COMPARISON OF SIMULATED ANNEALING ALGORITHMS FOR CONFORMAL THERAPY TREATMENT PLANNING

Purpose: The efficiency of four fast simulated annealing algorithms fo r optimizing conformal radiation therapy treatment plans was studied a nd the resulting planes were compared with each other and to optimized conventional plans. Methods and Materials: Four algorithms were selec ted on the basis of their reported successes in solving other minimiza tion problems: fast simulated annealing with a Cauchy generating funct ion, fast simulated annealing with a Lorentzian generating function, v ariable step size generalized simulated annealing (VSGSA), and very fa st simulated reannealing (VFSR). They were tested on six clinical case s using a multiple beam coplanar conformal treatment technique. Relati ve beam weights were computed that maximized the minimum tumor dose su bject to dose-volume constraints on normal organ doses. Following some initial tuning of the annealing parameters, each algorithm was applie d identically to each test case. Optimization tests were run using dif ferent random number sequences and different numbers of iterations. Re sults: The VSGSA algorithm consistently produced the best results. Usi ng long run times, it generated plans with the highest minimum tumor d ose in five of the six cases, For the short run times, the VSGSA solut ions averaged larger minimum tumor doses than those of the other algor ithms for all six patients, with increases ranging from 0.4 to 5.9 Gy. For three of the patients, the conformal plan gave a clinically signi ficant increase in the minimum tumor dose over the conventional plan, ranging from 8.2 to 13.0 Gy. In two other cases, there was little diff erence between the two treatment approaches. For one case, the optimiz ed conventional plan was much better than the conformal plan because t he conventional beam arrangement included wedges, which offset the mul tiple beam advantage of the conformal plans. Conclusions: For equal co mputing times of both long and short duration, the VSGSA algorithm con sistently produced conformal plans that were superior to those produce d by the other algorithms. The simple conformal technique used in this study showed a significant potential advantage in the treatment of ab dominal tumors. In three of the cases, the conformal plans showed clin ically important increases in tumor dose over optimized conventional p lans.