Secondary Standard Dosimetry Laboratory Research Articles

Development and validation of a Bayesian unfolding program using OpenBUGS open-source software for Bonner spheres neutron spectrometry

This study presents the development of a novel unfolding program based on a Bayesian method for Bonner spheres spectrometry. The program incorporates a priori information on the neutron spectrum, employing a linear superposition of three non-negative parametric functions: thermal-Maxwellian distribution, an intermediate region represented by a straight line in lethargy space (1/E behavior), and the Watt fission distribution for the fast region. The effectiveness of the developed program was validated through its application to two reference cases from the EURADOS 2018 exercise (LINAC and Skyshine), followed by its implementation in characterizing the neutron field around an OB26 neutron irradiator at the Secondary Standards Dosimetry Laboratory (SSDL) of the Nuclear Research Center of Algiers (CRNA), Algeria. While validation results for the LINAC case were promising, achieving comparable neutron spectrum shape and integral quantities to the reference, challenges were encountered with the Skyshine case. However, these challenges were partially addressed through sensitivity analysis, resulting in slightly improved outcomes compared to the previous participation and to the reference. Application of the program to characterize the neutron field around the OB26 irradiator yielded satisfactory results when compared to reference data. A two-step sensitivity analysis further enhanced the outcomes, initially substituting the Watt fission distribution with the evaporation distribution, thereby improving spectrum shape and integral quantities. Subsequently, utilizing the obtained neutron spectra as prior information for unfolding codes MAXED and GRAVEL ensured stability and agreement with reference data and preliminary results.

Influence of anode/filtration setup on X-ray multimeter energy response in mammography applications

Quality control and assurance of mammography X-ray generators include the use of solid-state detectors and/or ionization chambers calibrated in standard reference radiation fields. The IEC 61267:2005 standard defines reference mammography radiation fields for Mo/Mo anode/filtration, while various anode/filtration combinations are encountered in clinical mammography X-ray units. Not all Secondary Standard Dosimetry Laboratories have an X-ray generator with Mo/Mo radiation setup. Thus, traceability can be established only for the available anode/filter combinations, commonly limited to W/Al. In this study, W/Al radiation fields were established under laboratory conditions by performing half-value layer measurements. Then, four solid-state detectors were characterized. X-ray multimeter performance was evaluated in terms of energy response in the W/Al radiation fields. In the laboratory conditions, the energy response of the dosimeters had a large deviation from unity for dosimeters without appropriate anode/filter combination selected in the software settings, even though most of the dosimeters had a uniform relative response. The discrepancy in the response was further investigated by examining its variation induced by available detector software settings, and it was determined that the dosimeter response can vary up to 20 %. In a clinical setup, the half-value layer was determined, and detector performance was examined. Dosimeters were tested in clinical fields with Mo/Mo, Mo/Rh, W/Rh, W/Ag anode/filter combinations in the X-ray tube voltage range from 25 kV to 35 kV. For most clinical radiation fields, multi-element detectors had energy response deviation within ±5 %. The single-element detector had one software setting available and exhibited strong energy dependence. Extensive testing of detector response, such as presented in this paper. allows for correction factor interpolation based on the half-value layer.

Experimental and Monte Carlo Evaluation of Spherical Ionization Chambers’ Response to 137Cs Radioactive Source

Measurements were performed for the calibration of an ionization chamber in the secondary standard dosimetry laboratory of IFIN-HH. A 10-liter spherical ionization chamber was calibrated using a 1-literspherical reference standard ionization chamber. The ionization chamber’s response to 137Cs was also evaluated computationally by MCNP and FLUKA Monte Carlo codes. The models of the experimental setup are validated and can be used for further studies, especially in cases where the real experiment is hard or impossible to perform

Characteristics of the reference X-ray narrow-spectrum series at SSDL of Institute for Nuclear Science and Technology

This paper presents the characteristics of the reference X-ray narrow-spectrum series used in the Secondary Standard Dosimetry Laboratory (SSDL) at Institute for Nuclear Science and Technology (INST) with X-ray beam irradiator. In order to perform calibration works, it is highly important to verify the characteristics and qualities of reference X-ray beam recommended by the International Standardization Organization (ISO) 4037:2019. The characteristics of the X-ray beams in terms of the half-value layer, homogeneity coefficient and the air kerma rate are determined for the narrow-spectrum series in the 40 and 150 keV range. The related dosimetric quantities such as the ambient dose equivalent and personal dose equivalent also determined. The experimental values are well consistent with the recommended values of the ISO 4037 criteria. It implies that the reference X-ray narrow-spectrum series (N-series) can be applied in calibration works of X-ray measuring devices used in radiation safety assessment.

