Experimental determination of beam quality factors, k[Q], for two types of Farmer chamber in a 10 MV photon and a 175 MeV proton beam

NRC publication: Ye

In-situ calibration of clinical built-in KAP meters with traceability to a primary standard using a reference KAP meter

The air kerma-area product (KAP) is used for settings of diagnostic reference levels. The International Atomic Energy Agency (IAEA) recommends that doses in diagnostic radiology (including the KAP values) be estimated with an accuracy of at least +/- 7% (k = 2). Industry standards defined by the International Electrotechnical Commission (IEC) specify that the uncertainty of KAP meter measurements should be less than +/- 25% (k = 2). Medical physicists willing to comply with the IAEAs recommendation need to apply correction factors to KAP values reported by x-ray units. The aim of this work is to present and evaluate a calibration method for built-in KAP meters on clinical x-ray units. The method is based on (i) a tandem calibration method, which uses a reference KAP meter calibrated to measure the incident radiation, (ii) measurements using an energy-independent ionization chamber to correct for the energy dependence of the reference KAP meter, and (iii) Monte Carlo simulations of the beam quality correction factors that correct for differences between beam qualities at a standard laboratory and the clinic. The method was applied to the KAP meter in a Siemens Aristos FX plus unit. It was found that values reported by the built-in KAP meter differed from the more accurate values measured by the reference KAP meter by more than 25% for high tube voltages (more than 140 kV) and heavily filtered beams (0.3 mm Cu). Associated uncertainties were too high to claim that the IECs limit of 25% was exceeded. Nevertheless the differences were high enough to justify the need for a more accurate calibration of built-in KAP meters.Funding Agencies|Swedish Radiation Safety Authority</p

Comparison of air kerma area product and air kerma meter calibrations for X-ray radiation qualities used in diagnostic radiology. Report on the EURAMET project #1177, identified in the BIPM key comparison database (KCDB) as EURAMET RI(I) – S9

Kalibrointilaboratorioiden tarkkuutta ja luotettavuutta testattiin röntgendiagnostiikan annosmittareiden kalibrointiprojektissa EURAMET#1177 (vertailun tunnus EURAMET.RI(I)-S9). Mukana oli 22 eurooppalaista kalibrointilaboratoriota, joiden kalibroitavana kiersi annoksen ja pinta-alan tulon mittareita (DAP, KAP). Vertailu tehtiin vuosien 2011 ja 2012 aikana ja pilottilaboratorio oli kreikkalainen (IRCL/GAEC-EIM). Mittausvertailu oli ensimmäinen laajamittainen kansainvälinen kalibrointivertailu KAP-mittareille. Vertailu toteutettiin yhdessä EURAMET järjestön, IAEA/WHOn laboratorioverkoston ja EURADOS järjestön kanssa. Kaikkiaan 216 suoritetusta KAP mittarin kalibroinnista 176 oli 5% sisällä yhtäpitäviä. Kahdeksalla laboratoriolla tuloksissa oli yli 5% - 45 % ylityksiä vertailuarvosta. Tavanomaisten KAP mittareiden tuloksen riippuvuus röntgenspektristä ja käytetystä annosnopeudesta osoittautui arvioitua suuremmaksi ja myös nämä tekijät vaikuttivat myös joidenkin laboratorioiden tuloksiin. Vertailun tuloksia käytetään varmistamaan kansainvälisen paino- ja mittakomitean hyväksymiä mittaus- ja kalibrointisuoritteita (CIPM-MRA). STUKin kansallinen mittanormaalitoiminta on mukana em. sopimuksessa ja STUKin tulokset kalibrointivertailussa olivat tarkimpien joukossa

Comparison of air kerma area product and air kerma meter calibrations for X-ray radiation qualities used in diagnostic radiology

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, P-KA, and air kerma, K. It was conducted with the goal of testing the measurement and calibration capabilities for P-KA 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, K 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