at least one point in the region to be inspected •
• the radiation is generated by a pulsed source, and the repetition of at least steps (b) and (c) is synchronized with this source; at least steps (a), (b) and (c) are performed for at least two radiation incidences, and the radiation doses received determined in step (c) for each of the incidences are used jointly.
• the invention relates to a device for real-time measurement of a dose of radiological radiation absorbed by a region to be inspected subjected to a flux of radiological radiation, comprising: a dosimeter comprising at least a first bundle of optical fibers measuring, containing at least one fiber placed in said region to be inspected and adapted to generate a light signal when it receives radiological radiation, in order to detect the incident radiation at at least one point in the region to be inspected,
• This device also includes one and / or the other of the following provisions: the light signal is transmitted, to a detection device used to measure it, along the measuring optical fiber used to detect the radiation, this fiber comprising a first end, and at least one clear optical fiber extending from a first end of clear fiber connected to the first end of the measuring optical fiber, to a second end of clear fiber, arranged in sight of the detection device, and the means for determining the dose of radiation received at said point of said optical measurement fiber comprise a control unit containing parameters specific to the optical fibers used;
• the dosimeter further comprises a second bundle of optical fibers, comprising at least a second measuring optical fiber, and disposed in a second direction forming an angle with the first direction;
• each measuring optical fiber is between two optically insulating sheets
• each measuring optical fiber is molded in a reflective resin comprised between two optically insulating sheets; at least one bundle of optical fibers is integrated into a table.
• the invention relates to a radiological installation comprising:. a dosimeter comprising at least one beam comprising at least one optical measurement fiber, placed in a region to be inspected, and adapted to generate a light signal when it receives radiological radiation, in order to detect the incident radiation at at least one point of said region to be inspected,
• means for determining the dose of radiological radiation received by said measuring optical fiber from said light signal and further comprising. a radiation generator,. an X-ray detector, and
• means for viewing the dose of radiation received these means making it possible to view, in addition, radiographic images of the region to be inspected provided by the radiographic detector.
• This installation can also include one and / or the other of the following provisions: the installation also includes an examination table;
• the installation also comprises at least one additional device, not integrated into the examination table, for real-time measurement of a dose of radiological radiation absorbed by a region to be inspected subjected to a flow of radiological radiation, comprising: at least a first additional beam comprising at least a first additional measuring optical fiber, placed in said region to be inspected, and adapted to generate an additional light signal when it receives radiological radiation, for detecting the incident radiation at at least one point of said region to be inspected, additional means for measuring said additional light signal outside the region to be inspected after transmission along the additional measurement optical fiber, and
• additional means for determining the dose of radiological radiation received by said additional measurement optical fiber from said additional light signal are provided.
• FIG. 1 represents a diagram of implementation of the method according to the invention
• FIG. 2 represents an exploded perspective view of an example of a dosimeter according to the invention
• FIG. 3 represents the step of transmitting optical information according to the invention
• FIG. 4 represents a first embodiment of an installation implementing the method according to the invention
• FIG. 5 shows a second embodiment of an installation implementing the method according to the invention.
• a dosimeter 1 of rectangular or other shape, comprises first measurement fibers 2, directed along a first direction X of the dosimeter, and second measurement optical fibers 3, directed in a second direction Y dosimeter.
• Each of these measurement optical fibers 2, 3 comprises a first end 5 connected to a clear fiber 6, and a second end 4 optically closed, or reflecting.
• Each of the clear fibers 6 extends from a first end 14 of clear fiber 6, where it is connected to the first end 5 of the measuring fiber 2, 3, to a second end 15 of clear fiber 6, where it is opposite a detector 9.
• each of the clear fibers 6 can be mounted in a respective orifice 8 of an adapter 7, placed opposite the detector 9, in order to ensure the placement of the fiber claire 6.
• the detector 9 can be, for example, a multi-cell detector in which each of the cells 10 is placed opposite one of the orifices 8 of the adapter 7. If a radiation 11, coming from a radiation source 18 , passes through a measuring optical fiber 2, 3 oriented according to the first or the second direction of the dosimeter, a signal is transmitted by this measuring fiber, then by the clear fiber which is linked to it, up to the detector 9, possibly via the corresponding orifices 8 of the adapter 7.
