Calibration Of Dosimeters Research Articles

Implementation of a high dose routine dosimetry in a self-shielded irradiator

Introduction: Ionizing radiation is applied in various fields, and dosimetric control guarantees the quality and safety of products during the irradiation process. There is a need for dosimetric calibration procedures in industrial irradiation plants, specifically for self-shielded irradiation systems. Objective: To implement high dose dosimetry in the routine control of irradiated materials within a self-shielded irradiator. Methods: We worked with 32 dosimeters; we divided the dose range used into 8 points and used four RED Perspex dosimeters per point. We measured the specific absorbance for each dosimeter; plotted these values against dose and produced a third-degree polynomial fit as a calibration curve. Results: We obtained the calibration curve with an r2 of 0,9997. The uncertainties due to the dispersion of the dosimeters and the calibration curve were 1,39% and 0,22%, respectively, for a total uncertainty of 4,80%. This uncertainty includes dose determination with a factor coverage (k) equal to 2 for a 95% confidence interval. Conclusion: Perspex RED dosimeters can be used for routine control of irradiated products in a self-shielded irradiator system.

Simultaneous Double Dose Measurements Using TLD-100H

Thermoluminescent dosimeters (TLD) and optically stimulated luminescent dosimeters (OSLD) are practical, accurate, and precise tools for point dosimetry in medical physics applications. The objective of this study is to investigate the luminescence properties—both OSL and TL—of lithium fluoride (LiF) doped with magnesium (Mg), copper (Cu), and phosphorous (P) (LiF: Mg, Cu, P), commercially known as TLD-100H. The goal is to devise a methodological approach for dose measurement that allows for obtaining two independently measured dose values at each irradiation point, thereby improving accuracy and precision. The luminescence properties of TLD-100H were studied using a beta irradiation source (90Sr/90Y) integrated into the TL/OSL DA-15 automated Risø reader. This study identified the ideal experimental conditions for optimal dose evaluation and used them for dosimeter calibration across doses ranging from 0.5 to 4.0 Gy. The results demonstrated that, under optimal measurement parameters, the OSL and residual thermoluminescence (ResTL) signals—correlated to two trap systems within the dosimeter—exhibited high reproducibility, stability over multiple cycles, and high precision and accuracy (≤2%). Specifically, the OSL response showed good linear behavior across the investigated dose range, while the ResTL signal exhibited linear behavior between 0.5 and 2 Gy and sublinear behavior for doses >2 Gy.

A fast correction method of the scattering contributions in the area gamma dosemeter calibration field.

In the calibration procedure of area gamma dosemeters, how to accurately evaluate and correct the scattering contribution from the complex environmental factors to the point of test is the key problem to ensure the calibration accuracy. This paper proposed a fast correction method of the scattering contributions in the area gamma dosemeter calibration field. First, Monte Carlo method is employed to simulate the influence of scattering caused by different environmental factors in the calibration field, which is named as semi-panoramic reference radiation field. Then, a prediction model of the relationship between environmental factors and environmental scattering contribution is constructed based on the simulation data through the least squares support vector machine. With the model, the scattering contribution from the environmental factors can be fast estimated to correct the calibration results of the area gamma dosemeters, which will improve the accuracy of the calibration.

Air kerma reference field with high energy photons using a 15 MeV electron beam from a clinical linear accelerator.

In the medical and nuclear fields, there are environments where exposure to photons with energies above several MeV can result in problems. The National Metrology Institute of Japan has developed a high-energy photon field using a 15 MeV electron beam of a clinical linear accelerator with a copper target and an aluminium filter unit to facilitate dosimeter calibration in terms of air kerma. To determine the air kerma rate, the energy fluence distribution at a reference point was calculated, and both calculations and experiments evaluated the effective energy and spatial dose distribution. Moreover, to validate the air kerma measurement, two commercial cavity chambers were calibrated in a developed photon field. The results obtained exhibited a 4% difference compared with those in a Co-60γ-ray reference field.

Recent developments at the Calibration Laboratory for radiation protection instruments and dosemeters of the Paul Scherrer Institute.

