SU‐E‐T‐504: Intensity‐Modulated Radiosurgery Treatments Derived by Optimizing Delivery of Sphere Packing Treatment Plans

Abstract

PurposeTo minimize the number of monitor units required to deliver a sphere packing stereotactic radiosurgery (SRS) plan by eliminating overlaps of individual beam projections.MethodsAn algorithm was written in C++ to calculate SRS treatment doses using sphere packing. Three fixed beams were used to approximate each arc in a typical SRS treatment plan. For cases involving multiple isocenters, at each gantry and table angle position beams directed to individual spheres overlap to produce regions of high dose, resulting in intensity modulated beams. These high dose regions were dampened by post‐processing of the combined beam profile. The post‐process dampening involves removing the excess overlapping fluence from all but the highest contributing beam. The dampened beam profiles at each table and gantry angle position were then summed to produce the new total dose distribution.ResultsDelivery times for even the most complex multiple sphere plans can be reduced to consistent times of about 20 to 30 minutes. The total MUs required to deliver the plan can also be reduced by as much as 85% of the original plan's MUs.ConclusionRegions of high dose are removed. Dampening overlapping radiation fluence can produce the new beam profiles that have more uniform dose distributions using less MUs. This results in a treatment that requires significantly fewer intensity values than traditional IMRT or VAMT planning.