[Rigid phantom dosimetry of brachytherapy sources, with special reference to 125-I]

At present, the brachytherapy dosimetry requires the highest level of accuracy in determining the physical parameters of many different radiation sources. Brachytherapy sources differ not only in the nucleus (widely ranging between 30 keV and 1 MeV), but also in the strength and geometrical and filtration characteristics. This work reports the brachytherapy dosimetry carried out in a rigid perspex phantom which allows measurements by means of solid state dosimeters (TLD, semiconductor), ionization chamber and film. Film densities were measured by means of a computerized Perkin-Elmer 1010G microdensitometer, with a spatial resolution of 50 microns. The isodensity lines were dose calibrated by TLD measurements. The dosimetry of the 125I, 192Ir and 198Au sources is reported. The dose distributions of the low energy 125I source, in two different tissues (muscle and adipose) were studied, by means of laboratory built tissue-equivalent sections of the phantoms. The experimental data suggest that this dosimetric procedure is suitable for intercomparison measurements between different radiotherapy centers using the same nuclides in different sources.