• the second end 4 of the measuring optical fiber 2, 3 In the event of a weak signal, it it may be interesting to make the second end 4 of the measuring optical fiber 2, 3 reflective.
• the frequency of events measured by the detection device makes it possible to calculate the dose received by the measuring optical fiber.
• the measurement of an event in a first direction and of the same event in a second direction cannot be made to coincide in order to assess the extent to which this event has taken place, so a statistical method as described below is preferred.
• a multi-channel detection device such as a multi-anode photomultiplier (MAPMT)
• MAPMT multi-anode photomultiplier
• the gain of each electronic channel associated with the MAPMT may have been previously adjusted (once and for all, or periodically, or before each use, for example) so as to standardize the signal level of a photoelectron by setting a level of identical discrimination threshold for all electronic channels.
• FIG. 2 represents a first embodiment of the dosimeter according to the invention.
• a first set of measuring optical fibers 2, of diameter d y are aligned along a first dosimeter direction X, with a pitch, for example constant, of L y .
• These first measurement optical fibers are arranged between two sheets of a material 12, for example reflective, used to hold the optical fibers. This component thus formed, is in turn disposed between two sheets of an optically insulating material 13. This operation is repeated, in a second dosimeter direction Y, for the second optical fibers of measurement 3, of diameter d x , and spaced apart by a pitch L x .
• the two components thus formed are then superimposed, for example so that the first measuring optical fibers and the second measuring optical fibers form between them an angle of approximately 90 °.
• the dosimeter thus formed is completely radio transparent, which is a primary condition for using such a dosimeter, so as not to hinder the practitioner during his intervention.
• these measurement fibers are not necessarily arranged in two separate planes, and can for example form a single plane of woven fibers.
• FIG. 3 represents the path of the optical information from the detection by the optical measurement fiber to the detector 9. It is in particular necessary to connect the optical measurement fibers 2, 3, at their first end 5, to the fibers clear 6 extending them for example using glue, or any other connecting means for transmitting optical information.
• the first end 5 of each of the measurement fibers 2, 3, and the first end 14 of the clear fibers 6 are polished and are placed opposite one another to be glued using an optical adhesive. of index close to the material used in optical fibers.
• the two fibers can be held in a teflon tube or other rigid material, which can then remain permanently to guarantee the mechanical robustness of the optical connection .
• the second end 4 of the measurement optical fibers 2, 3 can also be connected to a second clear optical fiber 6, in a similar manner. In this case, of course, the second end 4 of the measurement optical fibers 2, 3 is neither optically closed, nor reflective. The second end 15 of these second clear fibers can then be placed opposite a cell of the detector 9, in the manner defined above.
• this second end can alternatively be placed near the second end 15 of the first clear fiber 16 which is connected at its first end 14 to the first end 5 of the optical fiber 2, 3 given, so that the signals from the first and second clear fibers 6 connected to the same measurement fiber 2, 3 are added by the detector. It may be necessary to evaluate the dispersion of the response of the detection channels of the device. If the characteristics of the measurement fibers 2, 3 and clear 6 are guaranteed to be little dispersed, the reproducibility of the quality of the optical bonding between them is to be studied, as well as the dispersion of the channels of the detection device. For a given radiation flux, the counting rate for each detection channel is different depending on:
• a known part 24 of each measuring fiber 2, 3 is for example located directly upstream of its first end 5 where the measuring fiber 2, 3 is bonded to the clear fiber 6, to radiation from a radiation source at a voltage V and an intensity I, which corresponds directly to a value of the known dose f, previously measured by conventional means such as an ionization chamber (non-radio-transparent).
• the set of surface dose values per counting unit F 0 k f / C ° k * sc, corresponding to a given fiber k, or to a fiber - multi-channel detector channel assembly, is stored in a control unit 22.
• a control unit 22 here represents the equivalent area of the detection fiber.
• the calibration of the optical fiber and detector channel assembly can be carried out separately by calibrating on the one hand the optical fibers by moving opposite each second end 15 of clear fiber 6 a single detector cell, for example d '' a single cell detector.
• the calibration of the multi-cell detector channels can be carried out separately, for example by having each channel measure a given known signal.
