Radiation Delivery

Abstract

Linear accelerators (linacs) are the most common source of therapeutic radiation. Radiation is produced by rapid acceleration of electrons through a microwave wave guide followed by their bombardment of a heavy metal target. These high-energy electrons are stopped in the target and lose most of their energy as heat, but they also lose a small portion of their energy as X-rays (see Fig. 6.1). The X-rays produced have a range of energies with a maximum equal to the energy of the accelerated electrons. The average X-ray beam energy produced is approximately one third that of the maximum energy. A linac is named after the maximum energy of an X-ray it produces. The most common machines used for stereotactic radiosurgery have maximum energies between 4 million electron volts (MV) and 15 MV. At the University of Florida we use a 6 MV linac for stereotactic radiosurgery. A more complete description of radiation beam production is available in several references in the bibliography.