Secondary Standard Ionization Chamber Research Articles

Characterization of Inorganic Scintillator Detectors for Dosimetry in Image-Guided Small Animal Radiotherapy Platforms.

The purpose of the study was to characterize a detection system based on inorganic scintillators and determine its suitability for dosimetry in preclinical radiation research. Dose rate, linearity, and repeatability of the response (among others) were assessed for medium-energy X-ray beam qualities. The response's variation with temperature and beam angle incidence was also evaluated. Absorbed dose quality-dependent calibration coefficients, based on a cross-calibration against air kerma secondary standard ionization chambers, were determined. Relative output factors (ROF) for small, collimated fields (≤10 mm × 10 mm) were measured and compared with Gafchromic film and to a CMOS imaging sensor. Independently of the beam quality, the scintillator signal repeatability was adequate and linear with dose. Compared with EBT3 films and CMOS, ROF was within 5% (except for smaller circular fields). We demonstrated that when the detector is cross-calibrated in the user's beam, it is a useful tool for dosimetry in medium-energy X-rays with small fields delivered by Image-Guided Small Animal Radiotherapy Platforms. It supports the development of procedures for independent "live" dose verification of complex preclinical radiotherapy plans with the possibility to insert the detectors in phantoms.

EURAMET DOSEtrace supplementary comparison in terms of the ambient dose equivalent/rate for photon radiation (EURAMET.RI(I)-S18)

Main textA supplementary comparison in terms of the ambient dose equivalent/rate was organized within EURAMET as a part of the DOSEtrace project, between 13 national metrology institutes and designated institutes. Calibration coefficients were compared for a secondary standard ionisation chamber for 3 X-ray and 2 γ-ray radiation qualities used in the field of radiation protection. Radiation qualities were established according to ISO 4037-1. Measurements were performed between 2019 and 2021.For the purpose of this comparison, it was considered that the reported uncertainty was confirmed if the relative deviation from the comparison reference value was smaller than or equal to the associated uncertainty. All the reported results by all the partners satisfied this criterium. Three participants were not able to perform calibrations in all mandatory radiation qualities, due to technical problems. The results are published in the Key Comparison Data Base (KCDB) of the BIPM as supplementary comparison EURAMET.RI(I)-S18.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Determination of beam quality correction factors for the Roos plane-parallel ionisation chamber exposed to very high energy electron (VHEE) beams using Geant4

Detailed characterisation of the Roos secondary standard plane-parallel ionisation chamber has been conducted in a novel 200 MeV Very High Energy Electron (VHEE) beam with reference to the standard 12 MeV electron calibration beam used in our experimental work. Stopping-power-ratios and perturbation factors have been determined for both beams and used to calculated the beam quality correction factor using the Geant4 general purpose MC code. These factors have been calculated for a variety of charged particle transport parameters available in Geant4 which were found to pass the Fano cavity test. Stopping-power-ratios for the 12 MeV electron calibration beam quality were found to agree within uncertainties to that quoted by current dosimetry protocols. Perturbation factors were found to vary by up-to 4% for the calibration beam depending on the parameter configuration, compared with only 0.8% for the VHEE beam. Beam quality correction factors were found to describe an approximately 10% lower dose than would be originally calculated if a beam quality correction were not accounted for. Moreover, results presented here largely resolve unphysical chamber measurements, such as collection efficiencies greater than 100%, and assist in the accurate determination of absorbed dose and ion recombination in secondary standard ionisation chambers.

Evaluation of a micro ionization chamber for dosimetric measurements in image-guided preclinical irradiation platforms

