Method for determining the dose rate of ionizing radiation and associated dosimetry system

Abstract

Method for determining an ionizing radiation dose rate and associated dosimetry system This description relates to a method for determining (200) a dose rate (15) of ionizing radiation received by a dosimeter, the method of determination comprising: - a measurement step (202), by the dosimeter, of a mixed beam (10) of ionizing radiation in order to generate a mixed spectrum (11); - a spectral deconvolution step (204), by a processing unit connected to the dosimeter, of the mixed spectrum into elementary spectra (21) from measurements, by the dosimeter, of reference beams (20) of ionizing radiation; - a determination step (206), by the processing unit, of elementary dose rates (25), from the elementary spectra and calibration coefficients (22) associated with the reference beams;and- a determination step (208), by the treatment unit, of the dose rate from the elementary dose rates. Figure for the abstract: Fig. 2;

Description

Title of the invention: Method for determining the dose rate of ionizing radiation and associated dosimetry system. Technical field

[0001] This description relates generally to dosimetry, that is, the determination, using a dosimeter, of a dose rate, or a dose, of ionizing radiation to which a person, or an object, is exposed. This description relates in particular to active dosimetry.

[0002] The present description relates in particular to a method for determining a dose rate of ionizing radiation and a dosimetry system enabling the implementation of such a method. Previous technique

[0003] A dosimeter can be defined as a device that allows the evaluation or measurement of a dose relative to at least one ionizing radiation, received during the exposure of a person, or an object, to that ionizing radiation.

[0004] Among the different families of dosimeters, we can mention passive dosimeters, the reading of which can only be taken after exposure, and active dosimeters, which make it possible to determine in real time the dose received by a person or an object. An active dosimeter can, for example, be associated with an alarm to warn a person wearing it if a predefined threshold is exceeded.

[0005] The present description relates particularly to active dosimeters, for example personal active dosimeters.

[0006] An example of an active dosimeter involves the use of a scintillator: a scintillator consists of a scintillating material sensitive to ionizing radiation and capable of emitting light in response to the ionizing radiation it receives. A scintillator is generally associated with a photodetector that measures the amount of light emitted by the scintillating material, so as to calculate a dose rate, or dose, received by the scintillator. The dose rate, or dose, is determined by processing an electrical signal generated by the photodetector when it receives the amount of light emitted by the scintillating material.

[0007] The publication "Applicability of a commercially available active extremity dose-rate meter to eye lens dose monitoring, Radiation Protection Dosimetry (2020), Vol. 192, No. 4, pp. 460-472" describes an extremity dosimeter that includes one or two silicon diodes, with at least one diode for low-energy radiation, and in some cases a diode for high-energy radiation. In the dosimeter As described in this publication, it is necessary to have two silicon diodes to cover several radiation energies.

[0008] A method for determining a dose rate is sought which makes it possible to determine a dose rate of several ionizing radiations at several energy ranges, or energy domains, and a dosimetry system enabling the implementation of such a method.

[0009] It would be advantageous for such a method and dosimetry system to allow for the precise measurement of ionizing radiation dose rates across several energy ranges, including high energies. High energies are defined as radiation energies above 60 keV. Low energies are defined as radiation energies less than or equal to 60 keV.

[0010] It would be advantageous if such a method and such a dosimetry system did not require the use of several different dosimeters to cover several energy ranges. Summary of the invention

[0011] An embodiment overcomes all or part of the drawbacks of known dosimetry processes and systems.

[0012] An embodiment provides a method for determining a dose rate of ionizing radiation received by a dosimeter, the determination method comprising: - a step of measuring, by the dosimeter, a mixed beam of ionizing radiation in order to generate a mixed spectrum; - a spectral deconvolution step, by a processing unit connected to the dosimeter, of the mixture spectrum into elementary spectra from measurements, by the dosimeter, of reference beams of ionizing radiation; - a step in which the treatment unit determines elementary dose rates from the elementary spectra and calibration coefficients associated with the reference beams; and - a step of determining, by the treatment unit, the dose rate from the elementary dose rates.

[0013] According to one embodiment, the process further includes, prior to the spectral deconvolution step, a measurement step, by the dosimeter, of the reference beams, in order to generate the elementary spectra.

[0014] According to one embodiment, the method further comprises, prior to the measurement step of the reference beams, a selection step of said reference beams, each selected reference beam being associated with a calibration coefficient.

[0015] According to one embodiment, the method further comprises, prior to the step of determining the elementary dose rates, a step of determining the calibration coefficients from the elementary spectra and reference dose rates of the reference beams.

[0016] According to one embodiment, the elementary spectra and calibration coefficients are stored in a database linked to the processing unit.

[0017] According to one embodiment, the spectral deconvolution step includes a least squares minimization method performing a fitting of a mixing function representing the mixing spectrum by elementary functions representing the elementary spectra associated with the reference beams.

[0018] According to one embodiment, the step of determining the elementary dose rates comprises: - the calculation of the counting rate of the elementary spectra; and, for each elementary spectrum: - the calculation of the elementary dose rate by the product of the calibration coefficient associated with the reference beam from which the elementary spectrum originates and the counting rate of said elementary spectrum.

[0019] According to one embodiment, in the dose rate determination step, said dose rate is determined by the sum of the elementary dose rates.

[0020] According to one embodiment, the mixture spectrum and the elemental spectra are obtained: - by calculating an integral over an integration window of an electrical signal, for example in the form of pulses, generated by the dosimeter; or - by calculating the maximum amplitude of an electrical signal, for example in the form of pulses, generated by the dosimeter.

[0021] According to one embodiment, the reference beams include narrow spectrum beams, for example X- or gamma-type photon radiation beams and / or particle-type beams generated by one or more radioelements.

[0022] An embodiment provides a processing unit configured to implement, by dedicated circuits and / or by the execution of instructions by one or more processors, the following steps of a method for determining a dose rate of ionizing radiation received by a dosimeter connected to the processing unit: - a spectral deconvolution step of a mixture spectrum, from a measurement, by the dosimeter, of a mixture beam of ionizing radiation, into elementary spectra from measurements, by the dosimeter, of reference beams of ionizing radiation; - a step of determining elementary dose rates from the elementary spectra and calibration coefficients associated with the reference beams; and - a step of determining the dose rate from the elementary dose rates.