The Calibration Laboratory of the Paul Scherrer Institute is responsible for the calibration and verification of radiation protection instruments and dosemeters for internal as well as external customers, such as nuclear power plants and hospitals. The Laboratory is authorised by the Federal Institute of Metrology METAS to perform legal verifications and is accredited as an inspection body, according to ISO 17020, and as a calibration laboratory, according to ISO 17025 by the Swiss Accreditation Service. In addition to routine activities (e.g. calibration of dosemeters, irradiation of passive and active dosemeters on phantoms), the Laboratory is involved in various research and development projects with the goal of supporting the increasingly complex calibration needs and to comply with new regulations, particularly those related to clearance limits in free release measurements. Here we present an overview of the currently on-going projects, which include the investigation of Monte Carlo methods for the calibration of clearance monitors and the development of new calibration procedures for wipe test counters. We also discuss the challenges encountered in these projects, since different stakeholders, ranging from legal authorities to equipment manufacturers and users, are involved in the calibration process.

PRECISION AND RELIABILITY: CALIBRATION COEFFICIENTS AND LONG-TERM STABILITY ANALYSIS OF RADIOTHERAPY DOSIMETERS CALIBRATED BY SSDL, NUKLEAR MALAYSIA

One of the main objectives of the Secondary Standard Dosimetry Laboratory (SSDL) in radiotherapy dosimetry is verifying the radiation dose provided to patients is accurate and meets globally recognised standards. Properly calibrating the therapy dosimeters used in the radiotherapy centres is the first step the SSDL must take to ensure this goal is attained. This study analyses the calibration coefficients and long-term stability of therapy dosimeters calibrated by Nuklear Malaysia's SSDL. The dosimeters were calibrated in the absorbed dose to water using 60Co gamma rays, following the procedure described in IAEA TRS No. 398 and IAEA TRS No. 469. Two hundred therapy dosimeters from 33 radiotherapy centres were evaluated for the percentage deviation of the calibration coefficients provided by the SSDL and the manufacturer. Furthermore, the variation in calibration coefficient and the long-term stability of therapy dosimeters from 2011 to 2021 were examined. The percentage deviation of calibration coefficients between the SSDL and manufacturers found that most (82%) user dosimeters were within the IAEA's acceptance limit of ± 1.5%. Overall, the stability of calibration coefficient values ranged between 33.25% and -27.24%, with an average of 0.03%. As predicted, only 15% of the therapy dosimeters fulfill the criteria for long-term stability of 0.5%. In conclusion, proper maintenance and annual calibration of therapy dosimeters are very important to improve accuracy, minimise measurement uncertainty, and thus reduce the likelihood of errors in radiotherapy dosimetry.

Investigating the performance of susceptibility-weighted images in Fricke gel dosimeter reading and optimizing the related imaging parameters

Fricke gel dosimeters are especially useful in small-field dosimetry and validation of treatment delivery in three-dimensional space with features such as tissue equivalence, non-toxicity, high spatial resolution, non-dependence on energy, and dose rate. The use of basic Magnetic Resonance Imaging (MRI) protocols (T1- and T2-Weighted) for reading Fricke gel dosimeters has always been considered the dominant method in many studies. However, the development and application of advanced MRI techniques for more accurate readings of Fricke gel dosimeters can be useful. Considering that in the main structure of Fricke gel, there are conversions of iron ions to each other, this study aimed to investigate the performance of Susceptibility-Weighted Imaging (SWI) and Quantitative Susceptibility Mapping (QSM) based on magnetic susceptibility in the reading of Fricke gel dosimeters and to optimize the related imaging parameters. For this purpose, a Fricke-Xylenol orange-gelatin was made at five concentrations of iron ammonium sulfate. To obtain gel dosimeter calibration curves, vials containing gel were subjected to irradiation at three different doses by a linear accelerator. The reading of gel dosimeters was performed using MRI imaging in three protocols, T1W, T2W, and SWI, and analyzed with a method unique to each one. Finally, the results obtained from the three protocols were compared with each other. The comparison of calibration curves in three imaging protocols shows that the sensitivity of calibration curves in SWI was about three times its value in T2W, and on the other hand, the reported sensitivity in T1W was very small compared to the other two protocols. The linearity factor was similar between SWI and T1W protocols and higher in T2W. Therefore, it is concluded that in addition to the relaxometry techniques that have been used as a conventional method for reading Fricke gel dosimeter, SWI imaging has high sensitivity and specificity for reading dosimeter gel based on iron.