Determination of Timer Error and Evaluation of Its Effect on Dose for OB6, GammaBeam X200 and X-Ray Irradiators at the Secondary Standard Dosimetry Laboratory in Nigeria

Determination of Timer Error and Evaluation of Its Effect on Dose for OB6, GammaBeam X200 and X-Ray Irradiators at the Secondary Standard Dosimetry Laboratory in Nigeria

PENDEKATAN ALGORITMA UNTUK EVALUASI DOSIS RADIASI DENGAN TLD-900 BARC PADA PENGUKURAN RADIASI ENERGI RENDAH

Accurate radiation dose evaluation for radiation workers is crucial to determine the radiation dose received from exposure. Using passive dosimeters such as TLD-900 can assist in monitoring and controlling radiation exposure by evaluating accumulated dose readings over a specific period. Due to its utilization in diverse radiation fields, the dose evaluation method should be able to differentiate the energy range employed. Energy dependence can pose a challenge in reading the received dose, particularly in the case of low-energy X-ray usage. Therefore, this study aims to develop an algorithm for individual equivalent dose evaluation Hp(10) in low-energy (<20 KeV) usage. The data will be obtained from the Nuclear Agency of Malaysia's Secondary Standard Dosimetry Laboratory (SSDL), including various ISO narrow series X-ray sources and several radioactive sources such as Cs-137, Co-60, Sr-90, Kr-85, and Pm-147. The evaluation method will involve a trumpet curve and ANSI bias plot, enabling an assessment of the performance of the developed algorithm. Ultimately, the algorithm will be used for long-term dose evaluation intercomparisons in low-dose reviews. The low-energy energy evaluation algorithm for equivalent doses has successfully been conducted. The algorithm performs very well in distinguishing energy types using the parameter r12. In contrast, the low-energy dose evaluation algorithm encounters difficulties due to the low-energy characteristics in energy deposition, which are similar for each element D. Keywords: Algorithm,radiation dose evaluation, TLD, Low Energy.

Evaluation of calibration factors of digital survey meters in a secondary standard dosimetry laboratory.

The calibration of radiological survey meters is an important consideration in achieving standardisation of doses. This provides traceability for field instruments to an International System of Units. Seventy-one digital survey meters were calibrated by the substitution method in a 137Cs beam in a secondary standard dosimetry laboratory using a PTW spherical ionisation chamber coupled to a Physikalisch-Technische-Werkstaetten (PTW) UNIDOS Electrometer. The calibration factors determined ranged from 0.59 to 1.98. Thirty-six pieces of equipment have their calibration factors within 0.9-1.1. A total of 36% of the survey meters recorded calibration factors corresponding to a percentage deviation above 20% whilst 64% fell within 20% deviations from the true value. The best value of a calibration factor obtained in this work was 1.00 from two survey meters. The errors due to survey meters being out of calibration can usually be corrected by frequent recalibration.

