Isotropic beam bouquets for shaped beam linear accelerator radiosurgery

In stereotactic radiosurgery and radiotherapy treatment planning, the steep est dose gradient is obtained by using beam arrangements with maximal beam separation. We propose a treatment plan optimization method that optimizes beam directions from the starting point of a set of isotropically convergen t beams, as suggested by Webb. The optimization process then individually s teers each beam to the best position, based on beam's-eye-view (BEV) critic al structure overlaps with the target projection and the target's projected cross sectional area at each beam position. This final optimized beam arra ngement maintains a large angular separation between adjacent beams while c onformally avoiding critical structures. As shown by a radiosurgery plan, t his optimization method improves the critical structure sparing properties of an unoptimized isotropic beam bouquet, while maintaining the same degree of dose conformity and dose gradient. This method provides a simple means of designing static beam radiosurgery plans with conformality indices that are within established guidelines for radiosurgery planning, and with dose gradients that approach those achieved in conventional radiosurgery plannin g.