Comparison of calibration of KAP meters in terms of air kerma area product
Project Description
1. Scope
Two KAP meters will be circulated between participating laboratories and the calibration coefficients in terms of PKA and the associate uncertainties will be compared.
Furthermore, two diagnostic radiology (DR) chambers suitable to measure the air kerma (rate) will be circulated and be calibrated in terms of air kerma. This will allow to compare separately the differences in the air kerma calibration coefficients and those of the air kerma area product.
The project will enable participating calibration laboratories to test and verify their calibration methods and capabilities and to support the relevant Calibration and Measurement Capabilities (CMCs) to the International System (SI) at BIPM.
2. Pilot laboratory
The ICRL/GAEC-EIM, Greece will be the pilot laboratory, which will be responsible for the overall coordination of the intercomparison. It will compile and analyse the results of the calibrations and prepare a summary with conclusions (incl. degree of equivalence) for comments and checking by each participating laboratory. The pilot laboratory will also prepare the final reports to EURAMET and BIPM (KCDB)
3. Comparison procedure
The first calibration will be carried out by the pilot laboratory (GAEC), including constancy checks of the KAP meters and DR chambers. The first calibration results will be given to the BIPM before instruments are distributed to the participants. The instruments will be shipped to the laboratories in sequence according to the agreed order and time schedule. After every three laboratories, the instruments will be returned to the pilot laboratory for an interim re-calibration and costency checks. Within 2 weeks after the calibration, each laboratory will send to the pilot laboratory: the calibration report with the calibration coefficients with uncertainties and the associate uncertainty budget, as well as as short description of the calibration procedure (including few photos and drawings if possible); the pilot laboratory having first submitted its own first set of results to the CCRI Executive Secretary.
4. Calibration method and calibration coefficients
The KAP meters will be calibrated in terms of PKA (in Gy cm2 / digit) for incident and/or transmitted radiation as indicated below, so the NPKA,inc and/or NPKL,trans will be deduced for each x-ray beam quality. The diagnostic radiology chambers will calibrated in terms of air kerma (Ki) (in mGy / digit), so the NK will be deduced for each x-ray beam quality. All appropriate correction factors (e.g. for air density, ion recombination, etc) should be taken into account and reported in details at the calibration report.
Results from the comparisons will be treated according to the CIPMs rules and will be strictly confidential during the intercomparison process. When the comparison is completed, the pilot laboratory will distribute a draft A report.
5. Radiation qualities for KAP meter calibration
The KAP meters and the DR chambers should be calibrated at the following radiation qualities:
• Reference beam qualities according to IEC 61264
RQR 3 (50 kV) - RQR 5 (70 kV) - RQR 6 (80 kV) - RQR 8 (100 kV) - RQR 9 (120 kV)
• Non reference beam qualities:
Non-reference beam qualities are selected to simulate the clinical x-ray beams.
On a voluntary basis the laboratories may perform the KAP meters and the DR chambers calibration at the non-reference beam qualities presented below.
A series : 3.0 mm Al 0.1 mm Cu at 50 kV, 80 kV, 100 kV and 120 kV
B series : 4.0 mm Al 0.2 mm Cu at 50 kV, 80 kV, 100 kV and 120 kV
C series : 1.5 mm Al 0.9 mm Cu at 80 kV, 100 kV and 120 kV
At such copper filtrations, the thickness of aluminium filtration is not so important. So, the laboratories may use aluminium thickness close to the proposed values - the Cu thickness should be precise.
The HVL values should be defined by the laboratories and the thickness of Al and Cu together with the HVL at every tube voltage should be reported. Details on the traceability of the standards, measurements and calibration at these qualities should be provided by the participating laboratory.
6. Radiation field sizes for KAP meter calibration. According to IAEA TRS 457, a circular or square lead aperture should be available with a known diameter or width between about 40 and 60 mm. The laboratory should be able to position this aperture in front of the plane of measurement. A suitable distance between the aperture and plane of measurement is 50 mm.
If the traceability of the PKA is the air kerma and the field size, the radiation field size (area) at the reference plane of measurement and its uncertainty should be reported in the calibration report. If the traceability is through a secondary standard KAP meter this is not needed.
In order for the calibration results to refer to the same irradiation area, the pilot laboratory (in cooperation with other volunteer laboratories) will investigate the irradiation area dependence of response of the KAP meters and appropriate correction factors will apply.
7. Comparison conditions
The calibration coefficients should refer to the standard reference environmental conditions:
temperature : 293.15 oK (20 oC) , Pressure : 101.325 kPa and R.H. : 50%. The actual environmental conditions during the calibrations, including the relative humidity, should be recorded and reported in the calibration report.
