TLD-100 Powder Research Articles

Determination of correction factors and correction coefficients for calculations of the absorbed dose

The need to control the dose received by a patient during radiation therapy (RT) is dictated by the quality assurance requirements, which encompass a broad system of organizational and technical measures aimed at achieving consistency and precision in dosimetry measurements. The ultimate goal of using a quality assurance system in RT is to ensure high accuracy in delivering the dose to the tumour, reducing the irradiation volumes of normal, healthy tissues and organs near the target (tumour lesion). It has been established that to enhance the effectiveness of radiation treatment and to reduce the number of complications in subsequent periods, it is necessary to irradiate the local target in the patient’s body with a dose error no greater than ±5%. To control the calculation of the absorbed dose in water using thermoluminescent (TL) dosimeters, irradiated on a gamma therapeutic device for remote radiation therapy, it is necessary to study the influence of various factors (fading, non-linearity of indications, energy dependence, reproduction of the TL signal, presence of a holder) on the magnitude of the TL signal. We have studied and identified various corrective factors and their error values that may affect the calibration of the system (TLD-100 powder (Rexon), thermoluminescent reader PCL-3). In determining the corrective factors to account for the daily drift of the PCL-3 device, the TL signal obtained during the exposure was adjusted based on the control powder indicators. As a control powder, TLD-100 (Rexon) was used, irradiated with an absorbed dose of 2 Gy under standard conditions and aged four months to obtain a stable TL signal.

Dosimetry audit for megavoltage photon beams applied in non-reference conditions

PurposeWe have conducted for the first time a Malaysian postal dosimetry audit of external beam under non-reference conditions by evaluating the output performance while screening for systematic errors within the dosimetry chain. The potential use from the choice of detector were investigated along with the search for other sources of discrepancies. MethodsTen radiotherapy centres were audited, encompassing 16 megavoltage photon beam arrangements, adopting the IAEA postal dosimetry protocol for non-reference conditions, with a holder modified to accommodate three TLD types: Ge-doped cylindrical silica fibres (CF), Ge-doped flat silica fibres (FF), and TLD-100 powder. ResultsEight of the centres operated within ± 5% of stated dose, one other exceeding tolerance for all measured points, and one did not return any dosimeters for analysis after failing the initial irradiations. Post remedial measures, the mean relative response for CF, FF, and TLD-100 was 1.00, 0.99, and 0.98 respectively, with associated coefficients of variation 6.87%, 6.45%, and 5.06%. ConclusionHigh quality radiotherapy clinical practice postal dosimetry audits that are based on sensitive TLDs are seen to be particularly effective in identifying and resolving dose delivery discrepancies.

Synthesis and dosimetry features of novel sensitive thermoluminescent phosphor of LiF doped with Mg and Dy impurities

Lithium fluoride doped with Mg and Dy was fabricated for the first time using melting method. The optimum concentrations of impurities and thermal treatment were studied to achieve high thermoluminescence (TL) sensitivity. TL sensitivity of the fabricated phosphor is close to that of TLD-100 powder. Tm-Tstop technique was used to identify the number of overlapped TL glow peaks. Initial rise, isothermal decay and computerized glow curve deconvolution (CGCD) methods were applied to obtain kinetic parameters of the prepared TL material. Three component glow peaks were distinguished at temperatures 395, 448 and 510 K. Other TL properties such as fading, linearity of dose response and reusability are also presented and discussed.

Thermoluminescence studies of calcium metaborate (CaB2O4) nanocrystals synthesized by solution combustion method

This study reports the thermoluminescence properties of calcium metaborate (CaB2O4) nanocrystals prepared by solution combustion method. The characterization by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX) analysis was presented here. The XRD patterns showed the orthorhombic structure with the crystallite size at about 27 nm and the FESEM micrograph revealed the formation of irregular spherical shape nanoparticles. Weight fraction obtained from EDX analysis consequently lead to determination of effective atomic number. It was found that the effective atomic number of CaB2O4, Zeff= 14.13 was equivalent to the effective atomic number of the bone, Zeff= 13.23 with percent error 6.83 %. The samples were annealed using the TLD oven type LAB-01/400 and exposed to cobalt-60 source (Gammacell 220 Excel). TL glow curves were recorded using a Harshaw model 3500 TLD reader. The TL glow curve of this material showed a simple, single, peak located at around 150 °C. The most striking dosimetric feature of this nanomaterial was the excellence linearity response of a dose range from 1 Gy up to 100 Gy with R2= 0.9827 compared to the TLD-100 powder with R2= 0.9276. The high linear correlation between dose and TL response to gamma radiation suggest that calcium metaborate nanocrystals can be considered as a promising material to be used in thermoluminescence dosimetry.

