Study has been made of the thermoluminescence (TL) response of silica-based Ge-doped cylindrical, flat and photonic crystal fibres (referred to herein as PCF-collapsed) to electron (6, 12 and 20 MeV) ...and photon (6, 10 MV) irradiation and 1.25 MeV γ-rays, for doses from 0.1 Gy to 100 Gy. The electron and photon irradiations were delivered through use of a Varian Model 2100C linear accelerator located at the University of Malaya Medical Centre and γ-rays delivered from a 60Co irradiator located at the Secondary Standard Dosimetry Laboratory (SSDL), Malaysian Nuclear Agency. Tailor-made to be of various dimensions and dopant concentrations (6-10% Ge), the fibres were observed to provide TL yield linear with radiation dose, reproducibility being within 1-5%, with insensitivity to energy and angular variation. The sensitivity dependency of both detectors with respect to field size follows the dependency of the output factors. For flat fibres exposed to 6 MV X-rays, the 6% Ge-doped fibre provided the greatest TL yield while PCF-collapsed showed a response 2.4 times greater than that of the 6% Ge-doped flat fibres. The response of cylindrical fibres increased with core size. The fibres offer uniform response, high spatial resolution and sensitivity, providing the basis of promising TL systems for radiotherapy applications.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This work builds upon a prior study, examining the dosimetric utility of pencil lead and thin graphitic sheets, focusing upon the measurement of skin doses within the mammographic regime. In ...recognizing the near soft-tissue equivalence of graphite and the earlier-observed favourable thermoluminescence yield of thin sheets of graphite, this has led to present study of 50 μm thick graphite for parameters typical of external beam fractionated radiotherapy and skin dose evaluations. The graphite layers were annealed and then stacked to form an assembly of 0.5 mm nominal thickness. Using a 6 MV photon beam and delivering doses from 2- to 60 Gy, irradiations were conducted, the assembly first forming a superficial layer to a solid water phantom and subsequently underlying a 1.5 cm bolus, seeking to circumvent the build-up to electronic equilibrium for skin treatments. Investigations were made of several dosimetric properties arising from the thermoluminescence yield of the 50 μm thick graphite slabs, in particular proportionality and sensitivity to dose. The results show excellent sensitivity within the dose range of interest, the thermoluminescence response varying with increasing depth through the stacked graphite layers, obtaining a coefficient of determination of 90%. Acknowledging there to be considerable challenge in accurately matching skin thickness with dose, the graphite sheets have nevertheless shown considerable promise as dosimeters of skin, sensitive in determination of dose from the surface of the graphite through to sub-dermal depth thicknesses.
•Graphite foils as TL skin dosimeters.•Dermal and epithelial doses evaluated.•Support provided via the TOPAS Monte Carlo code.•Stacked graphite layers applied in evaluating skin dose down to a depth of 150 μm.
This study compares the practicality of Ge-doped silica optical fibres as a potential remote dosimeter for radiotherapy postal dosimetry audit in non-reference conditions with a commercial ...thermoluminescence dosimeter (TLD-100). The optical fibre system consists of two types of fibres: cylindrical (CF) and flat fibres (FF). The dosimetric characteristics of the systems were investigated and compared, with particular attention to dose linearity, energy dependence, reproducibility, and fading. Measurements of absorbed doses of CF, FF, and TLD-100 were made, along with uncertainty budgets. A preliminary test was performed under non-reference conditions to evaluate the variations in absorbed doses measured with CF and FF versus TLD-100. For both 6 MV and 10 MV photon beams, CF, FF, and TLD-100 show a linear dose-response from 1 Gy to 3 Gy with a coefficient of determination (R2) greater than 0.99, minimal energy dependence, and good reproducibility with less than 3% deviation. The highest fading rates were 37.6%, 63.4%, and 14.2% for CF, FF, and TLD-100, respectively, at day 106 after irradiation. For irradiation with a photon beam of 6 MV, the combined relative standard uncertainty of absorbed dose determined from CF, FF, and TLD-100 measurements was estimated to be 4.3%, 5.56%, and 0.74%, respectively. Preliminary absorbed dose measurement tests under non-reference conditions showed that the mean ratios of Ge-doped silica optical fibres to TLD-100 for on-axis dose, wedge transmission, and output factor were 1.014, 0.991, and 1.013, respectively. The Ge-doped silica optical fibre systems have dosimetric performance commensurate with the TLD-100 and can be used as a potential remote dosimeter for mailed dosimetry audits if appropriate correction factors are applied to the absorbed dose measurements.
