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real-time dosimetry with radiochromic films - thin polyester film

by:Cailong     2019-07-10
real-time dosimetry with radiochromic films  -  thin polyester film
Radioactive chromium film dosing has been widely used in most applications of Radiation Physics for more than 20 years.
This is due to many attractive properties of the radioactive discolored film, such as reliability, accuracy, ease of use and cost.
However, based on the use of commercial densitters and scanners, the current radioactive discoloration Film reading technique only provides a dose value after the film is exposed to radiation.
In this work, the real innovation method
For some specific applications, a time reading of the radiation discolored film is proposed.
The new method is based on photoelectric
An electronic instrument that uses a fiber optic probe to measure the optical changes in the film caused by radiation, allowing for high accuracy and accuracy to measure the dose.
In addition, the dynamic range of some types of films, such as EBT3 Gafchromic films (
Widely used in medical physics)
Can be extended by more than one order of magnitude.
Due to the many advantages of commonly used reading technology, a national patent was submitted in January 2018.
Radiation chameleon film (RCFs)
It is a dosimeter based on the properties of modifying the structural features of its crystal-sensitive elements when exposed to ionization radiation.
The interaction of ionization radiation with the film produces the polymerization process in the monomer of the sensitive element.
This microscopic phenomenon is reflected in the color change at the macro level, and the color of the film can be related to the radiation dose.
The first job of displaying solid solutions for Radio employment
The synthesis after exposure to radiation dates back to 1965, by Mc Laughing. .
The follow-up to RCFs can be attributed to the National Institute of Standards and Technology (NIST).
The first prototype of RCFs is sensitive in the dose range of several hundred kGy to several hundred kGy, so these films are used for high doses
Dose application only.
A radioactive chromium medium sensitive to low doses (up to 5u2009Gy)
Known as the Gafchromic film, it was developed by the International Special Products company in 1986. (ISP).
Nowadays, RCF dose determination is considered to be a reliable technique for accurate dose evaluation and quality inspection in many applications of Radiation Physics.
There are currently several types of films on the market, covering a very wide range of doses from several mGy to several hundred kGy.
Its main application area is medical physics, but it is also widely used in other fields. g.
Radiation damage, beam diagnosis, radiation treatment and radiation research of electronic devices
Induced sterilization (
Food and medical devices.
This widespread use is the result of the inherent nature of the film.
Nowadays, RCFs is reliable, easy to use, cheap, portable and non-
Provide accurate and permanent dose values.
It must be noted that this last feature is very important for the legal aspects related to dosing.
RCFs has a high spatial resolution and most RCFs types are made of tissue
Equivalent material.
These properties are very suitable for the determination of medical physics, especially the percentage depth
Dose curves for photon and ion beam radiation therapy.
RCFs is sensitive to various ionization radiation used in applications (
Photon, electron, proton, heavy ion).
The response of the film is almost completely independent of the dose-
Although energy dependence is studied in depth in several works reported in the literature, energy dependence is more complex.
More details on the energy dependence of RCFs will be given in the next section.
Despite such attractive properties, RCFs cannot be used as a dosimeter or detector if it is true
Time information is required.
The current RCFs reading technology is mainly based on commercial density meters, scanners, and optical meters, and dose measurements are provided only after the film is exposed to radiation.
In practice, reading is carried out after the film is removed from the irradiation site.
Therefore, the current reading technique does not allow for timely measurement of dose trends, but only for comprehensive dose values.
This important limitation is overcome in the application (when needed)
Provide real-time response by using other probestime.
For example, gas
For this purpose, filling rooms, flashing detectors, fluorescent screens and semiconductor detectors are usually used;
However, RCFs can be used in conjunction with these detectors.
The most extensive reading technology based on plane
The bed scanner is affected by repetitive problems, including warmth
Up, uniformity and resolution of the scanner, and dependence on film size, direction and area of interest at the time of analysis, lateral non-
Uniformity and polarization effects.
All of these aspects have been widely discussed in the literature, resulting in uncertainty usually around 3-6%.
In this work, innovative methods based on photoelectric technology
Electronic instruments and meters are practical
Time reading for RCFs.
Mignani reported on previous works on the subject. and Rink . .
With America. S. patent.
Compared with the existing RCF reading technology, the proposed method here has several new interesting features.
Because it uses commercial RCFs directly (
Cut into small pieces)
It avoids the complex operation of depositing radioactive media at the tip of the optical fiber.
In addition, regarding the above-RCF Real offer-
Time technology, based on single
Using probes, this method uses fiber optic probes where RCF is disposable and can be quickly replaced with other RCFs for other measurements.
This allows to save all of the above
The features of the film are discussed.
Advantages of using an optical systemfiber-
Based on the instrument rather than the commercial RCF reading tool, not only does it allow the performance of the dose to be read in real time
Time, and also developed most of the potential of the RCF dose meter.
In fact, as will be shown in this work, the dose measurement can be carried out with very high accuracy and accuracy.
