External Beam Stereotactic Radiosurgery Physics

Radiosurgery or stereotactic radiosurgery (SRS) is defined as the irradiation of intracranial lesions with a single fraction of focused small ionizing radiation beams, such as x-rays or gamma rays, eliminating the need for conventional invasive surgery. Stereotactic radiation therapy (SRT) is the treatment of intracranial lesions with the stereotactic apparatus and multiple fractions. A stereotactic frame allows for rigid immobilization of the patient and accurate localization of the target. The goal of radiosurgery is to locate and define the intracranial lesion and deliver single or multiple doses to the target with small x-ray beams without exceeding the radiation tolerance of normal tissues adjacent to the target volume. Radiosurgery was initiated in 1950 by Lars Leksell to treat dysfunctional intracranial abnormalities originally using orthovoltage x-rays in conjunction with a stereotactic frame of his own design (Leksell 1951).