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 tra ditional nomograms but automatically generates optimized source config urations. An iterative algorithm is used that places one seed at a ste p. The volume dose of target is calculated at each step to determine t he coldest spot where the next source is to be placed, so that the dos e uniformity of target is best improved as source placement proceeds. At each step, the total activity required for the seed configuration a s 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 c linically acceptable seed configurations with similar total activity b ut different individual activities are generated simultaneously. In ou r computer generated treatment plans most of the seeds are distributed in the periphery of the target, similar to the Paterson-Parker patter n of a volume implant. (C) 1997 American Association of Physicists in Medicine.