TLD Response Research Articles

753: MR-guided proton therapy: Influence of magnetic fields and air gaps on TLD response

753: MR-guided proton therapy: Influence of magnetic fields and air gaps on TLD response

A phantom-based experimental and Monte Carlo study of the suitability of in-vivo diodes and TLD for entrance in-vivo dosimetry in small-to-medium sized 6 MV photon fields

In-vivo dosimetry is recommended for radiotherapy treatment verification. The main purpose of the study is to investigate the suitability of various dosimeters for performing in-vivo measurements in small 6 MV photon fields by measurement as well as Monte Carlo simulation. Two types of diode dosimeters designed for placement on skin for the purpose of in-vivo dosimetry (EDD-5 and EDP-10), 3.1 × 3.1 × 0.89 mm3 LiF TLDs, and an electron field diode (EFD) were used for dosimetric measurements in a custom-made PMMA phantom. An Elekta accelerator’s treatment head was Monte Carlo modeled in detail, which was used together with validated Monte Carlo models of the diodes. Dose perturbation effects of the dosimeters and their suitability for in-vivo measurements were investigated. In fields ≥2 × 2 cm2, differences in the measured response of EDD-5, EDP-10 and TLD from the Monte Carlo gold-standard were <2%. For the 1 × 1 cm2 field, however, the differences from the Monte Carlo gold-standard were all greater than 2% due to the influence of dosimeter size as well as any misalignment and set-up uncertainties. In fields ≥1 × 1 cm2, EDD-5, EDP-10, and TLD produced 2.2%–3.2%, 5.3%–6.6% and 0.8–1.1% dose perturbation (≤10 cm depths), respectively. A better than 2% dosimetric accuracy was not achieved by these diodes for field sizes smaller than 2 × 2 cm2. Routine patient in-vivo dosimetry is feasible with the EDD-5 diode and TLD for field sizes down to 2 × 2 cm2 without exceeding the 5% tolerance level for overall uncertainty. But the EDP-10 diode produces a higher perturbation making it much less suitable for this purpose.

Thermoluminescence Responses of TLD–100 Subject to Low Dose Irradiation

The increasing use of radiation especially low radiation in everyday life demands an evaluation of the performance of dosimeter in the respective environment. The present work is concerned with the investigation of the thermoluminescence (TL) response of TLD-100 in a low radiation dose environment. Ten Harshaw TLD-100s were collected from Health Physics Division, Atomic Energy Centre, Dhaka, Bangladesh and irradiated at different low dose radiation such as 46.82μGy, 93.82μGy, 140.73μGy, 187.54μGy and 234.1μGy with 90Sr/90Y Irradiator and readout by Harshaw 4500 TLD Manual Reader. Following the reading, detection limit, linearity, variation of standard deviation, and coefficient of variation were investigated. After that, the same TLDs were irradiated at a dose of 140.46μGy and fading test was incorporated for 7 days. TLD-100 upon low dose irradiation showed a good linear response (Coefficient of Determination, R2 ̴1) as well as a lower detection limit (DL). The value of DL has been found 40μGy. Standard deviation and coefficient of variation form a decreasing pattern with increasing low radiation. For a very short time period like 7 days, TLDs showed an irregular response. These investigations help conclude that TLD-100 can be used for low dose environments with proper calibration and correction factor calculation. DUJASE Vol. 6 (2) 59-63, 2021 (July)

Thermoluminescence properties of nanocrystalline BaSO4 doped with Eu2+ produced by solid state combustion synthesis