• the value F ° k for calibrating an optical fiber and detector channel assembly is then obtained by combining the value obtained for a single fiber and the value obtained separately for the channel opposite the detector.
• the measurement fibers 2, 3 have known characteristics, if it is known that the radiation dose was received at a distance d from the detection part 24 of the measurement fiber k along this fiber, the count can be found that would have been measured if the detection had been carried out in this detection part 24, from the count measured at the output of the detector, using the attenuation length ⁇ att of the measurement fibers by the following formula:
• FIG. 4 represents an embodiment of an installation implementing the method according to the invention.
• the dosimeter 1 consists of two crossed planes of 32 scintillating fibers of 1 mm in diameter, woven in 10 mm steps, thus covering a detection surface of approximately 310 ⁇ 310 mm 2 .
• the pitch is representative of the resolution of the mapping of the dose obtained, and the detection surface chosen is representative of the areas of investigation in this type of application, these two parameters obviously being able to be modified.
• the scintillating fibers 2, 3 used in the .dimeter are made of doped polystyrene and double "cladding". For example, Polifi 02 44-100 "blue" fibers (POL-
• Component 12 is here mylar of density 1.35 g / cm 3 , and composed of sheets of thickness 0.045 mm.
• the optically insulating component 13 is here black polycarbonate, density 1.2 g / cm 3 , and made up of sheets of thickness 0.015 mm.
• An epoxy adhesive is used to connect the measuring optical fibers 2, 3 and the sheets 12 and 13 to each other. The total thickness of the detector thus formed is approximately 2.4 mm.
• the measuring fibers 2, 3 can also alternately be incorporated in a molding, for example in black resin.
• Each optical fiber of measurement 2, 3, measures approximately 310 mm in length, and is bonded to a clear polystyrene fiber, for example of the simple Kurakay “cladding” type, of length approximately 1400 mm, of diameter approximately 1 mm, the first end 5 of these measuring fibers 2, 3 and first end 14 of these clear fibers 6 having been previously polished, with abrasive paper first of granularity 600P, then 1200P.
• the clear fibers 6, which are long, can for example also be quartz fibers having a better transmission rate, PMMA (Poly Methyl Metacrilate) fibers or the like. Only one clear fiber 6 is used here per measurement fiber 2,
• each measuring fiber 2, 3 could alternatively connect to a clear fiber at each of its ends
• the free ends of the 64 clear fibers are grouped together on an adapter, which is a black plastic mechanical part pierced with 64 holes, with a diameter of approximately 1.05 mm in steps of 2.3 mm.
• an 8x8 matrix of clear fibers 6 placed opposite the cells 10 of the detector 9, which is here a MAPMT 64-channel photo multiplier Hamamatsu H7546 MOD.
• This detector has an entrance window of approximately 20x20 mm 2 .
• each fiber may have a diameter smaller than that of the scintillating fiber 2,3, associated so that the assembly of clear fiber and sheath has a diameter. of the order of that of the associated scintillating fiber.
• the MAPMT detector is equipped with integrated analog electronics (2 chips of 32 channels) having a sensitivity at the level of the photoelectron fraction.
• Each electronic channel includes a programmable threshold discriminator providing a digital signal operated by counting up to a frequency of 10 MHz.
• the flexible and light-tight dosimeter 1 is intended to be placed on the body of the person to be examined. In FIG. 4, the dosimeter is thus placed under the patient's body, between the radiation source 18 and the patient 16.
• the dosimeter is placed facing the entry face of the beam 11 of radiation, for example of X-rays, produced by a tube 18 situated on a movable hoop not shown.
• the emitted X-ray beam can be emitted in a pulsed manner, in which case the detection device can be synchronized by carrying out the detection for each X-ray pulse, and the calculations between two given pulses.
• the detection device can be synchronized by carrying out the detection for each X-ray pulse, and the calculations between two given pulses.
• the supply to the detector of a synchronous signal and likewise duration as the pulse X-ray is used to trigger the counting on 'fiber during exposure.
• the transmitted X-ray beam can also be detected by a detector 19 which transmits the radiological information to a central unit 22.
