Robotic radiosurgery with noncylindrical collimators.

In radiosurgery, a moving beam of radiation acts as an ablative surgical instrument. Conventional systems for radiosurgery use a cylindrical radiation beam of fixed cross section. The radiation source can be moved only along simple, standardized paths. A new radiosurgical system based on a six-degree-of-freedom robotic arm has been developed to overcome limitations of conventional systems. We address the following question: Can dose distributions generated by robotic radiosurgery be improved by using noncylindrical radiation beams? This includes static noncylindrical collimators and collimators of adaptable cross section. Geometric methods for planning the shape of the beam in addition to planning beam motion are developed. Design criteria considered in this context are treatment time, radiation penumbra, and transparency of interactive treatment planning. An experimental evaluation compares distributions generated with our new radiosurgical system using cylindrical beams to distributions generated with beams of adaptable, noncylindrical shapes.