•Ge-doped silica optical fibres and TLD-100 dosimetric properties were investigated.•The uncertainty analysis was performed on Ge-doped silica optical fibres and TLD-100.•The absorbed dose measured by Ge-doped silica optical fibres is comparable to TLD-100.•Ge-doped silica optical fibres provide reasonable accuracy as a remote dosimeter.
Ge-doped silica fibre (GDSF) thermoluminescence dosimeters (TLD) are non-hygroscopic spatially high-resolution radiation sensors with demonstrated potential for radiotherapy dosimetry applications. ...The INTRABEAM® system with spherical applicators, one of a number of recent electronic brachytherapy sources designed for intraoperative radiotherapy (IORT), presents a representative challenging dosimetry situation, with a low keV photon beam and a desired rapid dose-rate fall-off close-up to the applicator surface. In this study, using the INTRABEAM® system, investigations were made into the potential application of GDSF TLDs for in vivo IORT dosimetry. The GDSFs were calibrated over the respective dose- and depth-range 1 to 20 Gy and 3 to 45 mm from the x-ray probe. The effect of different sizes of spherical applicator on TL response of the fibres was also investigated. The results show the GDSF TLDs to be applicable for IORT dose assessment, with the important incorporated correction for beam quality effects using different spherical applicator sizes. The total uncertainty in use of this type of GDSF for dosimetry has been found to range between 9.5% to 12.4%. Subsequent in vivo measurement of skin dose for three breast patients undergoing IORT were performed, the measured doses being below the tolerance level for acute radiation toxicity.
Various thicknesses of 2B grade polymer pencil lead graphite (PPLG) were used in the present study, which focussed on the alteration in crystalline lattice and the structural defect caused by the ...electron irradiation dosage ranging from 0.5 to 20 Gy delivered by an Elekta HD Linac. The fundamental trap parameters i.e. kinetics order (b), activation energy (E), and frequency factor (s) of the PPLG samples have been estimated using the initial rise and peak shape approaches by fitting the thermoluminescence (TL) glow peaks of the PPLG samples exposed to 20 Gy. The lifetime of the TL glow peak is also presented, which provides information on the stability of the TL signal at maximum temperatures. Raman, Photoluminescence (PL), and X-ray diffraction (XRD) spectra are being used to observe the structural changes that have occurred as a result of the radiation doses. These spectroscopies offer an understanding of the physical parameters that are related to the defects and taking part in the luminescence process. When all of the data are taken into account, it is anticipated that 0.3 mm PPLG is an effective material for dosimetry. The results of these lines of research are intended to educate the innovation of versatile graphite radiation dosimeters as a low-cost efficient system for radiation detection. The studied PPLG offers tissue equivalence as well as high spatial resolution, both are desirable criteria for a material to be used in the monitoring of ionising radiation or a variety of medical applications.
•Novel use of different diameters for polymer pencil lead graphite for radiation dosimetry subjected to electron irradiation.•Raman spectroscopy, photoluminescence spectroscopy, and x-ray diffraction were used to explore structural changes.•The principal trap parameters of the PPLG samples were estimated using the initial rise and peak shape methods.
