Thermoluminescent Dosimetric Research Articles

Characterisation of borosilicate glass media as potential thermoluminescent dosimeters

Thermoluminescence dosimetry applications range from environmental radiation monitoring to sensing of the doses delivered in radiotherapy, through to verifying the doses of large-scale industrial irradiation. Particular utilisations largely depend upon the sensitivity of the dosimetric medium. In present work the thermoluminescent dosimetric properties of commercial low-cost borosilicate glass slides and glass-fibre filters were characterized, use being made initially of a 250 kV clinical therapy x-beam facility. From this, reproducibility and linearity were determined for radiation doses of 0.5, 1, 2, 4, 6, 8, and 10 Gy. Reproducibility of +/5% was obtained following appropriate screening, excellent linearity to dose also being demonstrated for both the borosilicate glass slides and glass-fibre filters, sufficient to demonstrate the potential of these media for use in radiotherapy dosimetry. Of note is the appreciable but not unsurprising dose response of the nominal 1.0 mm thickness borosilicate glass slides, with a per unit dose response some twice that of the less substantial glass-fibre filters. Further work has characterized the borosilicate glass slides for the megavoltage photons and electrons produced by linacs. A further potential interest results from the boron content, recognizing the associated appreciable neutron cross-sections. It is posited that the additional response observed at 10 MV over that at 6 MV is partly a result of photo-neutron production, a matter that is expected to form the basis of further investigations.

Effective atomic numbers for photon energy absorption and energy dependence of some thermoluminescent dosimetric materials

Effective atomic number for photon energy absorption (Z peaeff ), the relative effective atomic number of the thermoluminescent dosimetric (TLD) materials with respect to air (Z reff ), and energy dependence (ED) of the TLD materials such as beryllium oxide (BeO), lithium tetraborate (Li 2 B 4 O 7 : Cu, Ag, P), aluminum oxide (Al 2 O 3 ), calcium fluoride (CaF 2 ), and titanium oxide (TiO 2 ) in the energy range of 1 keV to 20 MeV have been studied. The values of ZPEA eff and ZR eff show a broad peak and a maximum value around 20 keV for BeO, around 60 keV for CaF2 and TiO 2 , and around 40 keV for Al 2 O3 and Li 2 B 4 O 7 : Cu, Ag, P. Overall, the effective atomic number (Z eff ) varies linearly with ED for all the materials in the photon energy range of 1 keV to 20 MeV except TiO2 and thereby confirming the validity of a more commonly employed method of using the Z eff to calculate the measure of the ED in TLD. The ED values show a broad peak around 30 keV for CaF 2 and TiO 2 and around 20 keV for Al 2 O 3 and remain almost constant for the other two materials.

Studies on photon buildup for some thermoluminescent dosimetric compounds

Photon buildup for some SrSO4, BaSO4, MgSO4, MnSO4, FeSO4 and ZnSO4 thermoluminescent dosimetric (TLD) compounds was investigated in the present work. Photon energy absorption buildup factors and photon exposure build factors were computed for the TLD compounds using the five-parameter geometric progression fitting method in energy range 0.015–15 MeV for penetration depths up to 40 mean free path. The buildup factors were studied as a function of photon energy, penetration depth and chemical compositions. Effective atomic numbers and air-kerma for the TLD compounds were calculated and ICRU standard tissue equivalence was discussed.

Modeling of gamma ray energy-absorption buildup factors for thermoluminescent dosimetric materials using multilayer perceptron neural network: A comparative study

In this work, multilayered perceptron neural networks (MLPNNs) were presented for the computation of the gamma-ray energy absorption buildup factors (BA) of seven thermoluminescent dosimetric (TLD) materials [LiF, BeO, Na2B4O7, CaSO4, Li2B4O7, KMgF3, Ca3(PO4)2] in the energy region 0.015–15MeV, and for penetration depths up to 10 mfp (mean-free-path). The MLPNNs have been trained by a Levenberg–Marquardt learning algorithm. The developed model is in 99% agreement with the ANSI/ANS-6.4.3 standard data set. Furthermore, the model is fast and does not require tremendous computational efforts. The estimated BA data for TLD materials have been given with penetration depth and incident photon energy as comparative to the results of the interpolation method using the Geometrical Progression (G-P) fitting formula.

