3-Dimensional optimization of multiple arcs for stereotactic radiosurgery

Purpose: During linear accelerator-based radiosurgery, the physicians and physicists need to determine which combination of treatment arcs are "best" with regard to target coverage and incidental dose to adjacent structures. This is a complex problem, especially when targets are geometrically close to critical structures. The purpose of this article is to present a method to mathematically determine a set of arcs to produce desired target and normal structure dose distributions in linear accelerator radiosurgery. Methods and Materials: Nonlinear least squares regression was used to determine the table angles and gantry angle arc ranges and their associated beam weights appropriate to linear accelerator radiosurgery. Results: Three cases are presented: (a) critical structure close to target volume; (b) target volume too large for the largest collimator to cover the volume with one isocenter and a standard plan; (c) target volume located within one critical structure and close to another critical structure. The optimized treatment plans are all shown to be superior to a defined standard plan. Conclusion: The method successfully enables one to determine nonstandard arcs which achieve the desired results. In particular, the method enables one to find clinical treatment solutions, even when the desired results cannot be a priori defined.