Nanocrystalline powder samples of barium sulfate doped with Europium (BaSO4:Eu2+) were prepared, at a dopant concentration of 0.02 mol%, by the combustion solid-state technique in air atmospheres. Thermoluminescence (TL) response and dosimetric studies have been carried out for this phosphor in order to characterize it as a radiation dosimeter. The results showed that the TL glow curve of BaSO4:Eu2+present an intense TL peak at 200 °C accompanied by a small shoulder peak at 270 °C. The TL low detection limit for BaSO4:Eu (0.02 mol%) was found to be 17.8μGy for the gamma radiation emitted by 137Cs. The comparative study with the LiF:Mg, Ti (TLD-100) and calcium fluoride doped with thulium CaF2:Tm dosimeters showed that the TL response of the BaSO4:Eu(0.02 mol%) synthesized by the combustion solid-state technique is highly sensitive: it is 5.8 times higher than the response of the CaF2:Tm pellets and 9.4 times higher than the response of TLD-100. The high sensitivity of BaSO4:Eu and its linear dose response indicate that it can be used as sensor for gamma ionizing radiations.

Thermo-luminescence Response of Carbon Nanotubes and Some Other Familiar TL Materials Using Medical LINAC

Strain and impurity defects in carbon nanotubes (CNTs) particularly their potentiality as a new TL material has been studied over the years. In this research, our main objective is to explore the suitability of using CNTs and its composites in the area of TL dosimeter. For this purpose, a study was carried out between the TL responses of the dosimeters TLD-100, TLD-7000 and NaI-LiF pellets. To carry out this research, equivalent irradiations were performed with these pellets using clinical linear accelerator (LINAC) under 6 MV X-ray photon beam. The dose range was from 0.5 to 5 Gy. During irradiation, the dose rate was kept constant at 300 MU/min. TLD reader was used to readout the samples in a flowing N2 atmosphere to reduce surface oxidation.During readout, pre-heat temperature was set initially at 50 °C, acquired temperature rate 10 °C/s and maximum annealed temperature was 300 °C. Response of TLD-100 under varying dose was typically linear for any doses but other dosimeters TLD-7000 showed supra-linearity beyond 2 Gy and NaI-LiF pellets showed sub-linearity response after 2 Gy. The TL glow peak of CNTs indicated that it was lying somewhere away from 300 °C.

Design, fabrication and modeling of an AmBe neutron irradiator for TLD screening for neutron dose measurement in mixed radiation fields

TLDs dosimeters are frequently presented as a viable choice for dosimetric studies when dealing with mixed neutron-gamma radiation fields. However, this choice is not without some drawbacks, because not only TLD response is highly dependent on particle type but also on neutron energy spectrum. Therefore, a correct screening and calibration of the dosimeter are required, and a simple shift from gamma screening methodology for mixed field is not suitable. This paper presents the design, fabrication and tests of an irradiator for TLD screening for neutron dose measurement using an AmBe source and polyethylene as moderator material. The design of the irradiator was conducted through Monte Carlo simulations using the MCNP5 code. The experimental validation and tests were performed using Indium activation foils and TLD 600 dosimeters. The manufactured irradiator demonstrated to be suitable for TLD screening under neutron source radiation field, offering very good homogeneity conditions in the radiation field so to guarantee same radiation dose delivered to the TLDs.

Evaluation and clinical implementation of in vivo dosimetry for kV radiotherapy using radiochromic film and micro-silica bead thermoluminescent detectors

PurposekV radiotherapy treatment calculations are based on flat, homogenous, full-scatter reference conditions. However, clinical treatments often include surface irregularities and inhomogeneities, causing uncertainty. Therefore, confirmation of actual delivered doses in vivo is valuable. The current study evaluates, and implements, radiochromic film and micro silica bead TLD for in vivo kV dosimetry. MethodsThe kV energy and dose response of EBT3 film and silica bead TLD was established and uncertainty budgets determined. In vivo dosimetry measurements were made for a consecutive series of 30 patients using the two dosimetry systems. ResultsEnergy dependent calibration factors were required for both dosimetry systems. The standard uncertainty estimate for in vivo measurement with film was 1.7% and for beads was 1.5%. The mean measured dose was −2.1% for film and −2.6% for beads compared to prescription. Deviations up to −9% were found in cases of large surface irregularity, or with underlying air cavities or bone. Dose shielding by beads could be clinically relevant at low kV energies and superficial depths. ConclusionsBoth film and beads may be used to provide in vivo verification of delivered doses in kV radiotherapy, particularly for complex situations that are not well represented by standard reference condition calculations.

