Advantages and disadvantages of luminescence dosimetry

Visible proton Bragg curve imaging by colour centre photoluminescence in radiation detectors based on lithium fluoride films on silica

Passive solid-state radiation detectors, based on the visible photoluminescence (PL) of radiation-induced colour centres in optically transparent lithium fluoride (LiF), polycrystalline thin films are under investigation for proton beam advanced diagnostics. After proton exposure, the latent images stored in LiF as local formations of stable F2and F3+aggregate defects, are directly read with a fluorescence microscope under illumination in the blue spectral range. Adopting a suitable irradiation geometry, the energy density that protons deposit in the material can be recorded as a spatial distribution of these light-emitting defects, from which a luminous replica of the proton Bragg curve can be thereafter extracted and analysed to reconstruct the proton beam energy spectrum. Their peculiar properties, such as wide dynamic range and linearity of the spectrally-integrated PL response vs. dose, make the investigation of two-dimensional LiF film radiation detectors grown on several types of substrate highly attractive. Here, the case of a LiF thin film thermally evaporated on a silica substrate, irradiated at grazing incidence with a 35 MeV proton beam, is investigated and reported for the first time. A comparison of the measured photoluminescent Bragg curve with Monte Carlo simulations demonstrates that the Bragg peak in the film is located at the very same position that would be expected in the underlying silica substrate rather than in LiF. The film packing density is shown not to have a significant effect on the peak depth, while even small nonzero grazing angle of the impinging proton beam is able to significantly modify the shape of the Bragg curve. These findings are ascribed to the effects of multiple Coulomb scattering in both the film and the substrate and are interesting for proton beam diagnostics and dosimetry.

Photoluminescence and thermoluminescence dosimetry properties of Ag/Y co-doped ZnO nanophosphor for radiation measurements

This work explores the thermoluminescence (TL) and photoluminescence (PL) properties of Ag/Y co-doped zinc oxide (ZnO) nanophosphor. The proposed dosimeter was prepared by the coprecipitation method and sintered at temperatures from 400°C to 1000°C in an air atmosphere. Raman spectroscopy was studied to investigate the structural features of this composition. The new proposed dosimeter revealed two peaks at 150°C and 175°C with a small shoulder at high temperature (225°C). The PL spectrum showed strong green emissions between 500 to 550 nm. The Raman spectrum showed many bands related to the interaction between ZnO, silver (Ag), and yttrium oxide (Y2 O3 ). The rising sintering temperature enhanced the TL glow curve intensity. The Ag/Y co-doped ZnO nanophosphor showed an excellent linearity index within a dose from 1 to 4 Gy. The minimum detectable dose (MDD) of the Ag/Y co-doped ZnO nanopowder (pellets) equaled 0.518 mGy. The main TL properties were achieved in this work as follows: thermal fading (37% after 45 days at 1 and 4 Gy), optical fading (53% after 1 h and 68% after 6 h by exposure to sunlight), effective atomic number (27.6), and energy response (flat behavior from 0.1 to 1.3 MeV). Finally, the proposed material shows promising results nominated to be used for radiation measurements.

Synthesis, characterization and thermoluminescence properties of MgB4O7 phosphor co-doped with Tm and Dy

The luminescent and dosimetric properties of the MgB4O7 phosphor co-doped with Tm and Dy ions (MgB4O7:Tm,Dy) obtained by the solution combustion technique were investigated. With the prepared material, sintered dosimeters in pellet form were made. The MgB4O7 dosimeters doped with Tm and Dy with 0.25 and 0.10 mol% respectively and sintered at 1223 K for 3 h showed a sensitivity almost 11 times greater than the sensitivity of the TLD-100 commercial dosimeter. The TL response as a function of the gamma dose showed linearity up to 50 Gy followed by a supralinearity region and, above 500 Gy, the saturation region of the electron traps is reached. The fading of the main TL peak was negligible in the first five days after irradiation reaching 13% after 60 days and the lower detection limit was 43 μGy. The kinetic parameters were determined using the deconvolution method revealing general and second order kinetics. The morphology, crystallography and photoluminescence of the prepared phosphor samples are also reported.

