Intracavitary High Dose Rate Afterloading Therapy with Iridium-192: Basic Physical Measurements, Dosimetry, and Localisation

Abstract

The γ-ray emitting isotopes like radium 226, cobalt 60, iridium 192, and cesium 137 are used with intracavitary afterloading techniques. Though their physical parameters are quite different (Table 1), the isodose distribution does not change very much if therapy-relevant distances of 1–5 cm are respected. The dose decrease around a point source in water for the above-named isotopes, with small deviations, follows the inverse square law and is therefore independent of isotope and photon energy. This results from a nearly complete compensation of absorption by scattering in the vicinity of the source. Depending on the isotope, the correction F(r) for absorption and scattering up to distances of 5 cm ranges between 0% and 8% (Fig. 1) (Dutreix et al. 1982; Young 1983; Meisberger et al. 1968; Meli et al. 1988).