[0023] According to one embodiment, the processing unit comprises: - a spectrum acquisition module configured to generate the mixture spectrum from the dosimeter measurement of the mixture beam and the elemental spectra from the dosimeter measurements of the reference beams; and - a calculation module linked to the spectrum acquisition module and configured to implement the spectral deconvolution, elemental dose rate determination and dose rate determination steps.

[0024] One embodiment provides a dosimetry system comprising: - a dosimeter including a scintillator sensitive to ionizing radiation and capable of emitting light in response to the ionizing radiation it receives, and a photodetector capable of receiving the light emitted by the scintillator and converting the received light to generate an electrical signal; and - a processing unit as described above, said processing unit being connected to the photodetector.

[0025] According to one embodiment, the dosimetry system further comprises a database linked to the processing unit and configured to store the elemental spectra and calibration coefficients.

[0026] One embodiment provides a computer program comprising instructions for implementing the dose rate determination process described above, when the program is executed by the processing unit described above. Brief description of the drawings

[0027] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the accompanying figures, among which:

[0028] [Fig.1A] and [Fig.1B] schematically represent a dosimetry system according to one embodiment;

[0029] [Fig.2] illustrates schematically and in a simplified manner a method for determining a dose rate of ionizing radiation according to an embodiment;

[0030] [Fig.3] schematically illustrates a calibration phase of a method for determining a dose rate of ionizing radiation according to an embodiment;

[0031] Fig. 4A, Fig. 4B, Fig. 4C, Fig. 4D, Fig. 4E, Fig. 4F, Fig. 4G, Fig. 4H, Fig. 4I, Fig. 4J and Fig. 4K illustrate elementary spectra obtained by measuring reference beams using a dosimeter included in a dosimetry system according to one embodiment; and

[0032] [Fig.5] schematically illustrates a method for determining an ionizing radiation dose rate according to another embodiment. Description of the implementation methods

[0033] The same elements have been designated by the same reference numerals in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0034] For the sake of clarity, only the steps and elements necessary for understanding the described embodiments have been shown and are detailed. In particular, the scintillator and the photodetector have not been detailed, as the described embodiments are compatible with all or most scintillators and photodetectors, possibly with adaptations that are within the grasp of a person skilled in the art upon reading this description.

[0035] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than connectors, and when referring to two elements coupled together, this means that these two elements can be connected or linked through one or more other elements.

[0036] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "superior", "inferior", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures.

[0037] Unless otherwise specified, the expressions "approximately", "roughly", and "on the order of" mean to within 10% or 10°, preferably to within 5% or 5°.

[0038] In the following description, reference is made to a dose rate, which refers to the dose of ionizing radiation received by a material element per unit time. A dose can be determined from the dose rate and the duration of exposure. In this description, the terms dose and dose rate may be used interchangeably, as a person skilled in the art will be able to convert between dose rate and dose.

[0039] In the following description, a beam refers to a beam, or stream, of ionizing radiation, which may be of the particulate type, for example alpha particles (a beam of helium nuclei), beta particles (a beam of electrons or of positrons), or neutrons (neutron beam), or of the electromagnetic type, for example X-rays or gamma rays (photon beams). A reference beam is a beam for which data such as a mean energy and / or a reference dose rate are available. A reference beam may be monoenergetic. An elemental spectrum is a spectrum obtained by measuring a reference beam with a reference dosimeter, for example, the dosimeter described below. A mixing beam is a radiation beam that is not monoenergetic. The energy spectrum of a mixing beam may be referred to as a "mixing spectrum" in the description that follows. A mixing spectrum can be viewed as a weighted linear combination of several elemental spectra. Similarly, a mixing beam can be viewed as a weighted linear combination of several reference beams.

[0040] In the following description, an energy spectrum of an ionizing radiation beam may be referred to as an "energy spectrum", or "spectrum" for short.

[0041] In the following description, a calibration coefficient is a coefficient used to convert a spectrum into a dose rate or dose. A calibration coefficient is generally expressed in Sieverts (Sv) per second, or in millisieverts (mSv) per second, per reading unit (LU). The reading unit is, for example, the number of counts per second, so the calibration coefficient can be expressed in mSv per count.

[0042] Figures IA and IB schematically represent a dosimetry system 100 according to one embodiment. Figures IA and IB illustrate the dosimetry system 100 in two different configurations.

[0043] The dosimetry system 100 includes a dosimeter 101 which includes a scintillator 110 (SC) associated with a photodetector 120 (PM).

[0044] The scintillator 110 consists of a scintillating material sensitive to ionizing radiation and capable of emitting light in response to the ionizing radiation it receives. The scintillator 110 may be an organic or inorganic scintillating material, for example, an organic or inorganic scintillating composite material, for example, an organic glass.

[0045] The photodetector 120 allows a quantity of light emitted by the scintillator 110 to be measured, transforming this quantity of light into a useful signal, generally an electrical signal.

[0046] The photodetector 120 is for example a photomultiplier (PM), one or more photodiodes, a photomultiplier tube, or a silicon photomultiplier (SiPM).

[0047] The photodetector 120 delivers an electrical signal which is generally in the form of electrical pulses, or "pulses", whose amplitude and integral are proportional to the detected radiation energy.

[0048] The dosimeter 101 can be a millimeter-sized dosimeter (miniaturized dosimeter), for example sized to be positioned at the level of a finger for extremity dosimetry.

[0049] The dosimetry system 100 includes a processing unit 150, which is connected to the dosimeter 101. Figures IA and IB show an example of an embodiment in which the processing unit 150 is external to the dosimeter 101. Alternatively, the processing unit 150 could be integrated into the dosimeter 101 with the scintillator 110 and the photodetector 120, and the assembly could form an integrated dosimeter, which could be miniaturized (millimeter dimensions).

