LiF TLD-100 Research Articles

Dosimetric characteristics of the InterSource103 palladium brachytherapy source.

103Pd brachytherapy sources are being used for interstitial implants in tumor sites such as the prostate. Recently, the InterSource103 palladium source has been introduced, which has a design different from that of other sources presently on the market. Dosimetric characteristics (i.e., dose rate constant, radial dose function, and anisotropy function) of this source were experimentally and theoretically determined following the AAPM Task Group 43 (TG-43) recommendations and were related to the 1999 NIST calibration assigned to this source [Sk, 99std]. Measurements were performed in a solid water phantom using LiF thermoluminescent dosimeters. The measured data was compared with Monte Carlo simulations performed in solid water using the PTRAN code. The calculations were then performed in liquid water to obtain the dosimetric information for clinical applications as per TG-43 recommendation. The results indicated that the dose rate constant, lambda, of the InterSource103 palladium source was 0.664+/-5% cGy/h/U using TLD measurements and 0.660+/-3% cGy/h/U using Monte Carlo simulations in solid water. The calculated value in liquid water was found to be 0.696 +/- 3 % cGy/h/U. The radial dose function, g(r), of the new 103Pd source was measured at distances ranging from 0.5 to 10 cm using LiF TLD in solid water phantom material. The Monte Carlo simulations were performed at distances ranging from 0.1 to 10 cm from the source center in solid water and liquid water. The anisotropy function, F(r, theta), was measured at distances of 2, 3, 5, and 7 cm from the source center and calculated at distances of 0.5, 1, 2, 3, 5, and 7 cm from the source center. Complete dosimetric data are described in this paper. Per TG-43, the values reported in water should be used for clinical treatment planning systems.

In‐phantom response of LiF TLD‐100 for dosimetry of HDR source

An experiment was carried out to reevaluate the response of LiF TLD-100 rods (1 mmx1 mmx6 mm) at different depths in a water substituting phantom to provide an answer to a prevailing controversy about the over-response of LiF to the softened photon spectra of 192Ir HDR source at depths in phantom due to its photon energy dependence. Claims of some authors that LiF TLDs over-responds by 8.5% at 10 cm depth in phantom, necessitating depth-dependent correction factors even for an 192Ir source and of some others for no over-response were evaluated. The over-response of LiF TLD-100 rods, against a calibrated ion chamber having a photon energy-independent response within 2%, was found to be not exceeding 2.5% at a depth of 10 cm in the phantom as compared to a depth at 1 cm, for a precision of the order of +/- 1% (1sigma) in the TLD measurements. By using ISO equivalent photon beams, photon energy dependence of the dosimeters was evaluated and for LiF TLD-100 rods it was found to be in close agreement (within 3%) with the ratios of mass energy absorption coefficients of LiF and water in the range of effective photon energy from 26 keV to 1.25 MeV. Parameters that could contribute to the discrepancy in the reported values of experimental results have been discussed.

Effects of Pre- and Post-Irradiation Temperature Treatments on TL Characteristics and Radiation Induced Sensitisation of Various TL Peaks in LiF-TLD 100

Pre-irradiation annealing treatment at 150(C reduces the sensitivies of peak 4 (197(C) and peak 5 (209(C) whereas the intensity of peak 2 (108(C) is enhanced; the TL intensities of peak 7 (271(C) and peak 10 (441(C) remain practically unaffected. Another TL peak, peak 6 appears at about 230(C with this thermal treatment. For a 150(C, 6 h treatment, the intensity of peak 2 increases by a factor or 1.82 whereas peaks 4 and 5 are reduced by factors of about 26 and 36 respectively. Similar to TL peaks 5 and 7, TL peaks 2, 3 and 6 also show radiation induced sensitisation. For 103 Gy dosed and 340(C, 30 min post-annealing followed by 150(C, 6 h treatment, the sensitisation factors for TL peaks 2, 3 and 6 were found to be 5.02, 2.95 and 7.34 respectively. UV induced PTTL was observed in all the TL peaks except in peak 4 in all the samples which were post-annealed by different thermal treatments. PTTL results indicate that peak 10 is responsible for the PTTL response in all the TL peaks in LiF TLD-100. Similar to the TL peaks 7 and 10 the intensity of peak 6 is also reduced by a factor of about 2 for irradiations at 77 K as compared to its corresponding intensity for room temperature irradiation.

