External Beam Therapy (EBT) involves using teletherapy machines to deliver radiation from external gamma ray sources. Teletherapy machines are mounted isocentrically and have five main components: a radioactive cobalt-60 source, source housing including a collimator and movement mechanism, gantry and stand, patient support assembly, and control console. Cobalt-60 sources decay with a half-life of 5.26 years into nickel-60 while emitting beta particles and two gamma rays. Teletherapy machines allow defining radiation fields and delivering prescribed target doses.