hrvatski

Kalibracija brahiterapijskog izvora 192Ir velike brzine doze: analiza rezultata i nepouzdanosti

A lack of primary standards for HDR 192Ir brachytherapy has been known for years to cause the largest problem in obtaining lower uncertainties in RAKR measurements. The currently used calibration techniques where chambers are calibrated against interim standards based on interpolation techniques, provide typically an uncertainty of ± 2.5% (k=2) in the calibration factor. It constitues the largest contribution to the total uncertainty in RAKR and may be significantly reduced through the on-going developement of primary standards. In this work, RAKR values of 23HDR 192Ir sources were measured in the department in the past 10 years of clinical HDRBT application. All differences between the measured RAKR and manufacturers specification were lower than ± 3.5%. Upon the acceptance of a more rigorous protocol, through which the different variables, such as thermal stability and geometrical reproducibility, have been better controlled during the measurement, these differences dropped to less than ±2%. Two ionisation chambers tested in thos work showed very good precision, long term stability, small polarity effect and recombination equal to the manufacturers specification. Differences in repeated measurements of RAKR during the 6 weeks period, in which a source was also changed, were minimal ; RAKR-s stayed within 1%. The calibration technique on the re-entrant well type chamber is due to its simplicity, speed, accuracy and long term stability a highly recommended option for an institution performing HDR brachytherapy

HDR brahiterapija; 192Ir; kalibracija

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