Studies on mass attenuation coefficient, effective atomic number and electron density of some thermoluminescent dosimetric compounds

Mass attenuation coefficient, μm , effective atomic number, Zeff, and effective electron density, Nel, were determined experimentally and theoretically for some thermoluminescent dosimetric (TLD) compounds such as MgSO4, CdSO4, Al2O3, Mg2SiO4, ZnSO4, CaSO4, CaF2, NaSO4, Na4P2O7, Ca5F(PO4)3, SiO2, CaCO3 and BaSO4 at 8.04, 8.91, 13.37, 14.97, 17.44, 19.63, 22.10, 24.90, 30.82, 32.06, 35.40, 36.39, 37.26, 43.74, 44.48, 50.38, 51.70, 53.16, 80.99, 276.40, 302.85, 356.01, 383.85 and 661.66keV photon energies by using an HPGe detector with a resolution of 182eV at 5.9keV. The theoretical mass attenuation coefficients were estimated using mixture rule. The calculated values were compared with the experimental values for all compounds. Good agreement has been observed between experimental and theoretical values within experimental uncertainties.

Applicability of Topaz Composites to Electron Dosimetry

Thermoluminescent dosimetric topaz properties have been investigated and the results have shown that this mineral presents characteristics of a good dosimeter mainly in doses evaluation in radiotherapy with photons beams in radiotherapy. Typical applications of thermoluminescent dosimeters in radiotherapy are: in vivo dosimetry on patients (either as a routine quality assurance procedure or for dose monitoring in special cases); verification of treatment techniques; dosimetry audits; and comparisons among hospitals. The mean aim of this work was to evaluate the efficiency of topaz-Teflon pellets as thermoluminescent dosimeters in high-energy electron beams used to radiotherapy. Topaz-Teflon pellets were used as TLD.

Energy absorption buildup factors for thermoluminescent dosimetric materials and their tissue equivalence

Gamma ray energy-absorption buildup factors were computed using the five-parameter geometric progression (G-P) fitting formula for seven thermoluminescent dosimetric (TLD) materials in the energy range 0.015–15 MeV, and for penetration depths up to 40 mfp (mean free path). The generated energy-absorption buildup factor data have been studied as a function of penetration depth and incident photon energy. Buildup factors determined in the present work should be useful in radiation dosimetry, diagnostics and therapy. The tissue equivalence of TLD materials is also discussed.

Avaliação da dose no reto em pacientes submetidas a braquiterapia de alta taxa de dose para o tratamento do câncer do colo uterino

OBJETIVO: O objetivo deste trabalho foi desenvolver um sistema dosimétrico termoluminescente capaz de avaliar as doses administradas ao reto de pacientes submetidas a braquiterapia de alta taxa de dose para o tratamento do câncer do colo uterino. MATERIAIS E MÉTODOS: O material termoluminescente utilizado para a avaliação da dose no reto foi o LiF:Mg,Ti,Na na forma de pó. O pó foi separado em pequenas porções de 34 mg, que foram acomodadas em um tubo capilar. Este tubo foi colocado em uma sonda retal, que era introduzida no reto da paciente. RESULTADOS: As doses administradas ao reto de seis pacientes submetidas a braquiterapia de alta taxa de dose para o tratamento do câncer do colo uterino foram avaliadas com dosímetros termoluminescentes e apresentaram boa concordância com os valores planejados, com base em duas radiografias ortogonais da paciente, imagens ântero-posterior e lateral. CONCLUSÃO: O sistema de dosimetria termoluminescente utilizado no presente trabalho é simples e de fácil utilização quando comparado a outros métodos de dosimetria do reto. Ele mostrou-se eficiente na avaliação da dose no reto de pacientes submetidas a braquiterapia de alta taxa de dose para o tratamento do câncer do colo uterino.

Determination of trapping parameters of dosimetric thermoluminescent glow peak of lithium triborate (LiB 3O 5) activated by aluminum

Lithium triborate (LBO) is a newly developed ideal nonlinear optical (NLO) crystal used in laser weapon, welder, radar, tracker, surgery, communication, etc. The effective atomic number ( Z eff =7.3) makes it a tissue equivalent material and this encourages studies on its thermoluminescence (TL) properties for a radiation dosimetry. The previous studies have shown that Al-doped LiB 3O 5 is a promising thermoluminescent dosimetric (TLD) material for dosimetric purposes and continuous and systematic investigations to improve its quality to get ones suited for dosimeter applications are worthy. In the given study, the additive dose (AD), initial rise with partial cleaning (IR), variable heating rate (VHR), peak shape (PS), three-points method (TPM) and computerized glow deconvolution (CGCD) methods were used to determine the kinetic parameters, namely the order of kinetics ( b), activation energy ( E a ) and the frequency factor ( s) associated with the dosimetric thermoluminescent glow peak (P3) of Al-doped LiB 3O 5 after different dose levels with β-irradiation.