DOSIMETRIC CHARACTERISTICS OF THE NOVEL LiF:Mg,Cu,Ag PHOSPHOR.

In this study, the preparation procedure and dosimetric characteristic of LiF activated by Mg, Cu and Ag were investigated for the first time. It was observed that with the thermal annealing at 240°C for 10 min the sensitivity of the novel LiF:Mg,Cu,Ag powder was more than that of the TLD-100 powder. Also, the thermoluminescence intensity decreased with the increase of annealing temperature from 240 to 300°C. The glow curve structure of this sample that is similar to TLD-100H shows a mean peak at ~243°C along with four overlapping peaks. Also, the absorbed dose response increases linearly at low dose ranges. Other thermoluminescence characteristics of this phosphor such as low residual signal, low fading rate and good stability at repeatability and reusability make it useful for the dosimetric applications.

LiF TLD-100 as a Dosimeter in High Energy Proton Beam Therapy—Can It Yield Accurate Results?

In the region of high-dose gradients at the end of the proton range, the stopping power ratio of the protons undergoes significant changes, allowing for a broad spectrum of proton energies to be deposited within a relatively small volume. Because of the potential linear energy transfer dependence of LiF TLD-100 (thermolumescent dosimeter), dose measurements made in the distal fall-off region of a proton beam may be less accurate than those made in regions of low-dose gradients. The purpose of this study is to determine the accuracy and precision of dose measured using TLD-100 for a pristine Bragg peak, particularly in the distal fall-off region. All measurements were made along the central axis of an unmodulated 200-MeV proton beam from a Probeat passive beam-scattering proton accelerator (Hitachi, Ltd., Tokyo, Japan) at varying depths along the Bragg peak. Measurements were made using TLD-100 powder flat packs, placed in a virtual water slab phantom. The measurements were repeated using a parallel plate ionization chamber. The dose measurements using TLD-100 in a proton beam were accurate to within ±5.0% of the expected dose, previously seen in our past photon and electron measurements. The ionization chamber and the TLD relative dose measurements agreed well with each other. Absolute dose measurements using TLD agreed with ionization chamber measurements to within ± 3.0 cGy, for an exposure of 100 cGy. In our study, the differences in the dose measured by the ionization chamber and those measured by TLD-100 were minimal, indicating that the accuracy and precision of measurements made in the distal fall-off region of a pristine Bragg peak is within the expected range. Thus, the rapid change in stopping power ratios at the end of the range should not affect such measurements, and TLD-100 may be used with confidence as an in vivo dosimeter for proton beam therapy.

Calibration of a TLD-100 powder dosimetric system to verify the absorbed dose to water imparted by 137Cs sources in low dose rate brachytherapy at the oncology unit in the Hospital General de Mexico

A thermoluminescence dosimetry (TLD) system was characterised at SSDL-ININ to verify the air-kerma strength (S(K)) and dose-to-water (D(W)) values for (137)Cs sources used in low dose rate (LDR) brachytherapy treatments at the Hospital General de Mexico (HGM). It consists of a Harshaw 3500 reader and a set of TLD-100 powder capsules. The samples of TLD-100 powder were calibrated in terms of D(W) vs. nC or nC mg(-1), and their dose response curves were corrected for supralinearity. The D(W) was calculated using the AAPM TG-43 formalism using S(K) for a CDCSM4 (137)Cs reference source. The S(K) value was obtained by using a NE 2611 chamber, and with two well chambers. The angular anisotropy factor was measured with the NE 2611 chamber for this source. The HGM irradiated TLD-100 powder capsules to a reference dose D(W) of 2 Gy with their (137)Cs sources. The percent deviations between the imparted and reference doses were 1.2% < or = Delta < or = 6.5%, which are consistent with the combined uncertainties: 5.6% < or = u(c) < or = 9.8% for D(W).