Calibration of Thermoluminescent Dosimeters for Use in Photon Radiation Beams of Various Quality

Purpose: To describe the technology of dosimetric preparation of the same batch of TLD based on LiF
 activated by magnesium Mg and titanium Ti (LiF:Mg-Ti) for three qualities of photon radiation beams
 with energies of 1.25 MeV, 2 MeV and 192Ir beam with energy of 0.38 MeV for measurements during radiotherapy. The TLD calibration technology for 192Ir should be developed from scratch. To compare the
 energy dependences of the sensitivity coefficients for different qualities of the beams.
 Material and methods: 175 dosimeters were irradiated in photon radiation beams with al energy of
 2 MeV, 1.25 MeV and 0.38 MeV in a reproducible geometry several times determined by the same dose.
 Individual coefficients are obtained. A working batch of 12 TLD was selected with a production capacity
 of 2 %. Coefficients are estimated for the batch and graphs of the energy dependence of individual sensitivity coefficients are constructed.
 Results: The results obtained indicate the presence of an energy dependence of the individual sensitivity coefficients of TLD in the energy range from 0.38 to 1.0 MeV.

Assessment of energy and angular dependence of LiF:Mg,Ti dosimeters irradiated in the quantity Hp(0.07)

Radiation dosimetry has the purpose of quantifying the dose received by the occupationally exposed individual. The device used in this process is called a dosimeter, the dosimeter can be used in different situations, for example, the dosimeter used to quantify the dose received in the fingers is the ring model dosimeter, for the extremity, which is the focus of this work. In Brazil, we still do not have standards for the calibration of extremity dosimeters, therefore, in this work, the CASEC recommendations were used, adapted for extremity dosimetry. For a dosimeter to be used in its respective routine, it must present results within some pre-established limits in reference standards. For this purpose, energy dependence and angular dependence tests were carried out. To calibrate the LiF:Mg,Ti thermoluminescent dosimeters, a phantom rod was used. The phantom rod has the function of simulating the region of interest, in the case of this work, the fingers. The dosimeters were irradiated in the magnitude Hp(0.07), with the doses and energies recommended by the CASEC standard. The aim of this work is to characterize end dosimeters in the ring model with LiF:Mg,Ti detectors.

Медико-соціальні наслідки проблем безпеки пацієнтів в онкорадіології

The relevance of the problem of patient safety in oncoradiology in Ukraine and other countries has been substantiated. The purpose - is to assess the safety of patients receiving radiation therapy and the magnitude of the health and social consequences of human error in this area. Materials and methods. The material of the study was the results of international TLD audit (IAEA/WHO) of the dosimetry quality during procedures on cobalt telegram devices in Ukraine as well as the international and domestic regulatory framework on safety of the radiotherapy care, and scientific publications of domestic and foreign specialists on patient safety. The methods of the research: statistical, analytical, bibliographic, systems approach. Results. By the example of radiotherapy using the results of the international IAEA/WHO program on the TLD audit of the quality of the dosimetric calibration of the remote gamma-therapy units in Ukraine in 1998-2014, an attempt has been made to estimate the scale of medico-social consequences of the underestimation of medical errors in oncoradiology. The problems of regulatory nature of medical errors in oncoradiology had been tentatively identified. Conclusions. The problem of medical errors in the treatment of cancer patients with radiation oncology in Ukraine is extremely topical. Usually the problems of errors in oncoradiology are considered in the organizational, methodological, personnel and technical aspects, while the medico-social consequences of the problem are not covered. In the optimistic scenario, about 10,000 cancer patients for a year may suffer from dose-related errors alone, while in the pessimistic scenario the number may be as high as 15,000 over the same period. There are legal issues to be clarified in oncoradiology for patient safety reasons. The first priority for improving patient safety in oncoradiology is to record and analyze defects in radiotherapy and their consequences. No conflict of interests was declared by the authors.