Comparison of MCP-Ns and MCP-N detectors usefulness for beta rays detection

In this study thin LiF:Mg,Cu,P dosimeters (trade name MCP-Ns) designed for measurements in beta radiation fields were tested in comparison with classical LiF:Mg,Cu,P ones (trade name MCP-N). The readout stability as well as TLD response in low (∼kBq) and high (∼MBq) radioactivity fields (beta and beta-gamma) were verified. The stability of MCP-Ns decreased during first 10 complete measuring cycles and then detectors appeared to be stable. Unfortunately, around 60th cycle the stability was lost. In the MCP-N group the stabilization was observed from 20th cycle but it was maintained in further measuring cycles. The MCP-Ns response in low radioactivity fields (∼kBq) was difficult to verify (dose values oscillated around the “zero dose reading”), reliable results were observed for high radioactivity fields (∼MBq). The dose measured by MCP-Ns was ten times higher in beta fields and around five times higher in mixed beta-gamma fields in comparison to the MCP-N. MCP-Ns seems to be adequate and more sensitive to measure beta dose or mixed beta-gamma dose, however the uncertainty of a single measurement has to be under more careful control compared to MCP-N which have higher repeatability and stability.

Poster ‐ 24: Characterization of the energy dependence of high‐sensitivity MCP‐N TLD and Al2O3:C OSLD in‐vivo dosimetry systems for 40–100 kVp energies

Purpose:To characterize the energy dependence of high‐sensitivity MCP‐N TLD and Al2O3:C OSLD dosimetry systems at low (40–100 kVp) energies for in‐vivo dosimetry.Methods:We assessed the variation of response with energy of two detectors in the 40–100 kVp energy range: high‐sensitivity MCP‐N TLDs (LiF:Mg,Cu,P) and OSLDs (Al2O3:C).The detectors were irradiated with an XRad 320ix biological irradiator under reference conditions. The delivered dose was 10 cGy for 7 beam qualities ranging from 40–100 kVp, 1.7–4.0 mm Al, and effective energies 26.9–37.9 keV.Both sets of detectors were also irradiated under reference conditions at 6 MV using a Varian Clinac 21Ex to assess the change in response from high‐energy beams.Results:The MCP‐N high‐sensitivity TLDs were relatively insensitive to energies in the kV range, as their response varied by ±5%, i.e. well within the reproducibility limits of these detectors. However, the OSLDs exhibited a linearly‐decreasing response with energy with a response 18.7% higher at 40 kVp than at 100 kVp for the same nominal dose.Compared to the 6 MV beams used in conventional radiotherapy, OSLDs responded 3.3–3.9 times higher depending on beam quality while the MCP‐N TLD response was unchanged within experimental uncertainty.Conclusions:Unlike the more commonly used TLD‐100, the high‐sensitivity MCP‐N TLDs exhibit little to no energy response. OSLDs are shown to be highly energy‐dependent, both from MV to kV and within the kV range.

SU-G-201-08: Energy Response of Thermoluminescent Microcube Dosimeters in Water for Kilovoltage X-Ray Beams

