A good accuracy and long-term stability of the dosimeters used in Polish radiotherapy centres was observed. All measurements were carried out at the same laboratory, by the same staff, according to the same IAEA recommendations. On the basis of the long period of repetitive establishing of calibration coefficients for the same electrometers and ionization chambers, the accuracy of electrometers and the long-term stability of ionization chambers were examined. Unidos 10001, Unidos E (10008/10009) and Dose 1 electrometers from 14 radiotherapy centres were calibrated 3-4 times over a long period of time, together with Farmer type (PTW 30001, 30013, Nuclear Enterprises 2571 and Scanditronix-Wellhofer FC65G) cylindrical ionization chambers and plane-parallel type chambers (PTW Markus 23343 and Scanditronix-Wellhofer PPC05). Ulkowski, Piotr Bulski, Wojciech Chełmiński, Krzysztof Long-term stability of radiotherapy dosimeters calibrated at the Polish Secondary Standard Dosimetry Laboratory. The calibration standards were re-used after a period of 5 years and analysis of the results showed discrepancies in efficiency values. Comprehensive reconsideration on efficiency curves with respect to the ageing of calibration standards is presented in this paper. In order to assure Quality Control in accordance with ISO/IEC 17025, it was important, from metrological point of view, to examine the long-term stability of calibration standards previously prepared. Kandić, A Vukanac, I Djurašević, M Novković, D Šešlak, B Milošević, Z On the long-term stability of calibration standards in different matrices.
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