Optimization of permanent 125I prostate implants using fast simulated annealing

Abstract

Purpose : Treatment planning of ultrasound-guided transperineal 125I permanent prostatic implants is a timeconsuming task, due to the large number of seeds used and the very large number of possible source arrangements with 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 125I prostatic implants. Methods and Materials : Fast simulated annealing is used to optimize the dose distribution by finding the best see 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 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 approximatley 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 125I permanent transperineal prostate implants for early stage prostatic carcinoma.