METHOD FOR MEASURING AND REPRESENTING THE LEVEL OF LOCAL IRRADIATION DOSES

Abstract

A method for measuring and representing the level of local irradiation doses, in at least two dimensions, comprises: a step of positioning N probes S.sub.i sensitive to irradiating radiation, each corresponding to a local zone Z according to a known topology; a step of acquiring, by each of the probes, the level of radiation IS.sub.i detected and periodically recording numerical values IS.sub.i(t); and a step of converting the numerical values IS.sub.i(t) into values DS.sub.i(t) corresponding to the radiation dose applied to each of the Z zones associated with a probe S.sub.i, according to a calibration table. The method further comprises, during the measurement sequence, steps of spatial interpolation calculation of at least one estimated irradiation level value IS.sub.iv(t) of at least one virtual zone Z.sub.iv that is not associated with a probe. A measurement device for implementing this method is also described.

Claims

1. A method for measuring and representing, in real time, a level of local irradiation doses in at least two dimensions, comprising: positioning N probes S.sub.i, sensitive to irradiating radiation, each corresponding to a local zone Z.sub.i according to a known topology; acquiring, by each of the probes, a level of irradiation IS.sub.i detected, and periodically recording numerical values IS.sub.i(t); and converting the numerical values IS.sub.i(t) into values DS.sub.i(t) corresponding to the radiation dose applied to each of the zones Z associated with a probe S.sub.i, according to a calibration table; and performing a spatial interpolation calculation of at least one estimated irradiation level value IS.sub.iv(t) of at least one virtual zone Z.sub.iv that is not associated with a probe.

2. The method of claim 1, further comprising calculating at least one estimated irradiation level value IS.sub.iv(t) using a time interpolation function.

3. The method of claim 1, wherein performing the spatial interpolation calculation comprises applying a calculation processing taking into account a representation of human morphology.

4. The method of claim 1, wherein performing the spatial interpolation calculation comprises applying a calculation processing taking into account a relative position P(t) of a source of the probes and/or of a patient.

5. The method of claim 1, wherein performing the spatial interpolation calculation comprises applying a calculation process taking into account characteristics C(t) of the system delivering the irradiation doses.

6. The method of claim 1, wherein performing the spatial interpolation calculation comprises applying a calculation processing taking into account results obtained with other detectors or patient dose evaluation systems used in clinical routine to estimate the doses received by the patient in one or more dimension(s).

7. A system for measuring and representing, in real time, local irradiation doses in at least two dimensions, comprising a plurality of radiation-sensitive probes S.sub.i and a computer controlled by a microprocessor and at least one non-transitory computer-readable storage medium storing instructions thereon that, when executed by the at least one processor, cause the system to: acquire, by each of the probes, a level of irradiation IS.sub.i detected, and periodically record numerical values IS.sub.i(t); and convert the numerical values IS.sub.i(t) into values DS.sub.i(t) corresponding to the radiation dose applied to zones Z respectively associated with the probes, according to a calibration table; and perform a spatial interpolation calculation of at least one estimated irradiation level value IS.sub.iv(t) of at least one virtual zone Z.sub.iv that is not associated with a probe.

8. The system of claim 7, wherein at least a some of the probes are respectively associated with radiopaque markers.

9. The system of claim 8, wherein each of the radiopaque markers has a distinctive identifier.

10. The system of claim 7, wherein the probes S.sub.i are arranged according to a predetermined topology on a three-dimensional support adapted to a morphology of the target to be irradiated.

11. The method of claim 2, wherein performing the spatial interpolation calculation comprises applying a calculation processing taking into account a representation of human morphology.

12. The method of claim 11, wherein performing the spatial interpolation calculation comprises applying a calculation processing taking into account a representation of human morphology.

13. The method of claim 12, wherein performing the spatial interpolation calculation comprises applying a calculation processing taking into account a relative position P(t) of a source of the probes and/or of a patient.

14. The method of claim 13, wherein performing the spatial interpolation calculation comprises applying a calculation process taking into account characteristics C(t) of the system delivering the irradiation doses.