Purpose: To characterize the energy dependence for TLD-100 microcubes in water at kilovoltage energies. Methods: TLD-100 microcubes with dimensions of (1 × 1 × 1) mm3 were irradiated with kilovoltage x-rays in a custom-built thin-window liquid water phantom. The TLD-100 microcubes were held in Virtual Water™ probes and aligned at a 2 cm depth in water. Irradiations were performed using the M-series x-ray beams of energies ranging from 50-250 kVp and normalized to a 60Co beam located at the UWADCL. Simulations using the EGSnrc Monte Carlo Code System were performed to model the x-ray beams, the 60Co beam, the water phantom and the dosimeters in the phantom. The egs_chamber user code was used to tally the dose to the TLDs and the dose to water. The measurements and calculations were used to determine the intrinsic energy dependence, absorbed-dose energy dependence, and absorbed-dose sensitivity. These values were compared to TLD-100 chips with dimensions of (3.2 × 0.9 × 0.9) mm3. Results: The measured TLD-100 microcube response per dose to water among all investigated x-ray energies had a maximum percent difference of 61% relative to 60Co. The simulated ratio of dose to water to the dose to TLD had a maximum percent difference of 29% relative to 60Co. The ratio of dose to TLD to the TLD output had a maximum percent difference of 13% relative to 60Co. The maximum percent difference for the absorbed-dose sensitivity was 15% more than the used value of 1.41. Conclusion: These results confirm that differences in beam quality have a significant effect on TLD response when irradiated in water. These results also indicated a difference in TLD-100 response between microcube and chip geometries. The intrinsic energy dependence and the absorbed-dose energy dependence deviated up to 10% between TLD-100 microcubes and chips.

Comparison of Hp(0.07, 0°) for 90Sr/90Y Beta Radiation with CaF2:Dy TLD-200 Dosimeters.

The results for the comparison of Hp(0.07,0°) in 90Sr/90Y, carried out by the SSDL-ININ (pilot) and CPHR, are presented. Four calibration curves (CCs) are constructed with 32 TLD-200 dosimeters irradiated on a PMMA phantom. The CCs, TLD's Response RTLD (nC) vs Hp(0.07,0°), are in the range0.2-100 mSv. The SSDL-ININrate Hp(0.07, 0°) value is (43.85±0.57) µSv s-1 obtained with a primary extrapolation chamber serial 040. These same dosimeters are irradiated at the CPHR with a rate of Hp(0.07, 0°)=(14.94±0.36) µSv s-1, also calibrated with another primary standard extrapolation chamber serial 105. After irradiation at CPHR, the dosimeters are returnedto the SSDL-ININ for reading, and then irradiated again to construct the fourth CC (CC4). The comparison is based on a modification of the standard ANSI/HPS N13.11-2009, where the reference values are [Hp]ININ,ref. For the values of [Hp]CPHR the statistics bias B=0.002; standard deviation, S=0.099; and tolerance level L=0.099 are determined. The homoscedasticity test is performed for the variances associated to the mean performance quotientB.

Experimental determination of the photon-energy dependent dose-to-water response of TLD600 and TLD700 (LiF:Mg,Ti) thermoluminescence detectors

The aim of this study has been the experimental determination of the energy dependent dose-to-water response of TLD600 and TLD700 thermoluminescent detectors (Harshaw) in X-ray beams with mean photon energies from about 20 to 200keV in comparison with 60Co gamma rays and 6MV X-rays. Experiments were carried out in collaboration with the German secondary standard laboratory PTW Freiburg. The energy dependent relative responses of TLD600 and TLD700 thermoluminescence detectors were determined at radiation qualities between 30kVp and 280kVp. The overall uncertainty of the measured values was characterized by standard deviations varying from 1.2 to 3%. The present results agree with previous studies on the energy dependent dose-to-water response of TLD100. As an application example, the results were used to measure doses associated with X-ray imaging in image-guided radiotherapy.

Response of TLD and RPL personal dosimeters in a national inter-comparison test program

Background : Different kinds and models of personal dosimeters are used in individual monitoring by workers. Performance tesng as part of approval procedures is carried out to demonstrate that the essenal performance specificaons are rounely maintained. There are fou r service providers in Iran which use different luminescence techniques (i. e. TLD and RPL) with various kinds of dosimeter materials/reader instruments in personal dosimetry services. Materials and Methods : A naonal performance approval tests program was performed for the dosimeters of the service providers in energy range of so', 660 keV and 1.25 MeV, at the d oses values around the recoding, invesgaon and annual dose limits, and d ifferent angle of incidents (e. g. 0, 20, 40 and 60 degree). Results: The results of this tesng sasfies the overall accuracy criteria with 95% confidence levels specified by the ICRP, except that of RPL technique in low energy which overesmates the dose out of the acceptable accuracy band defined as the ICRP trumpet curves. Conclusion: The inter-comparison has proved that the personal dose equivalent quanty, H p(10), defined by the ICRU and recommended by the IAEA are becoming widely accepted and implemented in most parcipated laboratories.