Photon mass attenuation coefficients, effective atomic numbers and electron densities of some thermoluminescent dosimetric compounds

Photon mass attenuation coefficients of some thermoluminescent dosimetric (TLD) compounds, such as LiF, CaCO3, CaSO4, CaSO4.2H2O, SrSO4, CdSO4, BaSO4, C4H6BaO4 and 3CdSO4.8H2O were determined at 279.2, 320.07, 514.0, 661.6, 1115.5, 1173.2 and 1332.5 keV in a well-collimated narrow beam good geometry set-up using a high resolution, hyper pure germanium detector. The attenuation coefficient data were then used to compute the effective atomic number and the electron density of TLD compounds. The interpolation of total attenuation cross-sections of photons of energyE in elements of atomic numberZ was performed using the logarithmic regression analysis of the data measured by the authors and reported earlier. The best-fit coefficients so obtained in the photon energy range of 279.2 to 320.07 keV, 514.0 to 661.6 keV and 1115.5 to 1332.5 keV by a piece-wise interpolation method were then used to find the effective atomic number and electron density of the compounds. These values are found to be in agreement with other available published values.

Patient and personnel exposure during CT fluoroscopy-guided interventional procedures.

To estimate patient dose and personnel exposure from phantom measurements during computed tomographic (CT) fluoroscopy, to use the estimates to provide users with dose information, and to recommend methods to reduce exposure. Surface dose was estimated on a CT dosimetric phantom by using thermoluminescent dosimetric (TLD) and CT pencil chamber measurements. Scatter exposure was estimated from scattered radiation measured at distances of 10 cm to 1 m from the phantom. Scatter exposures measured with and without placement of a lead drape on the phantom surface adjacent to the scanning plane were compared. Phantom surface dose rates ranged from 2.3 to 10. 4 mGy/sec. Scattered exposure rates for a commonly used CT fluoroscopic technique (120 kVp, 50 mA, 10-mm section thickness) were 27 and 1.2 microGy/sec at 10 cm and 1 m, respectively, from the phantom. Lead drapes reduced the scattered exposure by approximately 71% and 14% at distances of 10 and 60 cm from the scanning plane, respectively. High exposures to patients and personnel may occur during CT fluoroscopy-guided interventions. Radiation exposure to patients and personnel may be reduced by modifying CT scanning techniques and by limiting fluoroscopic time. In addition, scatter exposure to personnel may be substantially reduced by placing a lead drape adjacent to the scanning plane.

Effective atomic numbers for photon energy absorption and energy dependence of some thermoluminescent dosimetric compounds

Effective atomic numbers for photon energy absorption and energy dependence (ED) of some selected pure thermoluminescent dosimetric (TLD) compounds such as LiF, CaCO 3, CaSO 4, CaSO 4 · 2H 2O, CdSO 4, SrSO 4 and BaSO 4 have been calculated in the energy region of 1 keV to 20 MeV. The more commonly used empirical formula for calculating the measure of ED in the energy region of interest in TL dosimeters through effective atomic numbers predicts higher values for all the materials studied compared to those ones calculated by direct method and by as much as 20% for SrSO 4. A modified formula fitted to directly calculated effective atomic number data gives better agreement within a maximum deviation of ±3.94% for all the TLD materials studied. Overall the effective atomic number varies linearly with ED in the photon energy range of 1 keV to 20 MeV and thereby confirming the validity of a more commonly employed method of using the effective atomic number to calculate the measure of the ED in TL dosimetry. Significant differences exist between the effective atomic numbers for photon interaction and photon energy absorption in the energy region 20–150 keV for LiF, 2–300 keV region for CaCO 3, CaSO 4 and CaSO 4 · 2H 2O, 3–1000 keV region for CdSO 4, 20–600 keV for SrSO 4 and 1–1000 keV for BaSO 4. The effect of absorption edge on effective atomic numbers and ED, their variation with photon energy and the possibility of defining two set values of these parameters below the K-absorption edge of high- Z element present in the TLD material are discussed.

