Medical Range Radiation Dosimeter Based on Polymer-Embedded Fiber Bragg Gratings

Abstract

Fiber Bragg gratings (FBGs) are valuable dosimeters for doses up to 100 kilograys (kGy), but have hardly been used for the low-dose range of a few grays (Gy) required in medical radiation dosimetry. We report that embedding a doped silica fiber FBG in a polymer material allows a minimum detectable dose of 0.3 Gy for γ-radiation. Comparing the detector response for different doped silica fibers with various core doping, we obtain an independent response, in opposition to what is reported for high-dose range. We hypothesized that the sensor detection is based on the radio-induced thermal expansion of the surrounding polymer. Hence, we used a simple physical model based on the thermal and mechanical properties of the surrounding polymer and obtained good accordance between measured and calculated values for different compositions and thicknesses. We report that over the 4 embedding polymers tested, polyether ether ketone and polypropylene have respectively the lowest (0.056 pm/Gy) and largest sensitivity (0.087 pm/Gy). Such FBG-based dosimeters have the potential to be distributed along the fiber to allow multipoint detection while having a sub-millimeter size that could prove very useful for low-dose applications, in particular for radiotherapy dosimetry.

Real-Time Temperature Correction of Medical Range Fiber Bragg Gratings Dosimeters

“…For a polymer-embedded FBGs dosimeter, we previously showed good accordance for BWS ( ) due to low-dose radiation response ( D ) between experimental data and theoretical model [ 21 ]: in which is the Bragg peak wavelength, is the photo-elastic coefficient, and are the coefficient of thermal expansion for the coating and for the fiber, and are the coating and the fiber cross-sectional areas and , are Young’s modulus of the coating and of the fiber, and are respectively the coating and fiber mass heat capacity, and is the thermo-optic coefficient. If we consider ambient temperature variation ( ) and set for convenience, the total BWS can be expressed as follows: …”

“…For this technique, the temperature coefficient ratio ( ) is 1.52, and the dose coefficient ratio ( ) is 1.18, which are different from one another as required. All theoretical coefficients are calculated with the constants presented in [ 21 ].…”

“…Once corrected, the 60 s pre-irradiation measurements are average and set to zero to allow fair comparison between each FBG. This technique was used in our previous work [ 20 , 21 ].…”

“…We previously showed that Bragg wavelength shifts (BWS) of polymer-embedded FBGs are usable for medical range dosimetry [ 20 ]. They would be an excellent candidate especially for small field radiotherapy multi-points dosimetry [ 21 ] because of their small detection volume (around 0.01 ) compared to a commonly used ion chamber [ 22 ]. Olusoji et al [ 23 ] have recently shown that FBGs written in a perfluorinated polymer could also be used for medical range dosimetry.…”

Radiation Effects on Fiber Bragg Gratings: Vulnerability and Hardening Studies

“…As with the coating, the embedding or packaging of the grating can also change its radiation sensitivity; an example of this is reported in [ 105 ]. Moreover, Lebel-Cormier et al recently reported a radiation dosimeter based on polymer-embedded FBGs [ 110 ]: they showed that, by gluing the FBG inside a square prism in different polymer materials and reducing the error in the peak detection to 0.03 pm, the induced shift depends linearly on the dose, up to 20 Gy, with a slope of about ~0.06 pm/Gy, which depends on the material choice and not on the fiber composition.…”