Double-film technique for the determination of the homogeneity of line sources

A new technique is presented for determining the homogeneity of the linear activity. The method uses two x-ray films that are firmly pressed against opposing sides of a needle containing a radioactive line source. The homogeneity of the linear activity of 68 iridium-192 wires has been measured. About 80% of the measured linear activities showed deviations of no more than 5% from the mean; about 20% of the measured linear activities showed deviations of 5%-10% from the mean. Individual wires may contain deviations of 5% or more extended over several centimeters, which causes the dose in the prescription point to deviate 5% from the desired value. Four wires (8%) were rejected for this reason.