Thermoluminescent dosimeters for low dose X-ray measurements

The response of TLD-100, CaSO4:Dy and LiF:Mg,Cu,P for a range of X-ray low dose was measured. For calibration, the TLDs were arranged at the center of the X-ray field. The dose output of the X-ray machine was determined using an ACCU-Gold. All dosimeters were exposed at the available air kerma values of 14.69mGy within a field 10×10cm2 at 80cm of SSD. Results of LiF:Mg,Cu,P X-ray irradiated showed 4.8 times higher sensitivity than TLD-100. Meanwhile, TL response of CaSO4:Dy exposed at the same dose was 5.6 time higher than TLD-100. Experimental results show for low dose X-ray measurements a better linearity for LiF:Mg,Cu,P compared with that of TLD-100. CaSO4:Dy showed a linearity from 0.1 to 60mGy

Thermoluminescence response of multimode fluorine-doped SiO2 optical fibers and TLD 100 with 6 mega volt photon irradiation

This study investigates and compares the results of thermoluminescence responses, its linearity, sensitivity with various dose ranges and TL glow curve of Fluorine-doped silica fiber and TLD-100 materials. The TL responses of the Fl-doped silica fibers and TLD 100 were kept in gelatin capsule and irradiated with 6-MV photon at the dose range from 0.5 Gy to 4.0 Gy. Siemens model Primus 3368 linear accelerator located at Hospital Sultan Ismail; Johor Bahru has been used to deliver the photon beam to the samples. The TL-signal of TLD 100 media exhibits a significant linear dose to signal relationship with an increase in doses. The sensitivity of Fl-doped optical fiber is negligible to TLD 100 media.

EP-1375: Non linear response of TLD-100 irradiated by an Intra Operative Radiation Therapy accelerator

EP-1375: Non linear response of TLD-100 irradiated by an Intra Operative Radiation Therapy accelerator

Characterization of the Risø TL/OSL DA-20 reader for application in TL dosimetry

The automated Risø TL/OSL Reader Model DA-20, often used in dating and retrospective dosimetry, was examined for possible applications in thermoluminescent dosimetry related to radiation protection. The investigations revealed that performance of the DA-20 is comparable with that of the Harshaw 3500 manual reader, which was used as a reference instrument. All studied parameters, like stability, reproducibility, low-dose measuring capabilities, were at the same level or only somewhat inferior to those of Harshaw 3500. In particular, using the highly-sensitive LiF:Mg,Cu,P dosimeters, it is possible to measure doses at the microgray level.The DA-20 reader possesses built-in alpha and beta sources, which cause an increased radiation background. At positions just under the closed sources the dose-rate rises to about 50 μGy/h. When the 90Sr/90Y source is open a quite high dose-rate of 100 mGy/h was measured at the position adjacent to the one being irradiated. Additionally the TLD response to the background radiation significantly depends on the TLD type (atomic number), as the radiation leaking through shielding is composed of low-energy photons. The dose-rate under the closed 241Am source was over 10 times higher, when measured with CaF2 dosimeters, than with LiF.In spite of these problems, the DA-20 reader due to its good stability, reproducibility and sensitivity, combined with such obvious benefits as a 48-dosimeter carousel, temperatures up to 700 °C and full automatics of measurements control, encourages the opinion that the DA-20 Risø reader can be successfully used in practical dosimetric measurements.

Application of whole-body personal TL dosemeters in mixed field beta-gamma radiation.