Camera-based radiotherapy dosimetry using dual-material 3D printed scintillator arrays.

To describe a methodology for the dual-material fused deposition modeling (FDM) 3D printing of plastic scintillator arrays, to characterize their light output under irradiation using an sCMOS camera, and to establish a methodology for the dosimetric calibration of planar array geometries. We have published an investigation into the fabrication and characterization of single element FDM printed scintillators intending to produce customizable dosimeters for radiation therapy applications. 1 This work builds on previous investigations by extending the concept to the production of a high-resolution (scintillating element size 3×3×3mm3 ) planar scintillator array. The array was fabricated using a BCN3D Epsilon W27 3D printer and composed of polylactic acid (PLA) filament and BCF-10 plastic scintillator. The array's response was initially characterized using a 20×20cm2 6 MV photon field with a source-to-surface (SSD) distance of 100cm and the beam incident on the top of the array. The light signals emitted under irradiation were imaged using 200ms exposures from a sCMOS camera positioned at the foot of the treatment couch (210cm from the array). The collected images were then processed using a purpose-built software to correct known optical artefacts and determine the light output for each scintillating element. The light output was then corrected for element sensitivity and calibrated to dose using Monte Carlo simulations of the array and irradiation geometry based on the array's digital 3D print model. To assess the accuracy of the array calibration both a 3D beam and a clinical VMAT plan were delivered. Dose measurements using the calibrated array were then compared to EBT3 GAFChromic film and OSLD measurements, as well as Monte Carlo simulations and TPS calculations. Our results establish the feasibility of dual-material 3D printing for the fabrication of custom plastic scintillator arrays. Assessment of the 3D printed scintillators response across each row of the array demonstrated a nonuniform response with an average percentage deviation from the mean of 2.1%±2.8%. This remains consistent with our previous work on individual 3D printed scintillators which showed an average difference of 2.3% and a maximum of 4.0% between identically printed scintillators.1 Array dose measurements performed following calibration indicate difficulty in differentiating the scintillator response from ambient background light contamination at low doses (<20-25cGy) and dose rates (≤100 MU/min). However, when analysis was restricted to exclude dose values less than 10% of the Monte Carlo simulated max dose the average absolute percentage dose difference between Monte Carlo simulation and array measurement was 5.3%±4.8% for the fixed beam delivery and 5.4%±5.2% for the VMAT delivery CONCLUSION: In this study, we developed and characterized a 3D printed array of plastic scintillators and demonstrated a methodology for the dosimetric calibration of a simple array geometry.

Characterization and calibration of thermoluminescent dosimeters of LiF:Mg, Ti in the quantity Hp(0.07)

The extremity dosimeters are devices used to quantifying the radiation dose that the occupationally exposed individual receives in specific regions of the body during the work time. Dosimeter calibration is essential so that the dosimeter response is equivalent to the received dose. Tests such as batch homogeneity and lower detection limit are part of the dosimeter calibration process. The rod phantom simulates the region of interest regarding the interaction with radiation and the scattered dose. The extremity dosimeters used were the LiF:Mg,Ti thermoluminescent dosimeters.

Bias-corrected Hp(10)-to-Organ-Absorbed Dose Conversion Coefficients for the Epidemiological Study of Korean Radiation Workers.

