TREATMENT PLANNING OPTIMIZATION FOR MULTIPLE ARCS STEREOTAXIC RADIOSURGERY USING A LINEAR-ACCELERATOR

Purpose: Multiarc stereotactic radiosurgery is a technique used to irr adiate an intracranial tumor with minimal damage to the surrounding no rmal tissue. The purpose of this paper is to present a method for and the results from optimizing three dimensional (3D) treatment dose for multiarc stereotactic radiosurgery. Methods and Materials: The normal procedure for a physician-physicist team designing a treatment plan fo r multiarc stereotactic radiosurgery is the trial-and-error approach o f changing the collimator size and the isocenter of radiation by viewi ng the isodose curves on a two dimensional (2D) computed tomography (C T) or magnetic resonance imaging (MRI) image plane, Not only is this t ime consuming, but the resulting treatment plan is not optimal in most , if not all, cases, One reason for such nonconformal isodose curves i s that the same collimator size is used for all arcs, However, it is v ery difficult to determine manually the different collimator sizes for different arcs, A derivative free optimization method is used to opti mize the collimator size for each are, as well as the 3D coordinates o f the isocenter(s). Results: One spherical and two ellipsoidal artific ial tumors, and one actual tumor, were used to show the utilities of t he optimization process, The 90% isodose curves resulting from optimiz ation conform very well with the tumor; whereas the 90% isodose curves from the conventional method either do not envelop the entire tumor w hen the collimator size is too small, or a large volume of normal tiss ue is also irradiated by the 90% dose when the next larger collimator size is used. Conclusions: When the collimator size for each are and t he location of the isocenters(s) are optimized in a multiarc stereotac tic surgery treatment plan, the 90% isodose curve conforms to the tumo r much better than when the same collimator size is used for all arcs.