1. A method of treatment planning for placement of radioactive seeds in a tumor in a region of a body comprising the steps of: (a) determining a desired dose pattern within the region of the body; (b) pre-calculating a preferred ranking of seed locations for a range of locations within the region of the body based on dose patterns produced by at least one seed moved throughout the range of different locations in a target region; (c) after step (b) and prior to placement of the seeds in a patient, determining the location of the seeds for a treatment plan by sequentially placing seeds at planning locations according to the preferred ranking of seed locations; and (d) outputting a proposed treatment plan providing planning locations of the sequentially located seeds for use in surgical implantation of the seeds.