Thermoluminescence Properties of Novel Thin Clear Fused Quartz Dosemeters

The thermoluminescence properties of novel thin (100 μm) dosemeters of clear fused quartz (CFQ) have been investigated as part of a progranime to optimise the measurement of the spatial beta dose distribution around hot particles and to provide benchmark measurements for the parallel validation of Monte Carlo code calculations. Using the isothermal annealing method seven TL peaks (P1-P7) have been identified for CFQ in the temperature range 122-310°C. The isothermal method has been used to determine the energy depth E and frequency factor s for peaks P2, P3 and P4. The heating rates method has been used to determine the values of E and s for peaks P1 and P6. The results have been compared with'those of computerised glow curve deconvolution. There were large disparities between the results of different methods. These are probably due to artefacts in the methods related to the large number of overlapping peaks. The reproducibility of individual CFQ on the basis of TL integration up to 400°C is good (±5%). On the other hand, the individual sensitivity is different among all the dosemeters (40) from the same batch and the difference in the TL signals sometimes reaches a factor of 5. An analysis of the TL dose response in terms of low and high temperature regions (PL, 50-150°C; P H , 250-350°C) showed a linear response up to ∼60 Gy for PL and a slightly sub-linear response up to only -2 Gy for PH. The sensitivity of CFQ has been found to be -15% of that of LiF TLD 100 and the minimum detectable dose (2σ above background) is ∼580 μGy. The TL response of CFQ was found to be sensitive to natural light exposure. The TL yield was reduced to typically 20% of is original value after only 10 h exposure to natural light at room temperature. After this period of time both peak P1 and peak P2 have been completely removed. Samples kept shielded from light suffered only a 12% decrease of total TL intensity after 48 h at room temperature, A feasibility study has been carried out successfully using CFQ to measure directly the dose distribution around a test 60 Co hot particle source using an imaging photon detector (IPD) technique. CFQ/IPD measurements have a much greater sensitivity than extrapolation chamber and radiochromic dye film techniques, which have previously been used for this application.

TLD dose measurement: a simplified accurate technique for the dose range from 0.5 cGy to 1000 cGy.

A simplified TLD technique characterized by high precision and reproducibility of dose measurement is presented. One hundred eighty LiF TLD rods 1 mm diam x 3 mm length as obtained from the manufacturer were annealed for 1 h at 400 degrees C followed immediately by 2 h at 105 degrees C. After exposure to a dose of 1 Gy of 4 MV x rays, TLDs were annealed for 15 min at 105 degrees C, then read out. TLDs were then sorted into five groups, ranging from 26 to 50 rods each with approximately equal sensitivity after correcting for the drift in the sensitivity of the TLD reader during the readout session. Maintaining group identity, the TLDs were again annealed, irradiated and read out. Fewer than 10% of the TLDs were removed from each group because the corrected readings differed from the respective group mean by more than 3.5%. The standard deviation of the readout was approximately 1.5% within each group. The planchet heater was not flushed with nitrogen gas. Various tests were performed to assess the stability of the group sorting technique and the linearity of TLD dose response. After reannealing, five TLDs were randomly drawn from one of the presorted groups, and subjected to various dose of 4 MV radiation over the range from 0.5 to 1000 cGy. This resulted in an average readout standard deviation of 1.2%. Response per unit dose was almost flat over the range from 0.5 cGy to 100 cGy, and increased by 15% over the range from 100 cGy to 1000 cGy. TLD sensitivity was affected by the duration of the anneal, but was virtually independent of the various time delays between irradiation, prereadout anneal, and readout. The group annealing and sorting (GAS) procedure provides a simple, reliable, precise, convenient, and accurate method for TLD measurements.

Indoor Radiation Measurements in Greece

A home-made, low cost, high speed, etched track detector measuring system, equipped with automatic track counting and classification procedures, was developed to measure and analyse quickly and accurately CR-39 etched track detectors used in indoor radon concentration surveys. The system provides increased detector throughput along with high measuring accuracy and it can therefore serve as a platform for the large scale measurements of the Greek National Radon Survey that will take place in the near future. In this context, pilot measurements of indoor radiation were performed in selected Greek regions. Indoor radon concentrations were found in the range of 4 to 583 Bq.m -3 with the highest levels observed near the water springs of Ikaria island. The indoor absorbed dose rate in air due to external irradiation from terrestrial sources was measured simultaneously, using thermoluminescence dosemeters (LiF TLD-100), and was found to be in the range of 19 to 107 nGy.h - with an arithmetic mean value equal to 49 ± 22 (1σ) nGy.h -1 . in good agreement with our previous study.

