Physics of Radiosurgery

From the very initial phases of the development of stereotactic radiosurgery (SRS), physics has been integral and pivotal in the design and commissioning of this high-precision, high dose rate, and highly accurate radiation treatment delivery technology. Physicists involved in stereotactic radiosurgery have raised the quality-of-care expectations for conventional radiation therapy by their early adoption of three-dimensional (3D) imaging, reproducible immobilization, image co-registration and fusion for target identification, and quality assurance measures that reduced setup and patient positioning from centimeter in conventional therapy to less than 1 mm in SRS. This chapter overviews the history of stereotactic development with the introduction of the Gamma Knife and continues with the sophisticated 3D imaging systems that are employed on linear accelerator-based devices. The contributions of early pioneers in transferring SRS technology from Gamma Knife are discussed, and the new and novel approaches of on-board 3D imaging from cone-beam computed tomography and magnetic resonance imaging (MRI) are presented. The future of SRS continues to rely heavily on physics, and newly emerging areas are also presented, including increased automation, functional molecular imaging, immunotherapy, and biological optimization.