Permanent implantation of I-125 sources in the prostate: Radical limits ofsimplicity

PURPOSE: To determine the effect of reducing the number of sources per impl antation on the dose coverage of the prostate volume. MATERIALS AND METHODS: Idealized source distributions were planned for four , eight, 16, 24, 32, and 48 sources. The peripheral loading technique was u sed to plan a uniform, conformal dose distribution to the target volume, wh ich was the prostate volume as visualized at ultrasonography. Source-placem ent error was estimated by using measured error magnitudes and was expresse d with systematic and random components. The relative sensitivities of the plans to the source-placement error were studied. RESULTS: Idealized planned target coverage can be adequately achieved with comparable dose distributions with eight or more sources. The sensitivity t o source-placement error is comparable for plans with 16 or more sources. CONCLUSION: It is theoretically possible to radically simplify implantation without compromising target coverage or error tolerance.