Prediction of breast dose in chest CT examinations using adaptive neuro-fuzzy inference system (ANFIS)

In chest computed tomography (CT), the breasts located within the scan range receive a substantial radiation dose. Due to the risk of breast-related carcinogenesis, analyzing the breast dose for justification of CT examinations seems necessary. The main goal of this study is to overcome the limitations of conventional dosimetry methods, such as thermoluminescent dosimeters (TLDs) by introducing the adaptive neuro-fuzzy inference system (ANFIS) approach. In this study, the breast dose of 50 adult female patients who underwent chest CT examinations was measured directly by TLDs. Then, the ANFIS model was developed with four inputs including dose length product (DLP), volumetric CT dose index (CTDIvol), total mAs, and size-specific dose estimate (SSDE), and one output (TLD dose). Additionally, multiple linear regression (MLR) as a traditional prediction model was used for linear modeling and its results were compared with the ANFIS. The TLD reader results showed that the breast dose value was 12.37 ± 2.46 mGy. Performance indices of the ANFIS model, including root mean square error (RMSE) and correlation coefficient (R), were calculated at 0.172 and 0.93 for the testing dataset, respectively. Also, the ANFIS model had superior performance in predicting the breast dose than the MLR model (R = 0.805). This study demonstrates that the proposed ANFIS model is efficient for patient dose prediction in CT scans. Therefore, intelligence models such as ANFIS are suggested to estimate and optimize patient dose in CT examinations.

Development of Ag-Doped ZnO Thin Films and Thermoluminescence (TLD) Characteristics for Radiation Technology

This work examined the thermoluminescence dosimetry characteristics of Ag-doped ZnO thin films. The hydrothermal method was employed to synthesize Ag-doped ZnO thin films with variant molarity of Ag (0, 0.5, 1.0, 3.0, and 5.0 mol%). The structure, morphology, and optical characteristics were investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), photoluminescence (PL), and UV-vis spectrophotometers. The thermoluminescence characteristics were examined by exposing the samples to X-ray radiation. It was obtained that the highest TL intensity for Ag-doped ZnO thin films appeared to correspond to 0.5 mol% of Ag, when the films were exposed to X-ray radiation. The results further showed that the glow curve has a single peak at 240-325 °C, with its maximum at 270 °C, which corresponded to the heating rate of 5 °C/s. The results of the annealing procedures showed the best TL response was found at 400 °C and 30 min. The dose-response revealed a good linear up to 4 Gy. The proposed sensitivity was 1.8 times higher than the TLD 100 chips. The thermal fading was recorded at 8% for 1 Gy and 20% for 4 Gy in the first hour. After 45 days of irradiation, the signal loss was recorded at 32% and 40% for the cases of 1 Gy and 4 Gy, respectively. The obtained optical fading results confirmed that all samples' stored signals were affected by the exposure to sunlight, which decreased up to 70% after 6 h. This new dosimeter exhibits good properties for radiation measurement, given its overgrowth (in terms of the glow curve) within 30 s (similar to the TLD 100 case), simple annealing procedure, and high sensitivity (two times that of the TLD 100).

Pixel Image Analysis and Its Application with an Alcohol-Based Liquid Scintillator for Particle Therapy

We synthesized an alcohol-based liquid scintillator (AbLS), and we implemented an auxiliary monitoring system with short calibration intervals using AbLS for particle therapy. The commercial liquid scintillator used in previous studies did not allow the user to control the chemical ratio and its composition. In our study, the chemical ratio of AbLS was freely controlled by simultaneously mixing water and alcohol. To make an equivalent substance to the human body, 2-ethoxyethanol was used. There was no significant difference between AbLS and water in areal density. As an application of AbLS, the range was measured with AbLS using an electron beam in an image analysis that combined AbLS and a digital phone camera. Given a range-energy relationship for the electron expressed as areal density, the electron beam range (cm) in water can be easily estimated. To date, no literature report for the direct comparison of a pixel image analysis and Monte Carlo (MC) simulation has been published. Furthermore, optical tomography of the inverse problem was performed with AbLS and a mobile phone camera. Analyses of optical tomography images provide deeper insight into Radon transformation. In addition, the human phantom, which is difficult to compose with semiconductor diodes, was easily implemented as an image acquisition and analysis system.