GUI development for SSDL to calibrate photon measuring equipment

Current legislation mandates the inspection and calibration of operational survey radiation monitoring instruments used in nuclear medicine, radiotherapy departments, and other fields utilizing ionizing radiation sources. To comply with national and international radiation protection standards, Morocco's National Secondary Standard Dosimetry Laboratory provides reliable calibration results with high accuracy and covers various measurement ranges using attenuators provided by the automated Gamma G10 irradiator or validated beam qualities produced by the X-ray irradiator type X80–320 kV.This study aims to develop a digital graphical user interface using Python programming language, designed for calibrating radiation protection measuring instruments . The interface is intended to facilitate all operations and calculations related to determining calibration factors and measurement uncertainties in accordance with the ISO 4037 standard, ensuring minimal processing time and minimizing potential error sources . The interface enables calculations to be recorded, as well as the establishment and electronic archiving of the calibration certificate and the report in PDF format using the Hypertext Preprocessor FPDF library (PHP FPDF). With the development of this interface, multiple instruments can be processed per day with high accuracy, streamlining the calibration process and improving efficiency.•The importance of compliance with international standards to ensure the quality and reliability of measurements in radiation protection was examined.•Description of X-ray and Gamma-ray irradiators designed for the calibration of radiation protection measuring instruments within the Secondary Dosimetry Calibration Laboratory (SSDL) which is a member of the WHO/IAEA network within the National Center for Radiation Protection of Morocco•Graphical User Interface using python for the calibration of photon measurement instruments for radiation protection purposes was developped.

Development of a motorized system for the characterization of the RQR reference x-ray beams at the KFSHRC's SSDL using an extrapolation chamber

An extrapolation chamber of type Böhm 23392, used for the dosimetry of RQR beam qualities at the Secondary Standard Dosimetry Laboratory of King Faisal Specialist Hospital, is presented. A computer-based motorized system consisting of a stepping motor coupled to the chamber's built-in micrometer screw was designed to expedite the measurements process, giving a linear relationship between the number of motor steps and the chamber depth with a Coefficient of Determination (COD) equal to 0.9990. The extrapolation chamber along with the motorized system was used to determine the extrapolation curves. The slope of the extrapolation curves, measured for the eight RQR beam qualities with a relative uncertainty between 0.17% and 0.58%, varies linearly with the beam quality expressed in terms of HVL, with a COD between 0.9995 and 1.0000.

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.

Challenges in Providing Facility of Calibration for X-Ray Multimeter in Indonesia: An Initial Study

Indonesia still needs calibration facilities for X-ray multimeters, so calibration is carried out abroad, requiring a significant budget and a relatively long time. This affects the services provided by the conformity testing laboratory (LUK) to be hampered. An initial review has been conducted to identify calibration laboratories capable of X-ray multimeter calibration services and review their readiness in Indonesia. The study was carried out by examining the radiation metrology scheme and the capabilities of the dosimetry laboratory. The review results show that a secondary standard dosimetry laboratory (LDSS) carries out X-ray multimeter calibration. However, LDSS in Indonesia still needs to be capable of X-ray multimeter calibration services. A more detailed study will be continued regarding the needs and technical infrastructure criteria for an X-ray multimeter calibration laboratory to complete this study. Keywords: calibration, X-ray multimeter, LDSS, calibration facility

Radiation Measurement with Data Acquisition Using LabVIEW

Radiation monitoring and measurement are important for radiation safety. Such monitoring and measurement must be carried out in order to investigate workplace conditions and individual exposures, to ensure that radiological conditions in the workplace are acceptable, safe, and satisfactory, and to keep records of radiation monitoring over a long period of time in accordance with regulations or as good practice. However, radiation monitoring instruments and system are expensive. A cost-effective radiation monitoring system using Geiger Muller (GM) radiation detector was developed. A high voltage generation circuit and data acquisition were implemented using LabVIEW software. The cost-effective radiation monitoring system is easy to use, and it can detect radiation, analyzed and record the data in a personal computer. This newly developed system is simple and can provide the radiation dose data for further analysis. An experiment was conducted to compare and calibrate the collected data at the Secondary Standard Dosimetry Laboratory (SSDL). The result shows that the new developed GM detector provides good correlation between counts per minute (cpm) and dosage units, which is good characteristic of a radiation counting system

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.