The effects of radiation on the health of radiation workers who are constantly susceptible to occupational exposure must be assessed based on an accurate and reliable reconstruction of organ-absorbed doses that can be calculated using personal dosimeter readings measured as and dose conversion coefficients. However, the data used in dose reconstruction contain significant biases arising from a lack of reality and could result in an inaccurate measure of organ-absorbed doses. Therefore, this study quantified the biases involved in organ dose reconstruction and calculated the bias-corrected -to-organ-absorbed dose coefficients for the use in epidemiological studies of Korean radiation workers. Two major biases were considered: (1) the bias in arising from the difference between the dosimeter calibration geometry and the actual exposure geometry and (2) the bias in air kerma-to- conversion coefficients resulting from geometric differences between the human body and slab phantom. The biases were quantified by implementing personal dosimeters on the slab and human phantoms coupled with Monte Carlo method and considered to calculate the bias-corrected -to-organ-absorbed dose conversion coefficients. The bias in was significant for large incident angles and low energies (e.g., 0.32 for right lateral at 218 keV), whereas the bias in dose coefficients was significant for the posterior-anterior (PA) geometry only (e.g., 0.79 at 218 keV). The bias-corrected -to-organ-absorbed dose conversion coefficients derived in this study were up to 3.09-fold greater than those from ICRP publications without considering the biases. The obtained results will aid future studies in assessing the health effects of occupational exposure of Korean radiation workers. The bias-corrected dose coefficients of this study can be used to calculate organ doses for Korean radiation workers based personal dose records.

Dosimetric calibration of nanodot optically stimulated luminescent dosimeter for intraoperative radiotherapy with low-energy X-rays

Dosimetric calibration of nanodot optically stimulated luminescent dosimeter for intraoperative radiotherapy with low-energy X-rays

ESTABLISHMENT OF RQT BEAM QUALITY (100 TO 150 kV) FOR COMPUTED TOMOGRAPHY APPLICATIONS

In Malaysia, the radiation beam qualities for calibration of dosimeters in computed tomography (RQT series) were established at the Secondary Standard Dosimetry Laboratory (SSDL) of the Malaysian Nuclear Agency by using a constant potential industrial X-ray machine and a 0.6 cc PTW UNIDOS ionization chamber calibrated at the International Atomic Energy Agency (IAEA). Through the experimental method of additional filtration determination, the results demonstrated that all measured first half-value layer (HVL) filtrations (mm Al) for each RQT 8 (100 kV), RQT 9 (120 kV) and RQT 10 (150 kV) comply with tolerance limits of ± 3% as recommended by the IEC-61676. For RQT 8, a repeated experiment to determine accurate additional filtration has to be done with different added filtration RQT (mm Cu) thickness as the value initially goes beyond the 3% difference. Compared to prior radiation quality series RQT determinations, the added filtration for RQT 8 changed from 0.1 mm Cu in 2019 to 0.2 mm Cu in 2020. When compared against values established over the previous three years, all three RQTs for 2020 exhibit differences in measured first HVL filtrations (mm Al), albeit remaining within the 3% difference standard recommended in the TRS 457 standard of the IAEA. This change arises from x-ray tube aging, anode roughening and inherent filtration alteration, leading to a perceived need for RQT trial and error re-evaluation to reduce the percentage decrement. Yearly monitoring of the beams should be performed to determine possible radiation quality changes, taking corrective action where necessary to remain within the prescribed tolerance limit. The standard radiation qualities should be maintained, allowing for calibration accuracy to confirm dosimeter readings.

Effect of MOSFET dosimeters’ calibration method on calibration factors and radiation doses measured with the dosimeters in radiology

MOSFET dosimeters have widely been used to measure radiation doses caused by x-rays. When using the MOSFET dosimeters, calibration factors (CFs) have a direct effect on reliability of dose measurements. The aim of this paper was to study the effect of various calibration methods on the CFs of the MOSFET dosimeters. The CFs were measured on clinical digital x-ray angiography (XA) and computed tomography (CT) devices using a calibrated CT ionization chamber and a standard polymethyl methacrylate (PMMA) phantom. The measurements were conducted by having the dosimeters (1) in air, (2) on the surface of the PMMA phantom and (3) inside the phantom. A statistically significant difference was seen between the CFs measured on the XA and CT devices. The CFs measured on the CT device were 20%–165% higher than those measured with the XA device (p < 0.001) in every calibration geometry. Furthermore, the calibration geometry had a notable effect on the CFs on CT. The CFs on the surface of the phantom were 18%–25% higher than in air (p < 0.05), and the CFs inside the phantom were 32%–39% smaller than in air (p < 0.05). These results suggest that the calibration of the MOSFET dosimeters should be conducted with the same device that is used in actual dose measurements. Also, the scattering conditions and the calibration geometry should be similar in the calibration and subsequent dose measurements.