[0050] The processing unit 150 includes a spectrum acquisition module 151 (SPECT) which allows an energy spectrum to be measured from the electrical signals delivered by the photodetector 120, for example, electrical pulses. The spectrum acquisition module 151 is connected to the photodetector 120.

[0051] Each electrical signal can be sampled in amplitude and time over a fixed period corresponding to an acquisition window. Each time sample within the acquisition window corresponds to an amplitude. The amplitudes of the electrical signal can be summed over a period corresponding to the size of an integration window, the integration window being contained within the acquisition window.

[0052] For example, the spectrum acquisition module 151 can be configured to calculate integrals of the electrical signals over the duration of the integration window, and classify them into different energy ranges. An integral corresponds to a more or less narrow energy range depending on the number of channels contained in the spectrum.

[0053] Alternatively, the spectrum acquisition module 151 can be configured to calculate maximum amplitudes of electrical signals and classify them into different energy ranges. A maximum amplitude corresponds to a more or less narrow energy range depending on the number of channels contained in the spectrum.

[0054] The processing unit 150 further includes a calculation module 152 (CALC) which allows processing the energy spectrum generated by the spectrum acquisition module 151. The calculation module 152 is connected to the spectrum acquisition module 151.

[0055] The dosimetry system 100 includes a database 140 (DB) linked to the processing unit 150. The database 140 is configured to store elementary spectra and elementary calibration coefficients (described later). It can be referred to as the measurement database.

[0056] The processing unit 150 further includes a calibration module 153 (ETAL) which allows elementary calibration coefficients to be determined, for example to feed the database 140.

[0057] The dosimetry system 100 further includes a reference database 130 (REF database) linked to the calibration module 153, and which includes data from the reference beams, in particular the reference dose rates of these reference beams.

[0058] Depending on the configuration of the dosimetry system 100, the processing unit 150 can retrieve data from the database 140 ([Fig. 1A]), or the processing unit 150 can populate the database 140 ([Fig. 1B]). In the example shown in Figures IA and IB, in a so-called calculation configuration ([Fig. 1A]), the database 140 is connected to the calculation module 152, and in a so-called calibration configuration ([Fig. 1B]), the database 140 is connected to the spectrum acquisition module 151 via the calibration module 153, which is connected to the reference database 130.

[0059] The dosimetry system 100 includes suitable links between the dosimeter 101 (scintillator 110 and photodetector 120), the processing unit 150 (spectrum acquisition module 151, calculation module 152 and calibration module 153), the database 140 and the reference database 130, in a manner known to a person skilled in the art.

[0060] According to a non-limiting embodiment, the scintillator 110 is a plastic scintillator (for example, an Eljen EJ200 model) and the photodetector 120 is a SiPM (for example, a SensL® microFC-30035-SMT model). The plastic scintillator used is, for example, parallelepiped-shaped with maximum dimensions of (x,y,z) = (3,3,3.5) mm³ to be associated with a SiPM comprising a pixel of (x,y) = (3,3) mm². The shape of the scintillator could be different, for example, cylindrical, provided that the radius of the cylinder fits within a square describing the surface of the SiPM pixel.

[0061] For example, the processing unit 150 may be processor-based adapted to execute a computer program comprising instructions for implementing steps in the dose rate determination process described below.

[0062] The processing unit 150 may include: an instruction memory comprising the instructions of the computer program; an input / output interface, in particular for retrieving the electrical signals generated by the photodetector 120; a user interface for interfacing the processing unit with a user, for example, a person wishing to know a value of ionizing radiation dose rate or an integrated dose over a given time; and a data storage, for example, a memory, for storing data generated by the processing unit 150.

[0063] This example is not limiting and a person skilled in the art may consider other processing units. For example, it may be a hardware-based processing unit, such as an application-specific integrated circuit, or ASIC, or a field-programmable gate array, or FPGA, or even a nano-computer or a single-board computer (SBC).

[0064] During operation, ionizing radiation interacts with the scintillator 110, which produces photons in response. These photons are converted into an electrical signal by the photodetector 120. The acquisition and analysis of the electrical signal at the output of the photodetector 120, as well as the extraction of an observable variable from this electrical signal, for example an integral or a maximum amplitude, by the processing unit 150, in particular the spectrum acquisition module 151, makes it possible to construct an energy spectrum of the ionizing radiation beam captured by the scintillator 110.

[0065] The electrical signal generated by the photodetector 120 and converted into an energy spectrum can be used to estimate the dose rate of ionizing radiation seen by the scintillator 110. However, when the ionizing radiation originates from different ionizing radiation beams, for example, photon beams of different energies and / or particle beams generated by several radioisotopes, obtaining an accurate estimate of the dose rate becomes more complicated, particularly because the sensitivity of the scintillator 110 varies with the energy of the incident radiation. The method for determining the dose rate of ionizing radiation, described below, allows for a more precise estimation of the dose rate of ionizing radiation from different ionizing radiation beams.

[0066] Fig. 2 illustrates schematically and in a simplified manner a method 200 for determining a dose rate of ionizing radiation according to an embodiment.

[0067] The determination method 200 is a method for determining a dose rate, or dose, of ionizing radiation received by a dosimeter. It is considered to be dosimeter 101 of Figures IA and IB, included in dosimetry system 100 of Figures IA and IB, which also includes processing unit 150 and database 140 of Figures IA and IB. It could be any other dosimeter included in a dosimetry system. More specifically, [Fig. 2] illustrates a measurement phase, which can be implemented by dosimetry system 100 in the measurement configuration of [Fig. 1A].

