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Medical procedures such as seed implantation, biopsies, and treatment injections require inserting a needle tip to a specific target location inside the human body. This is difficult because (1) needle insertion causes soft tissues to displace and deform, and (2) it is often difficult or impossible to obtain precise imaging data during insertion. We are developing a sensorless planning system for needle insertion that incorporates numerical optimization with a soft tissue simulation based on a dynamic FEM formulation that models the effects of needle tip and frictional forces using a 2D mesh. In this paper we describe a sensorless planning algorithm for radioactive seed implantation that computes needle insertion offsets that compensate for tissue deformations. We apply the method to seed implantation during permanent seed prostate brachytherapy to minimize seed placement error in simulation without relying on real-time imaging.