Three active detectors, Exradin A26 chamber, IBA RAZOR Nano chamber, and PTW 60019 microDiamond, were characterized for their use in electronic BrachyTherapy (eBT) dosimetry. The detectors were calibrated in terms of air kerma using the ISO “N” (narrow) and “TW” (therapy) X-rays series from 7.5 kV to 100 kV. The responses to mono-energetic photons and their uncertainties were determined with Bayesian parameter estimation, assuming a model that incorporated smoothness via a spline function. The response functions obtained this way are consistent with 18 calibration qualities simultaneously. This approach improves on the traditional procedure of associating the response to the mean energy of the corresponding spectra. The energy responses (with uncertainties) were obtained in 0.25 keV energy steps from 6 keV to 70 keV. With differences in magnitude due to their sizes and the nature of their active volumes, the energy responses of the 3 detectors follow a similar relative behaviour. Even when the response is far from flat at low energies, i.e. below about 20 keV, the determination of reliable energy dependence curves enables the use of these detectors for dosimetry in the vicinity of eBT units. The angular dependence of the three detectors with respect to beam incidence was also measured in air in a 180° range in steps of 10° using the Zeiss INTRABEAM system (50 kV). For both energy and angular response characterization, the detectors axis were aligned in parallel with the beam axis (end-on), since this is the expected orientation in further measurements of absorbed dose distribution in water around eBT sources at PTB. This work is an effort to provide traceability for detectors and measurement procedures for the determination of 3D dose distributions as part of the ongoing European EMPIR project “Primary standards and traceable measurement methods for X-ray emitting electronic brachytherapy devices” (PRISM-eBT)”.

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.

The air kerma calibration coefficients of a set of four transfer ionization chambers and the air kerma-length product calibration coefficients for a set of two transfer pencil-type ionization chambers were compared at the PTB, Germany, and the CPHR, Cuba, for 15 selected radiation qualities as used in mammography, general diagnostic radiology, computed tomography, radiation therapy and radiation protection. The CPHR performed its measurements in the period January to September 2017 and the PTB before (November 2016) and after (December 2017) that period. The comparison results for the selected beam qualities expressed as the ratio of calibration coefficients were in the range (0.98-1.01) and mostly (12 out of 18) consistent within the relative standard uncertainty of the comparison which ranged between 0.6 % and 1 %. Five results were within the extended (k=2) standard uncertainty. One result deviated relatively by 1.9%. A possible reason for the larger deviation is discussed. The results are published in the Key Comparison Data Base (KCDB) of the BIPM as supplementary comparison COOMET.RI(I)-S4.Main 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).

The air kerma calibration coefficients of a set of four transfer ionization chambers and the air kerma-length product calibration coefficients for a set of two transfer pencil-type ionization chambers were compared at the PTB, Germany, and the CPHR, Cuba, for 15 selected radiation qualities as used in mammography, general diagnostic radiology, computed tomography, radiation therapy and radiation protection. The CPHR performed its measurements in the period January to September 2017 and the PTB before (November 2016) and after (December 2017) that period. The comparison results for the selected beam qualities expressed as the ratio of calibration coefficients were in the range (0.98-1.01) and mostly (12 out of 18) consistent within the relative standard uncertainty of the comparison which ranged between 0.6 % and 1 %. Five results were within the extended (k=2) standard uncertainty. One result deviated relatively by 1.9%. A possible reason for the larger deviation is discussed. The results are published in the Key Comparison Data Base (KCDB) of the BIPM as supplementary comparison COOMET.RI(I)-S4. Main text 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 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).

the CT number of water, the CT number of iodine, the contrast-tonoise ratio (CNR) and linearity were evaluated in both image stacks using open-source image processing software.Results.In general, the Mono+ images resulted in better image quality.A significant noise reduction was found at low keV using this technique, with a maximum reduction of 50% at 40 keV, compared to the Mono images.The Mono+ images also provided an increased iodine CNR at lower keVs, moving the optimum CNR from 60 keV to 40 keV.Conclusions.The Mono+ algorithm for creation of virtual monoenergetic images was shown to be superior to the Mono algorithm, especially for low keVs.

The purpose of this work is to develop viable procedures for verifying the applicability of personalized dosimetry in computed tomography (CT) using Monte Carlo-based simulations. Mobile equipment together with customized software was developed and used for rapid, non-invasive determination of equivalent source models of CT scanners under clinical conditions. Standard and anthropomorphic CT dose phantoms equipped with real-time CT dose probes at five representative positions were scanned. The accumulated dose was measured during the scan at the five positions. ImpactMC, a Monte Carlo-based CT dose software program, was used to simulate the scan. The necessary inputs were obtained from the scan parameters, from the equivalent source models and from the material-segmented CT images of the phantoms. Post-scan 3D dose distributions in the phantoms were simulated and the dose values calculated at the five positions inside the phantom were compared to measured dose values. Initial results were obtained by means of a General Electric Optima CT 660 and a Toshiba (Canon) Aquilion ONE. In general, the measured and calculated dose values were within relative uncertainties that had been estimated to be less than 10%. The procedures developed, which allow the post-CT scan dose to be measured and calculated at five points inside anthropomorphic phantoms, were found to be viable and rapid. The procedures are applicable to any scanner type under clinical conditions. Results show that the procedures are well suited for verifying the applicability of personalized CT dosimetry based on post-scan Monte Carlo calculations.