[0068] The process 200 includes in particular: - a measurement step 202 (MIXED BEAM MEASUREMENT), by the dosimeter 101, of a mixed beam 10 (MIXED BEAM), in order to generate a mixed spectrum 11 (MIXED SPECTRUM), by the processing unit 150; - a spectral deconvolution step 204 (SPECTRAL DECONVOLUTION), by the processing unit 150, of the mixing spectrum 11 into elementary spectra 21 (ELEM SPECTRA) from measurements, by the dosimeter 101, of reference beams 20 (REF BEAMS); - a determination step 206 (DETERMINATION DOSES ELEM), by the processing unit 150, of elementary dose rates 25 (DOSES ELEM) from the elementary spectra 21 and elementary calibration coefficients 22 (COEFS ELEM) associated with the reference beams 20; - a determination step 208 (DOSE DETERMINATION), by the processing unit 150, of a dose rate 15 (DOSE) of ionizing radiation from the mixing beam 10 from the elementary dose rates 25.

[0069] For example, the generation of the mixing spectrum 11 is carried out by the spectrum acquisition module 151 of the processing unit 150, while the spectral deconvolution 204, the determination 206 of the elementary dose rates 25 and the determination 208 of the dose rate 15 are carried out by the calculation module 152 of the processing unit 150.

[0070] In step 206, it must be understood that the elementary dose rates 25 include an elementary dose rate for each of the elementary spectra 21 and that the elementary dose rate 25 of an elementary spectrum 21 is obtained from this elementary spectrum and the elementary calibration coefficient 22 associated with this elementary spectrum (associated with the reference beam 20 from the measurement of which the elementary spectrum 21 originates).

[0071] For example, in step 206, a count rate is calculated from each elementary spectrum 21, for example by calculating an integral of this elementary spectrum, the elementary dose rate 25 being obtained by the product of this count rate and the elementary calibration coefficient 22 associated with this elementary spectrum. Depending on whether one wishes to determine a dose or a dose rate, this integral may or may not be multiplied by an acquisition time.

[0072] If the elementary spectra 21 are constructed in count rate, they are normalized to their respective acquisition time, and the count rate of each elementary spectrum is given by calculating the integral of that elementary spectrum.

[0073] If, on the other hand, the elementary spectra 21 are constructed in terms of the number of events, the counting rate of each elementary spectrum is obtained by dividing the integral of this elementary spectrum by its acquisition time.

[0074] For example, in step 208, a summation of the elementary dose rates 25 is performed.

[0075] Preferably, the spectral deconvolution 204 allows the elementary spectra 21 to be determined by taking into account the proportion of each of these elementary spectra 21 in the mixture spectrum 11, so that each elementary dose rate 25 determined in step 206 takes into account the proportion of the associated elementary spectrum. Thus, when the summation of the elementary dose rates 25 is performed in step 208, the proportions of the elementary spectra 21 in the mixture spectrum 11 are indeed taken into account in this summation.

[0076] Spectral deconvolution 204 can be based on a least squares method, for example on a "dogbox" or "dogleg" type minimization algorithm. An example of a spectral deconvolution method is described later in the description.

[0077] For example, the dose rate 15 of the mixing beam 101 is an equivalent dose rate HN mix which is calculated by the following equation Eq. 1:

[0078] ( 0.07 ) w ■ RNI

[0079] Where the equivalent dose rate HN mix is ​​expressed here in mSv per second, HNi is the equivalent dose rate of the reference beam Ni (elemental dose rate) expressed here in mSv per second, NHp(0.07)Ni is the elemental calibration coefficient of the reference beam Ni expressed here in mSv per count (mSv per second and per unit reading which is in counts per second), and RNi is a counting rate of the elemental spectrum 21 associated with the reference beam Ni expressed here in counts per second.

[0080] Examples of Ni reference beams and elementary calibration coefficients NHp(0.07)Ni of these Ni reference beams, as well as their average energies, are given in Table 1 below.

[0081] [Tables 1] Reference beam N Average energy (keV) Elemental calibration coefficient NHp (mSv / s / UL) N20 16.1 8.562e-07 N30 24.7 5.867e-07 N40 33.2 7.101e-07 N60 47.8 9.583e-07 N80 65.3 5.813e-07 N100 83.6 3.058e-07 N120 101.0 2.570e-07 N150 117.0 2.733e-07 N200 163.0 3.272e-07 N250 207.0 4.044e-07 N300 243.0 4.817e-07

[0082] The elementary calibration coefficients 22 can be designated "calibration coefficients".

[0083] The elementary spectra 21 and the elementary calibration coefficients 22 are taken from the database 140 of figures IA and IB, and can be transmitted to the processing unit 150, more specifically to the calculation module 152.

[0084] The database 140 can be fed during a calibration phase, to generate the elementary spectra 21 from selected reference beams 20 and to obtain the elementary calibration coefficients 22 associated with these elementary spectra 21. This calibration phase can be implemented by the dosimetry system 100 in the calibration configuration of [Fig.1B].

[0085] Fig. 3 schematically illustrates a calibration phase 300 of a method for determining an ionizing radiation dose rate according to one embodiment.

[0086] As indicated above, the calibration phase 300 allows the generation of the elementary spectra 21 from selected reference beams 20 and the determination of the elementary calibration coefficients 22 associated with these elementary spectra 21. This calibration phase is carried out before the measurement phase, for example before the process 200 of [Fig.2] which corresponds to a measurement phase (or before the process 500 of [Fig.5] described later), and it is implemented by the dosimetry system 100 in the calibration configuration of [Fig.1B].

[0087] The calibration phase is not systematically carried out before each measurement phase.

[0088] In a step 302 (SELECT REF BEAMS), reference beams 20 are selected, preferably mono-energetic. Preferably, reference beams calibrated by an accredited body are selected. For each reference beam, a reference dose rate 23 (REF DOSE) is a known value. The data for the reference beams 23 are, for example, available in the reference database 130 of [Fig. 1B].

[0089] According to one example, reference beams can be selected from the series of narrow-spectrum N beams described in ISO 4037-1 "Radiation protection — Reference X-rays and gamma rays for calibration of dosimeters and flowmeters and for determining their response as a function of photon energy — Part 1: Radiation characteristics and production methods” of February 2021. These narrow-spectrum N beams are referred to as “radiation qualities” in this document and correspond to X-ray beams. Being narrow, these N beams can be considered monoenergetic. The following could also be selected as reference beam(s): the cesium (137Cs) beam, or S-Cs radiation quality, with an average energy of 662 keV, and / or the cobalt (60Co) beam, or S-Co radiation quality, with an average energy of 1250 keV, and / or any other beam, or radiation quality, cited in ISO 4037-1, or in any other document defining reference beams. All narrow-spectrum N beams are standardized and calibrated. by an accredited body.

