APPLICATIONS OF THE ITALIAN PROTOCOL FOR THE CALIBRATION OF BRACHYTHERAPY SOURCES

The Associazione Italiana di Fisica Biomedica (AIFB; Italian Associati on of Biomedical Physics) has adopted the Italian protocol for the cal ibration of brachytherapy sources. The AIFB protocol allows measuremen ts of the reference air kerma rate, K-r, within 1.7% (1 sigma). To mea sure K-r the AIFB protocol has identified a direct and an indirect pro cedure. The direct procedure is based on the use of spherical or cylin drical ionization chambers as local reference dosimeters positioned al ong the transverse bisector axis of the source. Once the source is spe cified by a K-r value, this can be used to calibrate a field instrumen t, such as a well-type ionization chamber, for further source calibrat ions by means of an indirect procedure. This paper reports the results obtained by the Physics Laboratory of the Universita Cattolica del S Cuore (PL-UCSC), in terms of K-r calibration of five types of source, Yb-169, Ir-192 and Cs-137. The role of the K-r determination for a bra chytherapy source has been underlined when a new source such as the Yb -169 seed model X1267 has been proposed for clinical use. The K-r valu es for Cs-137 spherical sources differed by 5% from the vendor's mean value. The five types of source calibrated in terms of K-r were used t o obtain the calibration factor, N-Kr(source), of an HDR-1000 well-typ e ionization chamber.