Re-evaluation of the BIPM international dosimetry standards on adoption of the recommendations of ICRU Report 90

Burns, D T; Kessler, C

doi:10.1088/1681-7575/aacb01

Cited by 19 publications

(13 citation statements)

References 16 publications

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“…Based on a detailed analysis by Burns [9] of over 40 experimental measurements of either I g , W air , or their product W air S g, a , ICRU-90 recommends a value of 33.72 eV for the product W air S g, a with 0.08% uncertainty and to continue using the 33.97 eV value for W air , but increasing its uncertainty from 0.15% to 0.35%. Consequently, from the above recommendations, an S g, a value of 0.9926 follows with a similar uncertainty as W air , implying a 0.8% decrease from the previously accepted value of 1.0010 and in excellent agreement with the BIPM adopted value of 0.9928 [10].…”

Section: Introductionsupporting

confidence: 71%

Adoption of ICRU report 90 recommendations in the Canadian Co-60 air-kerma primary standard

Mainegra-Hing¹

2022

Metrologia

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The Canadian air-kerma primary standard for Co-60 beams is updated according to ICRU report 90 recommendations. The effect of these recommendations and a more detailed chamber model on the primary standard is investigated. Dosimetric quantities and corrections required for the realization of air kerma are calculated using the EGSnrc Monte Carlo simulation system. The validity of Spencer-Attix cavity theory as function of Δ, the secondary particle production threshold energy, is investigated to assess the accuracy of its current selection criterion. Although individual changes in some correction factors are statistically non-negligible, the overall effect amounts to only a 0.04% increase of the standard. The mean restricted mass-electronic stopping-power ratio graphite to air decreases from the previous value of 1.0010 to a value of 0.9949. If this value is used with the recommended Wair value of 33.97 eV, the effect on the standard is a reduction of 0.613%. When the recommended WairSca value of 33.72 eV is used instead, the change results in a 0.835% reduction in Kair. Using SA cavity theory to obtain Kair with a Δ value of 20 keV, corresponding to the cavity's mean chord length, reproduces a direct Monte Carlo calculation at the 0.03% level. Type B uncertainties due to uncertainty in the photon and electron cross sections for the largest corrections Kwall and Kcomp are estimated to be 0.01% and 0.10%, respectively. No statistically significant effect on the standard is observed due to changes in the correction factors. Fano tests and comparison to single scattering calculations demonstrate EGSnrc's electron transport algorithm accuracy to be within 0.03% relative to its own cross sections. The latter also validates the criterion for selecting Δ based on the average chord length of the chamber's cavity. A 0.2% difference in the restricted stopping power ratio obtained in this work and the value resulting from ICRU-90 recommendations has the potential for affecting standards relying on the absolute value of Wair, thus further investigation is granted. The current update results in a 0.8% decrease of the Canadian Co-60 air-kerma primary standard with a reduced uncertainty of 0.2%. This change is in excellent agreement with the reported change to the BIPM Co-60 air-kerma standard

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Section: Introductionsupporting

confidence: 71%

Adoption of ICRU report 90 recommendations in the Canadian Co-60 air-kerma primary standard

Mainegra-Hing¹

2022

Metrologia

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“…The uncertainties of 𝜌, (𝜇 en /𝜌) air,c , 𝑔 air , 𝑘 h , 𝑘 s and 𝐼 were chosen in accordance with our previous work [3,12,13]. The uncertainty of the product 𝑊 air 𝑠 c,a /𝑒 was chosen in accordance with the work of Burns et al [17]. The type A uncertainties of 𝑘 wall,ps , 𝑘 st , 𝑘 pn and 𝑘 sa represent the statistical uncertainties of the Monte Carlo simulations.…”

Section: Uncertainty Budgetmentioning

confidence: 99%

Characterization of new primary air kerma standards for dosimetry in Co-60, Cs-137 and Ir-192 gamma ray sources

Pojtinger¹,

Büermann²

2021

J. Inst.

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Introduction. To be better suited for measurements at air kerma rates which are common for the calibration of detectors for dosimetry in brachytherapy and radiation protection, two graphite-wall, air-filled cavity ionization chambers (PS-10 and PS-50 built by PTW of Freiburg, Germany) were characterized for use as primary standards at the Physikalisch-Technische Bundesanstalt (PTB) for 60Co, 137Cs and 192Ir gamma ray sources. Methods. Applying experimental or Monte Carlo methods, corrections were determined for wall effects, stem scattering effects, point-source non-uniformity, saturation effects, and deviations from Spencer-Attix cavity theory. The geometrical cavity volume of the ionization chambers was determined by a special experimental method. Non-charge-collecting parts of the volume were calculated by finite-element simulations. In addition, mass electronic stopping powers and mass-energy absorption coefficients were reevaluated in close agreement with ICRU 90. To compare the results to an already established air kerma standard, measurements of air kerma rates were taken for gamma rays from all three sources. Results. In contrast to the standards currently in use, the newly characterized ionization chambers show significant wall effects up to 4.17% (192Ir). For the PS-10 ionization chamber, the geometric volume differs by 0.42% from the charge collecting volume. For the ^192Ir source, Spencer-Attix corrections were applied exceeding 0.30% for both ionization chambers. Applying the derived corrections factors, air kerma rates measured with the two ionization chambers at the three sources did not differ by more than 0.13%. Comparing the results to an already established air kerma standard, deviations ranged up to 0.61%. The uncertainty budget for the determination of air kerma rates resulted in a relative combined standard uncertainty of 0.35%. Conclusion. Both ionization chambers can be used as primary air kerma standards for 60Co, 137Cs and 192Ir gamma ray sources using the values of corresponding physical quantities and correction factors derived in this work.

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“…The simulated air kerma rate and measured air kerma rate are expressed by a linear regression equation [12] for comparative analysis. The linear regression equation used in the accredited calibration laboratory has traceability to international measurement standards for air kerma [14]. Thus, model benchmarking will be more reliable.…”

Section: Jinst 15 P12014mentioning

confidence: 99%

Benchmarking FLUKA Monte Carlo code with international measurement standard for air kerma

Bak¹,

Heo²,

Min³

2020

J. Inst.

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Various Monte Carlo codes have been used for a long time in gamma ray calibration. However, to the best of our knowledge, no studies have employed the FLUKA MC code for the simulation of photon transport in an accredited calibration laboratory. This study aimed to model the benchmark of the international standard of the air kerma rate and the air kerma rates calculated by FLUKA simulation. As a comparative analysis tool, the linear regression equation used in the accredited calibration laboratory was used. After normalizing the measured and simulated values, a deviation of up to 1.0% was observed, and all the calculated air kerma rates were consistent within the uncertainty. In the analysis using the linear regression equation, the slope and interpolation uncertainty were consistent. Furthermore, the regression error was extremely small, and excellent linearity was observed. Thus, the coefficient of determination was calculated to be five or more. Since calibration sets the standard of every measurement, our study will encourage the application of FLUKA for simulations in various fields involving photons.

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Re-evaluation of the BIPM international dosimetry standards on adoption of the recommendations of ICRU Report 90

Cited by 19 publications

References 16 publications

Adoption of ICRU report 90 recommendations in the Canadian Co-60 air-kerma primary standard

Adoption of ICRU report 90 recommendations in the Canadian Co-60 air-kerma primary standard

Characterization of new primary air kerma standards for dosimetry in Co-60, Cs-137 and Ir-192 gamma ray sources

Benchmarking FLUKA Monte Carlo code with international measurement standard for air kerma

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