Reduction of the gamma-ray component from fission neutron source - optimization for biological irradiations and comparison with MCNP code

Gamma-rays contribute 33% of the absorbed dose from an unfiltered fission neutron source. To reduce this gamma-ray component and to enable radiobiological experiments at as high a dose rate as possible, Monte Carlo calculations for several filter materials (Al, Fe, Pb and concrete) have been made using MCNP neutron and photon transport code version 4a. A lead filter of thickness 4 cm was found to reduce the gamma-ray component to 6.7% of the total dose whilst reducing the neutron dose by only about 10%. Such a filter was installed at the MRC neutron irradiation facility and dosimetric measurements were made using a TE-TE chamber and a LiF(Mg, Cu, P) TLD. Monte Carlo simulations agree with experimental measurements of neutron and gamma-ray doses within 6%. V79-4 Chinese hamster cells were irradiated with lead-filtered and unfiltered neutrons and also with gamma-rays at two dose rates. The survival fraction obtained for each radiation was consistent with the reduced gamma-ray dose. The relative biological effectiveness for neutrons alone, corrected for gamma-ray effects, was found to be from the initial slopes and at 10% survival, both relative to the acute gamma-rays.

Calibration of strontium-90 eye applicator using a strontium external beam standard

Four techniques for measuring the dose rate from Sr-90 concave eye plaques are presented. The techniques involve calibrating a concave eye plaque against a Sr-90 teletherapy unit using X-Omat film, radiochromic film, black LiF TLD discs and LiF chips. The mean dose rate predicted by these dosimeters is 7.5 cGy s-1. The dose rate quoted by the manufacturer is 33% lower than this value, which is consistent with discrepancies reported by other authors. Calibration against a 6 MV linear accelerator was also carried out using each of the above dosimetric devices, and appropriate sensitivity correction factors have been presented.

Monte Carlo and TLD dosimetry of an 192Ir high dose-rate brachytherapy source.

An analytical Monte Carlo simulation code has been used to perform dosimetry calculations around an 192Ir high dose-rate brachytherapy source utilized in the widely used microSelectron afterloaded system. Radial dose functions, dose rate constant and anisotropy functions, utilized in the AAPM Task Group 43 dose estimation formalism, have been calculated. In addition, measurements of anisotropy functions using LiF TLD-100 rods have been performed in a polystyrene phantom to support our Monte Carlo calculations. The energy dependence of LiF TLD response was investigated over the whole range of measurement distances and angles. TLD measurements and Monte Carlo calculations are in agreement to each other and agree with published data. The influence of phantom dimensions on calculations was also investigated. Radial dose functions were found to depend significantly on phantom dimensions at radial distances near phantom edges. Deviations of up to 25% are observed at these distances due to the lack of full scattering conditions, indicating that body dimensions should be taken into account in treatment planning when the absorbed dose is calculated near body edges. On the other hand, anisotropy functions do not demonstrate a strong dependence on phantom dimensions. However, these functions depend on radial distance at angles close to the longitudinal axis of the source, where deviations of up to 20% are observed.

Methodology of Retrospective Investigation on External Dose of the Downwind Area in Jiuquan Region, China

In order to know the cumulative effective dose from the Chinese nuclear tests (CNT) to the population living in the downwind area of the CNT site, and any possible health effects attributable to the tests, an investigation was carried out in the Jiuquan Region, the closest area downwind of the site, during 1987-1992. Both laboratory gamma ray spectrometry and in situ gamma ray spectrometry techniques were employed for the determination of the total inventory of 137Cs in the soil at 59 investigation sites. The net cumulative 137Cs deposition from the CNT is estimated for each site after subtracting the contributions of the atmospheric fallout and others. The radionuclides dating technique was used for estimating the time sequences of 137Cs deposition in a local lake. The measurement of absorbed dose rate in the air was performed with portable dosemeters and checked with environmental LiF TLD dosemeters. The external dose from the CNT is estimated based on the determinations of net 137Cs inventory in the soil of the region.

