EVALUATION OF THE SUBSTITUTION OF IR-192 SEED RIBBONS FOR WIRES IN PARIS SYSTEM USING DOSE NONUNIFORMITY RATIO

The substitution of Ir-192 seed ribbons for wires in the Paris system of interstitial implants was re-evaluated using the dose nonuniformity ratio. The dose nonuniformity ratio, which is based on volumetric data, measures the dose nonuniformity of the implant quantitatively. The lower the dose nonuniformity ratio value, the smaller the dose nonuniformity, and the better is the dose homogeneity for the implant. Implants configured in a single-plane and double-planes in the form of squares or triangles using Ir-192 wires or seed ribbons were considered. The difference between the particular reference dose rate that yielded a minimum in the dose nonuniformity ratio curve for wire implants and seed implants is about 4 cGy/hr. The difference between the minimum dose nonuniformity ratio value representing the optimal dose homogeneity of the implants is about 5%. The dose homogeneity may be considered better for implants configured using seed ribbons.