This document discusses brachytherapy, a type of radiation therapy where radioactive material is placed directly inside the body near the tumor being treated. It begins by explaining the two major categories of radiation therapy: external-beam therapy where a machine emits radiation from outside the body, and brachytherapy where radioactive sources are placed inside the body. It then provides details on brachytherapy, including how it works from inside the body compared to external beam therapy, common radiation sources used, and the typical procedure involving planning, applicator insertion, treatment delivery, and removal of sources.