Comparison of organ and effective dose estimations from different Monte Carlo simulation-based software methods in infant CT and comparison with direct phantom measurements

Purpose

Computational dosimetry software is routinely used to evaluate the organ and effective doses from computed tomography (CT) examinations. Studies have shown a significant variation in dose estimates between software in adult cohorts, and few studies have evaluated software for pediatric dose estimates. This study aims to compare the primary organ and effective doses estimated by four commercially available CT dosimetry software to thermoluminescent dosimeter (TLD) measurements in a 1‐year‐old phantom.

Methods

One hundred fifteen calibrated LiF (Mg, Cu, P)‐TLD 100‐H chips were embedded within an anthropomorphic phantom representing a 1‐year‐old child at positions that matched the approximate location of organs within an infant. The phantom was scanned under three protocols, each with whole‐body coverage. The mean absorbed doses from 25 radiosensitive organs and skeletal tissues were determined from the TLD readings. Effective doses for each of the protocols were subsequently calculated using ICRP 103 formalism. Dose estimates by the four Monte Carlo–based dose calculation systems were determined and compared to the directly measured doses.

Results

Most organ doses determined by computation dosimetry software aligned to phantom measurements within 20%. Additionally, comparisons between effective doses are calculated using computational and direct measurement methods aligned within 20% across the three protocols. Significant variances were found in bone surface dose estimations among dosimetry methods, likely caused by differences in bone tissue modeling.

Conclusion

All four‐dosimetry software evaluated in this study provide adequate primary organ and effective dose estimations. Users should be aware, however, of the possible estimated uncertainty associated with each of the programs.

THERMOLUMINESCENCE DOSIMETRY (TLD) IN MEDICINE: FIVE 'W'S AND ONE HOW

Thermoluminescence dosimetry (TLD) has a long history of applications in medicine. However, despite its versatility and sensitivity its use is anecdotally diminishing, at least in part due to the complexity and work intensity of a quality TLD service. The present paper explores the role of TLD in medicine using a common inquiry methodology (5W1H) which systematically asks 'Who, What, When, Where, Why and How' to identify what role TLD could and should play in medical applications.

A practical method for the reuse of nanoDot OSLDs and predicting sensitivities up to at least 7000 cGy

PURPOSE

Optically stimulated luminescence dosimeter (OSLDs) are often used to make in vivo dose measurements. Most users calibrate the OSLDs using the software provided by the vendor which typically is intended for doses up to about 300 cGy with an uncertainty of ±5.5%. OSLDs that reach that dose are then discarded, and new ones are purchased and calibrated. A method has been developed for reusing OSLDs and predicting dose sensitivity up to at least 7000 cGy.

MATERIALS AND METHODS

The nanoDot OSLDs used in this study were routinely used to do in vivo measurements for TBI patients. Instead of using the calibration program provided by the vendor, each nanoDot was bleached to about 100 counts (~0.1 cGy), then calibrated with 50 cGy to produce a sensitivity specific to each nanoDot prior to the patient measurement. NanoDots were read in the hardware mode and the sensitivity factor was applied manually to subsequent patient in-vivo TBI measurements. This was followed by bleaching prior to the next use. The changes of nanoDot sensitivity relative to accumulated dose were analyzed among nine nanoDots. In addition, a method to predict a nanoDot's sensitivity was investigated which aims to reduce the number of sensitivity calibrations while retaining dosimetric accuracy.

RESULTS

Individual per-use nanodot calibrations were performed up to 7000 cGy for 37 clinical TBI patients. Among the nine nanoDots analyzed in this paper, the sensitivity vs accumulated dose decreased linearly up to about 3000 cGy, with linear fitting curve R² values above 0.93. After 3000 cGy of accumulated dose, the sensitivity started to plateau and tended to increase by 6000 cGy, with 2nd order polynomial curve R² values above 0.94. With this finding, an efficient and accurate method to predict nanoDots' sensitivities was developed. With the method applied to the nine OSLDs, a total of 127 sensitivities were predicted and retrospectively compared with measured sensitivities. The predicted sensitivities agreed with measured sensitivities within ±4.0% with an average of -0.8%.