Comparing the data across the departments revealed no systematic differences based on the absorbed dose protocol each department followed.There may be a slight difference in the determination of relative output of the different applicators depending on the ion chamber used for output factor measurements, but with limited data available this remains inconclusive.The 90% and 85% dose to water range of x-rays agree between the departments within 1 mm for similar beam qualities, even though different methods were used to determine the depth dose deposition.Conclusions.A national comparison of kV radiotherapy units was conducted, and overall the units were found very similar.No systematic differences were observed based on the calibration protocol, but the available data hint that the choice of ion chamber for calibration measurements may have a small effect on the determination of output factors.

With improvements in CT technology, the need for reliable patient-specific dosimetry increased in the recent years. The accuracy of Monte-Carlo simulations for absolute dose estimation is related to scanner specific information on the X-ray spectra of the scanner as well as the form filter geometries and compositions. In this work a mobile measurement setup is developed, which allows both to determine the X-ray spectra and equivalent form filter of a specific scanner from just one helical scan in less than 2 minutes.

This report presents the results of the first international comparison of primary measurement standards of absorbed dose to water for the medium-energy X-ray range. Three of the participants (VSL, PTB, LNE-LNHB) used their existing water calorimeter based standards and one participant (ENEA) recently developed a new standard based on a water-graphite calorimeter. The participants calibrated three transfer chambers of the same type in terms of absorbed dose to water ( N D w ) and in addition in terms of air kerma ( N K ) using the CCRI radiation qualities in the range 100 kV to 250 kV. The additional NK values were intended to be used for a physical analysis of the ratios N D w / N K . All participants had previously participated in the BIPM.RI(I)-K3 key comparison of air kerma standards. Ratios of pairs of NMI's N K results of the current comparison were found to be consistent with the corresponding key comparison results within the expanded uncertainties of 0.6 % - 1 %. The N D w results were analysed in terms of the degrees of equivalence with the comparison reference values which were calculated for each beam quality as the weighted means of all results. The participant's results were consistent with the reference value within the expanded uncertainties. However, these expanded uncertainties varied significantly and ranged between about 1-1.8 % for the water calorimeter based standards and were estimated at 3.7 % for the water-graphite calorimeter. It was shown previously that the ratios N D w / N K for the type of ionization chamber used as transfer chamber in this comparison were very close (within less than 1 %) to the calculated values of (μ̄ en /ρ) w,a d , the mean values of the water-to-air ratio of the mass-energy-absorption coefficients at the depth d in water. Some of the participant's results deviated significantly from the expected behavior. Main text 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 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).

Introduction: While radiotherapy dosimetry is traceable to absorbed dose to water (Dw) primary standards in high-energy photon, electron, proton, and ion beams, this is not the case for other radiotherapy modalities, including low- and medium-energy x-rays. Activities within workpackage 1 (WP1) of the EMRP HLT09 project “MetrExtRT” have been outlined to fill this gap for medium-energies with reference conditions as in the IAEA 398 protocol.

Non-invasive methods to determine equivalent X-ray source models of a CT scanner are presented. A high-precision technique called TRIC ("Time Resolved Integrated Charge") was developed and used to characterize the bow tie filters (BT) of the CT scanner installed at Physikalisch-Technische Bundesanstalt (PTB). Aluminum (Al) and polymethyl methacrylate (PMMA) equivalent thicknesses of the BT filters at all tube high voltages were evaluated, assuming that those consist of only one material. Thereby two different dose probes were used, a solid state detector and an ionization chamber, the former characterized by a significant and the latter by an almost negligible energy dependence of the air kerma response. A method was developed to correct for the energy dependence of the solid state dose probe. Next, a two-component material was assumed and equivalent BT filters were evaluated. The latter method was also applied using the known real BT filter materials and compared with the shape of the real BT filters. Finally, the results obtained by the TRIC method were compared with those obtained by using the so-called COBRA method ("Characterization Of Bow tie Relative Attenuation"), the latter being more suitable for measurements in a clinical environment.

The EURAMET #1177 project, identified as EURAMET RI(I) - S9 comparison, was the first EURAMET wide scale supplementary comparison in the field of diagnostic radiology for air kerma area product, PKA, and air kerma, K. It was conducted with the goal of testing the measurement and calibration capabilities for PKA and K, as well as of supporting the relevant CMCs of the participating laboratories. Two commercial KAP meters and an ionization chamber were selected as transfer instruments and circulated between the 22 European participants. The measurements were performed from April 2011 until July 2012. The stability and the performance of the transfer instruments were tested by the pilot laboratory (IRCL/GAEC-EIM) and few other laboratories as well. The test results revealed that the energy (radiation quality), Q, irradiation area, A, and air kerma rate, K̇ dependences of response of the transfer KAP meters influence the comparison of the results when different measurement conditions were pertained and therefore, appropriate correction factors were obtained and applied to the reported calibration results of the laboratories, when necessary. The comparison reference values (CRVs) for each instrument were determined as the weighted mean of the calibration coefficients of the three participating primary laboratories. The relative standard uncertainty of the CRVs were in the range of (0.4 - 1.6)% depending on the transfer instruments and beam qualities. The comparison result as the ratio of the corrected calibration coefficient of participant and the respective CRV, and its uncertainty were calculated for all beam qualities and transfer instruments. The informative degrees of equivalence (DoE) were calculated for the refrence RQR 5 beam quality. In case of air kema area product measurements the results for the RADCAL PDC KAP meter were used. The 216 KAP meter calibration results of the two different transfer instruments in terms of air kerma area product were consistent within 5% except 40 results of 8 participants. The 103 air kerma calibration results were consistent within 1.7%, except 10 results of 4 participants. Main text 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 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).

