Brachytherapy is a form of radiation therapy in which radiation is delivered locally to a tumor (as opposed to external radiation). Since brachytherapy delivers radiation directly to a tumor, it is less likely than external radiation to damage healthy tissue.
With lung cancer, brachytherapy may be used if a tumor is present in the large airways. A tube is placed in to the bronchus during a bronchoscopy, and left in place for around 30 minutes to deliver the radiation.
Brachytherapy is most often used as a palliative therapy, a therapy done to relieve symptoms such as bleeding or to open airways, but not to cure lung cancer.