Treatment planning for prostate implant with loose seeds

A new method of treatment planning for the I-125 and Pd-103 permanent interstitial prostate implant is developed, which does not use the traditional nomograms but automatically generates optimized source configurations. An iterative algorithm is used that places one seed at a step. The volume dose of target is calculated at each step to determine the coldest spot where the next source is to be placed, so that the dose uniformity of target is best improved as source placement proceeds. At each step, the total activity required for the seed configuration as so established is calculated by normalizing the minimal dose to the prescribed dose. An optimized configuration is the one that takes the minimized total activity. Around its minimum the total activity has a very small variation with the number of seeds. Consequently multiple clinically acceptable seed configurations with similar total activity but different individual activities are generated simultaneously. In our computer generated treatment plans most of the seeds are distributed in the periphery of the target, similar to the Paterson-Parker pattern of a volume implant. (C) 1997 American Association of Physicists in Medicine.