COMPARISON OF PROTON AND X-RAY CONFORMAL DOSE DISTRIBUTIONS FOR RADIOSURGERY APPLICATIONS

Highly focused dose distributions for radiosurgery applications are su ccessfully achieved using either multiple static high-energy particle beams or multiple-are circular x-ray beams from a linac. It has been s uggested that conformal x-ray techniques using dynamically shaped beam s with a moving radiation source would offer advantages compared to th e use of only circular beams. It is also thought that, generally, char ged particle beams such as protons offer dose deposition advantages co mpared to x-ray beams. A comparison of dose distributions was made bet ween a small number of discrete proton beams, multiple-are circular x- ray beams, and conformal x-ray techniques. Treatment planning of a sel ection of radiosurgery cases was done for these three techniques. Targ et volumes ranged from 1.0-25.0 cm(3). Dose distributions and dose vol ume histograms of the target and surrounding normal brain were calcula ted. The advantages and limitations of each technique were primarily d ependent upon the shape and size of the target volume. In general, pro ton dose distributions were superior to x-ray distributions; both shap ed proton and shaped x-ray beams delivered dose distributions which we re more conformal than x-ray techniques using circular beams; and the differences between all proton and x-ray distributions were negligible for the smallest target volumes, and greatest for the larger target v olumes.