Impact of dosimeter size on energy dependence: An experimental study on glass TLDs

Practical Use of a dosimeter in a range of photon energies necessitates identification of radiation field as well as energy response of the dosimeter. Energy dependence of absorbed dose is caused by the unequal absorption properties of the material from various radiation energies, while the process of dosimeter response generation may also be energy dependent. The aim in this work is to measure the energy dependence of the response of sub-millimeter size glass silica fibre thermoluminescent dosimeters and to check whether there is a relation between energy dependence and the size of the dosimeter. Small size TLDs of capillary rod shape with the external/internal diameters of 870/544, 386/241 and 127/79 μm and 3 mm length prepared by a precision cutting process and appropriate preconditioning, were irradiated at various photon energies. Irradiations were performed in free-in-air condition at the secondary standard dosimetry laboratory (SSDL) of the Malaysian Nuclear Agency using X-ray narrow series spectra and gamma rays from a137Cs source as the reference photon energy. Theoretical energy dependence calculated by using the cavity theory was found in an acceptable agreement with the experimental results. The results show an increasing degree of energy dependence with the dosimeter size in the studied size range. This can be explained based on the low dimensions of the dosimeter that are comparable with the range of secondary electrons produced in the dosimeter, while luminescence efficiency may also play a role.

Experimental determination of k Q factors for two types of ionization chambers in scanned proton beams

Objective. Experimental determination of beam quality k Q factors for two types of Farmer ionization chambers, NE2571 and IBA FC65-G, in a scanned proton beam for three nominal energies (140 MeV, 180 MeV and 220 MeV) based on water calorimetry. Approach. Beam quality correction factors were determined comparing the results obtained with water calorimetry and ionometry. Water calorimetry was performed to determine the absorbed dose at a depth of measurement in water of 5 g cm−2, limited by the extension of the calorimeter glass vessel used. For the ionometry, two chambers of each type were included in the study. The ionization chambers were calibrated in terms of absorbed dose to water in 60Co at the Swedish Secondary Standard Dosimetry Laboratory, directly traceable to the BIPM, and were used according to the IAEA TRS-398 Code of Practice. Main results. The k Q values determined in the present work have been compared with the values tabulated in TRS-398 and its forthcoming update and also with those obtained in previous water calorimetric measurements and Monte Carlo calculations. All results were found to agree within the combined uncertainties of the different data. Significance. It is expected that the present work will serve as an experimental contribution to k Q -factors for the two chamber types and three scanned proton beam qualities used.

Determination of Calibration X-Ray Beam Qualities and Establish a Set of Conversion Coefficients for Calibration of Radiation Protection Devices Used in Diagnostic Radiology

The use of X-ray facilities in calibrating radiation measuring equipment in diagnostic radiology requires an exact knowledge of the radiation field. X-ray spectrums are made narrow beam by proper filtration recommended by several international organizations. In the present study, the experimental determination of X-ray calibration qualities and analysis of conversion coefficients from air Kerma to ambient and personal dose equivalent is carried for X-ray beam irradiator X80-225kV as per ISO narrow spectrum series at Secondary Standard Dosimetry Laboratory (SSDL) in Bangladesh. The X-ray beam involved in half value layer, effective energy, beam homogeneity coefficient and consistency of X-ray production from the generator (kV and mA) is conducted. A discrepancy of half value layer has been observed for N200 beam code by -8.5% which leads to the deviation of effective energy by -7.7% with a standard deviation of 1.3%. The conversion coefficients from the air kerma to dose equivalent that satisfying the condition of ICRU sphere is established to obtain radiation qualities and compared with values referred by other standard laboratories. A deviation of 0.87% has been observed for H*(10) and H¢(0.07) in between ISO and BCRU empirical relation which is insignificant. A set of conversion coefficients for Hp(10) and Hp(0.07) has also been calculated for ICRU four element tissue.

A performance analysis of a new secondary standard dosimetry laboratory irradiation system

This study reviews the performance analysis of a commercial 137Cs irradiation system that has recently been installed in the Secondary Standard Dosimetry Laboratory (SSDL) at the Soreq Nuclear Research Center (SNRC).The SSDL is responsible for calibrating calibration facilities and for calibrating most protection level radiation monitoring instruments used in medical, nuclear, industrial and academic settings in Israel. Until recently, these monitoring instruments have been calibrated by a 40-year-old irradiation system.At the end of 2018, a new Hopewell Designs Inc. ® irradiation system was installed at our SSDL. This system employs the most advanced radiation safety standards, along with 21st century source automation methods. In this work, we review the system’s performance. Our analysis shows excellent results in terms of repeatability, robustness, linearity, and beam uniformity. Additionally, the system accuracy was tested by participating in an international IAEA postal audit, and here too, excellent results were obtained.