Image-guided small animal irradiation platforms deliver small radiation fields in the medium energy x-ray range. Commissioning of such platforms, followed by dosimetric verification of treatment planning, are mostly performed with radiochromic film. There is a need for independent measurement methods, traceable to primary standards, with the added advantage of immediacy in obtaining results. This investigation characterizes a small volume ionization chamber in medium energy x-rays for reference dosimetry in preclinical irradiation research platforms. The detector was exposed to a set of reference x-ray beams (0.5–4 mm Cu HVL). Leakage, reproducibility, linearity, response to detector’s orientation, dose rate, and energy dependence were determined for a 3D PinPoint ionization chamber (PTW 31022). Polarity and ion recombination were also studied. Absorbed doses at 2 cm depth were compared, derived either by applying the experimentally determined cross-calibration coefficient at a typical small animal radiation platform ‘user’s’ quality (0.84 mm Cu HVL) or by interpolation from air kerma calibration coefficients in a set of reference beam qualities. In the range of reference x-ray beams, correction for ion recombination was less than 0.1%. The largest polarity correction was 1.4% (for 4 mm Cu HVL). Calibration and correction factors were experimentally determined. Measurements of absorbed dose with the PTW 31022, in conditions different from reference were successfully compared to measurements with a secondary standard ionization chamber. The implementation of an End-to-End test for delivery of image-targeted small field plans resulted in differences smaller than 3% between measured and treatment planning calculated doses. The investigation of the properties and response of a PTW 31022 small volume ionization chamber in medium energy x-rays and small fields can contribute to improve measurement uncertainties evaluation for reference and relative dosimetry of small fields delivered by preclinical irradiators while maintaining the traceability chain to primary standards.

THE IN-SITU CALIBRATION METHOD FOR AMBIENT DOSE EQUIVALENT DOSEMETERS.

Ambient dose equivalent dosemeters are widely distributed in nuclear facilities for routine continuous monitoring or nuclear accident emergency monitoring, they are inconvenient to be disassembled and sent to the metrology laboratory for calibration. To ensure the accuracy of such dosemeters, the research of in-situ calibration method has been carried out. Ambient dose equivalent secondary standard ionization chamber and portable gamma ray irradiation facility have been designed for in-situ calibration. The experiments of in-situ calibration were carried out in five typical sites located in China Institute of Atomic Energy, results showed that the relative deviation between in-situ calibration factors and metrology laboratory calibration factors are within 5%.The combined standard uncertainty of the in-situ calibration factor is 2.8%, and the expanded uncertainty is 5.6% (k=2).The in-situ calibration method can meet the calibration requirements of the fixed ambient dose equivalent dosemeters.

The operation of an ionization chamber with depleted gas for radioactivity measurement: Calibration procedure and utilising normalized manufacturer's radionuclide factors

At the National Metrology Institute of South Africa (NMISA) absolute activity measurements of γ-emitting radionuclides are maintained for longevity on a secondary standard ionization chamber. Because the ionization chamber has lower gas pressure than that normally produced by the manufacturer, this paper focuses attention on explaining a normalization scheme devised to allow NMISA to make use of the manufacturer's supplied radionuclide calibration factors when necessary. The applicability of the procedure is justified through analysis of some results from a comprehensive simulation of the chamber undertaken in an independent study. Comparisons of the derived normalized calibration factors against those obtained through measurement at NMISA are made for a variety of radionuclides.

Calibration and measurement of X-ray personal dose equivalent with a Hp(10) ionization chamber

The value of the personal dose equivalent at a 10 mm depth is to characterize the energy deposition of strong penetrating radiation in the human body and is derived by measurement of air kerma and application of conversion coefficients from the ISO report. However, the conversion coefficients depend strongly on the photon energy and angles of incidence for low-energy photons. In order to overcome the problem that the conversion coefficient of low energy rays changes greatly due to the small change of energy, a secondary standard ionization chamber was used to measure the personal dose equivalent directly. A matched reference field was established with 20-250 kV X-rays and correction factors with the Hp (10) chamber were calculated under these radiation qualities with different angles of incidence. The results showed that the differences were almost 22.7 % of correction factors for the low energy photons at angles of incidence 0?. With the conversion coefficient recommended in ISO 4037-3-2019, the performance of the chamber response with respect to Hp (10) in the energy range from 33 keV to 208 keV was within about 10 %, and in the energy range from 12 keV to 208 keV and for angles of incidence between 0? and 75? was within about ?19 %.