[0090] The reference dose rate 23 is, for example, a dose equivalent rate to the extremities (finger), at a depth of 0.07 mm, designated Hp(0.07)finger. Alternatively, the reference dose rate 23 may be a dose equivalent rate to the chest, at a depth of 10 mm, designated Hp(10), or a dose equivalent rate to the lens of the eye, at a depth of 3 mm, designated Hp(3), or any other dose equivalent rate of the selected reference beam.

[0091] In step 304 (REF BEAM MEASUREMENT), each of the reference beams 20 selected by the dosimeter 101 is measured. The measurement of each reference beam 20 generates an elementary spectrum 21 from the electrical signal delivered by the photodetector 120. This conversion of the electrical signal into an energy spectrum can be performed by the spectrum acquisition module 151, according to one of the methods described previously in connection with Figures IA and IB (integral or maximum amplitude). Several elementary spectra 21 are obtained (ELEMENTARY SPECTRA).

[0092] Figures 4A, 4B, 4C, 4D, 4E, 4F, 4G, 4H, 41, 4J, and 4K illustrate elementary spectra obtained by measuring reference beams with a dosimeter included in a dosimetry system according to one embodiment, for example, dosimeter 101 of Figures IA and 1B. The measured reference beams are the N beams identified in Table 1. Figure 4A illustrates the elementary spectrum obtained by measuring beam N20. Figure 4B illustrates the elementary spectrum obtained by measuring beam N30. Figure 4C illustrates the elementary spectrum obtained by measuring beam N40. Figure 4D illustrates the elementary spectrum obtained by measuring beam N60. Figure 4E illustrates the elementary spectrum obtained by measuring the N80 beam. Figure 4F illustrates the elementary spectrum obtained by the

[0093]

[0094]

[0095]

[0096]

[0097]

[0098]

[0099]

[0100] Measurement of the N100 beam. [Fig. 4G] illustrates the elementary spectrum obtained by measuring the N120 beam. [Fig. 4H] illustrates the elementary spectrum obtained by measuring the N150 beam. [Fig. 4I] illustrates the elementary spectrum obtained by measuring the N200 beam. [Fig. 4J] illustrates the elementary spectrum obtained by measuring the N250 beam. [Fig. 4K] illustrates the elementary spectrum obtained by measuring the N300 beam. The elementary spectra of figures 4A to 4K are obtained from the integral of the electrical signals, in the form of electrical pulses, delivered by the photodetector 120, with an integration window, for each pulse, on the order of the microsecond (1 ps). The inventors have advantageously adjusted the integration windows of the different reference beams to avoid the stacking effect of the signals (pile-up effect), which could distort the spectral response of dosimeter 101 and thus provide denatured or distorted elementary spectra. In a step 306 (DETERMINATION COEFS ELEM), an elementary calibration coefficient 22 is determined for each reference beam 20, from the reference dose rate 23 of the reference beam 20 and the elementary spectrum 21 associated with this reference beam 20. Several elementary calibration coefficients 22 (COEFS ELEM) are obtained for all the elementary spectra 21. Determining a calibration coefficient from a dose rate and an energy spectrum is a procedure familiar to those skilled in the art. An example calculation is given below for illustrative purposes. This calculation example allows the determination of elementary calibration coefficients NHp(0.07)finger_Ni from dose equivalent flow rates Hp(0.07)fingerNi at the extremities according to the following equation: Hp(0-07) Ni ..... Where the elemental calibration coefficient NHp(0.07)finger Ni associated with the reference beam Ni is expressed here in mSv per count, Hp(0,07)finger Ni is the end-dose equivalent rate associated with the reference beam Ni and expressed here in mSv per second, and R_Ni is a count rate calculated from the elemental spectrum 21 associated with the reference beam Ni and obtained in step 304, the count rate being expressed here in counts per second. In a step 308 (STORAGE OF ELEMENTARY SPECTRA), the elemental spectra 21 measured in step 304, as well as the elemental calibration coefficients 22 determined in step 306, are stored in the database 140 of figures IA and IB.

[0101] Figure [Fig. 5] schematically illustrates a method 500 for determining an ionizing radiation dose rate according to another embodiment.

[0102] The determination method 500 is a method for determining the dose rate of ionizing radiation received by a dosimeter 101. This is considered to be the dosimeter 101 of Figures IA and IB, included in the dosimetry system 100 of Figures IA and IB, which also includes the processing unit 150 and the database 140 of Figures IA and IB. More specifically, [Fig. 5] illustrates a measurement phase, which can be implemented by the dosimetry system 100 in the measurement configuration of [Fig. 1A].

[0103] Figure 5 has many elements in common with Figure 2; these common elements will not necessarily be repeated. Common elements between Figures 2 and 5 may retain the same reference numerals.

[0104] Steps 502 and 504 of [Fig. 5] correspond to steps 202 and 204 of [Fig. 2] respectively. Steps 505 and 507 of [Fig. 5] differ from steps 206 and 208 of [Fig. 2] respectively in that they include the use of a mixing calibration coefficient, i.e., a mixing spectrum calibration coefficient, from which a dose rate of the mixing beam is calculated, instead of using the elementary dose rates.

[0105] In step 502 (MIXED BEAM MEASUREMENT), as described in step 202 of [Fig.2], the mixed beam 10 is measured by dosimeter 101 in order to generate the mixed spectrum 11. The mixed spectrum 11, or energy spectrum of the mixed beam 10, is obtained from a conversion of the electrical signal delivered by the photodetector 120 into an energy spectrum, a conversion which can be carried out, for example, by the spectrum acquisition module 151, according to one of the methods described previously in connection with Figures IA and IB.

