Dose distribution of 125I sources in different tissues.

The low-energy photons of 125I deposit energy in tissues primarily by the photoelectric effect, which is strongly dependent on the atomic number Z. Thus dose distributions of 125I sources in media of different Z are not the same. LiF and CaF2 thermoluminescent dosimeters were used for relative dose distribution measurements in materials that are equivalent to muscle, breast, and bone. The experimental data are in good agreement with published results for muscle, and in reasonable agreement with Monte Carlo calculations for all the tissues tested. These measured data provide the basis for dose distribution calculations when 125I seeds are implanted in or near inhomogeneous tissues.