In addition, the sensitivity range of certain types of films can be extended by several orders of magnitude relative to the sensitivity announced by the manufacturer.
The originality of the invention, the technological progress of the existing RCF reading method and the potential distribution in the market have patented the invention.
To this end, a national patent was filed in January 2018.
In the next section, an overview of the main properties of RCFs will be discussed: how the film works and how it responds to radiation types, energy, and dosesrate.
In addition, different types of movies will be displayed according to their specific application.
Following this principle and experimental device
Innovative RCF reading methods will be presented and discussed.
Finally, in the last section, the operation of the invention method will be demonstrated for the two types of films widely used in the application: EBT3 and XR-
QA2 Gafchromic film exposed to Co gamma rays at two doses-rates.
This section provides an overview of the main features and application areas of RCFs.
Working Principle and dependence of related physical quantities such as radiation type, energy and dose
Rates are briefly described, and more details can be found in the reference publication.
The features discussed here make RCF dosing such a wide range of dosing techniques in several application areas.
Therefore, the proposed RCF implementation
The time reading method adds an important value to the properties of this kind of dosimeter.
RCFs consists of single-layer or double-layer radiation-
Sensitive material on thin polyester base with coating.
It may end up being transparent or opaque.
Ionization radiation produces an polymerization process in the monomer of the active layer, resulting in a change in the optical properties of the film.
The material responsible for the coloring of RCFs is dyacetilenes, especially the crystal polyacetylene, which exhibits excellent sensitivity to ionization radiation.
Unlike silver halogen film, RCFs is
That is, they do not need chemical or physical treatment after irradiation.
RCFs is sensitive to almost any type of ionization radiation (
Photons, electrons, and charged particles in a wide range of energy and dose)
At the same time, it is almost completely insensitive to room light.
The dependence of most RCFs responses on radiation quality is very low, at least for low radiation qualityLET (
Linear energy transfer)radiation (e. g. MeV-
Energy electrons and photons)
It is usually used for radiation therapy and radiation hardness applications.
RCFs is highly dependent on energy
Make radiation more complex.
Despite that, the film has a different LET-
By applying the relative validity coefficient, the composition of the charged particle beam can be considered.
For example, some types of RCFs, such as EBT2 and EBT3 gaffchromium films, are widely used in radiation therapy for photons, electrons, and laser beams and are known to understate the dose in the Peak area of Prague.
This is called "quenching effect" in the literature ".
However, RCFs was successfully used in radiation therapy to determine the percentage depth dose distribution of photons and ion beams.
About dose of RCFs-
Rate dependence, no difference in response was observed.
The sensitivity of neutrons is very low: So far, Bazioglou reported the results on the neutron sensitivity of RCFs. .
In practice, RCFs is not used to measure neutron doses and neutron beam profiles as is commonly used for other radiation.
The RCFs types available on the market cover multiple doses, from several mGy to several hundred kGy.
For this and the above reasons --
RCFs is currently used in many applications of Radiation Physics compared to other dosimeters and detectors.
The figure shows the field of application where RCFs is used as a Gy dose function.
All dose values reported in this work are called water, which is the standard for Medical Physics.
RCFs is used for quality inspection of typical diagnostic instruments such as X-, with doses ranging from dozens to hundreds of mGy
Ray tubes for radiography and computed tomography (CT).
For this purpose, the ISP offers the Gafchromic series XR.
Especially XR-
XR 2 film is suitable for radiation quality assurance test of XR-
CT2 measure beam slice width in CT scanner XR-
M2 tablets are specially used for breast X-ray examination and XR-
For peak skin dose measurement.
These films consist of a layer of 97 m of yellow polyester and an active layer of about 25 m between a layer of white polyester (opaque layer).
It should be noted that the structure of the film is an important parameter of the real film.
The time reading method will be explained in the next section.
The use of RCFs ranges from hundreds of mGy to dozens of Gy, which is used to measure the typical external beam treatment dose of photons and laser beams.
Some hospitals, clinics and cancer treatment centers have used film dosing as a successful method.
The application of close-range radiation therapy involves doses up to hundreds of Gy, and RCFs is also used for dose validation in this area.
EBT3 Gafchromic film is widely used for depth determination in medical physics.
Dose curves of photons, electrons, and ion beams.
These films are made from an active layer of about 28 m sandwiched between two 120 m polyester layers.
These films can be used as sheets of 8x10 inch for use when a large radiation field is required.
However, if the dose of a small area needs to be determined, the film can be cut into small pieces without losing its properties. For very high-
Dose applications such as industrial applications, radiation treatment, radiation hardness quality assurance testing, beam diagnostics, and high energy physics (HEP)
There are other types of movies to choose from.
The Gafchromic HDV2 film is sensitive in a dose range of 10 to 1000gy.
Outside kg ys, thin film (
Active Layer 12 µm and polyester substrate 97 m)are used.