[0106] In step 504 (SPECTRAL DECONVOLUTION), as described in step 204 of [Fig. 2], a spectral deconvolution is performed to obtain a decomposition of the mixing spectrum 11 into elementary spectra 21 obtained by measuring the selected reference beams 20. More specifically, in step 504, a spectral deconvolution of the mixing spectrum 11 is performed to obtain weighting coefficients 12 (WEIGHTING COEFS), each associated with an elementary spectrum 21, in a linear weighted combination of the mixing spectrum 11 into the elementary spectra 21.

[0107] We can thus find a decomposition of the mixing beam 10 into a linear combination weighted by the weighting coefficients 12 of the reference beams 20 associated with the elementary spectra 21.

[0108] Spectral deconvolution refers to any method of determining a distribution of a given spectrum, or mixture spectrum, into several elementary spectra.

[0109] We will now describe an example of a spectral deconvolution method, which can be applied to step 204 of [Fig.2] or to step 504 of [Fig.5].

[0110] This example of a spectral deconvolution method is developed on a database constructed using elementary spectra. It is based on a least squares method, which uses a "dogbox" or "dogleg" type minimization algorithm, or "fit fitting", and relies on fitting a mixing function fmix which represents the mixing spectrum.

[0111] This spectral deconvolution method differs from other deconvolution methods used, for example, in particle physics, such as the ROOT® software used for multiparametric data analysis. Among its features, ROOT® includes a class called "TFractionFitter," which is a maximum likelihood method, described, for example, in the publication "Fitting using finite Monte Carlo samples," Computer Physics Communications 77 (1993) 219-228. This TFractionFitter class allows for fitting an experimentally measured mixture histogram to a collection of individual histograms associated with known physical phenomena, often obtained through Monte Carlo simulation. This class is not suitable for the spectral deconvolution of energy spectra from ionizing radiation beams, as it would introduce biases in the measurement reproduction.It is not reliable for estimating the proportions of a complex spectrum, resulting in a large number of functions used and similarities in the shape of certain spectra associated with beams of different average energies. The spectral deconvolution method based on a "dogbox" or "dogleg" type minimization algorithm, or fit adjustment, allows for the handling of complex spectra.

[0112] Starting from the example of the narrow-spectrum reference beams N defined in Table 1, the mixing function fmix can be defined by the following equation Eq. 2a:

[0114] Where fmix is ​​the mixing spectrum normalized to its integral, fNi are the elementary spectra associated with the reference beams Ni normalized to their respective integrals and Pj are proportions from which the weighting coefficients PNi can be deduced.

[0115] Let Fmix be a mixing spectrum not normalized to its integral and FNi be elementary spectra Ni not normalized to their integrals, related by the following equation Eq. 3a:

[0116]

[0117] The normalized mixing spectrum with respect to its integral fmix is ​​expressed by the following equation Eq. 3b:

[0118] F^ = = J FmiJE)jiE )i) FmiJ.,E)dE ' Fmix(E)dE

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[0120]

[0121]

[0122]

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[0138] Where each elementary spectrum Ni normalized to its integral fNi is expressed by The following equation Eq. 3c: F^E) l0 Fyi.EidE We can thus express fmix according to the following equation Eq. 3d: f^E} = Lv. r+3« F^E) Jo FytEidE Jo F\(E)dE Jo F^E^E = LNfy(E).PNl With : FN[E]dE PNt= p 0 / -^EdE Once the proportions Pj have been determined by the fit adjustment method, the estimation of the weighting coefficients PNi from the proportions Pj can be carried out using the following equations Eq. 2b: P ^ P 1 Pn3Q=(1-Pi)P2 Pn40 = (1 - ^).(1 - ^)^3 p N( ^(lp i ).(l-p2).(l-p3')p4 ^=(1-^)-( l'^H 1-^).(1-^4)-(1-^5)-^ ^=(1-^).(1-^)-(1-^ p^5ü=(i-pL).(i-p2).(i-p3).a^ ^-(1-^0.(1-^).(1-^).(1-^0.(1^^ ^-(1-^0.(1-^2).(1-^3).(1-^4)-(1-^5).(1-^6).(1-^7).(1-^8).(1-^9)^10 PX'3O,(- (1-^0.(1-^).(1-^).(1-^4).(1-^).(1-^6).(1-^7).(1-^).(1-^).(1-^10) Equation Eq. 2a is constructed so that the sum of the proportions Pj is indeed equal to 100% while maintaining weighting coefficients PNi between 0% and 100%. The inventors tested this spectral deconvolution method on a controlled mixture spectrum, that is, with known proportions in spectra. elementary elements associated with the reference beams N. It was found that the proportions determined by the spectral deconvolution method were identical to the known proportions (theoretical proportions), as shown in Table 2 below. The inventors compared this spectral deconvolution method with the TFractionFitter method.

[0139] [Tables2] Elementary Spectrum (N-beam) Theoretical proportion Proportion determined by the dogbox method Proportion determined by the TFractionFitter method N20 5.58 5.58 6.53 N30 7.64 7.64 5.37 N40 3.24 3.24 3.91 N60 3.62 3.62 3.01 N80 2.62 2.62 0.00 N100 2.74 2.74 5.02 N120 4.76 4.76 5.10 N150 30.21 30.21 29.26 N200 11.26 11.26 13.99 N250 17.33 17.33 16.77 N300 11.02 11.02 11.07

[0140] Table 2 clearly shows the differences in proportions resulting from the use of the TFractionFitter method compared to the dogbox method, which shows no difference. Furthermore, the TFractionFitter method has another drawback: when calculating the sum of the measured proportions listed in Table 2, the result is not exactly 100% but 100.03%.

[0141] In step 505 (DETERMINATION OF MIXING COEFFICIENT), a mixing calibration coefficient 13, or mixing spectrum calibration coefficient 11, is determined from the elementary calibration coefficients 22 (ELEMENTARY COEFFICIENTS) of the elementary spectra 20 that compose it and the weighting coefficients 12 associated with these elementary spectra. More precisely, a linear combination weighted by the weighting coefficients 12 of the elementary calibration coefficients 22 associated with the elementary spectra 21 is performed.