15. The method of claim 14, wherein performing the spatial interpolation calculation comprises applying a calculation processing taking into account results obtained with other detectors or patient dose evaluation systems used in clinical routine to estimate the doses received by the patient in one or more dimension(s).

16. The method of claim 3, wherein the human morphology is a generic human morphology.

17. The method of claim 3, wherein the human morphology is a morphology of a human patient subjected to the irradiation.

18. The system claim 10, wherein target is human.

19. The system claim 10, wherein target is not human.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0079] The characteristics and advantages of the present disclosure will appear upon reading the following description, given only by way of a non-restrictive example while referring to the appended drawings, wherein:

[0080] FIG. 1 is a schematic view of a device for determining a dose according to the present disclosure;

[0081] FIG. 2 shows a schematic cross-sectional view of a probe embodying the present disclosure;

[0082] FIG. 3 is a schematic view of neuro-radiology equipment according to the present disclosure; and

[0083] FIG. 4 is a schematic view of a piece of equipment, in the form of a belt, according to the present disclosure.

DETAILED DESCRIPTION

[0084] Due to the plurality of techniques and fields concerned, many risks are inherent in interventional radiology, in particular, the various vigilance measures that include adverse effects of X-rays in the form of significant radiation protection events. Interventional radiology techniques generally involve the following body parts:

[0085] The abdomen (intestine, kidneys, liver, stomach);

[0086] The central nervous system (brain, spinal cord);

[0087] The thoracic cage (breathing system, lungs);

[0088] The cardiovascular system (arteries, veins);

[0089] The musculoskeletal system (bones, joints, spines); and

[0090] The genito-urinary system (reproductive organs, urinary system).

[0091] The doses delivered to patients in interventional radiology frequently exceed the value of 200 mGy, i.e., the conventional limit of low doses, and often reach a few grays. The possible effects of irradiation are no longer only stochastic in nature and deterministic effects can also be observed (example: radiodermatitis).

[0092] Since the dose absorbed by the various organs cannot be measured in real time on patients due to a lack of equipment, the equivalent doses are estimated by measuring the dose on anthropomorphic phantoms or by using software that simulates radiation interactions on mathematical phantoms or on data acquired on the patient. However, the PDS does not accurately reflect the importance of the maximum dose to the skin and its use will only be possible under special and specific conditions of procedures, installation and operators. On the other hand, the relationships between air kerma and PDS are complex and only applicable under specific conditions of realization.

[0093] The patient's characteristics (position, thickness, height, weight) are not taken into account, as well as the beam orientation or the physical characteristics thereof (on which the backscatter component is dependent) and/or the actual distances between the source and the patient. In general, the contribution of scopy to the total PDS can be of the order of 30% for diagnostic cardiac procedures and 50% for therapeutic procedures. Even though the recording of the scopy time is accompanied by the number of graphical images and the patient's weight, this evaluation presents a great uncertainty about the actual dose, ranging from +130% to 70%, it being understood that many ionizing radiation (IR) emitting devices do not provide the beam characteristics for each scopy sequence but only an irradiation time and a scopy dose for the entire examination. For example, a dose estimated at 2 Gy could actually have a probable value between 0.6 and 4.6 Gy. During the procedure, the exposure level must be known at all times and the operator must be notified when alert thresholds are reached.

[0094] The practice of interventional radiology is confronted with the revelation of numerous irradiation accidents leading to improved consideration of dose management. Many procedures are likely to induce skin lesions and the incidence of deterministic effects increases with the patient's weight, the nature and complexity of the procedure and the previous exposures. Depending on the procedures, scopy times can be particularly long, which means that all the doses cover the entire range of possible skin lesions, from erythema to skin necrosis. Diagnosing these lesions can be difficult, especially when the exposure is unknown to the clinician. It appears that these are often located on the back, the scalp and the breast.

Description of the Equipment

[0095] The dose measuring equipment includes a known beam of detector probes 11 to 14 based on the scintillator/optical fiber technology. These probes 11 to 14 are connected to a detection system 1 comprising at least one photodetector 2 and an electronic circuit 3 exploiting the signals delivered by the photodetector 2 into digital information exploited by a computer 4 executing a computer code for processing this information.

