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Développement et mise en place au BIPM d’un systéme international de comparaison et d’étalonnage pour la dosimétrie en mammographie

Abstract : Mammography is an x-ray examination of the breast, considered to be the most sensitive technique currently available for early detection of breast cancer. Because of risks of radiation-induced carcinogenesis associated with the use of x rays, accurate calibration of the x-ray unit is essential in order to minimize the radiation dose delivered to the patient breast but having a good image quality. The beam calibration is made using ionization chambers, commercial instruments that need to be characterized at standard reference dosimetry laboratories in well-defined x-ray beams similar to those used in the diagnostic institutes.Standard reference laboratories for radiation dosimetry are usually part of the National Metrology Institute of each country; they can either be Primary or Secondary Standard Dosimetry Laboratories. Primary Laboratories verify the accuracy of their measurements using the primary standards by taking part in international comparisons while the Secondary Laboratories, holding secondary standards, need the characterization of their reference instruments. In order to fulfil these requirements of the National Metrology Institutes (NMIs), the Bureau International des Poids et Mesures (BIPM) maintains stable reference standards for radiation dosimetry and provides to the its Member States an international facility for comparisons of primary standards and characterization of secondary standards to ensure world-wide uniformity of measurements and their traceability to the International System of Units (SI).The Ionizing Radiation Department of the BIPM started international comparisons and characterizations in low-energy x-ray beams in 1966 and in 2001, the NMIs required the BIPM to extend these activities to mammography beams. A description of the work I carried out at the BIPM to provide an international facility for comparisons and calibrations in the mammography field is presented in this thesis, divided into four stages: establishment of seven reference radiation beams using the combination tungsten-anode x-ray tube and molybdenum filtration (W/Mo beams); installation of a molybdenum-anode x-ray tube with molybdenum filtration and establishment of four reference radiation beams (Mo/Mo beams); design and construction of a new primary standard free-air chamber for the dosimetry of the mammography beams; establishment of a new ongoing international comparison in the new reference mammography beams, registered in the BIPM key comparison database KCDB as BIPM.RI(I)-K7 and a programme for the calibration of national secondary standards by including the new facility in the quality management system of the Ionizing Radiation (IR) Department of the BIPM.The experience obtained during this work is now transferred to the NMIs to help them in the development of primary standards and to improve their existing facilities.To date, six successfully comparisons have been carried out in the new facility established at the BIPM; the participation in the new ongoing key comparison allow the NMIs to support their calibration and measurement capabilities (CMCs). Characterization and calibration of national secondary standards have been done for five NMIs.
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Submitted on : Friday, July 5, 2013 - 11:32:12 AM
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Cecilia Kessler. Développement et mise en place au BIPM d’un systéme international de comparaison et d’étalonnage pour la dosimétrie en mammographie. Médecine humaine et pathologie. Conservatoire national des arts et metiers - CNAM, 2013. Français. ⟨NNT : 2013CNAM0864⟩. ⟨tel-00841601⟩



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