Characterization of standard fields for calibration of instruments, mammography level

The dosimetry and the diagnosis in mammography demand the use of specific ionization chambers in order to reduce the uncertainties of the measurements for quality control and radiation protection. Thus, it is important that these chambers are calibrated in X-ray standardized beams containing the characteristics of the mammography spectrum. In this work a study of the use of molybdenum filters, with 99,99% of purity, was performed at the exit of the X-ray beams originating from the interaction of the electron with a tungsten target, to establish standard fields, mammography level, in the Laboratory of Calibration of Instruments of the IPEN. As as reference instrument, an ionization chamber, recently calibrated at the Laboratory of Calibration of the Center for devices and Radiological Health, Food and Drug Administration, USA, was chosen. The half-value layers were determined for the energies between 14 and 23 keV, including measurements of exit beams. The results of the quality assurance program of the X-ray system and of the ionization chamber are in conformity with the national and international legislation. The characteristics of the established radiation qualities show and agreement between the equivalent energies of the two laboratories. (author)