Is it necessary to check the homogeneity of iridium 192 wires

Several aspects are involved in a brachytherapy quality assurance program including verification of computerized dose distribution, source calibration, uniformity of linear intensity along the source, tests to detect any radioactive leaks, etc. Our study is specifically confined to the verification of homogeneity and calibration of iridium 192 radioactive sources. After defining, H, as inhomogeneity and discussing the advantages, disadvantages and limitations of the different methods to derive it, the authors present the results obtained between January 1989 and March 1991 by checking 640 iridium wires from each of two European manufacturers (Cis Bio-International and Amersham International). Approximately 2% of the wires examined were found to have an heterogeneity greater than 10%, and in 8% of the wires a 3% discrepancy was detected between the calibration performed by the manufacturers and our own measurements. This observation indicates that source verification is mandatory. The effects of inhomogeneity on dose specification is analysed. The homogeneity criteria used in our department for quality control in clinical applications are presented; they take into account the absolute value of inhomogeneity as well as their length