Thermoluminescence analysis of - and -irradiated chemical vapour deposited diamond films

The thermoluminescent (TL) response of a set of synthetic diamond films obtained by chemical vapour deposition was investigated using gamma and beta radioactive sources over the dose range from 60 mGy to 3.5 Gy. A TL response linear with dose was generally observed. A numerical curve-fitting procedure was applied to deconvolute the complex-structured TL glow curves, which were found to be composed at most by five peaks in the temperature range between C to C. A short preheat treatment after irradiation allowed us to obtain a very stable smooth-shaped glow curve composed of a unique peak close to C. This isolated structure followed first-order kinetics over the whole dose range. The activation energy of the main peak, eV, was determined considering all samples and all irradiation doses using both the peak shape method and the fitting procedure. The corresponding frequency factor was estimated to be within the range -. The TL sensitivity of the diamond films calculated considering the isolated high-temperature peak compares favourably with that measured with a set of LiF TLD100 and TLD700 standard dosimeters.

A study of LiF GR-200 for radiotherapy mailed dosimetry

A study of the measurement performance of LiF GR-200 for radiotherapy mailed dosimetry is presented. The study was carried out in the practical working conditions of a mailed system where a lengthy delay between dosimeter preparation and the final readout can occur. Prompt and delayed TL measurements were employed to determine, among other characteristics, the reusability and the stability during storage at room temperature. From the results obtained it can be concluded that GR-200, although producing dose results adequate for mailed dosimetry, does not improve the performance attainable with LiF TLD-100.

The response of a MOSFET, p-type semiconductor and LiF TLD to quasi-monoenergetic x-rays

A metal oxide semiconductor field effect transistor (MOSFET), p-type semiconductor and a TLD can all be used for x-ray dosimetry, with each system having the common disadvantage of a response which is dependent upon the incident photon energy, particularly for energies . A Pantak HF-320 quasi-monoenergetic x-ray unit was used to determine the response of two Thomson and Nielson TN-502RD MOSFETs, a Scanditronix EDP-10 semiconductor (build-up cap 10 mm: tissue equivalence), an EDD-5 semiconductor (build-up cap 4.5 mm: tissue equivalence) and an LiF:Mg:Ti TLD over the energy range 12 - 208 keV. The sensitivity of each detector was normalized to the value produced by exposure to 6 MV x-rays. The maximum relative sensitivities of the two MOSFET detectors were and respectively, occurring at an incident x-ray energy of 33 keV. The maximum relative sensitivity of the Scanditronix EDP-10 of occurred at 65 keV, and for the EDD-5, it was at 48 keV. The TLD produced a maximum relative sensitivity of at 33 keV. Compared with available data based on heteroenergetic x-ray sources, these measurements have identified a more representative response for each detector to low-energy x-rays.

Influence of repeated use and annealing atmosphere on LiF TLD-100 response to α-particles

We study the possible effects of both the annealing atmosphere and the repeated use of chips on the response of LiF thermoluminescent dosimeters (TLD-100) irradiated with 5 MeV α-particles. No statistically significant differences were found between glow curve shapes or total deconvoluted response of dosimeter chips annealed either in N 2 or in air and irradiated to about 4.5 Gy up to ten consecutive times. Annealing in O 2, and repeated use of the chips up to five times, showed similar results. We conclude that TLD-100 dosimeters used under α-particle irradiation can subjected to a simple air annealing between a series of consecutive irradiations and readouts.

A comparative study of the thermoluminescent response to beta irradiation of CVD diamond and LiF dosimeters

The thermoluminescent (TL) response of Chemical Vapour Deposited (CVD) diamond films to beta irradiation has been investigated. A numerical curve-fitting procedure, calibrated by means of a set of LiF TLD100 experimental spectra, has been developed to deconvolute the complex structured TL glow curves. The values of the activation energy and of the frequency factor related to each of the TL peaks involved have been determined. The TL response of the CVD diamond films to beta irradiation has been compared with the TL response of a set of LiF TLD100 and TLD700 dosimeters. The results have been discussed and compared in view of an assessment of the efficiency of CVD diamond films in future applications as in vivo dosimeters.