CONCLUSIONS

This study is the first to demonstrate the reuse of nanoDot OSLDs on numerous patients with accumulated dose up to 7000 cGy. Our nanoDot re-usage methodology is accurate, cost-saving and feasible. A time-saving method is also provided that allows a user to reuse a nanoDot with sensitivities predicted with better accuracy than the 5.5% value provided by the conventional batch calibration method.

Protein-facilitated gold nanoparticle formation as indicators of ionizing radiation

The use of X-ray radiation in radiotherapy is a common treatment for many cancers. Despite several scientific advances, determination of radiation delivered to the patient remains a challenge due to the inherent limitations of existing dosimeters including fabrication and operation. Here, we describe a colorimetric nanosensor that exhibits unique changes in color as a function of therapeutically relevant radiation dose (3-15 Gy). The nanosensor is formulated using a gold salt and maltose-binding protein as a templating agent, which upon exposure to ionizing radiation is converted to gold nanoparticles. The formation of gold nanoparticles from colorless precursor salts renders a change in color that can be observed visually. The dose-dependent multicolored response was quantified through a simple ultraviolet-visible spectrophotometer and the peak shift associated with the different colored dispersions was used as a quantitative indicator of therapeutically relevant radiation doses. The ease of fabrication, visual color changes upon exposure to ionizing radiation, and quantitative read-out demonstrates the potential of protein-facilitated biomineralization approaches to promote the development of next-generation detectors for ionizing radiation.

A novel methodology to assess linear energy transfer and relative biological effectiveness in proton therapy using pairs of differently doped thermoluminescent detectors

A new methodology for assessing linear energy transfer (LET) and relative biological effectiveness (RBE) in proton therapy beams using thermoluminescent detectors is presented. The method is based on the different LET response of two different lithium fluoride thermoluminescent detectors (LiF:Mg,Ti and LiF:Mg,Cu,P) for measuring charged particles. The relative efficiency of the two detector types was predicted using the recently developed Microdosimetric d(z) Model in combination with the Monte Carlo code PHITS. Afterwards, the calculated ratio of the expected response of the two detector types was correlated with the fluence- and dose- mean values of the unrestricted proton LET. Using the obtained proton dose mean LET as input, the RBE was assessed using a phenomenological biophysical model of cell survival. The aforementioned methodology was benchmarked by exposing the detectors at different depths within the spread out Bragg peak (SOBP) of a clinical proton beam at iThemba LABS. The assessed LET values were found to be in good agreement with the results of radiation transport computer simulations performed using the Monte Carlo code GEANT4. Furthermore, the estimated RBE values were compared with the RBE values experimentally determined by performing colony survival measurements with Chinese Hamster Ovary (CHO) cells during the same experimental run. A very good agreement was found between the results of the proposed methodology and the results of the in vitro study.

CHARACTERIZATION AND PERFORMANCE TESTS OF A NEW OSL/TL PERSONAL DOSEMETER FOR INDIVIDUAL MONITORING

We propose a personal dosemeter based on the combination of thermoluminescence (TL) and optically stimulated luminescence (OSL) detectors employing the advantages of both techniques. The new OSL/TL dosemeter using a badge manufactured in a 3D printer was tested for assessment of photon doses in simulated and actual situations of exposure. Additionally, Brazilian national performance tests adapted to the new dosemeter were run as well as the performance tests of international standards on the passive dosimetry systems. The results showed the advantages of combined OSL and TL techniques when using the three different configurations of detector combination, Al2O3/BeO, BeO/CaSO4 and Al2O3/LiF. The dosemeter allowed corrections for radiation energy without the necessity of attenuation filters, the evaluation of single and accumulated doses and the triple check of the dose values. Further, the performance tests were consistent with national and international requirements, showing the viability of application of the new dosemeter to the assessment of equivalent doses.