Abstract
The radioluminescent (RL) dosemeter is excellent for real-time radiation measurement and can be used in various applications. A plastic scintillator is often the choice sensor because of its ...size and tissue equivalency. This study aims to characterise a novel plastic scintillator irradiated with high-energy photon beams. An RL dosimetry system was developed using the plastic scintillator. The RL dosimetry system was irradiated using a linear accelerator to characterise the dose linearity, dose rate, energy dependency and depth dose. The developed system showed a linear response toward the dose and dose rate. An energy dependency factor of 1.06 was observed. Depth dose measurement showed a mean deviation of 1.21% from the treatment planning system. The response and characteristics of the plastic scintillator show that it may be used as an alternative in an RL dosimetry system.
•13 types silica fibres are examined as potential sensor material for high dose dosimetry.•Thermoluminescence response of fibres are obtained at dose range of 0.1–100 kGy.•Various fibre types show ...different dose level of saturation starting from 5 kGy.•Borosilicate fibre demonstrates best performance with linear response till 100 kGy.•Further dosimetric characterisation of Borosilicate fibre are presented.
With high-dose applications lacking the benefit of an economic yet versatile dosimeter that provides for a wide dynamic dose range, ongoing research is seeking to introduce suitable thermoluminescent (TL) material for such needs. Acknowledging the high potential of silica fibres, as developed by members of this group over the past few years, in present work evaluation has been made of 13 types of fibre, differing in dopant, dopant concentration and diameter including P−, Al−, Er−, Ge− and Al-Tm-doped fibres, ultra-high numerical aperture and borosilicate fibre, and two non-doped fibres, quartz and suprasil F300. Evaluation is made in terms of TL response to photon and electron irradiations with the objective of determining a TL material that can offer sensitive yet extended dose capability, saturating only above the few tens of kGy range. The various silica fibres that have been investigated were found to show saturation levels from 5 kGy for Ge-doped fibre (4 mol %) to 80 kGy for 2 mol % Al−doped silica fibre. Borosilicate fibres demonstrated the greatest potential for high dose dosimetry, maintaining a highly-linear response, any tendency towards saturation only being indicated to beyond receipt of doses of 100 kGy. For this fibre type detailed TL characterizations were conducted, including glow curve analysis, reproducibility and fading tests. The results suggest borosilicate fibre to be suitable for high dose TL dosimetry, providing sufficient sensitivity and appropriate dosimetric characteristics.
The relatively new treatment modality electronic intraoperative radiotherapy (IORT) is gaining popularity, irradiation being obtained within a surgically produced cavity being delivered via a ...low-energy x-ray source and spherical applicators, primarily for early stage breast cancer. Due to the spatially dramatic dose-rate fall off with radial distance from the source and effects related to changes in the beam quality of the low keV photon spectra, dosimetric account of the Intrabeam system is rather complex. Skin dose monitoring in IORT is important due to the high dose prescription per treatment fraction. In this study, modeling of the x-ray source and related applicators were performed using the Monte Carlo N-Particle transport code. The dosimetric characteristics of the model were validated against measured data obtained using an ionization chamber and EBT3 film as dosimeters. By using a simulated breast phantom, absorbed doses to the skin for different combinations of applicator size (1.5-5 cm) and treatment depth (0.5-3 cm) were calculated. Simulation results showed overdosing of the skin (>30% of prescribed dose) at a treatment depth of 0.5 cm using applicator sizes larger than 1.5 cm. Skin doses were significantly increased with applicator size, insofar as delivering 12 Gy (60% of the prescribed dose) to skin for the largest sized applicator (5 cm diameter) and treatment depth of 0.5 cm. It is concluded that the recommended 0.5-1 cm distance between the skin and applicator surface does not guarantee skin safety and skin dose is generally more significant in cases with the larger applicators. Highlights: * Intrabeam x-ray source and spherical applicators were simulated and skin dose was calculated. * Skin dose for constant skin to applicator distance strongly depends on applicator size. * Use of larger applicators generally results in higher skin dose. * The recommended 0.5-1 cm skin to applicator distance does not guarantee skin safety.
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