GEX company deals B3 movies (
Activity layer: 18 m)
Sensitive in the range of 1-150 kGy;
FWT60 film launched by far west technology (
Activity layer: 18 m)
Application in the range of 0. 5–200 kGy.
It is worth noting that using RCFs as a dosimeter for hepfield is a topic under study.
Due to their features, RCFs can be a perfect tool for dose measurement monitoring in harsh environments like hepfacilities: there are no other detectors typical electronic devices, so there is no interaction with electric and magnetic fields.
However, it is very complicated to study the mixed radiation field of such facilities with RCFs, which consists of different radiation types and energies.
In order to measure the dose, the physical quantity representing the darkening of the film must be related to the radiation dose.
The relationship between this physical quantity and the dose of a film exposed to different doses of the known radiation field is calibration.
In the following contents, the principle of commercial RCF reading technology (
Scanner and density meter)
Explain by showing examples of calibrating a set of films with an Epson V800 scanner.
Therefore, innovative RCF reading instruments are proposed.
The physical quantity representing the darkness of the film can be the optical density (OD)or any OD-based-
Functions such as NetOD.
The density meter usually provides OD-relative to the calibration of the certification step-tablets.
The relationship between the physical quantity representing film dimming and the dose is usually non-linear;
Calibration data, however, is well suited for polynomial functions.
Therefore, the calibration with a density meter is a function of OD as a dose.
Reading RCFs using a commercial scanner is usually performed by digitizing film images.
Pixel value (PV)
It can be evaluated with appropriate image analysis software, calibration can be done as a function PV of the dose or as a function OD of the dose.
OD is calculated from PV.
As an example
The calibration of a set of EBT3 gafcro films exposed to a 1mev mev electron beam from ilu-is shown
6 Linear Accelerator, Warsaw Institute of Nuclear Chemistry and Technology (Poland).
The optical density increases with the increase of the dose.
In particular, where the sensitivity is very high, the growth rate has risen sharply to about 10 gy.
For higher doses, light density increases slowly until saturation is reached.
The diagram shows the schematic diagram of the experimental device used for the real environment
Time reading for RCFs.
It is basically composed of a fiber bundle with six illuminated fibers on the side of the fiber bundle, one light-
Collect fiber optics, RCF, light sources and spectrum analyzers connected to computers for data analysis in the center.
Six illuminated fibers transmit light from the light source to the probe tip for RCF positioning.
After entering the RCF, the light is first backscattered by the appropriate material, then collected by the central fiber, and then sent back to the spectrometer.
Due to the darkening caused by ionization radiation, changes in the optical properties of the film can be detected in reality in this waytime.
The selection of the backward scattering material affects the integral-
Time of the meter
This parameter is basic and related to the sensitivity of the method: it determines the minimum amount of time for the spectrometer to detect sensitive changes in light.
The diagram shows the schematic diagram of the terminal part of the innovation kit-up.
The design and implementation of this part has a dual purpose: to ensure the interaction of ionization radiation with RCF and to allow backward scattering of light with sufficient strength to be detected by the spectrometer.
The name of the reference chart.
, The element "2" is both a holder of the optical fiber bundle and a holder of the backward scattering material.
These materials can be plastic such as ABS or Teflon, in the form of a cylinder (
Height 6mm 1mm and diameter)
Or thin foil of Mylar (of thickness 1. 5 m).
It should be noted that the material of the design
The support allows the RCF itself to be used as a backward scattering material if required.
This is very useful if the RCF has an opaque layer;
This is the case, e. g.
XR of Gafchromic-models.
Element "4" allows the hosting of plastic cylinders.
This can be screwed on the element "2" and fixed.
If thin foil is used, the element "3" can be inserted into the material "-holder “4”. The elements 2-3-4 are holed.
For thin transparent RCFs like EBT3 Gafchromic film model, the only absorber is a plastic cylinder or 1.
5 m Mylar foil operated as a light mirror.
For opaque films such as XRQA2 Gafchromic film models, Element 3 and Element 4 are omitted so that there is no absorber between RCF and radiation.
The beam of the fiber can be made of different materials, such as stainless steel, plastic (
Less interaction with ionization radiation)
Alternatively, a single fiber can be used if needed.
Stainless steel probes were used in this work.
During the operation, the whole device is placed in the irradiation area.
The light source for this prototype is "avaliight-DH-S-
BAL balance power "and spectrometer" AvaSpec-ULS2048XL”.
The latter is controlled by computer.
As shown in the figure, RCF is located in the material Holder.
The picture shows the top view of the fiber bundle, with cereal paper and red light.
The effective area of the RCF sample involved in the dose reading depends on the size and location of the probe end lighting and collecting fibers;
In particular, it refers to the picture shown in Figure 1.
, The effective area corresponds to the circle of three fibers with a diameter of 200 m.
However, in order to allow the actual and reliable insertion of the read-out system, an RCF sample of 8 × 20mm was adopted.
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