An international multi-center investigation on the accuracy of radionuclide calibrators in nuclear medicine theragnostics

BackgroundPersonalized molecular radiotherapy based on theragnostics requires accurate quantification of the amount of radiopharmaceutical activity administered to patients both in diagnostic and therapeutic applications. This international multi-center study aims to investigate the clinical measurement accuracy of radionuclide calibrators for 7 radionuclides used in theragnostics: 99mTc, 111In, 123I, 124I, 131I, 177Lu, and 90Y.MethodsIn total, 32 radionuclide calibrators from 8 hospitals located in the Netherlands, Belgium, and Germany were tested. For each radionuclide, a set of four samples comprising two clinical containers (10-mL glass vial and 3-mL syringe) with two filling volumes were measured. The reference value of each sample was determined by two certified radioactivity calibration centers (SCK CEN and JRC) using two secondary standard ionization chambers. The deviation in measured activity with respect to the reference value was determined for each radionuclide and each measurement geometry. In addition, the combined systematic deviation of activity measurements in a theragnostic setting was evaluated for 5 clinically relevant theragnostic pairs: 131I/123I, 131I/124I, 177Lu/111In, 90Y/99mTc, and 90Y/111In.ResultsFor 99mTc, 131I, and 177Lu, a small minority of measurements were not within ± 5% range from the reference activity (percentage of measurements not within range: 99mTc, 6%; 131I, 14%; 177Lu, 24%) and almost none were outside ± 10% range. However, for 111In, 123I, 124I, and 90Y, more than half of all measurements were not accurate within ± 5% range (111In, 51%; 123I, 83%; 124I, 63%; 90Y, 61%) and not all were within ± 10% margin (111In, 22%; 123I, 35%; 124I, 15%; 90Y, 25%). A large variability in measurement accuracy was observed between radionuclide calibrator systems, type of sample container (vial vs syringe), and source-geometry calibration/correction settings used. Consequently, we observed large combined deviations (percentage deviation > ± 10%) for the investigated theragnostic pairs, in particular for 90Y/111In, 131I/123I, and 90Y/99mTc.ConclusionsOur study shows that substantial over- or underestimation of therapeutic patient doses is likely to occur in a theragnostic setting due to errors in the assessment of radioactivity with radionuclide calibrators. These findings underline the importance of thorough validation of radionuclide calibrator systems for each clinically relevant radionuclide and sample geometry.

Assessment of calibration coefficient ND, W in terms of absorbed dose-to-water of some ionization chambers

The absorbed dose-to-water calibration coefficients ND,W of some ionization chambers were determined in terms of the secondary standard chambers in 60Co gamma-ray beam based on the TRS-398 protocol. The reference absorbed dose-to-water Dw were measured using secondary standard ionization chambers of model NE 2781#0537 (0.60 cm3 volume) and NE 2771#1205 (0.69 cm3 volume) which are traceable to the dosimetry laboratory of the International Atomic Energy Agency (IAEA). This study mainly focuses on the comparative assessment of the determined ND,W coefficients of twenty cylindrical ionization chambers from various user groups. The determined ND,W coefficients were compared with the manufacturer provided ND,W coefficients. The observed percentage of deviation between the measured and the manufacturer’s ND,W coefficients among all the chambers were found to be in the range of 0.019% and -2.263% as the least and highest, respectively. The observed percentage of deviations for studied chambers were found within the IAEA’s acceptance limit of 1.5% with an exception for three chambers. This observed discrepancy with the IAEA’s acceptance limit for the three chambers out of the twenty chambers, indicates the calibration necessity before using chambers in routine reference dosimetry. In ND,W measurement, the uncertainty Uc is reported with the coverage factor k=1 that providing a level of confidence of approximately 68%.

Primary standardization of 224Ra activity by liquid scintillation counting

A standard for activity of 224Ra in secular equilibrium with its progeny has been developed, based on triple-to-double coincidence ratio (TDCR) liquid scintillation (LS) counting. The standard was confirmed by efficiency tracing and 4παβ(LS)-γ(NaI(Tl)) anticoincidence counting, as well as by 4πγ ionization chamber and NaI(Tl) measurements. Secondary standard ionization chambers were calibrated with an expanded uncertainty of 0.62% (k = 2). Calibration settings were also determined for a 5 mL flame-sealed ampoule on several commercial reentrant ionization chambers (dose calibrators).