Optical and thermal pre-readout treatments to reduce the influence of fading on LiMgPO4 OSL measurements

TL (Thermoluminescent) and OSL (Optically Stimulated Luminescence) techniques are both luminescent techniques widely applied in several areas into radiation dosimetry. The main difference between them are related to the employed stimulus (thermal or optical) for luminescent emission, as well as the advantages of each technique. Due to simplicity and not to be required heating, the OSL technique has been continuously improved and new researches in materials to be used with this technique have grown in the last decades. Nowadays the main problems in the application of the developed new materials are the poor stability and loss of OSL signal over time (fading). In this study, we performed a sequence of thermal (preheat) and optical (OSL with infra-red light stimulus) pre-readout treatments immediately before OSL readouts of LiMgPO₄ based detectors (LMP), aiming the applicability of novel materials, contributing to find solutions to minimize the influence of fading. Moreover, it was demonstrated that the influence of fading is minimized and the stability of OSL signal from LMP is achieved using just optical process, without heating the material.

Selecting passive dosimetry technologies for measuring the external dose of terrestrial wildlife

Dosimeters attached to wild animals can be used to validate regulatory assessment approaches and models for estimating radiation exposure of wild animals. Such measurements are also necessary to ensure that robust dose-effect relationships can be developed from the results of field research programmes. This paper presents the first comprehensive evaluation of the different dosimetry technologies available for specifically measuring the external exposure of wildlife. Guidance is provided on the selection of appropriate passive dosimetry approaches for directly measuring external exposure of terrestrial wildlife under field conditions. The characteristics and performance of four available dosimetry technologies (thermoluminescent dosimeter (TLD), optically stimulated luminescent dosimeter (OSLD), radiophotoluminescent dosimeter (RPLD) and direct ion storage, (DIS)) are reviewed. Dosimeter properties, detection limit and dose range, study organisms and the intended application are variables that need to be considered when selecting a suitable dosimetry technology. Evaluated against these criteria, it is suggested that LiF based and Al₂O₃:C TLDs, OSLD and RPLD could all be used to estimate doses to wildlife. However, only LiF based TLDs have been used to directly measure wildlife doses in field studies to date. DIS is only suitable for comparatively large species (e.g. medium to large mammals), but has the advantage that temporal variation in dose can be recorded. In all cases, dosimeter calibration is required to ensure that the dose measurements reported can be interpreted appropriately for the organisms of interest.

Retrospective Imaging and Characterization of Nuclear Material

Modern techniques for detection of covert nuclear material requires some combination of real time measurement and/or sampling of the material. More common is real time measurement of the ionizing emission caused by radioactive decay or through the materials measured in response to external interrogation radiation. One can expose the suspect material with various radiation types, including high energy photons such as x rays or with larger particles such as neutrons and muons, to obtain images or measure nuclear reactions induced in the material. Stand-off detection using imaging modalities similar to those in the medical field can be accomplished, or simple collimated detectors can be used to localize radioactive materials. In all such cases, the common feature is that some or all of the nuclear materials have to be present for the measurement, which makes sense; as one might ask, "How you can measure something that is not there?" The current work and results show how to do exactly that: characterize nuclear materials after they have been removed from an area leaving no chemical trace. This new approach is demonstrated to be fully capable of providing both previous source spatial distribution and emission energy grouping. The technique uses magnetic resonance for organic insulators and/or luminescence techniques on ubiquitous refractory materials similar in theory to the way the nuclear industry carries out worker personnel dosimetry. Spatial information is obtained by acquiring gridded samples for dosimetric measurements, while energy information comes through dose depth profile results that are functions of the incident radiation energies.

A comparative study of terrestrial gamma dose rate in air measured by thermoluminescent dosimeter, portable survey meter and HPGe gamma spectrometer

In this paper, three different widely-used measurement techniques for environmental gamma dose rate were studied and compared, i.e., the thermoluminescent dosimeter, the portable survey meter and the spectrometric analysis. Thirteen investigation sites were selected, and the TLDs were arranged to accumulate the radiation signals during an interval of about one quarter, the instant dose rates by using a portable survey meter were collected around the site, and top surface soils were sampled in the surroundings for radionuclides analyzing in laboratory. The results from these methods were compared, which revealed high correlations. The differences and possible uncertainties for the three methods were analyzed, inspired a further study should be conducted to have more successful estimation of dose rate in surface air.