Application of whole-body personal TL dosemeters based on a high-sensitivity LiF:Mg,Cu,P (MCP-N) in mixed field beta-gamma radiation has been characterised. The measurements were carried out with (90)Sr/(90)Y, (85)Kr and (137)Cs point sources to calculate the energy response and linearity of the TLD response in a dose range of 0.1-30 mSv. From the result, calibration curves were obtained, enabling the readout of individual dose equivalent Hp(10) from gamma radiation and Hp(0.07) from beta radiation in mixed field beta-gamma. Limitation of the methodology and its application are presented and discussed.

An investigation into the accuracy of Acuros(TM) BV in heterogeneous phantoms for a (192)Ir HDR source using LiF TLDs.

The aim of this study was to evaluate the accuracy of the new Acuros(TM) BV algorithm using well characterized LiF:Mg,Ti TLD 100 in heterogeneous phantoms. TLDs were calibrated using an (192)Ir source and the AAPM TG-43 calculated dose. The Tölli and Johansson Large Cavity principle and Modified Bragg Gray principle methods confirm the dose calculated by TG-43 at a distance of 5cm from the source to within 4%. These calibrated TLDs were used to measure the dose in heterogeneous phantoms containing air, stainless steel, bone and titanium. The TLD results were compared with the AAPM TG-43 calculated dose and the Acuros calculated dose. Previous studies by other authors have shown a change in TLD response with depth when irradiated with an (192)Ir source. This TLD depth dependence was assessed by performing measurements at different depths in a water phantom with an (192)Ir source. The variation in the TLD response with depth in a water phantom was not found to be statistically significant for the distances investigated. The TLDs agreed with Acuros(TM) BV within 1.4% in the air phantom, 3.2% in the stainless steel phantom, 3% in the bone phantom and 5.1% in the titanium phantom. The TLDs showed a larger discrepancy when compared to TG-43 with a maximum deviation of 9.3% in the air phantom, -11.1% in the stainless steel phantom, -14.6% in the bone phantom and -24.6% in the titanium phantom. The results have shown that Acuros accounts for the heterogeneities investigated with a maximum deviation of -5.1%. The uncertainty associated with the TLDs calibrated in the PMMA phantom is±8.2 % (2SD).

TU‐C‐108‐01: Verification of Deformable Dose Calculation with Phantom Measurements

Purpose: Dose accumulation involves many computational procedures which may introduce error. The purpose of this study is to utilize a novel deformable dosimetry phantom to experimentally verify the total dose accumulated by 4D dose calculation algorithms. Methods: Lung phantom consisting of heterogeneous sponge material and tissue‐equivalent tumor. The sponge is enclosed in a latex cylinder, compressed by a piston to simulate the diaphragm motion. TLD‐100 thermoluminescent dosimeters were placed in the sponge and inside the tumor for 4D‐dosimetry verification. Three TLDs were used at each point for better statistics. A four phase 4DCT was taken for planning purposes. A 5‐beam 6MV 3D conformal plan was developed with 95% of the ITV receiving the prescribed dose of 200 cGy, which may help to maintain a linear TLD response. The plan was delivered under the same deformation pattern with the BrainLab Novalis system, and exported to Eclipse and Pinnacle for comparison. CT phase images were registered to end‐exhale (EE) phase, when sponge is maximally compressed, using a B‐Spline‐based algorithm. The resultant displacement vector field was output for dose mapping. Dose was warped to EE phase using an in‐house developed, subvoxel projection method and accumulated for comparison with the TLD measurements. Results: The tumor dose agreed very closely to the accumulated dose and was measured to be 0.5% lower with the TLDs. Another point of measurement was ∼2 cm from the tumor, near the edge of the field, and was measured 5.4% higher with the dosimeter. A point of high field gradient ∼5 mm from the tumor was measured 12.5% higher than calculated. Larger uncertainties in the TPS are expected in this gradient region. Dose warping improved the tumor dose calculation by 29.4%. Conclusion: The deformable phantom could be a valuable tool to verify the total dose calculated by adaptive treatment plans. The research was supported by NIH/NCI R01CA140341.