[0142] An example calculation is given to obtain a mixing calibration coefficient NHp(0.07)finger mix at the ends, according to the following equation Eq. 4: NHp( 0.07) M^.x = LN,P^Hp ( 0.07)

[0144] where NHp(0.07)finger_Ni are the elementary calibration coefficients associated with the reference beams Ni that make up the mixing beam, and PNi are the weighting coefficients, or proportions, associated with the reference beams Ni (obtained from equations Eq. 2a and 2b). The calibration coefficients NHp(0.07)fingermix and NHp(0.07)fingerNi are expressed here in mSv per shot.

[0145] In step 507 (DOSE DETERMINATION), a dose rate 15 (DOSE) seen by the dosimeter 101 is determined by multiplying the mixing calibration coefficient 13 by a count rate calculated from the mixing spectrum 11, obtained by measuring the mixing beam 10 in step 502.

[0146] An example of dose calculation Hp(0.07)finger is given, based on the mixing calibration coefficient NHp(0.07)finger mix at the extremities, taking into account an acquisition time, according to the following equation Eq. 5:

[0147] Hp(0.07)finger ^NHp^)finger^ R^x. Tucq

[0148] Where Hp(0.07)finger is the total equivalent dose at the extremities expressed here in mSv, NHp(0.07)finger_mix is ​​the mixing calibration coefficient expressed here in mSv per count (obtained by equation Eq. 4), R_mix represents a counting rate over the entire mixing spectrum 11 associated with the mixing beam 10 and expressed here in counts per second, and Tacq represents the acquisition time expressed here in seconds.

[0149] A dose rate Hp(0.07)finger, expressed in mSv per second (mSv / s), or in Sv / hour (Sv / h) without taking into account the acquisition time Tacq, can be determined according to the following equation Eg. 6:

[0150] Hp(0.07)finger -NHp^.M)R_mix

[0151] In this example, the counting rate R_mix of the mixing spectrum 11 is given by calculating the integral of this mixing spectrum.

[0152] The inventors tested the determination method described above by measuring calibrated mixing beams, designated CCRI, which have specified energy characteristics and calibration coefficients, summarized in Table 3 below.

[0153] [Tables3] CCRI Calibrated Mixing Beam Average Energy (keV) Known Calibration Coefficient of the CCRI Calibrated Mixing Beam 25 16.4 1.15 x 10⁶ CCRI 50b 28.9 6.69 x 10⁷ CCRI 100 51.0 6.83.10 7 CCRI 250 122.0 3.89.10 7

[0154] The inventors implemented process 500 on these CCRI mixing beams using the reference beams N, with the data illustrated in Table 1. In particular, the inventors implemented steps 502, 504, 505 of process 500, and in particular Eq. 4, with the weighting coefficients obtained from equations 2a and 2b.

[0155] The CCRI calibrated mixing beams were measured under the same experimental conditions as the reference beams, through the same dosimeter.

[0156] Results are summarized in Table 4 below, and are expressed by comparing the calibration coefficients NHp(0.07)finger_mix associated with the calibrated mixing bundles determined by steps 502, 504, 505 of process 500 with the known calibration coefficients NHp(0.07)finger_mix of these calibrated mixing bundles.

[0157] [Tables4] Calibrated mixing beam NHp(0.07) finger t - determined mix (mSv / shot) NHp(0.07) finger t - known mix (mSv / shot) Relative deviation ER NHP (%) CCRI 25 0.86 x 10⁶ 1.15 x 10⁶ 25.43 CCRI 50b 6.84 x 10⁷ 6.69 x 10⁷ 2.12 CCRI 100 7.06 x 10⁷ 6.83 x 10⁷ 3.41 CCRI 250 5.45 x 10⁷ 3.89 x 10⁷ 39.99

[0158] During spectral deconvolution step 504, the inventors found the proportions of each CCRI mixing beam in the reference beams N, in percentages, according to Table 5 below.

[0159] [Tables5] CCRI 25 CCRI 50b CCRI 100 CCRI 250 N20 100 25.29 0 0 N30 0 51.58 25.17 14.99 N40 0 23.12 25.48 5.87 N60 0 0 23.95 16.33 N80 0 0 25.40 9.86 N100 0 0 0 0 N120 0 0 0 0 N150 0 0 0 9.84 N200 0 0 0 0 N250 0 0 0 43.11

[0160] In order to provide a criterion for the validity of the determination method tested on these calibrated mixing bundles, the inventors have defined three domains for estimating the relative deviation ER NHp: - ER NHp <10%; - 10% < ER NHp < 50% - ER NHp > 50%

[0161] It can be seen that for some calibrated mixing beams, the relative deviation is well below 10%, which gives very good accuracy. For other mixing beams, the relative deviation is less than 50%, which remains acceptable for a radiation protection application.

[0162] From the description of the embodiments, it appears that the method for determining a radiation dose rate described is advantageous since it only requires one dosimeter for ionizing radiation that can extend over several energy ranges, for example between 10 keV and 1.5 MeV.

[0163] The determination method, and in particular the use of a spectral deconvolution method, makes it possible to calculate a dose rate, or a dose, for each energy range. Indeed, it allows for the definition of calibration coefficients adapted to each energy range covered by a reference beam, without having to use several dosimeters. This particularly improves the response of the dosimetry system in the extreme low and high energy ranges, unlike using a single calibration coefficient for a wide energy range. The result is a readily adaptable dosimetry system.

[0164] Furthermore, the database of elemental spectra can be enriched with new elemental spectra as reference beams are measured by the dosimeter, as well as with new elemental calibration coefficients. Enriching the database makes it possible to increase the measurement accuracy of the dose rate, and for example, the accuracy of the elemental calibration coefficients.

[0165] The dose determination method and the associated dosimetry system can be applied to extremity dosimetry, for example, finger dosimetry, chest dosimetry, ocular dosimetry, or any other dosimetry. Examples of application include the medical field, for example, medical imaging, nuclear medicine, interventional radiology, and the nuclear field, for example, radiation protection in nuclear environments.