Introducing a chemical-based gel dosimeter for radiation measurement

Radiation dosimetry plays important role in the reproducibility of radiobiological experiments & the replicability of results and so the successful radiotherapy treatment. There exist several methods to measure doses such as chemical and gel dosimetry. In this study, a novel dosimeter was evaluated capable of reading with both MRI & spectrofluorometer.Trimesic acid with different concentrations and pH was mixed with a matrix of gelatin & acrylamide gel and were poured at different vials to be exposed at different doses up to 200 cGy at two temperature of 4 °C and 25 °C and the readings were used to extract calibration curves for MRI with different TE2s & spectrofluorometer methods which Pearson correlation coefficient (R2) for each method & their interaction were used to find out the best conditions.The results were obtained as dosimeter calibration curves with related R2 of two different reading methods of MRI & spectroflourimetry in dose range of 0–200 cGy. The R2 was a measure to compare different experimental groups & also an interaction between MRI and spectroflourimetry R2s was considered to determine which combination results to a better two reading, simultaneously.It was showed that in the considered dose range, at lower temperature of 4 °C, weak acidity & lower concentration of Trimesic acid, the proposed dosimeter seems to be a two reading or hybrid dosimeter.

Dosimetry of a novel focused monoenergetic beam for radiotherapy

Objective. A novel treatment modality is currently being developed that produces converging monoenergetic x-rays. Conventional application of dosimetric calibration as presented in protocol TG61 is not applicable. Furthermore, the dosimetry of the focal point of the converging beam is on the order of a few millimeters, requiring a high-resolution dosimeter. Here we present a procedure to calibrate radiochromic film for narrow-beam monoenergetic 60 keV photons as well as absolute dosimetry of monoenergetic focused x-rays. A study of the focal spot dose rate after passing through a bone-equivalent material was also done to quantify the effects of heterogeneous materials. Approach. This was accomplished by configuring a polyenergetic beam of equivalent energy using a clinical orthovoltage machine. Calibrated films were then used to perform absolute dosimetry of the converging beam by measuring the beam profile at various depths in water. Main Results. A method for calibrating radiochromic film has been developed and detailed that allows absolute dosimetry of a monoenergetic photon beam. Absolute dosimetry of a focused, mono-energetic beam resulted in a focal spot dose rate of ∼30 cGy min−1 at a depth of 5 cm in water. Significance. This work serves to establish a dosimetry protocol for mono-energetic beam absolute dosimetry as well as the use of such a method for measurement of a novel teletherapy modality.

Using a Scanner to Measure Absorbed Doses with Radiochromic Film Dosimeters

The article provides a sequence of steps for using RISØ calorimeters for calibration and subsequent use of B3 radiochromic film dosimeters (GEX corporation) and a scanner for measuring absorbed doses. Calibration was carried out with the help of electron beam accelerator in the range of absorbed doses of 3 – 40 kGy (measurement range of RISØ calorimeters). In the course of the work, the following was carried out: – calibration of B3 radiochromic dosimetry films using RISØ calorimeters; – plotting a calibration curve for B3 radiochromic dosimetric films; – calculation of approximation functions; – development of a technique for using a flatbed scanner to measure absorbed doses; – estimation of the measurement uncertainties of absorbed doses. Accelerator operation parameters: scanning frequency of the accelerated electron beam – 5 Hz, pulse frequency – 120 Hz, electron energy – 5 MeV, electron beam current – 60 μA. The measurement error of the absorbed dose is 5.8 %.

Development of an automated routine for the calibration of multi-point scintillation detectors for advanced dosimetry applications

Multi-point scintillation dosimeters have the advantage to allow real-time measurements of dose with a good spatial resolution, but these detectors must be accurately calibrated to perform precise dose measurements. This study demonstrates, by means of simulations and an experimental validation, that when the calibration dataset is well chosen, it is possible to perform an automated calibration of such dosimeters, with an accuracy on the measured output factors reaching (0.5 ± 0.1) %.