• the dose passing through each measuring fiber 2, 3 of the dosimeter 1, and therefore reaching the object to be examined, is transformed into optical information conveyed via clear fibers 6 to the multi-channel detector 9.
• the signals coming from the MAPMT photomultiplier are treated here by two integrated circuits of 32 channels each. After shaping the signals, this circuit is capable of supplying sequentially (channel after channel) the charge collected on each anode of the MAPMT by a signal whose amplitude is proportional to this charge, and therefore, from the values of calibration F ° k stored in the control unit 22, at the detected radiation.
• This output signal is digitized by an ADC (analog to digital converter), for example contained in the central unit 22, to provide information that can be displayed on the monitor 20.
• the circuit also provides an activated logic signal at the occurrence of each photoelectron produced at the MAPMT photo cathode. Measuring the frequency of this logic signal makes it possible to measure the activity of each channel and therefore the amount of radiation picked up by each of the measuring optical fibers 2, arranged in lines in a first dosimeter direction and measuring optical fibers 3 arranged in column according to a second dosimeter direction.
• This logic signal being the sum of signals attached to each channel, it is possible to individually measure the activity of a selected optical fiber of measurement 2, 3 by inhibiting all the channels except that selected so as to keep only the frequency corresponding to the selected measurement optical fiber. This same operation is subsequently carried out for each of the channels, which leads to the individual measurement of the dose received by each fiber.
• a logic signal can be associated with each channel, which allows simultaneous measurement of the count on the 32 channels with each pulse of the X beam.
• the sum on all the rows of the measured counts and the sum on all the columns of the measured counts are equal and correspond to the total intensity.
• the calculated values are then represented on the monitor 20, this at a sufficiently high speed to ensure rapid refreshment of the data on the monitor 20.
• the obtaining of the surface skin dose D ⁇ j being calculated in two different ways, a check of the reliability of the measurements, and of a possible failure of the dosimeter, can be carried out by comparing these two values.
• the result obtained can be weighted by the calculation made from the frequency measurement obtained at the end of the most efficient fiber, so that this number is preponderant in the result obtained. Counting the frequency of the logic signal
• a DSP processor Digital Signal Processor
• a DSP processor performs the following operations: - management of the high voltage of the MAPMT, generated locally by a compact Hamamatsu CA 4900-01 module, configuration of the integrated circuits, reading of the case temperature, and communication with the 'control unit.
• This communication with the control unit 22 consists in regularly raising the counting data so as to refresh the display of the monitor 20, to allow the user 21 to define the operating parameters, such as the mode of use, MAPMT voltage, sensitivity level of electronic cards or others.
• the control unit 22 or the user 21 can then take into account the information displayed by the monitor 20 for the continuation of the therapy. If the dose of skin radiation accumulated in a region or over the entire extent of irradiation exceeds a certain pre-established threshold, the control unit can thus for example trigger an alarm.
• the X-ray beam 11 may possibly be reoriented or moved by the user 21, for example in the event of movement of the person to be examined 16 on the examination table 23. This movement can be transmitted automatically to the central unit 22, or entered as a parameter by the user 21. In the event of significant displacement , it may indeed be necessary to modify the parameters specific to each measuring optical fiber 2, 3, which may have been calibrated only for a given set of positions of the radiation source.
• FIG. 5 represents a second embodiment of an installation implementing the method according to the invention. It is here provided that the dosimeter 1 is incorporated into the examination table 23, in order to cover all the anterior posterior X-ray incidences to which the person to be examined could be subjected. The pitch of the measuring fibers 2, 3 could possibly be adapted. It is thus possible to integrate into the examination table several dosimeters located opposite the most investigated parts of the body, and connected jointly or successively to the same detection device.
• Such a “whole body” dosimeter, integrated into the examination table and covering almost its entire surface can be used alone or coupled to additional non-integrated and used “surface” dosimeters as shown in FIG. 4.
• Such a device could be interesting in the fields of interventional radiology and in conventional or interventional tomography.
• Such an examination table 23 may contain several dwellings capable of receiving simultaneously or successively integrated dosimeters.

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• 2003
  • 2003-01-07 FR FR0300100A patent/FR2849697B1/fr not_active Expired - Fee Related
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