BATAN PERSONAL DOSE EQUIVALENT Hp (10) AND Hp (3) INTERCOMPARISON RESULTS AT 2018 & 2019

<p>One of the methods to ensure the quality of a laboratory is participating in an intercomparison activity. For the dosimetry laboratory network in Indonesia, the intercomparison activity is managed by the Secondary Standard Dosimetry Laboratory (SSDL) Jakarta. This paper describes the intercomparison among processing laboratory for personal dose equivalent H<sub>p</sub>(10) and H<sub>p</sub>(3) using thermoluminescent dosimeter (TLD)/films in 2018 & 2019. The SSDL Jakarta irradiated packages of participant's TLDs/films with Cs-137 and X-rays at a specific equivalent dose. The irradiated dosimeters were sent back to the participants by mail, and then the result was sent to the SSDL Jakarta for evaluation. The evaluation was carried out using the trumpet curve under the International Atomic Energy Agency (IAEA) publication. The results obtained for the 2018 intercomparison show the success rates of 98%, and 2% were outside the acceptable range, whereas for the 2019 Intercomparison, the success rates were 96% and 4% outside the acceptable range. The potential failure of reading the dose value was in the film dosimeter/badge. For those recent two years of intercomparison activities, the success rate was more than 95%. This result of the intercomparison activity showed the excellent quality of the personal dose equivalent H<sub>p</sub>(10) and H<sub>p</sub>(3) measurement in Indonesia.</p>

GAMOS/GEANT4 simulation and comparison study of X-ray narrow-spectrum series at the national Secondary Standard Dosimetry Laboratory of Morocco

This study aimed to simulate the X-ray Irradiator narrow-spectrum series and compare the results with experimental and recommended values in ISO standards. X-Ray beam qualities of N-40 to N-300 were established experimentally at the national Secondary Standard Dosimetry Laboratory (SSDL) of Morocco in purpose of calibrating radiation protection- level. The variations between the first half-value layer (1st HVL) and the second (2nd HVL) for experimental were within 5%. Also, homogeneity coefficients h were mostly between 0.75 and 1 according to ISO. GAMOS Monte Carlo code was used to simulate the radiation quality of narrow-spectrum series between N-40 to N-150. All 1st HVL, 2nd HVL, and h simulation values were compare with experimental and ISO values. In MC codes and GAMOS, there is no direct way to generate the X-ray spectrum if we do not have details of the X-ray tube geometry, dimensions and materials. Therefore, Institute of Physics and Engineering in Medicine report number 78 was used to generate the X-ray spectrums in purpose to test this method accuracy. The simulation results for the 1st HVL and 2nd HVL showed a good agreement with experimental data and with ISO 4037–1:1996 given values. Also, the comparison results showed that most of the homogeneity coefficients are within the ISO standard range.

A feasibility study of using a 3D-printed tumor model scintillator to verify the energy absorbed to a tumor

The authors developed a volumetric dosimetry detector system using in-house 3D-printable plastic scintillator resins. Three tumor model scintillators (TMSs) were developed using magnetic resonance images of a tumor. The detector system consisted of a TMS, an optical fiber, a photomultiplier tube, and an electrometer. The background signal, including the Cherenkov lights generated in the optical fiber, was subtracted from the output signal. The system showed 2.1% instability when the TMS was reassembled. The system efficiencies in collecting lights for a given absorbed energy were determined by calibration at a secondary standard dosimetry laboratory (kSSDL) or by calibration using Monte Carlo simulations (ksim). The TMSs were irradiated in a Gamma Knife® Icon™ (Elekta AB, Stockholm, Sweden) following a treatment plan. The energies absorbed to the TMSs were measured and compared with a calculated value. While the measured energy determined with kSSDL was (5.84 ± 3.56) % lower than the calculated value, the energy with ksim was (2.00 ± 0.76) % higher. Although the TMS detector system worked reasonably well in measuring the absorbed energy to a tumor, further improvements in the calibration procedure and system stability are needed for the system to be accepted as a quality assurance tool.