Comparison of air kerma and absorbed dose to water measurements of Co-60 radiation in radiotherapy

Project Description

This comparison is proposed with the aim of extending degrees of equivalence for those participants not already included in Appendix B of the CIPM MRA. The degrees of equivalence that by definition include the comparison uncertainties will then serve to support the relevant CMCs.

Under the project two key comparisons will be run in parallel for measurements of the two quantities. Almost the same protocol will cover them. Two sets of transfer instruments (PTW UNIDOSE 2.3 with 30001 and NE 2561 chambers with envelope in water, and PAM 2000 electrometer with Wellhöffer FC65-G and OMH ND 1006 waterproof chambers will be calibrated in terms of absorbed dose to water at 5 cm depth, and air kerma free in air. The NKair and NDw calibration coefficients will be the comparison parameters. Dose rate of Co-60 radiation in the range of 0,5 mGy/s-50 mGy/s, 100 cm² field, and FDD~1 m should be applied during the calibrations.

Detailed uncertainty budgets and traceability descriptions (whether using primary standards, dosimetry protocols or direct calibration of national secondary standard) of participant laboratories required, separately for the two quantities. All the 24 participants, except Russia, going to take part in both key comparisons.The organisation of the comparison programme will be star-shaped, with 3 weeks term for each participants to perform their measurements and max. 4 weeks to send the results back to the pilot laboratory (OMH). Each participants should pay their own transportation and insurance costs for the transfer instruments. (For the non EU member participants the OMH will issue the Ata-Carnet)

The OMH and another voluntary participant (primary lab.) will act as linking laboratories to the CIPM comparisons in Appendix B for both quantities, hence they will have no chance to change their existing degrees of equivalence.

Final Report 2009-11-04

The comparison is completed and the results are available in the KCDB.

An unprecedented international comparison involving 26 countries was conducted for the purpose of linking the measurement standards for air kerma and absorbed dose to water to each other.  High stability transfer instruments were used for this work which enabled each participant to establish the degrees of equivalence, DoE, of their national standards for air kerma and absorbed dose to water. This international effort allowed participating SSDLs to obtain for the first time their degrees of equivalence to be included in the BIPM KCDB. A total of 11 new air kerma and 14 new absorbed dose to water degrees of equivalence values will be added to the KCDB.  Furthermore, these new values can be used to support  the relevant CMC claims of each of these participants. The average calibration coefficient values, used for the calculations made in this work, indicated that the deviations from the key comparison reference values are within the  calculated expanded  uncertainty U(Di) (k = 2) for each participant for both quantities except for the BEV, PTB and the MKEH only in terms of air kerma, similar to their BIPM.RI(I)- K1 results.

Ionising Radiation (IR)
István Csete, MKEH (Hungary)
Coordinating Institute
BFKH (Hungary)
Further Partners
CNEA-CAE (Argentina)
ENEA (Italy)
Int. Atomic Energy Agency
IRB (Croatia)
LNMRI (Brazil)
NIST (United States of America)
NRC (Canada)
VNIIM (Russia)