TL dosimetry using extracted and cleaned sand to measure gamma-ray dose rate at a liquid sewage sludge irradiation facility

In an earlier study, we investigated the thermoluminescence (TL) properties of the sand collected from sewage sludge, after various extensive cleaning procedures and irradiation of gamma rays under controlled conditions in the laboratory. In the present investigation, the sand separated from the irradiated sludge was used to estimate the radiation processing absorbed dose to sludge at the sludge hygienisation research irradiator (SHRI), Baroda. Although, the relative TL sensitivity of H 2O 2- and HF-treated sludge sand samples was 4.00% and 0.07%, respectively, of that of LiF TLD-100, a well known TL phosphor used in radiation dosimetry, they were quite useful for dosimetry of the liquid sludge irradiator, when using TL calibrations of sand from sludge collected from sludge irradiator inlet. A useful dose range for such calibration is 0.3–4 kGy. A dose-vs-TL response calibration curve was plotted for the 220°C TL glow peak for H 2O 2- and HF-treated sludge sand samples collected at the sludge irradiator inlet from an unirradiated batch, in order to estimate dose absorbed in the corresponding batch of the irradiated sludge collected at the sludge irradiator outlet. Using this method, the absorbed dose rate delivered to the sludge during irradiation at SHRI was estimated to be 0.70 ± 0.02 kGy per hour. The paper also reports results of a dosimetry intercomparison for H 2O 2- and HF-treated sand samples, and LiF TLD-100 TL phosphor. The estimated gamma ray doses were nearly the same for all the three systems irradiated for the same exposure times.

Responses of LiF TLD in Different Media and Cavity Ionization Theory for Low Energy Photons below 200 keV

Calculated photon responses of LiF TLDs based on Burlin's cavity theory were compared with those measured using the TLDs sandwiched between two Teflon, aluminum, copper and gold foils for 30 to 200keV X-rays. The discrepancies between the calculations and the measurements were within 48% for gold, while 15% for the other media. In the cavity theory, the weighting factors related to the electron attenuation are used. The factors differed largely from those calculated with a Monte Carlo transport code ITS, of which the validity was confirmed by comparison with the response measurements. The ITS calculations also showed that the attenuation coefficients of electrons from the foils did not necessarily agree with those from the cavity theory, and the coefficients largely depended on the media. To obtain the more accurate response easily, another method are proposed, noticing that the electrons incident on the LiF are absorbed completely below 200keV. In the new method, total dose in LiF is calculated using energy transmission and reflection coefficients for the dose given by the electrons from the foils and using the mass energy absorption coefficients for the dose by the electrons generated in LiF. Responses calculated with this method agreed with those of the ITS within a difference of 6%.

Responses of LiF TLD in Different Media and Cavity Ionization Theory for Low Energy Photons below 200keV.

Calculated photon responses of LiF TLDs based on Burlin's cavity theory were compared with those measured using the TLDs sandwiched between two Teflon, aluminum, copper and gold foils for 30 to 200keV X-rays. The discrepancies between the calculations and the measurements were within 48% for gold, while 15% for the other media. In the cavity theory, the weighting factors related to the electron attenuation are used. The factors differed largely from those calculated with a Monte Carlo transport code ITS, of which the validity was confirmed by comparison with the response measurements. The ITS calculations also showed that the attenuation coefficients of electrons from the foils did not necessarily agree with those from the cavity theory, and the coefficients largely depended on the media. To obtain the more accurate response easily, another method are proposed, noticing that the electrons incident on the LiF are absorbed completely below 200keV. In the new method, total dose in LiF is calculated using ene...

A Simple UV Irradiator for Low Dose Reassessment with LiF TLD-100

A simple and efficient UV irradiator specifically designed for dose reassessment by phototransferred thermoluminescence is described. The instrument permits the automatic irradiation of loose TLD chips for a preselected time and at a controlled temperature. The good phototransference characteristics allow the efficient reassessment of absorbed doses of the order of 0.2 mGy with good measurement performance, well within the limits required for personnel dosimetry.

Preliminary Assessment of LiF and Alanine Detectors for the Dosimetry of Proton Therapy Beams

An experimental intercomparison between the proton response of LiF TLD-100 and alanine detectors is reported. The investigations were performed with LiF chips and alanine pellets in a 62 MeV proton beam at the Paul Scherrer Institut in Villigen (CH). Results were compared with reference dosimetry provided by a Markus type parallel plate ionisation chamber. The response of the detectors was studied, in a phantom, at different beam penetration depths in pristine and modulated beams. For both alanine and TL detectors, within the experimental uncertainty of the measurements, no significant energy dependence in the response was observed down to the Bragg peak region. The sensitivity of alanine and LiF detectors to protons was measured in the centre of a modulated Bragg peak and no significant difference was found with respect to 60 Co. Contrary to LiF, alanine also offers a remarkable tissue equivalence which favours its choice for in-phantom dosimetry.