Standardisation of Rhenium-188 and determination of calibration factors for secondary standard and radionuclide calibrator

The use of Rhenium-188 for various therapeutic applications in the field of nuclear medicine has increased in recent years due to its favourable properties like decay scheme, cost effective availability and easy chemistry. Two independent measuring setups were used to standardise 188Re radioactive solution. The modus operandi of standardisation was 4πβ-γ coincidence technique where the beta detection was done by proportional counting and liquid scintillation counting and the gamma detection was done by using NaI(Tl) detectors. The secondary standard, high pressure ionisation chamber type Centronic IG12, 20A was calibrated with the standardised 188Re solution and the sensitivity coefficient (pA MBq−1) was determined. To enhance the accuracy of the commercial radionuclide calibrator and to ensure that patients receive optimum dose of these radiopharmaceuticals, calibration number of the Capintec CRC-15β radionuclide calibrator was also verified. This paper presents the standardisation of 188Re radioactive solution by primary methods and calibration of BARC secondary standard ionisation chamber system and a Capintec CRC-15β radionuclide calibrator.

A reference material for evaluation of 137 Cs radiochronometric measurements.

A new nuclear forensic reference material has been characterized as a standard for radiochronometric determination of the model purification date for 137Cs sources. The purification date of a radioactive source is a potentially diagnostic nuclear forensic signature for determining the provenance of a radioactive material. Reference values have been measured for the attributes needed to use the 137Cs/137Ba chronometer: the molality (reported here as nmol g-1) of 137Cs and of the radiogenic portion of 137Ba in the material (hereafter referred to as 137Ba*). All measurement results were decay-corrected to represent the composition of the material on the reference date of July 7, 2011. The molality of 137Cs is (0.7915 ± 0.0073) nmol g-1; this value was calculated from the massic activity of 137Cs, (348.4 ± 3.0) kBq g-1, as measured in the NIST 4π-γ secondary standard ionization chamber (previously calibrated by 4π-(e+x)-γ-coincidence efficiency extrapolation counting) and the evaluated half-life of 137Cs, (30.05 ± 0.08) years. The molality of 137Ba*, (1.546 ± 0.024) nmol g-1, was measured by isotope dilution mass spectrometry using the measured relative proportion of 138Ba in the material to apply a correction for the 137Ba contribution from natural Ba. A model age of (47.04 ± 0.56) years, corresponding to a model purification date of June 22, 1964 with an expanded uncertainty of 200 days is calculated from the reference material values. This age is consistent with the date engraved on the capsule that contained the 137Cs starting material and with a prior independent determination of the model purification date. A full discussion of the uncertainties of the reference material values is included.

Production and standardization of an on-demand protactinium-233 tracer

Protactinium-233 (233Pa) was generated by neutron activation of thorium and isolated by column chromatography using an octanol-impregnated resin. Absolute activity standardization was performed on 233Pa using three independent methods, the results of which agreed within their associated uncertainties. The standardized 233Pa was used to calibrate a secondary standard ionization chamber and high purity germanium detectors to enable a rapid and traceable method for the production and quantification of this radiotracer.

P093] Long-term quality control and intercomparison results of radionuclide dose calibrators

Purpose Nuclear medicine procedure quality is critically dependent on the accuracy of dose calibrators. The aim of this study is to assess the accuracy of measurements of three dose calibrators. For a more accurate evaluation of the measuring equipment, a comparison was done between those dose calibrators and the secondary standard radionuclide calibrator traceable to National metrology institute. Methods The study was performed with Veenstra VDC-404, Veenstra VDC-405 and PITAGORA dose calibrators in Nuclear medicine department. These dose calibrators were compared with Capintec CRC-15R that was used as a secondary reference standard ionization chamber. This intercomparison was done with 99mTc, 18F, 123I and 137Cs. For relative response assessment 137Cs was used as a check source. Linearity checks were fulfilled with 99mTc for Veenstra VDC-405 and 18F sources for PITAGORA. Results The results of the intercomparison show that the uncertainty for Veenstra VDC-404 and Veenstra VDC-405 was 1.5 % at a coverage factor k = 2 when using 99mTc in both P6 vial and in a 1 ml syringe, while it was 3.5 % ( k = 2 ) for 123I, and a linearity deviation was less than 3.1 % ( k = 2 ) . The uncertainty for PITAGORA was 0.7 % ( k = 1) when using 18F in P6 vial, for 137Cs using P6 vial the geometry factor uncertainty was 0.7 % ( k = 1), the linearity deviation was 2.0 %. Constancy measurements accuracies were within 3 % ( k = 2 ) of the decay-corrected values for all radionuclide dose calibrators. Conclusions Quality control and intercomparison measurements of dose calibrators are an important part of nuclear medicine quality assurance program. In accordance with international recommendations, our results are within 5–10 % of the recommended values. Daily control with a long half-life check source allows detecting potential failure of the ionization chamber components and enabling the staff to reduce the probability of an incorrect injection of radiopharmaceuticals’ activity to the patients. The intercomparisons could identify problems in both calibration and uncertainty evaluation.

