Two-dimensional dose distribution of 125I seeds

Two-dimensional dose distribution has been measured for the new (model 6711) 125I seeds used in interstitial implants. Two independent methods, using a silicon diode or thermoluminescent dosimeters, yielded identical results. At any given distance r from the seed center, the dose varies with theta, the angle relative to the seed's axis. Similarly, the r dependence of the dose distribution is different at various theta values. These observations can be qualitatively understood in terms of several factors, namely, source encapsulation, geometrical relationship, and attenuation and scatter. Empirical expressions which approximate the measured results have been developed to facilitate clinical dose distribution calculations.