Radiosurgery

Radiosurgery is a blending of radiosurgery and radiation techniques that was pioneered by Dr. Lars Leksell at the Karolinska Institute in Stockholm, Sweden. This technique involves the ablation of intracranial targets and induction of desired biological effects in target tissues through the use of a high dose of highly conformal ionizing beams through the body. This technique has evolved over time to include the delivery of anywhere between one and five treatments or fractions. Since radiosurgery often involves targeting small radiographically deep lesions within the brain and spine, precision is absolutely essential and is readily obtained by immobilization. The vast majority of clinical experience with radiosurgery has been using photon-based sources, such as the Gamma Knife®, Cyberknife®, or other linear accelerator (LINAC)-based platforms. There are also facilities delivering radiosurgery with charged particles (e.g., protons). There are many similarities in both the delivery and physical principles between conventionally fractionated radiation therapy and radiosurgery. However, there are distinct differences between these two modalities which are employed by clinicians to maximize benefits to patients. This chapter will focus on the unique nature of radiosurgery with regard to medical physics and radiation biology.