Computer-aided design optimization with the use of a fast dose model for linear-accelerator-based stereotactic radiosurgery.

In order to efficiently plan non-spherical radiosurgical targets we have used computer-aided design optimization techniques with a fast dose model. A study of the spatial dose distribution for single or multiple non-coplanar arcs was carried out using a 18 cm diameter spherical head model. The dose distribution generated from the 3D dose computation algorithm can be represented by a simple analytic form. Two analytic dose models were developed to represent the dose for preset multiple non-coplanar arcs or a single arc: spherical and cylindrical. The spherical and cylindrical dose models compute dose quickly for each isocentre and single arc. Our approach then utilizes a computer-aided design optimization (CAD) with the use of two fast approximate dose models to determine the positions of isocentres and arcs. The implementation of CAD with fast dose models was demonstrated. While the fast dose models are only approximations of the true dose distribution, it is shown that this approximate model is sufficient to optimize isocentric position, collimator size and arc positions with CAD.