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EN
An analysis of the exposure calibration coefficients for ionization chambers used for dose determination in orthovoltage radiotherapy and in brachytherapy in the Polish SSDL was performed. The coefficients were determined by calibrating the chambers in the X-ray beam of 235 kV or 290 kV and HVL of 2.5 mmCu or 4 mmCu respectively, and also in the Co-60 gamma beam. Calibration procedures followed IAEA recommendations in Report No. TECDOC 1274 and Technical Reports Series No. 277. The characteristics of the energy dependence of various types of chambers used in orthovoltage radiotherapy and in brachytherapy are presented. On the basis of the summarized data and on the energy dependence curves it was possible to conclude that: 1) in he case of calibration of the chambers for orthovoltage radiotherapy the energy dependence has to be established for the full range beam qualities; 2) in the case of calibration, of the investigated chambers, for brahytherapy with Cs-137 and Ir-192 sources, establishing of the exposure calibration factor for Co-60 is sufficient.
EN
A comparison of calibration coefficients of Farmer-type cylindrical ionization chambers calibrated in a Co-60 beam according to the IAEA Reports 277 and 398 formalisms.91 calibration coefficients measured in air and in water.The 398ND, W/277ND, W ratios were calculated, taking into account the wall material of the chambers. The correlation between 398ND, W and NK, ND, air277ND, W was made and the equations of the regression straight lines were determined.Calibration coefficients, determined according to the IAEA Report 398, are higher by about 1% than those determined according to the IAEA Report 277, and they depend slightly on the wall material of the chamber.The introduction of the IAEA dosimetry Report 398 resulted in an increase in the doses delivered to patients by about 1% as compared with the period of application of Report 277. The regression equations may assure increased accuracy in retrospective comparative calculation of doses according to both reports as compared with the correction based on mean percent values.
PL
Celem pracy było opracowanie metody szacowania niepewności i wstępne określenie wartości szacowanych wielkości w przypadku wzorcowanych w LWWD dawkomierzy. Zastosowano metodę obliczania niepewności typu A i B wg międzynarodowej normy ISO. Uwzględniono stosowany w LWWD sposób wzorcowania dawkomierzy wg raportów Międzynarodowej Agencji Energii Atomowej. Przedstawione wyniki dotyczą wszystkich wzorcowanych w LWWD dawkomierzy. Zarówno szczegółowa analiza wszystkich etapów wzorcowania jak i otrzymane wyniki wskazują, że niepewność pomiarów jest w zakresie akceptowanym przez Polskie Centrum Akredytacji.
EN
The aim of the study was to work out a method of establishing the measurement uncertainty and determination of uncertainty values for calibration of dosemeters at the SSDL. For the determination of type A and B uncertainties, a method according to iternational ISO standard was used. The calibration procedures used at the SSDL, consistent with the reports of the International Atomic Energy Agency, were taken into account. The presented results apply to all dosimeters calibrated at the SSDL. The detailed analysis of every step of the calibration procedures and the results obtained show that the measurement uncertinty is within the limits accepted by the Polish Centre for Accreditation.
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