8. Uncertainties
The uncertainties should be evaluated according to the IEC GUM 1995 and reported in details at the calibration report of the laboratory. The overall expanded uncertainty should be evaluated with coverage factor k=2.
9. Instruments and calibration conditions
The instruments proposed to be used in this comparison are :
9.1 IBA Kerma-X plus (IBA SCANDITRONIX WELLHOFER)
Measuring device :KermaX-plus DDP TinO, Model 120-205, s/n 01E01232
KAP Ionization chamber : IBA Model 120-131 TinO, s/n 01A00120
Accessories: (i) SCANDITRONIX Power Supply Type 8713 MED, (ii) Cable AWM 20251 with adaptor end and (iii) Adaptor cable RS 232 port.
The instrument will be provided by the IRCL/GAEC-EIM, Greece
The reference point of the KAP ionization chamber is the geometrical center (middle line) of the effective volume, i.e. the reference plane is located half the KAP thickness below the front surface of the KAP ionization chamber.
9.2 Radcal Patient Dose Calibrator PDC (Radcal Corp)
The instrument will be provided by IAEA.
The main device consists of the measuring device (including the display unit) and the KAP ionization chamber. The PDC measures both the PKA and the air kerma (rate). Therefore, in this project, the PDC will be used both as a KAP meter and a DR chamber and it will be calibrated in terms of PKA and Ki.
The reference point of the KAP ionization chamber is the geometrical center of the front surface of the device, i.e. the reference plane coincident with the front surface of the device.
9.3 Parrallel plate ionization chamber EXRADIN MAGNA 650, 3 cc, REF 92650.
The instrument will be provided by the IRCL/GAEC-EIM, Greece.
The ionization chamber has a TNC connector and it can be connected to an electrometer. The polarizing voltage is 300 V, with the negative polarity to the middle shielding electrode (guard ring). The chamber is vented.The reference point is the geometrical center of the chamber front surface (entrance window). In this project, the chamber will circulated alone (without an electrometer). The laboratories should use their own electrometer.
10. Schedule and responsibilities for the costs
Each laboratory will have one week to complete the calibrations and another week to take care of the receipt, unpacking, re-packing and further sending of the instruments to the next laboratory.
11. Transport of instruments
Each laboratory will take all necessary provision for the safe transport of the instruments to next participating laboratory. The transport costs and insurance costs will be undertaken by each laboratory. An insurance of 15,000 Euros against damage or loss of the packages is proposed. The transport arrangements and shipping details will be announced by e-mail to the next participating laboratory and for information of the pilot laboratory. Upon receipt of the instrument package, the previous participating laboratory (the sender of the package) and the pilot laboratory should be informed. Package damages or signs of damage should be immediately reported as well to both laboratories.
12. Calibration protocol (technical protocol)
The calibration protocol of this intercomparison will be available at the web sites : www.euramet.org and www.gaec.gr.
Information about participating laboratories, time schedule, calibration methods and result analysis is provided in the protocol.
13. Criteria for evaluation and reporting of the results.
The criteria for determination of the degree of equivalence will be given in the comparison protocol. The final report will include a list of the degree of equivalence with respect to the reference value and associated expanded uncertainty for air kerma product of all participants. The results from the comparison will be published in Metrologia.
Final Report 2014-08-27
The comparison has been completed and results are published in the KCDB.
The EURAMET project 1177 was conducted with the goal of testing the measurement and calibration capabilities for air kerma area product and air kerma, 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 participantsThe comparison started on 28 March 2011. The first calibration and the relevant checks were carried out by the pilot laboratory and the instruments were sent to participating laboratories, according to the agreed schedule. After every three laboratories, the instruments were returned to the pilot laboratory for an interim re-calibration. The measurement part of the project was completed after seven (7) rounds on 25 July 2012. Each laboratory sent the calibration report by filling the report template excel sheets. Upon an open call between participants, a specific working group (WG) was established to support the coordinator in drafting this report on the EURAMET.RI(I)-S9 supplementary comparison: The final report was completed on 27/8/2014 and submitted to the CCRI Executive secretary and the EURAMET TC-IR chair.
Further Information
The IAEA Coordinated Research Programme (CRP E2.10.08), Activity 3, focuses on the KAP meter calibration intercomparison which will be carried out by the participating calibration laboratories (CZ, FI, GR, RS). Simultaneously, a similar intercomparison will be performed between the partner laboratories of EURADOS WG 12, SG 3: Technical aspects on DAP calibration and CT calibration (ES, IT, FI, GR, PL).