EURAMET supplementary comparison of ambient dose equivalent H*(10) in 137Cs and ISO Narrow Beam Series N-60 x-ray beams at low dose rates

Comparison measurements among national standards laboratories are required to demonstrate their equivalence in the realization and transfer of the quantity ambient dose equivalent, H*(10), for photon radiation by these laboratories.The first comparison of the radiation protection quantity H*(10) with focus on the special needs for calibration of area dosemeters, low dose rates and large fields, started in January 2013 and was completed in December 2014. The comparison was piloted by the PTB as EURAMET project No. 1132 known also as EURAMET.RI(I)-S11.The operation and results of the comparison are reported here. The transfer instrument was a secondary standard ionization chamber for H*(10) with a volume of 10000 cm3. The response of this transfer instrument in various photon reference fields (N-60 and 1 mSv/h, S-Cs and 10 μSv/h, S-Cs and 1 mSv/h, radiation quality according to ISO 4037-1:1996 [1]) was compared.Measurements were made by the fourteen participants from the following countries: Germany, Austria, Greece, Norway, Sweden, Finland, Portugal, Spain, Czech Republic, Romania, the Netherlands, Slovenia, Italy and by one international organization. The results obtained by almost all of the participants are consistent with the stated uncertainties.KEY WORDS FOR SEARCHDosimetry, comparison, ambient dose equivalent, ISO narrow beam, EURAMET, CIPM MRA, BIPM KCDBMain textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Development of the Australian Standard for Germanium-68 by two Liquid Scintillation Counting methods

In response to the increasing application of 68Ge/68Ga and 68Ga in nuclear medicine, an international comparison of activity measurement of 68Ge in equilibrium with 68Ga was organised. ANSTO standardised the comparison solution by the 4π(LS)β+-γ coincidence extrapolation and TDCR efficiency calculation methods, with excellent agreement between the two results. The primary standard was transferred to the ANSTO Secondary Standard Ionisation Chamber. Internationally traceable Australian Certified Reference Materials (ACRMs) of 68Ge/68Ga can now be prepared in various measurement geometries applied in nuclear medicine.

Standardisation of 90Y and determination of calibration factors for 90Y microspheres (resin) for the NPL secondary ionisation chamber and a Capintec CRC-25R

The use of 90Y resin microspheres (SIR-Spheres® microspheres) in Nuclear Medicine has dramatically increased in recent years due to its favourable outcome in the treatment of liver cancer and liver metastases (Rajekar et al., 2011). The measurement of administered activity before and residual activity after treatment in radionuclide calibrators is required to determine total activity delivered to the patient. In comparison with External Beam Radiotherapy (EBRT) where administered doses are often know to within ±5%, the actual administered activity in nuclear medicine procedures may only be known to within ±20% and subsequent dose calculations can result in even larger uncertainties (Fenwick et al., 2009). It is a well-recognised issue that ion chambers are instruments that are sensitive to the measurement geometry and matrix of a source, in particular for pure beta or low energy (<100keV) x-ray emitters (Gadd et al., 2006). This paper presents new calibration factors for NPL secondary standard ionisation chamber system (Vinten 671) and a Capintec CRC-25R radionuclide calibrator along with a discussion of the measurement problems associated with this radionuclide and matrix. Calibration of the NPL secondary standard system for this measurement matrix will enable NPL to provide standards for the Nuclear Medicine community and consequently increase the measurement capability.