Precision Dosimetry in Narrow Collimated Radiation Beams of the Leksell Gamma Knife

The Leksell Gamma Knife is a stereotactic radiosurgical instrument for non-invasive cerebral surgery without opening the skull. It contains some 200 60Co ? radiation sources of, totally, 220 TBq. Each source is individually collimated so that the beams converge precisely on a common focal region at the centre, where the tumour is positioned. With the smallest collimation of 4 mm focus diameter the radiation field has a volume of less than 10 mm3. In such a geometry precise determination of the absorbed dose rate (of the order of 3.5 Gy.min-1), essential for the result of tumour treatment, is difficult. Comparative measurements are described with a miniaturised ionisation chamber of 125 mm3, a calibrated semiconductor diode of 0.8 mm3 and TLD-100 powder in capsules of 21.1 and 28.7 mm3 respectively, taken at different focal diameters of 4, 8, 14 and 18 mm. It can be shown that extrapolation between the different methods allows for precise determination of the absolute absorbed dose rate, even for the smallest focus, traceable to the primary standards via the ionisation chamber measurements. Using the semiconductor diode, accurate dose rate profiles can be established. The method has been tested on two Gamma Knife installations at the Neurosurgical University Clinics at Graz and Vienna.

TSEE, TL and Optical Properties of LiF Single Crystals

LiF:Ti,Mg single crystals, of which the Ti content is 100 µmol.mol-1 and Mg concentration varies between 10 and 1000 µmol.mol-1, LiF single crystals (type DTG-4, Russian) and cold pressed LiF prepared from Harshaw TLD-100 powder were studied. TSEE and TL responses after beta or gamma irradiation were subsequently recorded using computer aided photon counting (Daybreak TL), and a multineedle counter type TSEE reader. TL and TSEE glow curves were studied in the temperature range of 50 to 500 oC. The optical absorbance and its dose dependence was measured in the 200-450 nm range. Properties such as TL and TSEE glow peak positions dose responses were determined and analysed. An explanation of probable TL-TSEE correlation is given with a discussion of the applicability of TL-TSEE readings for personal accident dose evaluation.

TSEE, TL and Optical Properties of LiF Single Crystals

Abstract LiF:Ti,Mg single crystals, of which the Ti content is 100 µmol.mol-1 and Mg concentration varies between 10 and 1000 µmol.mol-1, LiF single crystals (type DTG-4, Russian) and cold pressed LiF prepared from Harshaw TLD-100 powder were studied. TSEE and TL responses after beta or gamma irradiation were subsequently recorded using computer aided photon counting (Daybreak TL), and a multineedle counter type TSEE reader. TL and TSEE glow curves were studied in the temperature range of 50 to 500 oC. The optical absorbance and its dose dependence was measured in the 200-450 nm range. Properties such as TL and TSEE glow peak positions dose responses were determined and analysed. An explanation of probable TL-TSEE correlation is given with a discussion of the applicability of TL-TSEE readings for personal accident dose evaluation.

High-exposure dosimetry with LiF (TLD-100) by photo-acoustic spectrometry

Optical absorption of LiF:Mg, Ti (TLD-100) as-received and annealed powders was investigated in the 300-700 nm range by photo-acoustic spectrometry (PAS). Near-logarithmic behaviour was found between 3 kGy and 1 MGy for the observed absorption peaks at 380, 444 and 547 nm. Optical bleaching properties were studied with white light and monochromatic irradiations at 254 and 366 nm. Fading characteristics were determined. It is shown that PAS is an appropriate tool for measuring doses on powders, especially in the high-dose range. Suggestions are made for extending the dose range to lower levels. In this way LiF TLD-100 powder may be used continuously from the mu Gy (by thermoluminescent methods) to the MGy (by PAS) range.

Thermoluminescent response of LiF (TLD-100) to 5-30 keV electrons and the effect of annealing in various atmospheres

The response of single crystal and extruded ribbons of TLD-100 was investigated. If annealing is done in a vacuum, the sensitivity of TLD-100 single crystals to these electrons and the resultant glow curve are essentially the same as when irradiations are carried out with 137Cs gamma rays. All discrepancies in sensitivity can then be accounted for by the higher LET of electrons. The commonly used 'standard annealing' at 400 degrees C for one hour produced a change in the glow curve shape and a loss in sensitivity in contrast to the vacuum anneal results. Diffusion of hydroxyl ions into the sample during air annealing is believed to be the primary cause for this change. The results explain the source of the 'dead layer' proposed to explain the variation with particle size of the luminescent efficiency of X-ray irradiated TLD-100 powder and the low TL efficiency from low energy electron irradiations.

Single-crystal thermoluminescent lithium fluoride for dosimetry prepared by an edge-defined film-fed growth (EFG) technique

A novel edge-defined film-fed growth technique (EFG) has been used to prepare doped LiF single crystals. The high-temperature thermoluminescent glow peaks of these crystals are found to be greater than those of the TLD-100 powder used as starting material. The thermal resolution of all the glow peaks of single-crystalline specimens is also greater than that of the powder.