Effective Atomic Numbers and Mass Attenuation Coefficients of Some Thermoluminescent Dosimetric Compounds for Total Photon Interaction

Effective atomic numbers for total gamma-ray interaction with some selected thermoluminescent dosimetric compounds such as barium acetate, barium sulfate, calcium carbonate, calcium sulfate, calcium sulfate dihydrate, cadmium sulfate (anhydrous), cadmium sulfate, strontium sulfate, and lithium fluoride have been calculated in the 1-keV to 20-MeV energy region. Experimental mass attenuation coefficients and effective atomic numbers for these compounds at selected photon energies of 26.3, 33.2, 59.54, and 661.6 keV have been obtained from good geometry transmission measurements and compared with theoretical values. The effect of absorption edge on effective atomic numbers and its variation with energy, and nonvalidity of the Bragg’s mixture rule at incident photon energies closer to the absorption edges of constituent elements of compounds are discussed.

Intra-arterial 90Y brachytherapy: Preliminary dosimetric study using a specially modified angioplasty balloon

Purpose : Irradiation has been shown to be effective in preventing restenosis after dilatation in human peripheral arteries. We have developed a dedicated system for coronary intraarterial irradiation using a 90Y pure beta-emitting source inside a specially modified angioplasty balloon. This paper presents a preliminary dosimetric evaluation of this system. Methods and Materials : Specially fabricated titanium-covered and activated yttrium wires (outer diameter 0.32 mm) were used for these studies. Dosimetry was performed using small thermoluminescent dosimeters (TLDs) placed on the surface of the 2-cm long angioplasty balloons, inflated with contrast medium to a diameter of 2.5, 3, 3.5, and 4 mm. Radioactive 90Y wires were left in teh inner balloon catheter and the surface dose rate was measured and extrapolated to 72 h after activation to allow a comparison between the values obtained. After observing the poor centering of the source within the standard angioplasty balloon, a new centering balloon was developed. A conventional balloon was subdifived into four evenly spaced interconnecting chambers, thus assuring adequate centering of the inner catheter. Thermoluminescent dosimetric measurements were performed with a 3.5 mm centering balloon to evaluate the homogeneity of the surface doses compared to those measured with the conventional balloon. Results : Thermoluminescent dosimetric measurements using the standard balloons filled with contrast medium were plotted semilogarithmically as a function of distance from balloon surface. The logarithms ofthe measured doses fit a straight line as a function of depth. The doses at 1 mm and 3 mm are approximately 50 and 10% of teh surface dose, respectively. Due to the poor centering of the source in the conventional balloons, the dispersion and standard deviations (SDs) of the measured surface doses increased proportionally to the balloon diameter (SDs are 1.89, 5.52, 5.79 and 6.46 Gy for 2.5, 3, 3.5, and 4 mm balloon dimeters, respectively). Forthe 3.5 mm centering and conventional balloons the respective mean, minimum, and maximum surface doses were 8.41 Gy (min. 7.26; max. 9.46) and 7.89 Gy (min. 2.18; max. 16.06) and their standard deviations were 0.66 and 5.79 Gy, respectively. Conclusions : Conventional angioplasty balloons cannot ensure a homogneous dose delivery to an arterial wall with an intralumental 90Y beta source. Preliminary dosimetric results using a modified centering balloon show that it permits improved surface dose distribution (axial and circumferential homogeneity), making it suitable for clinical applications.

An automated thermoluminescence dosimeter reader

The use of all the commercially available thermoluminescent dosimetric readers is time consuming, because they are to be manually operated. Thus when thermoluminescence dosimeters are to be used on a larger scale, some form of automation is desirable. The two such designs proposed so far involve a significant amount of sophisticated electronic and machinery work, which makes the building of one very expensive. This report contains the description of a semi-automatic reader, developed to allow extensive use of thermoluminescence dosimeters in any physical form, for radiation dose measurements. The procedure outlined here is based primarily on a simple modification of one of the commercial readers. The modified version of this instrument has been in routine use for approximately 3 yr. During this time it has been proven to be very dependable and convenient for accurate dosimetric studies. The major advantage of this device is that it can be used in conjunction with any standard multichannel analyser. The analyser and the reader are readily coupled and decoupled, making it unnecessary to dedicate the analyser exclusively to this specific use. It can be employed with thermoluminescent phosphor in the powder and solid forms.