Traceability from governmental producers of radiopharmaceuticals in measuring 18F in Brazil

Since the inception of its proficiency test program to evaluate radionuclide measurement in hospitals and clinics, the National Metrology Laboratory of Ionizing Radiation-LNMRI, that represents Brazilian National Metrology Institute (NMI) for ionizing radiation has expanded its measurement and calibration capability.Requirements from the National Health Surveillance Agency from Ministry of Health (ANVISA), to producers of radiopharmaceuticals provided an opportunity to improve the full traceability chain to the highest level.Fluorodeoxyglucose (FDG-18F) is the only radiopharmaceutical simultaneously produced by all Brazilian radiopharmaceutical production centers (RPCs). By running this proficiency test, LNMRI began to provide them with the required traceability.For evaluation, the ratio of RPC to reference value results and ISO/IEC17043:2010 criteria were used.The reference value established as calibration factor on the secondary standard ionization chamber was obtained from three absolute measurements systems, and routinely confirmed in each round of proficiency test by CIEMAT/NIST liquid scintillation counting. The γ-emitting impurities were checked using a High-Purity Germanium (HPGe) detector.The results show that Brazilian RPCs are in accordance with (accuracy within ±10%) the Brazilian standard for evaluation of measurements with radionuclide calibrators (CNEN NN 3.05., 2013). Nevertheless, the RPCs should improve the methodology of uncertainty estimates, essential when using the statistical criteria of ISO/IEC 17043 standard, in addition to improving accuracy to levels consistent with their position in the national traceability chain

Dose measurements in pulsed radiation fields with commercially available measuring components.

Dose measurements in pulsed radiation fields with dosemeters using the counting technique are known to be inappropriate. Therefore, there is a demand for a portable device able to measure the dose in pulsed radiation fields. As a detector, ionisation chambers seem to be a good alternative. In particular, using a secondary standard ionisation chamber in combination with a reliable charge-measuring system would be a good solution. The Physikalisch-Technische Bundesanstalt (PTB) uses secondary standard ionisation chambers in combination with PTB-made measuring electronics for dose measurements at its reference fields. However, for general use, this equipment is too complex. For measurements on-site, a mobile special electronic system [Hupe, O. and Ankerhold, U. Determination of ambient and personal dose equivalent for personnel and cargo security screening. Radiat. Prot. Dosim. 121: (4), 429-437 (2006)] has been used successfully. Still, for general use, there is a need for a much simpler but a just as good solution. A measuring instrument with very good energy dependence for H*(10) is the secondary standard ionisation chamber HS01. An easy-to-use and commercially available electrometer for measuring the generated charges is the UNIDOS by PTW Freiburg. Depending on the expected dose values, the ionisation chamber used can be selected. In addition, measurements have been performed by using commercially available area dosemeters, e.g. the Mini SmartION 2120S by Thermo Scientific, using an ionisation chamber and the Szintomat 6134 A/H by Automess, using a scintillation detector.

Revision of the NIST Standard for (223)Ra: New Measurements and Review of 2008 Data.

After discovering a discrepancy in the transfer standard currently being disseminated by the National Institute of Standards and Technology (NIST), we have performed a new primary standardization of the alpha-emitter 223Ra using Live-timed Anticoincidence Counting (LTAC) and the Triple-to-Double Coincidence Ratio Method (TDCR). Additional confirmatory measurements were made with the CIEMAT-NIST efficiency tracing method (CNET) of liquid scintillation counting, integral γ-ray counting using a NaI(Tl) well counter, and several High Purity Germanium (HPGe) detectors in an attempt to understand the origin of the discrepancy and to provide a correction. The results indicate that a −9.5 % difference exists between activity values obtained using the former transfer standard relative to the new primary standardization. During one of the experiments, a 2 % difference in activity was observed between dilutions of the 223Ra master solution prepared using the composition used in the original standardization and those prepared using 1 mol·L−1 HCl. This effect appeared to be dependent on the number of dilutions or the total dilution factor to the master solution, but the magnitude was not reproducible. A new calibration factor (“K-value”) has been determined for the NIST Secondary Standard Ionization Chamber (IC “A”), thereby correcting the discrepancy between the primary and secondary standards.