RESUMO
Objective To fulfill the requirements for uncertainty of the calibration apparatus for dosimeters used in X-ray mammography through setting standard radiation quality at the SSDL and developing calibration procedures.Methods According to IEC 61267-2005 and IAEA TRS No 457 to recommend RQR-M and RQA-M series standard radiation quality,the calibration apparatus was evaluated for long term stability of the radiation field over 8 years from 2006 to 2014,including 10 response quantities,such as field homogeneity,change rate of mean air kerma and scatter radiation contributions and so on.In addition,the reference dose instrument was traced back to the PSDL of PTB in Germany by post during 2008 and 2012.Results The field homogeneity (φ 40 mm) relative error was ± 1.4％.The long term stability of the calibration apparatus was less than ± 2％ (limits of variation).The scatter radiation contributions at their points of test were below 0.12％.The calibration factors traced to PTB were 0.999-1.000.As a result of the calibration apparatus,the expanded uncertainty was ± 3％ (k =2,95％ confidence interval).Conclusions The calibration apparatus may meet the requirements of IEC 61267-2005 and IAEA TRS No 457 and has obtained the license of metrology from national regulatory authority.The laboratory now performs very well to calibrate dosimeters used in X-ray mammography.
RESUMO
Objective To evaluate whether eight kinds of dosimeters satisfy the clinical mammography dose measurement through the comparison of energy response.Methods According to GB/T 19629-2005,the energy responses of eight available mammography dosimeters were determined for ten standard radiation qualities in the range 25-40 kVp at the SSDL using a refrence-class dosimeter.Results Except 2000S,the energy response factors of all the other dosimeters were consistent within ±5%.Conclusions The energy response of ionizing chamber type is better than other types of dosimeters.