OSL and TL techniques combined in a beryllium oxide detector to evaluate simultaneously accumulated and single doses

Optically stimulated luminescence (OSL) and thermoluminescence (TL) are similar techniques widely used in radiation dosimetry. The main difference between these techniques is the stimulus to induce luminescence emission: TL technique uses thermal stimulation, whereas OSL uses optical stimulation. One of the main intrinsic characteristics of the OSL technique is the possibility of reading several times the dosimetric materials with a negligible loss of signal. In the case of BeO, recent studies have shown that TL stimulation up to 250°C does not affect its OSL signal. Taking the advantages of dosimetric characteristics of BeO combined with both techniques, in this study, we demonstrated the possibility of measuring accumulated and single doses in the same BeO-based detector in order to use it to improve individual monitoring of radiation workers exposed to X-ray or gamma-ray fields. Single doses were measured using TL technique by heating the detector up to 250°C, whereas accumulated doses were estimated using OSL technique in the same detector in a relatively short time of optical stimulation. The detectors were exposed to two energies: 28keV X-rays and 1.25MeV Co-60 gamma rays. The doses estimated by OSL and TL of BeO (Thermalox 995) were compared with those obtained with LiF (TLD-100) and recorded with a calibrated ionization chamber. The results indicate that combined OSL and TL signals of BeO detectors can provide additional information of accumulated dose, with additional exploration of the advantages of both techniques, such as speed in readouts with OSL, and double-check the doses using TL and OSL intensities from BeO.

A high-resolution map of gamma dose rates in Cluj County, Romania using LiF:Mg,Cu,P detectors

Outdoor gamma radiation measurements in Cluj County, Romania have been performed using solid-state thermoluminescent detectors in order to develop a high-resolution database for natural gamma dose rates. Integrated measurements have been carried out for an exposure time of minimum 3 weeks. According to European Union requirements, the territory has been divided into 69 grids of 10 × 10 km. The cells were monitored using LiF:Mg,Cu,P detectors. For two locations the results were 136 ± 7 and 150 ± 7 nGy h(-1), respectively. These results can be explained by the existent geological substrate. The values ranged from 56 ± 4 to 150 ± 7 nGy h(-1), with an average value of 91 ± 2 nGy h(-1), being in agreement with the 2008 United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) Report. A high-resolution map of gamma dose rates in Cluj County is presented for the first time.

Thermoluminescent Phosphors for Radiation Dosimetry

The use of thermoluminescence (TL) as a method for radiation dosimetry of ionizing radiation has been established for many decades and has found many useful applications in various fields, such as personnel and environmental monitoring, retrospective dosimetry, medical dosimetry, space dosimetry, high-dose dosimetry. Method of preparation, studies and applications of thermoluminescence (TL) dosimetric materials are reviewed. Several high sensitivity thermoluminescent dosimeters (TLDs) are now commercially available in different physical forms. These commercial TL dosimeters comply with a set of stringent requirements stipulated by the International Electrotechnical Commission (IEC). Specific features of TL phosphors for thermal neutron, fast neutron and high-energy charged particle (HCP) dosimetry are also considered. Some of the recent developments in the field of optically stimulated luminescence (OSL) and radiophotoluminescence (RPL) are also summarized. Comparative advantages of TL, OSL and RPL dosimeters are given. Results of recent studies of TL in nanosized materials are briefly presented. Future challenges in this field will also be discussed. Contents of Paper

Assessment of radiation exposure outside the radiotherapeutic room during medical accelerator beam emission with the use of TL detectors (radiation exposure outside a LINAC room)

Photon and neutron soft tissue absorbed doses near the entrance door to the medical LINAC treatment room were measured with the use of thermoluminescent detectors LiF:Mg,Cu,P in the anthropomorphic phantom. Two different therapeutic beams (6 and 15 MV) and four treatment techniques were involved in the present study. This allowed one to investigate the contribution of scattered X rays, secondary neutrons and gamma rays to the radiation field. Photon absorbed dose rates 50 cm away from the LINAC room door during emission of 15-MV X rays varied between 4.1×10(-4) and 5.6×10(-4) Gy h(-1), depending on the gantry position and the irradiation field size, whereas in the case of 6-MV therapeutic irradiation these doses are ∼1.5 times lower. In the case of 15-MV beam emission, a mixed radiation field near the bunker door is observed with the photon radiation as the main component, which includes a 33.1 % contribution of the induced gamma radioactivity and ∼2.1 % contribution of the neutron radiation.