Tailored Ge-doped fibres for passive electron radiotherapy dosimetry.

Siti Nurasiah Mat Nawi,N M Ung,K S Almugren,F H Alkallas,S F Abdul Sani,D A Bradley,M U Khandaker

doi:10.1371/journal.pone.0235053

Siti Nurasiah Mat Nawi, N M Ung + Show 5 more

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https://doi.org/10.1371/journal.pone.0235053

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Abstract

Study has been made of the thermoluminescence yield of various novel tailor-made silica fibres, 6 and 8 mol % Ge-doped, with four differing outer dimensions, comprised of flat and cylindrical shapes, subjected to electron irradiation. Main thermoluminescence dosimetric characteristics have been investigated, including the glow curve, dose response, energy dependence, minimum detectable dose, effective atomic number, linearity of index and sensitivity of the fibres. The studies have also established the uncertainties involved as well as the stability of response in terms of fading effect, reproducibility and annealing. In addition, dose-rate dependence was accounted for as this has the potential to be a significant factor in radiotherapy applications. The 6 and 8 mol % fibres have been found to provide highly linear dose response within the range 1 to 4 Gy, the smallest size flat fibre, 6 mol% Ge-doped, showing the greatest response by a factor of 1.1 with respect to the highly popular LiF phosphor-based medium TLD100. All of the fibres also showed excellent reproducibility with a standard deviation of < 2% and < 4% for 6 and 8 mol % Ge-doped fibres respectively. For fading evaluation, the smallest 6 mol% Ge-doped dimension flat fibre, i.e., 85 × 270 μm displayed the lowest signal loss within 120 days post-irradiation, at around 26.9% also showing a response superior to that of all of the other fibres. Moreover, all the fibres and TLD-100 chips showed independence with respect to electron irradiation energy and dose-rate. Compared with the 8 mol% Ge-doped optical fibres, the 6 mol% Ge-doped flat optical fibres have been demonstrated to possess more desirable performance features for passive dosimetry, serving as a suitable alternative to TLD-100 for medical irradiation treatment applications.

Highlights

In delivering a prescribed radiation dose to a well-defined target, the imperative [1] is to achieve accuracy to within < 5% while at the same time minimizing dose to surrounding healthy tissue, a matter discussed in detail by Kry et al (2017) [2]
Present work demonstrates that the proposed dosimeter fibres of different cross-sectional dimensions and dopant concentrations to be suitable for use as TL dosimeters, with reusability without any particular regeneration treatment, dose rate and energy independence and good linearity of response
Apart from this, the TL response of Ge-doped optical fibres clearly shows them to be capable of providing precise and accurate dosimetric evaluation for doses in areas subjected to acute radiation dose delivery

Summary

Introduction

In delivering a prescribed radiation dose to a well-defined target, the imperative (that of the International Commission on Radiological Units, ICRU) [1] is to achieve accuracy to within < 5% while at the same time minimizing dose to surrounding healthy tissue, a matter discussed in detail by Kry et al (2017) [2]. Optical fibre dosimetry therapies [3,4], hypo-fractionation [5]and FLASH radiotherapy [6]. This is due to the various influencing factors which necessarily effect the ability to achieve such accuracy. One particular factor of direct interest to the work concerns accurate assessment of the total dose delivered via multiple fractions [7,8]. Such optimized delivery is the product of exhaustive testing, both during acceptance testing as well as in routine use [9]

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