ABSTRACT
This chapter describes various external beam therapy equipment, and explores common questions and their solutions in using the external beam equipment in radiotherapy. The equipment includes X-ray machine, linear accelerators, magnetron, klystron and multileaf collimators. Linear accelerators are the most common megavoltage units for external beam radiotherapy treatments. The chapter discusses the advantages of linear accelerators over Co-60 machine. It explains the difference between narrow beam and broad beam geometry for photon beams, and provides examples of their use in radiotherapy. The chapter also describes radiation yield in the production of photon beams in a linear accelerator. Radiation yield refers to the total fraction of the energy that is emitted as electromagnetic radiation, while the electrons decelerate and come to rest. The chapter provides comparison of the usage of a magnetron and a klystron in a radiotherapy linear accelerator. It describes factors affecting the linear accelerator beam energy.