[0096] During an interventional radiology procedure, probes 11 to 14 are subjected to X-rays, under the action of which the scintillator 5 then emits a quantity of light directly proportional to the dose received.

[0097] This light is then collected and sent to one or more photodetector(s) 2. The light signal is converted into an electrical signal and then processed by an electronic circuit 3 to give the final dose rate delivered by the ionizing radiation emitting apparatus.

Detail of the Realization of the Probes

[0098] The probes 11 to 14 are composed of at least one organic or inorganic scintillating optical fiber 5 sensitive to radiation and connected at one end 6 to one end of a non-scintillating plastic or silica optical fiber 7 by a connecting sleeve 8. The non-scintillating optical fiber 7 is used to convey the light produced in the scintillating part.

[0099] The sleeve 8 providing the mechanical resistance can be placed inside or outside a sheath 10. It allows the mechanical reinforcement of the bonding between the non-scintillating optical fiber 7 and the scintillating optical fiber 5, which constitutes a frangible area.

[0100] The other end of the non-scintillating optical fiber 7 is equipped with a connection system allowing the optimal connection to a cell of a photodetector 2.

[0101] To respect the radiotransparency of the probes 11 to 14, they have a maximum diameter of 1 mm in diameter and opaque sheaths with a maximum thickness of 1 mm. For example, in the case of a tube type sheath, the wall thickness of the sheath is 250 m.

[0102] To ensure the punctuality of the scintillating optical fiber 5, the sleeve 8 and the glue are chosen so as to produce a minimum of parasitic light when they are irradiated and to limit the emission of parasitic light from plastics and solvents under irradiation. To further reduce this interference, the sleeve 8 is of the minimum size required to perform its mechanical reinforcement function. Similarly, the amount of glue used is reduced to a minimum.

[0103] This is all the more important as the scintillating optical fiber 5 is small, for example, 3 to 5 mm long.

Detection System

[0104] The probes 11 to 14 are connected to a photomultiplier or photodetector 2 via a connector, for example, a cookie type connector (architecture of the connector developed by the CNRS free of charge) or, for a single-channel probe, a SMA-905 type connector.

[0105] The photodetector 2 consists, for example, of a Hamamatsu H10721-110 or 210 (non-commercial) or multi-anode Hamamatsu H8804, H12700 sensor, etc.

[0106] It can also be made up of:

[0107] photodiode (SiPM), Avalanche Photodiode (APD), Multi-Pixel Photon Counter (MPPC);

[0108] charge-coupled photodetector (CCD sensors); and

[0109] or any other device performing the same function.

Electronic Part

[0110] Generally speaking, at the output of the photomultiplier 2, the electrical signal is processed by an electronic circuit 3, initially by a discriminator via an adjustable threshold and makes it possible to determine the counting rate (number of events/photon per time unit) and, in particular, to select the signals generated in the photodetector corresponding to 1 photon, 2 photons, . . . , n photons.

[0111] The material part to perform this operation can take two forms:

[0112] it can be based on an ASIC technique. In this case it is possible to use, for example a detection board Maroc3 (trade name) developed by the Weeroc company. This board makes it possible to process in parallel the analog signals at the output of the Hamamatsu Multianode PMs (64 channels). The main purpose of the Maroc3 board is to measure the charge and not the photon count. Nevertheless, it could be used in photon counting after modification of the FPGA internal program; and

[0113] it can also be based on a discrete electronic circuit. A board has been developed by us and its architecture is similar to the one developed for the product dedicated to scanning, with the difference that it integrates an FPGA allowing parallel multi-channel processing. The developed board can contain from 1 to n channels (n being the number of channels of the photomultiplier 2 used), connected to at least one photodetector.

[0114] These circuits allow the parallel acquisition of signals from one or more single photodetector(s) or one or more multi-channel photodetector(s) simultaneously. These circuits are designed in such a way that detection thresholds (as well as gain values) can be defined for each channel. This makes it possible to correct fluctuations due to the photodetectors or the different electronic channels.