A comparison of air kerma-length product determinations for standard radiation qualities defined for use in computed tomography was performed between the PTB and the IAEA as EURAMET project #1327, registered in the KCDB as the EURAMET.RI(I)-S12 comparison. A pencil type reference-class ionization chamber of the IAEA and the three RQT beam qualities established according to the IEC standard 61627:2005 were selected for the comparison. The calibration coefficients for the transfer chamber in terms of Gycm/C at the PTB and the IAEA using the partial irradiation method recommended in the IAEA TRS 457 were determined. The results show the calibration coefficients of both laboratories were in a very good agreement of about 0.2 % well within the estimated relative standard uncertainty of the comparison of about 0.8 %. Residual correction due to the additional aperture required for partial irradiation of pencil chambers and feasibility of the full irradiation method were also studied. Main text. 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 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).

In recent years dosimetry in computed tomography (CT) based on Monte Carlo (MC) simulation has significantly increased. A proper description of scanner parameters is required for an accurate MC simulation. The characterization of bow-tie filters (BT) in the CT scanners is a necessary part of MC simulations. Up to the present time, methods have been developed and used in different works to characterize the BT filters of different scanners [1,2]. The methods were based on a comparison of the calculated and measured air kerma attenuation profile as a function of the fan angle. Thereby, an aluminium-equivalent BT filter with an arbitrarily assumed central ray thickness was determined. The goal of the present work was to improve these methods by the absolute determination of the central ray thickness of the BT filter. The scanner used in this work was a GE Optima 660 with two different BT filters. An almost energy-independent responding ionization chamber (i-chamber) of the type Radcal 10x6-0.6CT was used to measure the air kerma rate profile along the x-axis of the CT gantry.

Ziele: Die Diagnostik der weiblichen Brust stellt höchste Anforderungen an die Bildgebung. Um diese zu erreichen, bestehen hohe Anforderungen an die verwendeten Mammografiegeräte. Die Qualität von Mammografiegeräten wird unter anderem mithilfe von Prüfkörpern, z.B. dem CDMAM-Prüfkörper, kontrolliert. Mängel an den Prüfkörpern wirken sich unmittelbar auf Prüfresultate und damit die Entscheidung aus, ob ein Mammografiegerät für Untersuchungen geeignet ist oder nicht.

The results of an unprecedented international effort involving 26 countries are reported. The EUROMET.RI(I)-K1 and EUROMET.RI(I)-K4 key comparisons were conducted with the goal of supporting the relevant calibration and measurement capabilities (CMC) planned for publication by the participant laboratories. The measured quantities were the air kerma (K-air) and the absorbed dose to water (D-w) in Co-60 radiotherapy beams. The comparison was conducted by the pilot laboratory MKEH (Hungary), in a star-shaped arrangement from January 2005 to December 2008. The calibration coefficients of four transfer ionization chambers were measured using two electrometers. The largest deviation between any two calibration coefficients for the four chambers in terms of air kerma and absorbed dose to water was 2.7% and 3.3% respectively. An analysis of the participant uncertainty budgets enabled the calculation of degrees of equivalence (DoE), in terms of the deviations of the results and their associated uncertainties. As a result of this EUROMET project 813 comparison, the BIPM key comparison database (KCDB) will include eleven new K-air and fourteen new D-w DoE values of European secondary standard dosimetry laboratories (SSDLs), and the KCDB will be updated with the new DoE values of the other participant laboratories. The pair-wise degrees of equivalence of participants were also calculated. In addition to assessing calibration techniques and uncertainty calculations of the participants, these comparisons enabled the experimental determinations of N-Dw/N-Ka ratios in the Co-60 gamma radiation beam for the four radiotherapy transfer chambers.

Results are presented of the COOMET key comparison of the national measurement standards of air kerma for 60Co γ radiation. Participants of the comparison were PTB (Germany, pilot institute), VNIIM (Russia), SMU (Slovakia), BelGIM (Belarus), CPHR (Cuba) and RMTC (Latvia). PTB, VNIIM and SMU had previously taken part in a key comparison with the Bureau International de Poids et Mesures (BIPM) and operated as link laboratories in order to evaluate the degree of equivalence of the participants' results with the key comparison reference value. These data form the basis of the results entered into the BIPM key comparison database for comparison COOMET.RI(I)-K1.