Brachytherapy is a form of radiation where the the radioactive source is brought close to the target tissue rather than treating from a distance with a machine (called external beam irradiation).

Common types of brachytherapy include implanting radioactive seeds into a tumor (see section on prostate seeds here). The seeds are left in permanently and give off radiation in a slow manner (called low dose rate radiation). Other techniques include implanting tubes of radium or cesium that will slowly radiate a tumor over a matter of hours (see section on gynecologic intracavitary radiation here).

New devices use highly radioactive isotopes that will treat a tumor in a matter of minutes and are referred to as high dose rate (HDR) devices (see section on Nucletron). This device has been used to treat gynecologic cancers, lung and esophagus.