[0115] The electronic circuit 3 receives a signal at the output of the photomultiplier 2 via a resistance bridge ensuring polarization at a voltage of 2.5V. Then, a comparator is used to select according to a predefined voltage level and transform the analog signal into a TTL digital signal. The latter is either sent directly to a counter in an FPGA or formatted (generation of a monostable) before being counted.

[0116] Data is then transmitted to a control and display device via a wired connection, for example, via a flash drive or Ethernet or wirelessly, for example, via Wifi or Bluetooth.

[0117] A remote or not remote screen, placed, for example, on the visualization screens in the operation room, allows the real-time visualization of the cumulative doses and/or the instantaneous dose received by the patient. Data can be transferred to this screen via wired network or wireless connection as before.

[0118] The photomultiplier 2, the electronic circuit 3 and the computer 4 are housed in a housing located outside the radiation field so as not to interfere with the X-ray flux. In particular, it can be positioned at the end of the table so as not to disturb the patient or the radio manipulator and/or the doctor interacting with the patient and can be operated on batteries.

Application to Neuro-Radiology

[0119] Interventional radiology is used in different fields of medicine. Examples include neuro-radiology and interventional cardio-radiology. Dosimetric probes must then respond to the different needs and constraints inherent to each domain. Their geometry will therefore be different, for example, depending on whether they are to be used in neuro-radiology or cardio-radiology.

[0120] For skull procedures (neuro-radiology), radiology equipment consists of a rotating head 20 that can be moved around the patient's head in a known manner, whereby an X-ray source 21 and an X-ray unit 22 are fixed diametrically opposite each other. A positioning arm 23 immobilizes the patient's head in a reproducible manner.

[0121] The probe can be placed according to a predetermined topology or not on a three-dimensional support adapted to the morphology of the target presented, for example, in the form of a cap 24 that can be integrated into the headrest or placed directly on the patient's skull. This cap is used as a support for the positioning of the end of one or more probe(s) 11 to 13 connected either to a multi-channel photodetector (preferably a PMT) or to several photodetectors (preferably PMTs) if, for example, the number of fibers is not very large.

Other Applications

[0122] For procedures at the thorax or on the abdo-pelvic area, the three-dimensional support can be in the form of a belt 30 as illustrated in FIG. 4 and can also support several probes 11 homogeneously distributed (constant area spacing) or not according to the areas of interest.

Software Processing

[0123] The software part makes it possible to visualize in real time (less than a second with data refreshing every 500 ms, for example,) the dose deposited on the patient's skin with a spatial resolution depending on the area of interest and the number of sensors.

[0124] The computer program also allows dose deposits to be mapped using 3D reconstruction/modelling of the patient, for example, from images of the patient, data relating to the dose deposited during the interventional procedure (patient images, mapping from DACS or manufacturers, dicom sr, other real-time manufacturer data, or gafchromic type detectors) and the dose measured for the various points of interest by the probes 11 to 14.

[0125] The DICOM data is defined by a standard for the computer management of data from medical imaging. This standard defines an organized structure of a series of fields and the image pixels that correspond to a particular field.

[0126] Each field is defined by:

[0127] a) for explicit encodings: [0128] a label (tag); [0129] a value representation (VRValue Representation) encoded by two characters; [0130] the value length; and [0131] value.

[0132] (b) for implicit encodings: [0133] a label (tag); [0134] the value length; and [0135] value. [0136] A label consists of: [0137] a group number encoded by two bytes; and [0138] an element number encoded by two bytes.

[0139] The DICOM data relating to the dose deposited and the machine characteristics is accessible in real and/or delayed time when the radiological installations allow it.

[0140] For example, the patient's modelling will be based on a scanographic examination performed prior to the operation.

[0141] The dose mapping can be represented by a color code. Alert thresholds, defined above, are used to report exceedances of the maximum skin dose (hot spot).

