Optimization of permanent I-125 prostate implants using fast simulated annealing

Purpose: Treatment planning of ultrasound-guided transperineal I-125 permanent prostatic implants is a time-consuming task, due to the large number of seeds used and the very large number of possible source arrangements within the target volume. The goal of this work is to develop an algorithm based on fast simulated annealing allowing consistent and automatic dose distribution optimization in permanent I-125 prostatic implants. Methods and Materials: Fast simulated annealing is used to optimize the dose distribution by finding the best seed distribution through the minimization of a cost function. The cost function includes constraints on the dose at the periphery of the planned target volume and on the dose uniformity within this volume, Adjustment between peripheral dose and the dose uniformity can be achieved by varying the weight factor in the cost function. Results: Fast simulated annealing algorithm finds very good seed distributions within 20,000 iterations. The computer time needed for the optimization of a typical permanent implant involving 60 seeds and 14 needles is approximately 15 min. An additionnal 5 min are necessary for isodose distribution computations and miscellaneous outputs. Conclusion: The use of fast simulated annealing allows for an efficient and rapid optimization of dose distribution. This algorithm is now routinely used at our institution in the clinical planning of I-125 permanent transperineal prostate implants for early stage prostatic carcinoma. Copyright (C) 1996 Elsevier Science Inc.