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Pencil ionization chambers are used for beam dosimetry in computed tomography equipment (CT). In this study, a new calibration methodology was established, in order to make the Calibration Laboratory of Instituto de Pesquisas Energeticas e Nucleares (LCI) suitable to international metrological standards, dealing with specific procedures for calibration of these chambers used in CT. Firstly, the setup for the new RQT radiation qualities was mounted, in agreement with IEC61267 from the International Electrotechnical Commission (IEC). After the establishment of these radiation qualities, a specific calibration methodology for pencil ionization chambers was set, according to Technical Report Series No. 457, from the International Atomic Energy Agency (IAEA), which describes particularities of the procedure to be followed by the Secondary Standard Dosimetry Laboratories (SSDL’s), concerning to collimation and positioning related to the radiation beam. Initially, PPV (kV) measurements and the determination of copper additional filtrations were carried out, measuring the half value layers (HVL) recommended by the IEC 61267 standard, after that the RQT 8, RQT 9 and RQT 10 radiation quality references were established. For additional filters, aluminum and copper of high purity (around 99.9%) were used. RQT’s in thickness of copper filters equivalent to the set “RQR (Al) + Additional Filtration (Cu)” was directly found by an alternative methodology used to determine additional filtrations, which is a good option when RQR’s have not the possibility of be setting up. With the establishment of this new methodology for the ionization pencil chambers calibration, the LCI is ready to calibrate these instruments according to the most recent international standards. Therefore, an improvement in calibration traceability, as well as in metrological services offered by IPEN to all Brazil is achieved.

Estabelecimento de um novo método de calibração de câmaras de ionização tipo lápis para dosimetria em feixes de tomografia computadorizada