[0142] This solution is designed in such a way that it can be combined with a software program for calculating the dose distribution. This allows:

[0143] to optimize such software by providing a real measurement of the dose at different points on the patient; and

[0144] to make more precise the mapping of the dose measured at x points (interpolation of the measurement points).

First Alternative Solution

[0145] When the installation allows the data relating to the dose deposited during the interventional procedure to be available in real time, the computer program can initially model the patient's skin by extracting the patient's external boundary from the patient's scanner images that were taken before the interventional radiology procedure. This external boundary is then converted into a surface mesh having a predetermined resolution. The computer program then projects each irradiation event described in the DICOM SR file from the interventional radiology device (in real time or delayed relative to the operation) onto the surface of the mesh of the patient's external boundary. The computer program accumulates the different irradiation events per mesh unit, which allows, after mathematical corrections (of the backscatter factor type), to have a differential mapping of the cumulative dose in mGy. As this first mapping is based on the information from the DICOM SRs, it must also be corrected with the actual dose information measured for the different points of interest by the probes 11 to 14 to obtain an absolute dose mapping. This absolute mapping based on the DICOM data from the interventional radiology device, supplemented by spot dose measurements made with the measuring device, is converted into a standard 3D format (example: vtk type) in order to be visualized.

[0146] The history of the results obtained for each patient is recorded in a database associated with the measuring equipment.

[0147] The results of the processings are displayed on a remote screen and exploited by an alert system. Given the recommendations and regulations in force, the system includes an alert system when the maximum skin dose of 2 Gy is exceeded, and then every subsequent 0.5 Gy.

Second Alternative Solution

[0148] When the installation does not provide data on the dose deposited during the interventional procedure in real time, an indicative map of the doses actually measured for the various points of interest by the probes 11 to 14 extrapolated by the barycenter method may be displayed during the operation and extrapolated by one of the techniques described above for greater precision at the end of the examination.

Third Alternative Solution

[0149] Also when the installation does not provide the dose data deposited during the interventional procedure in real time, the software for calculating the dose distribution determines the dose distribution from gafchromic films and at least one dose measurement for at least one point of interest located on the gafchromic film by at least one probe, the combination of these two measuring methods makes it possible to avoid having to calibrate the film batches.

Calibration Method

[0150] The solution as proposed above measures a dose and a dose rate deposited in the probe. Depending on the positioning of the probe, this is equivalent to a skin dose measurement. For example, a skin dose can be measured at the back or the pelvis for cardiac procedures, uterine embolizations, renal angioplasty, etc. and a skin dose measurement at the skull for neuroradiology procedures (treatment of arteriovenous cerebral malformations (AVM), intracranial aneurysms, etc.).

[0151] The system is calibrated against a reference ionization chamber in terms of air kerma. The result obtained with the ionization chamber is given in mGy. The system calibration factor is therefore given in mGy/TC (TC=Count Rate). It can also be calibrated against a dosimeter such as TLD or gafchromic.

[0152] In the case of a multipoint probe, each channel will be calibrated independently of the others. A calibration factor will then be defined for each channel.

[0153] In the case of a multi-anode PMT photodetector, the cross-talk effect must be taken into account, either from the manufacturer's data or by in-house measurements.

Dose Interpolation

[0154] For each detection point Si a series of measurements IS.sub.i(t), with t indicating the time of the data acquisition are obtained from the data provided by the probes 11 to 14 and processed by the electronic circuit 3 and the computer 4. Such data is converted into values DS.sub.i(t) corresponding to the radiation dose applied to each of the zones Z associated with a probe S.sub.i, according to a calibration table. These variables are recorded in a database to apply in real time a processing to calculate doses at points that have not been acquired by a probe 11 to 14, and thus define a high-resolution cartographic representation of the doses received by the patient.

[0155] The computer uses the variables recorded in the database to perform a spatial interpolation calculation of at least one estimated irradiation level value IS.sub.iv(t) of at least one virtual area Z.sub.iv not associated with a probe and record values DS.sub.v(t) corresponding to the estimated radiation dose in an area without a probe 11 to 14.