CLINICAL TREATMENT PLANNING OPTIMIZATION BY POWELLS METHOD FOR GAMMA-UNIT TREATMENT SYSTEM

Purpose: This article presents a new optimization method for stereotac tic radiosurgery treatment planning for gamma unit treatment system, M ethods and Materials: The gamma unit has been utilized in stereotactic radiosurgery for about 30 years, but the usual procedure for a physic ian-physicist team to design a treatment plan is a trial-and-error app roach. Isodose curves are viewed on two-dimensional computed tomograph y (CT) or magnetic resonance (MR) image planes, which is not only time consuming but also seldom achieves the optimal treatment plan, especi ally when the isocenter weights are regarded. We developed a treatment -planning system on a computer workstation in which Powell's optimizat ion method is realized. The optimization process starts,vith the initi al parameters (the number of isocenters as well as corresponding 3D is ocenters' coordinates, collimator sizes, and weight factors) roughly d etermined by the physician-physicist team. The objective function can be changed to consider protection of sensitive tissues. Results: We us e the plan parameters given by a well-trained physician-physicist team , or ones that the author give roughly as the initial parameters for t he optimization procedure, Dosimetric results of optimization show a b etter high dose-volume conformation to the target volume compared to t he doctor's plan, Conclusion: This method converges quickly and is not sensitive to the initial parameters. It achieves an excellent conform ation of the estimated isodose curves with the contours of the target volume, If the initial parameters are varied, there will be a little d ifference in parameters' configuration, but the dosimetric results pro ved almost to be the same, (C) 1997 Elsevier Science Inc.