[0166] Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these various embodiments and variants could be combined, and other variants will become apparent to them. In particular, the preceding description describes how the energy spectra are each constructed from an integral of the photodetector's electrical signal over a given integration window, for example, on the order of 1 ps. But, more generally, each energy spectrum could be constructed using any observable (and usable) variable of the electrical signal. Thus, as an alternative to the integral method, each energy spectrum could be constructed from a maximum amplitude of the electrical signal. This observable variable is less sensitive to the pile-up effect described previously.This avoids distorting the shape of the elementary spectra in the event of a significant pile-up effect. Indeed, unlike the integral method, which uses a larger portion of the electrical signal, the maximum amplitude method is limited to the highest part of the electrical signal. Even if there is a pile-up effect, the maximum amplitude of the electrical signal will be less affected than its integral. However, since this observable variable is based on only a sample of the electrical signal, there is a risk that it will be more sensitive to electronic background noise. If the aim is to minimize the risk of electronic background noise, then methods using the integral of the electrical signal can be preferred.

[0167] Finally, the practical implementation of the embodiments and variants described is within the reach of a person skilled in the art, based on the functional indications given above.

Claims

Demands

1. Method for determining (200) a dose rate (15) of ionizing radiation received by a dosimeter (101), the method of determination comprising: - a measurement step (202), by the dosimeter, of a mixed beam (10) of ionizing radiation in order to generate a mixed spectrum (11); - a spectral deconvolution step (204), by a processing unit (150) connected to the dosimeter (101), of the mixed spectrum into elementary spectra (21) from measurements, by the dosimeter, of reference beams (20) of ionizing radiation; - a determination step (206), by the processing unit (150), of elementary dose rates (25), from the elementary spectra (21) and calibration coefficients (22) associated with the reference beams (20); and - a determination step (208), by the treatment unit (150), of the dose rate (15) from the elementary dose rates (25).

2. A method according to claim 1, wherein the method further comprises, prior to the spectral deconvolution step (204), a measurement step (304), by the dosimeter (101), of reference beams (20), in order to generate the elementary spectra (21).

3. A method according to claim 2, wherein the method further comprises, prior to the measurement step (304) of the reference beams (20), a selection step (302) of said reference beams, each selected reference beam being associated with a calibration coefficient (22).

4. A method according to any one of claims 1 to 3, wherein the method further comprises, prior to the step of determining (206) the elementary dose rates (25), a step of determining (306) the calibration coefficients (22) from the elementary spectra (21) and reference dose rates (23) of the reference beams (20).

5. A method according to any one of claims 1 to 4, wherein the elementary spectra (21) and calibration coefficients (22) are stored in a database (140) linked to the processing unit (150).

6. A method according to any one of claims 1 to 5, wherein the spectral deconvolution step (204) comprises a least squares minimization method performing a fitting of a mixing function (fmix) representing the mixing spectrum (10) by elementary functions (fNi) representing the elementary spectra (21) associated with the reference beams (20).

7. A method according to any one of claims 1 to 6, wherein the step of determining the elementary dose rates (206) (25) comprises: - the calculation of the counting rate of the elementary spectra (21); and, for each elementary spectrum (21): - the calculation of the elementary dose rate (25) by the product of the calibration coefficient (22) associated with the reference beam (20) from the measurement of which the elementary spectrum (21) originates and the counting rate of said elementary spectrum.

8. A method according to any one of claims 1 to 7, wherein, in the dose rate determination step (208), said dose rate is determined by the sum of the elementary dose rates (25).

9. A method according to any one of claims 1 to 8, wherein the mixture spectrum (11) and the elementary spectra (21) are obtained: - by an integral calculation over an integration window of an electrical signal, for example in the form of pulses, generated by the dosimeter (101); or - by a maximum amplitude calculation of an electrical signal, for example in the form of pulses, generated by the dosimeter (101).

10. A method according to any one of claims 1 to 9, wherein the reference beams (20) comprise narrow-spectrum beams, for example X- or gamma-type photon beams and / or particle-type beams generated by one or more radioelements.

11. Processing unit (150) configured to implement, by means of dedicated circuits and / or by the execution of instructions by one or more processors, the following steps of a method for determining (200) a dose rate (15) of ionizing radiation received by a dosimeter (101) connected to the processing unit: - a spectral deconvolution step (204) of a mixture spectrum (11), from a measurement, by the dosimeter, of a mixture beam (10) of ionizing radiation, into elementary spectra (21) from measurements, by the dosimeter, of reference beams (20) of ionizing radiation; - a determination step (206) of elementary dose rates (25) from the elementary spectra (21) and calibration coefficients (22) associated with the reference beams (20); and - a determination step (208) of the dose rate (15) from the elementary dose rates (25).

12. Processing unit (150) according to claim 11, comprising: - a spectrum acquisition module (151) configured to generate the mixture spectrum (11) from the measurement, by the dosimeter (101), of the mixture beam (10) and the elemental spectra (21) from the measurements, by the dosimeter, of the reference beams (20); and - a calculation module (152) connected to the spectrum acquisition module (151) and configured to implement the spectral deconvolution (204), determination (206) of the elemental dose rates (25) and determination (208) of the dose rate (15).

13. Dosimetry system (100) comprising: - a dosimeter (101) including a scintillator (110) sensitive to ionizing radiation and capable of emitting light in response to the ionizing radiation it receives, and a photodetector (120) capable of receiving the light emitted by the scintillator and converting the received light to generate an electrical signal; and - a processing unit (150) according to claim 11 or 12, said processing unit being connected to the photodetector (120).

14. Dosimetry system (100) according to claim 13, further comprising a database (140) linked to the processing unit (150) and configured to store the elemental spectra (21) and calibration coefficients (22).

15. Computer program comprising instructions for implementing the dose rate determination method according to any one of claims 1 to 10, when the program is executed by the processing unit (150) according to claim 11 or 12.

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